Chemistry:Potassium tetrafluoroborate
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| Names | |
|---|---|
| IUPAC name
Potassium tetrafluoroborate
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Other names
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| Identifiers | |
3D model (JSmol)
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| ChEMBL | |
| ChemSpider | |
| EC Number |
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PubChem CID
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| RTECS number |
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| UNII | |
| UN number | 3260 |
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| Properties[2] | |
| KBF 4 | |
| 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)[5] |
| Boiling point | decomposes |
| Solubility in ethanol | slightly soluble |
| Band gap | 7.94 eV[3] |
Refractive index (nD)
|
1.3245[4] |
| Structure[3] | |
| Orthorhombic | |
| Pnma | |
| mmm | |
a = 5.36 Å, b = 6.94 Å, c = 8.53 Å α = 90°, β = 90°, γ = 90°
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Lattice volume (V)
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317.63 Å3 |
Formula units (Z)
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4 |
| Thermochemistry[2] | |
Enthalpy of fusion (ΔfH⦵fus)
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17.66 kJ⋅mol−1 |
| Hazards | |
| GHS pictograms | 
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| GHS Signal word | Danger |
| H314, H315, H319, H335 | |
| P260, P264, P280, P301+330+331, P303+361+353, P304+340, P305+351+338, P310, P363, P501 | |
| NFPA 704 (fire diamond) | |
Threshold limit value (TLV)
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2.5 mg/m3[5] (TWA) |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose)
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5854 mg/kg (rat, oral) |
LC50 (median concentration)
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>5300 mg/m3 (rat, inhalation, 4h) |
| NIOSH (US health exposure limits):[5] | |
PEL (Permissible)
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2.5 mg/m3 (TWA) |
REL (Recommended)
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2.5 mg/m3 (TWA) |
IDLH (Immediate danger)
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250 mg/m3 |
| Related compounds | |
Other anions
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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). | |
| Infobox references | |
Potassium tetrafluoroborate is an inorganic compound with the formula KBF
4. It is a colorless, odorless crystalline powder, and crystallizes into orthorhombic space group Pnma.[3]
Preparation
Potassium fluoroborate is obtained by adding a solution of potassium hydroxide (KOH) to a cold solution of boric acid (H
3BO
3) in 40% hydrofluoric acid (HF) in a platinum dish:[1]
- H
3BO
3 + 4 HF + KOH → KBF
4 + 4 H
2O
Reactions
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 BCl
3 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 (BF
3) by heating the molten salt with boron trioxide (B
2O
3) 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:
- KBF
4 + 2 B
2O
3 → BF
3 + KF · B
4O
6
The collected impure BF
3 is purified via fractional distillation.[1]: 219–220
Uses
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
- ↑ 1.0 1.1 1.2 1.3 Kwasnik, W. (1963). "4. Fluorine Compounds - Potassium Fluoroborate". Handbook of Preparative Inorganic Chemistry. 1 (2 ed.). New York, NY: Academic Press. p. 223. https://archive.org/details/Handbook_of_Preparative_Inorganic_Chemistry_1_2_Brauer/page/n247/mode/1up.
- ↑ 2.0 2.1 2.2 Template:RubberBible97th
- ↑ 3.0 3.1 3.2 "Materials Data on KBF4 by Materials Project". United States: Materials Project. 17 July 2020. doi:10.17188/1208492. https://next-gen.materialsproject.org/materials/mp-4929.
- ↑ 4.0 4.1 "Potassium tetrafluoroborate, 99%". ThermoFisher Scientific. https://www.fishersci.com/shop/products/potassium-tetrafluoroborate-99-min-typically-99-5-thermo-scientific/AA1155636.
- ↑ 5.0 5.1 5.2 5.3 "SDS - Potassium tetrafluoroborate". ThermoFisher Scientific. 21 December 2025. https://documents.thermofisher.com/DirectWebViewer/private/document.aspx?prd=ALFAA11556~~PDF~~MTR~~AGHS~~EN~~2025-12-21%2022:51:02~~Potassium%20tetrafluoroborate~~.
- ↑ 6.0 6.1 Danek, V.; Votava, I.; Matiasovsky, K. (1976). "Reactions of potassium tetrafluoroborate in molten alkali chlorides". Chem. Zvesti 30 (3): 377–383. https://www.chemicalpapers.com/file_access.php?file=303a377.pdf. Retrieved 29 July 2025.
- ↑ "How Potassium Tetrafluoroborate (KBF4) Powers the Electronics Industry: Key Principles and Advantages - Foshan Nanhai Shuangfu Chemical Co., Ltd". FSSF. 25 October 2024. https://www.df-chemicals.com/news/potassium-tetrafluoroborate-kbf4-electronics-industry-advantages.
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