GB578389A - Improvements in and relating to the electrodeposition of metals and alloys - Google Patents

Abstract

578,389. Electroplating. MALLORY METALLURGICAL PRODUCTS, Ltd. April 4, 1944, No. 6221. Convention date, March 11, 1943. [Class 41] [Also in Group II] In electroplating processes, the anode is used in a "semi-polarized" condition, i.e., the current density is raised to a value such that the surface becomes bright and the voltage ceases to be proportional to the current. This is done in order to prevent insoluble particles of the anode from falling into the electrolyte, to which corrosive ions are added to aid dissolution of the anode. A brightener is also added to produce a bright surface on the cathode. Examples given of the use of this anode are lead-plating, lead-silver alloy plating, silver plating, copper plating and copper-lead alloy plating. In each case the cathode is degreased and then electrolytically cleaned in an alkaline bath. Details of the composition of the electrolytes, the anode and cathode current densities, the intensity of agitation of the electrolyte, and the temperature of the latter are given for each process. A tapered anode is used because the anode surface area in contact with the solution is very small compared with that of the cathode and must be kept within limits to control accurately the extent of the deposit. The brightener used is a hydroxy-benzene, such as pyrogallol ; the corrosive ions vary with the anode used, e.g., with lead anodes, potassium tartrate is added to the electrolyte, and with silver anodes, potassium cyanide is used. The anode 12 which is supported loosely by insulating sleeve 22, which allows it to settle into the solution as it is dissolved rests on a perforated plate 14. The electrolyte 11 is agitated and circulated by a pump 17 driven by motor 19. The cathode 15, connected to the battery through covered conductor 18, also rests on plate 14. In depositing alloys an anode of each metal is used, Fig. 3 (not shown), the surface area of each subjected to the action of the electrolyte being proportional to the composition of the alloy desired, which may also be controlled by the position of the anodes with respect to the cathode and by variation of the currents through them. Alternatively, a composite anode, Fig. 5 (not shown), may be used, wherein the chief constituent of the allov forms the core of the anode, the lesser being formed around the core. Fig. 6, shows a modification of the anode sub-assembly, in which the anodes 65, 66 are clamped in an insulating yoke 67, the tip of anode 65 resting on plate 68. A means of introducing an anode in the side of the bath wherein the anode passes through a sealing ring and is fed into the bath by a spring is described with reference to Fig. 7 (not shown).