Borosilicate Pigments

Borosilicate pigments [59794-15-19] usually contain calcium or zinc ions in a matrix of silicon dioxide and boron trioxide, x (Ca,Zn)-y Si04 zB03. Aqueous slurries of this white pigment are alkaline (pH 9). Borosilicate pigments are 

A trade name for calcium borosilicate is Halox CW 291, -2230 (Halox Pigments, USA). 

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Calcium bentonites, 6 664—666, 696 Calcium borosilicate, allowed pigment in... 

Inorganic Cl are commonly used as a functional component of inhibited polymer coatings (see Chap. 3), and less often as inhibited films (sodium nitrate, protecting metal pigments, sodium-borosilicate layers of films). 

Chem. Descrip. Borosilicate-based pigments Uses Pigment tor coatings, plastics, automotive trim, powd. coatings, leather coatings, food pkg. 

More generally, acidic depolymerization products can be leached out of many films of paint, unless suitable pigments are incorporated. Zinc dust plus zinc oxide was the original acid scavenger. Zinc phosphate, zinc ferrite, and calcium borosilicate will each exert an anodic inhibitive function at pH values exceeding 7 while zinc chromate, zinc tetroxychromate, and strontium chromate act independently of pH value (Van Eijnsbergen, 1988). In general, the pH of aqueous paint film extracts should be between 7.5 and 8.5 and certainly not below 6 or above 10. 

Calcium borosilicate is a compiex composite of calcium siiicate avaiiabie commercially in grades differing in borate content and oii absorption value. Its anticorrosive properties are derived from the aikaiinity of the pigment as weii as anodic and cathodic passivation. 

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