Zinc borate

 ( Borate ) 

Zinc borate refers to a family of inorganic compounds consisting of borate of zinc. They are white solids with the formulas 4ZnO·B₂O₃·H₂O, ZnO·B₂O₃·1.12H₂O, ZnO·B₂O₃·~2H₂O, 6ZnO·5B₂O₃·3H₂O, 2ZnO·3B₂O₃·7H₂O, 2ZnO·3B₂O₃·3H₂O, 3ZnO·5B₂O₃·14H₂O, and ZnO·5B₂O₃·4.5H₂O. They are coordination polymers consisting of zinc(II) centers bonded to cyclic boron oxide rings.

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Variants Several variants of zinc borate exist, differing by the zinc/boron ratio and the water content:

• Zinc borate Firebrake ZB (2ZnO·3 B₂O₃·3.5H₂O), CAS number 138265-88-0
• Zinc borate Firebrake 500 (2ZnO·3 B₂O₃), CAS number 12767-90-7
• Zinc borate Firebrake 415 (4ZnO·B₂O₃·H₂O), CAS number 149749-62-2
• ZB-467 (4ZnO·6B₂O₃·7H₂O), CAS number 1332-07-6
• ZB-223 (2ZnO·2B₂O₃·3H₂O), CAS number 1332-07-6

The hydrated variants lose water between 290–415 °C.

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Uses Zinc borate is primarily used as a flame retardant in and , paper, and . It is also used in , , and . As a flame retardant, it can replace antimony(III) oxide as a synergist in both halogen-based and halogen-free systems. It is an anti-dripping and char-promoting agent, and suppresses the afterglow. In electrical insulator plastics it suppresses arcing and tracking.

In halogen-containing systems, zinc borate is used together with antimony trioxide and alumina trihydrate. It catalyzes formation of char and creates a protective layer of glass. Zinc catalyzes the release of halogens by forming zinc halides and zinc oxyhalides.

In halogen-free system, zinc borate can be used together with alumina trihydrate, magnesium hydroxide, red phosphorus, or ammonium polyphosphate. During burning the plastics, a porous borate ceramics is formed that protects the underlying layers. In presence of silica, borosilicate glass can be formed at plastic burning temperatures.

Zinc borate is used in polyvinyl chloride, , polyamides, epoxy resins, , thermoplastic , , etc. It is also used in some intumescent systems.

Zinc borate has synergistic effect with zinc phosphate or barium borate as a corrosion inhibitor pigment.

Zinc borate acts as a broad-spectrum fungicide in plastics and wood products.

Zinc borate can be used as a flux in some . In electrical insulators it improves the ceramics properties.

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