Protection of lead-containing anodes during chromium electroplating
AssigneeElf Atochem North America, Inc.
InventorKenneth R. Newby
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Abstract
The present invention provides a process for electroplating chromium using lead anodes while achieving the advantages of using methanesolfonic acid without suffering the excessive anode-corrosion characteristics associated with that acid. Accordingly, chromium is electrodeposited from a bath containing chromic acid, sulfate and an alkylpolysulfonic acid containing from one to about three carbon atoms. The invention also provides a plating process for chromium electrodeposition, a plating bath for use in the inventive process, and a replenishment composition for existing plating baths.
Claims26
The process of electroplating chromium from a high-efficiency, etch-free plating bath onto a basis-metal cathode with a lead anode in the substantial absence of a corrosion-producing monosulfonic acid, which comprises contacting a basis-metal cathode and the lead anode with a plating bath consisting essentially of chromic acid and sulfate ion in amounts sufficient to obtain the desired deposit of chromium, and at least one alkylpolysulfonic acid, halogenated alkylpolysulfonic acid, or salt thereof, which acid or salt contains from one to about three carbon atoms, and electrodepositing chromium at a cathode efficiency of at least 20% at a current density of at least 30 a.s.d. and at a plating temperature of about 45.degree. to about 70.degree. C. for a time sufficient to obtain a bright, adherent chromium deposit.
A chromium plating process which comprises electroplating from a bath comprising a lead anode, a basis-metal cathode and a plating bath consisting essentially of chromic acid and sulfate in amounts sufficient to obtain efficient functional electrodeposition in the substantial absence of a corrosion-producing monosulfonic acid, and at least one alkylpolysulfonic acid or salt having the formula ##STR2## where a and b are independently from 0 to 2, n is from 1 to 3, m and y are independently from 1 to 3, provided that the total number of sulfonic groups in the molecule is not less than 2, X is halogen or oxygen, R is unsubstituted lower alkyl, or substituted lower alkyl where the substituents on R are halogen or oxygen, and where hydrogen occupies any positions otherwise unaccounted for on carbon or oxygen, the bath producing bright, adherent chromium deposits.
Dependencies are inferred from the claim text.