Ammonium fluoride

Ammonium fluoride

The ammonium cation The fluoride anion
ball-and-stick model of an ammonium cation (left) and a fluoride anion (right)
Solid sample of ammonium fluoride
Names
IUPAC name Ammonium fluoride
Other names Neutral ammonium fluoride
Identifiers
CAS Number	12125-01-8  Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:66871
ChemSpider	23806  Y
ECHA InfoCard	100.031.975
EC Number	235-185-9
PubChem CID	25516
RTECS number	BQ6300000
UNII	4QT928IM0A
UN number	2505
CompTox Dashboard (EPA)	DTXSID6050463
InChI InChI=1S/FH.H3N/h1H;1H3 Y Key: LDDQLRUQCUTJBB-UHFFFAOYSA-N Y InChI=1/FH.H3N/h1H;1H3 Key: LDDQLRUQCUTJBB-UHFFFAOYAM
SMILES [F-].[NH4+]
Properties
Chemical formula	NH4F
Molar mass	37.037 g/mol
Appearance	White crystalline solid hygroscopic
Density	1.009 g/cm3
Melting point	100 °C (212 °F; 373 K) (decomposes)
Solubility in water	83.5 g/100 ml (25 °C) [1]
Solubility	slightly soluble in alcohol, insoluble in liquid ammonia
Magnetic susceptibility (χ)	−23.0×10−6 cm3/mol
Structure
Crystal structure	Wurtzite structure (hexagonal)
Hazards
GHS labelling: [2]
Pictograms
Signal word	Danger
Hazard statements	H301, H311, H314, H330, H331
Precautionary statements	P260, P261, P264, P270, P271, P280, P284, P301+P310, P301+P330+P331, P302+P352, P303+P361+P353, P304+P340, P305+P351+P338, P310, P311, P312, P320, P321, P322, P330, P361, P363, P403+P233, P405, P501
NFPA 704 (fire diamond)	3 0 0
Flash point	Non-flammable
Safety data sheet (SDS)	ICSC 1223
Related compounds
Other anions	Ammonium chloride Ammonium bromide Ammonium iodide
Other cations	Sodium fluoride Potassium fluoride
Related compounds	Ammonium bifluoride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y  verify  (what is  YN ?) Infobox references

Ammonium fluoride is the inorganic compound with the formula NH₄F. It crystallizes as small colourless prisms, having a sharp saline taste, and is highly soluble in water. Like all fluoride salts, it is moderately toxic in both acute and chronic overdose. ^[3]

Crystal structure

Ammonium fluoride adopts the wurtzite crystal structure, in which both the ammonium cations and the fluoride anions are stacked in ABABAB... layers, each being tetrahedrally surrounded by four of the other. There are N−H···F hydrogen bonds between the anions and cations. ^[4] This structure is very similar to ice, and ammonium fluoride is the only substance which can form mixed crystals with water. ^[5]

Reactions

On passing hydrogen fluoride gas (in excess) through the salt, ammonium fluoride absorbs the gas to form the addition compound ammonium bifluoride. The reaction occurring is:

NH₄F + HF → NH₄HF₂

Ammonium fluoride sublimes when heated—a property common among ammonium salts. In the sublimation, the salt decomposes to ammonia and hydrogen fluoride; the two gases can still recombine, i.e. the reaction is reversible:

[NH₄]F ⇌ NH₃ + HF

Uses

This substance is commonly called "commercial ammonium fluoride". The word "neutral" is sometimes added to "ammonium fluoride" to represent the neutral salt [NH₄]F as opposed to the "acid salt" (NH₄HF₂). The acid salt is usually used in preference to the neutral salt in the etching of glass and related silicates. This property is shared among all soluble fluorides. For this reason it cannot be handled in glass test tubes or apparatus during laboratory work.

Ammonium fluoride is a critical component of buffered oxide etch (BOE), a wet etchant used in microfabrication. It acts as the buffering agent in a solution of concentrated HF, creating an etchant with a more controllable rate of etching (than that of simple concentrated HF solutions). ^[6]

It is also used for preserving wood, as a mothproofing agent, in printing and dyeing textiles, and as an antiseptic in breweries. ^[7]

References

1. "Ammonium Fluoride". pubchem.ncbi.nlm.nih.gov.
2. "Ammonium Fluoride". pubchem.ncbi.nlm.nih.gov.
3. Bălan, H (January 2012). "Fluoride--the danger that we must avoid" (PDF). Romanian journal of internal medicine = Revue roumaine de medecine interne. 50 (1): 61–9. PMID   22788094 . Retrieved 10 December 2025.
4. A. F. Wells, Structural Inorganic Chemistry, 5th ed., Oxford University Press, Oxford, UK, 1984.
5. Brill, R.; Zaromb, S. (1954). "Mixed Crystals of Ice and Ammonium Fluoride". Nature. 173 (4398): 316–317. Bibcode:1954Natur.173..316B. doi:10.1038/173316a0. S2CID   4146351.
6. Wolf, Stanley; Tauber, Richard (1986). Silicon Processing for the VLSI Era: Volume 1 - Process Technology. pp. 532–533. ISBN   978-0-9616721-3-3.
7. Aigueperse, Jean; Paul Mollard; Didier Devilliers; Marius Chemla; Robert Faron; Renée Romano; Jean Pierre Cuer (2005). "Fluorine Compounds, Inorganic". In Ullmann (ed.). Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a11_307. ISBN   3-527-30673-0.