What Is Calcined Alumina Powder?

Calcined alumina powder is a high-performance inorganic material prepared by high-temperature heat treatment. It has excellent high temperature resistance, high hardness and chemical stability. It is widely used in ceramics, refractory materials, electronic components, abrasives and other fields.

一. Definition of calcined alumina powder

Calcined alumina powder refers to α-alumina powder formed by calcining aluminum hydroxide or industrial alumina at high temperature (usually above 1200°C) to remove crystal water and undergo crystal transformation.

The calcination process significantly changes the physical and chemical properties of alumina, such as:

• Removal of moisture and volatiles to improve purity;

• Crystal transformation from low-stability γ-Al₂O₃ to high-stability α-Al₂O₃ (corundum phase);

• Improve hardness and high temperature resistance, making it more suitable for industrial applications.

二. Preparation process of calcined alumina powder

(1) Raw material selection

The raw materials of calcined alumina powder mainly include:

• Aluminum hydroxide (Al(OH)₃): such as industrial gibbsite;

• Boehmite (AlOOH): monohydrated aluminum oxide with high conversion rate after calcination;

• Industrial alumina (γ-Al₂O₃): can be directly calcined into α-Al₂O₃.

(2) Calcination process

Calcination is usually divided into three stages:

1. Dehydration stage (200–500°C)

o Aluminum hydroxide decomposes and releases crystal water:

2Al(OH)3→Al2O3+3H2O↑2Al(OH)3→Al2O3+3H2O↑

o Transitional alumina (such as γ-Al₂O₃) is generated.

2. Crystal transformation stage (800–1200°C)

o γ-Al₂O₃ gradually transforms into α-Al₂O₃ (corundum phase);

o The specific surface area decreases and the particles become denser.

3. High temperature stabilization (>1300°C)

o Promote the growth of α-Al₂O₃ grains, improve hardness and thermal stability.

(3) Cooling and post-treatment

The calcined alumina needs to be cooled slowly to avoid thermal stress causing particle breakage. It can then be processed by:

• Crushing: adjust the particle size for different uses;

• Grading: screen by particle size to improve product uniformity;

• Surface treatment: such as silane coupling agent modification to enhance the bonding strength with resin or ceramics.

三. Characteristics of calcined alumina powder

四. Application of calcined alumina powder

(1) Refractory materials

• Used for high-temperature kiln linings, refractory bricks, castables, etc.

• Widely used in the steel, glass, and cement industries due to its high melting point and thermal shock resistance.

(2) Ceramic industry

• Electronic ceramics: integrated circuit substrates, insulators, piezoelectric ceramics, etc.

• Structural ceramics: wear-resistant parts (such as ceramic tools, bearings), bioceramics, etc.

(3) Abrasives

• Used for grinding wheels, cutting discs, polishing powders, etc., replacing silicon carbide and diamond abrasives.

(4) Catalyst carriers

• γ-Al₂O₃ with high specific surface area can be used for petrochemical catalytic reactions.

(5) Coatings and fillers

• Used for high-temperature resistant coatings, reinforced plastics, rubber, etc. to improve wear resistance and corrosion resistance.

(6) Electronics and semiconductors

• Used for LED packaging, heat dissipation substrates, insulation layers, etc.

五,The difference between calcined alumina powder and ordinary alumina