Potassium tetrafluoroborate

Chemical Properties

It appears as white powder or gelatinous crystals. It has hygroscopicity with bitter taste. It is slightly soluble in water and hot ethanol, insoluble in cold ethanol.

Application

• Used as the abrasive material of the thermosetting resin grinding wheel, the raw material of boron alloy, the fluxing agent of heat welding and brazing; it can also be used as the components of low chromic anhydride chrome and lead-tin alloy electrolyte.
• Used as analytical reagents and fluxes, also for the production of boron trifluoride, abrasive materials for the aluminum and magnesium casting, electrochemical engineering and chemical testing.
• Used as the fluxing agent of heat flux and brazing, and the raw material for the production of boron alloy using aluminum and magnesium casting; it acts as the filler in the heavy wheel using resin as abrasive adhesive. In the welding and fusion of silver, gold, stainless steel, it can clean up the dross of light metal. It is a raw material for the manufacture of boron trifluoride and other fluorine salts. Also used in electrochemical processes and reagents.
• Used as fluxing agent; also used for the metallurgical industry and for the preparation of boron trifluoride as well as the raw materials of other fluorine salt.
• Used as the resin finishing agents for textile printing and dyeing, improving agent of metal particle size and refining fluxes and the casting sand granules of the aluminum and magnesium alloy.

Preparative Methods

Fluoroboric acid-potassium hydroxide method:
Hydrofluoric acid and boric acid are sent into the reactor at a ratio of 25: 6.2 (weight ratio); the temperature does not exceed 40 ℃. The reaction continues for 6h. The prepared fluoroboric acid is fed to a neutralization tank and neutralized with a 5 mol/L potassium hydroxide under stirring and cooling (until the methyl orange is discolored). Precipitated potassium fluoroborate crystal is subject to centrifugal separation, washing and drying, obtaining the finished product of potassium fluoroborate. its
4HF + H3BO3 → HBF4 + 3H2O
HBF4 + KOH → KBF4 + H2O
Fluoroboric acid/potassium carbonate neutralization method: under the stirring of the coating container, apply the saturated potassium carbonate solution for neutralizing fluoroboric acid to until the methyl orange is discolored. The precipitated potassium fluoroborate is subject to centrifugal separation, washing and drying, obtaining the finished product of potassium fluoroborate. Its reaction is:
2HBF4 + K2CO3 → 2KBF4 + H2O + CO2 ↑

Chemical Properties

KBF4 is white odourlesss crystalline powder

Uses

Potassium tetrafluoroborate (KBF4) is used as an active filler in the preparation of resin-bonded abrasives. It is also used for extraction, refining and processing of metals in the chemical industry. It finds application as additive in alloying industry and welding agent. Further, it is used in the production of fluxing agents for brazing and soldering.

Uses

Has been proposed as a flux for soldering and brazing; filler in resin-bonded grinding wheels.

Hazard

Toxic by ingestion.

Flammability and Explosibility

Not classified

Battery Materials

Researchers demonstrate that potassium tetrafluoroborate (KBF4), a simple and inexpensive inorganic salt, functions as an effective fluoride activity modulator in tetraglyme-based electrolytes. It enables effective fluoride-ion transport by regulating fluoride activity rather than maximizing complexation^[1].

Safety Profile

Poison by intraperitoneal route. When heated to decomposition it emits very toxic fumes of F, K2O, and BOx. Used in sand casting of aluminum and magnesium, grinding, and in resinoid grindmg wheels. See also FLUORIDES and BORON COMPOUNDS.

Purification Methods

Crystallise it from H2O (solubility% (temperature): 0.3 (3o), 0.45 (20o), 1.4 (40o), 6.27 (100o), and dry it under vacuum. It is a non-hygroscopic salt. A 10% solution is transparent blue at 100o, green at 90o and yellow at 60o. [V.rlander et al. Chem Ber 65 535 1932, Kwasnik in Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol I p 223 1963.]

References

[1] Tabtimtong, N., Kaisook, P., Imai, Y., Ueda, T., Nakamoto, K., Segawa, Y., Neramittagapong, A., Neramittagapong, S., & Minato, T. (2026). Facilitated fluorination by potassium tetrafluoroborate in tetraglyme electrolytes for fluoride shuttle batteries. ACS Applied Energy Materials, 9(7), 3690–3696. https://doi.org/10.1021/acsaem.5c04132