Hydrothermal growth of calcite single crystal in NH 4Cl solution

Abstract

Calcite (CaCO 3) single crystals were grown from a solution mixture of NH 4Cl and CH 3COOH. The spontaneous crystallization was observed to predominate over the growth on the seed even with a temperature gradient of 1°C in a sole NH 4Cl solution. However, the growth of crystals from a solution mixture of NH 4Cl and CH 3COOH at the temperature gradient below 6°C resulted in high-quality calcite crystals without any spontaneous crystallization. When the temperature gradient exceeded the critical temperature gradient (6°C) by a few degrees, spontaneous crystallization occurred even in the above mixed solution. Adding CH 3COOH and controlling the temperature gradient precisely is thought to be most important for the hydrothermal growth of calcite without spontaneous crystallization in the NH 4Cl solution.