Hot cathode is also a name for a hot filament ionization gauge, a vacuum measuring device.

Closeup of the filament on a low pressure mercury gas discharge lamp showing white thermionic emission mix coating on the central portion of the coil. Typically made of a mixture of barium, strontium and calcium oxides, the coating is sputtered away through normal use, often eventually resulting in lamp failure.

In vacuum tubes, a hot cathode is a cathode electrode which emits electrons due to thermionic emission. (Cf. cold cathodes, where field emission is used and which do not require heating.) The heating element is usually an electrical filament. Hot cathodes typically achieve much higher power density than cold cathodes, emitting significantly more electrons from the same surface area. Note: Principals are mostly the same for hot cathode ion sources in particle accelerators to create electrons The Hot filament ionization gauge sometimes called a hot filament and hot cathode , is the most widely used vacuum (negative pressure) measuring device for the region from 10-1 to 10-9 pascals. ... Image File history File links Download high-resolution version (813x758, 148 KB) Closeup of a filament in a germicidal lamp showing thermionic coating. ... Image File history File links Download high-resolution version (813x758, 148 KB) Closeup of a filament in a germicidal lamp showing thermionic coating. ... General Name, Symbol, Number barium, Ba, 56 Chemical series alkaline earth metals Group, Period, Block 2, 6, s Appearance silvery white Atomic mass 137. ... General Name, Symbol, Number strontium, Sr, 38 Chemical series alkaline earth metals Group, Period, Block 2, 5, s Appearance silvery white metallic Atomic mass 87. ... General Name, Symbol, Number calcium, Ca, 20 Chemical series alkaline earth metals Group, Period, Block 2, 4, s Appearance silvery white Atomic mass 40. ... In electronics, a vacuum tube or (outside North America) thermionic valve or just valve, is a device generally used to amplify, switch or otherwise modify, a signal by controlling the movement of electrons in an evacuated space. ... Diagram of a copper cathode in a Daniells cell. ... The electron is a fundamental subatomic particle that carries an electric charge. ... Thermionic emission (archaically known as the Edison effect) is the flow of electrons from a metal or metal oxide surface, caused by thermal vibrational energy overcoming the electrostatic forces holding electrons to the surface. ... Note: Principles are mostly the same for cold cathode ion sources as in particle accelerators to create electrons. ... Also known as Fowler-Nordheim tunneling, field emission is a form of quantum tunneling in which electrons pass through a barrier in the presence of a high electric field. ... HEROW!!! A filament of a 60-watt light bulb at 75X magnification An electrical filament is a thread of metal, usually tungsten, which is used to convert electricity into heat and light for the incandescent light bulb as made in 1878 by Joseph Wilson Swan, among others. ...

Hot cathodes may be either directly heated, where the filament itself is the source of electrons, or indirectly heated, where the filament is electrically insulated from the cathode; this configuration minimizes the introduction of hum when the filament is energized with alternating current. The filament is most often made of tungsten. With indirectly heated cathodes, the filament is usually called the heater instead. The cathode for indirectly heating is usually realized as a nickel tube which surrounds the heater. City lights viewed in a motion blurred exposure. ... General Name, Symbol, Number tungsten, W, 74 Chemical series transition metals Group, Period, Block 6, 6, d Appearance grayish white, lustrous Atomic mass 183. ...

The cathode is typically covered with an emissive layer, made of a material with lower work function, which emits electrons more easily than bare tungsten metal, reducing the necessary temperature and lowering the emission of metal ions. Cathodes can be made of pure sintered tungsten as well; tungsten cathodes in the shape of a parabolic lens are used in electron beam furnaces. Thorium can be added to tungsten to increase its emissivity, due to its lower work function. Some cathodes are made of tantalum. The work function is the minimum energy (usually measured in electron volts) needed to remove an electron from the Fermi level in a metal to a point at infinite distance away outside the surface. ... Sintering is a method for making objects from powder, increasing the adhesion between particles as they are heated. ... A parabola A parabola (from the Greek: παραβολή) is a conic section generated by the intersection of a cone, and a plane tangent to the cone or parallel to some plane tangent to the cone. ... Look up lens in Wiktionary, the free dictionary. ... General Name, Symbol, Number thorium, Th, 90 Chemical series Actinides Group, Period, Block n/a, 7, f Appearance silvery white Atomic mass 232. ... General Name, Symbol, Number tantalum, Ta, 73 Chemical series transition metals Group, Period, Block 5, 6, d Appearance gray blue Atomic mass 180. ...

A common type is an oxide-coated cathode. The earliest material used was barium oxide; it forms a monoatomic layer of barium with an extremely low work function. More modern formulations utilize a mixture of barium oxide, strontium oxide and calcium oxide. Another standard formulation is barium oxide, calcium oxide, and aluminium oxide in 5:3:2 ratio. Thorium oxide is used as well. Oxide-coated cathodes operate at about 800-1000 °C, orange-hot. They are used in most small glass vacuum tubes. They are rarely used in high-power tubes, as they are sensitive to high voltage and oxygen ions and undergo rapid degradation under such conditions. [1] ... General Name, Symbol, Number barium, Ba, 56 Chemical series alkaline earth metals Group, Period, Block 2, 6, s Appearance silvery white Atomic mass 137. ... Strontium Oxide SrO is formed when strontium reacts with oxygen. ... Calcium oxide (CaO), commonly known as lime, quicklime or burnt lime, is a widely used chemical compound. ... Aluminium oxide is a chemical compound of aluminium and oxygen with the chemical formula Al2O3. ... Thorium dioxide (ThO2), also called thorium(IV) oxide (IUPAC) is a white, crystalline powder. ...

Lanthanum hexaboride (LaB₆) and cerium hexaboride (CeB₆) are used as the coating of some high-current cathodes. Hexaborides show low work function, around 2.5 eV. They are also resistant to poisoning. Cerium boride cathodes show lower evaporation rate at 1700 K than lanthanum boride, but it becomes equal at 1850 K and higher. Cerium boride cathodes have one and a half times the lifetime of lanthanum boride, due to its higher resistance to carbon contamination. Boride cathodes are about ten times as "bright" as the tungsten ones and have 10-15 times longer lifetime. They are used eg. in electron microscopes, microwave tubes, electron lithography, electron beam welding, X-Ray tubes, and free electron lasers. [2] Lanthanum hexaboride (LaB6, also called lanthanum boride and (incorrectly) LaB) is an inorganic chemical, a boride of lanthanum. ... Cerium hexaboride (CeB6, also called cerium boride, CeBix, CEBIX, and (incorrectly) CeB) is an inorganic chemical, a boride of cerium. ... The electronvolt (symbol eV, or, rarely and incorrectly, ev) is a unit of energy. ... The Kelvin scale is a thermodynamic (absolute) temperature scale where absolute zero—the lowest possible temperature where nothing could be colder and no heat energy remains in a substance—is defined as zero kelvin (0 K). ... A transmission electron microscope. ... Microwaves are electromagnetic waves with wavelengths longer than those of terahertz (THz) wavelengths, but relatively short for radio waves. ... // The practice of using a beam of electrons to generate patterns on a surface is known as Electron beam lithography. ... Electron beam welding is a welding process where the energy to melt the material is applied by an electron beam. ... An X-Ray tube is a vacuum tube designed to produce man made X-Ray photons on demand. ... This article needs to be cleaned up to conform to a higher standard of quality. ...

For manufacturing convenience, the oxide-coated cathodes are usually coated with carbonates, which are then converted to oxides by heating, and then the metal monolayer is formed in a process called electrode activation. The activation may be achieved by microwave heating, direct electric current heating, or electron bombardment while the tube is on the exhausting machine, until the production of gases ceases. The purity of cathode materials is crucial for tube lifetime. [3] In organic chemistry, a carbonate is a salt of carbonic acid. ...

Thoriated filaments are another option. A small amount of thorium is added to the tungsten of the filament. The filament is heated white-hot, at about 2400 °C, and thorium atoms migrate to the surface of the filament and form the emissive layer. Thoriated filaments can have very long lifetimes and are resistant to high voltages. They are used in nearly all big high-power vacuum tubes for radio transmitters, and in some tubes for hi-fi amplifiers. Their lifetimes tend to be longer than those of oxide cathodes. [4] General Name, Symbol, Number thorium, Th, 90 Chemical series Actinides Group, Period, Block n/a, 7, f Appearance silvery white Atomic mass 232. ...

The emissive layers degrade slowly with time, and much quicker when the cathode is overloaded with too high current. The result is weakened emission and diminished power of the tubes, or brightness of the CRTs, affected.

The activated electrodes can be destroyed by contact with oxygen or other chemicals (eg. aluminium, or silicates), either present as residual gases, entering the tube via leaks, or released by outgassing or migration from the construction elements. This results in diminished emissivity. This process is known as cathode poisoning. High-reliability tubes had to be developed for the early Whirlwind computer, with filaments free of traces of silicon. General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Atomic mass 15. ... General Name, Symbol, Number aluminium, Al, 13 Chemical series poor metals Group, Period, Block 13, 3, p Appearance silvery Atomic mass 26. ... In chemistry, a silicate is a compound containing an anion in which one or more central silicon atoms are surrounded by electronegative ligands. ... The Whirlwind computer was developed at the Massachusetts Institute of Technology. ... General Name, Symbol, Number silicon, Si, 14 Chemical series metalloids Group, Period, Block 14, 3, p Appearance as coarse powder, dark gray with bluish tinge Atomic mass 28. ...

Slow degradation of the emissive layer and sudden burning and interruption of the filament are two main failure modes of vacuum tubes.

Hot cathodes are the main source of electrons in electron guns in cathode ray tubes, electron microscopes, vacuum tubes, and in some fluorescent lamps. Electron gun from a cathode ray tube An electron gun is a component that produces an electron stream that has a precise kinetic energy, being used in all TVs and monitors which use cathode ray tube technology, and in other instruments, eg. ... Cathode ray tube employing electromagnetic focus and deflection Cutaway rendering of a color CRT Electron guns Electron beams Focusing coils Deflection coils Anode connection Mask for separating beams for red, green, and blue part of displayed image Phosphor layer with red, green, and blue zones Close-up of the phosphor... A transmission electron microscope. ... In electronics, a vacuum tube or (outside North America) thermionic valve or just valve, is a device generally used to amplify, switch or otherwise modify, a signal by controlling the movement of electrons in an evacuated space. ... Assorted types of fluorescent lamps. ...