Microwave plasma chemical synthesis of ultrafine powders

Abstract

The present invention relates to the production of ultrafine powders using a microwave plasma apparatus and chemical synthesis technique. Microwaves generated by a magnetron ( 1 ) are passed through waveguides ( 2 ) before they arrive at the head of a plasmatron ( 3 ). These high energy microwaves ionize a plasma gas, thus releasing large amounts of energy. The energy thus released is utilized to initiate and sustain chemical reactions between the desired elements being pumped in a spiral pattern into the plasmatron ( 3 ). The reaction products are quenched rapidly in a reactor column ( 4 ) into ultrafine powders.

What is claimed is:  
     
         1 . An apparatus for the microwave synthesis of materials, comprising: 
 microwave generator;    a waveguide through which a microwave generated by said microwave generator passes into a plasma zone in which a plasma heats reactants to form reaction products;    a plasma gas inlet offset at an angle so that plasma gas passing through the inlet enters the plasma zone in a spiral-shaped pattern; and    a reaction products collector downstream from said plasma zone for collecting the reaction products.    
     
     
         2 . The apparatus of  claim 1 , wherein said plasma zone comprises a microwave damper at a side of the plasma zone away from the waveguide for damping microwaves that have passed through the plasma zone to thereby reduce the power of a reflected microwave by at least 60%.  
     
     
         3 . The apparatus of  claim 2 , wherein the microwave damper is a water cooled glass tube.  
     
     
         4 . The apparatus of  claim 2 , wherein the microwave damper is a water cooled metal tube.  
     
     
         5 . The apparatus of  claim 2 , wherein the microwave damper is a water cooled rectangular tube.  
     
     
         6 . The apparatus of  claim 1 , comprising a column located between the plasma zone and the reaction products collector for cooling the reaction products leaving the plasma zone.  
     
     
         7 . The apparatus of  claim 6 , wherein the column is 8-12″ long.  
     
     
         8 . The apparatus of  claim 1 , comprising a plurality of plasma gas inlets.  
     
     
         9 . The apparatus of  claim 1 , wherein the plasma gas inlet is offset at an angle between 5-30°.  
     
     
         10 . The apparatus of  claim 1 , wherein the plasma gas inlet is offset at 15°.  
     
     
         11 . An apparatus for the microwave synthesis of materials, comprising: 
 a microwave generator;    a waveguide through which a microwave generated by said microwave generator passes into a plasma zone in which a plasma heats reactants to form reaction products;    a microwave damper at a side of the plasma zone away from the waveguide for damping microwaves that have passed through the plasma zone to thereby reduce the power of a reflected microwave by at least 60%; and    a reaction products collector downstream from said plasma zone for collecting the reaction products.    
     
     
         12 . A method for the microwave synthesis of materials, said method comprising: 
 introducing a plasma gas into a microwave applicator;    introducing at least one reactant into the microwave applicator;    generating a microwave in a microwave generator;    directing the microwave into the microwave applicator containing the plasma gas to create a heated plasma in a plasma zone;    absorbing the microwave to reduce the microwave reflection off of a surface of the microwave applicator by at least 60%; and    causing a reaction in the plasma zone thereby converting the at least one reactant into a reaction product.    
     
     
         13 . The method of  claim 12 , further comprising: 
 introducing the plasma gas into the microwave applicator in a spiral shaped pattern.    
     
     
         14 . The method of  claim 12 , further comprising: 
 introducing the plasma gas into the microwave applicator at an oblique angle to thereby produce a spiral shaped pattern.    
     
     
         15 . The method of  claim 12 , wherein at least one reactant is a powder material.  
     
     
         16 . The method of  claim 13 , wherein at least one reactant is chemical vapor.  
     
     
         17 . An aggregate of powders consisting essentially of particles having an average particle size less than 1 micron, and a particle size distribution of less than 50 nm.  
     
     
         18 . The aggregate of powders of  claim 17 , wherein the particles are metal particles.  
     
     
         19 . The aggregate of powders of  claim 17 , wherein the particles are ceramic particles.  
     
     
         20 . The aggregate of powders of  claim 19 , wherein the ceramic particles are selected from the group consisting of oxides, carbides and nitrides.