Alumina Trihydrate has a number of common names used throughout the chemical industry which include: Hydrate Alumina, Alumina Hydrate, Aluminium Tri Hydroxide, ATH, Aluminium Hydrate and Aluminium Hydroxide. Alumina Trihydrate is a white, odorless, powdery, solid substance. Alumina Trihydrate demonstrates a very low solubility in water but is considered to be amphoteric, meaning it will dissolve in both acids or a strong alkali. The most common use of Alumina Trihydrate is for the production of aluminum metal. It is also used as a flame retardant and smoke suppressant filler in polymers such as rubber products and carpet backing.
Annual production of Alumina Trihydrate is around 100 million tons which is nearly all produced through the Bayer process. The Bayer process dissolves bauxite (Aluminium Ore) in sodium hydroxide at elevated temperatures. Alumina Trihydrate is then separated from the solids that remain after the heating process. The solids remaining after the Alumina Trihydrate is removed is highly toxic and presents environmental issues.
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The Chemical Company’s Alumina Trihydrate (ATH) is a white, odorless, powdery crystalline solid and one of the most important inorganic chemicals produced globally. With annual production approaching 100 million metric tons, ATH is manufactured almost exclusively through the Bayer process, in which bauxite ore is dissolved in sodium hydroxide at elevated temperatures and pressure, and the trihydrate is precipitated and separated from the remaining iron-rich solids (red mud) — a highly toxic byproduct that presents significant environmental management challenges.
ATH is amphoteric — it dissolves in both strong acids and strong alkalis — and exhibits very low solubility in water. While over 90% of all ATH produced is calcined to aluminium oxide (alumina) for downstream aluminium metal production, the remaining fraction serves as a critically important non-halogenated flame retardant, smoke suppressant, and antacid across a wide range of polymer, construction, and pharmaceutical applications. Its low cost, abundance, and non-toxic profile make it the world’s most widely used mineral flame retardant.
When exposed to flame or heat above approximately 180–200°C, ATH undergoes endothermic decomposition, releasing up to 34.6% of its weight as water vapor. This reaction absorbs significant heat energy, dilutes flammable gases at the combustion zone, and forms a protective aluminium oxide char layer — all without generating toxic halogenated combustion byproducts, making it a preferred flame retardant in environmentally sensitive applications.
ATH is also a key raw material in the production of aluminium chemicals including aluminium sulfate, aluminium chloride, zeolites, and sodium aluminate. Its ultra-fine precipitated grades are used as functional fillers in solid surface materials such as Corian® and Staron®, where its white color, hardness, and translucency simulate the appearance of natural stone.
| Property | Value |
| Molecular Formula | Al(OH)3 / Al2O3·3H2O |
| Molecular Weight | 78.00 g/mol |
| Appearance | White, odorless crystalline powder |
| Crystal Structure | Gibbsite (monoclinic); also bayerite and nordstrandite polymorphs |
| Density | 2.42 g/cm³ |
| Melting Point | 300°C (decomposes; loses water of crystallization) |
| Decomposition Onset | ~180–200°C (endothermic; releases water vapor) |
| Heat of Decomposition | ~1.17 kJ/g (endothermic heat absorption) |
| Water Released on Decomp | ~34.6% by weight |
| Solubility in Water | Very low (~0.001 g/100 mL); amphoteric |
| pH (5% aqueous slurry) | ~8–10 |
| Refractive Index | 1.57 |
| Mohs Hardness | 2.5–3.5 |
| Available Grades | Standard, fine, ultra-fine, surface-treated, compacted |
Over 90% of all Alumina Trihydrate produced is converted to Aluminium Oxide (alumina) that is used to manufacture aluminum. As a flame retardant, Alumina Trihydrate is chemically added to a polymer molecule or blended in with a polymer to suppress and reduce the spreading of a flame through a plastic. Alumina Trihydrate is also used as an antacid that can be ingested in order to buffer the pH within the stomach.
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