Oxidation of refractory metal

Another example of H2 plasma reduction of oxides of refractory metals is the production of Mo ... 

As discussed in Chapter 4, the passivation potential and the passivation critical current density of stainless steel alloys depend upon the stabdity ofCr203. At temperatures higher than 1000-1200 °C, Cr203 forms volatile Cr03, which drastically decreases the alloy resistance to oxidation and its protectiveness [9,10]. The vapor pressure for oxides of refractory metals above 1000 °C are presented in Fig. 11.2 as Arrhenius plots of log (Pmo) vs. 1/T at constant oxygen pressure or log(po2) [8]-... 

The X-ray phase analysis confirmed that the synthesis products are TiC, ZrC, NbC and TaC carbides, which do not contain free carbon. Fineness of the carbides is determined by the grain size of the metal powder. The synthesis time depends on the diffusion rate of carbon into the volume of the grain or the crystallite. We used oxides of refractory metals as the starting materials for production of fine (1-5 pm) carbides. In this case the mass of the metallic calcium was increased taking into account its consumption for the calcium thermal reduction of the oxides. The presence of a higher amount of the calcium oxide in the salt melt did not incur large difficulties in the synthesis of the carbides and their washing with water to remove salts, because the calcium oxide easily dissolves in acidified water. This method of the carbide synthesis has been covered by a Russian Federation patent [6]. 

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