Reactive Spray Formation of Coatings and Powders

Abstract

An apparatus and method for open-atmosphere flame based spraying employs a nozzle to preheat, pressurize and atomize a mechanically pumped reactive and flammable liquid solution through a small orifice or a nozzle and then a set of pilot flames to combust the spray. The liquid feedstock is preheated to a supercritical temperature before reaching the nozzle and is pressurized before spraying due to a reduced size of the outlet port of the feedstock flow channel relative to the inlet. A supplementary collimating, or sheathing, gas is supplied to the flow channel of the feedstock and both the feedstock and the supplementary gas are uniformly heated before spraying. This arrangement helps to avoid clogging of the nozzle and results in satisfactory control of the properties of the particulate products of the spraying procedure.

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         11 . A method for spraying a reactive fluid feedstock, the method comprising
 providing a conduit having a first end and a second end respectively including an opening port and an exit port,   heating a reactive feedstock and then passing the reactive feedstock under pressure through the conduit from the opening port to the exit port to create a feedstock spray,   passing an auxiliary gas through a chamber into the feedstock spray, said auxiliary gas and said feedstock spray turbulently mixing within the chamber; and   igniting the turbulently mixed feedstock and the auxiliary gas spray resulting in a reactive fluid flame spray at the exit port.   
     
     
         12 . The method according to  claim 11  which further comprises introducing a spray of a supplementary material into the path of the reactive fluid flame spray in order to produce a combined coating resulting from the reactive feedstock and the supplementary material. 
     
     
         13 . The method according to  claim 12  wherein the spray of supplementary material is delivered into the reactive fluid flame spray downstream of entry of the non-flammable gas into the reactive fluid flame spray. 
     
     
         14 . The method according to  claim 11 , including controllably reducing the temperature of the reactive fluid flame spray to produce a desired degree of reaction and to control the properties of particulate products of the reactive fluid flame spray. 
     
     
         15 . The method of  claim 14  wherein the step of controllably reducing the temperature comprises blowing a curtain of non-flammable gas into a path of the feedstock spray. 
     
     
         16 . The method according to  claim 11  wherein the conduit is formed of a tube of gradually decreasing inner diameter from the first port to the second port. 
     
     
         17 . The method according to  claim 11  wherein the chamber is formed of a number of interconnected tubes of decreasing inner diameter from the first port to the second port. 
     
     
         18 . An apparatus for thermal spraying of a reactive liquid feedstock, the apparatus comprising:
 a feedstock container,   first heating means for heating contents of the feedstock container,   a conduit having a first port connected to the feedstock container and a second port for discharging feedstock, the second end forming or associated with a nozzle for collimating flow of the discharged feedstock,   pump means for delivering feedstock to the conduit,   a tubing connected to a source of an auxiliary gas and to the second port for generating a shearing force on the feedstock exiting the conduit,   second heating means disposed around the conduit and the sleeve for heating the feedstock flowing through the chamber, and   burner means disposed at the second port for igniting said feedstock when said feedstock leaves the second port along with the auxiliary gas.   
     
     
         19 . The apparatus according to  claim 18  wherein the tubing forms a sleeve surrounding the conduit and the second heating means are disposed around both the conduit and the sleeve for simultaneously heating the feedstock and the auxiliary gas. 
     
     
         20 . The apparatus according to  claim 19  wherein the sleeve for the auxiliary gas is arranged coaxially and concentrically around the conduit. 
     
     
         21 . The apparatus according to  claim 18  wherein the conduit is formed of a tube of gradually decreasing inner diameter from the first port to the second port. 
     
     
         22 . The apparatus according to  claim 18  wherein the chamber is formed of a number of interconnected tubes of decreasing inner diameter from the first port to the second port. 
     
     
         23 . The apparatus according to  claim 18  further comprising gas curtain means disposed for distributing a curtain of a non-flammable gas transversely into a path of burning feedstock discharged from the second port and the nozzle. 
     
     
         24 . The apparatus according to  claim 18  wherein the second heating means is inductive heating. 
     
     
         25 . The apparatus according to  claim 18  further comprising secondary reactant supply means disposed to deliver a spray stream of a secondary reactant into the stream of the feedstock after it has been discharged from the nozzle and ignited. 
     
     
         26 . The apparatus according to  claim 23  further comprising secondary reactant supply means disposed to deliver a spray stream of a secondary reactant into the stream of the feedstock downstream of the air curtain. 
     
     
         27 . The apparatus according to  claim 18  wherein the second heating means is disposed for uniform heating of essentially the entire feedstock conduit.