Niobium powder, process for producing the same and solid electrolytic capacitor therefrom

Abstract

A niobium powder can be used to manufacture a niobium capacitor of excellent electrical properties The niobium powder when formed into a sintered body of 3.15 to 3.9 g/cm 3 density exhibits a capacitance (CV value at a formation voltage of 20V) ranging from 80 to 240 kCV/g and a CV retention of 57% or higher. With respect to the production of the niobium powder, the employed potassium niobate fluoride has a water content of 1000 ppm or less as determined from the amount of water generated upon heating at 600° C. according to the Karl Fischer method.

1 . Niobium powder which has a capacitance (CV value at a formation voltage of 20V) ranging from 80 to 240 kCV/g and a CV retention of 57% or higher when formed into a sintered body of 3.15 to 3.9 g/cm 3  density.  
   
   
       2 . The niobium powder according to  claim 1 , wherein the capacitance ranges from 80 to 120 kCV/g and the CV retention is 84% or higher.  
   
   
       3 . The niobium powder according to  claim 1 , wherein the capacitance ranges from 120 to 160 kCV/g and the CV retention is 75% or higher.  
   
   
       4 . The niobium powder according to  claim 1 , wherein the capacitance ranges from 160 to 240 kCV/g and the CV retention is 57% or higher.  
   
   
       5 . The niobium powder according to  claim 1 , wherein a percentage of pore having a diameter of 0.11 μm or greater, measured by mercury porosimetry, with respect to all pores present in the sintered body is 90 vol % or greater.  
   
   
       6 . The niobium powder according to  claim 1 , wherein a total amount of nickel, iron, and chromium contained is 100 ppm or less, and a total amount of sodium, potassium, and magnesium contained is 100 ppm or less.  
   
   
       7 . A method of producing niobium powder, comprising the step of: 
 reducing potassium niobate fluoride in a diluent salt to produce niobium powder, wherein,    the potassium niobate fluoride has a water content of 1000 ppm or less as determined from an amount of water generated upon heating at 600° C. according to the Karl Fischer method.    
   
   
       8 . The method of producing niobium powder according to  claim 7 , wherein the diluent salt is potassium fluoride having a water content of 500 ppm or less as determined from an amount of water generated upon heating at 700° C. according to the Karl Fischer method.  
   
   
       9 . The method of producing niobium powder according to  claim 7 , wherein an amount of water in a reaction system of the reducing step is adjusted to be 9300 ppm or less with respect to the niobium powder produced.  
   
   
       10 . A method of producing niobium powder by reducing potassium niobate fluoride in a diluent salt to produce niobium powder, comprising the steps of: 
 introducing 1 to 20% of stoichiometric equivalence of a reducing agent in a reduction reaction into a reaction vessel in advance, and    adding a predetermined amount (reaction equivalent) of potassium niobate fluoride and the reducing agent, in that order, and repeating this process to carry out a reaction.    
   
   
       11 . A sintered body which is formed from the niobium powder as defined in  claim 1 .  
   
   
       12 . An anode for a capacitor which is formed from the niobium powder as defined in  claim 1  having a relative leakage current value (Wet value) of 4 nA/CV or less.  
   
   
       13 . A solid electrolytic capacitor, comprising an anode for a capacitor as defined in  claim 12 .  
   
   
       14 . The niobium powder according to  claim 2 , wherein a percentage of pore having a diameter of 0.11 μm or greater, measured by mercury porosimetry, with respect to all pores present in the sintered body is 90 vol % or greater.  
   
   
       15 . The niobium powder according to  claim 3 , wherein a percentage of pore having a diameter of 0.11 μm or greater, measured by mercury porosimetry, with respect to all pores present in the sintered body is 90 vol % or greater.  
   
   
       16 . The niobium powder according to  claim 4 , wherein a percentage of pore having a diameter of 0.11 μm or greater, measured by mercury porosimetry, with respect to all pores present in the sintered body is 90 vol % or greater.  
   
   
       17 . The niobium powder according to  claim 2 , wherein a total amount of nickel, iron, and chromium contained is 100 ppm or less, and a total amount of sodium, potassium, and magnesium contained is 100 ppm or less.  
   
   
       18 . The niobium powder according to  claim 3 , wherein a total amount of nickel, iron, and chromium contained is 100 ppm or less, and a total amount of sodium, potassium, and magnesium contained is 100 ppm or less.  
   
   
       19 . The niobium powder according to  claim 4 , wherein a total amount of nickel, iron, and chromium contained is 100 ppm or less, and a total amount of sodium, potassium, and magnesium contained is 100 ppm or less.  
   
   
       20 . The method of producing niobium powder according to  claim 8 , wherein an amount of water in a reaction system of the reducing step is adjusted to be 9300 ppm or less with respect to the niobium powder produced.