Process for making uniform aluminum oxide coating

Abstract

A process of making a dense, cohesive and uniform aluminum oxide coating on a metallic substrate includes electrodepositing polynuclear aluminum oxide hydroxide clusters from a polynuclear aluminum oxide hydroxide cluster solution on a metallic substrate to form a precursor coating, and post-treating the precursor coating to form a final aluminum oxide coating on the metallic substrate.

1 . A protective coating on a metallic substrate comprising a dense, cohesive first aluminum oxide layer formed from electrodeposited, heat-treated polynuclear aluminum oxide hydroxide clusters. 
     
     
         2 . The coating of  claim 1 , wherein the first aluminum oxide layer is diffusion bonded to the metallic substrate. 
     
     
         3 . The coating of  claim 1 , further comprising a second aluminum oxide layer formed from electrodeposited, heat-treated polynuclear aluminum oxide hydroxide clusters. 
     
     
         4 . The coating of  claim 3 , wherein the first and second aluminum oxide layers are diffusion bonded to each other. 
     
     
         5 . The coating of  claim 1 , wherein the first aluminum oxide layer has a thickness between 0.005 and 10.000 microns. 
     
     
         6 . The coating of  claim 1 , wherein the first aluminum oxide layer comprises amorphous aluminum oxide, pseudo-boehmite, boehmite, bayerite, gibbsite, transition-alumina, α-alumina, or a combination thereof. 
     
     
         7 . The coating of  claim 1 , wherein the metallic substrate is selected from the group consisting of aluminum, titanium, zirconium, hafnium, niobium, tantalum, tungsten, magnesium, zinc, iron, and alloys thereof. 
     
     
         8 . A protective coating on a metallic substrate comprising a dense, cohesive first aluminum oxide layer formed from electrodeposited, heat-treated polynuclear aluminum oxide hydroxide clusters diffusion bonded to the metallic substrate; wherein
 the metallic substrate is selected from the group consisting of aluminum, titanium, zirconium, hafnium, niobium, tantalum, tungsten, magnesium, zinc, iron, and alloys thereof;   the first aluminum oxide layer comprises amorphous aluminum oxide, pseudo-boehmite, boehmite, bayerite, gibbsite, transition-alumina, α-alumina, or a combination thereof; and   the first aluminum oxide layer has a thickness between 0.005 and 10.000 microns.   
     
     
         9 . The coating of  claim 8 , further comprising a second aluminum oxide layer formed from electrodeposited, heat-treated polynuclear aluminum oxide hydroxide clusters. 
     
     
         10 . The coating of  claim 9 , wherein the first and second aluminum oxide layers are diffusion bonded to each other.