US 2897250 A
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July 28, 1959 E. M. KLOPP 2,
CORROSION INHIBITORS FOR DRY CELLS Filed March 27, 1957 COQQOfi/ON INHIBITOR -N/TEO QUINOLINE o2 6 -CI-ILO20-QUWOLINE- IN I EN TOR. fowAeo M. KLoop BY UM, M
ATTOENEYfi CORROSION INHIBITORS FOR DRY C'ELLS- Edward M. Klopp, Medina, Ohio, assignor to P. R.
Mallory & Co. Inc., Indianapolis, Ind., a corporation of Delaware Application March 27, 1957, Serial No. 648,848
5 Claims. (Cl. 136-107) This invention relates to dry cells and more particularly to inhibitors for retarding or preventing corrosion of the zinc electrodes in dry cells of the Le Clanche ty e.
The conventional 'Le Clanche cell consists of a metal anode, preferably in the form of a zinc can, a carbon electrode surrounded by a body of depolarizing material, ordinarily known as the mix, and a separator between the depolarizer and the anode. The electrolyte, which may be a conventional solution containing ammonium chloride and zinc chloride, permeates the mix and the separator and comes in contact with the anode. The action of the electrolyte on the zinc anode, even when the cell is not in service, causes local electrolytic action and corrosion to take place on the zinc anode. Such corrosion reduces the shelf life of the cell, results in the generation of gases within the cell during shelf life and in general, reduces the shelf and service life of the cell.
Accordingly, it has long been the practice to incorporate corrosion resisting materials in cells of the Le Clanche type. For example, mercury has been used, either in the form of the metal which amalgamates with the zinc, or in the form of mercury salts that may be incorporated in the electrolyte or otherwise supplied to the cells. Mercury and its compounds are reasonably effective as inhibitors of corrosion at ordinary temperatures, but they rapidly lose their effectiveness at elevated temperatures. It has also been known that quinoline has the property of forming a coating on zinc that will inhibit corrosion in the presence of the ordinary electrolyte solutions used in conventional dry cells. However, quinoline has a very serious defect in that it forms a varnish like film on the surface of the zinc that has such high electrical resistance as to make quinoline itself en- 'tirely unsuited as a corrosion inhibitor in dry cells.
Accordingly, the general object of the present invention is to provide an organic corrosion inhibitor for dry cells that has the excellent corrosion inhibiting properties of quinoline and is superior to mercury compounds in its corrosion inhibiting qualities, particularly at high temperatures, and that at the same time does not deleteriously alfect the electrical performance of the cells in any substantial manner.
Specifically, I have discovered that two derivatives of quinoline have the desired characteristics. These derivatives are 8-nitro quinoline and 8-chloro quinoline.
The structural formula of 8-nitro quinoline is as follows:
2,897,250 Patented July 28, 1959 The structural formula of 8-chloro quinoline is as follows:
These materials act in substantially identical fashion insofar as I have been able to determine. They both provide excellent corrosion resistance and prevent undue gassing of the cells during shelf life attemperatures at least as high as F. and probably at even higher temperatures, although tests at higher temperatures have not yet been completed; these results are attained without any serious increase in the resistance of the cells or decrease in service life of the cells. Tests have shown that on the average, cells embodying inhibitors composed of either '8-nitro quinoline or 8-chloro quinoline have service lives within about 5% of the service lives of cells of the same construction embodying conventional mercuric inhibitors. Comparative tests made after prolonged exposure of the cells to elevated temperatures, show that cells with the substituted quinoline inhibitors forming the subject matter of the present invention are vastly superior to conventional cells that have been subjected to the same exposure. I
Contrary to experience with quinoline and other derivatives of quinoline with which I am familiar, '8-nitro quinoline and 8-chloro quinoline do not produce a varnish-like film on the inside of the zinccan, but rather produce a coating that is practically invisible and yet acts effectively to inhibit corrosion. The coating perf mits the passage of ions without apparent difficulty and produces unexpectedly different results from the films formed by quinoline and various other quinoline derivatives. e
I have determined from theoretical considerations that a film or coating of either 8-nitro quinoline or 8-chloro quinoline having a thickness of about 6000 molecules is probably the optimum. An increase in thickness does not improve the corrosion resistant qualities materially, but may reduce the service output of the cell. Such a coating may be produced by placing 0.8 cc. of a 3% solution of either of the inhibitors in a convenient org-anic solvent such as methyl alcohol, ethyl alcohol, benzine or the like in the ordinary zinc can utilized in the manufacture of conventional D size dry cells and spinning the can to distribute the solution over the interior surface of the can and continuing the spinning of the can until the solvent has evaporated. Another way in which the inhibitor can be applied is to mix the inhibitor in solution in the electrolyte; this is satisfactory but gives a less eificient use of the inhibitor because the inhibitor must migrate to the zinc. As much as /2 of -1% of the inhibitor can be used in the electrolyte without damaging elfccts. About 0.002% of inhibitor in the electrolyte appears to be the optimum quantity. The inhibitor can also be applied by coating the paper constituting the separator with a solution of the inhibitor in an organic solvent, letting the paper dry and then assembling the paper in a cell in the usual manner. This can be carried out by spraying ordinary paste coated paper witha solution of the inhibitor in an organic solvent, by wetting the paper in a solution of the solvent in any other convenient manner, or by Wetting the paper with an electrolyte containing the inhibitor. In any event, as noted above, a layer of inhibitor on the inner surface of the zinc having a thickness about the same as that produced by coating the inner surface of a can as described above and which I believe to be about 6000 molecules is apparently the optimum thickness for good a corrosion resistant qualities without undue increase in the resistance of the cell.
The drawing shows a conventional cell embodying my inhibitor, e Such a'cell may comprise an anode container or zinc can 10, a mass or cake of depolarizing mix 12 within the anode container and a carbon electrode 13 embedded in the mix and projecting upwardly above the top of the zinc cup. A paper separator having a layer of gelling material thereon is interposed between the mix and the zinc as shown at 14. The cell'is sealed by means of an ordinary wax seal 15 poured in while hot and supported by a paper Washer 16 which is impaled upon the carbon electrode, there being an expansion space 17 between the top of the mix cake and the washer l6. Preferably, the upper edge 18 of the can It] is turned inwardly as shown and the sealing material contacts and adheres to the upper portion 19 of the cardboard sheath 11. The carbon rod is provided with a terminal cap 20 having a flange 24 that is imbcdded in the sealing composition. All of these details ofthe construction of the cell are conventional and form no part of the present invention. Obviously, the present invention may'b'eapplied to cells ofany desired construction.
According to the present invention, the inner surface of the zinc can is protected as noted above by a coating of either 8-nitro quinoline or 8-chloro quinoline or a mixture of the two. This coating is indicated byrthe legend in the drawing; it is impossible to illustrate it. The coating is difficult, if not impossible to detect with the naked eye, but its presence can be felt if the inside of the can is scraped with the finger nail. The coating, however, substantially prevents corrosion and local electrolytic action from taking place on the surface of the zinc during shelf life of the cell even at elevated temperatures, and this result is accomplished without substantially reducing the efficiency or service life of the cell.
Those skilled in the art will appreciate that the foregoing description of the invention as applied to-a specific type of cell is, given primarily by way of example. 'The invention may be applied to cells of other types and constructions and modes of incorporating the inhibitor in the cell other than those disclosed herein may be employed. The essential characteristics of the invention are set forth in the appended claims.
1. A dry cell comprising a zinc anode, a separator, a, depolarizing mix, an electrolyte containing ammonium chloride and zinc chloride and an inhibitor for preventing corrosion of the zinc anode comprising a material from the group consisting of 8-nitro quinoline. and 8-chloro quinoline.
2. The method of inhibiting corrosion of the anode in cells of the Le Clanche type embodying a zinc anode, a depolarizer, a separator interposed between the anode and the depolarizer, and an electrolyte, which method includes the steps of coating the interior surface of the zinc anode with a coating comprising a material from the group consisting of 8-nitro quinoline and 8-chloro quinoline.
3'. The method according to claim 2, wherein the coating is applied directly to the inside of the anode container by depositing the material from a solution thereof in an organic solvent.
4. The method according to claim 2 wherein the coating is applied to the interior of the container by incorporating the inhibiting material in the electrolyte.
SyThe method according to claim 2 wherein the coating is applied to the interior of the container by applying the inhibiting material to the separator.
References Cited in the file of this patent UNITED STATES PATENTS Lawson Feb. 29, 1944 2,399,127 Lipinski Apr. 23, 1946 2,598,226 Coleman May 27, 1952 OTHER REFERENCES