Activated alumina will play a greater role as adsorbents, catalysts, catalyst carriers

Activated alumina is an important branch of the non-metallurgical alumina industry developed in recent decades, 

which refers to transitional aluminas such as γ, κ, θ, η, δ, χ; and alumina compounds containing part of water ( Molecular formula A12O3.nH2O, 0≤n<1), 

these aluminas have some common characteristics: large specific surface area, various pore structures, and reasonable pore size distribution. 

Based on the above characteristics, activated alumina is widely used in medicine, chemical industry, metallurgy , water purification, chemical analysis, 

waste gas treatment and other fields as adsorbents, catalysts, catalyst carriers, etc., have increasingly attracted the attention of people from all walks of life, 

and with the advancement of science and technology, it will play a greater role.

1. Properties of activated alumina

1.1 Specific surface area

Theoretically speaking, as long as the firing system of alumina is reasonably controlled, a specific surface area as high as 360m2/g can be obtained. 

However, if the activated alumina is prepared by decomposing colloidal aluminum hydroxide obtained by NaAlO2, its pore size is very small. 

The resulting specific surface area can be as high as 600m2/g

1.2 Pore size distribution

Due to the strong bonding ability of Al-O, the H2O generated by Al(OH)3 during heating and dehydration forms a high vapor pressure in the crystal, 

resulting in widely distributed micropores. Al(OH) 3 is different. Generally speaking, the medium pore size product can be obtained by calcination with pure aluminum hydroxide. 

Activated alumina prepared from aluminum glue can be used to produce products with smaller pore size, while certain organic substances, 

such as ethylene glycol and fibers are added during the preparation of activated alumina, and activated alumina with larger pore size can be obtained after combustion. , 

and even larger apertures can be obtained by sublimation.

2. Classification of activated alumina

2.1γ series low temperature alumina

Its molecular formula can be represented by the general formula Al2O3•nH2O, where 0<n<0.6, this form is formed at a dehydration temperature not exceeding 600℃, 

including ρ-, χ-, η-, γ-alumina, and the crystallization conditions are different. it is good.

2. 2δ series high temperature alumina

This type of alumina is basically a natural product called molecular agent at 800°C to 1000°C, including k-, θ-δ-alumina, etc., which are relatively well crystalline.

2.3. ρ-alumina

This activated alumina is an amorphous body, which is formed by rapid heating and dehydration of gibbsite. It has a very important characteristic: rehydration

ρ- Al2O3 +6H2O Al2O3.H2O Al2O3.3H2O

According to its hydration characteristics, many different kinds of activated alumina products can be prepared, such as rod-shaped, spherical and so on.

2.4 Basis for the distinction of activated alumina

Since these transition-phase aluminas are similar in chemical composition, they are only distinguished by their crystal structures. 

Therefore, the main means to distinguish these aluminas can only be X-ray diffraction pattern analysis, or infer from their origin and processing.