Preparation and characterization of scandia-doped tungsten powders prepared by a spray-drying method

Abstract

Scandium oxide-doped tungsten powders were prepared by a new method of spray drying combined with two-step hydrogen reduction. The particle size of doped tungsten, powder morphology, and distribution of doped scandium oxide were characterized by scanning electron microscopy, X-ray diffraction, and laser diffraction particle size analysis. Experimental results indicated that the predecessor powders prepared by spray drying were spherical in shape. Two compounds, WO 3 and Sc 2 W 3 O 12 , in the raw powder calcined at 600°C were transformed into metallic tungsten and scandia after reduction at 850°C by hydrogen for 1 h. The scandia-doped tungsten powders obtained had an average size of 950 nm and scandium oxide was distributed evenly throughout the tungsten powder. The mechanism of reduction of the doped tungsten oxide is discussed in this paper.

A Study of Scandia-Doped-Impregnated Cathode Fabricated by Spray Drying Method

“…The two hydrogen consumption peaks at 525°C and 700°C might be caused by the reduction of two stages for WO 3 → WO 2 and WO 2 → W, respectively. On the other hand, compared with the pure tungsten oxide powders [16], it is obvious that the TPR spectra of scandiadoped tungsten oxide powders have been shifted to a lower temperature, indicating that Sc 2 O 3 leads to a decrease of the reduction temperature of the doped powders. Based on the TPR result, it could be deduced that reduction at the temperature >700°C will get scandia-doped tungsten powders.…”

“…It can be found that doping with scandium oxide has a remarkable influence on the reduction process of the powders. It has been reported that the reduction of pure WO 3 → W consists of three reduction stages, i.e., WO 3 → WO 2.9 , WO 2.9 → WO 2 , and WO 2 → W [16], however, the reduction process of scandiadoped tungsten powders was divided into two stages. The results reveal that the hydrogen consumption corresponding to the two-step reduction of WO 3 → WO 2.9 → WO 2 has merged into one peak.…”

A Review of Sc-containing "Scandate" Thermionic Cathodes

“…3) Sc-in-oxides: A related approach implemented by Cui et al [123]- [125] prepares Sc 2 O 3 -doped pressed cathodes by fabricating Sc 2 O 3 and Ba-Ca-aluminate co-doped W powders using a spray drying method and a two-step hydrogen reduction process. In this "Ba scandate" or "scandiadoped powder (SDP)" fabrication approach, cathode pellets are pressed and sintered from a mixture of W powder and various Ba x Sc y O x+ 3 2 y powders [11], [126].…”