Effect of molding pressure on fabrication of low-crystalline calcite block

We have reported that low-crystalline porous calcite block, which is useful as a bone substitute or a source material to prepare apatite-type bone fillers could be fabricated by exposing calcium hydroxide compact to carbon dioxide gas saturated with water vapor. In the present study, we investigated the effect of molding pressure on the transformation of calcium hydroxide into calcite and the mechanical strength of the carbonated compact. Transformation into calcite was almost completed within 72 h, however, a small amount of Ca(OH)₂ still remained unreacted at higher molding pressure because of incomplete penetration of CO₂ gas into the interparticle space due to dense packing of Ca(OH)₂ particles. On the other hand, high molding pressure resulted in an increase in diametral tensile strength (DTS) of the calcite compact formed. Critical porosity of the calcite block was calculated as approximately 68%.