The present invention relates to a tantalum powder and a solid electrolytic capacitor using the same.
Tantalum powder for a solid electrolytic capacitor has customarily been produced by reducing potassium tantalum fluoride by metal sodium. An anode body for a solid electrolytic capacitor can be produced by adding an adequate binder to the tantalum powder, molding the resulting mixture, and then sintering the resulting molding. Generally, High CV powder with a great CV value has a small grain size and has a low mechanical strength when molded. In light of this, it is a common practice to increase the density of the molding in order to increase the mechanical strength. However, an increase in the density of the molding results in a decrease in CV value (capacity) and an increase in tan .delta. value (electrical characteristic), adversely effecting the characteristic of the capacitor.
Japanese Patent Laid-Open Publication No. 8-97095, for example, teaches tantalum powder for the anode of an electrolytic capacitor and capable of increasing the mechanical strength of a sintered body. This tantalum powder consists of tantalum powder having a mean grain size of 1.0.mu.m to 5.0 .mu.m and 10 nm to 500 nm tantalum powder having a mean particle size of 10 nm to 500 nm and added to the above tantalum powder in an amount of 1 wt % to 25 wt %. The tantalum powder whose mean grain size is 1.0 .mu.m to 5.0 .mu.m is selected from a group consisting of high pressure, low capacity powder whose CV value is 10,000 .mu.F/g to 15,000 .mu.F/g, high pressure, medium capacity powder whose CV value is 20,000 .mu.FV/g to 30,000 .mu.FV/g, and medium pressure, high capacity powder whose CV value is 30,000 .mu.FV/g.
However the problem with the above Laid-Open Publication No. 8-97095 is that the tantalum powder having a mean grain size of 10 nm to 500 nm promotes sintering and thereby reduces the cavity distribution of the resulting anode body. This adversely effects the electrical characteristic (tan .delta. value).