Carbon-arc electrode

Lanthanum fluoride is used in phosphor lamp coating. Mixed with other rare earths, it is used in carbon arc electrodes and lasers. Also, the fluoride is used in the production of lanthanum metal, an intermediate step in the manufacture of high purity metal. 

Highly pure lanthanum oxide is used to make optical glass of high refractive index for camera lenses. It also is used to make glass fibers. The oxide also is used to improve thermal and electrical properties of barium and strontium titanates. Other applications are in glass polishes carbon arc electrodes fluorescent type phosphors and as a diluent for nuclear fuels. In such apph-cations, lanthinum oxide is usually combined with other rare earth oxides. 

Huczko A, Lange H, Byszewski P et al (1997) Fullerene formation in carbon arc electrode gap dependence and plasma spectroscopy. J Phys Chem A 101 1267-1269... 

Use Phosphor lamp coating (gallium arsenide solid-state lamp), carbon arc electrodes, lasers. 

Use Calcium lights, optical glass, technical ceramics, cores for carbon-arc electrodes, fluorescent phosphors, refractories. 

In the early 1960 s the total consumption of lanthanides was 1.6x 10 metric tons, used mainly in lighter flints, carbon arc electrodes, and glass polishing powders (Petrick et al., 1973). By 1975 the consumption was more than 20 x 10 metric tons and the main uses were in metallurgy (—45%), catalysts and chemicals (—36%), glasses and ceramics (—17%), and electronics (—2%) (Cannon, 1976). The increase and changes in emphasis were the direct result of much research on the nature and possible applications of those elements. 

Electric-Arc Furnace. The electric-arc furnace is by far the most popular electric steelmaking furnace. The carbon arc was discovered by Sir Humphry Davy in 1800, but it had no practical appHcation in steelmaking until Sir William Siemens of open-hearth fame constmcted, operated, and patented furnaces operating on both direct- and indirect-arc principles in 1878. At that early date, the avadabiHty of electric power was limited and very expensive. Furthermore, carbon electrodes of the quaHty to carry sufficient current for steel melting had not been developed (see Furnaces, electric). 

Fullerenes are described in detail in Chapter 2 and therefore only a brief outline of their structure is presented here to provide a comparison with the other forms of carbon. The C o molecule, Buckminsterfullerene, was discovered in the mass spectrum of laser-ablated graphite in 1985 [37] and crystals of C o were fust isolated from soot formed from graphite arc electrodes in 1990 [38]. Although these events are relatively recent, the C o molecule has become one of the most widely-recognised molecular structures in science and in 1996 the codiscoverers Curl, Kroto and Smalley were awarded the Nobel prize for chemistry. Part of the appeal of this molecule lies in its beautiful icosahedral symmetry - a truncated icosahedron, or a molecular soccer ball, Fig. 4A. 

Fullerenes are a range of stable closed-shell carbon molecules and their derivatives, of which Qo is the archetype. The next highest stable member of the series is C70 which is found in small quantities with in arc electrode soot. C,o may be regarded as a Qo molecule with an extra belt of hexagons inserted at the... 

The carbon-arc plasma of extremely high temperatures and the presence of an electric field near the electrodes play important roles in the formation of nanotubes[ 1,2] and nanoparticles[3]. A nanoparticle is made up of concentric layers of closed graphitic sheets, leaving a nanoscale cavity in its center. Nanoparticles are also called nanopolyhedra because of their polyhedral shape, and are sometimes dubbed as nanoballs because of their hollow structure. 

Ytterbium oxide (Yb O ) is used to make special alloys, ceramics, and glass. It can be used for carbon arc-lamp electrodes that produce a very bright light. 

The carbon arc apparatus is shown schematically in Figure 10.2.2. The reaction chamber, which is usually made of stainless steel, is connected to vacuum pumps and a gas supply line through valves. The front of the chamber has an observation window to enable monitoring the arc discharge (19). Electrodes, mounted on the end flanges, are supported horizontally. Alternatively, the electrodes can be fixed vertically (20). The electrodes and chamber walls can be cooled by water-cooling devices if necessary. 

The use to which the machine will be put has a bearing on its choice. If it is used for sheets, films, or surface treatment, where only modest penetration, is called for, a low voltage machine, such as the ICT, is suitable. If greater penetration is necessary, a higher voltage machine is needed, and the choice is between the resonant transformer and the Dynamitron. For surface treatment, an ultraviolet light might be sufficient. This is created when an electric arc passes between electrodes separated by gas or vapor. There are two main classes of arcs open, such as the carbon arc, and closed as the various vapor lamps. 

Carbon nanotubes were first identified in high resolution transmission electron microscopy (HRTEM) [12] investigations of the carbon electrodes, which were used in the fullerene generators [2]. It appeared that carbon arcs in a helium atmosphere produced not only the familiar quasi-spherical fullerenes [1], but also other graphitic structures [89], including carbon nanotubes. 

In 1808, Davy invented the carbon arc lamp. He had proposed using carbon as the electrode material instead of metal. (Electrodes are conductors used to establish electrical contact with a nonmetallic part of a circuit.) With carbon electrodes, he made a strong electric current leap from one electrode to the other. This created an intense white light. Davy s invention marked the beginning of the era of electric light. Arc lamps are still used today. 

One of the most important uses of lanthanum compounds is in carbon arc lamps. In a carbon arc lamp, an electrical current is passed through the lamp electrode. The electrode is made of carbon and traces of other materials that have been added. The current causes the carbon to heat up and give off a brilliant white light. The exact color of the light depends on the other materials that have been added to the carbon. Lanthanum fluoride (Laf3) and lanthanum oxide (La203) are usually used for this purpose. 

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