ELECTRO-CHEMICAL BATTERY WITH AN ANODE FROM A ZINC ALLOY.
The present invention relates to an electrochemical cell containing an anode zinc alloy, more particularly to the composition of the zinc alloy whose anode is made. A zinc alloy known to buckets cell contains, in addition to zinc and unavoidable impurities, 0.2 - 0.3% 0.05 - 0,07% lead and cadmium (by the zinc is meant here and hereinafter zinc thermally refined or electrolytically, and by % weight percentage). This has the disadvantage of known alloy containing the toxic element CD's. Further, it has a high content of lead, which, although far less toxic than the cadmium, represents however a certain hazard to the environment. Another zinc alloy known to buckets cell contains, in addition to zinc and unavoidable impurities, only 0.4 - 0,8% lead. This alloy does not contain although not cadmium but its mechanical strength is lower than that of the alloy of cadmium and, further, its lead content is higher than that of the latter. The aim of the present invention is to provide a zinc alloy for an anode for an electrochemical cell, which does not contain cadmium and little lead and which, nevertheless, has a strength and a sufficient corrosion resistance. The alloy according to the invention is free of cadmium and it contains less than 0.05% of Pb and 0,005% -1% of Mn. The other components of the alloy according to the invention are either zinc and the " unavoidable impurities, or zinc alone, unavoidable impurities and minor amounts of other elements, such as 0.01 - 0.02% of In. The unavoidable impurities are impurities, which are present in the zinc or in the elements, which are added to the zinc for obtaining the alloy. Also, the above expression "the alloy according to the invention is cadmium-free" must include as follows: the alloy according to the invention is free of cadmium unless it is optionally present as an unavoidable impurity. Related to the lead content of the alloy according to the invention, it is to be noted that maintaining the applicant, a surprisingly, it has been found, contrary to what it formerly thought, that a zinc alloy containing 0,005 - 1% of Mn, 0.05% should not contain Pb or more so that the implement without difficulties. Also, the lead content of the alloy according to the invention is less than 0.05%, since the lead constitutes a hazard to the environment. The alloy can thus also be lead-free, of course as long as the lead is not present as an inevitable impurity, for example in zinc. the manganese content should be at least 0,005%; otherwise the mechanical strength and corrosion resistance are insufficient. The manganese content cannot exceed 1%, since if higher levels of manganese Zn Mn of intermetallic compounds are formed, which can lead to cracks during rolling of the alloy. The manganese content is preferably of 0.01 - 0.1%. It is noted herein that US-1,421,686 mentions that the hardness and bending resistance increase when zinc alloyed zinc with 0.5 - 4% of Mn and that such alloy may be substituted for the copper, brass and bronze. This teaching does not suggests that this alloy could be used to manufacture anodes for electrochemical cells. The description hereinafter of a comparative test demonstrates that a zinc alloy with 0.05% of Mn is not to contain 0.05% of Pb or more so that it can be implemented without difficulties. From thermally refined zinc (1) nine alloys were prepared whose composition is as follows: Zinc thermally refined to nine (1) (2) - alloys (10) have been converted into the buckets in a conventional manner in an industrial plant: the cast product has been rolled into strips, out of which are punched pads hexagonal shape; and the pellets were extruded in buckets. The tensile strength (in MPa) was determined on test specimens cut from the wall of the reservoir according to the direction of the extrusion; the pulling speed was 1 cm/min. to. Also on test specimens, cut out of the wall of the reservoir according to the direction of the extrusion, the index fold has been determined, the index fold being the number of shots until the break with a charge of 1 and 7 mpa count per second. The results of these measurements are summarized in table 1. It spring of these results that the tensile strength, elongation and the index of folding, and therefore also the machinability, are hardly or not influenced by decreasing the lead content for the alloy with manganese. It is actually the case with Zn-Pb-binary alloys, for which resistance decreased is observed. This example demonstrates that the mechanical strength and corrosion resistance of an anode for electrochemical cells according to the invention are substantially equivalent to those of an anode made of a zinc alloy known cadmium containing lead and more than 0.05%. Starting from two thermally refined zinc alloys were prepared whose composition is as follows: In the same way as in the example 1 these alloys have been transformed is buckets and their tensile strength determined. The results are summarized in table 2. To determine the corrosion resistance was used in industrial electrolyte of ZnCl2 . In a first test 5 buckets of each alloy were immersed for 14 days in the electrolyte maintained has 45 °c. In a second trial 5 cups also of each alloy were immersed for 65 days in the electrolyte is kept maintaining it at ambient temperature. After immersing the buckets were examined by microscopy. It has been found that alloys (11) and (12) are absolutely equivalent with respect to their resistance to pitting corrosion. (2) and alloys (11) are inventive alloys. Other examples of typical alloys of this invention have the following composition: During the preparation of these alloys is thermally refined zinc hand or electrolytically. The anode is made of a zinc alloy which is free from cadmium and which contains less than 0.05% of Pb and either 0.005-1% of Al and 0.0005-0.1% of REM, REM being a rare-earth metal or a mixture of rare-earth metals, or 0.005-1% of Mn, or 0.005-1.5% of a mixture of Al, of REM and of Mn. Such an alloy has mechanical strength and a sufficient corrosion resistance. Electrochemical battery containing a zinc alloy anode in cup form, characterized in that the anode is free from cadmium and contains less than 0.05% of Pb, 0.005-1% of Mn and optionally 0.01-0.02% of In, the other alloy components consisting of thermally or electrolytically refined zinc and the inevitable impurities. Electrochemical battery according to claim 1, characterized in that the anode contains 0.01-0.1% of Mn. Electrochemical battery according to one of the claims 1 or 2, characterized in that the anode contains up to 0.035% of Pb. Electrochemical battery according to one of the claims 1-3, characterized in that the anode contains up to 0.025% of Pb. Electrochemical battery according to one of the claims 1-4, characterized in that the anode contains up to 0.015% of Pb. Electrochemical battery according to one of the claims 1-5, characterized in that the anode is free from lead. Example 1
(1) 123 20 10 (2) 177 38 12 (3) 130 19 7 (4) 177 39 16 (5) 131 17 10 (6) 180 37 15 (7) 140 28 12 (8) 185 35 15 (9) 148 34 14 (10) 172 34 16 Example 2
(11) 185.6 39.2 (12) 179.4 37.1