Thermal decompositions of CB₃H₄(C: CaO, B: B₂O₃, H: H₂O), CB₃H₅, C₂B₇H₈ and C₂B₅H₅ were studied by means of TGA, DTA, X-ray diffraction analysis, chemical analysis and petrographic microscopy.
(1) The synthesized hydrated calcium borates showed the same X-ray diffraction pattern as those of CB₃H₄, CB₃H₅, C₂B₇H₈ and C₂B₅H₅. Their chemical compositions were nonstoichiometric owing to the deficiency of B₂O₃ component.
(2) When the molar ratio of B₂O₃/CaO was not less than 2.7, the formation of a new compound CB₃ was possible. Trace amounts of ethanol adsorbed on the hydrated calcium borate disturbed the formation of CB₃.
(3) Crystalline calcium borate CB₃ formed at about 650°C, and decomposed irreversibly to CB₂ and B₂O₃-rich liquid at temperatures above 870°C.
(4) The calcium borate CB₃ changed slowly to CB₃H₄ in moisture atmosphere, while in the case of the CB₂-B₂O₃ mixture formed by the above-mentioned decomposition, CB₃H₄ appeared very slowly by a reaction among CB₂, H₂O and H₃BO₃, following to the formation of H₃BO₃ from B₂O₃ and water vapor.
(5) The calcium borate CB₃ was optically biaxial with refraction indices α=1.530, β=1.535, γ=1.605, and its measured density D_m was 2.33g/cm³.

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Reactivities between fibrous alkali metal titanates and various oxides or carbonates at high temperature were investigated.
The fibers of K₂Ti₆O₁₃ and Na₂Ti₃O₇ prepared under hydrothermal conditions were mixed with oxides or carbonates and were heated in the range from 500° to 1200°C for 15h. The reaction products were examined mainly by X-ray powder technique.
The following results were obtained:
(1) K₂Ti₆O₁₃ and Na₂Ti₃O₇ did not react with Al₂O₃, CuO, NiO and Fe₂O₃.
(2) CoTiO₃, Co₂TiO₄, MgTiO₃, PbTiO₃, CaTiO₃, SrTiO₃ and BaTiO₃ were produced in the reaction of the fibers with CoO, MgO, PbO, CaCO₃, SrCO₃ and BaCO₃.
(3) In the reaction between the fibers and SiO₂, rutile was deposited.
(4) The temperature at which Na₂Ti₃O₇ began to react was somewhat lower than that in the case of K₂Ti₆O₁₃.
(5) With the progress of the reaction mentioned above, alkali metal titanate fibers disappeared and changed into aggregates of Ti-compound particles in the size of several microns meter or below that.

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The reaction process between siliceous sand and Al in N₂ atmosphere during heating up to 1500°C was examined by thermobalance and X-ray diffraction analysis with respect to N₂ flow rate, forming pressure and Al content in the starting mixture.
Following results were obtained:
(1) Nitriding of Al took place above about 500°C and its reaction rate increasd at the melting point of Al (660°C). The exothermic reaction AlN formation at 660°C induced the reaction between siliceous sand and Al to form Si and α-Al₂O₃ so rapidly.
(2) AlN⋅Al₂O₃ phase (spinel type) was observed in the heat treated compacts at the temperature range from about 660° to 1200°C. This AlN⋅Al₂O₃ formation revealed that the temperature of local parts in compacts reached at about near 2000°C by two exothermic reaction of AlN formation and alumino-thermite reaction.
(3) Si formed through alumino-thermite reaction reacted with N₂ to form β′-Si₃N₄(AlN⋅Al₂O₃) above 1150°C. The temperature of Si nitriding observed varied with forming pressure and Al content in starting mixture. At low N₂ flow rate of 0-30cc/min and at high forming pressure of 2000, 3000kg/cm², Si remained unreacted with N₂ in the compacts even if they were heated up to 1500°C, kept at the temperature for 1h.
(4) The reaction products heat-treated up to 1500°C varied with Al content in starting mixture. In the case of 40wt% Al, the compact consisted of β′-Si₃N₄, α-Al₂O₃, O′, mullite and X phases. With increasing Al content in starting mixture from 40wt% Al to 50 and 60wt% Al, silica rich phase such as O′, mullite and X phases disappeared and β′-Si₃N₄, α-Al₂O₃, 15R-AlN and 15R-AlN, β′-Si₃N₄, α-Al₂O₃ were observed, respectively.

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The crazing resistance of porcelain ware was investigated by measuring the stress in the glaze with respect to the firing condition and the composition of the body. The base body was composed of 40% pottery stone (Toseki), 30% kaolin, 15% ball clay (Gairome), 10% feldspar and 5% quartz, and was glost-fired at SK12RF for 42h in a mass-production tunnel kiln. Investigations were also carried out to find a proper body composition which was completely secure from crazing due to overfiring or refiring.
With an increase in the amount of residual quartz in the body, the thermal expansion coefficient of the body increased, and the stress in the glaze changed from tensile to compressive. The temperature difference ΔT(°C) of the quenching test was less than 130°C when the stress in the glaze was tensile and showed an increase of up to 200°C with an increase in the compressive stress in the glaze.
With an increase in the thickness of the glaze, the crazing resistance decreased, and the amount of residual quartz in the body should be kept larger to keep the crazing resistance the same.
The stress in the glaze of the porcelain of the base composition decreased to about +100kg/cm² by being glost-fired twice, and the porcelain became increasingly subject to crazing. This was caused by the dissolution of quartz in the glass phase of the body.
When 5 to 8% of quartz was added to the base body, the stress in the glaze showed a little improvement in the normal glost-firing condition, but it showed a tensile stress from +100kg/cm² to +150kg/cm² when glost-fired twice. These compositions were proved to be ineffective in preventing the crazing caused by overfiring or refiring.
When 3 to 6% of feldspar of the base body was substituted by the same amount of quartz, the stress in the glaze showed a little improvement when glost-fired in the normal condition, and it showed nearly the same compressive stress even when glost-fired twice.
It was concluded that the partial substitution of feldspar in the base body by the same amount of quartz was very effective in preventing the crazing caused by overfiring or refiring, and thus could improve the crazing resistance in the case of mass-production and sinkin decoration technique. However such a substitution tends to decrease the translucency, the optimum composition should be considered taking the translucency and the crazing resistance into account.

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Semi-hot generating duct wall of magnetohydrodynamic generator, being developed as one of national projects in Japan, will be constructed with settling many elements made of dense refractory ceramics by their holders (usually metals). In addition, these holders are also used to cool these elements in order to keep temperatures of operating conditions of materials in running. The usualest settling technique is soldering between a wall element and its holder. It has been reported in recent papers that thermal resistance has been neglected in this soldered part. However, there are many unsolderable materials among them. If unsolderable materials must be used for these wall elements, non-soldered holding techniques will have to be used, and there will cause great thermal resistances between these wall elements and their holders. For this reason, the heat transfer phenomenon between this element and its holder must be investigated for designing the duct wall. The author has studied the heat transfer phenomenon by model tests. The results of experiments are as follows:
Equivalent distances between test pieces and holders, calculated from their heat transfer characteristics, are 76μm for the couple of alumina test piece and stainless steel holder, and 85μm for the couple of magnesia and stainless steel. On the other hand, distances calculated from their surface roughnesses and undulations, measured by touching probe type surface roughness meter, are 65μm for the former and 76μm for the latter. Results are summarized as follows:
(1) Heat transfer between the MHD generator duct wall element and its holder is mainly caused by the thermal conduction through gas layer between them.
(2) The equivalent thickness of this gas layer is comparable to the distance determined from the surface roughness and undulation of each surface of both elements.

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Fine magnesia powder (<0.1μm) was compacted by hot pressing of 250-700kg/cm² at 700°-900°C, or by hydrostatic press of 500-3000kg/cm² at room temperature. The resultant compacts were pre-sintered at 1000°C for 1h to specimens with different relative densities (39.5-64.3%). Then the specimens were sintered at 1400°C for 5min-8h, and the microstructures of sintered bodies were measured on their polished and etched surfaces by stereological techniques, and the relations between measured microstructural parameters such as the porosity on grain boundaries (P_gb) and the grain diameter (D) were discussed.
The nonuniform pore structural change (P_gb∝1/D^1/3) obtained here could be explained from the wide distribution of dihedral angles for solid-solid-vapor equilibrium observed in the sintered bodies and from resultant nonuniform texture of grain agglomerates. Such relations between P_gb and D were not concerned with the porosity enclosed in the grains and initial packing conditions.
However the initial packing conditions affected the porosity enclosed in the grains of sintered bodies, When hot press compaction was used, the pores enclosed in the grains were not observed in the fired specimen that had been compacted into high density (_??_55%) before firing. But, in the case of room temperature compaction, the higher the relative green density became, the earlier the pores pinched off into separate parts and were trapped in the grains. From the results, it was inferred that if the reasonable compaction temperature and pressure were selected, the sintered body having arbitrary porosity in the grains and on grain boundaries for a constant grain diameter might be obtained.

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Hot-pressed ceramic compacts are commonly annealed to remove carbonaceous matters impregnated from graphite dies or oxygen defects formed by reduced atmosphere of the hot-pressing. But annealing in air very often resulted in opaque appearance and loss of transparency of the compacts. In order to study the phenomena occurred during annealing, hot-pressed magnesium aluminum spinel ceramics were annealed at 1100° to 1500°C for 0 to 4h, and change of their transparency and microstructure with annealing temperature and time were examined.
Transmittance of the specimens increased with annealing temperature up to 1200°C, but at higher temperature it decreased and the specimens showed opaque appearance. At 1300°C, the specimens began to opacify with annealing time. This change was accompanied with microstructure change of increase of pore size and volume without any growth of spinel grains. But above 1300°C both pore size and grain size of them increased and consequently their transparency markedly decreased. It was inferred that the following factors affected the opacification of specimens at 1300°C and above; (1) Carbonaceous matters impregnated from graphite die or gas-producing contaminants trapped in the bodies during sample preparation, which gasify during annealing and form pores in the bodies, (2) Preexisting small pores, which can explose by release residual strain caused by the hot-pressing and (3) After beginning of opacification or during annealing at higher temperature, pores coalesce and grow, which cause by difference in their inner gas pressure, radius of curvature or grain growth of the body.
However, if the specimens were pretreated at low temperature, e.g. 1150°C, gaseous impurities are expelled and residual strain is released from the bodies, which can prevent the opacification accompanied with annealing and certify their good transparency.

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Vapor pressures from MgO(s) in O₂-H₂O mixed atmospheres were measured at temperatures of 1670 to 2000K by means of the transpiration method using Pt-Rh alloy for both cell and condenser. Main species was confirmed to be Mg(OH)₂(g) in the pressure range of 2.7×10^-2-1.87×10^-1 atm of p_H2O from results of slopes of linear relation of logp_MgX vs. p_H2O to be near unity.
For the reaction MgO(s)+H₂O(g)=Mg(OH)₂(g), following values were obtained: logk_p=-(14500±600)/T+(2.91±0.35), ΔG_f°(Mg(OH)₂, g)=-(168400±3000)+(49.6±2)⋅T and ΔH₂₉₈°(Mg(OH)₂, g)=65.4±0.6kcal·mol^-1.
The reaction MgO(s)=MgO(g) was carried out in oxygen atmosphere in the temperature range of 1825 to 1975K, and following values were obtained: logp_MgO=-(30100±2300)/T+(8.82±2.56) atm, ΔG_f°(MgO, g)=-(37000±11000)+(8.6±1.1)T and ΔH₂₉₈°=143.6±2.4kcal·mol^-1.
Vapor pressures of Mg(g), MgO(g), MgOH(g), and Mg(OH)₂(g) were calculated and represented in the figures for the 4 series of p_O2 and p_H2O.

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To deal with surface treatments over the carbon fibres to be used in manufacturing ceramic- or metallic-matrix composite materials, mixtures of tetra-(octadecyl) titanate (TOT), a less reactive organic titanate, and pulverized carbon fibres were heated at a rate of 4°C/min up to each 100°C between 900°-1400°C, and other appropriate temperatures, and the products have been investigated by X-ray diffractometry and electron-microscopy.
The results have revealed that TOT has a good wettability to the carbon fibres, that the pulverized carbon fibres start to be covered at 500°C with particles mainly of titanium dioxide of less than 1000Å diameter, that the particles are converted to suboxides at between 700°C and 1200°C, and to the carbide by 1400°C. The results have further revealed that the temperatures at which these conversions take place are deeply related with crystallinity of the carbon fibres, that the threshold temperature of the reduction from titanium dioxide to its suboxides is catalytically lowered by sodium or its certain compounds, that the size of the particles remains little changed throughout the conversions, and that the volume change over the rutile-titan carbide conversion is partly compensated by formation of microvoids in the particles.

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