Aluminate

An aluminate is a compound containing aluminium and oxygen. When precipitated from solution, the anion condenses with more electropositive elements. The generally accepted form of the aluminate is a mononuclear tetrahedral complex that is negatively charged, Al(OH)₄⁻ or AlO₂⁻. Examples of aluminate compounds include sodium aluminate (Na₂Al₂O₄) and potassium aluminate (K₂Al₂O₄), both being alkali-ion precipitates of the tetrahedral monomer obtained from an alkaline solution. Aluminate can also refer to the polyatomic ion AlO3−
3.

Since aluminum is closer to the nonmetals, it has some nonmetal characteristics and some metal characteristics. Its oxide is amphoteric: it dissolves in both bases and acids. When dissolved in bases it forms the aluminate ion. An aluminate can be considered as the neutralization of aluminum oxide with a base, or an adduct of aluminum oxide with the base.

Minerals like chrysoberyl are sometimes called aluminates, although they are usually classified as mixed oxides. As minerals, aluminates are much less common than aluminosilicates.

Aluminate glasses

Alumina on its own cannot easily be made glassy with current techniques, however with the addition of a second compound many types of aluminate glasses can be formed. The glasses produced display a range of interesting and useful properties, such as high refractive index, good infrared transparency, and high melting point, as well as the ability to host laser active and fluorescent ions. Aerodynamic levitation is a key method used to study and produce many aluminate glasses. Levitation allows high purity to be maintained in the melt at temperatures in excess of 2000K.

Some materials that are known to form glass in binary combination with aluminium oxide are: rare earth oxides, alkaline earth oxides (CaO, SrO, BaO) lead oxide, and silicon dioxide.