Electrolytic production of powder

Abstract

A method of producing metallic powder comprises steps of arranging a volume of feedstock comprising a plurality of non-metallic particles within an electrolysis cell, causing a molten salt to flow through the volume of feedstock, and applying a potential between a cathode and an anode such that the feedstock is reduced to metal. In preferred embodiments the feedstock is a plurality of discrete powder particles and these particles are reduced to a corresponding plurality of discrete metallic particles. In advantageous embodiments, the feedstock may be sand.

We claim: 
     
         1 . A method for producing metallic powder comprising the steps of:
 arranging a cathode and an anode in contact with a molten salt within an electrolysis cell,   arranging a volume of feedstock comprising a plurality of non-metallic particles within the electrolysis cell,   causing a molten salt to flow through the volume of feedstock, and   applying a potential between the cathode and the anode such that the feedstock is reduced to metal.   
     
     
         2 . The method for producing metallic powder according to  claim 1 , in which the volume of feedstock is arranged on an upper surface of the cathode and a lower surface of the anode is vertically spaced from the feedstock and the upper surface of the cathode. 
     
     
         3 . The method according to  claim 1 , in which the particles making up the feedstock have an average particle diameter of less than 5 mm, preferably in which the average particle diameter is between 60 microns and 3 mm, more preferably between 250 microns and 2.5 mm, or between 500 microns and 2 mm. 
     
     
         4 . The method according to  claim 1 , in which the D10 particle size for the feedstock is greater than 60 microns and the D90 particle size for the feedstock is lower than 3 mm. 
     
     
         5 . The method according to  claim 1 , in which the D90 particle size of the feedstock is no more than 200% greater than the D10 particle size of the feedstock. 
     
     
         6 . The method according to  claim 1 , in which the feedstock is a bulk feedstock that has not been settled or compacted. 
     
     
         7 . The method according to  claim 1 , in which the feedstock has a voidage of greater than 43%, preferably in which the feedstock has a voidage of between 44% and 54%. 
     
     
         8 . The method according to  claim 1 , in which the particles making up the feedstock are substantially free from porosity, for example in which the particles are greater than 90% dense or greater than 95% dense. 
     
     
         9 . The method according to  claim 1 , in which the particles making up the feedstock are porous, for example in which the particles making up the feedstock have a porosity of between 10% and 50%. 
     
     
         10 . The method according to  claim 1 , in which the particles making up the feedstock have a density of between 3.5 g/cm 3  and 7.5 g/cm 3 , preferably between 3.75 g/cm 3  and 7.0 g/cm 3 , for example between 4.0 g/cm 3  and 6.5 g/cm 3 , or between 4.2 g/cm 3  and 6.0 g/cm 3 . 
     
     
         11 . The method according to  claim 1 , in which the particles making up the feedstock are crystalline and have an average crystallite size of greater than 10 micrometres, preferably greater than 50 micrometres, and more preferably greater than 100 micrometres. 
     
     
         12 . The method according to  claim 1 , in which the feedstock has an average crystallite size that is greater than 10% of the average particle size, preferably greater than 20% or more preferably greater than 30% or 50% of the average particle size. 
     
     
         13 . The method according to  claim 1 , in which the feedstock comprises a first set of particles having a composition in which a first metallic element forms the greater proportion by mass, and a second set of particles in which a second metallic element forms the greater proportion by mass, the feedstock being reduced under conditions such that there is no alloying between the first set of particles and the second set of particles. 
     
     
         14 . The method according to  claim 1 , in which the feedstock comprises one or more naturally occurring minerals. 
     
     
         15 . The method according to  claim 1 , in which the feedstock comprises a synthetic mineral. 
     
     
         16 . The method according to  claim 1 , in which the feedstock comprises a first non-metallic particle having a first composition and a second non-metallic particle having a second composition, in which the feedstock is reduced under conditions such that the first non-metallic particle is reduced to a first metallic particle having a first metallic composition and the second non-metallic particle is reduced to a second metallic particle having a second metallic composition. 
     
     
         17 . The method according to  claim 1 , in which the feedstock comprises a high proportion of titanium, and the resulting reduced metal comprises a high proportion of titanium. 
     
     
         18 . The method according to  claim 1 , in which the feedstock particles have an average diameter and the feedstock is loaded onto the upper surface of the cathode to a feedstock depth of between 10 and 500 times the average diameter of the feedstock particles. 
     
     
         19 . The method according to  claim 1 , in which the feedstock particles comprise crystallites having an average crystallite diameter and the feedstock is loaded onto the upper surface of the cathode to a feedstock depth of between 10 and 500 times the average diameter of the feedstock crystallites. 
     
     
         20 . The method according to  claim 1 , in which the upper surface of the cathode comprises a mesh having a mesh size smaller than the D10 particle size of the feedstock. 
     
     
         21 . The method according to  claim 1 , in which the cathode comprises a retaining barrier, such as a peripheral barrier, allowing feedstock to be supported on its upper surface to a depth of greater than 5 mm, preferably greater than 1 cm or greater than 2 cm. 
     
     
         22 . The method according to  claim 1 , in which the feedstock is reduced with substantially no sintering between particles such that a powder can be recovered having an average diameter of slightly lower than an average diameter of the particles making up the feedstock. 
     
     
         23 . The method according to  claim 1 , in which the reduced feedstock forms a friable mass of metallic particles that may be broken up to form the metallic powder, substantially each of the particles forming the metallic powder corresponding to one non-metallic particle in the feedstock. 
     
     
         24 . The method according to  claim 1 , in which the feedstock consists of free-flowing discrete particles of non-metallic material, preferably having an average particle size (D50) of between 100 and 250 microns as measured by laser diffraction. 
     
     
         25 . A metallic powder formed using a method that comprises the steps of:
 arranging a cathode and an anode in contact with a molten salt within an electrolysis cell,   arranging a volume of feedstock comprising a plurality of non-metallic particles within the electrolysis cell,   causing a molten salt to flow through the volume of feedstock, and   applying a potential between the cathode and the anode such that the feedstock is reduced to metal.   
     
     
         26 . A metallic powder comprising a plurality of discrete metallic particles, each of the metallic particles formed by the direct reduction of a discrete non-metallic particle. 
     
     
         27 . The method according to  claim 14 , in which the one or more minerals is one or more of rutile, ilmenite, anatase, leucoxene, scheelite, cassiterite, monazite, lanthanum, zircon, cobaltite, chromite, bertrandite, beryl, uranite, pitchblende, quartz, molybdenite or stibnite. 
     
     
         28 . The method according to  claim 1 , in which the feedstock comprises synthetic rutile.