Al₂O₃-SiC composites containing up to 30wt% SiC particle or whisker were hot-pressed at 1500°-1850°C for 1h under 25MN·m^-2, and their erosive wear was studied using SiC and Al₂O₃ abrasives. The erosion rate of Al₂O₃-SiC composites decreased with an increase in SiC content regardless of the abrasive. The erosion rate of Al₂O₃ containing 30wt% SiC whisker was four times smaller than that for pure Al₂O₃. The decrease in erosion rate was related to the increase of hardness and fracture toughness of composites due to SiC addition. The composites were considered to be homogeneous from erosive wear characteristics.

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The varistor characteristic was found to be dependent on oxygen behavior. Characterization with SIMS and EPMA indicated that there existed a high diffusion path inside the sample. Enhancement of oxygen diffusion was considered to be due to the segregated second phase network composed of mainly Bi₂O₃ or Pr₆O₁₁. A model to explain the diffusion enhancement is proposed based on the results of the tracer ¹⁸O measurement.

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R₂Zr₂O₇ and (R_1-xEu_x)₂Zr₂O₇ (R=La, Pr, Sm, Eu, Gd, Tb, Er, Y) were prepared at 1600°C in air and their fluorescence properties were studied. The crystal structures of these compounds were pyrochlorite-type for the light rare earths and CaF₂-type for the heavy rare earths, respectively. However, Gd₂Zr₂O₇ and Y₂Zr₂O₇ showed broad and small (111) X-ray diffraction peaks which were characteristic of the pyrochlorite-type structure. Further, annealing at 1500°C increased the intensity and the sharpness of the (111) peak of Gd₂Zr₂O₇. When the compounds were excited by the 254nm line, only the Eu-doped La₂Zr₂O₇, Gd₂Zr₂O₇ and Y₂Zr₂O₇ showed emission spectra due to Eu³⁺ ions. These spectra and X-ray diffraction, showed that in La₂Zr₂O₇ almost all rare earth ions occupy D_3d symmetry sites, but in Y₂Zr₂O₇ and Gd₂Zr₂O₇ most rare earth ions occupy most of the Oh symmetry sites and partially the D_3d sites.

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The relationship between carbon in the silicon nitride grain boundaries and mechanical properties has been studied. Silicon nitride powder was coated with carbon and hot pressed at 1873K and 20MPa. Vickers hardness, fracture toughness and flexural strength were determined. Behavior of carbon in the grain boundary interface was investigated by X-ray diffraction and Auger electron spectroscopy. The results can be summarized as follows:
(1) The amount of β-silicon nitride phase increases with increasing carbon content.
(2) The mechanical properties depends on the carbon content. The toughness improves above certain amount of carbon.
(3) During hot pressing of Silicon nitride powder with carbon film, the following chemical reaction is proposed at the grain boundaries. SiO₂+3C→SiC+2CO Ellingham diagram shows that the reaction is favorable over 1630K. Carbon mono-oxide becomes stable at the oxygen partial pressures above 10×10^-10Pa. The grain boundary glass phase is reinforced by silicon carbide precipitates.

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The effects of pretreament on the sintering was studied with spherical silica powders prepared by the hydrolysis of Si(OC₂H₅)₄.
(1) Calcination or autoclaving prevented the fracture of compacts in firing.
(2) The thermal shrinkage of the compacts of calcined powder occurred slowly near the calcination temperature, while the compacts of commercial silica gel shrank rapidly at lower temperature. The shrinking behavior of the autoclaved-powders was intermediate between calcined-powders and commercial silica gel.
(3) The bulk density and Vickers hardness of sintered compacts increased as the firing temperature was raised. Relative density of 99.8% was obtained at 1200° and 1150°C for calcined-powder and autoclaved-powder respectively.
(4) Spherical silica particles remained when fired at 1000°C, but the compacts became vitreous at 1150°-1200°C.
(5) The transparent sintered compacts were obtained when about 0.3μm diameter particles were sintered at 1200°C for 5h.
The sintering property of spherical silica powders was improved by precalcinaton, but the same effects of calcination were obtained from 400° to 800°C. Further, the sintering of spherical silica powders was improved when autoclaved in the presence of water.

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Clear PZT sols have been prepared by controlled hydrolysis of Pb, Ti and Zr mixed alkoxide solutions in methoxy-ethanol. The water/methoxy-ethanol ratio which gives clear sol decreases with increasing alkoxide concentration at a constant alkoxide composition, and decrease as Zr alkoxide in Pb and Zr mixed alkoxide is substituted by Ti alkoxide. Sols dried at 70°C were analyzed by XRD, TEM and EDX. The particle size of sols was 10-40nm by TEM, which depends on the composition. The XRD result showed that dried powders are amorphous, which crystallize at above 600°C. EDX analysis of particles showed that PbTiO₃ and PbZrO₃ powders are chemically homogeneous at a particle level. On the other hand, PZT powder was less homogeneous.

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Sinterability of bimodal Al₂O₃ powders with average sizes of 3.9μm (c particle) and 0.6μm (f particle) and bending strength of their sintered bodies were investigated. Sintering between f and c particles progressed gradually at 1500°C with time. Densification behavior of mixed powders between 1400° and 1600°C could be classified into three mixing ratio groups. The observed differences in densification were considered to be caused by the different arrangement of f and c particles in the compacts from the SEM observation. Bending strengths of the samples sintered at 1600°C for 2h showed almost constant values around 30kgf/mm² for mixing ratios c:f between 1:9 and 5:5, but dropped rapidly at the ratios more than 5:5.

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The effect of heat-treatment for nucleation on the crystallization of MgO-Al₂O₃-SiO₂ glass containing TiO₂ was investigated. The glass having a composition 16.7MgO⋅22.3Al₂O₃⋅61SiO₂ (wt%) and containing 10wt% of TiO₂ as nucleating agent shows phase separation, whereas the glass of a similar basic composition without nucleating agent does not show phase separation. The rate of nucleation of Mg-Al-titanates [x(MgO⋅2TiO₂)y(Al₂O₃⋅TiO₂)] crystals was the largest when heat-treated at 760°C. Spherical particles with a mean diameter of 100-150Å are confirmed to precipitate before the crystallization of main crystals β-quartz and petalite (MgO⋅Al₂O₃⋅SiO₂) takes place. The nucleation from the quenched glass takes place even at a temperature (730°C) lower than the glass transition temperature (T_g=750°C). The temperatures at which the precipitation of β-quartz and petalite take place become higher, and the size of Mg-Al-titanate crystal becomes smaller as the number of the small particles formed in the first heat-treatment increases.

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Borosilicate glasses containing MgO and Al₂O₃ ((1-x) [0.5Na₂O⋅B₂O₃⋅3SiO₂]⋅xM; x=0.05, M=MgO, Al₂O₃) were used in the present study as a simulated grain boundary phase of Si₃N₄-MgO and Si₃N₄-Y₂O₃/Al₂O₃ ceramics. Leach tests by the bulk glass specimens were carried out under hydrothermal conditions using an autoclave, and the leached layer was observed by EPMA and SEM. A large leaching weight loss and thick leached layer were observed in MgO-containing glasses. Another leach test with the same glass powder based on JIS R 3502 was carried out, and the component leach rate, L (g/cm²·h) was calculated from the results of leached solution analysis by ICP. The leach rate of MgO, L^MgO=1.23×10^-5g/cm²·h, was larger than that of Al₂O₃, L_Al2O3=0.23×10^-5g/cm²·h. Thus, the weight loss and film thickness of leached layer by bulk leach test has been correlated to the component leach rate, that is, leach resistance to water of Al₂O₃-containing glass was superior to that of MgO-containing glass. Results of bulk glass leach tests corresponded well to our previous results on hydrothermal corrosion of Si₃N₄-MgO and Si₃N₄-Y₂O₃/Al₂O₃ ceramics prepared under the same conditions except for the sintering aid; the former showed leach resistance lower than the latter. Thus, the characteristics of grain boundary of ceramics dominate the hydrothermal corrosion and the component leach rates of sintering aids such as MgO and Al₂O₃ play a major role in leaching.

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Thermal changes in hot-pressed TiSe_1.6 and TiSe_1.5 are investigated in an argon atmosphere up to 1500°C. X-ray powder diffraction analysis of synthesized TiSe_1.6 showed mixed diffraction patterns of hexagonal type TiSe_1.6 and monoclinic type Ti₅Se₈. Ti₅Se₈ disappeared after hot-pressing at 500°-600°C. Above this temperature range, only hexagonal phase was found. TiSe_1.6 releases some Se atoms and Se/Ti ratio decreases by hot-pressing above 1300°C. Hot-pressing at 1500°C gives an Se/Ti ratio approximately equal to 1.5. As reported in our previous paper, synthesized TiSe_1.5 is hexagonal. The X-ray diffraction pattern of TiSe_1.5 is similar to that of hexagonal type TiSe_1.6 except some small diffraction peaks which might be of superstructures. The lattice parameters of TiSe_1.5 are slightly different from those of hexagonal TiSe_1.6. TiSe_1.5 is stable up to 1500°C. Progressive densification and grain growth in TiSe_1.6 start at relatively low temperatures. In TiSe_1.5, densification and grain growth proceed at rather higher temperature range. These differences in sintering behavior between TiSe_1.6 and TiS_1.5 is ascribed to the difference in the stability of crystal phase and to the Ti concentration in partially Ti occupied layers of these phases. Sintered bodies with the highest compressive-strength and high density are obtained by hot-pressing TiSe_1.5 at 1400°C.

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A new method for preparing fine silica particles was developed by the reaction of silicon powder and water vapor at 990°-1200°C in the presence of hydrogen sulfide. If hydrogen sulfide was absent in the reaction system, oxidation of silicon occurred only on the silicon powder surfaces and no silica particles were produced. In contrast, a large amount of fine silica particles was formed at 990°-1200°C when hydrogen sulfide was mixed. Conversion of silicon to silica was maximun (63%) at 1060°C and the optimum reaction time was 2h in view of the conversion and the uniform particle size. The particle size. The particle size distribution was relatively narrow with the average particle diameter of 0.09-0.1μm for the products collected in a flask which was placed at the downstream of the reactor. Thermodynamic consideration suggested that silica particles form via volatile SiS or SiS₂ intermediates and that the morphology of fine particles is associated with homogeneous nucleation in the vapor phase.

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The friction and wear properties of alumina hot-pressed at various temperatures were measured with a pin-on-disk tester, and their abrasion wear was measured against fixed diamond grains. The bulk density of hot-pressed alumina reached almost theoretical at 1400°C, above which temperature the grain growth was extensive. The fracture toughness increased with increasing hot-pressing temperature, but the Vickers hardness showed a maximum at 1400°-1500°C, and then slightly decreased. The coefficient of friction and specific wear rate measured on the hot-pressed silicon carbide disk were fairly high for 1200°C-alumina, minimum at 1300°-1500°C, and then increased gradually with increasing hot pressing temperature. The specific wear rate of abrasion wear against fixed diamond grains was about a hundred times greater than that against silicon carbide, but the dependence on the hot-pressing temperature was similar. The negative correlation was confirmed between the hardness and the specific wear rate of hot-pressed alumina, which is a well-known relation for abrasion wear.

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Crystalline tricalcium phosphate (TCP) was directly prepared by the spray-pyrolysis technique from ethanol-nitric acid solution of calcium nitrate and phosphoric acid. The concentration of the solution ([Ca²⁺]+[PO₄^3-]) was 0.05-1.0mol/l. The spray-pyrolysis temperature ranged from 1100° to 1400°C. TCP powders of the α form were obtained under all experimental conditions studied. When the temperature of the powders being produced in the reaction zone was lower than the β→α phase transformation temperature, metastable α-TCP was obtained, though the β phase is thermodynamically stable. On the other hand, stable α-TCP was obtained when the temperature of the powders was higher than the transformation temperature. With increasing spray-pyrolysis temperature and decreasing solution concentration, the temperature at which α→β phase transformation started in as-prepared α-TCP increased and the fraction of the phase transformation decreased. For the stable α-TCP obtained from the solution of 0.05mol/l at spray-pyrolysis temperatures above 1250°C, no transformation to β phase was observed by heat-treatment in the stable temperature range of β-TCP for 1h.

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The formation and ionic conductivity of β-, β′′- and β′′′-alumina type ferrites in the systems Rb₂O-Fe₂O₃ and Cs₂O-Fe₂O₃ were studied. Rb⁺-β-ferrite was formed by heating powder mixtures of Rb₂CO₃⋅(6-6.5) α-Fe₂O₃ above 1200°C, while Rb⁺-β′′-ferrite was synthesized together with the β phase below 1150°C. Rb⁺-β′′′-ferrite was obtained at 1400°C from Rb₂CO₃⋅10 α-Fe₂O₃. When the mixtures of Cs₂CO₃⋅(6-6.5) α-Fe₂O₃ and Cs₂CO₃⋅10 α-Fe₂O₃ were heated at 1000° and 1400°C, respectively, Cs⁺-β-and Cs⁺-β′′′-ferrites were formed. However, the β′′ phase was not obtained from Cs₂CO₃ and α-Fe₂O₃. Single phase Rb⁺-β′′-and Cs⁺-β′′-ferrites were obtained by heating the mixtures of Rb₂CO₃⋅3Fe₃O₄ and Cs₂CO₃⋅₃Fe₃O₄ at 950°-1000°C in air, respectively. The β′′-ferrites transformed to β phase at 1050°-1150°C. The lattice constants c_o of M⁺-β-, β′′- and β′′′-ferrites (M⁺: K⁺, Rb⁺ and Cs⁺) increased with increasing size of M⁺ ion. The β- and β′′-ferrites were mixed conductors of ion and electron. Rb⁺- and Cs⁺-β′′-ferrites have higher ionic conductivities than the respective β phases. The ionic conductivities are higher than those of other Rb⁺ and Cs⁺ conductors.

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The reactions of ZrC or ZrN powder and H₂O have been studied at 190°-400°C under 100MPa. The reaction of ZrC with H₂O above 240°C for 3h yielded monoclinic ZrO₂ and CH₄, while the reaction of ZrN above 190°C for 3h yielded monoclinic ZrO₂, NH₃ and H₂. The oxidation rate calculated from the wegiht gain or the integrated peak intensity of the X-ray diffraction was compared with various model functions. A nucleation-controlled model was the best fitted one, while a core-shrinking model fitted as well. This suggested that the reaction was controlled by phase boundary reactions. TEM observation showed that the ultrafine particles about 10nm nucleated on the surface of ZrN or ZrC grains of about 1-3μm. These ZrO₂ fine particles did not from a protective layer on ZrN or ZrC particles, but formed clusters of particles because of large volume expansions about 40% during the oxidation. An Arrhenius plot of the rate constants gave apparent activation energies of 99kJ/mol and 78kJ/mol for the oxidation of ZrC and ZrN by H₂O, respectively, on the basis of the nucleation-controllod model. The difference of about 20kJ/mol in the activation energies for ZrC and ZrN migth be explained by the difference in the formation energy between the C-H bonding and N-H bonding.

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Chemically and electrically stable passivation glass was prepared in the PbO-ZnO-SiO₂-Al₂O₃-B₂O₃ system stabilized by alkaline earth oxides. Physical properties of the prepared glass were close to these of lead borosilicate passivation glass. There was a certain Al₂O₃ concentration range in which the reverse current in the diode, passivated by the glass, remarkably reduced. Increasing PbO/ZnO ratio reduced the reverse current, and enlarged the firing temperature ranges where the current was minimized, while the surface charge stability, obtained from C-V characteristic measurement on MGS capacitor before and after BT treatment, decreased by increasing the ratio. Higher firing temperature over the suitable range increased the reverse current, maybe caused by generation recombination center formation as the result of glass attack to the silicon surface. The increase in Al₂O₃ increased a negative surface charge in the glass, while BaO in the glass formed a positive surface charge. This surface charge behavior was thought to correspond to the change in the acid-base character of the glass.

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Fine AlN powder was synthesized by vapor phase reaction of AlCl₃ and NH₃ at 720°-1190°C. Most of the powder deposited separately in two regions in the reactor. The powder deposited in the range between the end of AlCl₃-feeding tube and the point 17cm apart there from consisted of one phase AlN. The particle size and its distribution became fine and uniform at high reaction temperature or at high total flow rate of NH₃ and N₂. Fine powder with the median diameter of 0.16μm was synthesized at 1190°C and particles were within a narrow range from 0.1 to 3.0μm. In the range between 20 and 33cm apart from the end of the AlCl₃-feeding tube, amorphous AlN deposited, which crystallized on heating at 1400°C. Byproduct, NH₄Cl which coexisted with amorphous AlN, was easily eliminated by heating at 500°C. The formation rate of crystalline AlN was 2.2g·h^-1 and the total yield of crystalline and amorphous AlN was 79%.

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The effect of boron dispersion on the sintering of SiC was studied by comparing the addition of soluble compounds (B₂O₃, B₁₀H₁₂C₂ and NaBF₄) in fluid form with that of amorphous boron powder. A large part of the boron in the fluid additions disappeared below 1550°C. The residual amount of boron was nearly constant up to the sintering temperature (2050°C). The density values for the residual boron contents were identical with that for powder boron addition. NaBF₄ gave the low mechanical strength, because of the remaining sodium till high temperature. However, in B₂O₃ or B₁₀H₁₂C₂, the mechanical strength was higher than 55kg/mm² (room temperature strength for boron powder addition). B₁₀H₁₂C₂ addition resulted in high strength (max. 82kg/mm², mean 68kg/mm², min 44kg/mm²: density 3.16g/cm³), even for a small amount of boron content (0.11wt%). The weak strength (40-50kg/mm²) was attributed to the large pore defects (0.05-0.2mm) which were considered to be formed in the initial stage of sintering by the rearrangement of SiC particles. In fluid addition, it may be assumed that the homogeneity of boron dispersion was improved, resulting in the suppressed particle rearrangement.

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Dihydrate (CaHPO₄⋅2H₂O; DCPD) and anhydride (CaHPO₄; DCPA) of dicalcium phosphate are studied on their hydraulicity (hydration and hardening) induced by the addition of CaCO₃ and properties of the resulting porous apatite. The hardening was caused by the entanglement of microcrystals of reaction products, i.e., carbonate-containing apatite and/or octacalcium phosphate. DCPD is hydrated and hardens more easily than DCPA. The addition of F^- accelerates the hydration reaction remarkably, however no hardening occurs. The resulting hardened apatite bodies have 70-80% porosity and a diametral tensile strength of 0.3-1.5MPa. Sintered apatite bodies prepared by heating the hardened bodies are densified to 45-60% and strengthened to 0.7-4.8MPa. An apatite packed column for HPLC (high-performance liquid chromatography) prepared by using the hydraulicity has a high flow rate (1.39ml/min·cm² at pressures of 1-2kgf/cm²), but it shows a low resolution producing chromatographic peaks with a large width; this is probably due to a heterogeneous packing structure.

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SiO₂-Al₂O₃ fibers and SiO₂-ZrO₂ fibers were prepared by a new method via polyaluminosiloxanes (PAS) and polyzirconosiloxanes (PZS) prepared from silicic acid and metal chelates. Silicic acid was brought to reaction with 2, 4-pentanedionatoaluminum diisopropoxide and bis (2, 4-pentanedionato) (ethyl 3-oxobutanato) zirconium isopropoxode to give PAS and PZS with spinnability and stability againt condensations. Precursor fibers were obtained by dry spinning of PAS and PZS. SiO₂-Al₂O₃ fibers and SiO₂-ZrO₂ fibers were formed by pyrolysis of the precursor fibers at 1000°C.

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