Study of the reduction of tungsten trioxide doped with NaCl/KCl,KBr or Li_2CO_3

摘要

The reduction of WO_3 dry-doped with a mixture of NaCl/KCl, with KBr or Li_2CO_3 was compared with the reduction of undoped WO_3. The powders were reduced in dry hydrogen in a laboratory furnace either by heating slowly from RT to 1100°C or by inserting the boat immediately into the 1100°C zone. The as-reduced powders were characterized for Bulk and Tap density, as well as Chemical analyses. Fisher number (FSSS) and Laser granulometry (Microtrac) were determined for both as-is and rod-milled samples. The powder morphology was evaluated via image analysis of suitably prepared cross sections. The Hausner ratio, FSSS and Microtrac were all used to assess agglomeration. The reduction mechanism of WO_3, doped with Li_2CO_3, differs from that doped with mixed NaCl/KCl or KBr. While sodium and potassium halides form sodium and potassium monotungstates, M_2WO_4, lithium doped WO_3 leads to the intermediate formation of Li_4WO_5 and Li_6WO_6 confirming previously published results. The effectiveness of an alkali dopant is based upon the nature and stability of the intermediate tungstate, more so than upon the characteristics of the starting dopant.