The study was made to investigate the shape control of calcium hydrogenphosphate dihydrate (CaHPO₄·2H₂O, DCPD) by hydrolyzing calcium dihydrogenphosphate monohydrate (Ca (H₂PO₄) 2· H₂O, MCP) in its aqueous suspensions and solutions using water, aqueous ammonia and urea as a precipitant of homogeneous precipitation. Characterization of the precipitate after hydrolysis was carried out by means of X-ray diffraction, scanning electron microscopic observation and chemical analysis.
DCPD crystals deposited by hydrolyzing MCP suspensions were so developed as increasing the concentration of the suspension in the range of 0.09-6.00 mol dm^-3. In the case of a high MCP concentration of 6 mol dm^-3 after aging for 10-20 days, well crystallized DCPD with hexagonal shape of 10-20μm in length and 2-5μm in thickness formed but the rate of hydrolysis was very small.
Hence, the hydrolysis of MCP was made at low concentrations in the range of 0.005-0.08 mol dm^-3 in the MCP-NH₃-H₂O and MCP-CO (NH₂) ₂-H₂O systems. An amorphous calcium phosphate (ACP, Ca/P atom ratio 1.1) formed by adding rapidly aqueous ammonia to the MCP solutions at 5-20°C and then it changed to thin flake-like whiskers about 2-5mm in length after aging for 2 days.
On the other hand, in the homogeneous precipitation method given by heating a mixed solution of MCP, CO (NH₂) ₂ and H₂O at 80°C, low crystalline octacalcium phosphate (Ca₈H₂ (PO₄) ₆·5H₂O, OCP) with a tape-like shape was formed and then aged for 5-8 days by rapid cooling down to 20°C as it was. As the resultant, OCP crystals were converted into DCPD fiber with about 100 of aspect ratio like 200 μm in length and 2 μm in diameter. As the above, it was successful to control the shape of DCPD as big thin-flake like whisker, hexagonal platy and fibrous crystals.

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A layer-structured calcium phosphate called octacalcium phosphate (Ca₈ (HPO₄) ₂ (PO₄) ₄· 5H₂O; OCP) and succinate-and methylsuccinate-intercalated OCP's were investigated with respect to dehydration-rehydration and related properties.
The basal spacing of OCP was increased from 18.7Å to 21.5Å by the intercalation of succinate ions and to 20.4Å by methylsuccinate ions. Reversibility of H₂O (zeolitic H₂O) was observed below 200°C for both OCP and the intercalated OCP's. The state of the zeolitic H₂O in the intercalated OCP's was similar to that of free water. The basal spacings of these OCP's with and without intercalation were contracted and reverted by the dehydration and rehydration treatment. Disappearance of the reversibility of H₂O was considered to be due to an excessive contraction in distance between layers of the OCP structure by dehydration and/or collapse or bending of pillar groups supporting the layers. The reaction HPO₄→P₂O₇ and the decomposition of OCP and the intercalated OCP's into apatite began at ca. 250°C, however the OCP layer structure still remained at 300°C in the case of OCP and at 600°C in the case of the intercalated OCP's.

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Ceramics of hydroxyapatite and its halogen-substituted solid solutions were found to exhibit dielectric characteristics at temperatures below ca. 500°C. Their dielectric constants, ε, and dielectric losses, tan δ, were dependent on both the sintering processing and the concentration of the substitutive halide ions.
The values of ε of the HAp and (X, H) Ap (X=F, Cl) ceramics sintered by hot-pressing (15 MPa) under reduced atmosphere (ca. 10^-2 Pa) was smaller than those of the specimens sintered under conventional conditions (1200°C, 4 h in the air), while the tan δ was much larger in the former ceramics, than in the latter. The activation energy for dielectric behavior was experimentally estimated as 0.4 eV to 0.5 eV.
The effects of halide ions were also found so distinct that the specimens with the composition of [F] =40% to 50% exhibited the maximum ε and the minimum tan δ.
Based on those results, it seems that the effects of vacancies are as important as substitutive halide ions.

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The ion-exchange characteristics of calcium carbonates (calcite, aragonite and vaterite) with Cd²⁺ ion in aqueous solutions containing various counter-anions (C1^-, NO₃^- and CH₃COO^-) have been investigated in detail at 25°C, using a normal batch method.
The reaction characteristics are independent on the kind of counter-anions. The order of the reaction rates was found to be as follows; vaterite> aragonite>> calcite, and about 80% of Cd²⁺ ion were taken up by aragonite and vaterite during long time reactions. Although Cd²⁺ ion in aqueous solutions were easily fixed as cadmium carbonates and calcium soluted cadmium carbonates by aragonite and vaterite, respectively, they were found to be hardly done by calcite. The values of the molar ratios of Cd²⁺/Ca²⁺ were about 1.0 and 0.9 for aragonite and vaterite, respectively. From the results, it was concluded that the immobilization of Cd²⁺ ion in aqueous solutions on calcium carbonates proceeds by lattice ion ion-exchange mechanism at room temperature.

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Al-substituted tobermorites were synthesized using rice husk ash as silica source. Properties of cation exchange and removal of heavy metal ions were studied in Al-substituted tobermorites. Tobermorite synthesized adding 15mo1% Al to Si had large cation exchange capacity to NH₄⁺ ion and its ion exchange curve was Langmuir type. Large cation exchange capacity of Al-substituted tobermorites had little effect on improving the removal of heavy metal ions. Low crystalline tobermorite was more suitable to remove heavy metal ions. Amount of removal of heavy metal ions decreased as follows : Ni>Cr>Cu>Zn=Pb in tobermorite samples. Amount of Ni removal was particularly large in tobermorite samples and it was superior to that of A type Zeolite.

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The catalyst effectiveness of Ca (OH) ₂ and CaCO₃ in steam gasification of five coals with low ranks is investigated with a thermobalance. These compounds kneaded with Yallourn brown coal in water are converted into more finely-dispersed calcium catalysts in the coal devolatilization step, compared with those physically-mixed with the coal. Such catalysts exhibit excellent activity in the gasification at 650°C; the coal is completely gasified within about 1 h. Ca (OH) ₂ kneaded with other four coals, such as Shori, South Beulah, Colowyo, Illinois No.6 coal, also promotes the gasification, but the catalyst effectiveness depends on the coal type. Ca (OH) ₂ is more effective for the gasification of low rank coals with smaller amounts of inherent calcium; the addition of Ca (OH) ₂ achieves about 25-fold rate enhancement.

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Natural lime produced from limestone was used as the raw material for the present study. Three kinds of the sintered lime were made. The first sample was molded by cold isostatic pressing (CIP) and then fired for 6 h at 1800°C (sample A). The second sample was molded by uni-axial dust pressing followed by CIP and the fired for 6 h at 1800°C (sample B). The third sample was molded by CIP and then fired for 10 h at 1750°C (sample C). Effect of the conditions of pressing and firing on the bending strength and hydration resistance of sintered lime was investigated. The following results were obtained :
(1) The bulk density for the sintered bodies was from 2.81 to 2.88 g/cm³. The apparent porosity of the sample C was smaller than the other samples.
(2) The mean bending strength for the bodies was from 79 to 81 MPa. The Weibull parameter (18.4) of the sample B was higher than the other samples.
(3) The weight gain of the sample C under a saturated water vapor pressure at 8°C was less than 5% after fifty days, while the other showed as much as 5% of gain only after twenty days under same conditions.

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