In order to explore the setting and hardening characteristics of calcium sulfate hemihydrate, CaSO₄·1/2H₂O, simultaneous measurement of calorimetry and conductimetry at 25°C was carried out during successive addition of three portions of the hemihydrate into water. In addition, the duratiorn of the constant-concentration period as a function of the amount of the hemihydrate was examined by chemical analysis of liquid phase. The results obtained are summerized as follows :
1) The initial concentration increases with the mass of the hemihydrate reaching up to ca. 50 mmol/l but the progress of transformation to the dihydrate from the supersaturated solution causes the reduction of the concentration.
2) Tentative solubility and heat of dissolution in water with respect to the hemihydrate are estimated to be ca. 22 mmol/l and 13.2 kJ/mol, respectively.
3) By mixing the hemihydrate in water, the dissolution and hydration processes occurr successively which are accomlpanied with distinct exothermal double peaks and variation in eletrical conductivity due to the difference in solubility between the hemihydrate and the dihydrate.
4) The thermal flow curves at hydration process of the hemihydrate in water, in dihydrate saturated solution and in an aqueous suspension containing the anhydrite are almost identical, whereas the double thermal peaks are tend to change to single peak with shoulder in the presence of the dihydrate grain. The nucleation and crystal growth of hydration product onto the dihydrate surface as a seed crystal is cleared by SEM observation.

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Improvement of thermal shock resistance of wollastonite (β-CaSiO₃) sintered body has been performed by adding spodumene (β-LiAlSi₂O₆) which has a low thermal expanson coefficient.
In this study, influence of spodumene content on sintering behaviour, mechanial properties (3-point bending strength, Vickers hardness), thermal properties (thermal expansion coefficient, thermal shock resistance), and microstructure of wollastonite/spodumene composites was investigated.
The results obtained are as follows;
1) Abrupt decreace in densification temperature can be observed on spodumene content of 25-75 mass%.
2) Bending strength has a clear dependency on spodumene cotent, however no dependency of spodumene content on Vickers hardness can be observed.
3) The thermal expansion coefficient decreased in proportion to spodumene content, and thermal shock resistance was improved with an increace of amount of spodumene.

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Improvement of thermal shock resistance of wollastonite sintered body has been performed by adding spodumene which has a low thermal expanson coefficient.
In this study, influence of average particle size of mixed powder on sintering behaviour, mechanial properties (3-point bending strength, Vickers hardness), thermal properties (thermal expansion coefficient, thermal shock resistance) and microstructure of wollastonite/spodumene composites was investigated.
The main results obtained are as follows;
1) Densification temperature decreased with decreasing average particle size.
2) Bending strength of composites increased with decreasing average particle size at lower spodumene contents. However, no particle size dependency was observed at higher spodumene contents because of void formation.
3) Vickers hardness of composites increased with decreacing average particle size.
4) Thermal expansion coefficient significantly decreased with increasing average particle size at higher spodumene contents.

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Spherical hydroxyapatite (HAp) was synthesized using wet chemical method of Ca (NO₃) ₂-KOH-H₃PO₄-H₂O system. When titrating aqueous solution of Ca (NO₃) ₂ and aqueous solution of KOH at same time into aqueous solution of phosphoric acid, spherical aggregate of CaHPO4 (DCP) was at first produced at 50-80°C, and when holding its spherical aggregate at pH 7.0, it changed to spherical HAp for 48 hours of stirring. The spherical aggregate of DCP appeared as aggregate of platy crystal of DCP. On the internal structure of spherical HAp, however, it was observed that the platy crystal of HAp grew from the dense outer shell toward the center of particle.

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