In recent years, researchers from many countries work on the synthesis, characterization and properties of various kinds of willemite ceramic pigments prepared from both natural and waste materials. Willemite is a mineral – zinc silicate (2ZnО.SiO2). It was discovered in the form of small brown crystals and it was named in 1830 after the King of Holland Willem I (Willem Frederik). Willemite can be green, yellow, brown, red-brown, orange, blue colored. It can be found in nature as prismatic translucent and small needle crystals. It is one of the not many silicates with orthogonal syngony which is more characteristic for the carbonates.
The ceramic pigments with structures of willemite 2ZnО.SiO2 and phenakite 2ВеО.SiO2 which crystalize in the trigonal syngony have been known for a long time. Such is the widely used cobalt silicate 2СoO.SiO2 with fine blue color. The color palette of willemite pigments today is quite large. If zinc oxide is substituted with nickel oxide, blue pigments can be obtained which successfully compete with the more expensive cobalt pigments. The introduction of FeO results in yellow and brown pigments and МnО – pink, purple and grey. Attempts were made to substitute not only ZnО but also SiO2 with other acidic oxides like SnO2, TiO2, ZrO2.
1. Technology of Ceramic Products and Materials, ISBN: 9549841154, Publisher: Saraswati, 2003, edited by Prof. Bachvarov
Pigment’s synthesis scheme by sol-gel method