Vacuum Technology
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Vacuum Technology, in physics and engineering, processes and equipment based on the principle that, when the quantity of oppressive gas such as air in a closed vessel is removed, the remaining molecules, atoms, or any electrically charged particles that are derived from them, such as ions and electrons, can move about more freely (see Vacuum). This freedom is proportional to the reduction in the gas pressure. See Atom; Electron; Ion; Molecule; Pressure.
Low and medium vacuums have been commonly used in such household equipment as vacuum bottles and vacuum cleaners since the late 19th century. The distillation of lubricating oils from petroleum residues and the removal of atmospheric oxygen from electric light bulbs also employ vacuum technology. Before World War II, however, high-vacuum techniques, achieving near-complete vacuum conditions, were mainly used in research laboratories, the one exception being radio-tube production (see Vacuum Tubes). During the war, techniques for coating optical lenses with extremely thin films of magnesium fluoride, using high vacuum, became established. This process improved the optical quality of the lenses by reducing light reflection (see Lens; Optics). High-vacuum techniques are also employed in the molecular distillation of fish oils to produce vitamin A concentrate, and in the electromagnetic separation of uranium-235 from nonradioactive uranium with which it is associated in nature. See Isotope; Radioactivity.
One of the more important recent applications of vacuum technology is in large-scale industrial refrigeration. The rate of evaporation of water is accelerated in vacuum conditions and the process is used for freeze-drying foods. The water in the food is removed by sublimation into ice that, at the same time, freezes the food. Metal evaporation in high vacuum is used to coat plastics and other objects to give them a high, metallic luster. This process was an outgrowth of the lens-coating process. Television-tube production rate was greatly accelerated by the introduction of high-speed, high-vacuum pumps. High-vacuum treatment of melted, cast, or sintered metals improves their physical properties by removing gases and other impurities. Single-metal crystals used in transistors and similar electronic devices are “grown,” or prepared, in high-vacuum furnaces (see Crystal; Furnace; Transistor). Electrical transformers and high-voltage cables are vacuum impregnated with high dielectric material to improve the insulation. To obtain maximum insulation from heat for flasks and pipes that store and transport liquid oxygen, nitrogen, and helium, the container walls are maintained at high vacuum. Substrates, or bases, used in making electronic microcircuits are prepared by sputter-coating them with refractory materials such as tantalum and tungsten under high-vacuum conditions.
Vacuum is very important in scientific and technological research. Atomic particle accelerators depend on high and very high vacuum to provide a relatively gas-free unobstructed path for the ionized particles to travel (see Ionization). Large chambers of up to thousands of cubic-meters capacity, and requiring great pumping speeds for gas removal, are used to test aerospace equipment in simulated outer-space conditions. In certain types of analyses, if the material to be analyzed must be in a gaseous state or in the form of electrically charged ions, then vacuum must be used to produce these requirements. The mass spectroscope, electron microscope, and vacuum-fusion and nuclear magnetic resonance analyzers are a few such instruments (see Chemical Analysis; Microscope; Spectroscopy). New uses for the unique capabilities of vacuum operation are continually being discovered.
Low and medium vacuums have been commonly used in such household equipment as vacuum bottles and vacuum cleaners since the late 19th century. The distillation of lubricating oils from petroleum residues and the removal of atmospheric oxygen from electric light bulbs also employ vacuum technology. Before World War II, however, high-vacuum techniques, achieving near-complete vacuum conditions, were mainly used in research laboratories, the one exception being radio-tube production (see Vacuum Tubes). During the war, techniques for coating optical lenses with extremely thin films of magnesium fluoride, using high vacuum, became established. This process improved the optical quality of the lenses by reducing light reflection (see Lens; Optics). High-vacuum techniques are also employed in the molecular distillation of fish oils to produce vitamin A concentrate, and in the electromagnetic separation of uranium-235 from nonradioactive uranium with which it is associated in nature. See Isotope; Radioactivity.
One of the more important recent applications of vacuum technology is in large-scale industrial refrigeration. The rate of evaporation of water is accelerated in vacuum conditions and the process is used for freeze-drying foods. The water in the food is removed by sublimation into ice that, at the same time, freezes the food. Metal evaporation in high vacuum is used to coat plastics and other objects to give them a high, metallic luster. This process was an outgrowth of the lens-coating process. Television-tube production rate was greatly accelerated by the introduction of high-speed, high-vacuum pumps. High-vacuum treatment of melted, cast, or sintered metals improves their physical properties by removing gases and other impurities. Single-metal crystals used in transistors and similar electronic devices are “grown,” or prepared, in high-vacuum furnaces (see Crystal; Furnace; Transistor). Electrical transformers and high-voltage cables are vacuum impregnated with high dielectric material to improve the insulation. To obtain maximum insulation from heat for flasks and pipes that store and transport liquid oxygen, nitrogen, and helium, the container walls are maintained at high vacuum. Substrates, or bases, used in making electronic microcircuits are prepared by sputter-coating them with refractory materials such as tantalum and tungsten under high-vacuum conditions.
Vacuum is very important in scientific and technological research. Atomic particle accelerators depend on high and very high vacuum to provide a relatively gas-free unobstructed path for the ionized particles to travel (see Ionization). Large chambers of up to thousands of cubic-meters capacity, and requiring great pumping speeds for gas removal, are used to test aerospace equipment in simulated outer-space conditions. In certain types of analyses, if the material to be analyzed must be in a gaseous state or in the form of electrically charged ions, then vacuum must be used to produce these requirements. The mass spectroscope, electron microscope, and vacuum-fusion and nuclear magnetic resonance analyzers are a few such instruments (see Chemical Analysis; Microscope; Spectroscopy). New uses for the unique capabilities of vacuum operation are continually being discovered.
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