Corrosion resistance passivation formulation and process of preparation thereof

Abstract

The present invention provides a passivation formulation and a process for forming trivalent chromium-based passivation film on zinc and zinc alloys. The passivation film incorporates nano-ceramic particles resulting in higher corrosion resistance as compared to a trivalent chromium passivation film without nano-sized ceramic particles. The corrosion resistance of the coating is further enhanced by a topcoat or a sealant

1 . A passivation formulation for providing corrosion resistant metal/alloy, the passivation formulation comprising:
 trivalent chromium ions in a range of 0.01 to 0.22 moles;   organic acid in the range of 0 to 0.022 moles;   transition metal ion in a range of 0 to 0.02 moles   boric acid in the range of 0 to 0.02 moles;   fluoride ions in a range of 0 to 0.1 moles;   ceramic nano-particles in a range of 0.08 to 0.4 moles; and   aqueous vehicle to produce 1000 ml of the passivation formulation.   
     
     
         2 . The passivation formulation of  claim 1 , wherein the trivalent chromium ions are selected from chromium chloride (CrCl 3 ), chromium nitrate Cr (NO 3 ) 3  and chromium sulphate Cr 2 (SO 4 ) 3 . 
     
     
         3 . The passivation formulation of  claim 1 , wherein the organic acids are selected from a group consisting of Ethanedioic acid, Butanedioic Acid, 2-3-dihydroxy butanedioic acid, Propanedioic acid and 3-carboxy-3-hydroxy penatanedioic acid. 
     
     
         4 . The passivation formulation of  claim 1 , wherein the transition metal ion is selected in a form of chlorides, sulphates, nitrates of Manganese (Mn), Nickel (Ni), Cobalt (Co), Vanadium (V) and Iron (Fe). 
     
     
         5 . The passivation formulation of  claim 1 , wherein the fluoride is selected from sodium fluoride, potassium fluoride, ammonium fluoride, ammonium bifluoride, fluorosalicylic acid, and fluorozirconic acid. 
     
     
         6 . The passivation formulation of  claim 1 , wherein the nano-particles of ceramic materials are selected from nanoparticles of silicon dioxide (SiO 2 ), aluminium oxide (Al 2 O 3 ), Zirconium oxide (ZrO2), titanium dioxide (TiO 2 ), and combination thereof 
     
     
         7 . The passivation formulation of  claim 1 , wherein the ceramic particles have particle size in the range of 5 nm to 30 nm. 
     
     
         8 . A process of application of passivation film on Zn/Zn alloys using passivation formulation claimed in  claim 1 , the process comprising steps of:
 plating zinc/zinc alloy;   rinsing the plated zinc/zinc alloy with water;   treating the rinsed zinc/zinc alloy with nitric acid for 10-60 seconds;   rinsing the treated zinc/zinc alloy with water;   applying a passivation formulation at pH 2.2 to 3.0 to the to the rinsed zinc/zinc alloy at temperatures ranging from 25° to 40° C. for about 30-90 seconds;   rinsing the passivated zinc/zinc alloy with water;   treating the rinsed zinc/zinc alloy with a top coat/sealer for about 30-90 seconds;   drying the coated zinc/zinc alloy; and   baking the dried zinc/zinc alloy at 80°-120° C. for 15-20 minutes to obtain a corrosion resistant zinc/zinc alloy surface.