Crystal-Shape Controls of Calcium Hydrogenphosphate Dihydrate by Hydrolyzing Aqueous Solution of Calcium Dihydrogenphosphate

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  • YASUE Tamotsu
    Department of Industrial Chemistry, Faculty of Science and Engineering,
  • SAKAKIDA Junko
    Department of Industrial Chemistry, Faculty of Science and Engineering,
  • YOSHIYAMA Akihiro
    Department of Industrial Chemistry, Faculty of Science and Engineering,
  • ARAI Yasuo
    Department of Industrial Chemistry, Faculty of Science and Engineering,

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Other Title
  • リン酸二水素カルシウム水溶液の加水分解によるリン酸一水素カルシウム二水和物の形状制御
  • リンサン 2 スイソ カルシウム スイヨウエキ ノ カスイ ブンカイ ニ ヨル

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Description

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.<BR>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.<BR>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.<BR>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.

Journal

  • Gypsum & Lime

    Gypsum & Lime 1990 (229), 387-395, 1990

    The Society of Inorganic Materials, Japan

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