Microcrystalline anodic coatings and related methods therefor
Methods of preparing metal and metal alloys with partially microcrystalline anodic coatings are disclosed. Associated article therefrom are correspondingly disclosed. The partially microcrystalline anodic coatings exhibit steam, superheated steam, alkaline and acidic resistance. Partially microcrystalline anodic coating can be prepared by impregnation of micropores of a metal or metal substrate with metal precursor species, conversion of the metal precursor species into metal hydroxides, thermal treatment to dry out moisture and to promote phase transformation of the metal hydroxide product into metal oxides solids and bonding with metastable metal oxide substance in the pore structure of the metal or metal alloy substrate, and hydrothermal sealing to create sealed partially microcrystalline anodic coating.
1. A method of producing an anodized aluminum substrate having structures of at least one of partially microcrystalline aluminum oxide and partially microcrystalline aluminum hydroxide from an aluminum substrate having cells with micropores and walls of at least one of amorphous aluminum oxide and amorphous aluminum hydroxide, comprising:
introducing a metal cationic species into at least a portion of the micropores;
converting at least a portion of the metal cationic species into a metal hydroxide;
converting at least a portion of the metal hydroxide into a metal oxide; and
converting at least a portion of the walls of at least one of amorphous aluminum oxide and amorphous aluminum hydroxide into structures of at least one of partially microcrystalline aluminum oxide and partially microcrystalline aluminum hydroxide.
2. The method of claim 1 , wherein converting at least a portion of the walls comprises immersing the aluminum substrate in an aqueous metal salt solution having a temperature in a range of from about 75° C. to about 95° C. to convert at least a portion of one of the amorphous oxide and amorphous hydroxide into at least one of partially microcrystalline aluminum oxide and partially microcrystalline aluminum hydroxide.
3. The method of claim 2 , wherein the aqueous metal salt solution comprises at least one of a metal acetate and a metal nitrate.
4. The method of claim 2 , wherein converting at least a portion of the metal hydroxide comprises heating the aluminum substrate in an oxidizing atmosphere at a temperature in a range of from about 150° C. to about 300° C. for an oxidizing period of at least about 30 minutes.
5. The method of claim 4 , wherein converting at least a portion of the metal cationic species comprises immersing the aluminum substrate in an alkaline solution having a pH of at least about 8 units.
6. The method of claim 5 , wherein introducing the metal cationic species into the at least a portion of the micropores comprises immersing the aluminum substrate in an aqueous metal solution comprising a metal fluoride and a surfactant.
7. The method of claim 5 , wherein introducing the metal cationic species into the at least a portion of the micropores comprises exposing the aluminum substrate to ultrasonic energy in an ultrasonic bath that is free of fluoride and free of a surfactant.
8. The method of claim 6 , wherein the metal is selected from the group consisting of nickel, iron, zinc, copper, magnesium, titanium, zirconium, aluminum, and silver.
9. A method of producing an anodized aluminum substrate, comprising steps of:
immersing the aluminum substrate in a first aqueous metal salt solution;
exposing the aluminum substrate to one of an alkaline solution having a pH in a range of from about 8 units to about 13 units and ultrasonic energy, after immersing the aluminum substrate in the first aqueous solution;
thermally treating the aluminum substrate in an oxidizing atmosphere at a drying temperature of at least about 150° C. after immersing the aluminum substrate in the alkaline solution; and
immersing the aluminum substrate in a second aqueous metal solution having a temperature in a range of from about 75° C. to about 95° C. after thermally treating the aluminum substrate.
10. The method of claim 9 , wherein the first aqueous metal salt solution comprises a fluoride of at least one of nickel, iron, zinc, copper, magnesium, titanium, zirconium, aluminum, and silver.
11. The method of claim 9 , wherein the first aqueous metal salt solution has a pH of less than about 7 units and a temperature in a range of from about 15° C. to about 35° C.
12. The method of claim 9 , wherein the first aqueous metal salt solution comprises less than about 100 ppm surfactant and about 0.5 to about 8.0 wt % metal cationic species.
13. The method of claim 9 , wherein exposing the aluminum substrate comprises immersing the aluminum substrate in the alkaline solution comprising an alkali metal hydroxide and a surfactant for a period in a range of from about 1 minute to about 5 minutes, the alkaline solution having a temperature in a range of from about 20° C. to about 60° C.
14. The method of claim 9 , wherein exposing the aluminum substrate comprises directing ultrasonic energy to the aluminum substrate in an ultrasonic bath for a period in a range of from about 10 minutes to about 25 minutes.
15. The method of claim 9 , wherein thermally treating the aluminum substrate comprises heating the aluminum substrate in an oven at a temperature in a range of from about 150° C. to about 300° C. for a period of from about 30 minutes to about two hours.
16. The method of claim 9 , wherein the second aqueous metal solution has a pH in a range of from about 5.0 units to about 6.0 units and comprises at least one of a metal acetate and a metal nitrate in a concentration of from about 4.5 wt % to about 6.5 wt %.