Method of manufacturing metal with biocidal properties

1. A method treating a metal object so as to form thereon a surface layer which is integral with the metal object, and which includes a biocidal material, the method comprising:

(a) immersing the metal object, which is to provide a substrate for the surface layer, in an anodising electrolyte containing a solvent, and anodising the metal object to passivate it by forming an anodised integral surface layer on the metal object by applying a positive voltage between 15 and 200 V;

(b) continuing the anodising of the metal object by the application of a positive voltage, to produce pits through the integral surface layer and into the substrate;

(c) then, after anodising the metal object during steps (a) and (b), producing a hydrous metal oxide or phosphate by:

(i) applying a negative voltage which is insufficient to cause electrolysis of the solvent to the metal object, while in contact with the anodising electrolyte, or

(ii) contacting the metal object with an electrolyte solution containing a reducible soluble salt of titanium or the substrate metal and an other solvent and applying a negative voltage which is insufficient to cause electrolysis of the other solvent;

(d) removing or separating the anodised metal object resulting from step (c) from the anodising electrolyte or the electrolyte solution; and

(e) then contacting the anodised metal object with a solution containing a biocidal material so as to incorporate said biocidal material into the surface layer.

2. The method of claim 1 , wherein the voltage applied in step (b) is a different voltage to that applied during the passivation of step (a).

3. The method of claim 1 , wherein step (c)(ii) is performed, and the electrolyte solution of step (c)(ii) contains a peroxy cationic complex of a metal of Groups IVa, Va and VIa of the Periodic Table.

4. The method of claim 1 , wherein the biocidal material comprises a biocidal metal.

5. The method of claim 4 , wherein the biocidal metal comprises silver.

6. The method of claim 1 , wherein the metal of the metal object comprises titanium, niobium, tantalum, zirconium and/or an alloy thereof.

7. The method of claim 1 , wherein the anodising electrolyte is phosphoric acid at a concentration in the range of 1.0 to 3.0 molar.

8. The method of claim 7 , wherein step (c)(i) is performed, and the negative voltage has a magnitude in a range of from −0.2 to −0.7 volt with respect to a Ag/AgCl reference electrode, and wherein the electrolyte has a phosphoric acid concentration of substantially 2.0 molar.

9. The method of claim 1 , wherein step (c)(i) or step (c)(ii) comprises applying the negative voltage to the metal object at least until the current through the object falls to a value no higher than 20% of its initial value.

10. The method of claim 1 , wherein the anodised metal object is treated with a solvent to remove electrolyte and soluble cations prior to contacting it with the solution containing the biocidal material.

11. The method of claim 1 , wherein the anodising is performed with a current density in a range of from 0.1 to 25 mA/cm 2 .

12. The method of claim 1 , wherein the anodising is performed at a voltage increasing at a rate in the range 0.1-10 V per second.

13. The method of claim 1 , wherein the amount of charge employed for anodising is in the range from 1 to 10 coulomb/cm 2 .

14. The method of claim 1 , wherein the anodising is performed in the presence of an electrolyte, and movement and circulation of the electrolyte relative to the surface of the metal object is inhibited or suppressed, at least during the pit growth phase of step (b).