White Pigments

The oldest and formerly most important of the white pigments is white lead, which is so longer permitted as a consistent of most points. Zinc oxide, another white pigment formerly widely used, is now of only minor importance.

The kind of white pigments such as follows:
  • Titanium Dioxide
  • Zinc Oxide
  • Lithophone
  • Zinc sulphide
  • Antimony oxide
Lithophone is a mixed zinc sulphide, barium sulphate pigment that contains about 30% zinc sulphide. The original light sensitiveness has been overcome by raw material purification and by addition of such agents as polythionates and cobalt sulphate. Lithophone is a brilliantly white, extremely fine, cheap, white pigment. It is particularly well adapted to interior coating.

The manufacture of this substance, barium, zinc and lithopone circuits are represented by different types of lines. The barium sulphide solution is prepared by reducing barite are (BaSO4) with carbon and leaching the resulting mass. The equation is:

BaSO4 + 4C ──→ BaS + 4 CO

Scrap zinc or concentrated zinc ores are dissolved in sulphuric acid, and the solution purified. The two solution are reacted, and a heavy mixed precipitate results which is 28 to 30% zinc sulphide and 72% barium sulphate.

ZnSO4 + BaS ──→ ZnS + BaSO4

This precipitate is not suitable for a pigment until it is filtered, dried, crushed, heated to a high temperature, and quenched in cold water. The second heating in a muffle furnace at 725oC produce crystals of the right optical size.

Lithopone are used in water based paints because of their excellent alkali resistance. They are also used as a whitener and reinforcing agent for rubber and as filler and whitener for paper.


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