The heats of formation of the alkali disilicates, digermanates and metaphosphates (alkali=Li, Na, K) were revised. The bond dissociation energies of the Si-O, Ge-O, P-O and O-R bonds were recalculated and compared among the silicate, germanate and phosphate glasses. Their physical meanings were also clarified based on the thermochemical cycles representing the dissociatation processes.

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Composition dependences of the heats of solution of the glasses and crystals in the systems MO-P₂O₅ (M=Mg, Ca, Sr) in 3N HNO₃ aqueous solution have been discussed in terms of the bond dissociation energies of P-O^b bridging bonds in the three composition regions; 0<MO+H₂O/P₂O₅(=r)<1, 1<r<2, 2<r<3. The calculated heats of formation of the M(PO₃)₂ glasses derived the bond energies of bridging and non-bridging P-O bonds (E(P-O^b), E(P-O^nb) and of O-M-O bonds (E(OM)), based on the assumption E(P=O)/E(P-O^b)=1.75 and 2.0.

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The relation between the soild solution formation of Nb₂O₅ in anatase and the inhibitory effect of Nb₂O₅ on the anatase-rutile transformation were studied. Niobium oxide inhibited the transformation. It was suggested that at 700°C Nb₂O₅ forms a substitutional solid solution below 0.4mol%, and an interstitial one over 0.6mol%. The inhibitory mechanism of the transformation by Nb₂O₅ was explained in terms of the solid solution types. The formation of a substitutional solid solution decreases the concentration of oxygen vacancies which act the nucleation sites of the rutile phase, and the formation of an interstitial solution hinders the movement of Ti⁴⁺ for rearrangement.

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Microstructure of the translucent alumina ceramic “Lucalox”was examined by the repeated step scanning method of X-ray powder diffraction and observed by the various microscopes and XMA. The analysis by the repeated step scanning method of X-ray diffraction clarified that Lucalox included a small amount of spinel phase, about 300ppm, besides corundum and that the lattice constant of spinel phase was a₀=8.04₉Å. The reflection microscope showed the presence of second phase particles at triple junction of grain boundary in inner parts of the specimen and not in the surface sides of specimen. From the measurement of XMA the chemical composition of second phase particles was about Al₂O₃ 77wt% and MgO 22wt%, corresponding to alumina rich spinel phase of which lattice constant was a₀=8.05Å. Emission spectroanalysis showed that Lucalox contained 300ppm of MgO which was larger value than the amount of MgO estimated from the content of spinel phases about 70ppm. The XMA examination detected the existence of MgO in the surface sides of specimen. From this evidence it was inferred that some amount of MgO dissolved into corundum to make a solid solution. As large corundum grains in the surface sides of specimen in which spinel phase was free did not include any pores, the MgO-enhanced densification of sintered alumina was thought to relate the solid solution of MgO into corundum.

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The effects of addition of various lanthanide oxides and their mixture with Y₂O₃ on the sintering of Si₃N₄ were investigated. The addition of simple and mixed lanthanide oxides promoted the densification of Si₃N₄ in the hot-pressing at 1800°C under 300-400kg/cm² for 60min. The crystallization of yttrium- and lanthanide-silicon oxynitrides which was observed in the sintered body containing yttrium-lanthanide mixed oxides as additive led to the formation of a highly refractory Si₃N₄ ceramic having the bending strength of 82 and 84kg/mm² at room temperature and 1300°C, respectively. In Y₂O₃+ La₂O₃ system, a higher molar ratio of La₂O₃ to Y₂O₃ gave a higher hardness and strength at high temperatures. It was found that 90min was an optimum sintering time for the highest strength.

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Some properties and sinterability of Ca₂P₂O₇ powders obtained by pyrolysis of reagent grade CaHPO₄⋅2H₂O were examined. The samples underwent relief of water of crystallization and then dehydration-condensation, while they still retained their original shapes. The heated samples consisted of agglomerated primary particles, which were comprised of smaller crystallites. The change in properties of powders during heat-treatment was explained in terms of rearrangement and growth of crystallites and neck growth between primary particles. The density of compacts increased in proportion to logarithm of pressure under a certain pressure, whilst it increased irregularly above this pressure with a smaller slope. The density of compacts and its pressure dependence were explained on the basis of three different types of void spaces during pressure treatment. Among the Ca₂P₂O₇ powders obtained at various temperatures, those heated at temperatures between 400°C and 600°C were found to sinter most densely.

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