Powdered — more precisely, fine crystalline — ammonium chloride is the material as it comes from crystallisation and drying, before any compaction step. Its defining characteristic is high specific surface area, and essentially every practical difference from granular material follows from that single property: it dissolves faster, it takes up moisture faster, it cakes more readily and it generates dust. It is bought where those trade-offs favour the buyer, chiefly as an ingredient rather than as a finished field product.
Substance identity
| Chemical name | Ammonium chloride |
| Synonyms | Sal ammoniac, salmiac, ammonium muriate |
| Formula | NH₄Cl |
| CAS | 12125-02-9 |
| PubChem CID | 25517 |
| Molar mass | 53.49 g/mol |
| Appearance | White to off-white fine crystalline powder, odourless in the dry state |
Specification
| Parameter | Value | Basis |
|---|---|---|
| NH₄Cl content | ≥ 94–96 % agricultural; ≥ 99.5 % technical | Typical commercial ranges; grade must be stated |
| Nitrogen (N) | ≥ 25.0–25.4 % on agricultural material | Typical commercial range |
| Moisture | ≤ 0.5–1.0 % agricultural; ≤ 0.3–0.5 % technical | Typical commercial ranges |
| Particle size | Crystalline grades commonly fall in a 0.1–0.5 mm band; finer milled cuts are produced | Typical commercial range |
| Bulk density, loose | Approximately 0.6–0.8 t/m³ | Typical, approximate |
| True density | 1.53 g/cm³ | Physical constant |
Where dissolution rate or blend homogeneity matters, specify the size distribution rather than a single nominal figure — two powders with the same median can behave differently if their fines fractions differ.
Properties
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Dissolution. Rapid, and markedly faster than granular material of the same purity, because rate scales with exposed surface area. Solubility approximately 37 g per 100 g water at 20 °C, rising to about 77 g at 100 °C.
-
Endothermic dissolution. About +14.8 kJ/mol. In a fine powder this is noticeable: dissolving a large charge quickly can drop the batch temperature enough to slow further dissolution, since solubility falls with temperature. Where this matters, add gradually or apply heat.
- Hygroscopicity. The critical relative humidity, near 77 % at 30 °C, is a property of the salt and not of the particle size — but a powder reaches equilibrium with humid air far faster, so in practice it behaves as the more hygroscopic material.
- Thermal behaviour. Dissociates to NH₃ and HCl on heating, apparent sublimation near 337.6 °C, no melting under ordinary conditions. The crystal structure changes from the caesium-chloride type to the sodium-chloride type at about 184 °C, well above any handling temperature.
- Solution pH. 4.5–6.0 for a 5 % solution at 25 °C.
Applications
Feedstock rather than finished product. It is the input to compaction granulation, where the powder is pressed into granules without a binder. It is used as a nitrogen source in compound NPK manufacture, where it is being co-processed anyway and granule integrity is irrelevant. It is the preferred form for solution make-up and for any application where dissolution rate is limiting. In premix and formulation work, a fine particle is what allows a small mass fraction to be distributed homogeneously through a large batch — a coarse granule at low inclusion cannot be made uniform by mixing alone.
Handling and storage
Powder is the most caking-prone form. Store sealed, dry, in stacks low enough to limit consolidation under load, and away from walls where condensation forms. Rotate stock. Dust control is a real requirement, not a formality: ammonium chloride is classified as harmful if swallowed and as causing serious eye irritation, and airborne fine salt reaches eyes and mucous membranes readily. Use local extraction at transfer points, eye protection and appropriate respiratory protection. In moist conditions the dust is corrosive to copper alloys, mild steel and galvanised surfaces, so settled dust on electrical panels and machinery is a maintenance problem as well as a housekeeping one.
Notes
If a supplier offers powder and granular at the same purity and the same price, the difference is entirely physical. Choose powder when dissolution speed or blend homogeneity dominates; choose granular when storage life, dust and spreader behaviour dominate. There is no chemical advantage either way.