Titanium dioxide is a broadband semiconductor material, which is often used to photocatalytic degradation of organic pollutants in gases or liquids. However, it is well known that titanium dioxide is not efficient enough to degrade pollutants in the environment. This is mainly because its wide band gap semiconductor can only respond to the ultraviolet band of sunlight, while ultraviolet light accounts for only 3%-5% of sunlight, which greatly limits the utilization of titanium dioxide to sunlight.

Tungsten powder is widely used in cemented carbide, tungsten products, chemical industry and steel industry. Tungsten powder is used as raw material for cemented carbide products and other tungsten products. Its particle size and size distribution have an important impact on product performance.

Tungsten carbide particles have a series of advantages, such as chemical stability, high hardness, almost comparable to the hardness of diamond, and extremely high wear resistance. The bonding strength between deposited tungsten carbide particles and Ni-P coatings will affect the performance of the composite coatings. Therefore, improving the bonding strength between coating and matrix and the bonding between deposited tungsten carbide particles and nickel phosphorus cells and avoiding the falling off of deposited particles become the key to ensure the effectiveness of composite coating.

Because tungsten can form soluble heteropoly acid (such as [PW₁₂O₄₀]₃^-) with impurities such as phosphorus, arsenic and silicon at the ratio of 1:6 to 1:12, a small amount of phosphorus can cause a large amount of tungsten dispersion and loss in the process of hydrochloric acid decomposition, so hydrochloric acid decomposition process mainly deals with high-grade Scheelite Concentrate (requiring low impurities such as phosphorus and arsenic).