Transition-metal oxide ceramics from II to IV, such as TiO2, ZnO, NiO, Fe2O3, SnO2, and others, exhibit semiconductor properties, and are used mainly for the applications of gas sensors, solar energy, and in the electronics industry. Aluminum oxide ( ) and magnesium oxide ( ) are the common oxide ceramics. An oxide which promotes ceramic fusion by interaction with other oxides. The oxides which are usually referred to as fluxes are the alkaline oxides because they interact with the glass-forming silica. Ceramic materials are brittle, hard, and strong in compression, weak in shearing and tension. They withstand chemical erosion that occurs in other materials subjected to acidic or caustic environments. Oxide ceramics have high melting points, low wear resistance, and a wide range of electrical properties. Alumina or aluminum oxide in its various levels of purity is used more often than any other advanced ceramic material.