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 fade and pattern removal resistance when subjected to sterilization processes. 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, and one or more additional treatments 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.
1. A method of coating an anodized aluminum substrate comprising:
immersing the anodized aluminum substrate in a first aqueous metal salt solution comprising at least one metal cationic species for a first predetermined length of time to form a partially impregnated aluminum substrate;
immersing the partially impregnated aluminum substrate in an alkaline solution for a second predetermined length of time to form a fully impregnated aluminum substrate; and
immersing the fully impregnated aluminum substrate in a second aqueous metal salt solution comprising at least one metal acetate and having a pH in a range of from about 5 units to about 6 units for a third predetermined length of time to form a coated anodized aluminum substrate.
2. The method of claim 1 , wherein the first predetermined length of time is less than 30 minutes.
3. The method of claim 2 , wherein the concentration of metal cationic species in the first aqueous metal salt solution is from about 0.5 to about 1.0 wt %.
4. The method of claim 3 , wherein the metal cationic species is selected from the group consisting of nickel, iron, zinc, copper, magnesium, titanium, zirconium, and mixtures thereof.
5. The method of claim 4 , wherein the first aqueous metal salt solution further comprises a surfactant.
6. The method of claim 4 , wherein the metal cationic species is a fluoride of at least one of nickel, iron, zinc, copper, magnesium, titanium and zirconium.
7. The method of claim 6 , wherein immersing the anodized aluminum substrate in the first aqueous metal salt solution comprises applying ultrasonic energy.
8. The method of claim 6 , wherein the concentration of fluoride ion is in a range from about 300 ppm to about 800 ppm.
9. The method of claim 1 , wherein the alkaline solution further comprises a surfactant at a concentration up to about 200 ppm.
10. The method of claim 1 , wherein the second predetermined length of time is for a period of from about 3 minutes to about 8 minutes.
11. The method of claim 1 , wherein the alkaline solution comprises at least one of sodium hydroxide and potassium hydroxide.
12. The method of claim 1 , wherein the third predetermined length of time is for a period of from about 20 minutes to about 45 minutes.
13. The method of claim 12 , wherein the second aqueous metal salt solution has a temperature in a range of from about 80° C. to about 95° C.
14. The method of claim 13 , wherein the at least one metal acetate comprises at least one of nickel acetate, magnesium acetate, titanium acetate, and zirconium acetate.
15. The method of claim 14 , wherein the concentration of the at least one metal acetate in the second aqueous metal salt solution is from about 4.5 wt % to about 6.5 wt %.
16. The method of claim 1 , further comprising thermally treating the fully impregnated aluminum substrate in an oxidizing atmosphere at a temperature in a range of from about 110° C. to about 350° C. for a period of at least about 20 minutes.
17. The method of claim 16 , wherein thermally treating the fully impregnated anodized aluminum substrate comprises heating the fully impregnated anodized aluminum substrate at a temperature in a range of from about 135° C. to about 300° C. for a period of at least about 30 minutes.
18. The method of claim 16 , wherein the fully impregnated anodized aluminum substrate is thermally treated prior to immersing in the second aqueous metal salt solution.
19. The method of claim 1 , further comprising subjecting the coated anodized aluminum substrate to a hydrothermal synthesis process.
20. The method of claim 19 , wherein the hydrothermal synthesis process comprises heating the anodized aluminum substrate in a chamber at a temperature of at least 110° C. and a pressure of at least 15 psi for a period of between about 20 minutes to about five hours.
21. An aluminum article comprising an anodized coating with a thickness of at least about 0.01 mm, wherein the anodized coating is dyed and has a fading of less than ΔL* of about 1.5, Δa* of about 2.0, and Δb* of about 2.5 values in accordance with a CIE (Commission Internationale d′Eclairage) 1976 L*, a*, b* color scale as performed in accordance with ASTM E 308, after exposure, for at least one cycle of a sterilization process.
22. The aluminum article of claim 21 , wherein the at least one cycle is at least 300 cycles.
23. The aluminum article of claim 22 , wherein the sterilization process is a hydrogen peroxide sterilization process.
24. The aluminum article of claim 23 , wherein each cycle includes 25 minutes of diffusion and 15 minutes of exposure to a hydrogen peroxide derived gas plasma.
25. The aluminum article of claim 21 , wherein the anodized coating is organically dyed.