High Purity Tungsten Powder Hydrogen Reduction Details

High purity tungsten above 5N has high resistance to electron migration, high-temperature stability and the formation of stable silicides. It is widely used in gate circuit electrode materials of large-scale integrated circuits. At present, there are two key points in the preparation of high purity tungsten powder by hydrogen reduction method: one is the improvement of smelting and purification technology, and the purity of raw materials meets the requirements of corresponding purity; the other is the cleanliness of the preparation process of tungsten powder, so as to reduce the pollution of impurities in the production process.

The traditional preparation and reduction process of high-purity tungsten powder is mainly divided into tungstate solution purification, reduction method for preparing tungsten metal and tungsten metal impurity removal. A great deal of work has been done at home and abroad on refining technology. The raw materials can generally meet the purity requirements of preparing 5N grade high purity tungsten powder. However, due to the introduction of impurities in the preparation process of tungsten powder, it is difficult to produce 5N grade high-purity tungsten powder with high-purity raw materials. Finally, the purity of tungsten powder is improved by the impurity removal process.

In order to solve the problem of impurity intervention in the process of hydrogen reduction, some scholars have put forward different opinions. Th, U, Li, F, P, S, Ti, V, Co, Cu, Zn, As, Zr, Mo, Cd, Sn, Sb, Pb and Bi are hereditary elements in the production of high-purity tungsten powder. The contents of these elements will not increase or decrease in the production of tungsten powder. K, Na, Cl are reactive and volatile elements, especially in the reduction process, controlling the cleanliness of equipment can reduce the content of reactive and volatile elements, while Mg, Ca, Si, Al, Fe, Cr, Ni are easy to increase elements, Mg, Ca, Si, Al are cyclic elements. Adding elements to the environment, while Fe, Cr, Ni are added to the equipment and process, therefore, the impurity elements introduced in the equipment and process are mainly controlled to ensure the purity of tungsten. The main equipments are nickel-based alloy boat vessel, 310 stainless steel rotary furnace, screw feeder coated with tungsten carbide series coating, etc.

High-purity ammonium paratungstate (APT) was put into rotary furnace tube by screw feeding mechanism using screw feeding mechanism coated with tungsten carbide series coating on slurry blade. As a result of friction between material and slurry blade of screw feeding mechanism, impurities such as Fe, Cr, Ni entered the material, the quality of the product fluctuated and high-purity ammonium paratungstate (APT) material entered the material. After calcination in 310 stainless steel rotary furnace tube, the diffusion of Fe, Cr and Ni is not obvious, so the trace elements in WO₃ will not increase obviously in calcination stage. In addition, the furnace contains a lot of water vapor, 310 stainless steel material can be used to prevent Fe, Cr, Ni impurities exceeding the standard, to control the agglomeration due to corrosion by screening rate, prevent pollution of high-purity WO₃.

The new process is an industrial method to prepare tungsten powder with low impurity content. It can effectively control the impurity content in the manufacturing process of tungsten powder and achieve the purpose of producing high purity tungsten powder.

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