Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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.
Zinc borate is primarily used as a flame retardant in plastics and cellulose fibers, paper, rubbers and textiles. It is also used in paints, adhesives, and pigments. 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.
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- "Zinc Borate (Boric Acid, Zinc Salt)". Chemical Land21. Retrieved 6 February 2010.
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- Zinc borate in the Pesticide Properties DataBase (PPDB)