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1
Zaikov, Vadim Guennadievich. "A study of poly(vinyl chloride) microstructure." W&M ScholarWorks, 1997. https://scholarworks.wm.edu/etd/1539623916.
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High-field {dollar}\sp{lcub}13{rcub}{dollar}C and {dollar}\sp1{dollar}H NMR spectroscopies were used to investigate some unusual features of the molecular microstructure of poly(vinyl chloride) (PVC).;Several model monochloroalkenes were synthesized in order to determine {dollar}\sp{lcub}13{rcub}{dollar}C shift increments for the replacement of H by Cl at positions that are near an isolated internal double bond. These increments then were used to predict the {dollar}\sp{lcub}13{rcub}{dollar}C shifts of the internal allylic chloride structure in PVC. The predictions were not satisfactory, because, as expected, the increments were not additive.;It was shown that during conventional VC polymerization, the chloroallylic chain end (-CH{dollar}\sb2{dollar}CH=CHCH{dollar}\sb2{dollar}Cl) does not copolymerize with the monomer and is not destroyed by a mechanism involving allylic rearrangement, macroradical addition, and chlorine-atom {dollar}\beta{dollar}-scission to produce a -CHClCH{dollar}\sb2{dollar}CH=CHCH{dollar}\sb2{dollar}CHCl- structure. Nevertheless, that mechanism was found to operate during the preparation of a special type of PVC (made at 0{dollar}\sp\circ{dollar}C with (t-Bu){dollar}\sb2{dollar}Mg initiation) which contained the rearranged chain end, -CH{dollar}\sb2{dollar}-CHClCH=CH{dollar}\sb2,{dollar} at an abnormally high concentration.;During the preparation of PVC under subsaturation VC pressures, small amounts of a 1,3-di(2-chloroethyl) branch structure were found to be formed by a "double backbiting" mechanism involving two intramolecular H abstractions in succession. The presence of this structural defect was established by the 125.77-MHz {dollar}\sp{lcub}13{rcub}{dollar}C NMR spectra of reductively dechlorinated PVC specimens. at 55-80{dollar}\sp\circ{dollar}C, the two backbites leading to the defect differ substantially in relative rate, in that the backbiting:addition rate ratio is larger for the second backbite by a factor of 15-16, irrespective of temperature. No evidence was obtained for the presence of the 2-ethyl-n-hexyl branch structure that would have resulted from double backbiting by an alternative route. These findings were confirmed by spectral comparisons with the {dollar}\sp{lcub}13{rcub}{dollar}C shifts of two separately synthesized models, 9,11-diethylnonadecane and 9-(2-ethyl-n-hexyl)heptadecane.;Polymerizations of VC were performed in the presence of two potential transfer agents, trans-1-chloro-2-hexene and trans-1,5-dichloro-2-pentene. Preliminary examination of the resulting polymers by high-field NMR provided evidence for the destruction of the -CH{dollar}\sb2{dollar}CH=CHCH{dollar}\sb2{dollar}Cl chain end, during polymerization, by a mechanism involving H abstraction to form the -CH{dollar}\sb2{dollar}CH=CHC{dollar}\sp{lcub}\cdot{rcub}{dollar}HCl radical, followed by the addition of that species to VC in order to give the -CH{dollar}\sb2{dollar}CH=CHCHClCH{dollar}\sb2{dollar}- structure.
2
Nedea, Maria Elena. "Microstructure and 13c-nuclear magnetic relaxation of bacterial poly (b-hydroxyalkanoates)." Thesis, McGill University, 1991. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=70194.
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A new method for the determination of the composition of poly($ beta$-hydroxybutyrate-co-$ beta$-hydroxyvalerate) (P(HB-co-HV)) copolyesters, by using optical rotation dispersion (ORD) spectra, was proposed. A linear equation based on the "optical superposition principle" has been shown to relate the specific rotation ($ alpha$) of P(HB-co-HV) samples with their content of $ beta$-hydroxyvalerate determined by $ sp1$H NMR.The microstructure of P(HB-co-HV) copolymers, based on fast atom bombardment mass spectrometry (FAB-MS) analysis of the partial methanolysis or ammonolysis products, is described. The interpretation of the data indicated that the sequence distribution of all samples were statistically random (Bernoullian model), and permitted the detection in one sample of traces of pure poly($ beta$-hydroxybutyrate), PHB.
$ sp{13}$C spin-lattice relaxation times and NOE were measured as a function of temperature in two magnetic fields, for poly ($ beta$-hydroxybutyrate) in chloroform-d and 1,1,2,2,-tetrachloroethane-d$ sb2$ (TCE). Among the various dynamic models used for the interpretation of the data, the Dejean-Laupretre-Monnerie (DLM) model offered the best description of the segmental motion along the PHB chain.
3
Glenne, Rita. "Preparation and Transport Properties of SrFeO. Based Materials with controlled Microstructure." Doctoral thesis, Norwegian University of Science and Technology, Department of Chemistry, 2001. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-463.
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This work consists of mainly two parts. The first part deals with the sintering behaviour and the microstructural stability of SrFe1-xCrxO3-δ, and the second with transport properties of membranes of the same compositions. The most important experimental tools have been dilatometry and oxygen permeability measurements. Supplementary tools were x-ray diffraction analysis (XRD), scanning electron microscope (SEM) and particle size distribution analysis.
4
Bowling, Robert John. "Effects of microstructure on heterogeneous electron transfer at carbon electrodes /." The Ohio State University, 1989. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487671108306195.
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Perkins, James M. "Microstructure and properties of (rare earth) doped oxide ceramics." Thesis, University of Warwick, 2006. http://wrap.warwick.ac.uk/3705/.
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A study of alumina (AI203 ) and magnesium aluminate spinel (MgAb04) was undertaken with the aim of investigating the changes in properties and microstructural characteristics upon doping with specific rare earth elements. Microscopic imaging and analysis of RE doped polycrystalline oxide ceramics has shown convincing evidence for monolayer segregation of RE cations to grain boundaries. State of the art aberration corrected scanning transmission electron microscopy (SuperSTEM I Daresbury Laboratories) has shown monolayer segregation to grain boundaries, and atomic resolution parallel electron energy loss spectroscopy has confirmed the presence of the RE cation at the grain boundary position. The region affected by segregation has been shown to extend no further than one monolayer from the centre of the grain boundary with RE cations occupying matrix cation boundary sites. The effect of RE dopants on the powder processing and sintering of high purity commercial grade precursor powders was investigated. Differences were found between doped alumina and spinel in the sintering whereby the alumina grain growth was restricted by grain boundary mobility such that the grain size was reduced for a given sintering temperature. The grain size of spinel was unaffected by sintering temperature. Differences in the fracture behaviour between doped alumina and spinel was found. The alumina samples manifested a change from trans-granular fracture to inter-granular fracture due to the addition of RE dopants. Spinel did not show such an effect. Alumina was shown to posess an approximate Hall-Petch relationship between hardness and grain size for both doped and undoped samples, such that sub-micron grain size samples posessed high hardness. Optical characterisation has shown the potential for the use of fine grained RE doped alumina and spinel samples for hard window applications. A reduction in the grain size of alumina to below 1 μm leads to a change in the scattering mechanism, thus reducing low angle scatter and birefringence due to the refractive index mismatch. The benefits to optical properties are in addition to the benefits in mechanical properties of a submicron grain structure.
6
Velazquez, Alberto. "Microstructure and thermal stability of PVC and chemically modified PVC." Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74243.
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This thesis describes a study of the effect of microstructure on the thermal stability of poly(vinyl chloride), PVC, vinyl chloride-ethylene, VC-E, and vinyl chloride-propylene, VC-P, copolymers obtained by chemical modification of PVC. The VC-E copolymers, with an ethylene content between 1.1 and 21 mole %, are random copolymers with approximately the same degree of polymerization as the original PVC. A decrease in the number of defect sites is observed with extent of reaction. Concomitantly, the syndiotacticity increases. The VC-P copolymers, with propylene content of ca. 0.1%, also have less labile chlorines than the homopolymer since these react preferentially.The thermal stability of solid state samples was studied, at temperatures between 150 and 190$ sp circ$C under a nitrogen atmosphere, using a conductimetric method to measure evolved HCl. The thermal stability of the modified samples is improved relative to that of the initial homopolymers. For the VC-E copolymers, a linear relationship is observed between the rates of degradation and the number of labile chlorines, total double bonds and the degree of syndiotacticity. The role of syndiotacticity on the thermal degradation behavior is confirmed in results obtained with two unmodified PVC samples, with a similar number of defect sites but different syndiotacticity. The more syndiotactic resin shows a higher thermal stability. The average polyene sequence length is independent of the ethylene concentration. Thus, the ethylene units do not interfere in the development of polyene sequences.
The VC-P copolymers also show improved thermal stability as compared to that of PVC. However, the improvement is less than that of the VC-E copolymers, due to a lower extent of substitution of labile sites.
PVC previously saturated with HCl shows a markedly increased rate of degradation reflecting the autocatalytic role of HCl. For the PVC coated samples, a decrease in the degradation rates with decreasing PVC film thickness is observed due to more efficient removal of HCl. The PVC mixtures with Chromosorb W or silica gel exhibit a decrease in the dehydrochlorination rate constants with decreasing PVC content. The inert substrate acts as a diluent and avoids agglomeration of the samples and thus facilitates the removal of HCl.
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Adams, Brandy Rogers. "Ceramic materials mimicking normal bone surface microstructure and chemistry modulate osteoblast response." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50292.
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Bone consists of collagen/hydroxyapatite (HA) composites in which poorly crystalline carbonated calcium phosphate is intercalated within the fibrillar structure. Normal bone mineral is a carbonated-apatite, but there are limited data on the effect of mineral containing carbonate on cell response. Although the exact biological role of silicate in bone formation is unclear, silicate has been identified at trace levels in immature bone and is believed to play a metabolic role in new bone formation. To mimic the inorganic and organic composition of bone we have developed a variety of bone graft substitutes. In the present body of research, we characterized the surface composition of human cortical and trabecular bone. When then characterized the surface compositions of the following potential bone substitutes: carbonated hydroxyapatite (CO₃²-HA), silicated hydroxyapatite (Si-HA), and collagen sponges mineralized with calcium phosphate using the polymer-induced liquid-precursor (PILP) process. In the latter substitutes, the PILP process leads to type I collagen fibrils infiltrated with an amorphous mineral precursor upon which crystallization leads to intrafibrillar HA closely mimicking physiological bone mineral. We then determined the osteoblast-like cell response to each bone substitute to characterize the substrate’s effect on osteoblast differentiation. The observations collectively indicate that cells are sensitive to the formatting of the mineral phase of a bone substitute and that this format can be altered to modulate cell behavior.
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Preece, Christopher V. J. "An investigation of the microstructure and grain-boundary chemistry of alloy 690." Thesis, University of Bristol, 1996. http://hdl.handle.net/1983/601c86b6-f4d4-482e-b11e-a9f2d97d270c.
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Li, Linlin. "Microstructure characterization of polymers by modern NMR techniques." University of Akron / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=akron1353000762.
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Serdaroglu, Gulcan. "Controlling the microstructure of the porous nickel electrodes in alkaline electrolysers." Thesis, University of Nottingham, 2018. http://eprints.nottingham.ac.uk/49141/.
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Ni-based electrodes have been extensively studied for hydrogen evolution reaction (HER) in alkaline electrolysers in an attempt to improve its electrocatalytic activity through alloying it with other metals and/or increasing the surface area. However, the role of microstructure on the electrochemical performance has received little attention. In this study, Ni-based catalysts have been prepared by a powder metallurgy technique including compaction and sintering of a mixture of Ni, starting alloy (consisting of Al3Ni and Al3Ni2) and binder. As-sintered samples were then treated in concentrated alkaline solution for leaching of Al. The microstructural properties are controlled by changing the parameters of the preparation process; i.e. sintering temperature, starting alloy to Ni ratio, leaching temperature and binder properties (concentration and particle size). Increasing the sintering temperature from 625 to 900 °C improved the mechanical strength but also increased the diffusion of Al from Al-rich phases into Ni, resulting in reduced Al-rich phases available after sintering. Since Al can only be leached from Al-rich phases, the specific surface area of micro- and mesopores (with the latter having a size range of 2-14 nm) created during the leaching reduced by almost 90 % from 625 to 900 °C sintering temperature. Although there was a ca. 15 times increase in the specific surface area by increasing the starting alloy concentration from 0 to 60 wt.%, the robustness of catalysts reduced since the compressibility of alloy powder is lower than that of Ni, resulting in increased macroporosity. This suggests that the starting alloy concentration should be in the range of 20-40 wt.% in order to achieve relatively robust and inexpensive porous catalysts without compromising too much the surface area. N2 sorption isotherms showed that leaching at 30 and 50 °C resulted in pores with a slit shape, whilst leaching at 60, 70 and 80 °C lead to ink-bottle pores. This was attributed to increasing leaching rate with higher leaching temperatures in comparison to speed of atomic rearrangement at the surface. Increasing the leaching temperature from 30 to 60 °C improved the specific surface area by almost 4 times, whilst leaching at 60, 70 and 80 °C gave similar surface areas. Greater binder concentrations led to increased macroporosity and surface roughness as well as greater numbers of windows between the adjacent cavities. Consequently, the mechanical strength of porous catalysts reduced due to the decrease in the wall thickness. It was also found that the size of the binder particles influences the robustness of the porous catalysts, with the smaller the binder size the greater the robustness. The comparison of trends in alkaline electrolyser cell voltage and compositional and microstructural properties showed that the surface area has a dominant effect on the electrocatalytic activity for HER in comparison to the composition of Ni-based electrodes. Despite greater Al contents, the cell voltage still decreased with increasing surface areas (with micropores accounting for ca. 80 %). However, it was found that the effective use of micro- and mesopores depends on the pore morphology, with slit-shaped pores being more effectively used during HER in comparison to ink-bottle pores which can be more subject to mass transport limitation. It was shown that H2 bubbles cannot form inside the micro- and mesopores, therefore generated H2 can only leave the pores through diffusion which appears to be favoured by a slit shape in comparison to ink-bottles. It was also found that increasing the amount of large macropores (> 15 μm) is not advantageous to the production of electrodes for alkaline electrolysers as it results in increased electrode thickness and reduced mechanical strength with no measureable improvement in electrochemical performance.
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Gerislioglu, Selim. "Microstructure Characterization of Polymers and Polymer-Protein Bioconjugates by Hyphenated Mass Spectrometry." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1534269781343128.
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Wang, Minshi. "Microstructure characterisation and creep modelling of HP40 alloys." Thesis, University of Birmingham, 2017. http://etheses.bham.ac.uk//id/eprint/7463/.
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The efficiency of steam reforming depends strongly on the creep resistance of the material used for the reformer tubes. The currently most widely used reformer tube material is HP40 (25 Cr, 35Ni, 40 Fe and 0.4C) austenitic stainless steel. A further improvement in the creep resistance of HP40 is needed for efficiency improvement and for a cost reduction in steam reforming. In order to develop a next generation creep resistant alloy, three HP40-based alloys, namely Alloy A, B and C, with different chemical compositions and/or solidification rate, were studied. Previous tests at 1000 oC and 40 MPa have shown that the creep properties of Alloy C are slightly better than those of Alloy B, both being significantly better than Alloy A. The microstructures of three alloys, under as-cast, crept and heat treated conditions, have been analysed so as to understand their relative creep performance. The small intragranular M23C6 may have contributed significantly to the smaller creep rate, and thus a longer creep life for Alloy B and Alloy C as compared with Alloy A. A microstructure-based climb-glide bypass creep model was described to predict the creep behaviour of HP40. Suggestion on the next generation HP40 alloy has been made.
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Srinivasan, Rekha. "Study of the microstructure of silk artifacts recovered from a historic deep-ocean site /." The Ohio State University, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=osu148820531850982.
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Filippov, Andrei. "Self-Diffusion and Microstructure of Some Ionic Liquids in Bulk and in Confinement." Doctoral thesis, Luleå tekniska universitet, Kemiteknik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-18055.
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An ionic liquid (IL) is a salt, which usually is in the liquid state at normal temperature and pressure. The properties of ILs can be adjusted for various processes and applications by choosing different combinations of ions. Similar to other salts, ILs contain only ions with positive (cations) and negative (anions) charges in equal proportions. However, to prevent solidification, ions in ionic liquids usually contain bulky organic chemical groups, which, apart from electrostatic interactions, promote other types of interactions between ions, such as: (i) van-der-Waals interactions; (ii) hydrogen bonding; (iii) - stacking, etc., depending on the particular chemical structure of the ions. All these interactions, in combination, may lead to formation of specific microstructures in ILs, which may vary with temperature caused by changing thermal rotational and translational energies of the ions. Ions in these microstructures may have preferential orientations relative to each other, maintain anisotropic properties similar to those in liquid crystals or, in some specific cases, may even separate into microscopically organised liquid phases. Therefore, the dynamics of ILs may also be dependent on their microstructure. In many practical applications ionic liquids are placed on surfaces or in confinements. Solid surfaces introduce extra forces, which may be specific to the charge of the ions or/and to functional groups in the ILs. The geometry and interactions of ions in confinements or/and pores of materials may also disrupt specific bulk microstructures of ILs. Both confinement effects and interactions of ions with surfaces are manifested in the translational dynamics of the ions. One of the most direct and informative methods to study translational dynamics of ILs is pulse-field-gradient nuclear magnetic resonance (PFG-NMR).In this thesis the results of PFG-NMR studies on a few classes of ILs are reported: (i) the historically “standard” (since Walden’s discovery in 1914) ionic liquid, the ethylammonium nitrate (EAN) and (ii) halogen-free orthoborate-based phosphonium, imidazolium and pyrrolidinium ILs with varied structure and lengths of alkyl chains in cations, and varied structures of orthoborate anions. These ILs were studied in bulk at different temperatures, and also in confinements, such as between parallel glass and Teflon plates and in mesoporous Vycor glass. It was found that diffusion coefficients of cations and anions in EAN, phosphonium and pyrrolidinium orthoborate ILs in bulk are different, but according to the standard Stocks-Einstein model, they correspond to diffusion of ions in homogeneous liquids. A change in the chemical structure of one of the ions results in a change in both the diffusion coefficient of the oppositely charged ion and the activation energy of diffusion for both ions in an IL. Similar effects were observed from the chemical shifts and diffusion coefficients measured by NMR for imidazolium orthoborate ILs dissolved in polyethylene glycol solutions, in which imidazolium cations strongly interact with PEG molecules, further affecting the diffusion of orthoborate anions via electrostatic interactions. A liquid-liquid phase separation was suggested for a few phosphonium and pyrrolidinium bis(mandelato)borate ILs, in which a divergence of diffusion coefficients and activation energies of diffusion for cations and anions was detected at temperatures below ca 50 °C. In addition, a free-volume theory was invoked to explain the dependences of density of ILs on the alkyl chain length in cations.It was also found that for a phosphonium bis(salicylato)borate IL confined in 4 nm mesoporous Vycor glass the diffusion coefficients of ions increase by a factor of 35! This phenomenon was explained by the dynamic heterogeneity of this IL in micropores and empty voids of the Vycor glass. For EAN IL in confinements between glass and Teflon plates, the diffusion of ethylammonium cations and nitrate anions is significantly anisotropic, i.e. slower in the direction of the normal to the plates and faster along the plates compared to diffusion of the ions in bulk. A plausible explanation of this PFG NMR data is that EAN forms layers near polar and non-polar solid surfaces. A similar phenomenon, to a lesser extent, was also observed for phosphonium cations of bis(mandelato)borate, bis(salicylato)borate and bis(oxalato)borate confined between glass plates. The results of these studies may have implications in modeling tribological performance, i.e., friction and wear reduction for contact pairs of different materials lubricated by various classes of ionic liquids.För godkännande; 2016; 20160420 (andfil)
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Coffy, Kevin. "Microstructure and Chemistry Evaluation of Direct Metal Laser Sintered 15-5 PH Stainless Steel." Master's thesis, University of Central Florida, 2014. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/6256.
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15-5PH stainless steel is an important alloy in the aerospace, chemical, and nuclear industries for its high strength and corrosion resistance at high temperature. Thus, this material is a good candidate for processing development in the direct metal laser sintering (DMLS) branch of additive manufacturing. The chemistry and microstructure of this alloy processed via DMLS was compared to its conventionally cast counterpart through various heat treatments as part of a characterization effort. The investigation utilized optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-Ray diffractometry (XRD), energy dispersive X-Ray spectroscopy (EDS) and glow discharge atomic emission spectrometry (GDS) techniques. DMLS processed samples contained a layered microstructure in which the prior austenite grain sizes were relatively smaller than the cast and annealed prior austenite grain size. The largest of the quantifiable DMLS prior austenite grains had an ASTM grain size of approximately 11.5-12 (6.7?m to 5.6?m, respectively) and the cast and annealed prior austenite grain size was approximately 7-7.5 (31.8?m to 26.7?m, respectively), giving insight to the elevated mechanical properties of the DMLS processed alloy. During investigation, significant amounts of retained austenite phase were found in the DMLS processed samples and quantified by XRD analysis. Causes of this phase included high nitrogen content, absorbed during nitrogen gas atomization of the DMLS metal powder and from the DMLS build chamber nitrogen atmosphere. Nitrogen content was quantified by GDS for three samples. DMLS powder produced by nitrogen gas atomization had a nitrogen content of 0.11 wt%. A DMLS processed sample contained 0.08 wt% nitrogen, and a conventionally cast and annealed sample contained only 0.019 wt% nitrogen. In iron based alloys, nitrogen is a significant austenite promoter and reduced the martensite start and finish temperatures, rendering the standard heat treatments for the alloy ineffective in producing full transformation to martensite. Process improvements are proposed along with suggested future research.M.S.M.E.
Masters
Materials Science Engineering
Engineering and Computer Science
Materials Science and Engineering
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Ray, Kenneth G. "Spatially resolved raman spectroscopy of carbon electrode materials : a study of surface microstructure and reactivity /." The Ohio State University, 1998. http://rave.ohiolink.edu/etdc/view?acc_num=osu14879495083686.
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Zhang, Junliang. "Controlling polymer microstructure using multiblock copolymers via reversible addition-fragmentation chain transfer polymerization." Thesis, University of Warwick, 2017. http://wrap.warwick.ac.uk/95273/.
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Reversible addition fragmentation chain transfer (RAFT) polymerization is a very versatile way to generate synthetic polymeric materials. Multiblock copolymers have received enormous scientific interest recently due to the ability to mimic the sequence-regulated microstructure of biopolymers. The objective of this thesis was to investigate RAFT polymerization and explore its potential in the synthesis of sequence-controlled multiblock polymeric chains, and their use to tune the micro-structure of the polymers, engineer single chain polymeric nanoparticles, and fabricate functional polymeric nanomaterials. This work firstly addresses the investigation of the enormous ability of sequence-controlled multiblock copolymer to tune the physical properties by altering their microstructure. A series of sequence controlled multiblock copolymers were synthesized by RAFT polymerization using ethylene glycol methyl ether acrylate and tert-butyl acrylate as monomers. These block copolymers were synthesized with an alternating order of the two monomers with a similar total degree of polymerization. The number of blocks was varied by decreasing the length of each block while keeping the ratio of monomers constant. Their microphase separation was studied by investigating the glass transition temperature utilizing differential scanning calorimetry analysis. Small angel X-ray scattering analysis was also applied to investigate the transition of the microphase separation with the variation of the segmentations of these multiblock copolymers. The study found the microstructure was significantly affected by the number of segments of the polymer chain whilst keeping the total length constant. Having demonstrated the enormous potential of sequence controlled multiblock copolymers to access defined microstructures, further studies were focused on mimicking the controlled folding process of the peptide chain to a secondary and tertiary structure using sequence controlled multiblock copolymers. RAFT polymerization was used to produce multiblock copolymers, which are decorated with pendant cross-linkable groups in foldable sections, separated by non-functional spacer blocks in between. An external cross linker was then used to cause the folding of the specific domains. A chain extension-folding sequence was applied to create polymer chains having individual folded subdomains. In order to achieve a further step on the way to copy nature’s ability to synthesize highly defined bio-macromolecules with a distinct three dimensional structure, linear diblock copolymer precursors were synthesized by RAFT polymerization. One block of the precursor with pendant functional groups was folded using an external cross-linker to form tadpole-like single chain nanoparticles (SCNPs). These tadpole-like SCNPs could then self-assemble into a more complex stimuli responsive 3D structure by adaptation to environmental pH changes. The stimuli responsive assemblies were found to be able to dissociate responding to low pH or exposure to glucose.
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Jing, Wu. "Microstructure and mechanical properties of Mg-Zn-(Y/Gd) alloys." Thesis, University of Birmingham, 2016. http://etheses.bham.ac.uk//id/eprint/7100/.
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As-cast Mg\(_9\)\(_4\)Zn\(_2\)Y\(_4\) alloy has been subjected to compression and equal channel angular pressing (ECAP) separately. The as-cast alloy contains mainly a long-period stacking ordered (LPSO) phase and a Mg\(_2\)\(_4\)Y\(_5\) phase as secondary phases. During compression, kinking occurs in the LPSO phase and LPSO/Mg mixture. Most kink boundaries of LPSO are composed of basal < a > type dislocations. The rotation axes of the kink boundaries in LPSO/Mg are preferentially located in the (0001) plane. ECAP processing develops a bimodal microstructure consisting of large deformed grains and sub-micron dynamically recrystallised (DRXed) grains. The DRXed grains are mainly located along the original grain boundaries. Kink boundaries also acts as DRX nucleation sites. The ECAP processing increased significantly the strength of the alloy. In the as-cast Mg-Zn-Y alloys, the main secondary phase changes when different ratios of Zn/Y are applied: LPSO (Zn/Y ratio is 0.5) → LPSO+W (Zn/Y ratio is 1, W is Mg\(_3\)Zn\(_3\)Y\(_2\)) → W (Zn/Y ratio is 2.33). When Y is half replaced by Gd, the types of phases are similar. When Y is replaced fully by Gd, W phase becomes the main secondary phase. The structure of the LPSO also changes with different Zn/Y ratios and the presence of Y or Gd.
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Wilson, William S. M. Massachusetts Institute of Technology. "Grinding of cement clinkers : linking multi-scale fracture properties to system chemistry, mineralogy and microstructure." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/82861.
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Thesis (S.M.)--Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 162-172).
Growing environmental concerns encourage the cement industry to improve its environmental performance, which in turn renews the interest in clinker grinding efficiency. Current knowledge on clinker grinding was built over the past decades, but contributions from fracture mechanics remained limited. This research aimed to contribute to this field by investigating industrial clinkers with innovative techniques such as multiscale microscratching and statistical electron-probe microanalysis (EPMA). Microstructure investigations were first performed with scanning electron microscopy (SEM), and three characteristic length scales were defined for clinkers: the nodules at the macroscale, the clinker matrix and porosity at the intermediate scale, and the clinker phases at the microscale. A statistical EPMA method was developed to allow simultaneous determination of the clinker bulk chemistry, the chemistry of the clinker phases, and their abundance. The microscratch test method was downscaled to measure the fracture properties at each characteristic scale of clinkers. Measurements on single silicate grains provided access to the intrinsic fracture toughness, which was three to four time lower than the macroscale fracture toughness. A combination of microstructure effects and toughening mechanisms (crack deflection, crack tip shielding by microcracks, crack trapping, and crack pinning) explained this behavior. Comparison of industrial clinkers showed that higher macroscale toughness (i.e., poor coarse grindability) was associated with oversized alite crystals, which was explained by the increase of microcracks toughening with larger grain size. In contrast, lower macroscale fracture toughness (i.e., better coarse grindability) was associated with either poorly burned clinkers showing excessive porosity or well burned clinkers having a good repartition of small silicates. However, difficulties in fine grinding were expected for the poorly burned clinkers because of the increased amounts of clustered belite. Overall, this thesis presents new experimental methods to investigate clinkers, as well as links between clinkers properties and grindability, both of which hold interest to the scientific community and the cement industry.
by William Wilson.
S.M.
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Tran, Hoang Vi. "The Influence of Microstructure on the Thermal Degradation Behavior of Poly(vinyl Chloride)." W&M ScholarWorks, 1997. https://scholarworks.wm.edu/etd/1539626102.
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Nyberg, Axel. "Microstructure and Magnetic Properties for Mn-Al based Permanent Magnet Materials." Thesis, Uppsala universitet, Fasta tillståndets fysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-325543.
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Manganese-Aluminium is an alloy with attractive ferromagnetic propertieswhenL10-structured ( -phase). If sucient permanent magnetic propertiescan be achieved at a low cost, it has potential to be a new permanentmagnet material on the market. In this thesis, drop synthesized ingots ofMn55Al45C2 were crushed and examined as solid pieces and as powders.The goal was to better understand how the material behaves magneticallyafter synthesis in relation to its chemical composition and cooling rate. Representativecross-sections of solid ingot pieces were created by mounting thepieces in polyfast followed by polishing. The surfaces were studied withScanning Electron Microscopy and Energy-dispersive X-ray spectroscopy tomap the chemical composition and then by Magnetic Force Microscopy andMagneto-optic Kerr eect to see how the chemical composition inuencesthe magnetic properties. It was found that areas richer in aluminium (Al),compared with the rest of the surface, behaved non-magnetically. The resultsfrom X-ray diraction on the powders suggests that the Al-rich areasconsists of the non-magnetic- and 2-phases.The powder that was extracted from the top of one of the drop synthesizedingots was nearly pure -phase but did not have an impressive magnetization.A complementary magnetic measurement was done on a solid piece from thetop part. This piece was found to reach a higher magnetization at a lowereld. The result indicates that crushing the material, even just by hand witha mortar and pestle, greatly reduces the magnetization.
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Donley, Carrie Lynn. "Interfaces in organic electronic devices: Surface characterization and modification and their effect on microstructure in molecular assemblies." Diss., The University of Arizona, 2003. http://hdl.handle.net/10150/280407.
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This dissertation has focused on (i) the characterization and optimization of the near-surface region of indium-tin oxide (ITO) thin films, and (ii) the characterization of the microstructure and electrical properties of thin films of several new self-organizing liquid crystalline phthalocyanines (Pcs). Commercial ITO surfaces were explored through a combination of high resolution X-ray photoelectron spectroscopy and electrochemical techniques. It was determined that sputter-deposited ITO films undergo hydrolysis immediately upon exposure to atmosphere, creating InOOH and In(OH)₃ species, which appear to inhibit charge transfer reactions. The surface coverage of these InOOH and In(OH)₃-like species can be controlled by various solution and vacuum pretreatments, including etching with EDTA solutions, and RF-plasmas. Characterization of new discotic mesophase Pc materials has focused on modifications of the original Pc in this series, CuPc(OCH₂CH₂OBz)₈, including a polymerizable version, CuPc(OCH₂CH₂OCH₂CH=CH-Ph)₈, and the sulfur analogs of these molecules, CuPc(SCH₂CH₂OBz)₈ and CuPc(SCH₂CH₂OCH₂CH=CH-Ph)₈. The self-organizing properties of these new Pcs are altered by the changes in side chain composition, but still show the same "column-forming" tendencies as the parent Pc, with long range order. The polymerizable Pc materials can be photolithographically patterned with features as small as 2 microns. Electrical anisotropies in these films were measured with a conductive tip AFM and with OFETs, and anisotropies in current (j(∥)/j(⊥)) were ca. 10 on the micron scale, and up to 1000 on the submicron scale. OFET measurements showed low hole mobilities, which are attributed to poor contact between the Pc column and the Au electrodes. Chemical modification of these electrodes shows that considerable improvements in OFET performance result from this modification strategy. Understanding and controlling the microscopic structure of these Pc films is important for optimizing their electrical properties. A considerable effort was focused on developing a quantitative protocol to combine transmission and reflectance vibrational spectroscopic data to determine the three Euler angles that determine the orientation of these Pcs in an LB-deposited film on a planar substrate. Changes in orientation upon annealing and polymerization were observed, but in general these molecules display tilt angles away from the surface normal of <20° and twists about the surface normal of ca. 25°.
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Domke, Andreas. "Chemistry and physics of diamond surfaces." Thesis, University of Liverpool, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367131.
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This thesis is concerned with the chemistry and physics of C(100) surfaces of diamond. The polished and cleaned C(100) surface is examined by surface microscopy (Atomic-force Microscopy), electron diffraction (Low-energy Electron Diffraction) and photoemission (X-ray Photoelectron Spectroscopy and Ultra-violet Photoelectron Spectroscopy). Results are presented on the presence of oxygen, nitrogen and hydrogen/deuterium on the C(100) surface. Finally, the valence band structure of diamond is probed by angle-resolved photoemission. We have confirmed by AFM that the grooves from the soft polishing process are present on a polished C(100) surface and found sporadic traces of hard polish on a surface polished in the soft polishing direction. XPS studies have verified heating cycles by electron beam bombardment as a suitable cleaning procedure for pure reconstructed C(100) surfaces. By allowing the crystal to cool slowly, the first experimental evidence of quarter-order LEED spots have been found, which suggest that buckled dimerisation might have occurred similar to those on Si(100) and Ge(100). We present the first experimental electron spectroscopy results for a nitrogen impurity in diamond by showing the N KLL Auger spectrum. An attempt to smooth a C(100) surface of diamond by an atomic hydrogen plasma did not succeed. AFM studies showed no evidence for the surface smoothing reported in other studies, but the results enable us to explain the different plasma published in the literature. The valence band of diamond is investigated by off-normal ARUPS. The features observed are consistent with possible transitions, which are determined using bulk band structure calculations and comparison with the experimental binding energies.
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Keong, Kim Ghee. "Characterization and modelling of the evolution of microstructure during thermal processing of electroless nickel-phosphorus depositions." Thesis, Queen's University Belfast, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.273032.
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Atkin, Neil Joseph. "Examination of the relationship between induced polymer microstructure and the physical properties of a polymer gel." Thesis, University of York, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.247036.
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Li, Hualong 1967. "Computer simulation of oxide texture and microstructure formation and their effects on oxidation kinetics." Thesis, McGill University, 1998. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=35467.
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Computer models of oxide texture and microstructure development and oxidation kinetics have been developed. The first computer model enables the evaluation of the effects of various factors on oxide texture and microstructure development. The second computer model enables the evaluation of the effects of oxide texture and microstructure on oxidation kinetics.Two examples of Ni single crystal and polycrystalline, Zr-2.5%Nb are used to illustrate the proposed computer models. Simplified oxidation mechanisms on Ni and Zr have been proposed.
In the first system, the simulation of oxide texture and oxidation kinetics on the {100} and {111} oriented single crystal Nickel substrate is analyzed. At the nucleation stage the oxide grain orientation is determined by lattice matching between the oxide and the metal substrate. At the stage of oxide grain growth, oxide surface free energy plays an important role. The simulated oxide textures are in good agreement with experimental results. The observed difference in the oxidation kinetics of the two samples is explained by difference in oxide textures formed on the two single crystal substrates. The high percentage of Sigma3 twin boundaries found in the oxide formed on the {111} substrate indicates that the presence of these boundaries significantly improves oxidation resistance.
In the second system where oxidation on Zr-2.5%Nb is simulated and analyzed, lattice matching between the oxide and the metal substrate is used to determine the oxide orientation at the nucleation stage. At the stage of oxide grain growth, oxide orientation is determined by minimizing the compressive stress that is parallel to the metal/oxide interface. Four samples with different substrate orientations have been used in study. The simulated oxide textures and microstructures are in good agreement with experimental results. During the simulation of oxidation kinetics, it is found that oxygen transport through Zr oxide film takes place mainly through two diffusion paths. The first diffusion path is through oxide grain boundaries formed in the bulk alpha-Zr grain region and the second one is through oxide grain boundaries formed at the alpha-Zr grain boundaries and beta-Zr grain region.
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MacDonald, James Edward. "Hot isostatic pressing of a high temperature Ni-superalloy CM247LC : processing-microstructure-properties." Thesis, University of Birmingham, 2017. http://etheses.bham.ac.uk//id/eprint/7645/.
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Hot isostatic pressing (HIP) is of interest to the aerospace industry due to the ability to produce polycrystalline components free from defects, which typically exhibit comparable or superior properties to their cast counterparts. The capability also exists with powder HIP to produce large parts with complex designs to near netshape (NNSHIP) in a single processing step, which can potentially reduce the buy-to-fly ratio ofhigh temperature gas turbine engine components. Such components, however, are manufactured from Ni-superalloys and certain issues exist with the HIP ofNi-superalloys that require addressing. The research presented in this thesis investigates HIP of a Ni-superalloy CM247LC to assess the viability of the process and the alloy for high temperature turbine and combustor casing components of the future. The influence of powder characteristics, post-HIP heat treatment and modification of the HIP procedure, have been investigated to assess the effects on high temperature properties. HIPped CM247LC can significantly outperform cast CM247LC in terms of hot tensile properties (particularly ductility), suggesting NNSHIP is potentially viable. In the current work, however, poor creep resistance was exhibited which is a concern for high temperature components.
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Ye, Haihui. "Microstructure and chemistry of grain-boundary films and triple-junction phases in liquid-phase sintered SiC ceramics." [S.l. : s.n.], 2002. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB9831555.
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Neikter, Magnus. "Microstructure and Texture of Additive Manufactured Ti-6Al-4V." Licentiate thesis, Luleå tekniska universitet, Materialvetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-66103.
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Additive manufacturing (AM) for metals is a manufacturing process that has increased a lot in popularity last few years as it has experienced significant improvements since its beginning, both when it comes to accuracy and deposition rates. There are many different AM processes where the energy sources and deposition methods varies. But the common denominator is their layer wise manufacturing process, melting layer on layer. AM has a great design freedom compared to conventional manufacturing, making it possible to design new structures with decreased weight and increased performance. A drawback is slow manufacturing speeds, making it more expensive. But when it comes to low lot sizes and complex structures AM is very competitive. So, for the aerospace and space industry AM is a good option as manufacturing cost is less of an issue and where saving weight is of great concern, both environmentally and economically. There are however many topics left to research before additive manufactured titanium can be widely adopted for critical components, such as microstructure and texture development and its correlation to mechanical properties. The aim of this work has been to investigate the microstructure and texture of various AM processes. Microstructural features such as prior β grains, grain boundary α (GB-α), α laths, α colonies have been characterized along with hardness measurements for 5 different AM processes. Some of these AM processes have also been investigated in the SKAT instrument in Dubna, Russia, to obtain their texture. These textures have then been compared with one another and correlated to previous microstructural investigations and mechanical properties. This is important knowledge as the microstructure and the texture sets the basis for the mechanical properties. In case there is a high texture, the material can have anisotropic mechanical behavior, which could be either wanted or unwanted for different applications. Some the findings are that α phase was found to increase in the prior β grain boundary for the AM processes with low cooling rates, while it was discontinuous and even non-present for the AM processes with high cooling rates. The prior β size are larger for the directed energy deposition (DED) processes than for the powder bed fusion (PBF) processes. Parallel bands were present for the DED process while being non-present for the PBF processes. Concerning the texture, it was found that LMwD had a higher texture than EBM and SLM. Texture inhomogeneity was also found for the LMwD process., where two parts of the same sample was investigated and the material closer to the surface had higher texture.
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Ochin, Patrick. "La Solidification Rapide : Relation élaboration, microstructure et propriétés d'un alliage." Habilitation à diriger des recherches, Université Paris-Est, 2010. http://tel.archives-ouvertes.fr/tel-00512464.
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« La solidification rapide : relation Elaboration – Microstructure et Propriétés d'un alliage » RESUME Si les propriétés intrinsèques des matériaux dépendent de la force des liaisons chimiques, qui ne peuvent être modifiées, il est bien connu que leurs propriétés extrinsèques dépendent de la microstructure. Les métallurgistes disposent de moyens techniques pour contrôler relativement bien cette microstructure et aussi faire en sorte que les propriétés associées correspondent aux besoins du cahier des charges de l'application. Classiquement, partant du lingot élaboré par fusion, des traitements thermomécaniques plus ou moins complexes engendrent la microstructure. Mais il est bien clair que les possibilités d'évolution de la microstructure dépendent dramatiquement de l'état initial de l'alliage. C'est ici qu'interviennent les techniques basées sur la solidification rapide. Elles vont engendrer des microstructures initiales pouvant être très différentes de celles qui sont conventionnelles, et qui pourront, par traitements thermomécaniques, aboutir à des microstructures finales également très différentes. Les méthodes de solidification rapide d'alliages métalliques ou céramiques ont pour but principal d'étendre ou de modifier les limites des domaines d'équilibre thermodynamique, ou d'obtenir de nouvelles structures atomiques, ce qui n'est généralement pas accessible par des méthodes dites conventionnelles de solidification. Les produits élaborés se caractérisent par exemple par réduction de taille de grains, par la précipitation d'une phase secondaire plus fine et homogène Ces procédés permettent dans le même temps d'obtenir les matériaux directement à partir de l'état fondu, sous la forme de produits minces finis ou dans un état intermédiaire, tels que des rubans (10 à 80 μm) par « planar flow casting PFC » (flot planaire), des tôles fines (de 200 μm à 3 mm d'épaisseur (en production industrielle) par « twin roll casting TRC» (coulée entre rouleaux) ou encore mais plus rarement des fils (100 à 200 μm de diamètre) par « In rotating water melt spinning INROWASP». J'ai dans ce manuscript décrit les méthodes et techniques d'élaboration que j'utilise en développant quelques aspects thermodynamiques et cinétiques tout en révélant l'essentiel des informations techniques. Un ensemble d'exemples tirés de mes travaux en collaboration et dans le cadre de projets de recherche internes au laboratoire, nationaux et internationaux illustrent ces techniques, notamment les verres métalliques massifs, les quasicristaux, les alliages à magnétorésistance géante, et particulièrement les alliages à mémoire de forme. Les relations entre d'une part la méthode de préparation, qui inclut la technique de fusion, de solidification, les traitements associés thermo-mécaniques, et d'autre part les caractéristiques structurales, microstructurales ainsi que les propriétés mécaniques et fonctionnelles ont été mises en évidence. Le choix de méthodes de production par solidification rapide, comme je l'ai écrit, peut dans certaines conditions autoriser l'obtention d'une phase qu'on ne peut pas obtenir par refroidissement classique (< 103 KS-1) ou, par l'abaissement de la taille de grains, optimiser certaines caractéristiques mécaniques. Néanmoins comme le montrent certains résultats mitigés sur les alliages à mémoire de forme, ces méthodes ne sont en aucun cas une panacée aux problèmes rencontrés comme le manque de ductilité à température ambiante. Le problème de la mise en forme à froid qu'on rencontre dans nombres d'alliages intermétalliques ou les verres métalliques ne sont pas ou seulement partiellement résolus par ces procédés. Mais la production en une seule ou un nombre limité d'étapes d'objets finis ou semi-finis reste un élément économique appréciable de ces méthodes. Les phases quasicristallines stables thermodynamiquement ainsi que les verres métalliques massifs ne nécessitent pas des vitesses de refroidissement supérieures à 103 KS-1 et peuvent être obtenus par des méthodes de préparation ce qui nécessite certaines précautions (c.a.d. par exemple sans contamination chimique) mais à vitesse de refroidissement classique. Néanmoins dans ce cas il a été démontré que seule une méthode de solidification rapide (telle que le melt spinning ou l'atomisation gazeuse) permet d'une part d'obtenir la précision compositionnelle requise et d'autre part d'atteindre, après traitement thermique, une qualité structurale de la phase optimale (cas des quasicristaux). En ce qui concerne les verres métalliques ces techniques nous permettent d'étudier plus facilement la capacité à l'amorphisation, la formulation et la déformation à froid de ces alliages : par exemple les essais de nanoindentations sur les rubans ou les tôles hypertrempées qui nous autorisent à remonter aux mécanismes de déformation des alliages massifs. L'obtention d'une précipitation de dispersoïdes nanométriques dans la matrice amorphe (VMM) ou la matrice paramagnétique des alliages magnétorésistifs à l'étude, n'est possible qu'en utilisant ces techniques.
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Reitmeier, Zachary J. "The Chemistry and Surface Microstructure of Si-Based Substrates and their Effect on the Evolution of the Microstructures of III-Nitride Films Grown via Metalorganic Vapor Phase Epitaxy." NCSU, 2005. http://www.lib.ncsu.edu/theses/available/etd-03202005-194018/.
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The present research was undertaken with the goals of understanding the evolution of defects and strain in heteroepitaxial AlN and GaN films deposited via metalorganic vapor phase epitaxy and minimizing those defects through manipulation of the substrate. As observed with atomic force microscopy (AFM), AlN initially grew in the form of flat-topped islands on as-received SiC substrates. Threading dislocations (TDs) observed in transmission electron microscopy (TEM) images initiated at the AlN/SiC interface as the result of defects at the surface of the mechanically polished substrate and/or condensation of point defects. GaN initially grew in the Stranski-Krastanov mode on AlN/SiC before transitioning to the dislocation-mediated step flow mode. The TDs in GaN resulted from the propagation of the TDs present in the AlN layer. The biaxial strain in the GaN layers varied with buffer layer material and layer thickness yet all samples investigated remained in residual compression due to incomplete relaxation of the coherent strain. The presence of strain during the initial growth of AlxGa1-xN layers directly on as-received SiC also resulted in phase-separated regions of Al-rich and Al-poor film. A high temperature hydrogen etch was then used to remove mechanical polishing scratches from the SiC substrates. Subsequently deposited AlN layers featured reduced pit density and the elimination of scratch-induced undulations. GaN layers deposited with AlN buffer layers on these substrates resulted in slightly reduced TD densities as observed by AFM, TEM, and high resolution X-ray diffraction (HRXRD). Regions of dramatically reduced dislocation densities were observed by HRXRD, TEM, and cathodoluminescence for GaN layers on stripe-patterned Si substrates. However, long growth times resulted in outdiffusion of Si from the substrate and subsequent film roughening. Finally, it was demonstrated that the presence of ammonia during heating of GaN templates to the growth temperature for homoepitaxy resulted in removal of carbon- and oxygen-based contaminants from the template surface.
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Dezellus, Olivier. "Elaboration, microstructure et propriétés des interfaces dans les multimatériaux métalliques et céramiques." Habilitation à diriger des recherches, Université Claude Bernard - Lyon I, 2010. http://tel.archives-ouvertes.fr/tel-00556122.
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Au niveau scientifique, la finalité des activités que j'ai développé est le développement de l'approche « élaboration-microstructure-propriétés », classique en science des matériaux, aux interfaces métal/métal ou métal/céramique. A l'intérieur de ce célèbre triangle ou trépied de base de la science des matériaux, mon activité scientifique fondamentale se situe sur l'arête élaboration-microstructure, c'est là que j'évolue en tentant d'apporter des contributions à la fois dans l'acquisition de données de base (équilibres thermodynamiques, angle et cinétiques de mouillage, mécanisme de croissance, etc.) et dans le développement et l'approfondissement de concepts (première phase formée, chemin de diffusion, nombres de couches dans une séquence réactionnelle, mouillage réactif, etc.). Le mémoire est structuré en trois parties. Les activités dans le domaine du mouillage métal/céramique (réactif ou non-réactif) sont présentées dans le premier chapitre car elles sont un préalable indispensable à tout étude de chimie d'interface. En effet, la réactivité nécessite tout d'abord l'obtention d'un contact intime entre les phases, ce que le mouillage permet de caractériser. Le mouillage constitue le sommet Elaboration de notre triangle. Par ailleurs, à l'autre bout de la chaîne, nous verrons que le mouillage impacte également de manière très importante les propriétés mécaniques d'adhérence puisqu'il conditionne la qualité de l'adhésion interfaciale. L'étude successive du mouillage non-réactif et du mouillage réactif constitue une transition naturelle vers le second chapitre de ce mémoire centré sur les problèmes de réactivité chimique aux interfaces. La réactivité, par ses mécanismes va modeler la microstructure de la zone interfaciale. Enfin, pour terminer, je présenterais les résultats obtenus lors de nos incursions dans le domaine des propriétés mécaniques, dans l'objectif de valoriser les résultats de chimie et d'étudier les relations chimie-mécanique.
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Eakes, Mark W. "Correlation of inclusion size and chemistry with weld metal composition and microstructure in arc weldments of high strength steels." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1994. http://handle.dtic.mil/100.2/ADA292024.
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Liu, Jing. "Nano and Grain-Orientated Ferroelectric Ceramics Produced by SPS." Doctoral thesis, Stockholm : Department of Physical, Inorganic and Structural Chemistry, Stockholm university, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-6800.
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Dumont, David. "Relations Microstructure / Ténacité dans les alliages aéronautiques de la série 7000." Phd thesis, Grenoble INPG, 2001. http://tel.archives-ouvertes.fr/tel-00370456.
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L'objectif principal de cette thèse était de comprendre l'influence du revenu, de la vitesse de trempe et de la composition de l'alliage sur le compromis limite d'élasticité / ténacité dans les alliages de la série 7000, compromis critique pour une conception performante des ailes d'avion. Nous avons essayé de maîtriser ces effets en les associant à l'évolution des principaux paramètres de la microstructure à toutes les échelles. Pour cela nous avons utilisé une approche partant de la caractérisation de la microstructure et des mécanismes de rupture, afin de dégager les paramètres dominants.L'approche suivie était donc avant tout expérimentale. Nous avons caractérisé le comportement mécanique du matériau à partir d'essais classiques de traction mais aussi à partir d'essais de déchirement sur éprouvettes entaillées de type Kahn. Parallèlement les techniques de diffusion centrale de rayons X, de microscopie électronique à balayage et en transmission ont permis de caractériser les différentes familles de précipités se formant pendant les traitements thermiques.
Ainsi à chaque effet du procédé de production sur le comportement en ténacité, nous avons pu associer une cause microstructurale : les précipités intergranulaires de revenu, les précipités intergranulaires et transgranulaires de trempe et les particules intermétalliques. Une fois identifiées, ces causes ont été traduites dans un modèle simple de résistance à l'entaille qui permet de rationaliser les grandes tendances.
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Morris, Christopher J. "Capillary-force driven self-assembly of silicon microstructures /." Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/5963.
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Ye, Changhuai. "Microstructure Alignment and Mechanical Properties of Block Copolymer and Crystalline Polymer Thin Films." University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1475553221643627.
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O'Brien, Lindsay Beth. "The effect of environment, chemistry, and microstructure on the corrosion fatigue behavior of austenitic stainless steels in high temperature water." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/97861.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 110-111).
The effect of sulfur on the corrosion fatigue crack growth of austenitic stainless steel was evaluated under Light Water Reactor (LWR) conditions of 288°C deaerated (less than 5ppb O₂) water, to shed light on the accelerating effect of the LWR environment and to explore the effect of high sulfur content on the retardation of fatigue crack growth rates. Fatigue tests were performed using a trapezoidal loading pattern with rise times of 5.1, 51, 510, and 5100 seconds (fall time of 0.9, 9, 90, and 900 seconds), with Kmzx of 28.6 or 31.9 MPa[mathematical symbol]m and stress ratios (R, Pmin/Pmax) of 0.4 or 0.7. Two test materials were used to evaluate the effect of sulfur: (1) a low sulfur (<0.0025 wt%) stainless steel and, (2) a high sulfur (0.032 wt% stainless steel. The low sulfur stainless steel exhibited increasing crack growth rates from 9.4 x10-5 mm/cycle to 1.2x1 0-⁴ mm/cycle as rise times were increased from 5.1 to 5100 seconds with a stress ratio of 0.7. The high sulfur stainless steel exhibited decreasing crack growth rates from 1.4 x10-⁴ mm/cycle to 7.9 x10-⁵ mm/cycle as rise times were increased for a stress ratio of 0.4, and crack growth rates from 6.4 x10 5 mm/cycle to 3.6 x10-⁵ mm/cycle with increasing rise time at a stress ratio of 0.7. Evaluation of the crack growth rates showed environmental enhancement of the crack growth rates for the low sulfur stainless steel, while the high sulfur stainless steel showed retardation of environmental crack growth rates, likely due to the increased corrosion at the crack tip associated with the high sulfur content. The crack surfaces were characterized using Scanning Electron Microscopy (SEM). The low sulfur material showed a light layer of corrosion product that decreased in thickness as the testing progressed, and faceting on the surface was highly crystallographic. Faceting ran both perpendicular and parallel to the crack for the short rise time steps of the test, but fewer perpendicular facets were evident at the longer rise times. The high sulfur material was heavily corroded throughout the fracture surface, and crystallographic faceting was seen for stages of the test with R=0.4 For R=0.7, the heavy oxidation on the surface made the facets hard to resolve. Striations were apparent during the 5100 second rise time for the low sulfur material (where corrosion was almost nonexistent) and throughout the entirety of the crack surface for the high sulfur material. Materials were also characterized by optical microscopy. The low sulfur material showed pitting along the grain boundaries, due to the boron concentration in this material, which resulted in boron precipitates, while the high sulfur material showed pitting throughout the surface, due to the MnS inclusions. Electrochemical tests were also performed at room temperature on both materials in pH 4 (using H₂SO₄), 7, and 10 (using NH₄OH). Peaks in the passive region of the high sulfur material were seen at potentials of 160, 630, and 1400 mVSHE, due to dissolution of the MnS inclusions. The results suggest that the high sulfur material provides an increase in corrosion when exposed to the environment, which leads to the retardation of crack growth rates at the longer rise times due to prolonged exposure of the crack tip to the environment. At low stress ratios, the proposed mechanism for retardation of crack growth rates is crack tip closure, due to a buildup of corrosion product at the fracture surface, which lowers the effective load that the crack tip experiences. At high stress ratios, the proposed mechanism for retardation is an increased in injected vacancies and enhanced creep, which disrupt the slip bands ahead of the crack tip, reducing the crack tip stresses. Fractography of the fracture surface and crack growth rate comparisons of the low and high sulfur material provide supportive evidence for the proposed mechanisms, and further work is proposed to examine the effect of increased corrosion ahead of the crack tip.
by Lindsay Beth O'Brien.
S.M.
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Chamorro, Coral William. "Microstructure, chemistry and optical properties in ZnO and ZnO-Au nanocomposite thin films grown by DC-reactive magnetron co-sputtering." Thesis, Université de Lorraine, 2014. http://www.theses.fr/2014LORR0253/document.
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Les matériaux composites peuvent présenter des propriétés qu'aucun des composants individuels ne présente. En outre, à l'échelle du nanomètre les nanocomposites peuvent présenter de nouvelles propriétés par rapport à l'état massif ou à des macrocomposites des mêmes composants en raison d’effets de confinement et d’effets quantiques liés à la taille. Les nanocomposites semi-conducteur/métal sont très intéressants en raison de leurs uniques propriétés catalytiques et opto-électroniques et la possibilité de les ajuster facilement. Ce travail de thèse étudie les interactions spécifiques et les propriétés physiques qui se manifestent dans les films minces de ZnO et nanocomposites ZnO-Au synthétisés par pulvérisation magnétron réactive continue. Premièrement, il est observé qu’il est possible d'ajuster les propriétés microstructurales et optiques des couches de ZnO en réglant les paramètres expérimentaux. La croissance épitaxiale de ZnO sur saphir a été réalisée pour la première fois dans des conditions riches en oxygène sans assistance thermique. En outre, une étude des propriétés optiques met en évidence la relation étroite entre les propriétés optiques et de la chimie des défauts dans les couches minces de ZnO. Un modèle a été proposé pour expliquer la grande dispersion des valeurs de gap rencontrées dans la littérature. Deuxièmement, il a été possible de révéler l'influence profonde de l'incorporation de l'or dans la matrice de ZnO sur des propriétés importantes dans des films nanocomposites. En outre, la présence de défauts donneurs (accepteurs) au sein de la matrice ZnO se permet de réduire (oxyder) les nanoparticules d’or. Ce travail de recherche contribue à une meilleure compréhension des nanocomposites semi-conducteurs/métal et révèle le rôle important de l'état de la matrice semi-conductrice et de la surface des particules pour les propriétés finales du matériauComposite materials can exhibit properties that none of the individual components show. Moreover, composites at the nanoscale can present new properties compared to the bulk state or to macro-composites due to confinement and quantum size effects. The semiconductor/metal nanocomposites are highly interesting due to their unique catalytic and optoelectronic properties and the possibility to tune them easily. This PhD work gives insight into the specific interactions and resulting physical properties occurring in ZnO and ZnO-Au nanocomposite films grown by reactive DC magnetron sputtering. The results can be summarized in two points: First, it was possible to tune the microstructural and optical properties of ZnO. Epitaxial growth of ZnO onto sapphire was achieved for the first time in O2-rich conditions without thermal assistance. Also, a study of the optical properties highlights the close relationship between the bandgap energy (E_g ) and the defect chemistry in ZnO films. A model was proposed to explain the large scatter of the E_g values reported in the literature. Second, the deep influence of the incorporation of gold into the ZnO matrix on important material properties was revealed. Moreover, the presence of donor (acceptor) defects in the matrix is found to give rise to the reduction (oxidation) of the Au nanoparticles. This research work contributes to a better understanding of semiconductor/metal nanocomposites revealing the key role of the state of the semiconductor matrix
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Clausen, Jonathan Ryan. "The effect of particle deformation on the rheology and microstructure of noncolloidal suspensions." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34680.
Full textAbstract:
In order to study suspensions of deformable particles, a hybrid numerical technique was developed that combined a lattice-Boltzmann (LB) fluid solver with a finite element (FE) solid-phase solver. The LB method accurately recovered Navier-Stokes hydrodynamics, while the linear FE method accurately modeled deformation of fluid-filled elastic capsules for moderate levels of deformation. The LB/FE technique was extended using the Message Passing Interface (MPI) to allow scalable simulations on leading-class distributed memory supercomputers.
An extensive series of validations were conducted using model problems, and the LB/FE method was found to accurately capture proper capsule dynamics and fluid hydrodynamics. The dilute-limit rheology was studied, and the individual normal stresses were accurately measured. An extension to the analytical theory for viscoelastic spheres [R. Roscoe. J. Fluid Mech., 28(02):273-93, 1967] was proposed that included the isotropic pressure disturbance. Single-body deformation was found to have a small negative (tensile) effect on the particle pressure.
Next, the rheology and microstructure of dense suspensions of elastic capsules were probed in detail. As elastic deformation was introduced to the capsules, the rheology exhibited rapid changes. Moderate amounts of shear thinning were observed, and the first normal stress difference showed a rapid increase from a negative value for the rigid case, to a positive value for moderate levels of deformation. The particle pressure also demonstrated a decrease in compressive stresses as deformation increased. The corresponding changes in microstructure were quantified. Changes in particle self-diffusivity were also noted.
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Peng, Hong. "Spark Plasma Sintering of Si3N4-based Ceramics : Sintering mechanism-Tailoring microstructure-Evaluationg properties." Doctoral thesis, Stockholms universitet, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-129.
Full textAbstract:
Spark Plasma Sintering (SPS) is a promising rapid consolidation technique that allows a better understanding and manipulating of sintering kinetics and therefore makes it possible to obtain Si3N4-based ceramics with tailored microstructures, consisting of grains with either equiaxed or elongated morphology. The presence of an extra liquid phase is necessary for forming tough interlocking microstructures in Yb/Y-stabilised α-sialon by HP. The liquid is introduced by a new method, namely by increasing the O/N ratio in the general formula RExSi12-(3x+n)Al3x+nOnN16-n while keeping the cation ratios of RE, Si and Al constant. Monophasic α-sialon ceramics with tailored microstructures, consisting of either fine equiaxed or elongated grains, have been obtained by using SPS, whether or not such an extra liquid phase is involved. The three processes, namely densification, phase transformation and grain growth, which usually occur simultaneously during conventional HP consolidation of Si3N4-based ceramics, have been precisely followed and separately investigated in the SPS process. The enhanced densification is attributed to the non-equilibrium nature of the liquid phase formed during heating. The dominating mechanism during densification is the enhanced grain boundary sliding accompanied by diffusion- and/or reaction-controlled processes. The rapid grain growth is ascribed to a dynamic ripening mechanism based on the formation of a liquid phase that is grossly out of equilibrium, which in turn generates an extra chemical driving force for mass transfer. Monophasic α-sialon ceramics with interlocking microstructures exhibit improved damage tolerance. Y/Yb- stabilised monophasic α-sialon ceramics containing approximately 3 vol% liquid with refined interlocking microstructures have excellent thermal-shock resistance, comparable to the best β-sialon ceramics with 20 vol% additional liquid phase prepared by HP. The obtained sialon ceramics with fine-grained microstructure show formidably improved superplasticity in the presence of an electric field. The compressive strain rate reaches the order of 10-2 s-1 at temperatures above 1500oC, that is, two orders of magnitude higher than that has been realised so far by any other conventional approaches. The high deformation rate recorded in this work opens up possibilities for making ceramic components with complex shapes through super-plastic forming.
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Puli, Goutham. "Effects of Xanthan/Locust Bean Gum Mixtures on the Physicochemical Properties and Oxidative Stability of Whey Protein Stabilized Oil-In-Water Emulsions." TopSCHOLAR®, 2013. http://digitalcommons.wku.edu/theses/1288.
Full textAbstract:
Scientific evidence shows that dietary intake of the omega-3 polyunsaturated fatty acids is beneficial to human health. Fish oil is a rich source of omega-3 fatty acids. However, fish oil with high levels of omega-3 PUFA is very susceptible to oxidative deterioration during storage. The objective of this study was to investigate the effect of xanthan gum (XG)-locust bean gum (LBG) mixtures on the physicochemical properties of whey protein isolate (WPI) stabilized oil-in-water (O/W) emulsions containing 20% v/v menhaden oil. The O/W emulsions containing XG/LBG mixtures were compared to emulsions with either XG or LBG alone. The emulsions were prepared using a sonicator by first mixing menhaden oil into the WPI solution and then either XG, LBG or XG/LBG mixtures were added. WPI solution (2 wt%) and gum solutions (0.0,0.05, 0.1, 0.15, 0.2 and 0.5 wt%) were prepared separately by dissolving measured quantities of WPI in distilled water. XG and LBG gums were blended in a synergistic ratios of 50:50 for the mixture. The emulsions were evaluated for apparent viscosity, microstructure, creaming stability and oxidative stability. Addition of 0.15, 0.2 and 0.5 wt% XG/LBG mixtures greatly decreased the creaming of the emulsion. The emulsion with 0.15, 0.2 and 0.5 wt% XG/LBG mixtures showed no visible serum separation during 15 d of storage. The apparent viscosity of the emulsions containing XG/LBG mixtures was significantly higher (p < 0.05) than the emulsions containing either XG or LBG alone. The viscosity was sharply enhanced at higher concentrations of XG/LBG mixtures. Microstructure images showed depletion flocculation for LBG (0.05-0.5 wt%), XG (0.05- 0.2 wt%) and XG/LBG mixtures (0.05 and 0.1 wt%) emulsions. Flocculation was decreased with the increased biopolymer concentration in the emulsion. The decrease in flocculation was much pronounced for the emulsion containing XG/LBG mixtures. The rate of lipid oxidation for 8 week storage was significantly (p < 0.05) lower in emulsions containing XG/LBG mixtures than in emulsions containing either of the biopolymer alone. The results suggested that the addition of XG/LBG mixtures greatly enhanced the creaming and oxidative stability of the WPI-stabilized menhaden O/W emulsion as compared to either XG or LBG alone.
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Cai, Yanbing. "Synthesis and Characterization of Nitrogen-rich Calcium α-Sialon Ceramics." Doctoral thesis, Stockholms universitet, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-8568.
Full textAbstract:
In this thesis, a synthesis concept has been developed, which uses nitrogen-rich liquid phases for sintering of Ca-α-sialon ceramics. First, keeping the Si/Al ratios constant, the effects of N/O ratio on the properties and microstructure were investigated through a liquid phase sintering process. Second, nitrogen-rich Ca-α-sialon ceramics, with nominal compositions: CaxSi12-2xAl2xN16, x < 2.0, was synthesized and characterized. Third, mechanical and thermal properties of nitrogen-rich Ca-α-sialons were investigated in terms of high temperature deformation resistance,reaction mechanism, phase stability and oxidation resistance, and further correlated to their phase assemblage and microstructure observation. It has been found that increasing the N/O and Ca/Al ratio simultaneously in the materials could result in development of a microstructure with well shaped, high-aspect-ratio Ca-α-sialon grains, and an improvement in both toughness and hardness. For the nitrogen-rich Ca-α-sialon, mono-phasic α-sialon ceramics were obtained for 0.51 ≤ x ≤ 1.32. The obtained Ca-α-sialon ceramics with elongated-grain microstructures show a combination of high hardness and high fracture toughness. Compared with the oxygen-rich Ca-α-sialons, the nitrogen-rich Ca-α-sialons exhibited approximately 150 oC higher deformation onset temperatures and decent properties even after the deformation. The α-sialon phase was first observed at 1400 oC, however the phase pure Ca-α-sialon ceramics couldn’t be obtained until 1800 oC. The nitrogen-rich Ca-α-sialons were thermal stable, no phase transformation observed in the temperatures range1400-1600 oC. In general, mixed α/β-sialon showed better oxidation resistance than pure α-sialon in the low temperature range (1250-1325 oC), while α-sialons with compositions located at α/β-sialon border-line showed significant weight gains over the entire temperature range (1250-1400 oC).
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Hodgdon, Travis K. "Cryogenic transmission electron microscopy as a probe of microstructural transitions in complex fluids." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 343 p, 2008. http://proquest.umi.com/pqdweb?did=1691645631&sid=3&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Peterson, Sarah M. 1975. "Influence of scale, geometry, and microstructure on the electrical properties of chemically deposited thin silver films." Thesis, University of Oregon, 2007. http://hdl.handle.net/1794/8453.
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xv, 101 p. ; ill. (some col.) A print copy of this title is available through the UO Libraries under the call number: KNIGHT QC176.84.E5 P47 2007Silver films with nanoscale to mesoscale thicknesses were produced by chemical reduction onto silica substrates and their physical and electrical properties were investigated and characterized. The method of silver deposition was developed in the context of this research and uses a single step reaction to produce consistent silver films on both flat silica coverslips and silica nanospheres of 250-1000 nm. Both the structure and the electrical properties of the silver films are found to differ significantly from those produced by vacuum deposition. Chemically deposited (CD) silver is not uniformly smooth, but rather is granular and porous with a network-like structure. By quantitatively accounting for the differences in scale, geometry, and microstructure of the CD films, it is found that the same models used to describe the resistivity of vacuum deposited films may be applied to CD films. A critical point in the analysis that allows this relation involves the definition of a geometric parameter, g, which replaces the thickness, t, as the critical length that influences the electrical properties of the film. The temperature dependent properties of electrical transport were also investigated and related to the microstructure of the CD films. A detailed characterization of CD silver as shells on silica spheres is also presented including physical and optical properties. In spite of the rough and porous morphology of the shells, the plasmon resonance of the core-shell structure is determined by the overall spherical shell structure and is tunable through variations in the shell thickness. Preliminary investigations into the electrical transport properties of aggregates of silver coated spheres suggest similarities in the influence scale, geometry, and microstructure to silver films on flat substrates. The aggregates of shells also exhibit pressure related resistance behavior due to the composite structure.
Adviser: Miriam Deutsch
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Reinhart, Guillaume, Henri Nguyen-Thi, Bernard Billia, and Joseph Gastaldi. "Dynamique de formation de la microstructure de solidification d'alliages métalliques : caractérisation par imagerie X synchrotron." Phd thesis, Université Paul Cézanne - Aix-Marseille III, 2006. http://tel.archives-ouvertes.fr/tel-00371700.
Full textAbstract:
Nous avons étudié in situ et en temps réel la solidification dirigée d'échantillons minces d'alliages binaires et d'un quasicristal en combinant radiographie et topographie X. Sur Al-3,5%pdsNi non-affiné, nous avons étudié la formation de l'état initial et la morphologie du front de solidification (croissance cellulaire puis dendritique). Les effets des contraintes mécaniques ont été mis en évidence. La transition colonnaire-équiaxe a été étudiée sur Al-3,5%pdsNi affiné. Nous avons décrit le blocage du front colonnaire et le régime de croissance équiaxe ultérieure. L'efficacité des affinants tend vers une limite. Une analyse de la morphologie des microstructures a été effectuée. L'étude du quasicristal i-AlPdMn montre la croissance de grains dodécaédriques facettés. Nous avons mis en évidence les effets de la convection thermosolutale. La visualisation des contraintes montre une forte déformation des grains. L'apparition de porosités a été observée au cours de la fusion des grains.
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Meille, Sylvain. "Étude du comportement mécanique du plâtre pris en relation avec sa microstructure." Phd thesis, INSA de Lyon, 2001. http://tel.archives-ouvertes.fr/tel-00477188.
Full textAbstract:
Le plâtre pris est couramment utilisé en construction, sous forme d'enduits ou d'éléments préfabriqués. Ses bonnes propriétés d'isolation thermique et acoustique, ainsi qu'une grande légèreté, le rendent particulièrement adapté à un emploi en intérieur. Peu d'études sont actuellement publiées sur le comportement mécanique du plâtre pris, seule la forte sensibilité de sa tenue mécanique avec la porosité est bien établie. Ce travail a pour objectif d'étudier les propriétés mécaniques du plâtre pris et de les relier à ses caractéristiques microstructurales. Le plâtre pris présente une microstructure complexe, formée d'un enchevêtrement de cristaux de gypse. La description de la microstructure est effectuée par un modèle numérique de placement de barres dans un volume. Le calcul des propriétés élastiques par la méthode des éléments finis sur ces modèles est en très bon accord avec les résultats expérimentaux. La loi de comportement du plâtre pris sec est linéaire élastique, mais l'étude de la propagation de fissures met en évidence des mécanismes de dissipation d'énergie dans le matériau. Un modèle de propagation est développé, basé sur l'interaction de la fissure avec les différents éléments de la microstructure, permettant d'interpréter le comportement expérimental. L'influence de l'eau sur le plâtre pris est considérée dans la dernière partie. L'eau entraîne une diminution des propriétés mécaniques, pouvant s'expliquer par un affaiblissement de la qualité de la liaison entre cristaux. Des essais originaux de frottement intérieur permettent de caractériser l'apparition de glissements entre cristaux de gypse, à l'origine de la non-linéarité du comportement mécanique. La sensibilité de la déformation du matériau à la vitesse de sollicitation est établie et interprétée par un modèle de comportement des contacts.
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Souillard, Chloé. "Impact de la microstructure chimique sur la mobilité moléculaire des élastomères en régime linéaire." Thesis, Lyon, INSA, 2015. http://www.theses.fr/2015ISAL0058/document.
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Ce travail porte sur les mouvements moléculaires dans les caoutchoucs composants les pneumatiques : les polybutadiènes (PB) et les copolymères de polystyrène et polybutadiène (SBR). L’intérêt de cette étude est double : Nous souhaitons à partir de résultat de spectroscopies mécanique et diélectrique, comprendre l’origine moléculaire des relaxations dans ces élastomères, mais aussi voir le rôle de la microstructure chimique dans la mobilité moléculaire. Nous travaillons donc sur des matériaux différents par leur microstructure chimique à travers leurs taux respectifs de butadiène 1,2 vinyle, de butadiène 1,4 cis/trans ou encore de styrène pour les SBR. L’étude de la modification de la microstructure passe aussi par l’ajout de diluants qui servent de perturbateurs à la mobilité. La gamme de température balayée est comprise entre 90K et 350K et permet ainsi l’étude systématique de toutes les relaxations présentent dans les polymères de l’étude : La relaxation β, à plus basse température, la relaxation α pour des températures proches de Tg mais aussi, à plus haute température, les relaxations de bouts de chaine et enfin les phénomènes de reptation de chaines libres pour des températures 90K supérieures à Tg. Les techniques de spectroscopie mécanique (1.10-4/1 Hz) et diélectrique (0,1/1.106Hz) permettent d’obtenir des résultats sur un large domaine fréquence /température. Par ailleurs, les couplages mécanique d'une part et électrique d'autre part étant de nature différente, les informations obtenues par les deux techniques sont complémentaires. Le développement d’un modèle nous permet de démontrer que les mouvements des groupements butadiène 1,2 (vinyle) sont responsables de la contribution haute température de la relaxation β alors que ceux des groupements butadiène 1,4 cis et trans sont responsables de la partie basse température. L’étude approfondie de la relaxation α à l’aide du modèle de Perez amène à penser que ces mêmes groupements butadiène 1,2 vinyles jouent aussi un rôle non négligeable dans cette relaxation α. La dilution par une huile polaire provoque la suppression de la partie haute température de la relaxation β et amène ainsi à une modification de sa mobilité basse température. Diminuer la réticulation dans un polymère entraine revient à augmenter la longueur des bouts de chaine. Ces bouts de chaines peuvent alors relaxer selon les lois de rétraction de bouts de chaine développées par Curro à partir des modèles de Pearson et Helfand. Enfin, les chaines libres introduites dans un polymère réticulé suivent la théorie de la reptation de De Gennes-Doi-EdwardsThis work deals with the study of the molecular mobility in rubbers used for pneumatic applications, namely, polybutadiene (PB) and styrene butadiene rubber (SBR). They exhibit relaxation processes, which are in fact responsible for their main behaviors (adhesion, energy consumption, etc.). From mechanical and dielectric spectroscopy data, we tried to understand the molecular origins of these elastomers relaxation, but, also the role of their chemical microstructure on molecular mobility. We studied materials with different chemicals microstructures, i.e., with different butadiene 1,2 vinyl, butadiene 1,4 cis and 1,4 trans and styrene (for SBR only) ratio. The impact of microstructure modification was also studied with addition of diluents, which modifies the molecular mobility. Experimental temperature range was between 90 and 350K, so all relaxations present in polymer can be studied: the β relaxation at low temperature, the α relaxation for temperature near Tg, the chain-end relaxation at higher temperature and free chain reptation phenomenon at Tg+90K. Mechanical (10-4 Hz to 1 Hz) and dielectric spectroscopy (0,1 Hz to 106 Hz) allow obtaining large frequency range. Besides that, mechanical and dielectric induced stresses are different so both methods are complementary. The β relaxation exhibits two main contributions, so-called here high and low temperature contributions. The use of modeling permits to show that movements responsible for the high temperature contribution are those of butadiene 1,2 vinyl, whereas butadiene 1,4 cis and trans are responsible from low temperature contribution. Perez model used for studying the α relaxation shows that 1,2 vinyl also impact it. High temperature contribution of the β relaxation disappears after dilution by polar oil. Decreasing the crosslinking density in polymers results in the increase of average chain-end length. These chain-ends relax, and it has been found that their relaxation processes follow the chain-end retraction model developed by Curro from Pearson and Helfand works. On the contrary, free chains motions, when introduced in the already cross-linked polymer network follow De Gennes-Doi-Edwards reptation theory
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Peng, Hong. "Spark Plasma Sintering of Si3N4-based Ceramics : Sintering mechanism-Tailoring microstructure-Evaluationg properties." Doctoral thesis, Stockholm University, Department of Physical, Inorganic and Structural Chemistry, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-129.
Full textAbstract:
Spark Plasma Sintering (SPS) is a promising rapid consolidation technique that allows a better understanding and manipulating of sintering kinetics and therefore makes it possible to obtain Si3N4-based ceramics with tailored microstructures, consisting of grains with either equiaxed or elongated morphology.
The presence of an extra liquid phase is necessary for forming tough interlocking microstructures in Yb/Y-stabilised α-sialon by HP. The liquid is introduced by a new method, namely by increasing the O/N ratio in the general formula RExSi12-(3x+n)Al3x+nOnN16-n while keeping the cation ratios of RE, Si and Al constant.
Monophasic α-sialon ceramics with tailored microstructures, consisting of either fine equiaxed or elongated grains, have been obtained by using SPS, whether or not such an extra liquid phase is involved. The three processes, namely densification, phase transformation and grain growth, which usually occur simultaneously during conventional HP consolidation of Si3N4-based ceramics, have been precisely followed and separately investigated in the SPS process.
The enhanced densification is attributed to the non-equilibrium nature of the liquid phase formed during heating. The dominating mechanism during densification is the enhanced grain boundary sliding accompanied by diffusion- and/or reaction-controlled processes. The rapid grain growth is ascribed to a dynamic ripening mechanism based on the formation of a liquid phase that is grossly out of equilibrium, which in turn generates an extra chemical driving force for mass transfer. Monophasic α-sialon ceramics with interlocking microstructures exhibit improved damage tolerance. Y/Yb- stabilised monophasic α-sialon ceramics containing approximately 3 vol% liquid with refined interlocking microstructures have excellent thermal-shock resistance, comparable to the best β-sialon ceramics with 20 vol% additional liquid phase prepared by HP.
The obtained sialon ceramics with fine-grained microstructure show formidably improved superplasticity in the presence of an electric field. The compressive strain rate reaches the order of 10-2 s-1 at temperatures above 1500oC, that is, two orders of magnitude higher than that has been realised so far by any other conventional approaches. The high deformation rate recorded in this work opens up possibilities for making ceramic components with complex shapes through super-plastic forming.
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Colas, David. "Renforcement d'alliages fer-aluminium ordonnés B2 : influence d'additions (Ni, B) et de la microstructure." Phd thesis, Université Jean Monnet - Saint-Etienne, 2004. http://tel.archives-ouvertes.fr/tel-00009539.
Full textAbstract:
Nous étudions les effets d'additions (Ni et B) et de la microstructure sur le comportement mécanique d'alliages fer-aluminium contenant 40 % at. Al. Au niveau macroscopique, nous montrons que le nickel renforce les alliages FeAl sur toute la gamme de température, mais qu'il conduit simultanément à une diminution de la contrainte de clivage, accentuant ainsi la fragilité à l'ambiante de ces alliages. Nous confirmons l'intérêt du raffinement de la taille des grains, par métallurgie des poudres, pour améliorer la limite d'élasticité et la résistance à la rupture. Nous montrons alors le caractère additif de l'effet du nickel sur la limite d'élasticité par rapport au renforcement de type "Hall et Petch". Nous montrons aussi que les phénomènes de durcissement (nickel ou taille de grains) provoquent le masquage de l'anomalie de la limite d'élasticité que ces alliages présentent habituellement. L'étude des mécanismes de déformation à l'échelle des dislocations nous permet de préciser que le durcissement en solution solide (DSS) dû au nickel à basse température ne peut être expliqué par les théories classiques de DSS mais plus vraisemblablement par un effet du nickel sur la contrainte de Peierls. En outre, nous montrons que nos résultats microscopiques et macroscopiques concernant l'anomalie peuvent être pris en compte par le modèle de traînage de tubes d'APB. Enfin, nous mettons en relation l'observation en dynamique (microscopie en transmission in situ) d'un mécanisme de multiplication des superdislocations, avec la tendance au clivage des alliages contenant du nickel.