Crystals and their manufacture

摘要

In a hydrothermal process for manufacturing crystals of metal carbonates, including single crystals of lead carbonate of the cerussite crystalline form, the nutrient material consists of a carbonate or basic carbonate of the said metal, the solvent medium consists of a 0.5 to 5.0 molar aqueous solution of an alkali metal bicarbonate, and the heating is carried out in an autoclave under controlled temperature conditions such that the exterior of the autoclave wall adjacent to the nutrient and the solvent medium in the vicinity thereof is maintained at 200 DEG C to 400 DEG C, and that the exterior of the autoclave wall adjacent to the region of the solvent medium remote from the nutrient is maintained at 170 DEG C to 315 DEG C and at a temperature from 5 DEG C to 150 DEG C lower than that of the exterior of the autoclave wall adjacent to the nutrient: a temperature gradient is thus produced in the solvent medium and crystalline metal carbonate is deposited in a region remote from the nutrient, as small crystals on the autoclave wall or as crystal growth on seeds.