Lanthanum boride, LaB

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. 

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. 

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... 

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