Hydrofluoric acid (HF) is an aqueous solution of hydrogen fluoride gas. At room temperature, it appears as a clear, colorless to light yellow fuming liquid with a pungent odor. The aqueous solution containing less than 60% hydrogen fluoride. Industrial aqueous solution usually contains 40-45% HF. When dissolved in water, HF can produce a highly corrosive acid, which is a medium-intensity acid. It is extremely smelly, and being very toxic, can cause ulceration when come into contact with the skin. Inhalation of the HF vapor can have fatal effects, thus strict attention should be paid during usage. Gold, platinum, lead, paraffin and some plastics (polyethylene, etc.) does not react with HF. Hence, these materials can be used to store HF.
HF can be produced using the sulfuric acid method. Dried fluorite powder and sulfuric acid is mixed in the ratio of 1:1.2~1.3 and sent into the rotary reaction furnace for reaction at 280°C ± 10°C. The gas produced is then distilled to remove most of the sulfuric acid, water and fluorite powder. The crude hydrogen fluoride gas is then condensed into a liquid by degassing and then rectified. The purified hydrogen fluoride is absorbed by water to obtain the hydrofluoric acid product. CaF2 + H2SO4 → 2HF + CaSO4.
Hydrofluoric acid is mainly used as the raw material of fluorine compounds in the manufacture of organic or inorganic fluoride, such as fluorocarbons, sodium fluoride, aluminum fluoride, uranium hexafluoride and cryolite. It can also be used as alkylation catalyst in semiconductor surface etching. Other than that, it is also used as the catalysts of organic synthesis such as alkylation, polymerization, condensation and isomerization. It can be used as analytical reagents for the preparation of high purity fluoride. It is the indispensable fluoride source for the production of refrigerants, "Freon", fluorine-containing resins, fluorine plastics, fluorine rubber and fluorine medicine and pesticides.
It can be used as a strong acid corrosion agent, being able to be used in conjunction with nitric acid, acetic acid, ammonia and hydrogen peroxide.
In the atomic energy industry and nuclear weapons production, it is the raw material for the manufacture of uranium hexafluoride, rocket fuel and additives.