Compositions for use in chromium plating
AssigneeAlbright & Wilson Limited
InventorsJeffrey Gyllenspetz, Stanley Renton
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Abstract
It is known to attempt to plate chromium from a solution containing trivalent chromium salts and organic complexants. The invention provides an aqueous chromium electroplating system containing trivalent chromium together with both a formate or acetate and a bromide. Optionally the solution also contains ammonium, borate, chloride, sulphate and alkali metal ions and a wetting agent. The invention has the advantage of providing a solution with commercially acceptable covering and throwing power whose effluent can easily be purified to acceptable standards.
Claims32
An aqueous chromium electroplating solution consisting essentially of from 0.1 to 1.2 molar trivalent chromium;
- at least 0.1 molar bromide;
- formate in a proportion of from 3 to 0.5 moles per mole of the chromium;
- at least 0.1 molar ammonium and at least 0.1 molar borate.
An aqueous chromium electroplating solution consisting essentially of from 0.1 to 1.2 molar trivalent chromium;
- from 0.05 to 0.3 molar bromide;
- from 2 to 1 moles formate per mole of chromium;
- from 1 to 3 molar ammonium;
- from 0.5 to 1 molar borate;
- and from 1 to 5 moles per liter of alkali metal ions selected from sodium and potassium.
An aqueous chromium electroplating bath consisting essentially of water, from 0.2 to 0.6 molar trivalent chromium, from 0.05 to 0.3 molar bromide, from 2 to 1 moles formate per mole of trivalent chromium, from 0.2 to 3 molar ammonium, from 0.5 to 1 molar borate, from 2 to 4 molar total of anions selected from chloride and sulphate including at least 0.5 molar chloride and at least 0.5 molar sulphate and from 2 molar to saturation of alkali metal cations selected from the group consisting of sodium and potassium, and having a pH between 1 and 4.
A method for the preparation of trivalent chromium electroplating baths comprising dissolving in water:
- a. a composition consisting essentially of
- i. borate ions present as a borate compound selected from boric acid and alkali metal and ammonium borate;
- ii. at least one alkali metal salt selected from sodium chloride, potassium chloride, sodium fluoride, potassium fluoride, sodium sulphate and potassium sulphate;
- iii. bromide present as a salt selected from sodium, potassium and ammonium bromide;
- and
- iv. an ammonium salt selected from ammonium chloride, ammonium fluoride, ammonium sulphate and said ammonium borate, said borate ions being present in a proportion of at least 1% of the total weight of the components a, b, c and d, said bromide being present in a proportion of at least 0.5%, measured as HBr of the total weight of the components a, b, c and d, said alkali metal salt being present in a proportion of at least 2% by weight of the dry weight of the composition, said ammonium salt being present in a proportion of from 5 to 80% by weight of the total weight of the components a, b, c and d in a proportion sufficient to provide at least 0.01 molar bromide and up to saturation;
- b. sufficient of a trivalent chromium salt to provide of from 0.1 to 1.2 molar trivalent chromium;
- c. sufficient of a water soluble formate to provide of from 2 to 1 moles of formate per mole of trivalent chromium;
- and adjusting the pH of the bath of a value of between 1 and 4.
A method for the maintenance of a trivalent chromium electroplating bath which comprises adding thereto at separate intervals each of less than three days:
- a. a composition consisting essentially of
- i. borate ions present as a borate compound selected from boric acid and alkali metal and ammonium borate;
- ii. at least one alkali metal salt selected from sodium chloride, potassium chloride, sodium fluoride, potassium fluoride, sodium sulphate and potassium sulphate;
- iii. bromide present as a salt selected from sodium, potassium and ammonium bromide;
- and
- iv. an ammonium salt selected from ammonium chloride, ammonium fluoride, ammonium sulphate and said ammonium borate, said borate ions being present in a proportion of at least 1% of the total weight of the components a, b, c and d, said bromide being present in a proportion of at least 0.5%, measured as HBr of the total weight of the components a, b, c and d, said alkali metal salt being present in a proportion of at least 2% by weight of the dry weight of the composition, said ammonium salt being present in a proportion of from 5 to 80% by weight of the total weight of the components a, b, c and d in an amount sufficient to maintain the concentration of bromide in the bath at least 0.1 molar.
- b. a trivalent chromium salt in an amount sufficient to maintain the concentration of chromium in the bath between 0.1 and 1.2 molar.
- c. a formate in an amount sufficient to maintain a concentration of formate in the bath from 1 to 2 moles per mole of trivalent chromium.
- d. sufficient of an aqueous alkali to maintain the pH of the bath between 1 and 4.
An aqueous electroplating bath for electrodepositing chromium-iron alloys consisting essentially of water, from 0.2 to 0.6 molar trivalent chromium and iron cation in an amount up to saturation for the electrodeposition of chromium-iron alloys, from 0.05 to 0.3 molar bromide, from 2 to 1 moles formate per mole of trivalent chromium, from 0.2 to 3 molar ammonium, from 0.5 to 1 molar borate, from 2 to 4 molar total of anions selected from chloride and sulphate including at least 0.5 molar chloride and at least 0.5 molar sulphate and from 2 molar to saturation of alkali metal cations selected from the group consisting of sodium and potassium and having a pH of between 1 and 4.
Dependencies are inferred from the claim text.