Ammonium aluminium sulfate, also known as ammonium alum or just alum (though there are many different substances also called "

alum An alum () is a type of chemical compound, usually a hydrated double salt, double sulfate salt (chemistry), salt of aluminium with the general chemical formula, formula , where is a valence (chemistry), monovalent cation such as potassium or a ...

"), is a white crystalline double sulfate usually encountered as the dodecahydrate,

formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwee ...

(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 Tschermigite is a mineral form of ammonium alum, formula N H4 Al( S O4)2·12(H2O). It is found in burning coal seams, bituminous shale and fumarole A fumarole (or fumerole) is a vent in the surface of the Earth or other rocky planet fro ...

Production and basic properties

Ammonium alum is made from

aluminium hydroxide Aluminium hydroxide, Al(OH)3, is found in nature as the mineral gibbsite (also known as hydrargillite) and its three much rarer polymorphs: bayerite, doyleite, and nordstrandite. Aluminium hydroxide is amphoteric, i.e., it has both basic and ...

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...

and

ammonium sulfate Ammonium sulfate (American English and international scientific usage; ammonium sulphate in British English); (NH4)2SO4, is an inorganic salt with a number of commercial uses. The most common use is as a soil fertilizer. It contains 21% nitrogen a ...

. It forms a

solid solution A solid solution, a term popularly used for metals, is a homogenous mixture of two different kinds of atoms in solid state and have a single crystal structure. Many examples can be found in metallurgy, geology, and solid-state chemistry. The word ...

with

potassium alum Potassium alum, potash alum, or potassium aluminium sulfate is a chemical compound: the double sulfate of potassium and aluminium, with chemical formula KAl(SO4)2. It is commonly encountered as the dodecahydrate, KAl(SO4)2·12H2O. It crystalli ...

Pyrolysis The pyrolysis (or devolatilization) process is the thermal decomposition of materials at elevated temperatures, often in an inert atmosphere. It involves a change of chemical composition. The word is coined from the Greek-derived elements ''py ...

leaves alumina. Such alumina is used in the production of grinding powders and as precursors to

synthetic gem A gemstone (also called a fine gem, jewel, precious stone, or semiprecious stone) is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks (such as lapis lazuli, opal, ...

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

deodorant A deodorant is a substance applied to the body to prevent or mask body odor due to bacterial breakdown of perspiration or vaginal secretions, for example in the armpits, groin, or feet. A subclass of deodorants, called antiperspirants, prevents s ...

s 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

{{DEFAULTSORT:Ammonium Aluminium Sulfate Aluminium compounds Ammonium compounds Sulfates Double salts Astringent flavors E-number additives