Si₃N₄ is one of the most promising structural ceramics due to its unique properties, while the large scale applications are still limited by its high cost and low reliability. Combustion synthesis (CS) is a feasible approach to synthesize Si₃N₄ in large scale and low cost. This work focused on the mechanism of CS Si₃N₄ during commercial production process. Temperature profile analysis of the on-line measured data indicates that the conversion ratio was only 40% when combustion reaction temperature reached the highest value. Post-combustion nitridation could last as long as 660s. A model was proposed to account for the combustion synthesis of α-Si₃N₄, the CS process was optimized to regulate the phase composition and particle size of the combustion-synthesized product. Based on the understanding of the Si-N₂ reaction, a breakthrough was achieved ---- a new method of CS of Si₃N₄ at normal nitrogen pressure was established.

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Abstract The effect of mechanical activation on simultaneous reaction and consolidation of materials by the SPS method was investigated. Mechanical activation was accomplished by high-energy ball milling of reactant powders and synthesis and consolidation is achieved in one step in the SPS apparatus. Three examples will be presented and discussed: (a) the influence of product formation during milling on the initiation of the SPS reaction, (b) the formation of dense bulk nanometric monolithic (ceramic, intermetallic) and composite materials, and (c) the feasibility of microalloying of MoSi2 for mechanical property improvements. For case (a), we investigated the effect of phase evolution during milling on the SPS synthesis reaction of MoSi2. In the second examples we describe the synthesis of nanometric, high-density ceramics, intermetallics, and composites. And in the third example, we discuss the evidence for the first successful incorporation of Mg into the Si sub-lattice of MoSi2 for mechanical property improvements.

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Generally, most of polycrystalline ceramics have been made from fine powders via their shape forming and sintering, not via melt/casting, because melt/solidified ceramics would crack during cooling. In order to prevent the accumulation of residual stresses, we have tried to make the samples by rapid solidification of the eutectic systems. In the ternary systems of Zirconia(Hafnia)-Alumina-YAG, we have succeeded to fabricate nano-structured bulk ceramics by just simple solidification of the melt. The mixed powders were melted into a globule with 3 - 5 mm diameter by an arc-imaging furnace, then cooled rapidly. The spherical samples were transparent, no cracking and consisted of 20-100 nm size crystals: Zirconia-Hafnia-Alumina-YAG. Zirconia-Hafnia-Alumina-ABOperovskite system would give transparent amorphous phases, which can be charged into nanocrystalline bulk composites by appropriate annealing. Those ceramic nano-composites can be applied for wide areas; structural, functional, and coating materials.

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The most important four-level solid-state laser host, a YAG (Y₃Al₅O₁₂) single crystal, uses the fluorescence of a small content of Nd³⁺ ions as active species in the 1064 nm wavelength. In recent years, Nd-doped YAG laser has been applied widely in various industrial capacities, medical operation, metal processing, and others applications. The present author demonstrated in 1994 that the effective laser oscillation was performed successfully for the first time in the world using polycrystalline Nd:YAG ceramics. The present work can be summarized as follows. 1) High-quality Nd:YAG ceramics were fabricated successfully by simple solid-state reaction and vacuum sintering. 2) Such properties of Nd:YAG ceramics as thermo-mechanical properties were nearly the same as those of Nd:YAG single crystal by Cz method. 3) The absorption and fluorescence characteristics of the Nd:YAG ceramics measured were similar or superior to those for an Nd:YAG single crystal.

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Polycarbosilane is a representative pre-ceramic polymer for preparing SiC ceramics, for example, Hi-Nicalon fiber and Tyranno Fiber. Furthermore, oxide or nitride ceramics can also be produced from the polycarbosilane by firing in air or ammonia, respectively. We developed highly heat-resistant SiC fibers and photocatalytic fiber by improvement of pre-ceramic polymer and production process.These fibers contribute to the environmental purification as the important material for diesel particulate filter (DPF), high efficiency gas turbine or decomposition system for harmful organic substances in water.

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Geopolymers are made by adding aluminosilicates to concentrated alkali solutions for dissolution and subsequent polymerisation to take place. They are amorphous to semi-crystalline three dimensional aluminosilicate networks. They have been studied for many years as a possible improvement on cement in respect of compressive strength, resistance to fire, heat and acidity, and as a medium for the encapsulation of hazardous or low/ intermediate radioactive waste. In this work we investigated the microstructure by scanning and transmission electron microscopy and compressive strength of geopolymers made by using New Zealand flyash. X-ray diffraction showed them to be amorphous with a small amount of crystalline phases such as calcite and quartz. Amorphous phases were confirmed by transmission electron microscopy. Compressive strength testing of pastes and mortars was carried out after 1, 7 and 28 days of curing. Their strength is discussed with respect to microstructural features with curing.

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Synthesis of strontium niobates via single crystals of Sr-Nb mixed alkoxides has been attempted in this study. New single crystals of Sr-Nb mixed alkoxides were synthesized by a reaction of Sr(OEt)₂ and Nb(OEt)₅ in ethanol. The composition of Sr_xNb_y etoxides obtained was Sr₂Nb₂, Sr₄Nb₂ and Sr₅Nb₄. By heat treatment at 200~300 degrees C of these Sr-Nb mixed etoxides, Sr₂Nb₂O₇, Sr₄Nb₂O₉ and Sr₅Nb₄O₁₅ were formed according to the atomic ratio of Sr_xNb_y in the alkoxides. The lattice parameters of the strontium niobates heated at 800 degrees C for 1.5h in air were a=0.39nm, b=2.705nm and c=0.454nm for Sr₂Nb₂O₇, a=4.289nm, b=1.167nm and c=1.014nm for Sr₄Nb₂O₉ and a=0.568nm, c=1.137nm for Sr₅Nb₄O₁₅. The crystallite sizes of the strontium niobates were found to be 20~60nm.

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We have been studying the synthesis of nano sized particles using hydrothermal treatment, and developed various kinds of oxided particles such as aluminum oxide, cerium oxide, zirconium oxide, indium tin oxide and barium titanate and so on. Characteristics of synthesized particles are as follows. (1) Particle size is controlled in the range of about 10 to100 nm by changing the condition of precipitation of hydroxides and hydrothermal treatment. (2) Particles have plate like shape. (3) The synthesis is applied to various kinds of complex oxided particles. (4) Each particles shows crystal structure standing comprison with balk materials. We report detailed synthetic methods and the characteristics such as particle shape using high resolution TEM and analysis of crystal structure.

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Solvothermal treatment is a promising process for producing well-dispersed nanocomposites, especially in metal and oxide system. Ag/gamma-alumina is a novel catalyst for decomposition of nitrogen oxide in the lean burn condition with the oxygen rich environment for diesel engine. In the present study, Ag/gamma-alumina nanocomposite was prepared by solvothermal treatment of gamma-alumina in an ethanol-water mixed medium with silver nitrate and the influence of the ratio of ethanol to water on the phase evolution of solvothermal products was investigated by using XRD, TEM, TG-DTA, XPS and BET methods. It is found that with increasing ratio of water to ethanol, more and more fiberous gamma-alumina phase changes into rhombic gamma-AlOOH, which results in the distinct influence in character of the microstructure such as BET specific surface area, pore distribution etc.

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Dye-sensitized solar cells are widely investigated as a cost-effective solar power system. Adachi, Yoshikawa et al., recently reported that the dye-sensitized solar cell system using the titania nanotubes showed promising sunlight-electricity conversion characteristic. In this study, several types of ceramic nanotubes were prepared and their photovoltaic properties were evaluated.

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If a material absorbs microwave energy well, the material can be heated through microwave-material interactions. The interactions are identified as energy losses in the material, resulting in rapid volumetric heating. During our extensive study on microwave processing of inorganic materials, it is concluded that conduction in solids due to the mobile electrons, holes, or ions is the most important mechanism for coupling millimeter-wave energy in solid state materials. Various conductive oxides were synthesized by microwave irradiation using 28 GHz frequency. The current topics of microwave processing of conductive oxides achieved in our laboratory are presented. The topics include examples of defect formation, rapid grain growth, and the importance of microwave penetration depth on processing of conductive materials.

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Our previous study, production of Al₂O₃-TiC composite powders from carbon coating of TiO₂/Al mixture has shown that there are many advantages of using this method such as nanoparticles, high chemical purity, low cost and so on. In this study, we calculate the adiabatic and ignition temperatures in Al-TiO₂-C system synthesized from carbon coated method. From XRD and DTA results, the initial reaction between Al and TiO₂ leads to the formation of Al₂O₃, Al₃Ti, and Ti₂O₃ according to 5Al + 3TiO₂ → Al₂O₃ + Ti₂O₃ + Al₃Ti whose adiabatic and ignition temperatures are 1630K and 1023K, respectively, which are much lower than those reported ones because carbon coated TiO₂/Al mixture leads to an intimate mixing of the reactant and can be very effective way for the control of reaction path and rate. The ignition and adiabatic temperatures can also be controllable without using any diluents.

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This study investigated shock-activated reaction synthesis of Ti₃SiC₂ and Ti₂AlN, which are ceramics having relatively high stiffness and low hardness. Dynamically densified compacts of Ti, SiC, and graphite and Ti and AlN precursors were prepared using explosive loading techniques. Subsequent reaction behavior of the shock-densified, activated compacts was studied via heat treatments and differential thermal analysis performed at varying heating rates. In both systems, shock activation led to an accelerated rate of reaction at temperatures less than 1600 ^oC, and, above that temperature, it promoted the formation of almost 100% of the ternary compounds. A kinetics-based mathematical model based on mass and thermal transport was developed to predict the effect of shock activation and reaction synthesis conditions that ensure the formation of the ternary compounds. In this paper, results of the effects of shock activation on subsequent reaction synthesis will be presented along with correlation to the kinetics-based mathematical model.

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The goal of the study is to fabricate laminated WC-Co cutting tool inserts with residual thermoelastic stress states tailored to counteract the thermal and mechanical stresses imposed during the machining process. Advanced ceramic processing was employed to produce cutting tools with a graded weight fraction of cobalt. Spark plasma sintering (SPS) was utilized for densification of the laminated tools at sub-eutectic temperatures over short times in order to maintain nanocrystallinity and to prevent homogenization of the graded cobalt structure. Microstructural defects found in laminated tools sintered by other methods, such as hot pressing, were not observed in SPS tools. Laminated tools showed improved performance in interrupted cutting of Titanium-6Al-4V alloy when compared to the best performing, commercially available tools. The effect of SPS on microstructural development, mechanical properties, and the resultant machining performance will be presented. Supported by the Center for Innovative Sintered Products at Penn State.

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Spark plasma sintering combined with heat-treatment was investigated to prepare transparent ceramics in a short sintering time. PbZrO₃-PbTiO₃-Pb(Zn_1/3Nb_2/3)O₃ ceramics with high transmittance of 13% at 633 nm was prepared by spark plasma sintering at 900^oC for 10 min and heat-treatment at 900^oC for 1h. Suitable addition of PbO or La₂O₃ was found to increase the transmittance of PZ-PT-PZN ceramics. Transmittance at 700 nm of the (Pb_1-xLa_x)(Zr_y,Ti_z)_1-x/4O₃ prepared by spark plasma sintering at 900^oC for 10 min and heat-treatment at 800^oC for 1h was 31%. The transmittance of PLZT ceramics increased with increasing sintering temperature up to 900^oC and thereafter decreased. The effects of the calcination temperature and the heat-treatment temperature upon the microstructure and transmittance of PLZT ceramic were also investigated.

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A recently developed shock-sintering technique was employed to fabricate dense TiO2 ceramics at low temperatures in short times. The densification and grain-growth behaviors as well as the anatase-to-rutile transformation of a nanocrystalline titania powder without any additives were investigated as a function of sintering temperature. It has been shown that densification proceeds simultaneously with phase transformation. At 1100C for a sintering time of 2 min, a 100% density was achieved, while 98% anatase was transformed into rutile. On the other hand, grain growth was observed to occur mainly after the anatase-to-rutile transformation. This suggests that it is possible to produce nano-structured TiO2 ceramics with high densities.

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Gel-combustion synthesis was applied for CoZ-ferrite (Ba3Co2Fe24O41) fine powder. Either citric acid or glycine was added to the mixed aqueous solution of Ba(NO3)2, Co(NO3)2•6H2O and Fe(acac)3. The product gel was ignited at 150^oC and then fired again up to a temperature of 500^oC to 1200^oC. The ignited and fired products were respectively a mixture of CoFe2O4 and Ba(NO3)2 and that of CoZ-, CoY-, M-ferrites and BaFe2O4 when citric acid was used as a gelling agent. The ignited product was a mixture of CoFe2O4 and BaFe2O4 because higher temperature was attained in the ignition of glycine gel than citric acid gel. CoZ-ferrite fine powder was obtained in firing the ignited product at 1000^oC. Crystallite and average particle sizes were 45 and 200nm, respectively. Saturation magnetization was 250G and coercivity was 0.6 to 0.9kOe.

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Na_xCoO₂ powders with sub-micron, narrow-size-distribution, and phase-pure particles were synthesized by ultrasonic spray pyrolysis method from an aqueous cobalt nitrate and sodium carbonate solution. A tubular furnace with six independently controlled heating zones was used in the synthesis. The effect of gas flow rate and axial temperature profile in the reactor on the composition of as-prepared powders was examined with X-ray diffraction (XRD), inductively coupled plasma spectroscopy (ICP) and energy dispersion X-ray (EDX) analysis. Nano-structured β-Na_xCoO₂ fine particles were successfully synthesized at both constant temperature distribution (1073K) and increasing one (473K-473K-673K-873K-1073K-1073K) in the reactor at various gas flow rates. The phase transfer from β-phase to γ-phase Na_xCoO₂ occurred after the as-prepared samples were heated at 1073K for 2h in air.

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Scandia is a ceramic material having a unique combination of interesting thermal and optical properties but difficult to be grown as single crystals. So as an alternative, we fabricated in this work transparent scandia polycrystalline ceramics via sintering. The starting powders for ceramics fabrication were synthesized by ourselves via precipitation from scandium nitrate solution, using hexamethylenetetramine as the precipitant and ammonium sulfate as an engineering reagent for powder properties (precursor composition and particle morphology). Characterizations of the powders were achieved by chemical analysis, DTA/TG, XRD, BET, and FESEM. Densification behaviors of the resultant scandia powders were studied in air via dilatometry. Scandia ceramics showing an inline transmittance of ~76% in the visible wavelength region (corresponding to ~92% of sapphire single crystal) have been fabricated by vacuum sintering at a relatively low temperature of 1700 ^oC.

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When we sinter ceramic powder, we often add seed grains to grow selected grains. It is very important for such microstructural design to know their grain sizes and the amount of addition. Grain growth behavior of large grains in a matrix with small grains is studied to understand a role of seed grains. We first postulate that excess free energy of a solid drives mass-transport to decrease total free energy. This concept yields new rate equation for mass transport which is applied to the grain growth phenomenon of ceramic powder. We use the Ostwald ripening model for the study. From the model and the free energy theory, rate equations for grain growth are derived, and growth rates are calculated numerically. We will discuss optimum grain size and the amount of addition of seed grains from the results of calculations.

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A novel method for controlling the bulk structure of a ceramic green body has been proposed. In this method, spherical granules with uniform and several ten micronmeter size were placed mechanically in a regular array on a mesh with several centimeter square and then pressed to make a compact.(Granule assemblage). Defects and non-homogeneity in the granule compact govern a reliability of ceramics. In this method, a detrimental defects and non-homogeneity diminish. To demonstrate the potential of this method, alumina granules with several ten micron meter size were used as a model and a hexagonal close packed structure was made. Uniaxial pressing of this array can create a uniform and orderly structured green body.

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The Nb-peroxo compound aqueous solution was prepared by peptization of niobic acid precipitate with hydrogen peroxide. The heat treatment of the Nb-peroxo compound aqueous solution at 348 K for 24h formed crystallized Nb₂O₅ nanoparticles. Potassium nitrate was dissolved into the Nb-peroxo compound solution, which was dried at 573 K to obtain the oxide complex containing K⁺ and Nb⁵⁺ ions. When the complex was fired at 873 K for 1h, single perovskite phase of KNbO₃ was obtained. In the case that the Nb-peroxo complex was used as the precursor for preparation of KNbO₃, the Raman spectra indicated that the obtained KNbO₃ had the tetragonal structure which is the high pressure phase. The UV-VIS spectra and the lattice parameter of the obtained KNbO₃ from the Nb-peroxo complex showed the presence of defect structures which can not be obtained by ordinary powder process.

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Singly-doped and doubly-doped CeO₂ with nominal compositions of Gd_0.2Ce_0.8O_1.9 and (Gd_0.9Sr_0.1)_0.175Ce_0.825O_1.9, respectively, have been synthesized via a simple and effective carbonate coprecipitation method, employing nitrates as the starting salts and ammonium hydrogen carbonate as the precipitant. The AHC/RE³⁺ molar ratio (R) and the reaction temperature (T) affect significantly the final yield and precursor properties, including chemical composition and particle morphology. The precursors and the resultant oxides are characterized by elemental analysis, differential thermal analysis/thermogravimetry (DTA/TG), X-ray diffractometry (XRD) and high resolution scanning electron microscopy (HRSEM). Oxide solid-solutions are formed directly upon thermal decomposition at a very low temperature of ~400^oC, and can be further densified at a low temperature of ~1000^oC by pressureless sintering. The effects of additional Sr-doping on the particle morphology of the precursor, the densification behavior of the solid solution oxides as well as the bulk electrical conductivity were also investigated.

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Strong and subtle ultrasound was applied to a reacting solution and a starting solution, respectively, for ceramic powder preparation. The magnetite precipitation involves the dissolution of the initial precipitate of Fe(OH)2, the oxidation of Fe2+ to Fe3+, and the nucleation & growth. Effect of ultrasound was separatedly discussed at each stage. Two methods of ultrasonication, i.e., travelling wave and standing wave, were compared. Conspicuous difference of the two methods appeared when the initial concentration of Fe(OH)2, which decreases the particles size of magnetite, is as low as 0.001mol/l. That is, magnetite particles could not be formed under a strong macroscopic flow, even that made by a magnetic stirrer. However, 10nm-sized magnetite was successfully prepared by the standing wave treatment. Aparent transparency of a starting solution may include microscopic inhomogeneity which could be modified by aging or subtle ultrasonication. Effect of them on ceramic particles synthesis is discussed.

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Recently, it was reported that the band gap of titania could be narrowed by doping with nitrogen. In the present study, nitrogen ion-doped titania nanoparticles were prepared by the solvothermal reactions. After dissolving urea or hexamethylenetetramine in titanium trichloride aqueous solution, the sample was obtained by heating the solution at 90^oC for 1 h to precipitate amorphous titania by the homogeneous precipitation reaction, followed by crystallization at desired temperatures. Various phases of titania such as anatase, rutile and brookite were obtained. Crystallite size, specific surface area and color also greatly changed as 5-50 nm, 20-200 m²g^-1 and light gray-yellow, respectively, depending on the reaction condition. All colored titania showed photocatalytic activity under visible light irradiation for the oxidative decomposition of NO in air. Especially, the nanoparticles of brookite obtained by the homogeneous precipitation using hexamethylenetetramine followed by heat treatment around 200^oC showed excellent photocatalytic activity under visible light irradiation.

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Anatase-type TiO2 / SiO2 composite particles were directly synthesized as combination of nanometer-sized anatase particles and amorphous silica from solutions of TiOSO4 and tetraethylorthosilicate by hydrolysis under hydrothermal condition at 200°C. The composites possessed far more improved photocatalytic activity and phase stability than pure anatase-type TiO2. By making composite with SiO2 and with increasing SiO2 content, onset of optical absorption of anatase was slightly shifted to shorter wavelengths and its photocatalytic activity and phase stability were considerably enhanced. In the composite containing 48.2 mol% SiO2, crystallite size (15-16 nm) of as-prepared anatase was maintained after heating at 1000°C, and the anatase phase existed up to 1300°C without appearance of a trace of rutile phase.

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Well-faceted hexagonal platelet β-Co(OH)₂ has been prepared by a precipitation method. It has been found that an α-Co(OH) ₂ with an interlayer spacing of ~ 8 Å was formed first, and then transformed to β-Co(OH)₂ with a typical size of 0.6 × 0.15 μm. Growth of β-Co(OH)₂ micro-crystals was carried out in NaOH aqueous solutions under hydrothermal conditions. The basal plane of the synthesized β-Co(OH)₂ platelets was (001), as revealed by the oriented particulate monolayer (OPML)-XRD measurements, which was maintained after hydrothermal growth. The obtained platelets are suitable templates for fabrication of textured cobalt-based thermoelectric ceramics by the RTGG method.

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Phospho-olivine LiFePO₄ was synthesized by hydrothermal reaction. FeSO₄•H₂O with high purity of 99.999 % was used as an iron source, and ascorbic acid was used as a reducing agent for sustaining Fe²⁺ in the starting solution. The powder prepared by the hydrothermal reaction at 170 oC for 12 h was characterized as LiFePO₄ with olivine structure by x-ray diffraction method. In addition, the prepared powder was improved by a heat-treatment at 400 oC for 1 h. The sample with the heat-treatment showed excellent charge and discharge capacity near to theoretical one of LiFePO₄ at relatively high rate (0.1 C), meaning that well crystallized LiFePO₄ was obtained by the hydrothermal reaction, and the particles were stabilized by the heat-treatment. Therefore, it can be said that the hydrothermal reaction is very useful method for the preparation of LiFePO₄, which is an attractive cathode candidate for rechargeable lithium battery with high thermal stability.

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In the previous study, hollow calcium carbonates were successfully synthesized by CO₂ bubbling in aqueous solution of calcium chloride with the presence of ammonia at temperature about 27 ⁰C. The precipitation was carried out by controlling the pH of starting solution that was adjusted by adding of HCl solution. Hollow calcium carbonates were precipitated when the crystal phase was mainly vaterite. The aim of the present study is to investigate the precipitation conditions of the hollow calcium carbonate using a bubble column. In a bubble column, hollow calcium carbonate could be obtained without adjust of the pH solution. The effects of organic additives on the precipitation of hollow calcium carbonate were also studied.

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The formation of calcium carbonate films has been achieved in aqueous solutions containing specific polymers such as poly (acrylic acid) (PAA). However, details of the formation mechanism were not clarified. In this study, morphological variation of calcium carbonate crystals was investigated by changing the concentration and molecular weight of coexisting PAA. Low weight PAA (M_w:2,000) induced fibrillation of calcite with adsorption on the surfaces parallel to the c axis. In this case, we obtained indefinite aggregates of calcite on a glass plate. In contrast, coexistence of high weight PAA (M_w:250,000) formed calcite films on the surface. Adhesiveness of the crystals was improved by high weight PAA anchored on the surface. We found parallelogram plates and sharp horns of calcite on a glass with the combination of low and high weight PAAs by the adhesive effect on the substrate and moderate suppression of crystal growth.

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Oriented MFI zeolite films were prepared on ceramic substrates by hydrothermal method, using bulk glass as a source material. When dissolution rate of the bulk glass was less than 3.39 g h^-1 L^-1 under hydrothermal conditions, the b axis oriented MFI zeolite films were successfully formed. SEM observations showed that the oriented MFI films were ~ 450 nm in thickness and pin hole free. A formation mechanism of the oriented MFI films will be discussed, based on the microstructural changes and the pH variation of reaction solution.

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This study presents observations of the microstructural development of epitaxial KTaO₃ films grown hydrothermally at 170^oC in 7M KOH solutions. KTaO₃ is used in tunable microwave devices and, as a buffer layer, improves the alignment of epitaxial KNbO₃ films grown hydrothermally at 200^oC on SrTiO₃ substrates. KNbO₃ is a very promising material for applications such as frequency doubling, wave guiding and holographic storage. The KTaO₃ film formed by the island growth mode and the island size decreased with increasing precursor concentration. As a result, films grown with higher precursor concentrations coalesced earlier at smaller film thicknesses. Film cracking also occurred at smaller thickness when higher precursor concentrations were used. Therefore, it is believed that film cracking occurred as a result of grain coalescence or the ′zip-up′ effect. The cracking occurred at the edges first where the critical thickness was reached earlier.

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Porous Al₂O₃ and Al₂O₃/TiO₂ particles, about 1mm in diameter, were prepared from Al(OH)₃/alginate gel composite precursors. In this process, urease was immobilized in Al-bridged alginate gel matrices and then urea was allowed to diffuse into the matrices. The bridging Al³⁺ ions were then hydrolyzed by the enzymatically produced ammonia to form Al(OH)₃ within the pores of the alginate gel. Both hollow and solid particles were able to be prepared by controlling the synthesis procedure. The specific surface area of calcined particles was in the range about 100m²/g, depending on the calcination temperature. The pore size distribution was quite narrow, and the distribution profile was also controllable. Photocatalytic activity was characterized for TiO₂-modified particles.

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ZnO films were prepared by a nearby vaporizing chemical vapor deposition (NV-CVD) method with ultrasonic using bis(2,4-pentanedionato)zinc as a source material. The substrate was heated by a hot Al suscepter with a resistance cartridge heater. To control the intensity of radiant heat from the nearby substrate, distance between the substrate and the surface of source material was adjusted by using a micrometer. The surface morphology of the film was observed using a scanning electron microscope (SEM) and an atomic force microscope (AFM). The structure of the films was characterized by X-ray diffraction (XRD). C-axis preferred orientation ZnO films were obtained in the temperature range from 100 to 600°C.

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Thermal protection materials and systems (TPS) are used to protect spacecraft during reentry into Earth′s atmosphere or entry into planetary atmospheres. As such, these materials are subject to severe environments with high heat fluxes and rapid heating. Catalytic effects can increase the temperatures substantially. These materials are also subject to impact damage from micrometeorites or other debris during ascent, orbit, and descent, and must be able to withstand damage and maintain function following damage. Thermal protection materials and coatings developed at NASA Ames Research Center and used in reusable launch vehicles will be reviewed. These will include recent advances in surface treatments to improve impact resistance and temperature capability of tile materials. New TPS materials may enable the use of sharp nose cones and leading edges on future reusable space transportation vehicles. The needs and directions for new materials to enable new vehicles with greater performance will be included.

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MWCNTs were coated with SiC layer using SiO vapor. The growth mechanism of SiC and the oxidation resistance of the SiC-coated MWCNTs were studied. The growth of the SiC layer was controlled with the partial pressure of CO using the carbon felt placed in a crucible for SiC coating. The nanometer sized SiC particles were deposited by the reaction between SiO(g) and CO(g). On the other hand, the thin surface of MWCNT was converted to the SiC layer when the carbon felt was not used. The oxidation durability of MWCNTs was improved by the SiC coating. MWCNTs were oxidized completely in air at 650^oC for 60 min. However, about 90 mass % of the SiC-coated MWCNTs remained after the same oxidation test.

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A thin film including β-silicon carbide was synthesized by a reaction of gaseous silicon monoxide and carbon source derived from polyimide film (PIF). Formation mechanism of β -SiC film formed by the reaction from carbon film and SiO gas at 1400°C was investigated through relationship among formation ratio of the SiC, synthesis time and atmospheres, and formation processes were simulated kinetically by the calculations solving differential equations. The sample obtained had film shape similar to that of the carbon source film. Two reacted regions were found on both surfaces of the source film, as well as the un-reacted region in the middle of the sample with less than 3 h synthesis time. Results of the simulated curves calculated from 5 chemical equations and 10 rate constants have a good agreement with the experimental results of the formation ratio for the SiC as a function of synthesis time.

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The low hardness and weak wear resistance of Ti3SiC2 has been critical problems and preventing the potential use as structural material. It is well known SiC has promising mechanical properties in strength, hardness and wear resistance. Fabricating Ti3SiC2/SiC composites may be one of the possible approaches to utilize the merits of both Ti3SiC2 and SiC. Laminated structure has been proved an effective way to improve fracture toughness and damage resistance of ceramics. Ti3SiC2/SiC composites with different SiC content have been fabricated at 1500 °C and 25MPa by hot pressing (HP). The morphology of the fracture sections has been observed by SEM. The residual thermal stress distribution in the laminated Ti3SiC2/SiC structure has been simulated by FEA. Laminated structure of Ti3SiC2/SiC has been fabricated by HP. The damage resistance behavior of this laminated material was characterized. The mechanism of the crack propagation along the interface between the laminates has been stated.

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The fabrication of ceramic-layers using the electrospray pyrolysis method has been attractive because of the simplicity. Although conductive substrates were normally used in the electrospray, insulator substrates like glass and alumina are also necessary for applying the layers as electroceramics. In this work, the deposition mechanism is investigated in respect of the charge neutralization of the generated droplet/particle. The particle layer of SnO₂ deposited onto glass substrates exhibited the high sensitivity against H₂. The layer thickness increases with the spray time. The particle sizes varied between 80 and 150 nm due to spraying conditions and these values were comparable to the estimated from the droplet size in Gañán-Calvo′s empirical formula.

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In an attempt to improve the luminance efficiency of PDP, discharge cells of the PDP were prepared using mono-dispersed ceramic powders. The powders used were either mono-dispersed SiO₂ or TiO₂ coated SiO₂ powders. The powders were prepared through hydrolysis and condensation reactions of silicon alkoxides in the presence of ammonia and its polydispersity was less than 5%. A slurry dispersed with those powders were infiltrated through the channels of barrier ribs morphology and the solvent was evaporated in a controlled manner to form a superlattice structure of FCC. Using those cells formed, the luminance efficiency of the cells was measured and compared with conventional cells. In addition, the effect of a thin layer of TiO₂ coating on the surface of the crystals on the luminance efficiency was examined. The results indicated that the application of photonic band gap materials on the barrier ribs improves the luminance efficiency significantly.

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The ternary oxide system AlPO4-B2O3-Na2O resembles a well known ternary system SiO2-B2O3-Na2O, and forms a phase-separated glass. The as-prepared glass AlPO4-B2O3-Na2O was already phase-separated from the beginning, and the B2O3-Na2O rich phase was easily removed by washing with water. The remaining AlPO4-based glass has a mesoporous structure with exchangeable Na ions. The porous structures can be chemically modified through the ion-exchange of the Na ions with various kinds of inorganic and organic cations. The pore size distributions and thermal stability of the resulting solids will be discussed.

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An effective fabrication method of rod-shaped γ-LiAlO₂ particles for molten carbonate fuel cell matrices via the synthesis of porous β-LiAlO₂ agglomerates that are easily washed and dispersed with DI-water has been investigated. In order to make large pores and high porosity in the reaction mixture, powder types of carbon and ammonium carbonate that make little ash and undesired material during the whole process were utilized. Regardless of the kind of pore-formers used, most of the rod-shaped β-/γ-LiAlO₂ particles were 1 μm in diameter and 10 to 15 μm long (aspect ratio of 10 ~ 15). The crystal structure of rod-shaped γ-LiAlO₂ particles synthesized from the reaction mixture with pore-formers coincided exactly with that of commercial γ-LiAlO₂ powders, and showed a type of single crystal. As a consequence, cell performances using rod-shaped γ-LiAlO₂ particle reinforced matrices were highly improved in comparison with non-reinforced standard matrices.

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Uniformly porous and porosity-graded piezoelectric ceramics were prepared by sintering powder compacts consisting of lead zirconate titanate (PZT) and organic material powders as pore-forming agents (PFA) in air atmosphere. Three kinds of PFA materials, such as, stearic acid, polymethyl methacrylate (PMMA) and urea, were compared, and PMMA was revealed to be most suitable for controlling the porosity of PZT ceramics. The experiments were focused on the influences of PFA and its amount on the porosity of the sintered PZT. The dielectric, elastic and piezoelectric properties of uniformly porous PZT ceramics were investigated as a function of the porosity volume fraction. Furthermore, beam-shaped PZT actuator samples with graded porosity across thickness were fabricated by sintering PFA-graded powder compacts, and their electric-field-induced deflection characteristics were measured and compared with the values calculated from the modified classical laminate theory using the elastic and piezoelectric constants of the non-FGM porous PZT ceramics.

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Currently, the non-lead treads of pigments in coating industry are nourishing in that European Union has categorized all lead compositions into the type of twice-born toxin. Therefore the substitution for lead chromate pigments is becoming a vital subject. Through the research and development, a few kind of new non-toxic yellow pigments with brilliant hue have been synthesized, in which Bi-Zn-O yellow pigment was claimed to be one of the most excellent. In order to optimize the synthesis process, the phase diagrams and thermodynamic dates for ZnO-Bi2O3 system have been evaluated. According to thermodynamic theory, a replaced solid solution model for ZnO-Bi2O3 system phase diagram calculation has been constructed. With the help of Thermo-Calc computer program, an integrity phase diagram for ZnO-Bi2O3 system has been obtained. In terms of phase diagram of ZnO-Bi2O3, the characteristics for synthesis powder of ZnO-Bi2O3 inorganic pigment have been explored.

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Hydrothermal technique is an effective method for metal phosphates crystallization. These compounds exhibit various structures of three-dimensional open frameworks, two-dimensional layers, and one-dimensional chains. Since organic medium was introduced into metal phosphates synthesis systems, a lot of phosphates with novel layered or chain structures have been crystallized. With the aim to open up a new synthetic system for this class of compounds and obtain some new structures, in the present work, we studied the synthesis and characterizations of crystalline zirconium phosphates in a non-aqueous organic medium. Several zirconium phosphates crystals have been prepared from ZrOCl₂ - H₃PO₄ - organic anime - NH₄F - organic solvent systems. Through the systematical investigation of synthetic conditions, the effects of non-aqueous solvents, organic amines and F^- cations on products crystallization are further clarified. Moreover, the probable reaction mechanisms were estimated, and the ion-exchange properties of the compounds have also been investigated.

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Nanometer-sized particles of anatase-type TiO2 doped with ZrO2 up to 9.8 mol% were directly formed from acidic precursor solutions of titanium(III) sulfate (Ti2(SO4)3) and zirconium sulfate (Zr(SO4)2) in the presence and absence of ammonium peroxodisulfate ((NH4)2S2O8) by simultaneous hydrolysis under hydrothermal condition at 200°C. Although yield of TiO2 from Ti2(SO4)3 solution was accelerated at 100~180°C via the presence of (NH4)2S2O8, nanoparticles of ZrO2-doped anatase could be formed under hydrothermal condition at 200°C for 24 h in the absence of (NH4)2S2O8. Crystallite size of anatase decreased with increasing doped ZrO2 content. Doping ZrO2 into TiO2 retarded the phase transformation from anatase-type to rutile-type structure and the anatase-type structure was maintained after heating at 1000°C for 1h.

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GaN powder in carbon crucible was heated at various temperatures in an induction furnace in nitrogen atmosphere. Some deposition was observed on the crucible cap above 800^oC. Recrystallization of GaN was detected in the deposit at 850^oC probably because Ga metal reacted with an active nitrogen released in the decomposition of GaN. GaN was also obtained by a reaction of Ga metal with nitrogen atmosphere at 1000^oC. The recrystallization was also observed on the GaN powder heated at 850^oC for 1hour in a sealed evacuated tube. Hexagonal platy crystals of about 10μm diameter were obtained.

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