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 the combustion reaction temperature reached the highest value. Post-combustion nitridation could last as long as 660 s. 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.

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Nitrogen-doped titania nanocrystals were prepared by “Homogeneous Precipitation-Solvothermal Process” in TiCl₃-hexamethylenetetramine (C₆H₁₂N₄) mixed solution. The phase composition, crystallinity, microstructure and specific surface area of titania greatly changed depending on pH and temperature. The titania powders prepared in TiCl₃-hexamethylenetetramine solutions at pH 1-6 and 190°C for 2 h consisted of single phase of brookite and that prepared at pH 9 was single phase of rutile. All titania powders prepared in the present study were yellow and showed excellent visible light absorption property and photocatalytic ability for nitrogen monoxide destruction under irradiation of the visible light (λ>510 nm). The photocatalytic activity of brookite prepared at pH 1-6 was superior to that of rutile prepared at pH 9. The photocatalytic activity under irradiation of visible light (λ>510 nm) slightly decreased with increasing calcination temperature up to 700°C and then greatly decreased at 800°C.

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Zeolite has been recognized as one of the materials used for inorganic membranes. To improve the reproducibility of preparation and high permselectivity, the seed technique has been applied to the zeolite membrane under hydrothermal synthesis. Here, electrophoretic deposition (EPD) mechanism of zeolite (A-4) powder, as with the fabrication of the separation membrane, has been investigated under constant applied voltages as one of seed crystal coating techniques. Zeolite- n-propanol suspension is used as the EPD bath. The potential gradient in the n-propanol depended on the distance between the electrodes and the applied voltages. The zeta potential of zeolite particles was -26.5 mV in n-propanol and the resistibility of the EPD bath decreased by dispersing zeolite powder. On the other hand, potential gradient in the bulk EPD bath was constant with the progress of EPD, and the actual working potential gradient decreased 35% against the applied potential and electrode distance. Moreover, current density was constant with the progress of EPD, and the deposition layer in the EPD bath had low resistivity. Therefore, the velocity of zeolite particles was constant in the progress of EPD and the amount of deposited zeolite powder increased linearly against the deposition time and applied voltage. In addition, EPD efficiency is approximately 80% up to the amount of deposit at 25 g/m². EPD is a useful technique for the coating of zeolite particles onto substrates because deposition can be easily controlled and it has high deposition efficiency.

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We synthesized various kinds of nanosize oxide particles with the particle size of 2-100 nm by the combination of precipitation method and hydrothermal treatment at temperature lower than 200°C. The cerium oxide particles obtained only by the hydrothermal treatment were single crystal with platelet shape even at a particle size of about 2 nm, and the platelet plane was identified to be (111) from the observation of lattice images. By the heating at 100-600°C in air, the particle size was increased from about 2 nm to 15 nm maintaining the platelet shape with elevating the temperature. In the zirconium oxide particles, it was confirmed that both monoclinic and tetragonal phases were obtained by the control of synthesis conditions in the precipitation hydrothermal treatment at a temperature lower than 200°C without heating at higher temperature. The typical particle sizes of monoclinic and tetragonal phases were about 7 nm and 100 nm. The crystal constants of these cerium and zirconium oxide particles were nearly in agreement with those of balk oxides.

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Unique mica ceramics with micropores were fabricated from alumina-pillared fluorine micas by pulse electric current sintering (PECS) at a temperature range of 600-800°C under a uniaxial pressure range of 10-30 MPa. The effects of PECS conditions and the nature of alumina-pillared mica powders on the formation and properties of the mica ceramics were studied. The mica ceramics obtained at lower temperatures and lower uniaxial pressures retained the pillared structure of alumina-pillared micas and gave a maximum BET specific surface area of ∼300 m² g^-1, while those obtained at higher temperatures and higher uniaxial pressures lost the pillared structure and microporous characteristics. The mica ceramics thus obtained were machinable due to the interlocking microstructure of the flaky pillared mica crystals. Fully densified mica ceramics could be also produced by PECS at ∼1035°C under a uniaxial pressure range of 10-30 MPa.

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Three new zirconium phosphates, [NH₄]₂[H₃N(CH₂)₂NH₃]₂[Zr₃(OH)₆(PO₄)₄] (ZrPO-1), [NH₄]₂[Zr(OH)₃(PO₄)] (ZrPO-2) and [NH₄]₃[Zr(OH)₂(PO₄)(HPO₄)] (ZrPO-3), have been prepared in ZrOCl₂-H₃PO₄—organic anime-NH₄F—organic solvent systems, and characterized by single crystal X-ray diffraction, powder X-ray diffraction, thermal analysis, scanning electron microscope, infrared spectroscopy, ICP, and CHN elemental analysis. Through the systematical investigation of crystal structures and synthesis conditions, the effects of organic solvents, organic amines and F^- cations on product crystallization are further clarified. Moreover, the ion-exchange properties of the compounds have also been investigated.

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A series of giant magnetoresistance materials La_0.5A_0.5MnO₃ (A=Ba, Sr, Ca) was hydrothermally prepared at 240°C for 1∼3 days and characterized by powder X-ray diffraction, scanning electron microscope, iodometry, and DC four-terminal method. The alkalinity and molar ratio of Mn(VII)/Mn²⁺ in the initial reaction mixture, associated with hydrothermal reaction temperature, dominate the crystallization of the products. The SEM images of the as-prepared La_0.5Sr_0.5MnO₃ indicated that the product is cubic crystal about 2-5 μm, and the La_0.5Ba_0.5MnO₃ is cubic crystal about 100-500 nm. The average valence state of manganate in all the products is 3.5.

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GaN powder, in carbon crucibles was heated at various temperatures in an induction furnace in a nitrogen atmosphere. Deposition of Ga₂O₃ was observed on a substrate that covered the crucible during heating at above 800°C. The recrystallization of GaN was detected in the deposit formed only at 850°C probably because Ga metal deposited on the substrate reacted with an active nitrogen released in the decomposition of GaN powder. GaN also recrystallized on the substrate at 1000°C in a reaction of the evaporated Ga metal with nitrogen atmosphere. Such recrystallization was also observed when GaN powder was heated to above 850°C in an evacuated sealed quartz tube. Hexagonal thin platy crystals of about 4 μm diameter were obtained. Short duration heating at temperature close to 850°C was preferable to grow crystals because its decomposition simultaneously occurred with the recrystallization. It appears that GaN crystals do not grow in the sublimation process proposed previously but rather in the recrystallization.

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The complex between the Nb-peroxo compound and KNO₃ was prepared by heating the Nb-peroxo compound aqueous solution with KNO₃ at 573 K for 1 h. The single phase of KNbO₃ was obtained by firing the complex between the Nb-peroxo compound and KNO₃ at 873 K for 2 h. The obtained KNbO₃ had tetragonal crystal system. On the other hand, when the stoichiometric mixed powder of Nb₂O₅ and K₂CO₃ with the molar ratio of Nb : K=1 : 1 was fired at 873 K for 2 h, orthorhombic KNbO₃ was obtained. In general, tetragonal phase can be obtained under high pressure condition at more than 6.6 GPa. When the complex between the Nb-peroxo compound and KNO₃ was used for the KNbO₃ preparation, the tetragonal KNbO₃ was obtained at normal pressure condition. The lattice parameter of a axis of the KNbO₃ obtained from the Nb-peroxo compound solution was less than that of the stoichiometric one. According to this fact and the result of UV-VIS spectra, the KNbO₃ prepared by firing the complex between the Nb-peroxo compound and KNO₃ had oxygen vacancies, which affected the lattice parameter and the crystal system.

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10 mol% Gd₂O₃-doped CeO₂ solid-solution (20GDC) powders have been synthesized via carbonate coprecipitation using nitrates as the starting salts and ammonium hydrogen carbonate (AHC) as the precipitant. Characterizations were achieved by elemental analysis, XRD, DTA/TG, and FESEM. The thus-processed precursor is an amorphous hydroxyl carbonate with an approximate formula of Ce_0.8Gd_0.2(OH)(CO₃)•2H₂O, which directly yield oxide solid-solutions upon thermal decomposition at a very low temperature of approximately 430°C without any phase detected corresponding to Gd₂O₃. The 20GDC oxide powder calcined at 700°C shows excellent reactivity and were densified to >99% of the theoretical via pressureless sintering at a low temperature of 1150°C for 6 h. Electrical conductivity of the densified ceramic was measured in air in the range 400-700°C by the DC three-point method, and an activation energy of ∼60.92 kJ/mol was derived from the experimental data.

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Solvothermal treatment of AgNO₃ in alcohol-water mixed solvent dispersed with γ-alumina (γ-Al₂O₃) powders at 498 K for 2 h was conducted to prepare Ag/(γ-Al₂O₃) composite powders for catalysts. The influence of ethanol content on the crystalline phase and microstructure of solvothermal products was investigated. With decreasing ethanol content in the solvent, the alumina matrix phase gradually changes from γ-Al₂O₃ to boehmite (γ-AlOOH), accordingly, the ratio of larger rhombic γ-AlOOH to smaller needle-like γ-Al₂O₃ increased. This phase change resulted in the decrease of the BET specific surface area and total pore volume and a shift of the characteristic pore size and pore size distribution. During the solvothermal treatment in ethanol/water mixed solvents, silver nanoparticles precipitated from the solution to form Ag/(γ-AlOOH, γ-Al₂O₃) nano-composites whereas no precipitation occurred in pure water.

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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°C for 60 min. However, about 90 mass% of the SiC-coated MWCNTs remained after the same oxidation test.

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KTaO₃ thin films have been synthesized on single crystal SrTiO₃ substrate with La_0.7Sr_0.3MnO₃ buffer layer (LSMO/STO) by hydrothermal electrodeposition at 80-110°C. At first, the preparation of KTaO₃ powder was investigated under hydrothermal condition. As a result, the powders consisting of single phase KTaO₃ were prepared in high concentration KOH solution of 18.5 M at temperature higher than 80°C. Under this condition, KTaO₃ thin film was grown on LSMO/STO substrate by hydrothermal electrodeposition. The only (l00) peaks of cubic KTaO₃ were observed in XRD patterns of KTaO₃ thin film grown on LSMO/STO substrate, suggesting the (100) orientation. The KTaO₃ (200) peak appeared at 45.39-45.52° and shifted to lower degree side with increasing film thickness. The film growth started from the deposition of fine and cubic particles (ca. 10 nm). Then the fine particles were united to form larger and flat crystallites (ca. 400 nm). Interestingly, KTaO₃ film was deposited on both positive and negative electrodes, but the growth mode was slightly different from each other.

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Phospho-olivine LiFePO₄ as a cathode material for rechargeable lithium batteries was successfully synthesized by hydrothermal process with an additional heat treatment in order to realize a theoretical electrochemical capacity. Several solutions with various concentrations of Li, Fe, and P were examined, and ascorbic acid was also used as a reducing agent. From an x-ray diffraction measurement, all of the samples synthesized with the molar ratio of Li : Fe : P=2.5 : 1 : 1 were characterized as a phospho-olivine LiFePO₄, independent of the addition of ascorbic acid. In order to improve the discharge and charge capacities, a heat-treatment was carried out. A remarkable increase in the charge and discharge capacities was accomplished for all of samples. The best performance was obtained when LiFePO₄ was prepared under the conditions as follows, the molar composition of Li : Fe : P : Ascorbic acid=2.5 : 1 : 1 : 0.2 in the starting solution, and annealing at 400°C for 1 h under argon atmosphere.

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The electrophoretic deposition characteristics of alumina particles in aqueous media were investigated under a constant current condition. The apparent deposition rate and green density of the deposits were dependent on the pH and salt concentration of the suspensions. The isoelectric point (i.e.p.) of alumina in aqueous media was pH 7.9 and no deposition of the particles was observed for the suspension prepared at the i.e.p. As the pH of the suspension slightly decreased from the i.e.p., the deposition rate rapidly increased. The maximum deposition rate was observed at pH 7.0. As the suspension became more acid, the zeta potential of alumina particles increased, however, the deposition rate decreased. At a fixed pH, the higher concentration of the salt, sodium chloride, produced a smaller amount of deposits and the higher solid concentration produced a the larger amount of deposits. The apparent transport number of the surface-charged alumina particles estimated from the total electrical current and deposit weight was low. The predominate carrier of the electric charge in the solvent was considered to be other ions, such as protons.

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Well-formed single crystals of R₄Mo₇O₂₇ (R=Ce and Pr), novel phases in the R₂O₃-MoO₃ system, have been obtained by thermal degradation of R-containing polyoxomolybdate precursor, [R₂(H₂O)₁₂Mo₈O₂₇]•nH₂O, in air at 800°C 12 h. Both compounds crystallize in a flux of the dehydrated precursor as a result of loss of excess MoO₃. The two species are isomorphous with space group C2/c, Z=8, a=4.6354(2) and 4.6046(2) nm, b=0.74853(3) and 0.74712(2) nm, c=1.43536(9) and 1.42640(5) nm, and β=100.897(2) and 101.006(2)°, for R₄Mo₇O₂₇ (R=Ce and Pr), respectively. The structure is built up with two kinds of {R(MoO₄)}₂ double-layers and one {Mo₃O₁₁} mono-layer, which are stacked alternately parallel to the (110) plane. An arrangement of [R(MoO₄)]⁺ unit is different between the two {R(MoO₄)}₂ double-layers. The Mo₃O₁₁ group in the mono-layer consists of one MoO₅ trigonal bipyramid corner-shared with two MoO₄ tetrahedra. In comparison with other rare earth molybdates, we found that several materials commonly have similar {R(MoO₄)}₂ double-layers. Details of their layer structures are discussed.

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Well-faceted hexagonal plate-like particles of β-Co(OH)₂ have been prepared by a precipitation method. α-Co(OH)₂ was formed first, and then transformed to β-Co(OH)₂ with a typical size of 0.5×0.1 μm. Growth of β-Co(OH)₂ micro-crystals up to 9×0.5 μm 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 oriented particulate monolayer X-ray diffraction (OPML-XRD), which was kept after hydrothermal growth. The obtained platelets are considered to be suitable templates for the fabrication of textured layered-cobaltite thermoelectric ceramics by the reactive-templated grain growth (RTGG) method.

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A recently developed shock-sintering technique was employed to fabricate dense titania (TiO₂) ceramics. The densification and grain-growth behaviors as well as the anatase-to-rutile transformation of a nanocrystalline TiO₂ powder without any additives were investigated as a function of sintering temperature and/or sintering time. It has been shown that densification proceeds simultaneously with phase transformation. At 1100°C for a sintering time of 2 min, a 100% density was achieved, while 98% anatase was transformed into rutile. On the other hand, significant grain growth was observed to occur at temperatures above 1100°C.

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For the utilization of the paper sludge (PS) ash, we investigated a novel method to remove high concentrated Pb ions from water and fix them. PS ash zeolite (PSZ), which was prepared through an alkali hydrothermal treatment of PS ash with the addition of sodium silicate, was soaked into an aqueous solution of Pb(NO₃)₂ to include Pb ions. The PSZ was heated at a temperature more than 400°C to form PS ceramics (PSC) after being mixed with sodium silicate. The PSC was characterized in terms of morphology, constituent minerals and chemical bonding. In addition, we evaluated the Pb ions fixability of PSC by the determination of Pb concentration eluted from PSC. As a result, detected minerals of PSC's were quartz, albite, nepheline and wollastonite. Each of them appeared or disappeared with changing heating temperature and/or amount of sodium silicate added. Especially in the case of high heating temperature (≥800°C) and large amount of sodium silicate added (≥0.03 molSi/10 gPSZ), nepheline and albite were principal assemblage of PSC and mechanical strength of PSC increased. When nepheline existed in PSC, Pb concentration eluted from PSC was extremely low, showing high ability on fixing of Pb ions. At the same time, the PSC that contained nepheline showed high acidic resistant.
Therefore, it was concluded that the transformation of Pb-included PSZ to PSC that contained nepheline as a principal constituent mineral was much effective for fixing of Pb ions. This novel method will be also applicable to the removal of other heavy metal ions in the water.

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Nickel aluminate (NiAl₂O₄) spinel has a high electric conductivity and a good stability at high temperature, and it becomes a promising candidate as anode material in aluminum electrolysis. The self-propagating high-temperature synthesis (SHS) technique was employed in the present work to produce NiAl₂O₄ spinel by using Al and NiO as reactants. The synthesized powders were studied by SEM and XRD. The XRD results show that the formation of NiAl₂O₄ depends on the molar ratio (R) of NiO/Al, and NiAl₂O₄ spinel could only be formed when the molar ratio is higher than 1.5. The amount of the NiAl₂O₄ spinel reaches maximum when the molar ratio was 2. The reaction chemistry and the reaction mechanism are also discussed in this article.

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The Copper phthalocyanine (CuPc)/transition metal oxide (TiO₂)-CuPc-SDS/TiO₂ composite thin film has been successfully prepared from the aqueous solution by a novel wet process, liquid-phase deposition (LPD) method. It may open up a new way to prepare the CuPc thin film, and develops the formation processes of CuPc thin films. For LPD method, this is the first attempt to prepare the insoluble organic substance/inorganic metal oxide composite thin film with using a surfactant sodium dodecyl sulfate (SDS) as dispersing agent. The CuPc-SDS/TiO₂ composite thin film was formed directly on to the substrate upon immersion into a mixed solution of [NH₄]₂TiF₆, H₃BO₃ and CuPc-SDS aqueous solution. The deposited composite thin films were characterized by ultraviolet-visible (UV-Vis) absorption spectroscopy in the range of 350-850 nm, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and inductive coupled plasma atomic emission spectrometry (ICP-AES). The results revealed that most of the CuPc existed as dimer species both in the film and in the treatment solution, illustrating that the CuPc is not further aggregated by LPD process. According to the study of the XRD patterns of the composite thin films, the CuPc-SDS/TiO₂ composite thin film was proved to be α-form CuPc composite thin film. The effects of changing SDS and CuPc concentration on the composite thin films were studied, indicating that the deposited amount of CuPc increased with an increase of SDS and CuPc concentrations. The dependences between the deposited amount of Ti and Cu with the reaction time were investigated, which indicated that the deposited amount of Ti and Cu are nearly directly proportional to the reaction time, and suggested the growing of the composite thin film was controllable readily.

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Surface treatments, such as calcination, acid solution leaching and alkali solution leaching, were used to improve the dispersibility and increase the electrophoretic deposition (EPD) weight for a fine SiC powder. Main impurities including hydrophobic free carbon and hydrocarbon on the particle surface caused the low dispersibility and less deposition for the as-received powder in aqueous suspension. After calcination, the dispersibility and deposition weight were enhanced obviously. Acid leaching and alkali leaching were more effective to improve the dispersibility. The deposition weights of the two kinds of powders were about 4 times larger than that of the as-received powder. Slight oxidation on the particle surface after acid leaching led to the largest deposition weight for the acid leached powder. The reason for the improvement caused by different treatments was discussed according to the results of zeta potential, FTIR, XPS, and surface acidity analyses.

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In an attempt to improve luminance efficiency of plasma display panel (PDP), its discharge cells were coated with photonic crystal (PC) layer. The powders used were monodispersed SiO₂, which were prepared through hydrolysis and condensation reactions of silicon alkoxides in the presence of ammonia. Polydispersity of the powder was less than 5%. A suspension of the powder was filled into the cells on rear plate of PDP and solvent was evaporated from the cells in a controlled manner to form a PC layer. Luminance efficiency of the cells with the layer was measured and compared with cells without the layer. The results indicated that application of PC layer significantly improved luminance efficiency of the PDP cells.

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A thin film including beta-silicon carbide (β-SiC) was synthesized by carbon silicification through a reaction between gaseous silicon monoxide (SiO) gas and carbon source derived from polyimide film (PIF). The sample obtained had film shape similar to that of the carbon source film. Two reacted regions were found on both surfaces of the carbon source film, as well as the un-reacted region in the middle of the sample with less than 3 h synthesis time. Formation mechanism of β-SiC film formed by the reaction between SiO gas and carbon source film at 1400°C was investigated based on relationship among SiC conversion ratio, reaction time and atmospheres. Formation processes were simulated thermodynamically and kinetically by the calculations solving differential equations concerning with a rate of chemical species. Results of the simulated curves for the SiC conversion ratio calculated from 6 chemical equations, 12 rate constants, 2 diffusion constants, 9 chemical species and 9 differential equations have a good agreement with the experimental results of the SiC conversion ratio as a function of reaction time.

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Geopolymers synthesised using New Zealand fly ash have been investigated for their potential application as matrices for encapsulation and immobilisation of hazardous and radioactive waste. Knowledge of the long-term behaviour and macroscopic and microscopic properties of these materials will be essential. Pastes aged for between 1 day and 2 years after were investigated in this study. The material exhibited a complex microstructure, consisting of both crystalline and amorphous regions. While no changes in crystalline phases were detected in fresh and aged samples, significant differences in porosity and surface area were noted on ageing of the samples. Very high early strengths of 85 MPa were achieved but were observed to decline in samples after 7 days ageing. It is believed that on-going reactions within the geopolymer matrix are contributing to these changes after the material has set and hardened.

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Mesoporous crystalline titania with large surface area was obtained with polymer templating. The wet gels, prepared by hydrolysis of Ti-alkoxide in ethanol, were immersed in a solution of triblock-copolymer, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) [Pluronic, M.W. 12600], dried, and annealed. After annealing at 500°C, diffraction peaks of anatase were found. Pore size, pore volume and BET surface area of the annealed gels depended on the concentration of pluronic. The micelle-like aggregates of pluronic, which consisted of hydrophobic and hydrophilic blocks, were incorporated in the wet gel, and the shrinkage of gels during drying was restricted. Thus, the pore size and the surface area of annealed gels increased.

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A new layer structured chromium titanate Cs_xTi_2-xCr_xO₄ (x=0.70) with a lepidocrocite (γ-FeO(OH)) type structure was prepared by solid state reaction at 800°C using Cs₂CO₃, anatase type TiO₂ and Cr₂O₃ under an argon atmosphere. Ion exchange reactions of Cs⁺ in the interlayer space of the chromium titanate were studied in aqueous solutions. The host layer of the chromium titanate was maintained on the ion exchanges and the products were found to contain an interlayer water. The single phases of hydrated H⁺, Li⁺ and Na⁺ exchange products were obtained from the chromium titanate. Cs⁺ in the interlayer space was leached out up to 91% in the ion exchange. The ion exchange products were characterized by chemical analysis, TG-DTA, X-ray diffraction and optical absorption.

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We have conducted joining between AlN ceramics by spark plasma sintering (SPS) process and examined the effects of TiH₂ coating on AlN and the insertion of Ti and Cu foils. Titanium hydride was decomposed and a joint was formed by heating at 500°C for 10 min. The resultant reaction layer has a shear strength of 24.8 MPa. The interface layer was characterized using scanning electron microscope (SEM), electron-probe microanalyzer (EPMA) and x-ray diffraction (XRD).

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Gel-combustion synthesis was used to synthesize a fine powder of Co₂Z-ferrite (Ba₃Co₂Fe₂₄O₄₁). Either citric acid or glycine was added, as a peptizer, to the mixed aqueous solution of Ba(NO₃)₂, Co(NO₃)₂•6H₂O and Fe(acac)₃. The product gel was ignited at 150°C and then fired again in a temperature range of between 500°C and 1200°C. The ignited product was a mixture of CoFe₂O₄ and Ba(NO₃)₂ when citric acid was used as a gelling agent. Its fired product was a mixture of Co₂Z-, CoY-, BaM-ferrites and BaFe₂O₄. A higher temperature was attained during the ignition of the glycine gel rather than the citric acid gel. The ignited product of the glycine gel was a mixture of CoFe₂O₄ and BaFe₂O₄. Pure Co₂Z-ferrite fine powder was subsequently obtained by firing this ignited product at 1000°C. This temperature is much lower than the firing temperature of 1300°C required by the solid state reaction. Its crystallite and average particle sizes were 42∼48 nm and 180∼200 nm, respectively. Saturation magnetization was 45∼47 emu/g and coercivity was 0.59∼0.90 kOe.

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Compacts of spherical alumina particles with and without c-axis orientation were prepared in high magnetic field and were employed to separate the shape and crystalline factors for the anisotropic sintering in alumina compacts. The compact of the spherical particles showed markedly anisotropic shrinkage in sintering when they are oriented. Isotropic shrinkage was noted when the particles were randomly oriented. Clearly, the crystalline factor plays an important role in the anisotropic shrinkage in sintering. The shape factor also plays a role in the anisotropic shrinkage in alumina compacts made of industrial grade powder.

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Microwave sintering is a process in which objective materials absorb microwaves and heat themselves from the inside. When microwave energy is effectively absorbed by the material, energy consumption for the sintering can be reduced. In this work, a domestic microwave oven (multimode cavity, 2.45 GHz) was employed for sintering ceramics. However, it is difficult to absorb microwaves effectively for long waves. Therefore, a method of efficiently absorbing the microwaves is needed. In general, dielectric loss of ceramics is low at room temperature, but high at high temperatures. A material with high dielectric loss at room temperature was used as a susceptor. The present investigation describes optimization of the heating system set up for the sintering of ZnO. Microwave processing resulted in a reduction of sintering time. A comparative study of ZnO using microwaves and by conventional heating was done using scanning electron microscopy (SEM) observation. The density and average grain size of microwave and conventionally sintered specimens at 1100°C were similar.

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A repeated co-extrusion process was used to fabricate fibrous composites of both 11 vol%-zirconia/alumina composite and 11 vol%-alumina/zirconia composite. A bundle of feedrods composed of ordinary arranged alumina and zirconia green rods was co-extruded through a 6 : 1 reduction die. After the first co-extrusion, the individual pieces were bundled and co-extruded again, reducing the lateral size of each phase and multiplying the number of continuous monofilaments. The extrudates were pressureless sintered at 1600°C for 3 h after the decomposition of organic residuals. In both composites, first and second extrusion steps produced composites with cracks. Finally, a crack-free, high density alumina/zirconia composites could be obtained after third extrusion step, though the filaments were not found to be continuous. The fracture toughness of both the composites after third extrusion step was improved by introducing fine second phase filaments into the matrix.

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The packing structure of alumina green body prepared by slip casting method was examined using an optical method based on polarized light microscopy. Minor particle orientation was noted in the green body made by slip casting. The alumina compact was fabricated by slip casting in gypsum molds. Alumina particles in commercial grade powders have an elongated shape. The alumina particles in the green body were always oriented parallel to gypsum surface. The oriented packing structure was observed throughout the compact.

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Use of natural polymers as gelling agents was attempted in order to develop a new gelcasting process under ambient atmosphere for fabrication of porous building materials composed of waste resources. Agar, curdlan and carrageenan were selected as natural polymers. The slurry with an appropriate composition of wastes and polymer was foamed by a mixer after addition of a surfactant. The foamed slurries were in situ solidified after casting into a plastic mold under ambient atmosphere. Effects of a type and concentration of polymer on the properties of wet-green bodies, dry-green bodies and sintered bodies were examined. The strength of the obtained wet-green bodies was sufficient enough for de-molding and successive handling. The compressive strength of wet-green bodies increased with polymer content and showed the highest value at the addition of agar. However, carrageenan and curdlan have advantages that the foamed slurries can be solidified by heating after casting into the mold. On the other hand, the slurries should be heated before casting and cooled for gelation when agar is used. It is obvious that the gelling is quite easy in the former procedure. The flexural strength of dry-green bodies and sintered bodies depended on their porosity rather than on the type and concentration of the polymer. The values of strength ranged from 15 to 45 MPa enough for application as a ceramic tile, even though the porous materials have high porosities of around 60%. These results revealed the in situ solidification method using carrageenan and curdlan as a promising technique to produce porous building materials.

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Three-dimensional electroconduction pattern of Si₃N₄-TiN system was prepared using the ink jet printing method. Two kinds of 20 vol% ink were prepared by milling insulative powder (Si₃N₄) and electroconductive powder (TiN), of which the viscosity and the dispersibility were carefully adjusted. The droplet formation process and the compact characters were examined, and the effect of the ink characters on both printing and forming behaviors was studied. It was revealed that the viscosity and the structure of the ink influenced the printing behavior and the compact characters. The laminated body was processed by patterning on a compact of Si₃N₄, followed by firing for 3 h at 1750°C in N₂. The sintered body showed an interesting structure with three-dimensional electroconduction pattern.

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Porous carbon substrates have been sealed completely with a molten silicate glass, where the wettability of the carbon to the molten glass was improved by infiltration and pyrolysis of perhydropolysilazane. The interfacial structure between the carbon and glass depended on the N₂ partial pressures during sealing. Coating of the glass at a higher N₂ partial pressure was not followed by formation of cristobalite due to oxidation of the products pyrolyzed on the carbon substrate. The molten glass easily infiltrated into the substrate. Under lower N₂ partial pressures such as in Ar, the glass covered only the carbon substrate and seldom penetrated into the substrate. In this case, cristobalite was produced at the interface, with many pores also forming at the interface. The pores are due to the large amount of SiO produced by oxidation of the pyrolyzed species, leading to suppression of molten glass infiltration into the carbon. The structural changes occurring as a result of variation in N₂ partial pressures are described in terms of thermodynamic calculations.

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Non-aqueous suspensions are preferred for electrophoretic deposition (EPD) to prevent electrolysis of the solvent and to obtain a bubble-free deposit. On the other hand, aqueous systems have the advantages of low cost and low environmental burden. However, water is decomposed into hydrogen and oxygen when a dc current is passed through an aqueous media. It is well known that hydroquinone (HQ) is easily oxidized to quinone (Q), and this reaction decreases the levels of dissolved and electrolytically produced oxygen. In the EPD process, oxygen produced electrolytically would be consumed by the chemical oxidation of HQ, followed by bubble-free deposition on the anode. In this study, we investigated EPD on various anodes of aqueous alumina and zirconia suspensions with HQ and also attempted to fabricate bubble-free alumina/zirconia gradiented composites.

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Patterned ceramic structures composed of two different materials with a feature resolution in the micrometer range have been generated by microfluidic lithography. Micro-channels made of poly (dimethylsiloxane) (PDMS) were filled with well-dispersed suspensions followed by solidification upon solvent evaporation. The cross-inserted comb-type ceramic structures with 100 μm in the width were fabricated in a relatively large area of 2×2 cm² for Al₂O₃ and NiO. It was found that controls of suspension characteristics and its drying play an important role in determining pattern quality. Micro-channel filling was significantly influenced by viscosity and surface tension of suspension and interfacial interaction of suspension with surfaces of the substrate and PDMS. Once filled, a proper drying condition must be met. Otherwise, the micro-channels were disconnected due to capillary stress, resulting in an incomplete pattern generation.

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Very high tensile strengths of SiC and its joint material over 1200 MPa and 500 MPa were achieved by newly developed reaction sintering (RS) technique. The design study of ceramic type H₂SO₄ vaporizer was performed on the base of these material data and testified its applicability for nuclear heat IS hydrogen production plant. Present study also demonstrated applicability of the RS-technique to full scale ceramic block unit(110 mm×110 mm×110 mm) with heat channels for the vaporizer.

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Both p- and n-type Si_0.8Ge_0.2 powders (Si : Ge : B=79.7 : 20.1 : 0.20 mol% for p-type and 79.8 : 20.0 : 0.20 mol% for n-type) were prepared by gas atomization of the melts from starting solids, followed by densification using a pulse-current sintering technique. These Si-Ge powders were characterized and their sinterability was studied, and the thermoelectricity of the Si-Ge dense bodies was then elucidated. The effect of ball-milling on both the sinterability and thermoelectricity was discussed. Ball-milling made the particle size of as-prepared powders small, presumably together with the introduction of the distortion to the crystal lattice. The densification of as-prepared powders was abruptly promoted above 1500 K by pulse-current sintering, while this densification behavior of the pulverized powders occurred at a lower temperature by approximately 100 K. The grain size and elemental inhomogeneity of the dense body from pulverized powders were also reduced. The pulse-current sintering of the gas-atomized and their pulverized powders led possibly to a density of the shaped bodies of more than 99% at 1523 and 1433 K, respectively, in a short time of 3 min. The following results obtained here were all attributed to the thermoelectric properties such as thermal conductivity, electrical resistivity and the Seebeck coefficient of the dense bodies. The figure of merit of dense body from gas-atomized n-type powder was the highest among the four kinds of the dense bodies tested. It is proved that the figure of merit of the dense bodies from gas-atomized powders was higher than those from pulverized powders, and that further pulverization by ball-milling was ineffective.

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Tetragonal zirconia polycrystal (TZP) compact was made via colloidal processing by the high-speed centrifugal compaction process (HCP). A pure zirconia powder of 0.14 μm was prepared into aqueous slip and compacted by the HCP under 10,000 g. The compact was presintered, then yttria phase stabilizer was impregnated in the form of an aqueous solution of yttrium nitrate.
The slip with the maximum powder concentration (72.2 mass%) yielded the highest green density of 46% and suppressed the segregation of particles during the HCP. The yttria-doped specimens were densified up to 99% at 1623 K without pressure assistance. The microstructure consisted of grains of 0.5 μm diameter of the tetragonal phase. The highest values of hardness and fracture toughness, Hv 1270 and 9.1 MPa m^1/2, respectively, were obtained with a specimen doped with 2.7 mol% yttria.

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Sintering of translucent polycrystalline alumina has improved through optimization of dopants and sintering atmosphere. The role of the magnesia dopant and mechanisms of the densification process in alumina have been active topics for numerous studies in the literature. It is widely recognized that the mass transport required for densification involves grain-boundary diffusion, and oxygen vacancies play an important role. The retardation of grain growth has been ascribed to drags due to solute and/or spinel second phase particles. Some researchers have conceived the notion that magnesia solubility in alumina is dependent on grain size. In this paper, we will report that the solid solubility of magnesia in alumina is indeed a strong function of grain size in the range of submicron to one micron. The grain-boundary enrichment factor and width appear to be a function of grain size. Grain growth occurs in small-grained MgO-doped alumina at temperatures as low as 1150°C. During the initial stage of grain growth and sintering of compacts of magnesia-doped, submicron alumina powders, the grain size, enriched dopant level at grain boundaries, boundary width, and equilibrium dopant content in the lattice, undergo dynamic evolution, in a background of boundary motion, precipitation of spinel second phase, and diffusional flux of the dopant.

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Lithium titanate (Li₂TiO₃) pebbles are considered to be a candidate material of the tritium breeders for fusion reactor from viewpoints of good tritium recovery, chemical stability, etc. In the present study, fabrication tests of ⁶Li-enriched Li₂TiO₃ pebbles were carried out by a wet process with a dehydration reaction and their characteristics were evaluated in preparation of an irradiation experiment in a material testing reactor. Based on the results, ⁶Li-enriched Li₂TiO₃ pebbles and TiO₂-doped ⁶Li-enriched Li₂TiO₃ pebbles with the target values (density: 80-85%T.D., grain size:<5 μm, diameter: 0.85-1.18 mm) were successfully fabricated by this wet process. Sphericity of the Li₂TiO₃ pebbles, which is the ratio of the longest diameter to the shortest diameter, was a satisfying value of less than 1.1.

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The dispersion and fluidity of aqueous carbon slurries were studied to elucidate the optimum preparation conditions to obtain well-dispersed and fluidized aqueous carbon slurries. The mean particle diameter of the carbon powder used was 13 nm. Styrene/maleic copolymer (SM), polystyrenesulfonic acid (HPSS), and naphthalene sulfonic acid formalin condensate ammonium salts (DEMOL-AS) were selected as dispersants. The rheological behavior of aqueous carbon slurries with various dispersants was examined and evaluated. The electrokinetic behavior of the carbon particles in the presence of DEMOL-AS, SM, or HPSS indicated that the surface properties of the carbon particles changed from hydrophobic to hydrophilic by adsorption of dispersants. The fluidity of aqueous carbon slurries was effectively enhanced by the addition of DEMOL-AS, as compared with the addition of SM or HPSS. DEMOL-AS containing a naphthalene nucleus was an effective dispersant to improve the surface of carbon particles. The dispersion and fluidity of the carbon slurries were dependent on electrokinetic and steric interactions. The carbon slurries with DEMOL-AS were well dispersed and fluidized over a wide range of pH. These observations indicated that DEMOL-AS is an effective dispersant for preparing aqueous carbon slurries.

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Development of ceramic materials for high-voltage insulators tends to substitute the quartz portion with alumina in order to achieve greater product reliability. However, the compositions with high alumina content require additional processing or increasing sintering temperature resulting in an economic disadvantage for the alumina porcelain. The introduction of alumina-mullite porcelain is another alternative which reduces structural stresses induced by quartz and, at the same time, lower the operating cost. This work will present the effect of changing composition by varying the amount of raw materials on the fired strength along with an evaluation of phases and microstructures. The results will give practical guidance for the manufacturers who need to improve their products for high-voltage applications with a slight change in the sintering conditions.

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Preparation of ceramic slurries is an important process in colloidal processing. Planetary mixing allows the preparation of zirconia slurries in less time than conventional ball milling, and the slurries have low viscosity. However, there are two problems with slurries prepared by planetary mixing with water alone: a film forms on the surface of the slurry because of the increase in temperature of the slurry, and the fluidity of the slurries prepared by planetary mixing alone are poor as demonstrated by sedimentation tests. In this study, we investigated techniques to resolve these problems. Planetary mixing with zirconia milling balls and ice blocks for 150 s yielded slurries retaining low viscosity up to 83.5 mass%.

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Hot centrifugal pressing has been proposed as a new processing technology of material integration. This process utilizes high centrifugal acceleration under various heating atmospheres. The potential of present process has been demonstrated in a variety of processes such as constrained sintering, diffusion bonding, and porous material structuring by means of its process selectivity. It was found that anisotropic shrinkage in centrifugal sintering was effective for suppressing crack formation in constrained sintering. Furthermore, sintering progress along rotational radius direction has been observed. Self-pressurized diffusion bonding has been also attempted, by which joining of ceramics with complex shapes has been successfully applied.

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A powder mixture of 60 vol% Al+40 vol% Al(OH)₃ was used to fabricate Al₂O₃/Al supports by pressureless sintering, in vacuum, at a temperature of 600°C. Two unidirectional pressures of 30 and 120 MPa were used to prepare green compacts. A high surface area was obtained due to the transitional Al₂O₃ phases that were produced by the decomposition of Al(OH)₃. At the same time, the Al₂O₃ supports retained high fracture strength due to a metal network that was formed after sintering. The surface area of the specimen sintered from the compact prepared by 30 MPa was much higher than that by 120 MPa, because the high compaction pressure resulted in the high green compact density so that the pores in the sintered specimen were closed.

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Machining damage was examined on alumina ceramics with various grain sizes, which were prepared using a dry-pressing method with spray-dried granules, followed by sintering at 1570°C for 2-27 hours. The grain sizes of the sintered bodies were 3-9 μm. After machining, the specimens were placed in an alcohol solution of fluorescent dye and then dried. The fracture strength was measured by 4 point bending. The fracture surface was observed using a confocal scanning laser fluorescence microscope. The fluorescent dye in the specimen shows the machining flaw directly. The machining flaw was spread almost uniformly in the specimen with small grain size. The fracture resulted from the machining flaws. The fracture strength was strongly dependant on the extent of the machining damage.

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The sol-gel method was used for the preparation of high proton-conducting glasses. The proton conductivities were investigated to relate with the pore structure, adsorbed water molecules and glass compositions. The conductivities follow the Arrhenius equation and the activation energy decreases with increasing the logarithm of the product of proton and water concentration. The proton conduction is promoted by the dissociation of proton from the hydroxyl bonds and the proton hopping through water molecules, the conductivities of which proportionally increase in log-log scale with the increasing content of both the hydroxyl and water molecules in the pores. The effect of pore size and the glass components on the proton conduction was quaintly elucidated. High conductivity of ∼10^-2 S/cm at room temperature was achieved for the P₂O₅-SiO₂ glasses. The preparation of pore-controlled glass films was also described.

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