Alumina hydroxide, also known as hydrated alumina, alumina hydrate, etc.,It  is a typical amphoteric compound, which is soluble in acid and alkali solution,but insoluble in water and alcohol.General formula is Al2O3•H2O, melting point is 300 ℃ (loss of water).According to how much water it contains, aluminum hydroxide  can be divided into aluminum hydroxide trihydrate, aluminum hydroxide monohydrate, low crystallinity aluminum oxide and amorphous aluminum hydroxide.Except extracting from bauxite, it can also be made by aluminum salt and sodium hydroxide and ammonia water, there are crystalline and amorphous (gel) two kind.

1. Application fields of crystalline aluminum hydroxide

Crystalline aluminum hydroxide mainly has low alkali type, low iron type, fine grain type, fine particle type, high white type.It has high hardness, heat resistance and wear resistance, good chemical stability, non-toxic, tasteless, non-volatile, It get dehydration and heat absorption when it is heated to more than 250℃, which has good smoke resistance and flame retardant properties.Its application field mainly has the following several kinds.

A. Used in plastic material industry

Aluminum hydroxide is a kind of purified inorganic filler with low impurity content. The polymer series with aluminum hydroxide as filler are polyurethane resin, epoxy resin, polyethylene, polypropylene, styrene butadiene rubber and so on.Alumina hydroxide has been used as an effective flame retardant and smoke suppressor in the field of unsaturated resin for many years.

The flame retardant mechanism is as follows: ATH is added to the polymer to reduce the concentration of combustibles;The dehydration and heat absorption of aluminum hydroxide at 250℃ inhibited the rise of polymer temperature.The water vapor produced by decomposition dilutes the concentration of oxygen and slows down combustion.The formation of alumina on the combustible surface can prevent the combustion reaction from continuing.

B. Aluminum hydroxide is used in the paper industry

Alumina hydroxide in the paper industry, mainly used for surface coatings, fillers and production of non-combustible paper.Aluminum hydroxide can improve the luster of paper, reflection, light resistance, smoothness and printing performance.Aluminum hydroxide can also be used as a substitute for titanium oxide clay for coated paper.The particle size of aluminum hydroxide in common use is 0.7-1.4μm.

Fireproof paper: with flame retardant properties, in case of fire carbonization, but does not burn.It is made by copying asbestos or by treating the paper with appropriate flame retardants such as aluminium hydroxide.

C. Aluminum hydroxide is used in the production of toothpaste friction agent

Aluminum hydroxide avirulent insipidity, insoluble in water, it is a good neutral abrasive, industrial production of aluminum hydroxide abrasive mohs hardness of 2.5-3.5, the purity of 99.0% or higher, pH 8.0 to 9.5, D50 value is 8 to 15 microns, moderate price, a more excellent abrasive, and fluoride compatibility, excellent performance, is one of the ideal drug toothpaste abrasive.

D. Raw materials for synthetic mullite

Mullite (or monite) is a series of minerals collectively composed of aluminosilicate. Mullite is the only stable binary compound in the Al2O3-SiO2 system, and this kind of minerals are relatively rare.It is a high quality refractory material, when artificial heating aluminum silicate will form mullite.Mullite is mainly used in refractory materials, ceramics, metallurgy, casting, electronics and other industries, has the characteristics of high temperature resistance, high strength and small thermal conductivity.

In addition, aluminum hydroxide can also be used as artificial marble, agate, artificial carpet filler;Chemical raw materials for the production of aluminum sulfate, alum, alumina, alumina hydrate and sodium aluminate;Flame retardant for rubber products;Fillers and supplements for adhesives and sealants;Synthetic molecular sieve;Used for anti-gastric acid medicine, etc.

2, the application of amorphous aluminum hydroxide

Gel - type aluminum hydroxide mainly includes aluminum hydroxide gel, pseudo - bores, amorphous aluminum glue.It has good adhesion, formability, high temperature resistance, large heat capacity, small thermal conductivity, good corrosion resistance and oxidation resistance, high strength and smooth surface.