Book excerpt: The continuous and ever expanding development of high-temperature tech nology involves the use of high -temperature refractory materials and one of the most important classes of these is the oxides, i.e., compounds of elements with oxygen. Oxides are the oldest refractory compounds known in technology and this is connected with their high chemical stability and abundance in nature. In addition to the use of oxides as raw materials for metallurgical processes, the refractoriness, chemical stability, and magnetic and other technically important properties of oxides have been put to use since antiquity. At the present time the importance of oxides as bases of many materials for new technology is substantial and is growing rapidly with the development of processes for the direct conversion of various forms of energy into electrical energy, the development of nuclear technOlogy, electronics, semiconductor and dielectric technOlogy, and cosmic technology, where the refractoriness and chemical stability of oxides are used in combination with their specific physical properties. Oxides are the foundation of the so-called oxygen -containing or oxygen refractory materials, which are fundamental to high-temperature tech nology. Oxides are no less important as the bases of practically all structural ma terials and rocks. A number of oxides are involved in biological processes.