Лако-красочные материалы — производство

Crystal growth of ZnS can be achieved by using a hydrothermal process instead of by calcination. The raw lithopone is precipitated with a slight excess of sulfide at pH 8.5. The pH is then adjusted to 12-13 with sodium hydroxide solution, and 0.5% sodium carbonate is added. The suspension is then autoclaved for ca. 15­20 min at 250-300 °C. In contrast to the wurtzite structure of the calcined product,

the hydrothermal product has a sphalerite structure with a ca. 10% greater scattering power. Although the product is of better quality, the hydrothermal process is less economic due to the high cost of the materials required for lining the autoclave (e. g., tantalum or a zirconium alloy).

2.2.2.5