Nanocrystalline metal powders comprising tungsten, molybdenum, rhenium and/or niobium can be synthesized using a combustion reaction. Methods for synthesizing the nanocrystalline metal powders are characterized by forming a combustion synthesis solution by dissolving in water an oxidizer, a fuel, and a base-soluble, ammonium precursor of tungsten, molybdenum, rhenium, or niobium in amounts that yield a stoichiometric burn when combusted. The combustion synthesis solution is then heated to a temperature sufficient to substantially remove water and to initiate a self-sustaining combustion reaction. The resulting powder can be subsequently reduced to metal form by heating in a reducing gas environment.

The invention relates to a method for preparing high-melting-point metal powder through multi-stage deep reduction, and belongs to the technical field of preparation of powder. The method includes the following steps of mixing dried high-melting-point metal oxide powder with magnesium powder and performing a self-propagating reaction, placing an intermediate product into a closed reaction kettle, leaching the intermediate product with hydrochloric acid as a leaching solution so as to obtain a low-valence oxide Me.sub.xO precursor of the low-valence high-melting-point metal; uniformly mixing the precursor with calcium powder, pressing the mixture, placing the pressed mixture into a vacuum reduction furnace, heating the vacuum reduction furnace to 700-1200° C., performing deep reduction for 1-6 h, leaching a deep reduction product with hydrochloric acid as a leaching solution and performing treatment, so as to obtain the high-melting-point metal powder.

A tantalum or tantalum alloy which contains pure or substantially pure tantalum and at least one metal element selected from the group consisting of Ru, Rh, Pd, Os, Jr, Pt, Mo, W and Re to form a tantalum alloy that is resistant to aqueous corrosion. The invention also relates to the process of preparing the tantalum alloy.

A tantalum or tantalum alloy which contains pure or substantially pure tantalum and at least one metal element selected from the group consisting of Ru, Rh, Pd, Os, Jr, Pt, Mo, W and Re to form a tantalum alloy that is resistant to aqueous corrosion. The invention also relates to the process of preparing the tantalum alloy.

A method for preparing a tantalum power of capacitor grade, comprising: solid tantalum nitride is added when potassium fluotantalate is reduced by sodium. The method increases the nitrogen content in the tantalum powder, and at the same time improves the electrical performance of the tantalum powder. The specific capacitance is increased, and the leakage current and loss is improved. The qualification rate of the anode and the capacitor product is also improved. The method is characterized in that the nitrogen in the tantalum nitride diffuses between the particles of the tantalum powder, with substantially no loss, and thus the nitrogen content is accurate and controllable.

A method for preparing a tantalum power of capacitor grade, comprising: solid tantalum nitride is added when potassium fluotantalate is reduced by sodium. The method increases the nitrogen content in the tantalum powder, and at the same time improves the electrical performance of the tantalum powder. The specific capacitance is increased, and the leakage current and loss is improved. The qualification rate of the anode and the capacitor product is also improved. The method is characterized in that the nitrogen in the tantalum nitride diffuses between the particles of the tantalum powder, with substantially no loss, and thus the nitrogen content is accurate and controllable.

Methods for niobium concentration from a carbonatite host rock are presented. A basic process for niobium mineral concentration involves performing niobium mineral flotation, on a sufficiently liberated ore slurry, using at one least aromatic hydroxamate collector; and at least one lead salt as a performance modifier. A more optimized process further includes dispersion. A further optimized process includes: magnetic separation, dispersion, sulphide removal, fine suspended particle removal, and niobium cleaner flotation stages. The use of one of number of tested lead salts during flotation improves the yield, and lowers the cost as a significantly lower amount of the collector is required. The process is useful for recovering a variety of species of niobium minerals such as fersmite, pyrochlore, columbite, fergusonite, niobium-containing rutile, and niobium-containing ilmenite.

Methods for niobium concentration from a carbonatite host rock are presented. A basic process for niobium mineral concentration involves performing niobium mineral flotation, on a sufficiently liberated ore slurry, using at one least aromatic hydroxamate collector; and at least one lead salt as a performance modifier. A more optimized process further includes dispersion. A further optimized process includes: magnetic separation, dispersion, sulphide removal, fine suspended particle removal, and niobium cleaner flotation stages. The use of one of number of tested lead salts during flotation improves the yield, and lowers the cost as a significantly lower amount of the collector is required. The process is useful for recovering a variety of species of niobium minerals such as fersmite, pyrochlore, columbite, fergusonite, niobium-containing rutile, and niobium-containing ilmenite.

A tantalum or tantalum alloy which contains pure or substantially pure tantalum and at least one metal element selected from the group consisting of Ru, Rh, Pd, Os, Ir, Pt, Mo, W and Re to form a tantalum alloy that is resistant to aqueous corrosion. The invention also relates to the process of preparing the tantalum alloy.

A tantalum or tantalum alloy which contains pure or substantially pure tantalum and at least one metal element selected from the group consisting of Ru, Rh, Pd, Os, Ir, Pt, Mo, W and Re to form a tantalum alloy that is resistant to aqueous corrosion. The invention also relates to the process of preparing the tantalum alloy.