US2729580A - Method of improving the uniformity of corrodibility of welded nickel anodes - Google Patents

Description

Jan. 3, 1956 w. L. PINNER ET AL 2,729,580

METHOD OF IMPROVING THE UNIFORMITY OF CORRODIBILITY 0F WELDED NICKEL ANODES Filed Nov. 16, 1950 9 II 9; 3 O 1 g2 a o 8 o N Z 2 s? :1 8332-1930 N! HHDLVHEIdWBl.

.[ZTVEUZUFE 51 214759 L. Bwwse Oewu 5 D. 15 0275 United States Patent Ofiice 2,729,580 Patented Jan. 3, 1956 METHOD OFIMPROVING THE UNIFORMITY OF CURRODIBILITY F WELDED NICKEL AN ODES Application November 16, 1950, Serial No. 196,032 1 Claim. 01. 148 -13) This invention relates to a method of improving the corrodibility of welded nickel anodes.

In the patent to one of us, Walter L. Pinner, No. 2,467,852, datedApril 19, 1949, there is disclosed an electrolytic sheet nickel anode composed of sheets of electrolytic nickel welded together to form an elongated panel. As disclosed in that patent, in order to prevent the Welded joint from preferential electrolytic attack during use, the welded joint is shielded, as by the use of a rubber band, anode scrap so arranged as to overlie the welded joint, or by other suitable means. By the term anode scrap is meant partly used up anodes, or anodes that have been severely corroded but are still large enough to be usable if welded to an electrolytic sheet nickel panel. While such means of shielding the welded joints against preferential electrolytic attack are highly satisfactory in the case of relatively high chloride nickel plating baths, such as baths containing well over 75 g./l. of nickel chloride (NiC12.6H2O), they do not present sufiicient protection for the welded joints against premature and excessive corrosion where the nickel plating bath is of the low chloride type, that is, below 75 g./l. of nickel chloride. Apparently, even though rubber bands are used around the Welded joints, the electrolyte penetrates to the joint and causes suificiently rapid corrosion of the welded metal to bring about an actual separation of the sections of the welded panel before the rest of the metal of the panel has been used up.

The probability is that in the presence of a lowconcentration of chloride, sufficient polarization occurs on the body of the Welded nickel sheet anode that preferential corrosion takes place in the vicinity of the weld, due to the fact that the shielding means do not completely out off the current. This undesirable result has been particularly noted where a low chloride, bright nickel plating solution is used with welded sheet metal anodes.

We have now found that the objectionable preferential attack on the metal of the Weld in the case of welded nickel sheet anodes used in low chloride baths can be largely reduced or even completely inhibited by proper heat treatment of the welded sheet nickel anodes. Heat treatment of nickel can promote changes in metallographic structure in addition to grain growth, and by effecting a more or less equalized grain growth of the metal throughout the extent of the anode, We find that more uniform corrosion of the nickel of the welds and of the body of the anodes takes place. If the time and temperature of heat treatment are properly selected, the overall corrosion of the composite welded nickel sheet anodes is sufficiently uniform that it is unnecessary to shield the welded joints against preferential corrosion by the electrolyte.

It is therefore an important object of this invention to provide a method of improving the corrodibility characteristics of welded sheet nickel anodes.

It is a further important object of this invention to provide a method of equalizing the corrodibility characteristics of welded and unwelded portions of a jointed, or welded, nickel sheet so that a more uniform corrosion of the nickel of the sheet and of the welds takes place where the welded nickel sheet is used as an anode in a nickel plating bath.

Other and further important objects of this invention will become apparent from the following description and appended claim.

The method of our present invention will be particularly described in connection with the heat treatment of welded electrolytic nickel anodes for use in bright nickel plating baths of a low chloride content, since the method is particularly applicable in that case to securing uniform corrosion of the metal of the anode, including that of the welded joints. However, it should be understood that the method of heat treatment is more widely applicable to any welded body of nickel where uniformity of corrosion is desirable throughout the entire surface area, including the weld, of the nickel body.

Composite electrolytic nickel sheet anodes may be made in the manner disclosed in the above mentioned Pinner patent by welding together two or more electrolytic nickel sheets at their abutting edges. in this way, composite anodes of the desired length may be made from sheets which, as they come from the refinery, may be 32 inches long and 4% inches wide. In the welding operation, nickel welding rod is used to effect the weld. Alternatively, the metal of the sheets themselves may constitute the metal of the weld. In either case, the welded joint, if not heat treated in accordance with the method of our present invention, will be found to corrode more rapidly than the metal of the sheets that has not been raised to temperatures approximating the temperature of the welding operation.

We have found that the heat treatment of the welded electrolytic nickel sheet should be carried out at term peratures within the broad range of from 1400 to 2100 F. for periods varying from around four hours up to as long as one hundred hours, the longer periods of time being used with the lower temperatures of heat treatment and vice versa.

This relationship of time to temperature is indicated in the chart shown in the accompanying drawing, in which the dash line represents the optimum time and temperature conditions for heat treatment, and wherein the area A below the dash line indicates conditions of time and temperature that give increasingly beneficial results as the optimum line is approached, while the area B above the line indicates time and temperature conditions that result in decreasingly beneficial treatment as the conditions recede from the optimum line. Temperatures in excess of about 2100 F. for any period of time do not produce results so good as those represented by the optimum line and the areas lying in close proximity thereto. For practical purposes, heat treatment at about 1800" F. for four to ten hours has been found most satisfactory.

At temperatures and times represented by the optimum line on the chart, the weld boundary, that is, the metal in the vicinity between the weld and the parent metal of the sheet, corrodes at the same rate as the parent metal, and the weld metal corrodes at a slower rate than the parent metal. No shield for the welded joint is therefore necessary.

For purposes of comparison, a welded anode which had been heat treated at 1800" F. for five hours, and a second, exactly similar welded anode that had not been heat treated, were subjected to the same electrochemical corrosion. it was found that the weld in the unheattreated piece was corroded to a considerably greater extent than in the case of the heat treated piece. Also, the heat treated piece, even in areas far removed from the weld, corroded in a superior manner. Photomicrographs of various samples of heat treated and unheattreated electrolytic nickel sheet anodes were compared.

3 In the case of" the unheat-treated samples, the welded section is a fine-grain material, whereas after five'hours of heat treatment at 1800" F., the crystal growth is clearly evident, bothin the metalvof the. weld and also in the body of the, nickel in the immediate vicinity of the'weld; a

As a result of the heat treatment of the welded electrolytic nickel sheet anodes, thestructure of the metal of the weld andthat immediately adjacent thereto is changed, and, in addition, grain growth occurs. The original structure of'the weld is that typical of a d'en'dritic cast metal, but after heat'treat'ment, the structure resembles that of annealed metal and thus very closely resembles that throughout the. body of the anode. A moreuniform corrosion rate is thereby obtained; such that; it is no longer necessary: to" shield} the welded joint when the composite anodes" are used in nickel plating baths, andparticularlyin low chloride, bright nickel types ofbaths;

The'term nicke ,as used herein, is intended to mean pure nickel and nickel containing not more than 5% of other metals orimpurities; The term "electrolytic sheet nickel, as used'herein, is intended to mean nickel that has been deposited as the cathode in an electrolytic nickel refining method.

We claim as our invention:

v The methodofmaking a composite welded anode which comprises welding together metal sheets to form an anode wherein both the weld metal and the metal sheets are electrolytic nickel, and then subjecting the welded anode to heat treatment within the range of l400 to 2100 F. for a sufiicient period of time to effect asubstantially equalized grain growthof the nickel in .said anode in and around the Weld and to decrease corrodibility of the weld.

References Cited in the file of this patent UNITED STATES PATENTS 226,616 Kleinhans Apr. 20, 1880 2,167,128 Skelt'on July 25, 1939 2,237,872 Badger Apr. 8, 1941 2,289,566 Adamoli July 14, 1942 2,429,320. Kennedy .Oct-. 21, 1947 2,504,238 Wesley Apr. 18, 1950 OTHER REFERENCES Working,InstructionseAnnealing Monel, Nickel and Inconel, The International Nickel Co., Inc., 67 Wall Street, New York, N. Y., Spages, April 10, 1939.

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