In industry, higher purity metals have been expected for a variety of reasons. For tantalum, a higher purity metal is particularly needed because it can be used as a sputtering target and in electronic components such as capacitors. In this way, impurities in the tantalum metal have an adverse effect on the properties of products made of tantalum.
In processing tantalum, the tantalum is derived from the ore, which is then broken, separated from the crushed ore by an acid solution, and then separated from the acid solution containing niobium and other impurities in a density containing tantalum acid solution. The acid solution containing the tantalum is then crystallized into a salt, and the salt containing the tantalum is reacted with pure sodium in a container with agitation, usually made of a nickel alloy material of which tungsten or molybdenum is a component. The vessel is usually double-walled and has an inner surface of pure nickel. The salt is then dissolved in water to obtain tantalum powder. However, in this treatment, the tantalum powder is contaminated by various surfaces in contact with it, such as those containing tungsten and/or molybdenum. Many contaminants can be volatilized in subsequent smelting processes, with the exception of easily soluble refractory metals such as Nb, Mo, and W. These impurities are extremely difficult or impossible to remove, thus preventing the acquisition of tantalum products of extremely high purity.
Therefore, it is expected to obtain higher purity tantalum products, which basically avoid the pollutants from the above processing process. At the same time, tantalum with higher purity, finer grain size and/or uniform texture is expected. This fine grain size is an important characteristic for sputtering targets made of tantalum, because fine grain size can improve the thickness uniformity of the sputtering deposited film. In addition, other tantalum-containing products of fine grain size can improve deformation uniformity and enhance deep drawing ductility, which are beneficial for the manufacture of capacitor casings and laboratory crucible, and increase the killing power of explosive formed penetrators (EFP's). The uniform texture of tantalum-containing products can improve the sputtering efficiency (such as greater sputtering rate) and vertical anisotropy (such as improved deep drawing) of the products used.
