Ding Bingjun

Nano-composite Powder of Tungsten Coated Copper Produced by Thermo-chemistry Co-reduction

Abstract Two kinds of copper oxide with different particle sizes and 1.5 μm tungsten trioxide powder were employed to prepare the high-purity CuWO4 powder. By two stage hydrogen-reduction of the CuWO4 at 360 and 750 °C respectively and continuously, nano-composite powder of tungsten coated copper was synthesized. Micro-morphology, crystallization-components and grain-size of the products were investigated by scanning electron microscope (SEM), X-ray diffract meter (XRD) and transmission electric microscope (TEM) and laser particle size analyzer (LPSA) was also applied to measure the particle-size of CuWO4. The W film thickness of nano-composite powder synthesized by smaller-sized CuWO4 is thinner than that made from bigger-sized CuWO4. The average particle size of nano-composite powder of tungsten coated copper is about 50 nm under the two-stage hydrogen reduction.

Effect of Oxide Particle Size on Electron Emission and Vacuum Arc Characteristic of Mo-La2O3 Cathode

Abstract A nanocomposite Mo-4wt% La2O3 cathode was prepared by a high-energy ball-milling and hot pressing technique. The sizes of lanthana particles in the nanocomposite Mo-La2O3 cathode are less than 100 nm; in contrast, the sizes of thoria particles are about 1∼2 μm in a commercial W-4wt% ThO2 cathode. The average vacuum arc-starting field intensity of the nanocomposite Mo-La2O3 cathode is 2.97×107 V/m, which is 62.7% lower than that of the commercial W-ThO2. The nanocomposite Mo-La2O3 cathode exhibits superior electron emission performances, and its distribution area and thickness of electron emission spots are remarkably larger, as compared to those of the commercial W-ThO2 cathode. The size of oxide particles has a great effect on the electron emission performances and vacuum arc characteristics of cathode. The electron emission performance of Mo-La2O3 cathode will be improved with decreasing of the lanthana particles size. When La2O3 particle size decreases to less than 100 nm, the electron emission area and ability of the Mo-La2O3 cathode significantly increase. The much enhanced electron emission performance of the nanocomposite Mo-La2O3 cathode is attributed to the formation of a higher inter electric field and space-charge regions at the interphase boundaries between Mo and La2O3 phases.