Zinc Oxide

	Zinc Oxide
	Color Index	Pigment White 4  CI 77947
	Formula	ZnO

Structure

Zinc oxide has a nodular powder form.
It is cristallizing in an hexagonal system that has empty spaces due to the big difference in size between zinc and oxygen atoms. This structure induces semi-conductor properties.

Properties

Zinc oxide is an amphoteric oxide. By its basic character, it can react with acids contained in binders.
In a binder with a low acid index, zinc oxide is producing zinc soaps which improve the wet out of the pigment and make the dispersion easier. They also little improve the viscosity of the paint and reduce the sedimentation.
In a binder with a high acid index, it can cause severe thickening in the can.

Properties of zinc oxide
Property	Zinc Oxide
Refractive Index	2.03
Density	5.67
Surface Area	3-11 m2/g
Oil Absorption	12-20
Heat Stability	excellent
Light fastness and Weatherability	excellent

Hiding power

Zinc oxide has a weaker hiding power than Lithopone and Titanium Dioxide.

Whiteness

ZnO can have a good white color when it has a high purity (> 99.5%). It has a yellower color when it is containing lead or cadmium impurities. It has a grayer color when it is containing zinc metal or mineral traces.

Uses

It was widely used before the introduction of titanium dioxide, but its use has now declined. It can be used as additional pigment with TiO2 to improve chalking resitance, or with lithopone. It is not very interesting as a white pigment, but it can be used as UV absorber, curing agent or fungicide.

Storage

Zinc oxide can react with humidity in the air and carbon dioxide: a carbonated white is obtained that contains agglomerates. These agglomerates disperse badly.