Academic literature on the topic 'Fiber Coating Reactor'

In order to meet a need of application of photocatalyst, a slurry dipping method was adopted for nano-TiO2 coating on optical fiber. Three slurry states were designed and their effects on coating quality were investigated. Experimental results showed that paste state may lead to surface cracks in coating. Both flocculent and dispersive slurry states can form high quality coatings whose coating microstructures are different, the former resulted in a loose and thicker coating and the later resulted in a dense and thinner coating, which supplied a basis for further study on effect of photocatalytic reaction and design of photocatalyst reactor.

Lanthanum-doped anatase TiO2coatings, which are composed of assemble crystalline of 50 nm diameter particles, when the percentage of dopant is 0.5 wt%, have been successfully fabricated by solgel dip-coating process on light leakage silica fiber (LSF) which length is 15cm and diameter is 125μm. This was achieved by adjustment of the lanthanum-doped solgel parameters such as molar ratio of precursors in lanthanum-doped TiO2-sols, the ratio of titanium tetrabutoxide to polyvinyl alcohol, dip-coating velocity, drying duration in air, thermal treatment and number of cyclical time of the process. Titania nanocrystals were prepared at ambient temperature in a liquid media using titanium tetrabutoxide as precursor, and the crystallization of amorphous precursor was preceded by peptizing with acid and then refluxing for a periodic time in homothermal water-bath. The photocatalytic properties of the La-TiO2films had been testified by the photo degradation of methyl orange. The lanthanum-doped anatase TiO2thin films were characterized by XRD and TEM. The products show much improved photocatalytic activity that will be useful in the design of a novel antibacterial, deodorant and antipollution new photo reactor.

The DISCOMS project, which stands for “DIstributed Sensing for COrium Monitoring and Safety”, considers the potential of distributed sensing technologies, based on remote instrumentations and Optical Fiber Sensing cables embedded into the concrete floor under the reactor vessel, to monitor the status of this third barrier of confinement. This paper focuses on the selection and testing of singlemode (SM) optical fibers with limited RIA (Radiation Induced Attenuation) to be compliant with remote distributed instruments optical budgets, the ionizing radiation doses to sustain, and their reduction provided by the concrete basemat shielding. The tests aimed at exposing these fibers and the corresponding sensitive optical cables, to the irradiation doses expected during the normal operation of the reactor (up to 60 years for the European Pressurized Reactor), followed by a severe accident. Several gamma and mixed (neutron-gamma) irradiations were performed at CEA Saclay facilities: POSÉÏDON irradiator and ISIS reactor, up to a gamma cumulated dose of about 2 MGy and fast neutron fluence (E > 1 MeV) of 6 x 1015 n/cm2. The first gamma test permitted to assess the RIA at various optical wavelengths, and to select three radiation tolerant singlemode fibers (RIA < 5 dB/100 m, at 1550 nm operating wavelength). The second one was performed on voluminous strands of sensitive cables encapsulating the selected optical fibers, up to approximately the same accumulated dose, at two temperatures: 30°C and 80°C. A significant increase of the RIA, without any saturation tendency, appeared for fibers inserted into cables, correlated with the increase of the hydroxyl attenuation peak at 1380 nm. Molecular hydrogen generated by the radiolysis of compounds of the cable is at the origin of this phenomenon. A third gamma irradiation run permitted to measure the radiolytic hydrogen production yield of some compounds of a dedicated temperature cable sample. The efficiency of a carbon coating layer over the silica cladding, acting as a barrier against hydrogen diffusion, was also successfully confirmed. Finally, the efficiency of this carbon coating layer has also been tested under neutron irradiation, then qualified as a protection barrier against hydrogen diffusion in the optical fiber cores.

The corrosion behaviors of SiC/SiC composite constituent materials in pure water at operating conditions, such as 300 °C and 8.5 MPa, were studied for potential application in accident-tolerant light water reactor (LWR) fuel cladding and core structures. Five kinds of SiC fibers, four kinds of SiC matrices, and three kinds of fiber/matrix interphase materials were examined in autoclaves. The potential constituent materials for future use in SiC/SiC composites were selected by considering corrosion rates and residual strength characteristics. The mass changes and the residual strength of each specimen were measured. SEM images of the surface layers were also inspected. The SiC fibers, regardless of their purity, crystallinity or stoichiometric ratio, decreased in strength due to the hydrothermal corrosion. For its part, the hydrothermal corrosion resistance of CVD-SiC, as a SiC matrix, was found to be affected by manufacturing conditions such as raw material gas type and synthesis temperature, as well as post-machining morphology. The CVD-carbon (CVD-C), as a fiber/matrix interphase material, showed good hydrothermal corrosion resistance. In order to protect the SiC fibers and the SiC matrices from hydrothermal corrosion, it would appear to be necessary to apply a dense CVD-C coating to both every fiber and the entire surface of the SiC matrices.

Greenhouse gas such asCO2is the primary cause of global warming. Alternative energy source should be provided without producing moreCO2, such as solar energy. One of the best routes to remedyCO2is to transform it to hydrocarbons using photo reduction. In our study,CO2was photocatalytically reduced to produce methanol using a Hg lamp with wavelength 365 nm in a steady-state optical-fiber photo reactor. The optical-fiber photo reactor, comprised of near 120 Cu/TiO2-coated fibers, was designed and assembled to transmit and spread light uniformly inside reactor.TiO2film was coated on optical fiber using dip-coating method. Titania and Cu-loaded solutions were prepared by a thermal hydrolysis method. The thickness of Cu/TiO2film was 53 nm and consisted of very fine spherical particle with diameter of near 14 nm. The XRD spectra indicated the anatase phase of allTiO2and Cu/TiO2films. The wavelength of absorption edge was on 367 nm, equivalent to near 3.3 eV. Most active Cu species onTiO2surface wereCu2Oclusters, and played an important role for the formation of methanol. The methanol yield increased with UV irradiative intensity. Photo activity increased with increasing Cu loadings. Maximum methanol rate was 0.45μmole/g-cat•hr using 1.2 wt%-Cu/TiO2catalyst under 16 W /cm2irradiation, 1.3 bar pressure ofCO2, and 5000 seconds mean residence time. Higher than 1.2 wt% Cu loading gave less rate of methanol yield because of the masking effect ofCu2Oclusters on the surface of TiO2.

Lanthanum-doped anatase TiO2coatings, which are composed of assemble crystalline of 50 nm diameter particles, when the percentage of dopant is 0.5 wt%, have been successfully fabricated by sol–gel dip-coating process on light leakage silica fiber (LSF) which length is 15cm and diameter is 125μm. This was achieved by adjustment of the lanthanum-doped sol–gel parameters such as molar ratio of precursors in lanthanum-doped TiO2-sols, the ratio of titanium tetrabutoxide to polyvinyl alcohol, dip-coating velocity, drying duration in air, thermal treatment and number of cyclical time of the process. Titania nano crystals were prepared at ambient temperature in a liquid media using titanium tetrabutoxide as precursor, and the crystallization of amorphous precursor was preceded by peptizing with acid and then refluxing for a periodic time in homothermal water-bath. The photocatalytic properties of the La-TiO2films had been testified by the photo degradation of methyl orange. The lanthanum-doped anatase TiO2thin films were characterized by XRD and TEM. The products show much improved photocatalytic activity that will be useful in the design of a novel antibacterial, deodorant and antipollution photo reactor.

Carbon fibers were treated with siloxane spin-on-glass and reaction bonded silicon oxycarbide coatings. The spin-on-glass (SOG) coatings were prepared by pyrolyzing solutions of polymethylsilsesquioxane (PMSO), polydimethoxysilane (PDSO), and poly(ethoxysilane)ethyltitanate copolymer (ESET). Since the flexibility of the coatings was found to be dependent on the concentration of the siloxane solution, only those of PMSO and PDSO below 1.25% were determined to be suitable for fiber coatings, and an alternative approach to the formation of a pliable silicon-based ceramic coating on the fibers was developed. Carbon fiber tows were impregnated by ethanolic solutions of organosilicon chlorides and fired at temperatures up to 900 °C to form a flexible reaction bonded silicon oxycarbide (RB–SiOC) coatings. Uncoated, SOG coated, and RB–SiOC coated carbon fibers were embedded in aluminum metal at 1000 °C. While both silica-based coatings protected the carbon surface, no wetting was observed, leading to fiber pull-out. When the coated fibers were treated with a mixture of Ti and B prior to immersion into the molten aluminum, complete wetting of the fibers occurred. In the presence of molten aluminum, the Ti/B coating enabled the exothermic formation of TiB2 and titanium aluminides, which facilitate wetting. This reaction is termed ASPIRE (Aluminum Self-Propagating Interfacial Reaction) and in combination with silicon-based ceramic coatings provides a scientific approach to the formation of stable carbon fiber/aluminum metal-matrix composites. The coated fibers and composites were characterized by scanning electron microscopy (SEM) with energy dispersive x-ray (EDX) analysis, and x-ray photoelectron spectroscopy (XPS).

AbstractWe report the synthesis of carbon nanowires (CNWs) via chemical vapor deposition using catalytic decomposition of ethanol on nanosized transition metals such as Co, Fe, and Ni. Dip-coating process was used for the formation of catalytic nanoparticles, inducing the growth of CNWs on the surface of the carbon fiber paper (CFP). The liquid ethanol used as carbon source was atomized by an ultrasonic atomizer and subsequently flowed into the reactor that was heated up to a synthesis temperature of 600–700°C. Microscopic images show that CNWs of <50 nm were densely synthesized on the surface of the CFP. Raman spectra reveal that a higher synthesis temperature leads to the growth of higher crystalline CNWs. In addition, we demonstrate the successful decoration of platinum nanoparticles on the surface of the prepared CNWs/CFP using the electrochemical deposition technique.

Research on carbon fiber oxide coatings is primarily focused on metal matrix composites. Such coatings act as a diffusion barrier between a matrix and a fiber and, in addition, they can be weak boundaries that significantly increase the mechanical properties of metal matrix composites. A simple and economical method of coating deposition is the sol–gel method. However, it does not allow for control of the thickness of the carbon fiber coating. To eliminate this limitation, a combined method is used that includes sol–gel technology and electrochemical deposition. The paper presents the results of studies on the production of SiO2 coatings on carbon fibers by the above method. The effect of current density, deposition time, salt concentration, pH of the reaction medium, TEOS/H2O molar ratio, and alcohol concentration in the reaction medium on the structure and thickness of the coatings was studied.

The main goal of this dissertation was to show that the principle of atomic layer deposition (ALD) can be applied to “endless” fibers. A reactor of atomic layer deposition has been designed, especially for coating depositions onto meter long bundles of fibers. Aluminum oxide (alumina), titanium oxide (titania), double layers of alumina and titania, as well as aluminium phosphate have been deposited onto bundles of carbon fibers using the home-built reactor. Scanning electron microscopic (SEM) and transmission electron microscopic (TEM) images indicate that the coatings were uniform and conformal onto fiber surface. There was a good adhesion of the coatings to the fibers. Alumina has been deposited using two separate aluminum sources (aluminum trichloride and trimethylaluminum), and water as a source of oxygen. In case of alumina deposition using aluminum trichloride and water, initial deposition temperature was 500 °C. In these conditions, a part of the fiber bundle has been damaged. Thus, the deposition temperature was decreased to 300 °C and the fibers were unaffected. In addition, during this process hydrochloric acid is formed as a byproduct which is a corrosive substance and affects the reactor and there was a chloride impurity in the coatings. Thus, aluminum trichloride precursor was replaced by trimethylalumium. Alumina deposition onto carbon fibers using trimethylaluminum and water was carried out at a temperature of 77 °C. SEM images revealed that the fibers were unaffected and the coatings were uniform and conformal. Oxidation resistance of the carbon fibers was improved slightly after alumina deposition. Oxidation onset temperature of the uncoated fibers was about 630 °C. The resistance was linearly increased with the coating thickness (up to 660 °C) and getting saturated over a thickness of 120 nm. Titania coatings have been deposited using titanium tetrachloride and water. The physical appearances of the titania coatings were similar to the alumina coatings. The oxidation onset temperature of the titania coated carbon fibers was similar to the uncoated fibers but the rate of oxidation was decreased than the uncoated fibers. Two double layer coatings were deposited, alumina followed by titania (alumina/titania), and titania followed by alumina (titania/alumina). If the fibers were coated with the double layer of alumina/titania, they had almost same oxidation onset as alumina coated fibers but the rate of oxidation was decreased significantly compared to alumina coated fibers. This feature is independent of the thickness of the titania layers, at least in the regime investigated (50 nm alumina followed by 13 nm and 40 nm titania). On the other hand, the oxidation onset temperature of fibers coated with titania/alumina (20 nm titania /30 nm alumina) was approximately 750 °C. The fibers were burned completely when temperature was further increased to 900 °C and held another 60 minutes at 900 °C. This is significantly better than any other coating used in this dissertation. ALD of titania and alumina in principle was known beforehand, this dissertation here applies this knowledge for the first time to endless fibers. Furthermore, this dissertation shows for the first time that one can deposit aluminum phosphate via ALD (planar surface as well as fibers). Aluminum phosphate might be special interest in the fiber coating because it is a rather soft material and thus might be used to obtain a weak coupling between fiber and matrix in composites. Aluminum phosphate was deposited using trimethylaluminum and triethylphosphate as precursors. Energy dispersive X-ray spectroscopy and solid state nuclear magnetic resonance spectra confirmed that the coating comprises aluminum phosphate (orthophosphate as well as other stoichiometries). Scanning electron microscopic images revealed that coatings are uniform and conformal. In cases of alumina and titania, it was observed that the coatings were delaminated from the ends of cut fibers and thus formed of clear steps. On the other hand, for aluminum phosphate coating it was observed that the border between coating and underlying fiber often being smeared out and thus formed an irregular line. It seems in case aluminum phosphate cohesion is weaker than adhesion, thus it might be act a weak interface between fiber and matrix. Alumina, titania, and double layer microtubes have been obtained after selective removal of the underlying carbon fibers. The carbon fibers were selectively removed via thermal oxidation in air at temperatures exceeding 550 °C. SEM and TEM images indicate that the inner side of the tube wall has the same morphology like the fibers. In addition, it was observed that the individual microtubes were separated from their neighbors and they had almost uniform wall thicknesses. The longest tubes had a length of 30 cm
Das Hauptziel dieser Dissertation bestand darin nachzuweisen, dass die Atomlagenabscheidung (engl. atomic layer deposition (ALD)) auf „endlose“ Fasern angewendet werden kann. Es wurde ein Reaktor zur Atomlagenabscheidung gestaltet, der speziell für die Beschichtung meterlanger Faserbündel geeignet ist. Aluminiumoxid, Titanoxid, Doppelschichten aus Aluminiumoxid und Titanoxid sowie Aluminiumphosphat wurden mit Hilfe des selbstgebauten Reaktors auf Kohlefaserbündel abgeschieden. Rasterelektronenmikroskopische (REM) und transmissionselektronenmikroskopische (TEM) Aufnahmen zeigten, dass die Beschichtung auf den Fasern einheitlich und oberflächentreu war. Des Weiteren wurde eine gute Adhäsion zwischen Beschichtung und Fasern beobachtet. Das Prinzip der Beschichtung mit Titanoxid und Aluminiumoxid mit Hilfe der ALD war bereits vorher bekannt und im Rahmen dieser Dissertation jedoch erstmals auf "endlose" Fasern angewendet. Des Weiteren wird in dieser Dissertation erstmals gezeigt, dass es möglich ist, Aluminiumphosphat mittels ALD abzuscheiden (sowohl auf planaren Oberflächen als auch auf Fasern). Aluminiumphosphat könnte von besonderem Interesse in der Faserbeschichtung sein, da es ein relativ weiches Material ist und könnte daher als eine Art „schwacher“ Verbindung zwischen Faser und Matrix in Kompositen dienen. Die Oxidationsbeständigkeit von beschichten Kohlefasern wurde im Vergleich zu unbeschichteten Fasern bis zu einem gewissen Grad erhöht. Monoschichten von Aluminiumoxid und Titanoxid waren dafür wenig effektiv. Aluminiumphosphatbeschichtete Fasern waren deutlich besser geeignet als die beiden anderen. Eine Doppelschicht aus Titanoxid gefolgt von Aluminiumoxid verbesserte die Oxidationsbeständigkeit nochmals deutlich gegenüber allen anderen Beschichtungen, die in dieser Dissertation verwendet wurden. Mikroröhren aus Aluminiumoxid, Titanoxid und Doppelschichten wurden durch die selektive Entfernung der zugrunde liegenden Kohlefasern erhalten. Einzelne Mikroröhren waren von benachbarten Röhren getrennt und sie weisen eine nahezu einheitliche Wanddicke auf

Climate change is one of the greatest challenges facing humanity. Fossil fuels are the primary source of energy on Earth. Since the global economic growth is closely linked to the global energy demand, fossil fuel usage remains the largest contributor to the steadily increasing atmospheric carbon dioxide concentration (CO2). CO2 mitigation through carbon capture and conversion are of great interest. Capturing CO2 from point source emitters is possible by absorption in a basic, sodium hydroxide (NaOH) containing solution, which is then converted into sodium bicarbonate (NaHCO3). Conversion of CO2 is thermodynamically demanding as it will require a large amount of energy, which renders currently used technologies infeasible. A promising alternative is the conversion of captured NaHCO3 into useful hydrocarbons at moderate operating conditions using solar energy, by a process called photocatalysis. Photocatalysis is the acceleration of a photo-induced reaction in the presence of a catalyst. Photocatalytic reactors have not yet been commercialised due to suboptimal catalyst and reactor designs. The typically low catalyst activity has to be countered by efficiently loading a large amount of catalyst in the reactor. This results in a problem regarding the photon transfer limitations to the catalytically active site, which limits illumination of the catalyst in the reactor. This can be overcome by using optical fibre to guide photons, which are coated with the photocatalyst. However, it is estimated that a reactor containing ca. 1 g of catalyst will require ca. 1.8 km of identically coated optical fibre. The aim of the project is to design, construct and commission an automated controllable process to increase the production volume of catalyst coated optical fibre using either a solgel suspension or a slurry containing P25 (TiO2). A multi-step optical fibre coating process was developed to achieve the desired coated optical fibre as a product. It consists of 6 major units that process raw (polymer-coated) optical fibre into catalyst coated optical fibre. The steps include the 4 essential steps required for optical fibre preparation by-hand, these steps are stripping, washing, coating and heat treatment. This automated optical fibre catalyst coating process (AOFCCP) can make the coating of optical fibres time-efficient and controllable. The latter can be achieved by controlling the effect various process parameters affecting the coating thickness and homogeneity of the coating, such as pH, heat treatment, catalyst slurry concentration as well as pulling speed. The AOFCCP produced coating thicknesses ranging from 0.47 µm - 0.59 µm and 0.37 µm - 0.46 µm for the P25 slurry and sol-gel coating methods respectively. The pH of the P25 slurry was found to have a negligible effect on both the coating thickness and surface morphology, therefore is no longer regarded as a process variable in the AOFCCP. The thickness of the coating increased with an increase in P25 slurry concentration with a maximum achievable coating thickness of 0.87 µm using a slurry concentration of 20 wt.-%. The temperature of heat treatment which was tested showed different relationships between the coating methods. For the sol-gel coating method, the increase in temperature resulted in a decrease in coating thickness possibly due to the decrease in porosity whereas for the P25 slurry method the increase in temperature showed an increase in coating thickness possibly due to the higher evaporation rates. An increase in the pulling speed in the AOFCCP resulted in an increase in coating thickness on the optical fibre independent of the coating method; coating thicknesses ranging from 0.41 µm - 0.71 µm and 0.23 µm - 2.14 µm were obtained using the P25 slurry and sol-gel coating methods, respectively, by varying the pulling speed. The critical cracking thickness is defined as the thickness of the film, produced by the sol-gel method, at which coating deformations become observable which was found to be 0.37 µm at 600 °C, and 0.77 µm at a pulling speed of 2.30 mm.s -1 . The results obtained from the commissioning experiments showed that the AOFCCP can produce coated optical fibre with controllable thickness. The controllability was discovered to be in the adjustment of the process variables investigated which showed a significant effect on the coating thickness, except for pH. Based on the statistical analysis that was performed, it was confirmed that the results obtained from the system were repeatable and that the coating was uniform for all process variables that were investigated except for sol-gel coating at high speeds of 2.88 mm.s -1 – 3.46 mm.s -1 . The system was able to produce fibre with coating thickness's between 0.4 – 1.1 µm. It is recommended that a combination of the process variables be used in order to achieve better controllability in the process and to achieve thicker coating layers. Furthermore, the operating ranges of the process variables should be increased in order to determine the extent of the relationship between the process variable and the coating thickness and surface morphology.

碩士
國立臺灣大學
化學工程學研究所
91
Titania solutions were prepared by thermal hydrolysis, sol-gel method, and obtained from P25-suspension, Hombikat XXS100 and Hombikat UV100WP TiO2 solution (Sachtleben Chemie GmbH Com., Germany). The TiO2 films were coated on glass plates and optical fibers by the dip-coating method. The thickness of films ranged from 60~600 nm after calcinations at 500°C. Process parameters for coating TiO2, such as the concentration of TiO2 solution, the rate of dipping and the times of coating were studies. The films became thicker, and the crystal size increased by increasing the concentration of TiO2 solution, the dipping rate and the numbers of coating. However, films were found crack or aggregate when the film thickness was thick. From SEM micrographs, AFM surface profiles and the ASTM adhesion tests, the films coated by thermal hydrolysis and Hombikat XXS100 solution were among the best, following by the films coated by sol-gel, P25-suspension, and Hombikat UV100WP solution. From the result of XRD, the anatase phase was found for all films. Furthermore, the wavelength of absorption was under 400nm from the UV-Vis spectra. For TiO2 superhydrophilicity property, it was found that the contact angle of water decreased to near zero under UV-light irradiation, and recovered to the initial contact angle in darkness. An optical-fiber reactor (OFR) with TiO2-coated fibers was designed and assembled to transport UV light to fiber-supported TiO2 and conducted a photocatalytic reaction. Gas-phase ammonia was decomposed in the OFR under UV-light irradiation showing a good photocatalytic reactivity of TiO2-coated fibers.

The main goal of this dissertation was to show that the principle of atomic layer deposition (ALD) can be applied to “endless” fibers. A reactor of atomic layer deposition has been designed, especially for coating depositions onto meter long bundles of fibers. Aluminum oxide (alumina), titanium oxide (titania), double layers of alumina and titania, as well as aluminium phosphate have been deposited onto bundles of carbon fibers using the home-built reactor. Scanning electron microscopic (SEM) and transmission electron microscopic (TEM) images indicate that the coatings were uniform and conformal onto fiber surface. There was a good adhesion of the coatings to the fibers. Alumina has been deposited using two separate aluminum sources (aluminum trichloride and trimethylaluminum), and water as a source of oxygen. In case of alumina deposition using aluminum trichloride and water, initial deposition temperature was 500 °C. In these conditions, a part of the fiber bundle has been damaged. Thus, the deposition temperature was decreased to 300 °C and the fibers were unaffected. In addition, during this process hydrochloric acid is formed as a byproduct which is a corrosive substance and affects the reactor and there was a chloride impurity in the coatings. Thus, aluminum trichloride precursor was replaced by trimethylalumium. Alumina deposition onto carbon fibers using trimethylaluminum and water was carried out at a temperature of 77 °C. SEM images revealed that the fibers were unaffected and the coatings were uniform and conformal. Oxidation resistance of the carbon fibers was improved slightly after alumina deposition. Oxidation onset temperature of the uncoated fibers was about 630 °C. The resistance was linearly increased with the coating thickness (up to 660 °C) and getting saturated over a thickness of 120 nm. Titania coatings have been deposited using titanium tetrachloride and water. The physical appearances of the titania coatings were similar to the alumina coatings. The oxidation onset temperature of the titania coated carbon fibers was similar to the uncoated fibers but the rate of oxidation was decreased than the uncoated fibers. Two double layer coatings were deposited, alumina followed by titania (alumina/titania), and titania followed by alumina (titania/alumina). If the fibers were coated with the double layer of alumina/titania, they had almost same oxidation onset as alumina coated fibers but the rate of oxidation was decreased significantly compared to alumina coated fibers. This feature is independent of the thickness of the titania layers, at least in the regime investigated (50 nm alumina followed by 13 nm and 40 nm titania). On the other hand, the oxidation onset temperature of fibers coated with titania/alumina (20 nm titania /30 nm alumina) was approximately 750 °C. The fibers were burned completely when temperature was further increased to 900 °C and held another 60 minutes at 900 °C. This is significantly better than any other coating used in this dissertation. ALD of titania and alumina in principle was known beforehand, this dissertation here applies this knowledge for the first time to endless fibers. Furthermore, this dissertation shows for the first time that one can deposit aluminum phosphate via ALD (planar surface as well as fibers). Aluminum phosphate might be special interest in the fiber coating because it is a rather soft material and thus might be used to obtain a weak coupling between fiber and matrix in composites. Aluminum phosphate was deposited using trimethylaluminum and triethylphosphate as precursors. Energy dispersive X-ray spectroscopy and solid state nuclear magnetic resonance spectra confirmed that the coating comprises aluminum phosphate (orthophosphate as well as other stoichiometries). Scanning electron microscopic images revealed that coatings are uniform and conformal. In cases of alumina and titania, it was observed that the coatings were delaminated from the ends of cut fibers and thus formed of clear steps. On the other hand, for aluminum phosphate coating it was observed that the border between coating and underlying fiber often being smeared out and thus formed an irregular line. It seems in case aluminum phosphate cohesion is weaker than adhesion, thus it might be act a weak interface between fiber and matrix. Alumina, titania, and double layer microtubes have been obtained after selective removal of the underlying carbon fibers. The carbon fibers were selectively removed via thermal oxidation in air at temperatures exceeding 550 °C. SEM and TEM images indicate that the inner side of the tube wall has the same morphology like the fibers. In addition, it was observed that the individual microtubes were separated from their neighbors and they had almost uniform wall thicknesses. The longest tubes had a length of 30 cm.:Bibliographische Beschreibung und Referat 2 Abstract 4 List of abbreviations 10 1. General introduction and outline of this dissertation 12 1.1 References 20 2. Atomic layer deposition: Process and reactor 25 2.1 Introduction 25 2.2 Principle of atomic layer deposition 26 2.3 Materials and methods 29 2.3.1 Precursors 29 2.3.2 Precursors transportation 31 2.3.3 Carrier and purge gas 32 2.3.4 ALD reactors 32 2.4 Flow-Type ALD reactor for fiber coating 33 2.5 Conclusion 35 2.6 References 35 3. Single layer oxide coatings 38 3.1 State of the art 38 3.2 Alumina coating using non-flammable precursors 39 3.2.1 Introduction 39 3.2.Result and discussion 39 3.3 Alumina coating using organometallic precursor 46 3.2.1 Introduction 46 3.2.2 Results and discussion 46 3.4 Titania coating using titanium tetrachloride and water 59 3.4.1 Introduction 59 3.4.2 Results and discussion 59 3.5 Experimental Part 67 3.5.1 General experiments 67 3.5.2 Alumina coating using aluminum chloride and water 69 3.5.3 Alumina coating using trimethylalumium and water 69 3.5.4 Titania coating 72 3.6 Conclusions 72 3.7 References 74 4. Coating thickness and morphology 78 4.1 Introduction 78 4.2 Results and discussion 80 4.2.1 Purge time 15 s 81 4.2.2 Purge time 30 s 85 4.2.3 Purge time 45 s to 100 s 85 4.3 Experimental part 88 4.4 Conclusions 89 4.5 References 89 5. Alumina and titania double layer coatings 91 5.1 Introduction 91 5.2 Results and discussion 92 5.3 Experimental part 102 5.4 Conclusions 103 5.5 References 103 6. Atomic layer deposition of aluminum phosphate 105 6.1 Introduction 105 6.2 Results and discussion 106 6.3 Experimental part 113 6.4 Conclusions 114 6.5 References 115 7. Alumina microtubes 117 7.1 Introduction 117 7.2 Results and discussion 118 7.2.1 Fibers before coating deposition 118 7.2.2 Coatings on the carbon fibers 118 7.2.3 Microtubes 121 7.3 Experimental part 127 7.4 Conclusions 128 7.5 References 128 8. Conclusions 131 Acknowledgements 136 Curriculum Vitae 138 Selbständigkeitserklärung 142
Das Hauptziel dieser Dissertation bestand darin nachzuweisen, dass die Atomlagenabscheidung (engl. atomic layer deposition (ALD)) auf „endlose“ Fasern angewendet werden kann. Es wurde ein Reaktor zur Atomlagenabscheidung gestaltet, der speziell für die Beschichtung meterlanger Faserbündel geeignet ist. Aluminiumoxid, Titanoxid, Doppelschichten aus Aluminiumoxid und Titanoxid sowie Aluminiumphosphat wurden mit Hilfe des selbstgebauten Reaktors auf Kohlefaserbündel abgeschieden. Rasterelektronenmikroskopische (REM) und transmissionselektronenmikroskopische (TEM) Aufnahmen zeigten, dass die Beschichtung auf den Fasern einheitlich und oberflächentreu war. Des Weiteren wurde eine gute Adhäsion zwischen Beschichtung und Fasern beobachtet. Das Prinzip der Beschichtung mit Titanoxid und Aluminiumoxid mit Hilfe der ALD war bereits vorher bekannt und im Rahmen dieser Dissertation jedoch erstmals auf "endlose" Fasern angewendet. Des Weiteren wird in dieser Dissertation erstmals gezeigt, dass es möglich ist, Aluminiumphosphat mittels ALD abzuscheiden (sowohl auf planaren Oberflächen als auch auf Fasern). Aluminiumphosphat könnte von besonderem Interesse in der Faserbeschichtung sein, da es ein relativ weiches Material ist und könnte daher als eine Art „schwacher“ Verbindung zwischen Faser und Matrix in Kompositen dienen. Die Oxidationsbeständigkeit von beschichten Kohlefasern wurde im Vergleich zu unbeschichteten Fasern bis zu einem gewissen Grad erhöht. Monoschichten von Aluminiumoxid und Titanoxid waren dafür wenig effektiv. Aluminiumphosphatbeschichtete Fasern waren deutlich besser geeignet als die beiden anderen. Eine Doppelschicht aus Titanoxid gefolgt von Aluminiumoxid verbesserte die Oxidationsbeständigkeit nochmals deutlich gegenüber allen anderen Beschichtungen, die in dieser Dissertation verwendet wurden. Mikroröhren aus Aluminiumoxid, Titanoxid und Doppelschichten wurden durch die selektive Entfernung der zugrunde liegenden Kohlefasern erhalten. Einzelne Mikroröhren waren von benachbarten Röhren getrennt und sie weisen eine nahezu einheitliche Wanddicke auf.:Bibliographische Beschreibung und Referat 2 Abstract 4 List of abbreviations 10 1. General introduction and outline of this dissertation 12 1.1 References 20 2. Atomic layer deposition: Process and reactor 25 2.1 Introduction 25 2.2 Principle of atomic layer deposition 26 2.3 Materials and methods 29 2.3.1 Precursors 29 2.3.2 Precursors transportation 31 2.3.3 Carrier and purge gas 32 2.3.4 ALD reactors 32 2.4 Flow-Type ALD reactor for fiber coating 33 2.5 Conclusion 35 2.6 References 35 3. Single layer oxide coatings 38 3.1 State of the art 38 3.2 Alumina coating using non-flammable precursors 39 3.2.1 Introduction 39 3.2.Result and discussion 39 3.3 Alumina coating using organometallic precursor 46 3.2.1 Introduction 46 3.2.2 Results and discussion 46 3.4 Titania coating using titanium tetrachloride and water 59 3.4.1 Introduction 59 3.4.2 Results and discussion 59 3.5 Experimental Part 67 3.5.1 General experiments 67 3.5.2 Alumina coating using aluminum chloride and water 69 3.5.3 Alumina coating using trimethylalumium and water 69 3.5.4 Titania coating 72 3.6 Conclusions 72 3.7 References 74 4. Coating thickness and morphology 78 4.1 Introduction 78 4.2 Results and discussion 80 4.2.1 Purge time 15 s 81 4.2.2 Purge time 30 s 85 4.2.3 Purge time 45 s to 100 s 85 4.3 Experimental part 88 4.4 Conclusions 89 4.5 References 89 5. Alumina and titania double layer coatings 91 5.1 Introduction 91 5.2 Results and discussion 92 5.3 Experimental part 102 5.4 Conclusions 103 5.5 References 103 6. Atomic layer deposition of aluminum phosphate 105 6.1 Introduction 105 6.2 Results and discussion 106 6.3 Experimental part 113 6.4 Conclusions 114 6.5 References 115 7. Alumina microtubes 117 7.1 Introduction 117 7.2 Results and discussion 118 7.2.1 Fibers before coating deposition 118 7.2.2 Coatings on the carbon fibers 118 7.2.3 Microtubes 121 7.3 Experimental part 127 7.4 Conclusions 128 7.5 References 128 8. Conclusions 131 Acknowledgements 136 Curriculum Vitae 138 Selbständigkeitserklärung 142

Volume 2 presents the fundamental principles related to polymer processign operations including the processing of thermoplastic polymers and thermosets. The objective of this volume is not to provide recipies that necessarily guarantee better product quality. Rather, emphasis is placed on presenting a fundamental approach to effectively analyze processing operations. The specific polymer processing operations for thermoplastics include plasticating single-screw extrusion, morphology evolution during compounding of polymer blends, compatibilization of immiscible polymer blends, wire coating extrusion, fiber spinning, tubular film blowing, coextrusion, and thermoplastic foam extrusion. The specific polymer processing operations for thermosets include reaction injection molding, pultrusion of fiber-reinforced thermosets, and compression molding of thermoset composites.

Two-dimensional C/C-ZrB2-ZrC-SiC composites with three phases of ultra high temperature ceramics (UHTCs) are fabricated for the first time using blending pre-ceramic polymeric precursors through the traditional polymer infiltration and pyrolysis (PIP) technique, in which a porous carbon fiber reinforced pyrolytic carbon (C/C) with a porosity of about 60% is prepared as preforms. The fabricated composite possesses a matrix of 20ZrB2-30ZrC-50SiC, which is obtained by co-pyrolysis of three pre-ceramic polymers solution in xylene with certain molar ratios. Pyrolysis of these ZrB2-ZrC-SiC pre-ceramic precursors is studied with XRD characterization of the residual solids. The gas phase products are analysized with an on-line GC-MS-FTIR coupling technique, which confirms the formation of crystalline ZrC and ZrB2 from these precursors at temperatures above 1400°C. Possible mechanisms of pyrolysis and formation of pure ZrB2 from the precursors with various B/Zr molar ratios are suggested. The densification process and microstructures of the fabricated composite are studied. It is found that a composite with a bulk density of 2.06 g/cm3 and open porosity of 9.6% can be obtained after 16 PIP cycles. The formed matrix exhibits homogeneous dispersion of three matrix ceramics without any oxide impurities, i.e., the nano sized ZrB2 and ZrC particles dispersed in a continuous SiC ceramic with clean crystalline boundaries and particle dimensions less than 200 nm. No erosion or interface reaction occurs upon the carbon fiber reinforcement, which therefore avoids a dramatic deterioration of mechanical strength of carbon fiber and the composite. Improvement of PIP benefits from two aspects; firstly, the dense pyrolytic carbon interphase deposited on fiber surface by CVI serves as barrier coating and secondly, pyrolysis of the novel organic polymeric precursors does not release corrosive by-products such as hydrogen chloride.

Because of the great importance of the surface properties of the polysiloxanes, this topic is treated separately in this chapter. Hydrophobic polysiloxanes having simple aliphatic or aromatic side groups have surfaces that show essentially no attraction to water. In fact, polysiloxanes can serve as water repellants. This property is very useful for applications such as protective coatings on historical monuments and for controlling the surfaces of other polymers, sensors, and quantum dots. Hydrophobic surfaces can be readily regenerated if the surface becomes damaged. Regeneration occurs by rearrangements of the polysiloxane chains so that the hydrophobic methyl groups are once again covering the surface. The flexibility of the siloxane chain backbone facilitates this process. It is also possible to prepare hydrophobic films using methyl-modified siloxane melting gels. Glass surfaces or wool fibers can be coated with polydimethylsiloxane (PDMS) to make them more hydrophobic. In some cases, it is necessary to modify a polysiloxane surface to make it hydrophilic or hydrophobic. Hydrophobization is one aspect of the general topic of modifying and managing the properties of polymer surfaces. An important example involves soft contact lenses that contain PDMS, which is often used because of its very high permeability to oxygen, which is required for metabolic processes within the eye. Such lenses do not feel comfortable however because they do not float properly on the aqueous tears that coat the eye. There are a number of ways to modify the surfaces. There is even a way to make “unreactive” silicones react with inorganic surfaces. In some applications it is useful to have hydrophilicity in the bulk of the polymer instead of just at the surface. One way of doing this is by simultaneously end linking hydrophilic poly(ethylene glycol) (PEG) chains and hydrophobic PDMS chains. Another way is to make a PDMS network with a trifunctional organosilane R’Si(OR) end linker that contains a hydrophilic R’ side chain, such as a polyoxide. Treating only the surfaces is another possibility, for example, by adding hydrophilic brushes by vapor deposition/hydrolysis cycles. Such hydrophilic polysiloxanes can also serve as surfactants.

A numerical heat transfer study of the chemical vapor deposition coating process used in the manufacture of optical fibers is conducted. A finite volume model, developed to study gas flow and heat transfer in the reactor and heat transfer within the fiber itself, is used. A parametric correlation relating percent temperature drop to the Peclet number and dimensionless fiber radius is determined. This correlation is expanded upon to obtain a correlation for the amount of energy loss as the fiber travels through the reactor. These equations are valid for fiber radius values ranging from 62.5 to 200 μm, and for draw rates ranging from 0.25 to 2.0 m/s.

In this paper, we study the chemical vapor deposition (CVD) process used to hermetically coat optical fibers during draw. Temperature is calculated by coupling radiation and convection heat transfer by the reactor walls and gas flow with a radially-lumped heat transfer model for the moving optical fiber. Multi-component species diffusion is modeled using the Maxwell-Stefan equations. Gas-phase reaction kinetics is modeled using a 2-step chemical kinetics mechanism derived from RRKM theory with detailed kinetics data compiled from literature. Surface reaction kinetics are described using collision theory in which a sticking coefficient is used as an empirical parameter to predict surface reactions. A parameter study is carried out with various optical fiber inlet temperature and drawing speed, and validated with experiment results.

This study investigates the chemical vapor deposition (CVD) process used to hermetically coat optical fibers during draw using propane as the precursor gas. Temperature is calculated by coupling radiation and convection heat transfer from the reactor walls and gas flow with a radially-lumped conduction heat transfer model for the moving optical fiber. Multi-component species diffusion is modeled by the Dixon-Lewis method, which is based on the molecular theory for ideal gases. Gas-phase reaction kinetics is modeled using a 3-step gas phase chemical kinetics mechanism. Surface reaction kinetics is described using collision theory in which a sticking coefficient is used as an empirical parameter to predict surface reactions. A parameter study is carried out with various optical fiber inlet temperature and drawing speed, and validated with experiment results.

Carbon coated optical fibers are produced by the chemical vapor deposition process which includes multi-species mass transport with chemical reactions. A proper numerical model of this process will help elucidate the basic mechanisms and optimize the process to improve coating quality. A heat transfer model has been developed in our research group. We are now developing an applicable chemical kinetics model to include mass transport with gas phase and surface reactions. Several different chemical reactor models have been tried, including a continuous-stirred tank reactor (CSTR) model, a plug flow reactor (PFR) model and a multi-component diffusion model with the Maxwell-Stefan approximations. We found that in reactor conditions with well-mixed or large mass Peclet number, the CSTR and PFR models validate well with experimental results. But a multi-component gas diffusion model is needed for low mass Peclet number conditions. The model has been extended to a wider range of temperatures necessary for this optical fiber coating process.

Permeability of helium gas of Silicon carbide ceramic composites material, which is one of the most important properties in application of SiC composite for advanced reactors, is studied by using a simple, low-cost test system. The test system can not only qualitatively determine whether the sample is permeable or not, but also quantitatively measure the permeability for the permeable ones by water displacement. The tests are conducted with low pressure in room temperature. The permeability of the SiSiC composite depends on the preparation method. In four flat-plate materials prepared by different processes for the test, the splint based SiSiC and cordierite coated fiber reinforced SiSiC are hermetic, the permeability of uncoated fiber reinforced SiSiC and CVD carbon coated fiber reinforced SiSiC are 0.216cm2/s and 0.109cm2/s, which imply that the permeability is cut in half with the coating. The samples are scanned under SEM to analyze their microscopic structures and verified that the difference of permeability is related to their coatings as well as the pores and cracks.

In this paper, we investigated the effect of the film thickness on heat transfer and subsequent film temperature distribution of an optical fiber as it traverses through a chemical vapor deposition (CVD) reactor. A 50 nm thick carbon coating is applied on the optical fiber as it moves through the CVD reactor. In this process, the only heat source is the hot optical fiber entering the CVD reactor from the draw furnace. Radiation heat transfer from the optical fiber as it is being coated plays an important role during CVD carbon film growth. The carbon film will change the effective emissivity of the optical fiber as it traverses through the CVD reactor. This study will calculate the effective emissivity of this film-fiber structure based on wave theory, and evaluate the optical fiber’s resulting temperature field and rate of heat transfer loss during chemical vapor deposition. Results are correlated to operating conditions.

In this paper, we studied the effect of thermal diffusion (Soret effect), the heat flux due to species concentration gradient (Dufour effect) and the heat by chemical reactions in a chemical vapor deposition (CVD) process used to hermetically coat optical fibers. Using a previously developed mass and heat transfer model to investigate the transport phenomena in this process, the Soret and Dufour effects are compared to ordinary mass diffusion. The thermal conductivity, molecular diffusivity and thermal diffusivity are calculated using a multi-component model. The contribution of heat of chemical reactions to overall heat transfer in the CVD is also discussed. Soret effect and heat by chemical reactions are found to be very important in this process, and their effect is related to operating conditions such as draw speed and optical fiber inlet temperature.

A dense silicon carbide matrix composite reinforced by Hi-Nicalon fibers coated with boron nitride was fabricated by slurry impregnation and subsequent reaction sintering with molten silicon. The effect of the fiber coating structure and the infiltrating metal composition on the mechanical properties of the composite was investigated. The fabrication process for the combustor liner and the shroud segment for a 15 MW gas turbine was developed. The small combustor liner and the shroud segment with some machined notches were evaluated in a combustion test at 1773 K and atmospheric pressure. Excellent durability for gas turbine hot parts was recognized.

Hard water is unsuitable for industrial and domestic purposes given its high levels of calcium and magnesium divalents which generate scale, oxidation and are antagonistic of optimal performance of detergents and industrial equipment. Conventional methods for water softening generate by-products that need to be treated, which makes these methods economically and environmentally unsustainable and open the opportunity to develop new technology for this application. The ion exchange behavior during the charge and discharge processes (i.e. oxidation / reduction), of conducting polymers and the combination of these materials with other such as fibers, to develop new hybrid materials that exhibit the inherent properties of both components, has been the object of many studies in the last years. The aim of this study is to evaluate the applicability of vegetable cellulose microfibers as a base to obtain a conducting polymer composite membrane with polypyrrole and to analyze the membrane performance to remove ions dissolved in hard water. The application of conducting polymer composite on water softening is based on the use of pyrrole’s electrochemical properties jointed to the flexibility and relatively high surface areas associated with cellulose, to promote an ion exchange reaction between the composite membrane and the hard water. The cellulose membranes obtained from banana plant waste (raquis), were uniform with individual and well separated fibers. The fibers were successfully encapsulated by a continuous coating of polypyrrole through in situ oxidative chemical polymerization. The amount of polypyrrole deposited on the fiber increased with increasing concentrations of the monomer, which was easily identified through the observation of differences on the intensity of the light to dark colour shift that coated the fibers after the polymerization. The applicability of the conducting polymer composite on water softening was tested using an experimental device, finding reductions on the conductivity for hard water within 23 to 66 μs/cm after 6 hours of the assay.

Strong, tough, high temperature ceramic matrix composites are currently being developed for application in advanced heat engines. One of the most promising of these new materials is a SiC fiber-reinforced silicon nitride ceramic matrix composite (SiCf/Si3N4). The interfacial shear strength in such composites is dependant on the integrity of the fiber’s carbon coating at the fiber-matrix interface. The integrity of the carbon rich interface can be significantly reduced if the carbon is oxidized. Since the thermal diffusivity of the fiber is greater than that of the matrix material, the removal of carbon increases the contact resistance at the interface reducing the thermal diffusivity of the composite. Therefore thermal diffusivity images can be used to characterize the progression of carbon depletion and degradation of the composite. A new thermal imaging technique has been developed to provide rapid large area measurements of the thermal diffusivity perpendicular to the fiber direction in these composites. Results of diffusivity measurements will be presented for a series of SiCf/Si3N4 (reaction bonded silicon nitride) composite samples heat-treated under various conditions. Additionally, the ability of this technique to characterize damage in both ceramic and other high temperature composites will be shown.