Foundamental Research On Preparation Of Tungsten And Tungsten Carbide By Gas-base Reduction Of Tungsten Oxide

Tungsten carbide,which has excellent physical and chemical properties such as high strength,high thermal resistance and good heat corrosion resistance,is widely used in the production of cemented carbide.With the advancement of science and technology,thermal spraying materials produced by using tungsten carbide have been widely used in the fields of aerospace and military weapons.In addition,tungsten carbide plays an increasingly important role in the field of catalysis.At present,tungsten carbide is produced by high temperature carbonization with tungsten powder as raw material,but the preparation of tungsten powder also requires a complicated process.Therefore,the production of tungsten carbide is a complicated process,high production cost and low efficiency.In this thesis,the process of preparing tungsten and tungsten carbide powder with tungsten trioxide as raw material,methanol or carbon monoxide as reducing agent was studied.The phase transition,morphology evolution,particle size change and reaction mechanism of tungsten trioxide under different reaction conditions?different carbon sources,reaction temperature and time?were studied by Factsage,thermodynamic analysis,X-ray diffraction,transmission electron microscope,scanning electron microscope and BET specific surface area analysis.Experimental studies on the reduction of tungsten trioxide by methanol show that as the reaction temperature increases,the reduction rate of tungsten oxide increases,but the carbonization process will slow down.The morphology of tungsten carbide changes with increasing temperature:at lower temperatures,the reduction carbonization path of tungsten trioxide is WO₃?W₁₈O₄₉?WO₂??W₂C/W??WC;the whole reduction process follows pseudomorphic The transformation mechanism,the prepared tungsten carbide is a large-sized particle composed of small rod-shaped particles?similar to the morphology of tungsten trioxide?;at a higher temperature,WO₃?W₁₈O₄₉?WO₂?W?WC;reduction reaction to chemistry The vapor phase deposition mechanism is mainly used to prepare a spheroidal tungsten carbide powder.When the reaction temperature is higher than 1225K,the final product is tungsten,and the reduction path of tungsten trioxide is WO₃?W₁₈O₄₉?WO₂?W,and as the reaction temperature continues to increase,the prepared tungsten powder will be spherical.The appearance changes to the opposite body shape,and the particle size also becomes larger.The results of the reduction of tungsten trioxide at different temperatures using carbon monoxide as a reducing agent show that the products prepared in the temperature range of 1131K¹366K are rod-shaped tungsten carbide powder,but follow different step-by-step reaction processes at different reaction temperatures.At lower temperatures,the formation path of tungsten carbide is:WO₃?W₁₈O₄₉?WO₂?W₂C?WC;at higher temperatures,the formation path of tungsten carbide is:WO₃?W₁₈O₄₉?WO₂?W?WC.The specific surface area of tungsten carbide prepared at 1131K?858°C?can reach 4.395 m²/g,and the equivalent average particle diameter is 87.34 nm.As the reaction temperature increases,the rate of reduction increases,but complete carbonization requires a longer reaction time,and the particle size of the finally prepared tungsten carbide powder also becomes larger.By comparing with the results of methanol reduction of tungsten oxide,it is found that the presence of water vapor at a higher temperature will have a great influence on the morphology and particle size of the finally prepared tungsten carbide powder.The experimental results of this thesis show that the process of reducing tungsten trioxide to reduce tungsten carbide by using methanol as a reducing agent is feasible,and tungsten carbide powder with different morphology can be prepared by controlling the reaction temperature.It is also proposed to use carbon monoxide as a reducing agent to reduce tungsten trioxide at a lower temperature to prepare tungsten carbide powder with larger specific surface area.This method not only reduces the carbonization temperature,but also can directly obtain tungsten carbide powder from one-step carbonization of tungsten trioxide.It is beneficial to reduce the production cost of tungsten carbide powder.