Related compounds Appearance White crystals | Density 1.5 g/cm³ | |
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World ammonium bifluoride market trend growth data forecast report 2020
Ammonium hydrogen fluoride is the inorganic compound with the formula NH4HF2 or NH4F·HF. It is produced from ammonia and hydrogen fluoride. This colourless salt is a glass-etchant and an intermediate in a once-contemplated route to hydrofluoric acid.
Contents
Global and china ammonium bifluoride industry 2013 market research report
Structure
Ammonium bifluoride, as its name indicates, contains an ammonium cation (NH4+) and a bifluoride, or hydrogen(difluoride), anion (HF2−). The centrosymmetric triatomic bifluoride anion features the strongest known hydrogen bond, with a F−H length of 114 pm. and a bond energy greater than 155 kJ mol−1.
In solid [NH4][HF2], each ammonium cation is surrounded by four fluoride centers in a tetrahedron, with hydrogen-fluorine hydrogen bonds present between the hydrogen atoms of the ammonium ion and the fluorine atoms. Solutions contain tetrahedral [NH4]+ cations and linear [HF2]− anions.
Production and applications
Ammonium bifluoride is a component of some etchants. It attacks silica component of glass:
SiO2 + 4 [NH4][HF2] → SiF4 + 4 [NH4]F + 2 H2OPotassium bifluoride is a related more commonly used etchant.
Ammonium bifluoride has been considered as an intermediate in the production of hydrofluoric acid from hexafluorosilicic acid. Thus, hexafluorosilicic acid is hydrolyzed to give ammonium fluoride, which thermally decomposes to give the bifluoride:
H2SiF6 + 6 NH3 + 2 H2O → SiO2 + 6 NH4F 2 NH4F → NH3 + [NH4]HF2The resulting ammonium bifluoride is converted to the sodium bifluoride, which thermally decomposes to release HF.