Method For Producing White Anodized Aluminum Oxide

Abstract

A method for forming substantially white anodized aluminum oxide on an aluminum or aluminum alloy substrate is provided. A porous aluminum oxide layer is formed on the aluminum or aluminum alloy substrate by anodization in an acid electrolyte. Following formation of the anodized porous layer of aluminum oxide, the aluminum/aluminum alloy substrate is sequentially immersed in at least two reaction material solutions. The two or more reaction materials react to deposit a substantially white pigment material in the pores of the anodized aluminum oxide.

What is claimed is: 
     
         1 . A method for forming a substantially white anodized aluminum oxide layer on an aluminum or aluminum alloy substrate comprising:
 forming a porous aluminum oxide layer on the aluminum or aluminum alloy substrate by anodization in an acidic electrolyte;   sequentially immersing the aluminum or aluminum alloy substrate with the porous aluminum oxide layer formed thereon in at least first and second reaction material solutions such that the first reaction material solution infiltrates pores of the porous aluminum oxide layer and the second reaction material solution infiltrates the pores of the porous aluminum oxide layer to react at least portions of the first and second reaction material solutions with each other to form one or more substantially white metal compound pigment reaction product deposited in the pores to create an anodized aluminum oxide layer having a substantially white appearance.   
     
     
         2 . The method according to  claim 1  further comprising anodizing the aluminum or aluminum alloy substrate having the porous aluminum oxide layer formed thereon and the one or more substantially white metal compound pigment reaction product deposited in the pores of the porous aluminum oxide layer to form branched channels in the porous aluminum oxide layer. 
     
     
         3 . The method according to  claim 1  wherein the one or more substantially white metal compound pigment reaction product includes one or more of aluminum hydroxide, aluminum phosphate, aluminum silicate, antimony hydroxide, barium carbonate, barium oxalate, barium sulfate, barium titanate, barium tungstate, bismuth subnitrate, boron nitride, calcium carbonate, calcium oxalate, calcium sulfate, calcium silicate, magnesium silicate, magnesium carbonate, magnesium hydroxide, silver chloride, silver oxalate, tin (II) oxide, zinc oxide, zinc phosphate, zinc sulfide, lead sulfate, lead chloride, lead carbonate, lead hydroxide or lead phosphate. 
     
     
         4 . The method according to  claim 3  wherein the first reaction material solution is a chloride, nitrate, or sulfate of a metal component of the metal compound pigment reaction product, and the second reaction material solution includes a hydroxide, phosphate, carbonate, silicate, or oxalate component. 
     
     
         5 . The method according to  claim 1  further comprising pore sealing the porous aluminum oxide layer following deposition of the one or more substantially white pigment reaction products. 
     
     
         6 . The method according to  claim 5  wherein the pore sealing is performed using steam or boiling water. 
     
     
         7 . The method according to  claim 5  wherein the pore sealing is performed using a polymer material. 
     
     
         8 . The method according to  claim 7  wherein the pore sealing is performed by immersion in a polymer liquid followed by drying. 
     
     
         9 . The method according to  claim 1  where the thickness of the anodized aluminum oxide layer is approximately 10-30 μm. 
     
     
         10 . The method according to  claim 1  wherein the average pore diameter is approximately 6-20 nm. 
     
     
         11 . The method according to  claim 1  wherein the first reaction material solution comprises barium chloride and the second reaction material solution comprises sodium sulfate and the substantially white metal compound pigment reaction product is barium sulfate. 
     
     
         12 . A substantially white anodized aluminum oxide layer on an aluminum or aluminum alloy substrate formed according to the process of  claim 1 . 
     
     
         13 . A substantially white anodized aluminum oxide layer on an aluminum or aluminum alloy substrate formed according to the process of  claim 11 .