Лако-красочные материалы — производство

Micaceous iron oxide consists of pure or doped hematite (a-Fe2O3). Its density is 4.6-4.8 g/cm3. Micaceous iron oxide can also be obtained by hydrothermal synthe­sis in alkaline media. However, the dull dark color is as unappealing as that of the natural product. If substantial amounts of dopants are incorporated, the aspect ratio can be increased up to 100, resulting in a much increased luster. The color can be also shifted to a more attractive reddish brown so that the products can be used for decorative purposes [1, 11].

The most important dopants are Al2O3, SiO2, and Mn2O3. These can enforce a spinel structure. SiO2 yields thin small platelets, Al2O3 yields thin larger platelets, and Mn2O3 reduces the thickness.

The starting material Fe(OH)3 or better FeOOH is heated in an alkaline suspen­sion together with the dopants to temperatures above 170 °C, typically 250-300 °C. After several minutes to hours, platelets of doped iron oxide are obtained. In a second reaction phase, the pH is further increased so that platelets grow and form flat basal faces.