Procedure for anodising aluminium or aluminium alloys
This invention refers to a procedure for anodising aluminium or aluminium alloys in which an aluminium or an aluminium alloy part is submerged an in an aqueous solution at a temperature between 0° C. and 140° C., preferably between 0° C. and 130° C., in which said solution includes: sulphuric acid, tartaric acid, and at least one inorganic salt of an element selected between at least one transition metal, a lanthanide element, an actinide, and combinations of them, and applying a controlled potential difference, obtaining layers of aluminium oxide with properties as good as or even better than those obtained through anodising in traditional chromic acid solutions.
1 . An anodising procedure for aluminium or aluminium alloys characterised in that it comprises in submerges an aluminium or aluminium alloy part in an aqueous solution, said solution comprising:
sulphuric acid,
tartaric acid, and
at least one inorganic salt of an element selected between at least one transition metal, one lanthanide element, one actinide, and a combination of them,
and apply a controlled potential difference.
2 . An anodising procedure according to claim 1 , characterised in that said aqueous solution also includes one inorganic salt of a transition metal with a concentration between 1·10 −6 and 1 M.
3 . An anodising procedure according to claim 1 , characterised in that said inorganic salt is a molybdenum salt.
4 . An anodising procedure according to claim 1 , characterised in that as the anode is the same aluminium or aluminium alloy parts to be anodised.
5 . An anodising procedure according to claim 1 , characterised in that one aqueous acidic electrolyte is used.
6 . An anodising procedure according to claim 1 , characterised in that said aqueous acidic electrolyte is an aqueous, tartaric-sulphuric solution.
7 . An anodising procedure according to claim 6 , characterised in that said solution has a concentration of sulphuric acid between 0.2 M and 0.9 M, L(+)-tartaric acid with a concentration between 0.2 and 0.8M.
8 . An anodising procedure according to claim 6 , characterised in that said solution has a concentration of sulphuric acid between 0.2 M and 0.9 M, L(+)-tartaric acid with a concentration between 0.2 and 0.8M, and one or several inorganic salts with at least one or several transition metals with a concentration between 1·10 −6 and 1 M.
9 . An anodising procedure according to claim 1 , characterised in that the temperature of the aqueous solution is maintained during the anodising process between 0° C. and 130° C.
10 . An anodising procedure according to claim 1 , characterised in that a difference of electrical potencial between 1V and 120V is applied to the electrolytic cell.
11 . An anodising procedure according to claim 1 , characterised in that it takes between 5 and 120 minutes of time.
12 . An anodising procedure according to claim 1 , characterised in that a steel plate is used for the cathode.
13 . An anodising procedure according to claim 1 , characterised in that an aqueous solution of tartaric-sulphuric acid and a molybdenum salt are used.
14 . An anodising procedure according to claim 1 , characterised in that the aqueous solution is made up of sulphuric acid whose concentration is between 0.20 and 0.50 M, L (+)-tartaric acid with a concentration between 0.4 and 0.55 M, and molybdenum salt whose concentration is between 0.20 M and 0.30 M.
15 . An anodising procedure according to claim 1 , characterised in that it comprises:
a cathode made of AISI 321 stainless steel whose area is equal to or larger than the area of the anode,
an aqueous solution made up of 0.40 M sulphuric acid, 0.53 M L (+)-tartaric acid, and 0.25 M molybdenum salt, and
an electrolytic cell's temperature maintained at 37° C.±1° C., comprising a potential difference of 0 to 14 V applied at rate of 2.8 V·min −1 and maintained during 20 minutes.