Lanthanum boride

The electron sources used in most sems are thermionic sources in which electrons are emitted from very hot filaments made of either tungsten (W) or lanthanum boride (LaB ). W sources are typically heated to ca 2500—3000 K in order to achieve an adequate electron brightness. LaB sources require lower temperatures to achieve the same brightness, although they need a better vacuum than W sources. Once created, these primary electrons are accelerated to some desired energy with an energy spread (which ultimately determines lateral resolution) on the order of ca 1.5 eV. 

Electron microscopes allow a close view of structures. Lanthanum boride provides the electrons. 

This soft, silver white metal reacts with air and water. The oxide is applied in optical glasses with high refractive indices (special lenses for powerful cameras and telescopes). Used for special effects in optoelectronics and electronics. Lanthanum exhibits catalytic properties. It is a component of flint and battery electrodes. Lanthanum boride (LaB6) is the superior electron-emitter for electron microscopes. Lanthanum is the first of the series of 14 lanthanides, also called the "rare-earth" metals, whose inner N shells are filled with electrons. They do not belong on the "red list" of endangered species they are neither rare nor threatened with depletion. China is particularly rich in lanthanide ores. 

LaB6 lanthanum boride 12008-21-8 25.00 4.7600 1 2422 MgH16l208 magnesium iodide octahydrate 7790-31-0 25.00 2.1000 1... 

To eorreet for instrumental misalignment an internal standard, e.g. 10% silieon (Si) or eorundum (a-Al203) powder (1 am Fisher Comp. 122651 K) should be mixed with the sample. The peak width must be eorreeted for the instrumental broadening using a well crystalline standard, sueh as lanthanum boride LaB. As an example, a Rietveld fit of an X-ray pattern from a mixture of synthetic hematite and goethite is shown in Fig. 3-9. 

Fertilizers containing small amounts of REE have been found to lead to increased growth of wheat, rice and peanut crops. Highly pure lanthanum boride crystals are used for manufacturing electron microscope guns. 

Lanthanum Boride. LaB m.p. 2100°C sp. gr. 4.7 thermal expansion (25-lOOG -C), 5.7 X 1(H Lanthanum Carbide. LaC exists in various forms the tetragonal room-temperature form changes to hexagonal at intermediate temperatures at 1750 C, through reaction with excess carbon, a cubic phase is produced. 

Lancasta microindentation tester, 50 Lanthanide dicarbides pendulum hardness, 295 Vickers hardness, 304 Lanthanum boride, LaB , 297 Lanthanum oxide (1 03) effect on silica hardness, 238 as network modifier, 238 Lanthanum silicate (La2 i207) hardness, 242 precipitate in silica, 238 Lateral vent crack, 55, 126, 148, 154, 158-161, 235 analysis of, 159-161 circular contours of, 159 critical flaw size, 154 length as a function of load, 161 and surface distortion, 159 at thin film interfaces, 205 Lattice energy and fracture energy, 198 and hardness, 22, 24 of silicon, 24... 

Mhere materials are labelled with an asterisk, a large number of powders were successfully deposited using the suspension medium described. Mizuguchi et al included alumina barium, strontium and calcium carbonates magnesia, zinc oxide, titanium dioxide, silica, indium oxide, lanthanum boride, tungsten carbide, cadmium sulfide and several metals and phosphors. The list of materials described by Gutierrez et al included several metals carbides of molybdenum, zirconium, tungsten, thorium, uranium, neptunium and plutonium zirconium hydride, tantalum oxide and uranium dioxide. In addition, many metallic and oxide powder suspensions in alcohols, acetone and dinitromethane were studied by Brown and Salt ... 

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