Fabrication of calcite blocks from gypsum blocks by compositional transformation based on dissolution-precipitation reactions in sodium carbonate solution.

Calcium carbonate (CaCO ₃ ) has been used as a bone substitute, and is a precursor for carbonate apatite, which is also a promising bone substitute. However, limited studies have been reported on the fabrication of artificial calcite blocks. In the present study, cylindrical calcite blocks (ϕ6×3mm) were fabricated by compositional transformation based on dissolution-precipitation reactions using different calcium sulfate blocks as a precursor. In the dissolution-precipitation reactions, both CaSO ₄ ·2H ₂ O and CaSO ₄ transformed into calcite, a polymorph of CaCO ₃ , while maintaining their macroscopic structure when immersed in 1mol/L Na ₂ CO ₃ solution at 80°C for 1week. The diametral tensile strengths of the calcite blocks formed using CaSO ₄ ·2H ₂ O and CaSO ₄ were 1.0±0.3 and 2.3±0.7MPa, respectively. The fabrication of calcite blocks using CaSO ₄ ·2H ₂ O and CaSO ₄ proposed in this investigation may be a useful method to produce calcite blocks because of the self-setting ability and high temperature stability of gypsum precursors.
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