The chemical formula \(\text{Al}_2\text{O}_3\) represents a compound formed from aluminum and oxygen. This white, odorless solid is a fundamental material in modern industry, known for its strength, heat resistance, and electrical insulation capabilities. Its importance extends across diverse fields, from the aerospace industry to the manufacturing of common household goods like sandpaper and spark plugs.
Naming Aluminum Oxide
The systematic name for \(\text{Al}_2\text{O}_3\) is Aluminum Oxide, determined by the rules for ionic compounds. Aluminum is a metal and oxygen is a nonmetal, forming strong ionic bonds. Chemical nomenclature rules dictate that the metal’s name (aluminum) is stated first, followed by the nonmetal’s name (oxygen) changed to “-ide,” resulting in “oxide.”
This simple convention is used because aluminum has a fixed oxidation state of +3, meaning it only forms the \(\text{Al}^{3+}\) ion. Since the charge is predictable, it is not necessary to include a Roman numeral, such as in “Aluminum(III) Oxide.” The prefixes “di-” and “tri-” (as in “Dialuminum Trioxide”) are generally reserved for molecular or covalent compounds, not ionic ones like \(\text{Al}_2\text{O}_3\).
Alumina and Corundum
While Aluminum Oxide is the systematic chemical name, the compound is more frequently referred to by the common industrial term, Alumina. Alumina is the general name used for the material in its processed or manufactured form, often as a white powder refined from bauxite ore. This powder is the starting material for various high-tech ceramics and is a primary source for producing aluminum metal.
The other common name for \(\text{Al}_2\text{O}_3\) is Corundum, which specifically refers to the naturally occurring, crystalline mineral form. Corundum is an extremely hard mineral that forms in a stable hexagonal crystal structure, known as the alpha-phase of aluminum oxide. Its various color-tinted versions are classified as precious gemstones.
Rubies and sapphires are both varieties of corundum, with their vibrant colors arising from trace metallic impurities within the crystal lattice. Rubies get their distinct red color from chromium ions substituting for aluminum ions. Sapphires, traditionally blue, can exhibit almost any color—including pink, yellow, or green—due to the presence of other transition metals like iron or titanium.
Essential Physical Properties and Applications
Aluminum oxide’s utility stems from its physical properties. It is hard, registering a 9 on the Mohs scale, second only to diamond’s 10. This hardness makes it a low-cost substitute for industrial diamond in many applications.
The compound is refractory, resisting decomposition at high temperatures, with a melting point of approximately \(2,072^\circ \text{C}\) (\(3,762^\circ \text{F}\)). This stability is used for manufacturing high-temperature ceramics, furnace linings, and electrical insulators. Furthermore, \(\text{Al}_2\text{O}_3\) is an electrical insulator, yet it possesses relatively high thermal conductivity for a ceramic, allowing heat to pass through it without conducting electricity.
Common applications include its use as an abrasive in sandpaper, grinding wheels, and cutting tools. In electronics, high-purity alumina is used as a substrate for integrated circuits and in high-voltage devices due to its dielectric strength. The material’s bio-inertness and wear resistance also make it suitable for medical applications, including artificial bones and joint replacements.