Technical grade ammonium chloride is used across a wider range of industries than almost any other simple inorganic salt, and the applications look unrelated until you notice that nearly all of them exploit one of three properties: thermal dissociation into hydrogen chloride and ammonia, high ionic conductivity in solution, or the ammonium ion’s behaviour as an exchangeable cation. This page sets out the applications together with the mechanism each depends on. The 99.5 % purity specification is treated separately on its own page.
Substance identity
| Chemical name | Ammonium chloride |
| Synonyms | Sal ammoniac, salmiac, ammonium muriate, muriate of ammonia |
| Formula | NH₄Cl |
| CAS | 12125-02-9 |
| PubChem CID | 25517 |
| Molar mass | 53.49 g/mol |
| Appearance | White crystalline powder or granules, odourless when dry |
Specification
| Parameter | Value | Basis |
|---|---|---|
| NH₄Cl content, dry basis | ≥ 99.5 % is the common technical floor | Typical commercial range |
| Moisture | ≤ 0.3–0.5 % | Typical commercial range |
| Water-insoluble matter | ≤ 0.02–0.05 % | Typical commercial range |
| Sulfate (SO₄) | ≤ 0.02–0.05 % | Typical commercial range |
| Iron (Fe) | ≤ 5–10 mg/kg | Typical commercial range |
| pH, 5 % solution at 25 °C | 4.5–6.0 | Typical range |
| Form | Powder, crystalline or granular as required | — |
Properties
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Thermal dissociation. On heating, NH₄Cl separates into ammonia and hydrogen chloride, which recombine on cooling — the basis of its apparent sublimation near 337.6 °C. It is a solid that delivers gaseous HCl at a work surface, on demand, at temperature.
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Ionic conductivity. Fully dissociated in water, giving high conductivity at modest concentration. Solubility approximately 37 g per 100 g water at 20 °C.
- Acidity. 5 % solution pH 4.5–6.0, from hydrolysis of NH₄⁺ (pKa 9.25).
- Complexation. Ammonia liberated from the ammonium ion forms ammine complexes with several transition metals, notably zinc, copper, nickel and silver — relevant in plating and in metal cleaning.
- Endothermic dissolution. About +14.8 kJ/mol, exploited directly in freezing mixtures and instant cold packs.
- Not flammable. Fire decomposition products are ammonia, hydrogen chloride and nitrogen oxides — corrosive and irritant.
Applications
Soldering and tinning flux. At soldering temperature the salt dissociates and the HCl released reacts with the metal oxide film on the workpiece, forming chlorides that are volatile or readily displaced, leaving clean metal for the solder to wet. This is the classic use, and it is why a sal ammoniac block was traditionally used to clean and tin a soldering iron.
Hot-dip galvanising flux. Used with zinc chloride in the flux bath applied before immersion. The flux removes residual iron oxide and prevents re-oxidation between pre-treatment and the zinc bath.
Zinc–carbon (Leclanché) dry cells. Ammonium chloride paste is the electrolyte, providing the ionic conduction between the zinc anode and the manganese dioxide cathode. Zinc dissolving at the anode is complexed by ammonia derived from the electrolyte.
Electroplating and metal finishing. A component of ammoniacal and chloride zinc plating baths, contributing conductivity and complexing capacity; also used in pickling and in metal-cleaning formulations.
Urea–formaldehyde and similar adhesives. Acts as a latent acid catalyst. It reacts with free formaldehyde in the resin to release hydrogen chloride, lowering pH and triggering cure — the delay is what makes the adhesive workable before it sets.
Oilfield and drilling. Used as a clay and shale stabiliser. The ammonium ion exchanges onto clay interlayer sites in a similar manner to potassium, reducing the swelling of smectite clays on contact with water-based fluids.
Textiles and leather. Used in dyeing and printing operations and in tanning, where controlled acidity and electrolyte strength are required.
Laboratory and process chemistry. With ammonia it forms a buffer centred near pH 9.25. It is a nitrogen source in microbiological growth media and an intermediate in the manufacture of other ammonium salts.
Handling and storage
Store dry, sealed and away from strong alkalis, which release ammonia gas on contact; from strong oxidisers; and from silver salts, chlorates and nitrites, all of which present recognised reactivity hazards with ammonium compounds. Control dust: harmful if swallowed and causes serious eye irritation. In hot applications, the fume evolved is corrosive HCl and ammonia and requires effective local extraction — this is a routine and predictable exposure in fluxing work, not an upset condition. In moist conditions the salt attacks copper and its alloys, mild steel, galvanised steel and aluminium, and chloride raises the pitting risk on austenitic stainless steels; ventilation of stores prevents corrosion of nearby plant as well as caking of the product.
Notes
Ammonium chloride is not normally classified as a dangerous good for transport, but transport classification should always be confirmed against the current edition of the applicable regulations rather than assumed. Pharmacopoeial and food grades of this salt exist and are specified differently; technical grade must not be substituted for them.