8. Brightness and whiteness of kaolin

8. Brightness and whiteness of kaolin

Whiteness is one of the main parameters of technological properties of kaolin, and high purity kaolin is white. The whiteness of kaolin can be divided into natural whiteness and calcined whiteness. For ceramic raw materials, the whiteness after calcination is more important, and the higher the whiteness, the better the quality. Ceramic technology stipulates that drying at 105 is the grading standard of natural whiteness and calcining at 1300 is the grading standard of calcined whiteness. The whiteness can be measured by a whiteness meter. The whiteness meter is a device for measuring the reflectivity of wavelength light from 3800 to 7000 & Aring (i.e. E, 1 E = 0.1 nanometer). In the whiteness meter, the reflectivity of the sample to be measured is compared with that of the standard sample (such as BaSO4, MgO, etc.), that is, the whiteness value (such as whiteness 90, which means 90% of the reflectivity of the standard sample).

Brightness is a technological property similar to whiteness, equivalent to 4570-Aring; (E) whiteness under wavelength light.

The color of kaolin is mainly related to its metal oxides or organic matter. Generally, Fe2O3 is rosy red and brown yellow; Fe2 + is pale blue and green; MnO2 is pale brown; organic matter is pale yellow, gray, green and black. The presence of these impurities reduces the natural whiteness of kaolin, in which iron and titanium minerals also affect the calcined whiteness, resulting in stains or melting scars on porcelain.