Ammonium alum

Ammonium aluminium sulfate, also known as ammonium alum or just alum (though there are many different substances also called "alum"), is a white crystalline double sulfate usually encountered as the dodecahydrate, formula (NH₄)Al(SO₄)₂·12H₂O. It is used in small amounts in a variety of niche applications. The dodecahydrate occurs naturally as the rare mineral tschermigite.

Production and basic properties

Ammonium alum is made from aluminium hydroxide, sulfuric acid and ammonium sulfate. It forms a solid solution with potassium alum. Pyrolysis leaves alumina. Such alumina is used in the production of grinding powders and as precursors to synthetic gems.

Uses

Ammonium alum is not a major industrial chemical or a particularly useful laboratory reagent, but it is cheap and effective, which invites many niche applications. It is used in water purification, in vegetable glues, in porcelain cements, in deodorants and in tanning, dyeing and in fireproofing textiles. The pH of the solution resulting from the topical application of ammonium alum with perspiration is typically in the slightly acid range, from 3 to 5.

Ammonium alum is a common ingredient in animal repellent sprays.

References

1. Alum
2. Ammonium iron(III) sulfate
3. Potassium alum
4. Tapioca pearl
5. Deodorant
6. Haematoxylin
7. Ammonium sulfate
8. Ammonium dichromate
9. Aluminium
10. Aluminium sulfate
11. History of aluminium
12. Tschermigite
13. Indium(III) sulfate
14. Sodium alum
15. Double salt
16. Salammoniac
17. Paul-Émile Lecoq de Boisbaudran
18. Godovikovite
19. Baking powder
20. Tetrafluoroberyllate