Ammonium bifluoride (ABF), also known as ammonium hydrogen fluoride, is an inorganic compound with the formula NH4•HF2. ABF is commonly used for etching and cleaning of metals before they are further processed. ABF is manufactured and sold in solid form or in liquid solution. It appears as a white crystalline crystal and its solution is clear and colourless with a slight sharp, pungent odour. Ammonium bifluoride is corrosive and upon skin contact, can result in severe irritation and may even burn the skin. Direct contact with eyes may even cause permanent eye damage. Inhalation of ammonium bifluoride can severely irritate and burn the nose, throat, and lungs, causing nosebleeds, cough, wheezing and shortness of breath. It may also cause nausea, vomiting and loss of appetite. Upon contact with water, ABF can release hydrofluoric acid, which is very corrosive. Exposures to fluorides for too long may cause poisoning with symptoms such as stomach pain, weakness and may even lead to death. Repeated exposures to fluorides can cause deposits in bones and teeth, which can lead to a condition called fluorosis.
Ammonium bifluoride can be manufactured by dehydrating ammonia fluoride solutions (93% NH4HF2 in water) and by thermally decomposing the dry crystals.
Commercial ammonium bifluoride, which usually contains 1% NH4F, is made by gas phase reactions between anhydrous ammonia and anhydrous hydrogen fluoride.
During the processing of glass, ammonium bifluoride is used instead of hydrofluoric acid as it is safer for use, storage and transportation and is less harmful. Also, it is able to reduce costs.
Ammonium bifluoride is used for aluminium anodisation and metal surface treatment. Metal surface treatment involving ammonium bifluoride includes cleaning and etching of metals, which are typically done before the metals are processed.
It is an intermediate in the production of hydrofluoric acid from hexafluorosilicic acid. The hexafluorosilicic acid is hydrolysed to give ammonium fluoride, which further decomposes to form ammonium bifluoride. The ammonium bifluoride formed is converted to sodium bifluoride.