The change in S-o bonding of calcium sulfite hemihydrate during its thermal reactions in air was investigated.
The oxidation reaction expressed by CaSO₃ + 1/2O₂→ CaSO₄ occurred at 440-1100°C, and the decomposition from the sulfite to oxide, CaSO₃ CaO + SO₂, also occurred at 850-1100°C.At first, the SO₃^2- in CaSO₃ was coordinated through the oxygen to the calcium.With heating, the structure of SO₃^2- changed to have several kinds of symmetry, and then it became the sulfur-coordinated sulfite species.
The oxidation of CaSO₃ and the oxygen-coordinated sulfite species were observed. These phenomena were similar to the case of strontium and barium sulfite. Furthermore, the decomposition and the sulfur-coordinated sulfite species were recognized in CaSO₃. These were similar to those of magnesium sulfite.

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Study was made to investigate the effect of the supersaturation degree on crystal shape and modification of α-gypsum hemihydrate depositing from calcium sulfate solution which was prepared from liquid-reaction system of CaCl₂ -H₂SO₄ or Ca (NO₃) ₂-H₂SO₄ at 100°C. The supersaturation degree of the solution is controlled by the concentration of HCl or HNO₃ liberated in the reaction CaCl₂-H₂SO₄ or Ca (NO₃) ₂-H₂SO₄. Characteristics of gypsum hemihydrate as the reaction product was determined by means of X-ray diffraction, scanning electron microscopy, thermal analysis (TG-DTA) and chemical analysis.
The crystal shape of the hemihydrate was affected remarkably by the induction-period interval and the deposition velocity depending on the supersaturation degree changing in progressing the liquid-phase reaction. The induction-period for waiting precipitation appeared at the supersaturation degree less than 0.3 in the both reaction systems but the induction-period interval was more prolonged in the Ca (NO₃) ₂-H₂SO₄ system than in the CaCl₂-H₂SO₄ system, even at the same supersaturation degree. Therefore bigger needle-crystals were obtained in the nitrate system because the deposition velocity is slower than the chloride system. It was assumed that those findings were caused by selective adsorption of NO₃^- or Cl^- to different crystal-faces of the hemihydrate. The aspect ratio of the needle-like crystals increased at the supersaturation degree less than 0.3 in the both systems but the increase much accelerated in the nitrate system. Especially, in the nitrate system, the big-sized whisker of the hemihydrate with aspect ratio of 150 (length 1500μm×diameter 10μm) were obtained at the degree of 0.13. Also the modification of the hemihydrate thus obtained was identified as α-hemihydrate in the case of lower degree than 0.3. Usually, α-hemihydrate consisting of big crystals is useful as mold materials for casting metal but it is high-priced to produce by autoclaved reaction of gypsum dihydrate. This method to be atmospheric reaction could be expected as the new production method of lower-priced α-hemihydrate.

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Crystal growth of apatite on calcium salts was studied by the constant composition method. Hydroxyapatite, amorphous calcium phosphate, β-tricalcium phosphate and CaF₂ were used for seeds.
Octacalcium phosphate often formed from the solutions with high degree of supersaturation concerning hydroxyapatite (HAp), while apatites crystallized in the presence of fluoride even under the same saturation conditions. Epitaxial relation between seeds and apatite was needed for the rapid growth of pure HAp.

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トリイミドシクロ三リン酸ナトリウムを酢酸水溶液中で65℃で加水分解して, ジイミドシクロ三リン酸ナトリウム-水和物, Na₃P₃O₇ (NH) ₂・H₂Oを合成した。ジイミドシクロ三リン酸ナトリウム-水和物を空気中で400℃まで加熱すると, モノイミドシクロ三リン酸塩, シクロ三リン酸塩, 水に不溶なイミノ基を含んだ高分子状ポリリン酸塩を生じた。これらのリン酸塩は約600℃でNaPO₃Iに変化した。このジイミドシクロ三リン酸塩の全熱反応はつぎの式で表すととができる。
Na₃P₃O₇ (NH) ₂+2H₂O (NaPO₃) ₃ + 2NH₃

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The expansion of quick lime in the hydration has been observed since ancient times. Although there are a number of theories to explain the mechanism of this expansion, none have been clearly proven to date.
In order to discuss the mechanism of expansion, the expansive stress, degree of quick lime hydration and pore structure were examined. The results are as follows.
1) So long as the same demolition agent is used, the expansive stress depends solely on the amount of Ca (OH) ₂ produced. However, in the case of different type of the demolition agent is used, it does not determined solely by the amount of Ca (OH) ₂ produced.
2) The total pore volume decreases with increasing the expansive stress. This relationship is irrespective of the type of agents.
3) The total pore volume decreases with increasing the amount of Ca (OH) ₂ produced. This relationship differs according to the type of agents.
4) The mechanism of the expansion stress to generate is as follows. Ca (OH) ₂ crystals produced during the hydration push against one another, and create expansive force. Free expansion can not be made when outside ends are fixed firm, and then expansive force is generate on the materials.

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