The metastable phase, named δ-phase, of SrCO₃ or BaCO₃ is able to obtained by a rapid quenching for a mixed powder with 10 mol% of BaSO₄ from the phase transition temperature of the host carbonates.
The study was carried out to clarify the formation mechanism of those δ-phases using DTA and high temperature X-ray diffractometer.
The results obtained are summarized as follows;
1) Mutual substitution between CO₃ and SO₄ ions was accelerated around the phase transition temperature of the carbonate.
2) It was identified the the stable phase above the transition temperature was not δ-but α-phase (hexagonal) incorporated with BaSO₄.
The result suggests that the δ-phase is formed at the quenching process which brings about a lattice shrinkage to prevent the reversible transition.

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Magnesium basic carbonate was synthesized by using so called “the sodium carbonate method”. The process composed of following steps such as precipitation and dissolution of the amorphous basic carbonate, crystallization and dissolution of the carbonate (nesquehonite), and the formation of the basic carbonate.
The results obtained are summarized as follows :
1) The crystallinity of nesquehonite depends on the concentration ratio of [CO₃^2-] / [OH^-] ².
2) The formation rate of the basic carbonate depends on the dissolution rate of nesquehonite and the concentration ratio of [OH^-] / [HCO₃^-].
3) The composition of basic carbonate depends on aging conditions, that is 4MgCO₃·Mg (OH) ₂·8H₂O is stable at high concentration of [OH^-] and low temperature, 4MgCO₃·Mg (OH) ₂·5H₂O (dypingite) is stable at low concentration of [OH^-] and high tempbrature.
4) Ultimate composition of basic carbonate depends on the drying temperature. 4MgCO₃·Mg (OH) ₂· 5H₂O (giorgiosite) is stable at room temperature, on tne other hand, 4MgCO₃·Mg (OH) ₂·4H₂O (hydromagnesite) is stable at about 110 °C.
Above results indicate that the concentration of initial solution, the aging temperature, and the pH of mother's solution play the important role on the synthesis of magnesium basic carbonate.

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Tetracalcium phosphate (Ca₄ (PO₄) ₂O) was studied with respect to its preparation, thermal change, hydration and catalytic characteristics.
Reaction products by heating the stoichiometric mixture of Ca₂P₂O₇+2 CaCO₃ in air were as follows : Ca₂P₂O₇+2CaO (≥650°C), Ca₃ (PO₄) ₂+CaO (≥700°C), 1/3 Ca₁₀ (PO₄) ₆ (OH) ₂+2/3 CaO (≥ 800°C), and Ca₄ (PO₄) ₂O (≥1200°C). When Ca₄ (PO₄) ₂O was heated up and then cooled down gradually in air, the reaction Ca₄ (PO₄) ₂O→1/3 Ca₁₀ (PO₄) ₆ (OH) ₂ +2/3 CaO_??_Ca₄ (PO₄) ₂O occurred, where the first process started at 300-420°C with absorbing H₂O vapor in air, and the second reversible process at 1200°C for the forward reaction and at ca. 1050°C for the reverse. The reverse reaction could be prevented by rapid cooling or by using dry atmosphere. Actually, Ca₄ (PO₄) ₂O was prepared in air by rapid cooling from 1350°C. The formation of hydroxyoxyapatite (Ca₁₀ (PO₄) ₆ (OH, O) ₂) was suggested at 850-1200°C. The hydration activity of Ca₄ (PO₄) ₂O was lower than that of α-Ca₃ (PO₄) ₂, and higher than that of β-Ca₃ (PO₄) ₂· For the catalytic thermal decomposition of 2-propanol, Ca₄ (PO₄) ₂O was a typical basic catalyst, However, it was considered that Ca₄ (PO₄) ₂O changed into a mixture of 1/3 Ca₁₀ (PO₄) ₆ (OH) ₂+2/3 CaO during the catalytic experiment.

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Hydrothermal reaction of akermanite at 210°C and 350°C under saturated steam pressure was investigated.
1) The reaction products from akermanite were hillebrandite, illcrystalline magnesium silicate hydrate and kilchoanite at 210°C, and kilchoanite, xonotlite and magnesium silicate hydrate at 350°C. Rate determining process was diffusion process, at first, resulting in slow reaction rate. And reaction became fast, in later stage, because that the interface reaction became the rate determining step.
2) Ca (OH) ₂ addition changed the reaction products completely. Mg (OH) ₂ was produced instead of magnesium silicate hydrate. Calcium silicate hydrates formed in this system were calcio-chondrodite and γ-Ca₂SiO₄ hydrate. Reaction rate also changed in a complicated way.
3) Magnesium silicate hydrate was formed when quartz was co-existed. Calcium silicate hydrate were gyrolite, truscottite and xonotlite. Hydrothermal reaction was promoted by quartz, as the rate controlling process was interface reaction from early stage.

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The paper deals with the condition of preparation of a condensed phosphate pigment, Mineral Violet, and it's chemical composition including the state of phosphate and valence of Mn ion by several analytical methods.
The Mineral Violet was obtained by heating the mixtures of manganese (IV) oxide and am monium dihydrogenphosphate in a mole ratio of 1/8-10 for 1.5 hours at 260°C. The hue of the pigment showed vivid reddish purple (complementary wavelength λ_c ; 554.4nm, lightness Y;10.6%, excitation purity Pe; 48.7%). From paper chromatographic analysis, di-and orthophosphate groups were recognized to coexist together and the ratio was considerably affected by the preparation temperature. Also the complex ion MnP₂O₇-formed by bonding the both of manganese ion and diphosphate group. In addition, the valence number of manganese was confirmed to be trivalent from fluorescent X-ray and infrared spectra data. The decomposition of Mineral Violet started at about 362°C and then converted to Mn₃ (P₃O₉) ₂ at about 550°C.

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Globular secondary particles of xonotlite were obtained by hydrothermal treatment of silica and lime under stirring in a large amount of water at 191°C for 8 hours. Quartzite, byproduct. silica and rice hull ash were used as starting materials of silica. In the present study, xonotlite crystals and their secondary particles were investigated by X-ray diffraction, optical and electron microscopic observations and mesaurement of specific surface area.
Xonotlite prepared from byproduct silica and rice hull ash had higher crystallinity (smaller specific surface area) and grew up preferentially in the direction of b axis than that from quarzite. Moreover, xonotlite from rice hull ash had larger ratio of crystallite size of D₀₄₀/D₀₀₁ and D₀₄₀/D₄₀₀.
The secondary particles of xonotlite prepared from byproduct silica and rice hull ash were smaller in size and the particles of xonotlite protruding from the surface were longer than those from quartzite. The particles from byproduct silica were transparent and the samples from quartzite consisted of irregular massive xonotlite, were opaque and had smooth surface due to dense interlocking of xonotlite, but those particles from rice hull ash had rough surface due to loose interlocking and were mixtures of pervious and impervious particles in those interior space.

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