Search

In this work, high pure Mo-10 wt% Cu composite powders with a ultrafine particle size are prepared by a two-step reduction process (first carbothermal reduction and then hydrogen reduction). Ammonium heptamolybdate and copper nitrate trihydrate powders are used as molybdenum and copper source, respectively. The mixtures of raw materials are calcined at 400 °C firstly to form the composite oxides which are then reacted with insufficient carbon black at 1050 °C for 2 h. The as-prepared powders are further reduced by hydrogen at 750 °C for 2 h to obtain the ultrafine Mo-10 wt% Cu composite powders. The experimental results show that the residual carbon of the Mo-10 wt% Cu powders can be decreased to 0.015 wt%, and the composite powders have an average particle size of 200 nm. The sintering behavior of ultrafine Mo Cu powders and the properties (vickers hardness and thermal conductivity) of samples after sintering are investigated. High sintering temperature is beneficial to increase the density of the compact. At 1200 °C, the relative density of the Mo Cu compacts is 98.8%. The vickers hardness and thermal conductivity of the Mo-10 wt% Cu composites sintered at 1200 °C for 3 h are 233 HV and 130 (W/m·k), respectively.

In this paper, high quality Mo-(10–40) wt% Cu and W-(10–40) wt% Cu alloys were prepared by powder metallurgy using the ultrafine molybdenum and tungsten powders as raw materials. The molybdenum powder with the size of 100–200 nm and tungsten powder with the size of 50–100 nm were prepared by a two-step reduction-process composed of an insufficient carbothermal reduction reaction and the following deep reduction reaction by hydrogen. From the experimental results, it was concluded that at the sintering temperature of 1200 °C to 1300 °C, relative densities of the Mo-(10–40) wt% Cu and W-(10–40) wt% Cu sintered blocks can reach >98%, and at the same time, excellent physical and mechanical properties were achieved. Meanwhile, the larger the content of copper in the alloy, the lower the temperature required for densification. At 1300 °C, the relative density, microhardness and thermal conductivity of the Mo-10 wt% Cu and W-10 wt% Cu sintered blocks are 98.83% and 99.36%, 167 HV and 283 HV, 138.38 W·m−1·k−1 and 154.15 W·m−1·k−1, respectively. Whereas, at 1200 °C, the relative density, microhardness and thermal conductivity of the Mo-40 wt% Cu and W-40 wt% Cu sintered block are 99.68% and 98.87%, 150 HV and 207 HV, 138.38 W·m−1·k−1 and 154.15 W·m−1·k−1, respectively. The present method was much more convenient relative to the traditional infiltration method.

In the present study, the solid state reactions between molybdenum disulfide (MoS2) and molybdenum trioxide (MoO3) under different mixing molar ratios and different reaction temperatures have been investigated in order to produce industrial grade molybdenum dioxide (MoO2). It was found that it was difficult to react completely when the temperature was less than 873 K. However, when the temperature was up to 923 K or 973 K, the final product MoO2 with low residual sulfur can be obtained. Results of the residual sulfur levels at different conditions show that the content of residual sulfur decreases with the increase of temperature. In addition, the excess additions of MoO3 are effective and necessary in order to decrease the residual sulfur level. When the mixing molar ratio of MoS2 to MoO3 is 1:6.5, the content of residual sulfur can decrease down to 0.075% at 973 K. It was also found that the reaction between MoS2 and MoO3 obeyed the shrinking core model.