Zinc borate
Chemical compound
From Wikipedia, the free encyclopedia
Zinc borate refers to a family of inorganic compounds consisting of borate of zinc. They are white solids with the formulas:
- ZnO·B2O3·1.12H2O
- ZnO·B2O3·~ 2H2O
- ZnO·5B2O3·4.5H2O
- 2ZnO·3B2O3·3H2O
- 2ZnO·3B2O3·7H2O
- 3ZnO·5B2O3·14H2O
- 4ZnO·B2O3·H2O
- 6ZnO·5B2O3·3H2O
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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They are coordination polymers consisting of zinc(II) centers bonded to cyclic boron oxide rings.[1]
Variants
Several variants of zinc borate exist, differing by the zinc/boron ratio and the water content:[2]
- Zinc borate Firebrake ZB (2ZnO·3B2O3·3.5H2O), CAS number 138265-88-0
- Zinc borate Firebrake 500 (2ZnO3·3B2O3), 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 (554–779 °F).
Uses
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.[3] 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.[4]
Zinc borate is used in polyvinyl chloride, polyolefins, polyamides, epoxy resins, polyesters, thermoplastic elastomers, rubbers, etc. It is also used in some intumescent systems.[5]
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.[6]
Zinc borate can be used as a flux in some ceramics. In electrical insulators it improves the ceramics properties.