OrthoPlumbate, calcium

Etch primers are widely used. They are mostly based on polyvinyl butyral and contain chromates and phosphoric acid. They are said to act both as primers and as etching solutions because it is believed that the chromates and phosphoric acid form an inorganic him, which provides adhesion, while oxidised polyvinyl butyral provides an organic him. For direct application to new galvanised steel, the best known primers are based on calcium orthoplumbate pigment and metallic lead, but these are now less used for environmental reasons. Zinc-dust paints and zinc-phosphate pigmented paints are also used, but the trend is to use pretreatments to assure good adhesion. 

Precooked tung oil-alkylphenolic resin combinations, chilled with drying oil modified alkyd resins. Dehydrated castor oil (DCO)-modified alkyd resin, pigmented with calcium orthoplumbate (COP) as main pigment in the priming coat. 

Pigments such as calcium orthoplumbate will oxidize the zinc surface and also form calcareous deposits with good bond properties at the interface. A similar but weaker effect has been observed by Van Eijnsbergen when primers containing red lead, zinc chromate, and basic lead sulfate are applied to zinc surfaces. 

The metaplumbates of strontium and bariiun M"Pb03 are made by fusion of strontium or barium nitrates with lead(II) oxides. The oxides of nitrogen released convert the lead(II) to lead(IV). Calcium orthoplumbate Ca2Pb04 is formed when calcium nitrate and lead(II) oxide are fused in the stoichiometry Ca(N03)2.Pb0. The barium and strontium orthoplumbates are prepared by heating barium or strontium carbonates with lead(II) oxide in the stoichiometry [MC03]2.PbO the necessary oxidation is caused by the atmo-sphere o. 

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