２ＣａＯ・Ｐ２Ｏ５～３ＣａＯ・Ｐ２Ｏ５共晶組成融液の一方向凝固

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タイトル別名
  • Unidirectional Solidification of the 2CaO⋅P<sub>2</sub>O<sub>5</sub>-3CaO⋅P<sub>2</sub>O<sub>5</sub> Eutectic
  • 2CaO P2O5 3CaO P2O5 キョウショウ ソセイ ユウエキ ノ 1

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説明

Calcium phosphate ceramics with high mechanical strength are of potential use as artificial bones. Fundamental conditions for preparing this kind of ceramics by unidirectional solidification of their melts were investigated. Starting materials with nominal compositions of the 2CaO⋅P2O5-3CaO⋅P2O5 eutectic and its neighbors (Table 1) were prepared by melting the mixtures of reagent grade chemicals of CaHPO4⋅2H2O and CaCO3 in a platinum crucible at 1400°C for 30min and casting them into another platinum crucible. The starting materials were remelted except for their lowest part about 15mm thick in the platinum crucible placed in a temperature gradient furnace (Fig. 2) and unidirectionally solidified upwards under various conditions (Table 2). The lowest part of the starting material left unmolten acted as seed crystals. When the starting material with the exact eutectic composition (E+1.0P2O5 in Table 3) were first remelted below 1350°C and then unidirectionally solidified at rates of 2-20mm/h under a thermal gradient of 20°C/cm (d-d′′′ in Table 2), ingots with regular structure were obtained (Fig. 5, E+1.0P2O5), In these ingots, lamellar α- and β-3CaO⋅P2O5 crystals were aligned parallel to the solidification direction in a α-2CaO⋅P2O5 crystal matrix. The crystallographic direction perpendicular to the (002) plane of the α-2CaO⋅P2O5, and those perpendicular to the (113) and (220) planes of the α- and β-3CaO⋅P2O5 crystals, respectively, coincided all with the solidification direction (Fig. 6), The lamellar spacing λ decreased from 16.5 to 6.0μm with increasing solidification rates R from 2 to 20mm/h according to the relation λ∝R-1/2, like for other eutectic systems (Fig. 7). The ingots were pore-free but contained some microcracks, as shown in Fig. 8. These microcracks arose probably from thermal stresses due to a large difference in thermal expansion between the 2CaO⋅P2O5 and 3CaO⋅P2O5 crystals, which were formed during cooling of the solidified ingots (Fig. 9 and Table 5). When the composition of the starting material deviated from the eutectic even by 0.5%, the resultant unidirectionally solidified ingots showed irregular structure and contained many pores (Table 3 and Fig. 5). The compositional deviation were found to occur when the starting material was prepared by melting above 1400°C, where the P2O5 constituent tended to vaporize separately from the melt. The formation of the irregular strlucture was attributed to a constitutional supercooling of the melts at the front of the growing crystals (Figs. 10 and 11).

収録刊行物

  • 窯業協會誌

    窯業協會誌 90 (1042), 295-304, 1982

    公益社団法人 日本セラミックス協会

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