What is Aluminum Hydroxide CAS 21645-51-2?

Aluminum hydroxide, also called alumina trihydrate or ATH, is an inorganic white powder with the formula Al(OH)3. It is used mainly as a halogen-free flame-retardant filler, smoke suppressant and high-whiteness functional filler in polymers and solid-surface materials.

How does Aluminum Hydroxide work as a halogen-free flame retardant?

ATH decomposes endothermically, typically beginning around 180-200 C and peaking near 220-240 C. It releases chemically bound water, cools the polymer, dilutes combustible gases and forms a protective alumina layer, which also helps suppress smoke.

Why is ATH used in solid-surface and artificial-marble products?

High-whiteness ATH provides controlled translucency, fine particle size, low iron content and flame resistance. These properties improve appearance, wear and safety performance in filled acrylic, MMA or unsaturated-polyester solid-surface sheets and artificial marble.

What are the main industrial applications of Aluminum Hydroxide CAS 21645-51-2?

Beyond solid-surface products, ATH is used in wire and cable compounds, thermoset plastics, rubber, adhesives, coatings, electronic laminates and as an intermediate for alumina or aluminum salts.

Which Aluminum Hydroxide grade should I choose for solid surface or cable compounds?

Match the grade to the resin and process. Solid-surface and artificial-marble work usually needs high whiteness, low iron and controlled D50; cable and plastic formulations often prioritize a flame-retardant grade with suitable particle size, moisture and surface treatment.

What specifications should I request before ordering Aluminum Hydroxide?

Request Al(OH)3 content, loss on ignition, moisture, D50 or particle-size distribution, whiteness, oil absorption and trace metal content such as iron. These values affect resin demand, viscosity, color consistency, loading level and final performance.

Aluminum Hydroxide CAS 21645-51-2

Aluminum Hydroxide (ATH, Al(OH)₃), CAS 21645-51-2, is a halogen-free inorganic flame-retardant filler and smoke suppressant supplied for cables, thermoset plastics, rubber, coatings and high-whiteness artificial-marble fillers. Confirm the required grade, then request a quotation with COA/TDS/SDS for bulk supply.

CAS: 21645-51-2
Synonyms: Alumina trihydrate, ATH, Hydrated alumina, Aluminum trihydroxide
Einecs: 244-492-7
Molecular Formula: Al(OH)₃
Grade: Flame Retardant Grade (ATH), Industrial Grade, High Whiteness Filler Grade, Ultra-fine Grade
Package: 25kg/bag (paper-plastic composite), 500kg/1000kg Jumbo bags, or customized neutral packaging.

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Product Description

Aluminum Hydroxide, CAS 21645-51-2, also known as alumina trihydrate or ATH, is the inorganic compound Al(OH)₃; the EC/EINECS number is 244-492-7.

Synonyms: alumina trihydrate; ATH; hydrated alumina; aluminum trihydroxide.

CAS: 21645-51-2.

Molecular formula: Al(OH)₃.

Molecular weight: 78.00 g/mol.

EC number: 244-492-7.

It is a non-toxic, halogen-free white powder produced by the Bayer process and ground to controlled particle sizes.

It decomposes endothermically from about 200 °C, releasing water vapor to cool the polymer and dilute combustible gases.

The decomposition forms a protective alumina layer and provides flame retardancy, smoke suppression and filling.

It is widely used as a halogen-free flame-retardant filler in PVC, PE, EVA, epoxy, wire and cable compounds, insulators and conveyor belts.

High-whiteness grades are used as functional fillers in artificial marble and acrylic or polyester solid surfaces.

It is used in glass, ceramics, paper coating, adhesives and coatings to improve chemical and thermal resistance.

It is used as a raw material for polyaluminum chloride and aluminum sulfate coagulants in water treatment.

High-purity grades are used as catalyst carriers in the petrochemical industry.

Confirm Al(OH)₃ content, loss on ignition, moisture, D50 or particle-size distribution, whiteness, oil absorption and trace metals such as iron.

Store in tightly sealed bags in a cool, dry, ventilated area away from strong acids and alkaline substances; keep off concrete floors on pallets.

Confirm packaging with the requested quantity and destination requirements.

The page is an RFQ entry point and does not state stock, price, MOQ or fixed lead time.

For an RFQ, state the intended use, required grade, quantity, packaging, destination and document needs.

FAQ - Technical & Supply Chain

Q:
What is Aluminum Hydroxide CAS 21645-51-2?

A: Aluminum hydroxide, also called alumina trihydrate or ATH, is an inorganic white powder with the formula Al(OH)3. It is used mainly as a halogen-free flame-retardant filler, smoke suppressant and high-whiteness functional filler in polymers and solid-surface materials.
Q:
How does Aluminum Hydroxide work as a halogen-free flame retardant?

A: ATH decomposes endothermically, typically beginning around 180-200 C and peaking near 220-240 C. It releases chemically bound water, cools the polymer, dilutes combustible gases and forms a protective alumina layer, which also helps suppress smoke.
Q:
Why is ATH used in solid-surface and artificial-marble products?

A: High-whiteness ATH provides controlled translucency, fine particle size, low iron content and flame resistance. These properties improve appearance, wear and safety performance in filled acrylic, MMA or unsaturated-polyester solid-surface sheets and artificial marble.
Q:
What are the main industrial applications of Aluminum Hydroxide CAS 21645-51-2?

A: Beyond solid-surface products, ATH is used in wire and cable compounds, thermoset plastics, rubber, adhesives, coatings, electronic laminates and as an intermediate for alumina or aluminum salts.
Q:
Which Aluminum Hydroxide grade should I choose for solid surface or cable compounds?

A: Match the grade to the resin and process. Solid-surface and artificial-marble work usually needs high whiteness, low iron and controlled D50; cable and plastic formulations often prioritize a flame-retardant grade with suitable particle size, moisture and surface treatment.
Q:
What specifications should I request before ordering Aluminum Hydroxide?

A: Request Al(OH)3 content, loss on ignition, moisture, D50 or particle-size distribution, whiteness, oil absorption and trace metal content such as iron. These values affect resin demand, viscosity, color consistency, loading level and final performance.

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