A novel nanocomposite Mo-4%La2O3 cathode has been prepared by sol-gel method and hydrogen reduction process and then hotpressing sintering technique. The lanthana particles in the nanocomposite cathode were less than 100nm, and they were about 300-400nm in the coarse-grained cathode. The particle size of lanthana has a strong effect on the field emission characteristics of cathode. The nanocomposite cathode has superior field electron emission ability than that of the coarse-grained cathode. The sites of field electron emission of the nanocomposite cathode nearly extend over the whole surface of cathode, whereas the emission sites of the coarse-grained cathode concentrate on a small area of the cathode surface. The reasons for the different distribution of emission sites were discussed.

Nanostructured W-La2O3 electrode materials with a high content of La2O3 have been prepared by mechanical alloying (MA) and hot pressing and sintering (HPS). An investigation has been made on operation characteristics for nanostructured W-La2O3 cathodes. The service lifetime of the nanostructured W-La2O3 cathode is longer than that of commercially used W-2wt.% La2O3 cathodes. These operation characteristics depend on the content of the rare-earth oxide. Specially, the content of La2O3 governs resistance to arc erosion of the electrodes.

The CuCr25 alloys prepared by vacuum induction melting (VIM) were investigated. The experimental results show that Wand Ni had significant influence on the microstructure of CuCr25 alloys. For CuCr25Ni0.5 and CuCr25W1 alloys, the Cr phase was dramatically refined and presented nodular morphology. Wcould increase the breakdown strength of CuCr25. The electric conductivity of CuCr25Ni0.5 decreased, but still reached the level of conventional CuCr alloys. The other properties of CuCr25Ni0.5 and CuCr25W1 alloys did not degrade.

Arctracks on the surface of coarse crystalline, amorphous, and nanocrystalline Cu60Zr28Ti12 cathodes were investigated. On the surface of coarse crystalline Cu60Zr28Ti12, cathode spots were restricted to a small zone, while on the surface of amorphous and nanocrystalline Cu60Zr28Ti12 cathodes, the spots spread over a wide area, of about 15×2.4mm2 and more. The arc tracks on the amorphous ribbons had a worm-like form, which is attributed to continuous cathode spot motion. The arc track on nanocrystalline Cu60Zr28Ti12 alloys, crystallized from the amorphous alloy, consisted of densely distributed～3 μm craters.

By hot swaging, the nano-composite W-4.5%ThO2 cathode was fabricated. A comparative investigation has been made on the operation characteristics for a conventional W-2%ThO2 cathode, a conventional W-4%ThO2 cathode and a nano-composite W-4.5%ThO2 cathode. The results showed that the arc starting and arc voltage-current characteristic of the nano-composite W-4.5%ThO2 electrode was the best among the three cathodes. These operating characteristics depended on the content and the size of thoria. The anti-erosion ability of the nano-composite W-4.5%ThO2 cathode was slightly better than that of conventional W-4%ThO2 cathode, but was obviously improved as compared to W-2%ThO2 cathode, indicating that the content of thoria governs the resistance to arc erosion of the electrodes.