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What it is. Ammonium bifluoride (ammonium hydrogen difluoride, NH4HF2) is a white crystalline salt supplied here as technical-grade flakes in a 1 kg size. It is one of the most practical solid fluoride sources for glass etching, metal pretreatment, scale and silica removal, and masonry cleaning.
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Chemical structure. The salt combines an ammonium cation (NH4+) with a bifluoride anion (HF2-), in which a hydrogen atom sits between two fluorine atoms in one of the strongest known hydrogen bonds. This loosely held hydrogen fluoride makes the compound a convenient, solid carrier of HF activity.
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Why flakes. The flake form pours and weighs more cleanly than fine powder, which reduces airborne dust during handling and dosing. Flakes dissolve readily in water, about 630 g per liter at 20 °C, so you can quickly prepare concentrated etching, pickling, and cleaning baths at the strength a process needs.
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How it reacts. Once dissolved, ammonium bifluoride releases fluoride and bifluoride ions that behave like dilute hydrofluoric acid. A dilute solution is strongly acidic, around pH 2. The fluoride reacts with silicon dioxide in glass, quartz, and siliceous deposits to form soluble fluorosilicates, and it dissolves thin oxide films on aluminum and other metals. The solid is deliquescent and absorbs moisture from air.
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Physical properties. The salt melts at about 125 °C and has a density of about 1.5 g/cm3. On stronger heating, it decomposes, releasing ammonia and hydrogen fluoride. It has a pungent odor caused by trace hydrogen fluoride above the solid.
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Why technical grade. Technical-grade ammonium bifluoride typically assays at 94-95% or higher NH4HF2, with a few percent ammonium fluoride. That purity suits industrial etching, finishing, and cleaning, where consistent reactivity and cost matter more than trace-impurity limits. Lab Pro's Glossary of Common Chemical Grades explains how technical grade compares with ACS and reagent grades.
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Why it is often chosen over liquid HF. As a dry solid, ammonium bifluoride is easier to ship, store, and dose than liquid hydrofluoric acid, and it generates fluoride activity only once dissolved. It still carries real fluoride hazards in solution, including deep tissue burns and systemic toxicity, so it is a more convenient form rather than a harmless substitute.
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Where it is used. Common uses include frosting and etching glass and quartz, brightening and pickling aluminum before anodizing or plating, removing rust, scale, and silica in descaling formulations, cleaning brick and masonry, controlling pH in some textile and laundry processes, and acidizing in oil-well treatments to dissolve siliceous deposits. For a ready-made fluoride solution, see Lab Pro's Ammonium Fluoride 40% (w/v).
Technical Specifications
| Chemical Name |
Ammonium bifluoride |
| CAS Number |
1341-49-7 |
| EC Number |
215-676-4 |
| Synonyms |
Ammonium hydrogen difluoride, ammonium acid fluoride, ammonium hydrogen fluoride |
| Formula |
NH4HF2 (NH4F·HF) |
| Molecular Weight |
57.04 g/mol |
| Grade |
Technical |
| Typical Composition |
Ammonium bifluoride above 94%; ammonium fluoride about 4% (per technical-flake SDS) |
| Appearance |
White crystals or flakes, pungent odor |
| Melting Point |
125 °C |
| Density |
About 1.5 g/cm3 |
| Water Solubility |
About 630 g/L at 20 °C |
| pH |
About 2 (5.7 g/L solution, 20 °C) |
| Package Size |
1 kg |
Applications / Common Uses
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Glass and quartz etching: Produces frosted or etched finishes on glass and quartz surfaces.
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Aluminum pretreatment: Brightens and deoxidizes aluminum before anodizing, painting, or plating.
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Silica and scale removal: Dissolves siliceous deposits in industrial descaling and cleaning formulations.
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Masonry and ceramic cleaning: Removes mineral stains and efflorescence from brick and ceramic surfaces.
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Fluoride chemistry: Serves as a solid fluoride source for synthesis and surface treatment processes.
Storage, Handling & Shipping
Caution: Ammonium bifluoride is toxic if swallowed and causes severe skin burns and eye damage. In contact with moisture or skin, it forms hydrofluoric acid, which can penetrate tissue and cause delayed deep burns and systemic fluoride poisoning. Handle with HF-level precautions: chemical goggles, a face shield, HF-rated neoprene or nitrile gloves, and calcium gluconate gel within reach.
Keep ammonium bifluoride tightly closed in a cool, dry, well-ventilated area. The flakes are deliquescent and absorb moisture from the air, causing caking and promoting acid release, so close the container immediately after each use. Store it away from acids, which liberate toxic hydrogen fluoride gas, and keep Calgonate 2.5% Calcium Gluconate Gel wherever it is handled. Prepare solutions only in polyethylene, polypropylene, or fluoropolymer labware, because fluoride attacks glass.
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Incompatible materials: Acids (release hydrogen fluoride), strong bases, glass, silica, ceramics, and reactive metals.
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Exposure limit (fluorides): OSHA PEL 2.5 mg/m3 as F (TWA).
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Spill response: Sweep up solids without raising dust, keep dry, and treat residues with lime or calcium carbonate. Avoid water runoff to drains.
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First aid: Skin: flush with water, then massage calcium gluconate gel into the area and get medical attention even if pain is mild. Eyes: flush for 15 minutes and seek immediate care.
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GHS signal word: Danger. Toxic if swallowed; causes severe skin burns and eye damage.
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DOT / shipping: UN1727, Ammonium hydrogendifluoride, solid, Class 8, Packing Group II.
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