Tantalum is preferably of at least 99.995% purity and preferably of at least 99.999% purity. In addition, the tantalum metal and its alloy having a grain size of approximately 50 microns or less; Or it has such texture that the strength of (100) within any 5% thickness increment is less than about 15random or the logarithm of the strength ratio of (111)∶(100) is greater than about -4.0; Or any combination of these properties. The invention also describes articles and components made of tantalum metal, including but not limited to sputtering targets, capacitor housings, resistive films, wires, etc. The invention also describes a method for preparing a high purity tantalum metal including a step in a reaction vessel in which a tantalum-containing salt is reacted with at least one compound capable of reducing the salt to tantalum powder and a second salt. The reaction vessel or the lining of the reaction vessel and the agitator or the lining on the agitator are made of metallic materials having the same or higher vapor pressure as molten tantalum. The high purity tantalum preferably has fine and uniform microstructure.
In industry, higher purity metals have been expected for a variety of reasons. For tantalum, higher purity metals are particularly needed because of its use as sputtering targets and in electronic components such as capacitors. Thus, impurities in tantalum metal have an adverse effect on the properties of tantalum products.
In processing tantalum, tantalum comes from ore and is then crushed. Tantalum is separated from the crushed ore by an acid solution, which is then densified from an acid solution containing niobium and other impurities. The tantalum-containing acid solution is then crystallized into a salt and the tantalum-containing salt is then reacted with pure sodium in a vessel with a stirring, usually made of a nickel alloy 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. In this process, however, tantalum powder is contaminated by surfaces in contact with it, such as surfaces containing tungsten and/or molybdenum. Many contaminants can evaporate during subsequent smelting, with the exception of soluble refractory metals such as Nb, Mo and W. These impurities are extremely difficult or impossible to remove, thus impeding the availability of exceptionally high purity tantalum products.
Therefore, it is desirable to obtain higher purity tantalum products that are largely free of contaminants derived from the above processes. At the same time, tantalum with higher purity, finer grain size and/or uniform texture is expected. This fine grain size is an important property for tantalum sputtering targets because it improves the uniformity of the thickness of the sputtering films. In addition, other tantalum containing products with fine grain size can improve deformation uniformity and enhance deep drawing ductility, which are beneficial for capacitor enclosures and laboratory crucible manufacturing, and increase the lethality of explosively formed penetrators (EFP's). The uniform texture of tantalum products can improve sputtering efficiency (e.g., higher sputtering rate) and vertical anisotropy (e.g., enhanced deep drawing).
