Matter & Energy


Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.

Uses of Silicon

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Silicon is used in the steel industry as a constituent of silicon-steel alloys. In steelmaking, molten steel is deoxidized by the addition of small amounts of silicon; ordinary steel contains less than 0.03 percent of silicon. Silicon steel, which contains from 2.5 to 4 percent silicon, is used in making the cores of electrical transformers because the alloy exhibits low hysteresis (see Magnetism). A steel alloy, known as duriron, containing about 15 percent silicon, is hard, brittle, and resistant to corrosion; duriron is used in industrial equipment that comes in contact with corrosive chemicals. Silicon is also used as an alloy in copper, brass, and bronze.

Silicon is a semiconductor, in which the resistivity to the flow of electricity at room temperature is in the range between that of metals and that of insulators. The conductivity of silicon can be controlled by adding small amounts of impurities, called dopants. The ability to control the electrical properties of silicon, and its abundance in nature, have made possible the development and widespread application of transistors and integrated circuits used in the electronics industry.

Silica and silicates are used in the manufacture of glass, glazes, enamels, cement, and porcelain, and have important individual applications. Fused silica, a glass made by melting quartz or hydrolyzing silicon tetrachloride, is characterized by a low coefficient of expansion and high resistance to most other chemicals. Silica gel is a colorless, porous, amorphous substance; it is prepared by removing part of the water from a gelatinous precipitate of silicic acid, which is formed by adding hydrochloric acid to a solution of sodium silicate. Silica gel absorbs water and other substances and is used as a drying and decolorizing agent.

Sodium silicate, an important synthetic silicate, is a colorless, water-soluble, amorphous solid that melts at 1088° C (1990° F). It is prepared by reacting silica (sand) and sodium carbonate at a high temperature or by heating sand with concentrated sodium hydroxide under pressure. The aqueous solution of sodium silicate, called water glass, is used for preserving eggs; as a substitute for glue in making boxes and other containers; as a binder in artificial gemstones; as a fireproofing agent; and as a binder and filler in soaps and cleansers. Another important silicon compound is the silicon-carbon compound Carborundum, which is used as an abrasive.

Silicon monoxide, is used as a coating to protect other materials, the outer surface oxidizing to the dioxide. Such layers are applied also as components of interference filters.