The comparative study of the internal friction of ZrO₂ polycrystals containing 2mol% Y₂O₃, 8mol% Y₂O₃ and 12mol% CeO₂ (2Y-TZP, 8Y-FSZ and 12Ce-TZP) was performed at high frequencies around 100kHz. The data of 2Y-TZP around 100kHz revealed an anelastic relaxation peak with the activation enthalpy H=82.5±1.4kJ/mol, the relaxation strength Δ=1.34±0.08×10^-2, and τ₀=5.4±1.1×10^-14s. The relaxation is considered to be the same as the dielectric one with H=79.0±3.8kJ/mol and τ₀=5.9±3.1×10^-13s. The internal friction for 2Y-TZP and 8Y-FSZ indicated the existence of the same relaxation process and consequently the possibility of similar local cation-anion (or vacancy) interaction in Y₂O₃ doped ZrO₂ regardless of the symmetry (tetragonal and cubic). The internal friction was small for the 12Ce-TZP, but was large after the reduction and increased at elevated temperature, accompanied by the trace peak. The results indicate directly significant contribution of the oxygen vacancy to the generation of the internal friction of ZrO₂.

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The microstructure of the cubic perovskite Ba{(Mg, Co)_1/3Nb_2/3}O₃-based dielectric has been investigated. The secondary phase was determined to be Ba₅Nb₄O₁₅; this phase was detrimental to the microwave properties of Ba{(Mg, Co)_1/3Nb_2/3}O₃. Eliminating the secondary phase, the precise control of A-site/B-site ratio of the perovskite and long time annealing improved the microwave characteristics.

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Mullite fibers were prepared by a new sol-gel method from Al(OPrⁱ)₃-Al(NO₃)₃-TEOS-H₂O system. In this system, the spinnable range varied depending on solution preparation procedures. When TEOS and Al(OPrⁱ)₃ were added simultaneously to an Al(NO₃)₃ aqueous solution, precursor fibers could be obtained from solutions in a compositional range of H₂Omol/(Al+Si)mol=20/1-200/1 and Al(OPrⁱ)₃mol/Al(NO₃)₃mol≤6/1. On the other hand, the spinnable range was narrow, when TEOS was added to the solution of Al(OPrⁱ)₃ in an aqueous Al(NO₃)₃. When Al(OPrⁱ)₃ was added after TEOS was dissolved in an Al(NO₃)₃ aqueous solution, no spinnable solutions were obtained. Aluminoxane polymer, oligomer of siloxane or that containing Si-O-Al bond, Al-O dimer, Si(OH)₃-O-Si(OH)₃ and [Al(H₂O)₆]³⁺ were observed by ²⁷Al-and ²⁹Si-NMR spectroscopy of the spinnable solutions. To the contrary, the unspinnable solutions contained Al₁₃⁷⁺ polycation and three-dimensional polymer having Al-O bonds. The existence of aluminoxane-polymer, Al and Si atomic scale component was deemed necessary for the appearance of spinnability. The DTA curves of all precursor fibers showed a unique and sharp exothermic peak at 1000°C, while those of gels obtained from unspinnable solutions showed only small peaks. The X-ray diffraction analysis revealed that the precursor fiber crystallizes directly from amorphous to mullite at temperature as low as 600°C. It was deduced that structure which has a similar composition to mullite exists in precursor fibers.

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To study the effect of process-related oxidation on microstructure and mechanical properties of β′-o′ sialon, green compacts of a Silicon nitride powder and boehmite sol were prepared through mixing, calcination and dewaxing processes, followed by sintering and HIPing. With progressive oxidation of the Silicon nitride powder in processing, the amount of o′-phase increased and the grain size of o′-phase was changed. With increasing amount of o′-phase in the sintered body, the lattice constants of β′-phase and the hardness increased. The high temperature flexural strength of β′-o′ sialon ceramics was governed by mixing conditions rather than by the o′-phase ratio.

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Internal friction and shear modulus in MgAl₂O₄ spinel doped with gallium oxide or alumina were measured from room temperature to 1473K. An internal friction peak was observed at 1123K and the peak area was proportional to the concentration of gallium oxide or alumina in the spinel. The activation energy of the stress induced diffusion of cation vacancies increases from 200kJ/mol to 450kJ/mol with increasing gallium oxide concentration. Effects of ionic radius and gallium and aluminium ion concentration on internal friction peaks have been discussed.

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Morphology of diamond which was deposited on a molybdenum substrate by a radio-frequency thermal plasma CVD method in methane, hydrogen and argon atomosphere was investigated using a scanning electron microscope (SEM). It was found that with increasing deposition temperature the habit changed from octahedral to cubic, via intermediate cubo-octahedral forms. Columnar-like crystals of half-octahedron and of multiple twin were grown at low and high deposition temperatures, respectively at a CH₄/H₂ ratio of 0.04. Twins such as a spinel twin and a 5-fold twins were observed. Growth layers such as triangles on {111} and {100} faces, well-defined composite spirals with 4-fold rotation axis and closed loops were observed.

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A precursor gel powder with the composition of CaTi₄(PO₄)₆(CTP) was prepared by sol-gel process. On heating, this powder was amorphous up to 700°C and changed into a single phase of CTP at about 800°C. The relative density showed that the sinterablity of the amorphous powder was better than that of the crystallized powder. Some precursor gels with excess amounts of P₂O₅ (1wt%-9wt%) were also prepared by the same process. The presence of a small amount of P₂O₅ was effective for the sintering of compacts. Sintered material with the relative density of 94% and the bending strength of 72MPa was fabricated in the presence of 4wt% of P₂O₅.

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The hot isostatic pressing (HIP) treatment of plasma-sprayed ceramic coatings was studied in order to improve the coating characteristics, such as microstructure and bonding strength. Stabilized ZrO₂, Al₂O₃ and Y₂O₃ were coated by plasma-spraying on two kinds of metal substrates (Nb and Type 304 stainless steel). HIP treatment was performed at from 1100° to 1300°C under fixed pressure (98.1MPa) for 1h. The porosity and bonding strength of ceramic coatings were measured. The residual stress analysis was carried out and compared with the cracking of ceramic coatings. The experimental results indicated that, for Nb substrate specimens, the porosity remarkably decreased and the bonding strength increased with increasing HIP temperature. But the cracks were observed at high HIP temperature. Such cracking behavior of HIP treated ceramic coatings was explained by the residual stress calculated by FEM analysis. On the other hand, no crack was observed in coatings on Type 304 substrate, because of the compressive residual stress in coatings induced by HIP treatment. But the bonding strength decreased with increasing HIP temperature.

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Pollucite (Cs₂O⋅Al₂O₃⋅4SiO₂) powders were prepared from a combination of Al₂O₃ sol, SiO₂ sol and CsNO₃ starting materials by sol-gel processing, and a stable region of single phase pollucite was investigated. The pollucite powders of single phase were synthesized when Cs₂O:SiO₂ and Al₂O₃:SiO₂ molar ratios were 0.91-1.02:4 and 0.96-2.38:4, respectively, by standerdizing SiO₂ molar ratio. The lattice parameters at room temperature were affected mainly by the Cs₂O/SiO₂ ratio. It was confirmed by a high temperature X-ray diffractometry that the thermal expansion for the pollucite powders is greatly affected by the change of compositions: The thermal expansion coefficient decreased with decreasing Cs₂O/SiO₂ ratio from room temperature to 200°C, and increased with increasing Al₂O₃/SiO₂ ratio above 600°C. An increasing tendency of the latter has turned out to be caused by a slight amount of α-Al₂O₃ formed in the course of calcination. However, such behavior was not observed at the Cs₂O/Al₂O₃ ratio of less than 1.

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The sintering property of powder mixture compacts of TiC and Si in a nitrogen atmosphere at 1350°C is discussed. TiC formed TiN and free carbon on reaction with nitrogen, and a small portion of this free carbon was converted into β-SiC on reaction with Si. A large portion of the Si formed Si₃N₄ on reacton with nitrogen. Approximately half of the TiC remained unreacted when heated for 10h at the final sintering temperature of 1350°C. Thus, composite ceramics having a composition of TiC⋅TiN⋅Si₃N₄⋅C⋅β-SiC were obtained. The porosity of this composite was much smaller than that of ordinary Si₃N₄ bonded ceramics because of the volume increase caused by the conversion of Si to Si₃N₄ and additionally of TiC to TiN, C and β-SiC. Carbon, in particular, seemed to have a remarkable effect on reducing the number of pores in the sintered body. The sample dimensions increased in the sintering stage partly because TiC particles formed porous clusters of TiN by reacting with nitrogen.

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High T_c superconductors have been prepared using a plasma-arc melting and rapid quenching (PMQ) method. Homogeneous and dense superconductors were obtained by this method through the crystallization of a superconducting phase from an amorphous-like state. Particularly in YbBa₂Cu₃O_x, a relative density of 7.14g/cm³ (98% of the theoretical density 7.27g/cm³) and a large activation energy, 1.5eV, which was related to the flux pinning, were realized by this method. Furthermore, the formation of insulating Yb₂BaCuO₅ films on the PMQ processed YbBa₂Cu₃O_x substrate was attempted by rf magnetron sputtering. No deterioration of the YbBa₂Cu₃O_x substrate was observed. It was found that the new method produces a dense and homogeneous high T_c superconductor for device applications.

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Mixed powders containing silica and carbon were chemically synthesized by spraying a mixture of silicon tetrachloride and heavy oil into air-propane flame. The particle size of the mixed powders was less than 1 micron and each particle contained both silica and carbon. Fine SiC powders were obtained by heating compressed tablets of the mixed powders. The powders sintered to high density by pressureless sintering method. SiC whiskers were also obtained by heating the mixed powders without compression. The whiskers had high crystallinity.

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The chlorination of a mixture of rice hull ashes and carbon containing alkaline and alkaline earth salts was investigated by FT-IR-PAS. It was thought that the relative ratio of totally symmetric SiO₄ stretching vibration (ν₁) to antisymmetric SiO₄ degenerate stretching vibration (ν₃) in infrared frequencies for SiO₂ whose constituent oxygen atoms occupy the corners of a tetrahedron shows structural changes of SiO₂ network. The results of ν₁/ν₃ of SiO₂ before and after chlorination showed that the values of ν₁/ν₃ increased and the chlorination was accelerated because K⁺ increased. The ν₁/ν₃ of SiO₂ by addition of Na⁺, Mg²⁺ and Ca²⁺ was smaller than that of K⁺ and these additives did not accelerate the chlorination. KCl, NaCl, MgCl₂ and CaCl₂ which formed during the chlorination melted at 900°C.

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High grade Amakusa pottery clays mixed with 10, 20 and 30wt% zirconia were fired at 1250°, 1300° and 1350°C. Zircon, quartz, mullite, monoclinic- and tetragonal-zirconia were identified in the porcelain bodies with 20 and 30wt% zirconia fired at 1350°C. The content of the tetragonal phase in the fired bodies increased with increasing zirconia and with increasing firing temperature. The bending strength and fracture toughness of porcelain bodies containing zirconia increased with increasing firing temperature and with increasing amount of tetragonal zirconia, and those with 30wt% zirconia fired at 1350°C were 1.5 times higher than those without zirconia.

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The mechanical properties of high thermal conductive SiC ceramics were studied. The bending strength was 430MPa at room temperature and raised to 720MPa at 1400°C, but it decreased to 630MPa at 1500°C. The fracture toughness was 3.8MPa·m^1/2 at room temperature and increased with increasing temperature, while Young's modulus was 460GPa at room temperature and decreased above 1300°C

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Lattice parameters of La-doped barium titanate were measured to elucidate the mechanism of insulation induced by excess La₂O₃ addition from the viewpoint of the second-phase precipitation and the change in the substitutional site for La. Neither second-phase precipitation nor anomalous change in lattice parameter was observed even above the critical concentration (0.4mol%) at which BaTiO₃ is converted to an insulator. The phase transition from tetragonal to cubic system occurs at 5mol% La₂O₃ doping, but this is higher than the critical concentration. The concentration at which the second-phase precipitation occurs was higher than 15mol%. The lattice parameter changed according to the Vegard's law, and the substitution of La for B-site was not clearly indicated. It was suggested that the insulation induced by excess La₂O₃ addition was not caused by the change in bulk crystal properties.

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This paper is concerned with the relationships between the morphology of carbon films and the intensity of emission spectra in ECR plasma CVD of the system CH₄-H₂. A sample holder was connected in series to DC bias and it was negative to the apparatus. The application of negative bias caused an abrupt increase in emission intensity at about -100V bias. At the same time, smooth and flat carbon films were formed. The abrupt increase in emission spectra intensity was caused by the cooperative effects between DC and ECR powers. The formation of flat and smooth surface was attributed to the abrupt increase in plasma density which gives high speed ions, molecules and electrons. They might prevent the formation of secondary particles through aggregation of primary particles and/or enhance the peening effect on the substrate.

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Porous mullite ceramics with porosity of 26-57% were prepared from needle-like mullite crystals of 3-5μm long and 0.5-1.0μm in diameter synthesized by firing New Zealand kaolin at 1650°C. Pore characteristic (porosity, pore diameter), three points bending strength and thermal conductivity were examined on the porous mullite ceramics sintered at 1550°-1700°C in air. With increasing sintering temperature, the pore volume decreased, resulting in an increase in the bending strength. However, the pore size distribution was almost independent of the sintering temperature. The average pore diameters for the porous mullite ceramics sintered at 1550°-1700°C were in the range of 0.46-0.58μm. Thermal conductivity at room temperature decreased linearly with increasing porosity.

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