Zirconium silicate - White Pigment Zirconite Zircon Hyacinth Zircosil Excelopax

ZrSiO₄ 

Zirconium silicate, also zirconium orthosilicate, ZrSiO4, is a chemical compound, a silicate of zirconium. It occurs in nature as zircon, a silicate mineral. Powdered zirconium silicate is also known as zircon flour. Zirconium silicate is usually colorless, but impurities induce various colorations. It is insoluble in water, acids, alkali and aqua regia. Hardness is 7.5 on the Mohs scale.

Application

The major applications exploit its refractory nature and resistance to corrosion by alkali materials. Two end-uses are for enamels, and ceramic glazes. In enamels and glazes it serves as an opacifier. It can be also present in some cements. Another use of zirconium silicate is as beads for milling and grinding. Thin films of zirconium silicate and hafnium silicate produced by chemical vapor deposition, most often MOCVD, can be used as a high-k dielectric as a replacement for silicon dioxide in semiconductors.

Zirconium silicates have also been studied for potential use in medical applications. For example, ZS-9 is a zirconium silicate that was designed specifically to trap potassium ions over other ions throughout the gastrointestinal tract.

Uses in Pottery

Zircon is normally used in glazes for opacification (converting a transparent glaze to an opaque). The silicate form or zirconium does not matte glazes (like pure zirconium oxide, actually, zirconium dioxide, does). The exact amount needed varies between different glaze types. 10-12% is normal, but up to 20% may be required to opacify some transparent glazes. When the saturation point is achieved crystallization begins to occur. It is most effective at low temperatures. Tin oxide can be a more effective opacifier than zircon (it has various advantages and disadvantages). As a glaze opacifier the white color produced by zirconium silicate is often characterized as 'toilet bowl white'. Tin oxide, by contrast, can produce more of a blue-white, but tin is subject to alteration of the color (toward pink) if there is any chrome in the kiln atmosphere. If the shade of white is too harsh, it can be toned by shifting part of the opacification burden to tin or by adding a tiny amount of stain (e.g. blue, brown, grey). The low expansion or zircon will tend to reduce crazing in glazes. In a non-crazed glaze, the presence of sufficient zircon can reduce thermal expansion enough that there is a danger of shivering (the glaze formulation may need to be adjusted to accommodate, e.g. more Zircon lowers glaze thermal expansion). It is best to exclude the chemistry of the zircon materials from participation in glaze chemistry calculations, treating it simply as an addition (then take into consideration its effect on glaze properties on a physical rather than chemical level).

More about Zirconium silicate in Wikipedia 

Formula: ZrSiO₄

Molar mass: 183.305 g/mol
Form: Colourless crystals
CAS Number: 10101-52-7
Density: 4.56 g/cm³
Synonyms: Zirconium(IV) silicate, Zirconite, Zircon, Silicic acid, zirconium(4+) salt, Hyacinth, Zircosil 15, Excelopax, Zircosil, Micro-Pax, Oscal 1224, Tam 418