Aluminum Hydroxide CAS 21645-51-2

Aluminum Hydroxide – Inorganic Opacifier, Thickener, and Stabilizer for Cosmetics and Pharmaceuticals

Basic Information

• CAS Number: 21645-51-2

• Chemical Formula: Al(OH)₃

• Molecular Weight: 78.00 g/mol

• Synonyms: Alumina trihydrate, Aluminum oxide trihydrate, ATH

• Appearance: White, fine, odorless powder

• Solubility: Practically insoluble in water; insoluble in organic solvents

• Storage: Store in a cool, dry place, protected from moisture and direct sunlight

Overview
Aluminum hydroxide is an inorganic compound widely used as an opacifier, thickener, stabilizer, and matting agent in cosmetic, pharmaceutical, and industrial formulations. Its high inertness, low cost, and safety profile make it a versatile ingredient. In cosmetics, it is commonly used in sunscreens, powders, foundations, and skin care products to improve texture, provide a matte finish, and enhance product stability. In pharmaceuticals, it serves as an antacid and as a component in controlled-release drug delivery systems. It is also used as a flame retardant and filler in industrial applications.

Synthesis
Aluminum hydroxide is produced by precipitation methods, typically by neutralizing soluble aluminum salts (e.g., aluminum sulfate or aluminum chloride) with alkali (e.g., sodium hydroxide or ammonia), followed by filtration, washing, and drying. The product can be obtained in various forms, including amorphous gel and crystalline phases, depending on synthesis conditions and processing.

Physicochemical Properties

• White, fine powder: Provides clean, neutral appearance in formulations.

• Insoluble in water: Stable in aqueous systems; acts as a solid particulate.

• Opacifying effect: Scatters and reflects light, providing coverage and a matte finish.

• Thickening and stabilizing: Imparts viscosity and helps stabilize emulsions and suspensions.

• High surface area: Adsorbs oils and active ingredients.

• Inert and non‑reactive: Compatible with most cosmetic and pharmaceutical ingredients.

• Thermal stability: Decomposes at high temperatures (above ~200°C) releasing water.

Applications

• Cosmetics and personal care: Used as a bulking agent, opacifier, thickener, and stabilizer in sunscreens (to disperse UV filters and reduce shine), powders, foundations, primers, and skin care products. Provides a matte, non‑greasy finish.

• Pharmaceuticals: Used as an antacid in over‑the‑counter medications and as an excipient in tablet and capsule formulations.

• Industrial: Used as a flame retardant and smoke suppressant in plastics, rubber, and coatings; as a filler in paints, paper, and adhesives.

• Other: Used in water treatment, as a catalyst support, and in ceramics.

Key Benefits

• Provides opacifying, matting, and thickening effects.

• Improves product texture and stability.

• Safe, inert, and non‑irritating – suitable for sensitive skin.

• Compatible with a wide range of cosmetic and pharmaceutical ingredients.

• Acts as a carrier for active ingredients and UV filters.

• Improves product spreadability and reduces greasiness.

• Non‑comedogenic and dermatologically tested.

Recommended Use
Typical usage levels vary depending on the application:

• Sunscreens and powders: 1–20% for opacity and matte finish.

• Creams and lotions: 1–5% as a thickener and stabilizer.

• For optimal dispersion, incorporate into the oil phase with high‑shear mixing or pre‑disperse in a suitable medium.

Safety and Handling

• Generally recognized as safe (GRAS) for use in cosmetics and pharmaceuticals at recommended concentrations.

• Low irritation potential; well‑tolerated by skin.

• Avoid inhalation of dust – use appropriate personal protective equipment (gloves, dust mask, safety goggles).

• Store in a cool, dry place, away from direct sunlight and moisture.

• Shelf life: typically 24–36 months under recommended storage conditions.

Quality Assurance
Each batch is tested for purity, heavy metals (lead, arsenic, mercury), particle size distribution, and microbial contamination to ensure compliance with cosmetic and pharmaceutical standards.