Aluminum Hydroxide

Definition - What does Aluminum Hydroxide mean?

Aluminum hydroxide, Al(OH)3, is a naturally occurring mineral and can refer to any of several white gelatinous or crystalline hydrates of alumina. It occurs as a white or whitish yellow powder. Aluminum hydroxide is formed when unoxidized aluminum is immersed in pure water. It is present in the form of a thin layer that provides corrosion resistance for aluminum in natural and fresh water at slightly acidic or neutral pH levels.

Corrosionpedia explains Aluminum Hydroxide

Aluminum hydroxide is amphoteric, which means it occurs as both basic and acidic in nature. Naturally it is found as the mineral gibbsite and its three polymorphs bayerite, doyleite and nordstrandite. Gibbsite has a metal hydroxide structure with hydrogen bonds, and is commonly used as an over-the-counter antacid.

The formation of aluminum hydroxide often does not provide enough protection to an aluminum surface to prevent corrosion in basic and strongly acidic environments. Therefore, other measures such as the addition of ethylene glycol to a metallic environment aids the reactions required to form protective coating layers on the metal's surface.

Some properties of aluminum hydroxide:

  • Specific gravity: 2.42
  • Melting point: 155°C (311°F)
  • Soluble in strong acids, such as hydrochloric acid


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