A reaction between sepiolites and H₂SO₄ was carried out at 30 to 80°C at atmospheric pressure. The reaction proceeded rapidly within 10 min and thereafter remained almost constant irrespective of reaction time. The reaction data could be expressed by an interfacial equation derived. The activation energy obtained from the rate constants in the equation was 8.83 kJ·mol^-1, which was attributed to that of calcium dissolution from sepiolite. The reaction products were CaSO₄·1/2H₂O, MgSO₄·3H₂O, and SiO₂.
CaSO₄·₂H₂O was precipitated by the addition of C₂H₅OH from a solution containing CaSO₄, MgSO₄, and Si (OH) ₄. After separating CaSO₄·₂H₂O, MgSO₄·7H₂O was precipitated by the addition of NH₃ solution from a solution containing MgSO₄ and Si (OH) ₄. Finally SiO₂ was obtained by vaporizing water from a solution with Si (OH) ₄. The reaction is considered to provide useful information not only for fixing SO₂ but also for obtaining gypsum, magnesium sulfate, and silica as reaction products.

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Al置換11Åトバモライトをライムー非晶質シリカおよび石英を用い, Ca/ (Al + Si) =0.80およびAl / (Al +Si) = 0.00 ～ 0.15として水熱合成した.合成試料はXRD, ATEMおよびNMRを使用して, それぞれAl置換11Åトバモライトの格子定数, 化学組成およびシリケートアニオソ構造について検討した. AlによるSiの置換量の増加に伴い, c軸のみが大きく伸張した.出発物質をAl / (Al + Si) = 0.15として合成したすべての試料について, 電子顕微鏡下で11Åトバモライトと少量のハイドロガーネットとの共生が観測されたことから, 11Åトバモライトの最大置換量はAl / (Al + Si) =0.13～0.14であることがわかった. NMRの結果は11Åトバモライトが二重鎖シリケートアニオン構造をもち, Alが選択的にQ³席を占有することを示した.

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Tetracalcium phosphate (Ca₄ (PO₄) ₄O, TetCP) is readily reacted with water vapor in the furnace yielding hydroxyapatite (HAp) and CaO. The weight gain (%) due to the hydrolysis of TetCP, calcined at 1300°C 40 h previouslly, was measured at the temperatures between 400 and 1100°C, and the resulting hydrolyzed products were subjected to dissolve in an aqueous suspension containing H-R, a strongly acidic ion exchange resin, to follow the hydrolysis process. The results obtained are summerized as follows;
1) The hydrolysis starts at around 400°C with abrupt weight gain. The maximal weight gain of 2.61% at 475°C is in excess of that needed to produce HAp and CaO suggesting the formation of fully hydration products, HAp and Ca (OH) ₄, which is followed to sluggish decrease to theoretical weight gain of 1.64% to form HAp and CaO at 1000°C.
2) The heats of dissolution (kJ·mol^-1) of TetCP, HAp and CaO in the aqueous suspension with excess H-R were measured as-332.55, -358.73 and-195.49, respectively. Thus the heat of hydrolysis of TetCP to yield 1 mol of HAp and 2 mols of CaO is assumed to be-247.94 kJ. The variation of the heat of dissolution of the reheated products is identical with the weight change supporing the formation of HAp and CaO in the hydrolysis process.
3) However, the existence of Ca (OH) ₄ to be formed at the initial hydrolysis can not be confirmed.

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Coatings of a-tricalcium phosphate (α-TCP) and hydroxyapatite (HAp) were prepared on titanium plates by a plasma spraying technique. Powders of β-TCP and HAp were used as plasma sprayed materials for α-TCP and HAp coatings, respectively. The characterizations for the a-TCP and HAp coatings were investigated by X-ray diffraction analysis, SEM observation, X-ray fluorescence analysis, and surface roughness measurements. Thin film X-ray diffraction patterns were measured with various angles of incident beam..As a result, in the HAp coatings on titanium plate, broad amorphous-like peaks were observed for the interior layers of coating near to the substrate, while crystalline peaks were observed for the surface layer. In the α-TCP coating, crystalline peaks were observed for the whole coating layers. Besides, cytotoxicities of these coating layers were investigated by cell cultivations using L-cells and MC3T3-E1 cells in vitro. Morphological evaluations were carried out by phase-contrast micrographs and SEM observations, and cell proliferations were examined for the cells. Results from the proliferation tests of the cells on the coating layers indicated that both the α-TCP-and HAp-coatings had better biocompatibility than the titanium plate without coatings.

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The reactions between PbCl₂ aquaous solution and hydroxyapatite (Ca₁₀ (PO₄) ₆ (OH) ₂, HAp) samples of various compositions (Ca/ (P + C) molar ratio) and purities (with or without trace metallic elements) were investigated in detail.
The purity of the samples did not influenced on the reactivity. Ca-deficient type samples removed well Pb²⁺ ion from a high concentration solution. Furthermore, Ca-rich type samples removed them only from a low concentration solution. The samples reacted with PbC1₂ in the aquaous solution became the mixture of HAp and pyromorphite (Pb₁₀ (PO₄) ₆Cl₂, Pyr) analyzed by XRD, TEM observation and EDS. So it was found that Pb²⁺ ion was not removed from solution by ion-exchange reaction and but eliminated by Pyr precipitation reaction.
This reaction is the reaction among Pb²⁺ ion, Cl^- ion and H₂PO₄^- generated from dissolution of HAp by H⁺ ion, and forming of the compound on the surface of HAp particle.

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The bovine bone is composed of hydroxyapatite (HAp) and collagen, which are expected to resources recycling from large amount of waste bovine bone. The persent work was investigated about novel process of using ion-exchange resins for purpose of complete resources recycling of waste bovine bone to calcium phosphate and collagen. The products were characterized by means of infrared spectroscopy (FT-IR), thermal analysis.
The recovery ratio of Ca²⁺ ion was recovered 100%, when dipped cation-exchange resin into suspension of bovine bone for 6 hours at tomperature of O°C. Also, PO₄^3- ion was recovered completely by dipping for 1 hour anion-exchange resin into solution after removed Ca²⁺ ion. Further, the ion-exchange resins after exchange of Ca²⁺ and PO₄^3- ions were regenerated with HCl or NaOH solution, and were used once again. The collagen sheet was obtained by filtering the solution with residual after the removed inorganic ions, and the sheet was very small denaturation. Finally, the process for the resources recycling of waste bovine bone was proposed.

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Structural stabilities of Ag-I and I intercalated Bi₂Sr_1.5Ca_1.5Cu₂O_δ compounds at elevated temperatures were investigated by X-ray diffraction and thermogravimetric analyses. A structural change of the intercalation compounds into the host Bi₂Sr_1.5Ca_1.5Cu₂O_δ (Bi2212) was observed with the release of I at elevated temperatures. The I intercalated Bi₂Sr_1.5Ca_1.5Cu₂O_δ (I-Bi2212) structure was maintained below around 330°Cat which the chemical composition was I : Bi2212=1 : 1. The complete change into the Bi2212 Occurred above 480°C. On the other hand, the Ag-I intercalated Bi2212 (Ag-I-Bi2212) structure was maintained at 480°C. However, the Ag-I-Bi2212 disappeared when treated above 610°C. An unknown phase was formed in the range of 610 to 720°C. The completely structural change into the Bi2212 was observed above790°C.In this report, their structural stabilities at elevated temperatures are discussed in terms of the release of I from the intercalation compounds.

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電子セラミックスの出発材料としての利用を目的として, Na₂O-TiO₂非晶質球状粒子の合成を均一核生成法とエマルジョン法を用いたイオン交換一ゲル化法で合成した.均一核生成法による合成では, 凝集が激しくみられ, 単分散球状粒子は得られなかった.しかし, 粒子中のNa/Ti比のコントロールは比較的容易で, Na/Ti=1.0を超える広い組成範囲でその制御か可能であることがわかった.これは, 均一核生成法で合成した粒子はゲル中に残存するOH基が多いためである.それに対して, エマルジョン法で合成した粒子の組成は, Na/Ti=0.8のあたりで飽和がみられ制御可能な組成範囲は狭いが, 均一核生成法と比較して非常に分散性の良い粒子が得られることがわかった.

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The present work was made to investigate preparation of gypsum block from waste gypsum board specimen. The lining paper was perfectly separated from gypsum hemihydrate specimen which was dehydrated to formation ratio of above 45% as gypsum hemihydrate by heating the waste gypsum specimen (70 × 40 × 12.5 mm) at 200°C. The gypsum block was prepared by pilling up some gypum hemihydrate specimens which was sprayed with water or saturated solution of gypsum dihydrate. The compressive strength of hardened gypsum specimen was increased under conditions of formation ratio of 55% as gypsum hemihydrate, spraying with saturated solution of gypsum dihydrate and amount of hydration water (H₂O/CaSO₄·1/2H₂O molar ratio) of about 3.0. The compressive strength of gypsum block prepared by hydrating after pilling up seven pieces of the gypsum hemihydrate specimen was 3.1 MPa by exerting load of 0.18 kg·cm^-2. This finding was the same compared with that of stacked seven pieces of the waste gypsum specimen which was mechanically removed lining paper.

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Heating a porous SiC body added with CaCl2 and AICI3 at 1400°C in air produced highly oxidation-resistive silica film on its surface layer. A main component of this film was β-cristobalite which, unlike α-cristobalite, do not exhibit the β⇔α transition at 200-400°C. The high oxidation resistivity of this Ca-and Al-codoped SiC was preserved after repeated heating and successive cooling treatments, which could be explained by the low degree of the crack evolution on its surface layer as observed by SEM. Chemical durability of β-cristobalite in a HCl-containing atmosphere above 1000°C was confirmed. This suggests that the Ca-and Al-doped SiC can be used as a refractory material of a kiln for incinerating chlorine-containing compounds.

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