Change in Surface Properties during Thermal Treatment of Powderly CaHPO<sub>4</sub>·2H<sub>2</sub>O

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  • ＣａＨＰＯ４・２Ｈ２Ｏの脱水物の粉体表面物性
  • CaHPO4 2H2O ノ ダッスイブツ ノ フンタイ ヒョウメン ブッセイ

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The surface area, pore size distribution and pore volume of powderly CaHPO4·2H2O heat-treated were investigated by nitrogen adsorption and desorption measurements at 77K. The surface area of the sample powder was found to increase markedly at 200 and 400°C. It is well known that the crystal water of CaHPO4·2H2O is removed in the temperature range of 115-215°C and the dehydration-condensation of CaHPO4 occurs at 360-450°C. X-ray diffraction and weight loss measurements indicated that considerable parts of CaHPO4 and Ca2P2O7, which are the heating products at the above respective temperature, were both amorphous. Moreover, a large increment of the pore volume was recognized to be accompanied by the occurrence of each dehydration. Therefore, an increase of surface area is considered to be mainly due to the formation of mesopores. On the other hand, decreases of the surface area and pore volume at above 550°C may be explained in terms of crystal growth and sintering of the sample.

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