In the process of hydrogen reduction of tungsten oxide, the effect of the reduction is not only the metal elements, there are some trace elements, such as rare earth elements.
The effects of trace elements are related not only to quantity, but also to the shape and location of individual elements and the entry stage, for example, the elements that form fine grain particles at grain boundaries are different from the same elements in solid solutions. They are soluble in the bonding phase and different from the tungsten carbide grains.
Some scholars believe that the addition of lanthanum or yttrium (La) (Y) in hydrogen reduction of tungsten oxide, can play a similar role to that of Al.
In the process of research, scholars used the doping method of wet mixing and flow drying to prepare the blue tungsten powder, and push the boat by reverse hydrogen, the decomposition process is performed in two stages, namely at 500 °C, 850 °C, 900 °C, 950 °C, 1000 °C temperature point five 4h reduced with hydrogen. Study found that while maintaining the hydrogen flow rate, the amount of loading the boat, and the holding time, the higher the temperature, the tungsten blue powder particles increases. But with the addition of La2O3, tungsten powder particles gradually became thin, the surface gradually increased, in addition, the addition of 2% Y2O3 is better than the effect of adding 3% La2O3.
The research shows that in the process of blue tungsten oxide hydrogen reduction, the study shows that in the process of blue tungsten oxide hydrogen reduction, the morphology of tungsten powder is changed into quasi regular polyhedron without quasi La or Y by adding rare earth element La or Y; La or Y is present in the form of La2O3 or Y2O3. The La and Y contents determine the distribution of La2O3 or Y2O3 in the crystal. When the content of La2O3 or Y2O3 is high, the La2O3 or Y2O3 particles are dispersed distributed.
The results show that the oxides and tungstate forms in the blue tungsten hydrogen reduction tungsten powder exist in the tungsten blue hydrogen reduction tungsten powder, the addition of an oxide film of La or Y on the surface of the tungsten crystal can prevent the precipitation of the vapor phase tungsten oxide on the surface of the tungsten powder particles Or the chemical reaction of the solid phase, and thus inhibit the growth of tungsten powder particles, it is of great help to the preparation and reduction of ultrafine tungsten powder.
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