Patent ID: 8673052
Filing Date: 2014-03-18
Classification: B22F,C01G,C01P,H01G

Abstract:
1. A process for preparing tantalum powder with super-high specific capacity for capacitors by reducing tantalum oxide powder through three steps of reductions, which process consists of the steps of: (1) a first reduction step: mixing tantalum oxide powder and a first reducing agent powder homogenously, and then carrying out a reduction reaction in hydrogen and/or inert gas or vacuum atmosphere to obtain a tantalum suboxides powder; wherein said first reducing agent is selected from the group consisting of rare earth metals, hydrides of rare earth metals and mixtures thereof; and wherein the amount of the reducing agent in the first reduction step is 0.3-0.65 times the stoichiometric amount of reducing agent required for removing oxygen content in the tantalum oxide powder; the reaction temperature in the first reduction step is 400-1000° C., and the reaction time is 3-10 hours; (2) a second reduction step: mixing the tantalum suboxides powder obtained from step (1), in which impurities have been removed, with a second reducing agent powder homogenously, and carrying out a reduction reaction in hydrogen and/or inert gas or vacuum atmosphere to obtain a tantalum powder having a high oxygen content; wherein the second reducing agent is selected from the group consisting of rare earth metals, hydrides of rare earth metals and mixtures thereof; and wherein the amount of the reducing agent in the second reduction step is 0.4-0.85 times the stoichiometric amount of reducing agent required for removing oxygen content in tantalum suboxides; the reaction temperature in the second reduction step is 400-1000° C., and the reaction time is 3-10 hours; and (3) a third reduction step: mixing the tantalum powder having high oxygen content obtained from step (2), in which impurities have been removed, with a third reducing agent powder homogenously, and then carrying out a reduction reaction in hydrogen and/or inert gas or vacuum atmosphere to obtain a tantalum metal powder suitable for capacitors; wherein the third reducing agent is magnesium or magnesium alloy; and wherein the amount of the reducing agent in the third reduction step is 1.0-2.0 times the stoichiometric amount of reducing agent required for removing oxygen content in tantalum powder having high oxygen content; the reaction temperature in the third reduction step is 300-900° C., and the reaction time is 2-6 hours; wherein after each reduction step, the oxidation product of the reducing agent and the residual reducing agent are removed from the reaction product; and wherein the first and second reduction steps are solid-solid reactions.