Potassium tetrafluoroborate
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| Names | |
|---|---|
| IUPAC name
Potassium tetrafluoroborate | |
Other names
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| Identifiers | |
3D model (JSmol) |
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| ChEMBL | |
| ChemSpider | |
| ECHA InfoCard | 100.034.466 |
| EC Number |
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PubChem CID |
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| RTECS number |
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| UNII | |
| UN number | 3260 |
CompTox Dashboard (EPA) |
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| Properties[1] | |
| KBF4 | |
| Molar mass | 125.90 g·mol−1 |
| Appearance | colorless orthorhombic crystals |
| Odor | odorless |
| Density | 2.505 g/cm3 (20 °C (68 °F)) |
| Melting point | 530 °C (986 °F; 803 K)[2] |
| Boiling point | decomposes |
| Solubility in ethanol | slightly soluble |
| Band gap | 7.94 eV[4] |
Refractive index (nD) |
1.3245[5] |
| Structure[4] | |
| Orthorhombic | |
| Pnma | |
| mmm | |
a = 5.36 Å, b = 6.94 Å, c = 8.53 Å α = 90°, β = 90°, γ = 90° | |
Lattice volume (V) |
317.63 Å3 |
Formula units (Z) |
4 |
| Thermochemistry[1] | |
Enthalpy of fusion (ΔfH⦵fus) |
17.66 kJ⋅mol−1 |
| Hazards | |
| GHS labelling:[5] | |
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| Danger | |
| H314, H315, H319, H335 | |
| P260, P264, P280, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P363, P501 | |
| NFPA 704 (fire diamond) | |
Threshold limit value (TLV) |
2.5 mg/m3[2] (TWA) |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose) |
5854 mg/kg (rat, oral) |
LC50 (median concentration) |
>5300 mg/m3 (rat, inhalation, 4h) |
| NIOSH (US health exposure limits):[2] | |
PEL (Permissible) |
2.5 mg/m3 (TWA) |
REL (Recommended) |
2.5 mg/m3 (TWA) |
IDLH (Immediate danger) |
250 mg/m3 |
| Related compounds | |
Other anions |
Potassium tetrahydroborate |
Other cations |
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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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Potassium tetrafluoroborate is an inorganic compound with the formula KBF4. It is a colorless, odorless crystalline powder, and crystallizes into orthorhombic space group Pnma.[4]
Preparation
[edit]Potassium fluoroborate is obtained by adding a solution of potassium hydroxide (KOH) to a cold solution of boric acid (H3BO3) in 40% hydrofluoric acid (HF) in a platinum dish:[3]
- H3BO3 + 4 HF + KOH → KBF4 + 4 H2O
Reactions
[edit]Potassium tetrafluoroborate has been reacted with molten lithium chloride (LiCl), sodium chloride (NaCl), and potassium chloride (KCl).[6] Lithium ions cause the decomposition of tetrafluoroborate leading to the production of BCl3 gas. The other liquid alkali chlorides do not decompose the tetrafluoroborate, even though they are at higher temperatures.[6]
It may be used to produce boron trifluoride (BF3) by heating the molten salt with boron trioxide (B2O3) at 600 °C (1,112 °F) in an iron tube connected to a drying tube filled with dry potassium fluoride (KF) followed by a liquid nitrogen cooled trap:
- KBF4 + 2 B2O3 → BF3 + KF·B4O6
The collected impure BF3 is purified via fractional distillation.[3]: 219–220
Uses
[edit]Potassium tetrafluoroborate is used in p-type semiconductor doping to introduce boron into the silicon lattice in an easily controlled way. It is also used in etching solutions for silicon wafers and as a soldering flux in high temperature soldering.[7]
References
[edit]- 1 2 3 Haynes, William M., ed. (2016). CRC Handbook of Chemistry and Physics (97th ed.). Boca Raton, Florida: CRC Press. pp. 4–80, 6–160. ISBN 9781498754293.
- 1 2 3 4 "SDS - Potassium tetrafluoroborate". documents.thermofisher.com. Revision Number 4. ThermoFisher Scientific. 21 December 2025 [15 December 2011]. Retrieved 31 May 2026.
- 1 2 3 4 Kwasnik, W. (1963). "4. Fluorine Compounds - Potassium Fluoroborate". In Brauer, Georg (ed.). Handbook of Preparative Inorganic Chemistry. Vol. 1. Translated by Riley, Reed F. (2 ed.). New York, NY: Academic Press. p. 223.
- 1 2 3 "Materials Data on KBF4 by Materials Project". next-gen.materialsproject.org. United States: Materials Project. 17 July 2020. doi:10.17188/1208492. OSTI 1208492. DOE Contract AC02-05CH11231, mp-4929. Retrieved 31 May 2026.
- 1 2 "Potassium tetrafluoroborate, 99%". www.fishersci.com. ThermoFisher Scientific. Retrieved 31 May 2026.
- 1 2 Danek, V.; Votava, I.; Matiasovsky, K. (1976). "Reactions of potassium tetrafluoroborate in molten alkali chlorides" (PDF). Chem. Zvesti. 30 (3): 377–383. Retrieved 29 July 2025.
- ↑ "How Potassium Tetrafluoroborate (KBF4) Powers the Electronics Industry: Key Principles and Advantages - Foshan Nanhai Shuangfu Chemical Co., Ltd". www.df-chemicals.com. FSSF. 25 October 2024. Retrieved 31 May 2026.