Preparation And Property Of Nano-Powder Of Tungsten Added With Rare Earth Oxides

The tungsten cathode materials added rare earth oxide have wide application foreground because of a variety of advantages including work function, electronic emission ability and work temperature. The key point to improve material's emission ability is how to refine grain size of tungsten matrix and how to homogenize the rare earth elements in the matrix materials. The processing of ultra-fine grain tungsten powder was studied in this thesis.The effects of different doping methods (solid-solid, solid-liquid and liquid-liquid ) on the uniformity of the mix powder materials before reduction has been investigated. The rare earth oxide added powders by above three different methods were reduced in industry processing condition. The properties of reduced powder materials were studied by means of XRD, SEM, TEM. The results showed that the uniformity of the powder particle of solid-liquid method is improved and the size(about 1 # m) is much smaller than that of the solid-solid particle which is 1 ~4 # m. The liquid-liquid processing, from rare earth nitrate and ammonium metatungstate is uniform on ion level. The final reduced powders from the liquid-liquid processing were finest and their grain size distribution was more uniform than that of the powder materials of other two methods. The particle size was between 500nm and 1 micron.In order to make superfine powder, the three-step processing of nanometer tungsten materials was mainly investigated in this paper, which included following steps: liquid-liquid doping, freeze-drying and twice reduction. Four kinds of solutions (AMT, AMT+ La(NO3 )3, AMT+ Ce(NO3 )3, AMT+ Y(NO3 )3) were madefrom ammonium metatungstate, rare earth nitrate and distilled water. The freeze-drying powders were obtained by freeze-drying. The powder structure and heat stability from the freeze-drying ammonium metatungstate powder added with and without rare earth were studied by TG-DTA and IR. The optimum reduction processing parameter were determined as 450癈 X lh+700癈 X lh. Under different reduction temperature, the ultra-fine grain tungsten powder materials can be obtained from ammonium metatungstate freeze-drying powder. The tungsten particle was studied by means of XRD and TEM. The finally tungsten powder with regular form has gotten and the particle size distribution was about 30~100 nm.