# US 10,309,029 B2 · Method for forming a multi-layer anodic coating > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,309,029 B2 - Document ID: US10309029B2 - Status: Granted - Kind: B2 - Application number: 15/105,785 - Filed: 2014-12-19 - Published: 2016-10-27 - Granted: 2019-06-04 - Earliest claimed: 2013-12-20 - Assignees: Technological University Dublin - Applicants: Dublin Institute of Technology - Inventors: Brendan Duffy; Michael Whelan - Web page: https://patentgrep.com/patent/US10309029B2 ## CPC - C25D 11/12: Anodising more than once, e.g. in different baths - C25D 11/024: {Anodisation under pulsed or modulated current or potential} - C25D 11/04: of aluminium or alloys based thereon - C25D 11/06: characterised by the electrolytes used - C25D 11/08: containing inorganic acids - C25D 11/16: Pretreatment {, e.g. desmutting} - C25D 11/24: Chemical after-treatment - C25D 11/246: {for sealing layers} - C25D: PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR ## Abstract A method for producing a multi-layer anodic coating on a metal is described. The method comprises the steps of (i) placing the metal in a first electrolytic solution and applying a current to form a first anodic layer having a barrier region; (ii) reducing the applied current to cause a reduction in thickness of the barrier region; and (iii) placing the metal in a second electrolytic solution and applying a current to form a second anodic layer. ## Claims ### Claim 1 A method for producing a multi-layer anodic coating on a metal which comprises the steps of: (i) placing the metal in a first electrolytic solution and applying a current as a steady state current to form a first anodic layer having a barrier region; (ii) reducing the applied current to cause a reduction in thickness of the barrier region; and (iii) placing the electrolytically modified metal in a second electrolytic solution and applying a current to form a second anodic layer, wherein the multi-layer anodic coating comprises the first anodic layer and the second anodic layer, and wherein the first anodic layer comprises pores having relatively large pore diameter size and the second anodic layer comprises pores having relatively small pore diameter size, and wherein step (i) comprises a first anodizing process having a final forming voltage and step (iii) comprises a second anodizing process having an initial forming voltage; wherein following step (ii), the final forming voltage of the first anodizing process is less than the initial forming voltage of the second anodizing process and wherein the final forming voltage after step (ii) is in the range of 2V to 10V. ### Claim 2 (depends on 1) The method according to claim 1 wherein the current in step (ii) is reduced by an amount of up to 50% from the steady state current in step (i). ### Claim 3 (depends on 2) The method according to claim 2, further comprising the step of repeating step (ii) sequentially for a period of time. ### Claim 4 (depends on 1) The method according to claim 1 wherein the multi-layer anodic coating comprises a duplex anodic layer. ### Claim 5 (depends on 1) The method according to claim 1 wherein the pores having relatively large pore diameter size have a diameter in the range of 50 to 150 nm. ### Claim 6 (depends on 1) The method according to claim 1 wherein the pores having relatively small pore diameter size have a diameter in the range of 10 to 25 nm. ### Claim 7 (depends on 1) The method according to claim 1, wherein the first electrolytic solution is selected from the group consisting of phosphoric acid, oxalic acid, sulphuric acid solution and mixtures thereof. ### Claim 8 (depends on 1) The method according to claim 1 wherein the second electrolytic solution is selected from the group consisting of sulphuric acid solution, oxalic acid solution, tartaric acid solution, boric acid solution and mixtures thereof. ### Claim 9 (depends on 1) The method according to claim 1 wherein the first electrolytic solution comprises from 1 to 20% phosphoric acid and the second electrolytic solution comprises from 1 to 30% sulphuric acid. ### Claim 10 (depends on 1) The method according to claim 1 wherein the first anodic layer comprises a phosphoric acid anodic layer comprising pores having a diameter in the range of 50 to 100 nm. ### Claim 11 (depends on 1) The method according to claim 1 wherein the second anodic layer comprises a sulphuric acid anodic layer comprises pores having a diameter in the range of 10 to 25 nm. ### Claim 12 (depends on 11) The method according to claim 11, further comprising the step of applying a sealing or corrosion inhibiting treatment to said sulphuric acid anodic layer. ### Claim 13 (depends on 12) The method according to claim 12 wherein said corrosion inhibiting treatment is selected from the group consisting of nitrogen heterocycles, triazoles, triazines and tetrazines. ### Claim 14 (depends on 12) The method according to claim 12 wherein the sealing treatment includes hydrothermal, nickel acetate, nickel fluoride, sodium silicate or other conventional sealing treatments. ### Claim 15 (depends on 11) The method according to claim 11 wherein the first and second anodizing processes can be carried out using any electrochemical process that forms the appropriate porous oxide layer on the metal. ### Claim 16 (depends on 15) The method according to claim 15 wherein the formation of the appropriate porous oxide layer is optionally conducted simultaneously with an additional surface electrochemical process. ### Claim 17 (depends on 16) The method according to claim 16 wherein the additional surface electrochemical process comprises an electrobrightening process. ### Claim 18 (depends on 16) The method according to claim 16 wherein the additional surface electrochemical process comprises the tailoring of the first anodizing process to form the appropriate porous oxide layer while simultaneously consuming the native oxide present on the metal surface; wherein the metal comprises aluminium. ### Claim 19 (depends on 18) The method according to claim 18 wherein the first anodizing process is optionally tailored to remove intermetallics from the metal surface that anodize at a slower rate than the aluminium metal. ### Claim 20 (depends on 19) The method according to claim 19 wherein the first anodizing process is used to prepare the aluminium surface and remove any said intermetallics; and the second anodizing process is then conducted with the appropriate porous oxide layer thereby exhibiting optimum protection properties. ### Claim 21 (depends on 20) The method according to claim 20 wherein the multi-layer anodic coating comprises a duplex anodic structure wherein the first anodic layer comprises a phosphoric acid anodic layer comprising pores having a diameter in the range of 50 to 100 nm and wherein the second anodic layer comprises a sulphuric acid anodic layer comprising pores having a diameter in the range of 10 to 25 nm. ### Claim 22 (depends on 1) The method according to claim 1 wherein step (i) is conducted at 10 to 200V volts for 1 to 240 minutes. ### Claim 23 (depends on 22) The method according to claim 22, wherein step (i) is conducted at between 30 to 50V. ### Claim 24 (depends on 23) The method according to claim 23, wherein step (i) is conducted at about 40V. ### Claim 25 (depends on 1) The method according to claim 1, further comprising the step of sealing an interface between the first anodic layer and the second anodic layer. ### Claim 26 (depends on 25) The method according to claim 25 wherein the first anodic layer comprises a phosphoric acid layer and the second anodic layer comprises a sulphuric acid layer. ### Claim 27 (depends on 26) The method according to claim 26, further comprising the step of applying a coating or adhesive to the phosphoric acid layer. ### Claim 28 (depends on 27) The method according to claim 27, wherein the coating comprises a sol-gel. ### Claim 29 (depends on 28) The method according to claim 28 wherein the sol-gel is selected from the group consisting of an inorganic, organic or hybrid precursors. ### Claim 30 (depends on 1) The method according to claim 1 wherein the first anodic layer comprises a structure of pores having openings formed at intervals along the longitudinal axis of the pore such that adjacent pores are in fluid connection thereby allowing a material to flow laterally between one columnar pore and a neighbouring columnar pore such that lateral porosity is achieved thereby enabling full encapsulation of a material throughout the first anodic layer. ### Claim 31 (depends on 30) The method according to claim 30 wherein the first anodic layer comprises a phosphoric acid layer. ### Claim 32 (depends on 1) The method according to claim 1 wherein the first and second electrolytic solutions are maintained at a temperature in the range of between 0° C. to 90° C.