Method for Producing a Tungsten Metal Powder Having a High Specific Surface Area

Abstract

The present invention relates to a method for producing a tungsten metal powder having a specific BET surface area of greater than 8 m 2 /g and to a tungsten metal powder that can be obtained by this method.

1 . A process for producing a tungsten metal powder having a specific surface area of more than 8 m 2 /g, as determined by the BET method according to DIN ISO 9277, in which a powdery tungsten source is heated in a hydrogen flow at first with a first heating rate HR 1  to a first temperature T 1  and subsequently with a second heating rate HR 2  to a second temperature T 2 , where T 1 <T 2  and HR 1 >HR 2 , characterized in that the dew point temperature T of the process exhaust gases does not exceed +10° C. 
     
     
         2 . The process according to  claim 1 , characterized in that T 1  is from 400 to 500° C. and/or the heating rate HR 1  is <10 K/min. 
     
     
         3 . The process according to  claim 1 , characterized in that T 2  is from 500 to 650° C. and/or the heating rate HR 2  is <2 K/min. 
     
     
         4 . The process according to  claim 1 , characterized in that the dew point temperature T of the process exhaust gases meets −40° C.<T<+10° C. 
     
     
         5 . The process according to  claim 1 , characterized in that said hydrogen flow is preheated to a temperature of from 350° C. to 650° C. 
     
     
         6 . The process according to  claim 5 , characterized in that the hydrogen employed has a dew point temperature T of <−20° C. 
     
     
         7 . The process according to  claim 1 , characterized in that the process is effected in a heated reaction space, wherein the temperature of the reaction space is not more than 900° C. 
     
     
         8 . The process according to  claim 1 , characterized in that the hydrogen flow is temporarily replaced by an inert gas flow. 
     
     
         9 . The process according to  claim 1 , characterized in that the hydrogen flow has a Reynolds number Re (H 2 ) of from 60 to 600. 
     
     
         10 . The process according to  claim 1 , characterized in that the process includes another step of passivating the tungsten metal powder. 
     
     
         11 . The process according to  claim 1 , characterized in that said process is performed by using a reaction container having a gas-permeable bottom. 
     
     
         12 . A tungsten metal powder having a particle size of from 10 μm to 1000 μm, as determined by laser diffraction, and a specific surface area of larger than 8 m 2 /g, as determined by the BET method according to DIN ISO 9277, characterized in that said tungsten metal powder has an oxygen content of from 900 to 1500 ppm/m 2 /g as determined by carrier gas hot extraction. 
     
     
         13 . The tungsten metal powder according to  claim 12 , characterized in that said tungsten metal powder is obtainable by the process according to  claim 1 . 
     
     
         14 . The tungsten metal powder according to  claim 12 , characterized in that said tungsten metal powder has an oxygen content of from 950 to 1050 ppm/m 2 /g as determined by carrier gas hot extraction.  15  (New) The process according to  claim 2 , characterized in that T 1  is from 430 to 460° C., and/or the heating rate HR 1  is <5 K/min. 
     
     
         16 . The process according to  claim 3 , characterized in that T 2  is from 550 to 590° C. and/or the heating rate HR 2  is from 1 to 1.7 K/min. 
     
     
         17 . The process according to  claim 16 , characterized in that the heating rate HR 2  is 1.5 K/min. 
     
     
         18 . The process according to  claim 6 , characterized in that the hydrogen employed has a dew point temperature T of <−40° C. 
     
     
         19 . The process according to  claim 7 , characterized in that the process is effected in a heated reaction space, wherein the temperature of the reaction space is from 550 to 700° C. 
     
     
         20 . The process according to  claim 9 , characterized in that the hydrogen flow has a Reynolds number Re (H 2 ) of from 75 to 300.