Zinc Phosphate (CAS: 7779-90-0)

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Zinc phosphate (Zn3(PO4)2) is an inorganic chemical compound used as

a corrosion resistant coating on metal surfaces either as part of anelectroplating

process or applied as a primer pigment (see also red lead). Zinc phosphate coats

better on a crystalline structure than bare metal, so a seeding agent is often used

as a pre-treatment. One common agent is sodium pyrophosphate.

Natural forms of zinc phosphate include minerals hopeite and parahopeite,

Zn3(PO4)2•4H2O. A somewhat similar mineral is natural hydrous zinc phosphate

called tarbuttite, Zn2(PO4)(OH). Both are known from oxidation zones of Zn ore

beds and were formed through oxidation of sphalerite by the presence of phosphate-rich

solutions. The anhydrous form has not yet been found naturally.

Zinc phosphate is formed from zinc phosphate cement and used in dentistry. Zinc phosphate

dental cement is one of the oldest and widely used cements, and is commonly used for luting

permanent metal restorations and as a base for dental restorations. Zinc phosphate cement is

used for cementation ofinlays, crowns, bridges, and orthodontic appliances and occasionally

as a temporary restoration. It is prepared by mixing zinc oxide and magnesium oxidepowders

with a liquid consisting principally of phosphoric acid, water, and buffers. It is the standard

cement to measure against. It has the longest track record of use in dentistry. It is still commonly

used; however, resin-modified glass ionomer cements are more convenient and stronger

when used in a dental setting.