Alkali metal fluorozincate and method for producing it

Abstract

Novel methods for producing alkali metal fluorozincates, especially potassium fluorozincate. Products having defined particle size ranges are obtained depending on the sequence of introduction of the reactants alkali metal hydroxide, zinc oxide and hydrogen fluoride. The resulting alkali metal fluorozincates are particularly suitable for use as a fluxing agent or fluxing agent additive during brazing of aluminum or aluminum alloys and can be applied by wet or dry fluxing methods depending on the particle size of the alkali metal fluorozincate particles.

What is claimed is:  
     
         1 . A method for producing alkali metal fluorozincate from alkali metal hydroxide, zinc oxide, and alkali metal fluoride or hydrogen fluoride in aqueous phase, wherein: 
 a) to produce fine alkali metal fluorozincate, alkali metal hydroxide and zinc oxide are mixed into a suspension and hydrogen fluoride is added, or    b) to produce medium fine alkali metal fluorozincate, hydrogen fluoride and zinc oxide are mixed with one another and alkali metal hydroxide is added, or    c) to produce coarse alkali metal fluorozincate, hydrogen fluoride and zinc oxide are mixed with one another and alkali metal fluoride is added.    
     
     
         2 . A method according to  claim 1 , for producing fine alkali metal fluorozincates, wherein alkali metal hydroxide is mixed into a suspension with zinc oxide in aqueous phase, and the suspension is reacted with hydrogen fluoride to form fine alkali metal fluorozincate.  
     
     
         3 . A method according to  claim 1 , wherein the alkali metal hydroxide is potassium hydroxide and potassium fluorozincate is produced.  
     
     
         4 . A method according to  claim 1 , wherein potassium hydroxide is used in the form of as an aqueous potassium hydroxide solution.  
     
     
         5 . A method according to  claim 3 , wherein the atomic ratio of K:Zn is in the range from 1:1±0.05, and the atomic ratio of (K+Zn):F is in the range from 1:3±0.05.  
     
     
         6 . A method according to  claim 1 , further comprising isolating and drying the alkali metal fluorozincate produced.  
     
     
         7 . A method according to  claim 2 , wherein the suspension of alkali metal hydroxide and zinc oxide is produced at a temperature in the range from 15 to 85° C., and the suspension subsequently is reacted with hydrogen fluoride at a temperature up to 90° C.  
     
     
         8 . A fine alkali metal fluorozincate produced by the method of  claim 1 , and having a grain spectrum in which 50% of all particles have a diameter <5 μm.  
     
     
         9 . An alkali metal fluorozincate according to  claim 8 , wherein alkali metal is potassium.  
     
     
         10 . A potassium fluorozincate according to  claim 9 , having a grain spectrum in which 50% of all particles have a diameter <3.8 μm.  
     
     
         11 . A medium fine alkali metal fluorozincate produced by the method of  claim 1 , and having a grain spectrum in which 50% of all particles have a diameter <11 μm.  
     
     
         12 . A coarse alkali metal fluorozincate produced by the method of  claim 1 , and having a grain spectrum in which 50% of all particles have a diameter >11 μm.  
     
     
         13 . A method of fluxing an aluminum or aluminum alloy component for brazing, said method comprising applying to said component a fluxing agent comprising an alkali metal fluorozincate according  claim 8 .  
     
     
         14 . A method according to  claim 13 , wherein said fluxing agent is applied by electrostatic dry fluxing.  
     
     
         15 . A method of fluxing an aluminum or aluminum alloy component to be brazed, said method comprising applying to said component a fluxing agent comprising an alkali metal fluorozincate according to  claim 11 .  
     
     
         16 . A method of fluxing an aluminum or aluminum alloy component to be brazed, said method comprising applying to said component a fluxing agent comprising an alkali metal fluorozincate according to  claim 12 .  
     
     
         17 . A method according to  claim 16 , wherein said fluxing agent is applied by wet fluxing from an aqueous or organic suspension.