Conductive Additive Electric Current Sintering

Abstract

The present disclosure is directed to an electric current sinterable material containing a minority portion being significantly more electrically conductive than the primary material being sintered. This includes forming an inorganic body or sintered coating as well as an apparatus for and method of making use of such a variable composition powder. An electrical current is used to cause a combined energy and temperature profile sufficient for powder-powder sintering. This preferred method for powder-substrate bonding is referred to as flame-assisted flash sintering (FAFS).

1 . A method of electric current-induced sintering of materials with varying degrees of electrical conductivity, the method comprising:
 a) providing a first electrically conductive surface or fluid acting as a first electrode,   b) providing a powder having a plurality of particles of which there is a larger amount of more electrically insulating material and a smaller amount of more electrically conductive material,   c) attaching a green body to said powder or disposing said powder on said first surface to form a powder layer on said first electrode,   d) providing an opposing electrically conductive surface or fluid opposing the first conductive surface, acting as a second electrode, and   e) creating an electric circuit that connects the electrodes so that a current passes through the material between the electrodes, causing said materials to sinter.   
     
     
         2 . The method of  claim 1  wherein said more electrically conductive material becomes less electrically conductive during the sintering. 
     
     
         3 . The method of  claim 1  wherein one or both of the electrodes are ionic gases. 
     
     
         4 . The method of  claim 3  wherein said ionic gas is a flame in the temperature range of 1000° C. to 3000° C. and produces chemically and thermally generated ions as constituents of a plasma. 
     
     
         5 . The method of  claim 4  wherein said flame produces chemically and thermally generated ions as constituents of a flame plasma and the electrical potential creates an arc-like plasma in the flame that is rastered over the coating or body of material being sintered. 
     
     
         6 . The method of  claim 5  wherein the gas flow over the surface is moved such that the area of current flow does not cover all the coating, resulting in areas of more sintered material where the gas makes contact with the coating. 
     
     
         7 . The method of  claim 1  wherein sintering occurs at a voltage at least 20% less than of that possible without a conductivity-enhancing additive in the composition. 
     
     
         8 . The method of  claim 1  wherein the electric arc is traversed over select areas where coating material is desired to remain for the product being made and subsequently the more sintered powder layer is removed when the substrate is subjected to a cleaning or unsintered powder removal method. 
     
     
         9 . The method of  claim 1  wherein the material being sintered is composed of areas with different compositions. 
     
     
         10 . A process for sintering a powder comprising
 a) having two electrodes on opposing sides of a material to be sintered,   b) providing between said electrodes a powder having a plurality of particles of which there is a larger amount of less electrically conductive material and a smaller amount of more electrically conductive material, and   c) passing a current through said powder sufficient to sinter said powder.   
     
     
         11 . The process of  claim 10  wherein said more electrically conductive material becomes less electrically conductive during the sintering. 
     
     
         12 . The process of  claim 10  wherein the sintered material has an electrical conductivity at least 10 times less than that of said material to be sintered. 
     
     
         13 . The process of  claim 10  wherein said more electrically conductive material is carbonaceous. 
     
     
         14 . The process of  claim 10  wherein said more electrically conductive material is a mixture of electrically conductive materials. 
     
     
         15 . The process of  claim 10  wherein said less electrically conductive material is a mixture of less conductive materials. 
     
     
         16 . The process of  claim 10  wherein said sintering is started at below 600° C. 
     
     
         17 . The process of  claim 10  additionally comprising an electrical circuit configured to apply at least part of the range of 100 V to 5000 V of electrical potential and control a desired flow of current of 1 mA to 5 A through said electrodes. 
     
     
         18 . A composition of starting materials for use in electric-current sintering comprising:
 a) a majority of a first material comprising an inorganic powder of at least one composition,   b) a minority of a second material at least three times more conductive than said first material,   c) so that said starting material can be formed into a body or coated onto a surface when sintered.   
     
     
         19 . The composition of  claim 18  wherein the said second material is at least 10 times more conductive than said first material. 
     
     
         20 . The composition of  claim 18  wherein the second material is a metalloid, metal, or semiconductor.