Dissertations / Theses on the topic 'Reducing atmosphere'

This thesis presents algorithms for performing the next two reduction steps, namely orthogonalization and extraction. More specifically, this thesis addresses the following research question: What are proper methods of orthogonalizing spectral images in preparation for extraction?

Corals face serious worldwide population declines due to global climate change in combination with direct anthropogenic impacts. Global climate change is difficult to manage locally, but policy makers can regulate the magnitude of local stressors affecting reefs. The objective of this experiment is to investigate if reducing sedimentation will enable reef corals to better endure global climate change. It has been shown that some coral species can handle climate change stress when provided with additional energy resources. Here I tested if the capacity of corals to cope with climate change can be improved when their ability to feed and photosynthesize was not compromised by increased sedimentation. Sedimentation can impede coral feeding and their ability to photosynthesize due to direct polyp blocking and increased turbidity, which reduces light availability. To evaluate the potential of enhancing coral ability to tolerate climate change by reducing a local stressor, I examined the survival and growth of brooding coral Porites astreoides juveniles when exposed to ambient and elevated water temperatures under differing sedimentation rates. I also assessed if sediment composition has significant impacts on these results. I used sediment from a reef and sediment from a boat basin within a port to mimic natural and anthropogenic sediment types and processes (e.g. dredging). Experiments were conducted to quantitatively assess the synergistic effects of sediment concentration and composition, along with increased temperature on the survival and growth of juvenile P. astreoides. The most detrimental effects were observed with anthropogenic sediment, when both sediment concentration and water temperatures were high. However, increased natural reef sediment was found to be beneficial to juvenile corals. More interestingly, I found that corals capacity to deal with higher temperatures is improved when anthropogenic sedimentation is maintained at minimal levels and turbidity resulting from sedimentation was low. Therefore, this information will aid managers in making decisions that regulate dredging and construction activities to minimize sedimentation, which will contribute to increase coral survival under climate change.

Stony corals of Pompano Ledge, First Reef, Broward County, Florida were sampled in situ using a new reef assessment method. The circular-radial method was used to assess the effectiveness of mooring buoys in reducing damage to reefs. Data will be part of a long-term monitoring study of·buoy impacts. The parameter of recent injury was used to provide preliminary information on buoy effectiveness. Results were as follows: approximately 6% of the study area was covered by stony corals, with an average of 3 colonies per square meter. Diversity based on abundance (H'n) was 1 .7, and diversity based on relative coverage (H'c) was 1.1. Evenness based on abundance (J'n) was nearly .8, and evenness based on relative coverage (J' c) was .5. Approximately 6% of all colonies surveyed were observed under the shelter of ledges or overhangs. An average of 2% of colonies were observed to be recently injured in the Winter, compared with 6% in the Summer. Twenty-nine species of scleractinian corals were observed, 26 of which were present in sample areas. Montastrea cavernosa dominated stony coral coverage, and Siderastrea spp. and M. cavernosa were the most abundant. Mooring buoys appear to be an effective management tool for minimizing damage to corals on Pompano Ledge. The percentage of corals that had been recently injured was lower in the buoyed site (p = .082) even though the buoyed site was more heavily visited by both boats and divers . Future studies will be able to further assess buoy impacts by noting any changes in coral population parameters. The buoys have only been in place two years, so it will be interesting to see if the coral communities of the two sites begin to diverge in the future .

碩士<br>國立屏東科技大學<br>材料工程所<br>100<br>Stabilized zirconia is a useful structural material with incomparably high toughness due to stress-induced phase transformation, and, moreover, is widely utilized as a carrier substrate, an electrolyte of a solid oxide fuel cell and an oxygen sensor. Recently, it was found that the carrier substrate of zirconia could cause some effects on MLCC sintered at high temperature. Besides, the substrates which were used will easily degrade. The reason for this may be due to the high temperature phase-transformation of zirconia. This article studies the microstructure and phase transformation of a ZrO2 ceramic under different amount of Y2O3 and CaO doping. X-ray diffraction shows that Y3+ and Ca2+ were diffused into the lattice of ZrO2 to form a solid solution with a pure cubic structure. The sintered ceramics were tested under a aging condition (top temperature 1300 ℃ for 2 h in partial O2 pressure 1×10-10 Pa, it was called a thermal cycle). The influence of thermal cycle times on the phase stability of ZrO2 ceramics was studied. In addition, that studies the microstructure and phase transformation of a ZrO2 ceramic under different amount of Mn3O4 doping. Doping 1 mol.% Mn3O4 into 6 mol.% Y2O3 of ZrO2 ceramic is helpful to forming the stable-zirconia and promoting the grain growth. For Mn3O4 doping into 10 mol.% Y2O3 of ZrO2 ceramic, we could found that the phase structure was also ZrO2 with a single cubic after aging 60 cycles. When the 12.5 mol.% CaO of ZrO2 ceramic was doped with Mn3O4, the intensity of monoclinic peak decreases with Mn3O4 concentration, until a single cubic phase (x=0.3 mol.%). However, it was found that the phase structure changed from a single cubic phase into coexistence of cubic and monoclinic, and the ratio of the monoclinic phase is 12.9% after aging 60 cycles.

碩士<br>義守大學<br>材料科學與工程學系<br>91<br>In order to increase the capacitance per unit volume, the multilayer ceramic capacitors (MLCCs) have to adopt the using of sub-micron or nano-sized barium titanate powders to control the grain size during sintering to decrease the thickness of the active layer increase the number of the dielectric layers, and the packing density of capacitance per unit volume the capacitance is increasing. X7R is dielectric formulation the temperature coefficient of capacitor are within ±15﹪between the temperature range -55℃∼125℃ and the dielectric constant 3000∼4000, is suitable to be used to thin AD high number of layers MLCC fabrication. In this study, 0.3∼0.5μm sub-micron barium titanate powders was adopted to synthesize the dielectric formulation of X7R to form the complex structure of donor and acceptor using the coprecipitation coating method and manufacture the base metal electrode multilayer ceramic capacitors from the dielectric powder that are suitable to sinter in reducing atmosphere. It is observe that the concentration of dopant equals to 2mol.﹪of Er、Mg , the temperature coefficient of capacitor is close to the EIA requirement of X7R, dielectric constant 4000, and the grain exhibits core-shell structure, the Curie temperature is toward to the direction of lower temperature. The dissipation factor of sample added La、Sm is lower than the sample added Er、Dy and the insulation resistance is higher than the sample added Er、Dy. There is a dielectric peak of the temperature coefficient of capacitor at low oxygen partial pressure when sample sintering in reducing atmosphere that is different when the sample sintering in air. The densification of the sample sintering in reducing atmosphere is the best than the sample sintering in air. It is the influence factor of the electrical property that the nickel diffuses into the active dielectric layers in MLCCs, so that, we add the nickel element to the dielectric powder to investigate the relation between the sintering, grain growth, and insulation resistance. We use the dielectric powders that the electrical properties close to the EIA requirement of X7R, to manufacture the devices of base metal electrode multilayer ceramic capacitors, and investigate the microstructure, dielectric properties and the relation between the electrodes and the active dielectric layers.

碩士<br>國立成功大學<br>材料科學(工程)學系<br>85<br>The Ca-doped BaTiO3 ceramics are the raw materials of the commercial multilayerceramic capacitors with nickel inner electrodes.The mechanisms of the inhibitionof reduction are the defect mechanism(CaTi),the 214 phase and the hexagonal phase.The major factor of the Ti-site occupied by the Ca2+ is that (Ba+ Ca)/Ti>1.The purpose of this study is to (1)discuss the mechanism of non-semiconductor of theCa-doped BaTiO3 ceramics,(2)why (Ba+Ca)/Ti>1 is the major factor causing the Ti- siteoccupied by the calcium ions.According to the relation of the dielectric constant to the temperature,the curie point of the conventional processed samples,whether via powder calcination or not,shift to the low teperature.The curie point of the semiwet processed sample with powder calcination do not shift obviously,but that without powder calcination shifts as the same as the conventional process samplewith the powder calcination.The sintering atmosphere has no effect on the curie temperature for the same process and the same composition samples.According to the x-ray powder diffraction and the resistivity at the room temperature as a function of the ratio m,the hexagonal phase and the 214 phase has no effect on the resistivity at the room temperature,but when the ratio m>1,the Ca-doped BaTiO3solid solution has the significant effect on the resistivity.According to the statistical ALCHEMI analysis,when m>1,there are some calcium ion to occupy the Ti-site,so the mechanism for the Ca-doped to resist the attack of the reducing atmosphere from becoming semiconductors is the defect chemistry mechanism(CaTi).When the ratio m>1 and in the convention process powders,BaCO3,CaCO3 and TiO2 powders will first react to form BaTiO3 and CaTiO3 and the residual BaCO3,then when the temperature increases continuously and when CaTiO3 and BaCO3 would like to diffuse into BaTiO3 to form a single phase,because the effect of that the ABO3would become A2BO4 phase when (A-B)/ B>100ppm,that the barium ions in the BaCO3 powder like to occupy the Ti-site when diffusing into BaTiO3 lattice,and that the radius difference between the Ca and the Ti is near to the one between the Caand the Ba ions,there are some calcium ions occupying the Ti-site and it leads to the formation of the defect CaTi,when the Ca ions in the CaTiO3 diffuse into the BaTiO3 lattice.

碩士<br>義守大學<br>材料科學與工程學系<br>91<br>It is trends that multilayer ceramic capacitors (MLCC) with base metal inner electrode will substitute for other capacitors in market gradually. These capacitors must be fired in reducing atmosphere to protect nickel electrode from oxidation. The main powder formulation with barium titanate creates oxygen vacancy in reducing atmosphere. That vacancy could be moved by electric field to make barium titanate powders in dielectric layers resulting in semiconducting. For this reason, the additions of donor and acceptor simultaneously will form complex to solve conducting and reliability problems. Use traditional solid state methods to prepare barium titanate based Y5V powder formulation in the system of [(Ba0.996Ca0.004)O] 1.004[(Ti0.82Zr0.18)O2]. The formulation has high dielectric constant and very popular in the market. We can compare difference by varying atmosphere and different ratio of ytterbium cation and magnesium cation in the powder. The effect could be studied in electric properties and microstructure. Elements distribution could be investigated by TEM and EPMA. The results indicated that 1.0at% ytterbium cation formulation has better dielectric constant and insulation resistance in reducing sintering, and 0.1 at% ytterbium cation and 0.3 at% magnesium cation simultaneously formulation also has same result. These compositions meet Y5Vspecification in EIA, owing to complex composed of donor and acceptor. We can further study microstructure in multilayer ceramic capacitors by SEM and diffusion of nickel from electrode into the active dielectric layers by use of TEM and EPMA.

碩士<br>國立成功大學<br>材料科學及工程學系<br>87<br>(Ba,Ca)(Ti,Zr,Mn)O3 would possess high dielectric constant. Because of the utilization of the base metals such as Ni and Cu, the multilayer capacitor must be sintered in a reducing environment and at lower temperature to reduce the stress of interface. The purposes of this study were to evaluate the effect of flux additive of MST on the sintering behavior and the dielectric properties in the different atmospheres. It was found that the reducing environment could enhance the sintering rate. It prevents the formation of the liquid phase and delays the diffusion of calcium ions into barium titanate. But it will be dedensified owing to the pore growth. The sintering temperature could be lowered to 1100℃ when more than 2% MST were added . The more MST was added, the more uniform the grains were but the more the pore growth was. Reducing atmosphere would enhance dielectric constant, in which Mn+3 would become Mn+2 and the Curie temperature would shift from 65℃ to 30℃. Higher sintering temperature would develop more oxygen vacancies which in turn would lower resistance and enhance dielectric loss. Mn would diffuse in BCTZM when MST was added, which would reduce dielectric loss and dielectric constant and make Curie temperature shift to lower temperatures. For preparing MnSiO3 and MnTiO3, the mixture of MnO2 and SiO2 was calcined in air to form MnMn6SiO12 first. At 1200℃, it melted and did not form MnSiO3 completely. However, when it was calcined at 1100℃ for 8 hours in the reducing atmosphere, more pure MnSiO3 could be obtained. MnTiO3 could be synthesized at 1250℃ for 4 hours in a reducing atmosphere. MST calcined in different atmospheres would possess different colors, which might be due to the different oxidation states of Mn.

碩士<br>國立臺灣科技大學<br>機械工程系<br>99<br>High-frequency mobile communication and wireless local area networks (LAN) are widespread used in recent years. For instance, components use in the systems of bluetooth or high-frequency radio frequency (RF) are produced based on miniature size in order to make them use in high-frequency modules, which require low dielectric constant (εr) and high quality factor (Q×f). Hence, the materials, which are developed by means of Low Temperature Co-fired Ceramics (LTCC), are an important research issue in recent years. This study aims to research on the composition of glass-ceramic system of CaMaSi2O6 Diopside. ZrO2 added in this system is acting as nucleation agent on electricity and Diopside phase. Moreover, the addition of ZrO2 makes the main body of the material has good densification after sintering. When 5.05mol% ZrO2 is added to Diopside phase, the best density value is about 3g/cm3. By means of XRD, it is found that addition of different ZrO2 nucleation agents make Diopside phase and T-ZrO2 obviously appear, and peak values of T-ZrO2 will be higher as the increase of ZrO2 added. By means of SEM, it is observed that the Diopside phase without nucleation agent is mainly in disordered glassy state and there is obvious crystal growth in the phase with the addition of nucleation agent. The addition of ZrO2 exactly increases the efficiency of heterogeneous nucleation and reduces free energy of growth. Moreover, in BEI images, it is found that precipitation of white-spot particles and the result of the EDS analysis revealed that T-ZrO2 formed because of the solid dissolution of Ca and Mg in Zr lead ZrO2 to change from M phase into T phase. The dielectric constant is basically below 10 within low dielectric constant range and Qxf of Diopside phase with crystal growth relatively increases higher. ZrO2 added in 5.05 mol% shows better performance of Qxf is 7310 GHz. In the second part of this study, in order to make glass-ceramic material system of Diopside phase to be applied in co-firing the electrode of base metal in the process of LTCC. Different sintering atmospheres are applied to affect the addition of 5.05 mol% ZrO2 in Diopside phase and to contrast the different sintering results in general atmosphere and Nitrogen. In the part of electricity, the value of Qxf in the condition of Nitrogen sintering apparently reduces into 3330 GHz. In the analysis of XRD, it is found that the peak value of specimen in the condition of Nitrogen sintering widens because many gaps form inside the crystal of the specimen that cause the larger strain value in the crystal. In addition, in the analysis of XPS, it is proved that there is an obvious tendency of restoration in Diopside phase; thus, glass ceramic after heat treatment in the atmosphere of hypoxia Nitrogen causes the phenomenon of restoration to make the material become the state of Semiconductor and affect the electrical properties. In the third part, in order to improve the sintering characteristic in Nitrogen, the addition of ZnO is used as reductive-resistance agent to analyze changes of ZnO in Diopside phase according to different ratios. By means of XRD, it is found that as the addition of ZnO ranges between 0.5 and 4mol%, Diopside phase and T-ZrO2 are basically maintained. And R-Zn2SiO4 forms after 6 and 8 mol%, but these phases belong show lower dielectric constant; therefore, dielectric constant still maintains between 7 and 8. In the condition of 3.31mol%, cell volume starts to have the tendency of increasing expansion and it is speculated that the large amount of Zn occupies the place of Si because the radius of Zn ion is larger than that of Si to cause the distortion of phase crystal. The tendency of crystal expansion and the increase of Qxf are consistent. In the analysis of XPS, it is verified that as ZnO increases in 3.31~8mol%, bonding energies of Diopside phase deviate toward high bonding energy (eV). It is also proved that distortion of crystal makes Oxygen difficult to separate and causes the effect of reductive-resistance. The addition of ZnO exactly helps improve the property of Qxf in Nitorgen. The addition of ZnO in 4mol% shows the best electrical properties. Dielectric constant is 7.25 and Qxf is 8330.

碩士<br>國立中山大學<br>材料與光電科學學系研究所<br>101<br>In this study, the samples are prepared from TiO2 intial powder via die pressing method, and then sintered at 1500oC/1h in reducing atmospheres. The crystalline phase and microstructure of the sintered samples are analyzed using X-ray diffractometry (XRD), scanning and transmission electron microscopy (SEM and TEM). The experiment results show that rutile readily undergoes some loss of oxygen when it sinters in pO2 = 10-25 atm reducing atmospheres. It slips for removing oxygen vacancies in oder to reach stable structure, and then it forms long-range ordering crystallographic shear structures. These strucutures are identified as Magnèli phase (Ti8O15) by XRD. (12 ̅1) crystallographic shear plane is α-boundary and displacement vector R = 1/2[01 ̅1] by contrast analysis using the 2πg‧R= 0 or 2nπ criteria crystallographically via TEM. Finally the crystallographic orientation relationships of rutile and Ti8O15 ( [111]TiO2 // [010]Ti8O15及[012]TiO2 // [110]Ti8O15 ) are determined by selected area diffraction patterns (SADP) and described by transformation matrices.

碩士<br>國立屏東科技大學<br>材料工程所<br>96<br>Sintering behavior in reducing the atmospheres, it will produce semiconductor and drop in the insulating resistance with ceramics. Add Calcium or Manganese, inhibit and resist this situation to produce semiconductor. The additive will produce oxygen vacancy while sintering under reducing the atmosphere. Enable the electricity degradation of the component, and the reliability is reduced. Therefore, we usually improve the question by adding some dopant. In the article, we try to understand in reducing atmospheres the effect of SiO2 on the sintering behavior and dielectric properties of BCTZ. For example, phase structure, dielectric properties, macrostructure etc. In addition, we use which X-ray powder diffraction, SEM and TEM analyze second phase, phase compositions and macrostructure. 0.3 mol% SiO2, add it in BCTZ ceramics powder, the density of trying one frits to reach the dense result in the liquid phase, improving dielectric properties. We observed obvious second phase from grain size above 3 mol% SiO2 after Sintering behavior in reducing the atmospheres. In addition, we prove that second phase had existence Si-rich by SEM-EDS. By creating synthetic phase, BaTiSiO5, we can get some results. BaTiSiO5 will make the insulating resistance drop, produced the semiconductor. Making use of analyzing physical and dielectric properties after sintering behavior, Effect of analyze structure in the physical and dielectric properties form SEM macrostructure.

Turbulent boundary layers approximating those found on the NASA Orion Multi-Purpose Crew Vehicle (MPCV) thermal protection system during atmospheric reentry from the International Space Station have been studied by direct numerical simulation, with the ultimate goal of reducing aerothermodynamic heating prediction uncertainty. Simulations were performed using a new, well-verified, openly available Fourier/B-spline pseudospectral code called Suzerain equipped with a ``slow growth'' spatiotemporal homogenization approximation recently developed by Topalian et al. A first study aimed to reduce turbulence-driven heating prediction uncertainty by providing high-quality data suitable for calibrating Reynolds-averaged Navier--Stokes turbulence models to address the atypical boundary layer characteristics found in such reentry problems. The two data sets generated were Ma[approximate symbol] 0.9 and 1.15 homogenized boundary layers possessing Re[subscript theta, approximate symbol] 382 and 531, respectively. Edge-to-wall temperature ratios, T[subscript e]/T[subscript w], were close to 4.15 and wall blowing velocities, v[subscript w, superscript plus symbol]= v[subscript w]/u[subscript tau], were about 8 x 10-3 . The favorable pressure gradients had Pohlhausen parameters between 25 and 42. Skin frictions coefficients around 6 x10-3 and Nusselt numbers under 22 were observed. Near-wall vorticity fluctuations show qualitatively different profiles than observed by Spalart (J. Fluid Mech. 187 (1988)) or Guarini et al. (J. Fluid Mech. 414 (2000)). Small or negative displacement effects are evident. Uncertainty estimates and Favre-averaged equation budgets are provided. A second study aimed to reduce transition-driven uncertainty by determining where on the thermal protection system surface the boundary layer could sustain turbulence. Local boundary layer conditions were extracted from a laminar flow solution over the MPCV which included the bow shock, aerothermochemistry, heat shield surface curvature, and ablation. That information, as a function of leeward distance from the stagnation point, was approximated by Re[subscript theta], Ma[subscript e], [mathematical equation], v[subscript w, superscript plus sign], and T[subscript e]/T[subscript w] along with perfect gas assumptions. Homogenized turbulent boundary layers were initialized at those local conditions and evolved until either stationarity, implying the conditions could sustain turbulence, or relaminarization, implying the conditions could not. Fully turbulent fields relaminarized subject to conditions 4.134 m and 3.199 m leeward of the stagnation point. However, different initial conditions produced long-lived fluctuations at leeward position 2.299 m. Locations more than 1.389 m leeward of the stagnation point are predicted to sustain turbulence in this scenario.<br>text