Cerium hexaboride

Uses. In spite of unique properties, there are few commercial appUcations for monolithic shapes of borides. They are used for resistance-heated boats (with boron nitride), for aluminum evaporation, and for sliding electrical contacts. There are a number of potential uses ia the control and handling of molten metals and slags where corrosion and erosion resistance are important. Titanium diboride and zirconium diboride are potential cathodes for the aluminum Hall cells (see Aluminum and aluminum alloys). Lanthanum hexaboride and cerium hexaboride are particularly useful as cathodes ia electronic devices because of their high thermal emissivities, low work functions, and resistance to poisoning. 

Ca4Ti3O10 4-CALCIUM 3-TITANIUM 1(K)XIDE 472 CeB6 CERIUM HEXABORIDE 509... 

Thermionic cathodes consist of a directly heated tungsten hairpin cathode at = 2500 -3000 K, or an indirectly heated pointed rod of lanthanum or cerium hexaboride (LaB, CeB(,) at 1400 - 2000 K. The electrons must overcome the work function of 4.5 eV (W) or 2.7 eV (LaBfe) by thermal activation (Fig. 78, curve a). Between the cathode at the potential -V and the grounded anode, a negatively biased Wehnelt electrode forms a crossover of diameter 20-50 pm (W) or 10-20 pm (LaBe) as an effective electron source. The emitted electrons show an energy spread A = 1 - 2 eV (W) or 0.5- 1 eV (LaBft). A measure of the quality of an electron gun is the axial gun brightness [i ... 

A second thermionic emission source uses lanthanum hexaboride (LaBe). This has a much lower work function than tungsten and so will emit electrons when heated to only 1,800 K (tungsten operates at -2,500 K). LaBe is reactive at its operating temperature, but the emitter is a direct replacement for a tungsten filament, requiring only very minor alteration of the instrument. Cerium hexaboride is an alternative source material of the same type. 

Studies on the thermal properties of lanthanum, cerium, neodymium, and gadolinium hexaborides in the cryogenic region from 5° to 350°K. 193) have shown the presence of two types of anomalies in the latter three substances. At temperatures near 10 °K. there appears a lambda-type anomaly in each which is rather characteristic of a magnetic transformation. At slightly higher temperatures this is followed by Schottky-... 

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