Potassium Tetrafluoroborate KBF₄

Potassium tetrafluoroborate, with the chemical formula KBF₄ and a molecular weight of 125.90, is also known as potassium tetrafluoroborate or potassium fluoroborate. It is a white crystalline powder or gel-like solid, odorless, non-hygroscopic, and belongs to the orthorhombic crystal system. Its density is approximately 2.50 g/cm³, and its melting point is approximately 530℃ (melts before decomposition). It is slightly soluble in water (solubility at 20℃ is approximately 4.4 g/L), slightly soluble in hot ethanol, and almost insoluble in cold ethanol and most organic solvents.

• It has good high-temperature stability, starting to decompose above 530℃, releasing BF₃ and KF.
• It has strong oxidizing and fluorinating capabilities, but its chemical properties are relatively stable at room temperature.
• Its aqueous solution is weakly acidic and will slowly hydrolyze to produce boric acid and hydrofluoric acid.
• It is a moderately toxic compound; precautions should be taken to prevent dust inhalation and prolonged skin contact.

First, hydrofluoric acid and boric acid are slowly reacted at low temperature (<40℃) to produce a solution of fluoroboric acid (HBF₄):

Then, it is neutralized with potassium hydroxide (or potassium carbonate) to a pH of approximately 7, precipitating KBF₄:

The product is obtained by filtration, washing, and drying. The product quality is high, but hydrofluoric acid is highly corrosive, requiring high-quality equipment.

• First, ammonium fluoride solution is obtained by decomposing fluorosilicic acid with ammonia water.
• Potassium borate solution is prepared by adding boric acid to potassium hydroxide solution.
• The two solutions are mixed, heated, and concentrated to precipitate KBF₄ crystals.

Advantages: Low raw material cost, waste utilization, and the byproduct ammonia water can be recycled.

Industrial waste acid containing hydrofluoric acid or fluorine-containing wastewater is directly reacted with boric acid, followed by pH adjustment with alkali (NaOH/KOH), and then KBF₄ is separated by extraction or crystallization.

In recent years, driven by environmental protection concerns, such as processes have become increasingly common.

Industrial product purity is typically 98%~99.5%, while high-end electronic grade can reach over 99.9%.

• Aluminum-Magnesium Alloy Refining and Grain Refinement (Largest Consumption Area)

  Used as an aluminum melt refining agent and grain refiner, significantly improving the grain structure of aluminum and aluminum-magnesium alloy castings and enhancing mechanical properties.

  Often added in the form of an aluminum-boron intermediate alloy.

• Welding and Brazing Flux

  A high-quality flux component for hot welding, copper welding, silver welding, and brazing, especially suitable for welding stainless steel, titanium alloys, and refractory metals.

  It can effectively remove oxide films and reduce slag viscosity.

• Abrasives and Resin Grinding Wheels

  Used as an active filler in heavy-duty thermosetting resin grinding wheels to improve grinding efficiency, heat resistance, and service life.

• Metallurgy and Electrochemistry

  Additives in aluminum electrolysis and magnesium electrolysis processes.

  A component of low-chromium plating solutions and lead-tin alloy plating solutions.

  Raw material for the production of borides (such as BF₃).

• Emerging and Special Uses
  • Additive for lithium/potassium ion battery electrolytes to improve cycle stability.
  • Additive for perovskite solar cell precursors.
  • Source of fluoroborate salts in organic synthesis (e.g., NHC catalyst synthesis).
  • Isotope ¹⁰B enriched KBF₄ used as a neutron absorption material in the nuclear industry.

Potassium fluoroborate, as a boron- and fluorine-containing fine chemical intermediate, has a steadily growing demand in metallurgy, welding, new energy materials, and other fields. With increasing environmental pressure, clean processes utilizing by-products from phosphate fertilizer/fluorochemical industries will become a key focus for future development.