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Salts & Minerals

Aluminum hydroxide

CAS: 21645-51-2

Overview

Aluminum hydroxide (CAS 21645-51-2 ), also sold as hydrated alumina, is an inorganic mineral compound used across industrial and pharmaceutical markets as a flame retardant, antacid active, and catalyst precursor.

Its function shifts significantly by grade and particle size, making specification alignment critical at the sourcing stage. In plastics and polymer compounding, it acts as a halogen-free flame retardant and smoke suppressant.

The material is incorporated into cable jacketing, flooring, and construction panels to meet fire safety standards. Pharmaceutical manufacturers use it as an active ingredient in antacid formulations where it neutralizes excess gastric acid.

Sold historically under the brand Amphojel, it is used in OTC tablet and suspension products. In the paper and textile industries, it functions as a mordant and surface treatment agent, improving dye fixation and coating adhesion.

Catalyst producers also use it as a precursor for alumina-based catalysts applied in refining and chemical synthesis. The product is supplied as a fine white powder, with particle size and surface area varying by intended application.

Standard grades include USP and BP for pharmaceutical use, and technical or flame-retardant grades for industrial polymer applications. FCC -grade material is available for food-contact and food-additive applications.

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Physical Properties

Melting Point300 °C
Boiling Point2980°C[at 101 325 Pa]
Density2.42 g/cm³
Appearancewhite amorphous powder
ColorWhite
OdorOdorless
Formcolloidal suspension
Water Solubilityinsoluble
Vapor Pressure<0.1 hPa (20 °C)
Refractive IndexAverage refractive index: 1.57-1.59
pH8-9 (100g/l, H2O, 20℃)(slurry)
Log P-1.380 (est)

Safety & Handling

Warning GHS07 Hazard Statements H315 Causes skin irritation H319 Causes serious eye irritation H335 May cause respiratory irritation Precautionary Statements P261 Avoid breathing dust/fume/gas/mist/vapours/spray. P264 Wash … thoroughly after handling. P271 Use only outdoors or in a well-ventilated area. P280 Wear protective gloves/protective clothing/eye protection/face protection. P319 Get medical advice/attention if you feel unwell. P321 Specific treatment (see … on this label). P405 Store locked up. P501 Dispose of contents/container in accordance with local regulations. P264+P265 Wash … thoroughly after handling. P302+P352 IF ON SKIN: Wash with plenty of water. P304+P340 IF INHALED: Remove person to fresh air and keep comfortable for breathing. P332+P317 Get emergency medical help. P337+P317 If eye irritation persists: Get medical advice/attention. Get emergency medical help. P362+P364 Take off contaminated clothing and wash it before reuse. P403+P233 Store in a well-ventilated place. Keep container tightly closed. P305+P351+P338 IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing.

Trade & Regulatory

HS Code28183000
Storage Class13 - Non Combustible Solids

Other Names

aluminium hydroxide | Hydrated alumina | Amphojel | aluminum hydrate | Dried aluminium hydroxide | Aluminum hydroxidedried | Aluminium hydroxidedried | Alu-Cap

Related Products

Chemical Properties

CAS Number
21645-51-2
EC Number
244-492-7
Mol. Weight
78.004
HS Code
28183000

Industries

Documentation