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WC grain size has significant effect on WC-Co cemented carbide alloy properties. In order to inhibit WC grain growth during sintering process, grain growth-inhibitor Cr 3 C 2 is usually added to tungsten carbide powder in advance through mechanical milling. While, homogeneous distribution of Cr 3 C 2 in the tungsten carbide powder is difficult to achieve and result in abnormal growth of WC grains. For this purpose of growth-inhibitor uniform distribution, (CH 3 COO) 3 Cr is added into ammonium tungstate solution during evaporation and crystallization process to prepare Cr-doped APT powder, which can be used as precursor for ultrafine-grained WC-Co cemented carbide alloy preparation. Compared with conventional APT powder, the Cr-doped APT has smaller particle size and bulk density, moreover, chromium is evenly distributed within it. The Cr-doped APT is then used to produce Cr-doped tungsten powder, which also has smaller particle size than that of conventional tungsten powder. Cr-doped tungsten powder is subsequently prepared into tungsten carbide powder and WC-Co cemented carbide alloy through carbonization and sintering process, respectively. Compared with conventional WC-Co cemented carbide alloy, the obtained WC-Co cemented carbide alloy has smaller mean WC grain size (0.36 μm), and more uniform microstructure. Furthermore, the phenomenon of WC grain abnormal growth during sintering process is not observed, because the grain growth-inhibitor Cr 3 C 2 is well dispersed in tungsten carbide and cobalt composite powder. Results show that the obtained WC-Co cemented carbide alloy presents better mechanical properties (HRA, bending strength, coercive force) than those of conventional WC-Co cemented carbide alloy. Accordingly, the novel addition of (CH 3 COO) 3 Cr during the evaporation and crystallization process is the key factor of ultrafine-grained WC-Co cemented carbide alloy production.

Scheelite was successfully prepared by solid-state calcination synthesis using wolframite [(Fe,Mn)WO 4 ] and calcium carbonate as materials in air atmosphere. The effects of processing parameters, such as calcination temperature, holding time and calcium carbonate dosage on conversion ratio of wolframite were investigated. The conversion of wolframite increased with increasing of temperature, holding time and calcium carbonate dosage. The results demonstrated that 97.58% of wolframite was converted to scheelite in 2 h at temperature of 800 °C under the condition of calcium carbonate stoichiometric ratio of 1.3, and the corresponding reaction products are scheelite, iron oxide and manganese dioxide.