What is the hot cathode?
Cathode is an electrode of an electrical device in which the electric current flows from the device. The hot cathode can be a cathode that warms directly or indirectly. The cathode fiber is a source of electrons in the case of a directly heated cathode. The government is electrically isolated from the cathode in the case of an indirectly heated cathode. The hot cathode emits more electrons than the cold cathode with the same surface area.
The first hot cathodes used direct heating. They were made of pure tungsten and heated into white hotness. Later fibers were covered with a material that emits electrons more easily than tungsten, which reduces the operating temperature of the hot cathode. Other improvements to hot cathodes that use indirect heating include fibers made of salivated tungsten, Thorium-Tungsten and tantalum alloys. Some hot cathodes are also shaped as parabolic mirrors. When using AC current, because this configuration produces less hum than the cathode that uses direct heating. Government in hot cathodeThe indirect heating is commonly called heating. The heater is usually made of tungsten and surrounded by a nickel tube.
Oxide coating for the fiber of hot cathode can reduce the operating temperature of the fiber. The first choice was pure baryum oxide and later formulations used a mixture of Barria oxide, calcium oxide and strontium oxide. Hot cathodes covered with these compounds have a maximum operating temperature of 1,832 degrees Fahrenheit (1,000 degrees Celsius). They are exposed to rapid degradation under high -voltage conditions and are most often used in low -power vacuum tubes.
Hot cathodes, which must handle high current, have common hexaboride coatings such as hexaboride Ceru (CEB6) or Lanthanum hexaboride (Lab6). Other types of hexaborides that are commonly used for the coat of hot cathodes include hexaboride baryum, calcium hexaboride and hexaboride Stroncia. These types of hot cathodes are burningThey have a longer lifetime than hot cathodes of tungsten, but are also more expensive.
fibers that contain a small amount of Thoria are another option for hot cathodes. The government warms up white glow in the atmosphere containing hydrocarbons, causing thorium migration to the fiber surface. Thorium fibers can handle high tension and have a long life. The primary disadvantage of fiater fibers is that thorium is radioactive. Alternatives to Thorium in hot cathode fibers include Cerium, Lanthanum, Yttrium and Zirconium.