DE1086309B - Process for the production of a galvanic primary or secondary element - Google Patents

Description

Process for the production of a galvanic primary or secondary element The present invention relates to a method for producing a galvanic Primary or secondary element, which is a solution electrode that using is made of fine zinc of preferably more than 99.99% zinc, and one has acidic, neutral or alkaline electrolytes.

In the case of galvanic elements, one electrode of which is made of zinc, the shelf life is limited by the self-discharge of the zinc electrode. the Self-discharge arises from the fact that the zinc corrodes; H. that it is through chemical Reactions with substances present in the electrolyte liquid even without drawing electricity is consumed. The zinc has a strong tendency to such reactions, which is expressed in it comes that it is not only made of dilute acids, but also in alkaline and neutral Liquids such as alkaline solutions, aqueous ammonia and ammonium salt solutions under Formation of hydrogen and the corresponding zinc compounds (salts, zincates, Ammonium zinc complexes) is attacked more or less quickly, the fastest of strongly acidic solutions.

The well-known galvanic chain Pb02 H2 S O4 Zn has a lead dioxide and a zinc electrode immersed in sulfuric acid, in spite of its opposite to others Galvanic current sources of very high voltage of 2.5 volts per cell have not yet been used found permanent use in practice because it was previously not possible to Zinc in an amount sufficient for practical use and without impairment the other functions of the galvanic element safely and permanently before the Protect attack of acid. The attack of the acid is that the zinc in the resting element and also during the current draw with evolution of hydrogen dissolved and thus lost together with the corresponding amount of acid for the supply of electricity (»Self-discharge«).

In cases where neutral or weakly acidic electrolyte solutions are used Are used, for example in the galvanic chain Mn 02 N H4 Cl-Zn, which is widely used in the form of dry elements, the currentless one takes place Consumption of the zinc here with the formation of hydrogen and diammine zinc chloride is essential slower, but the self-discharge of the zinc electrode has an unfavorable effect here too on the durability of the element. The same applies to electrode combinations, in which alkaline electrolytes are used.

The common method used to protect the zinc is amalgamation. The amalgamation prevents corrosion of the zinc in the electrolyte liquid generally strongly inhibit. However, the protective effect of mercury is specific in the case of strongly acidic electrolyte solutions (e.g. with the Pb 02 H2 S 04-Zn element) itself when using very pure zinc, which experience has shown is stronger against acid attack resisted as impure zinc, practically insufficient, especially since it is always expected must be that also a little gassing, d., h. apparently usable electrode earlier or later gets so-called pitting, in which case it occurs at individual points Strongly gassing indentations or through holes in the zinc form which the rapid Consumption and destruction of the electrode.

The object of the present invention was now to address the disadvantages outlined to avoid the previously known solution electrodes made of zinc and a method to create through the one. galvanic primary or secondary element can be produced can, which is characterized by a particularly high corrosion resistance of its solution electrode excels.

According to the invention this object is achieved in that the electrolyte Indium compounds are added and / or indium metal is alloyed to the fine zinc will.

Thorough investigations have shown that the corrosion of zinc, even in highly acidic electrolyte solutions, affects weight loss lower than 1 mg zinc per day and per square centimeter of surface and at the same time the dangerous pitting corrosion can be prevented by the fact that according to the invention the electrolyte solution small amounts (of the order of 0.01 to 0.1 ° / u) indium ions in the form of a suitable indium compound or the zinc itself Adds indium metal (In) in amounts of the order of 0.01 percent by weight.

The measure of using zinc to protect against corrosion is known to provide a thin coating of indium. However, it is necessary that this indium coating completely covers the zinc in the form of a closed film. In contrast, it could not be foreseen that with zinc electrodes for galvanic elements the addition of indium to fine zinc or the addition of an indium compound causes corrosion protection for the electrolyte, since these measures do not the formation of a closed indium coating on the zinc can be expected can. It is also known that electrodes made of refined zinc, such as those used for galvanic Elements commonly used contain indium as a natural impurity can, but the process, fine zinc with a content of at least 99.5 "/ o zinc with indium for the purpose of corrosion protection electrodes made from it alloy is new and inventive.

The inhibitory effect of indium as an alloy or electrolyte component can, as was further found, through the use of zinc with a content of the order of 0.01% cadmium (Cd) or by adding such small amounts Improve cd to pure zinc to some extent. Definitely affect low Cd contents of the zinc up to about the mentioned percentage the effect of the Indiums do not. Significantly higher Cd additions (order of magnitude 0.1 ° / a), however, have an effect unfavorable by reducing the effect of the indium and the tendency to Increasingly intensify the formation of pitting.

Magnesium (Mg) supplements used by us in some cases were to increase the pourability and homogeneity of the melt, interfere with the the corrosion-inhibiting effect of the indium or the In compounds is not the difference of Cd even if the Mg content is increased to almost 1%: on the contrary, It was found that the corrosion resistance of the Inprotected samples - can be increased by adding small amounts of Mg by alloying.

In order to bring the protective effect of the indium to full effect, it is Of course, it is essential to ensure that neither through the electrode material nor by the electrolytes and their solvents nor by the others to build up The materials used in the cell introduce foreign metals into the electrolyte fluid which increase the rate of corrosion or dissolution of the zinc. to such foreign metals include, in addition to precious metals, copper and iron, above all, such as has been shown to include antimony (Sb). The exclusion of harmful foreign metals is in cases where, as with the Pb 02-H2 S O4 Zn element, worked with strongly acidic electrolytes will naturally pay special attention.

It has been found that the addition of In ions to the solution or achievable by adding In metal (or In + Cd, In + Mg or In + Cd + Mg) to the zinc Inhibition of acid attack by the presence of a Pb 02 electrode as positive Electrode is not impaired, provided that its framework is made of soft lead is. In the presence of a hard lead electrode containing SB, even an In-protected one becomes Zinc electrode attacked by the acid more than the corresponding pure zinc electrode in the presence of a soft lead electrode. When building Pb 02-H2 S 04-Zn batteries are therefore SB-free Pb 02 electrodes should be used or those in which the structural lead, if this is hardened with Sb, so is covered with SB-free lead that the acid has no access to the hard lead. As was further found, it is to the full to achieve degrees of protection in acid evident from the following numerical examples, It is advisable to use zinc types or Zn alloys, the Fe content of which is 0.002% does not exceed.

Against the risk of contamination of the acid by others in the Corrosion-promoting foreign metals such as precious metals contained in electrode materials and copper, offers the use of 99.9950% zinc as a starting material for the production of Zn electrodes and the use of commercially available Pb02 electrodes (SB-free positive accumulator plates) a high degree of security, as on the one hand the 0.005% / a foreign matter in zinc consists only in the smallest part of such metals - 0.005114 lead are harmless - and on the other hand the Pb 02 electrodes are manufactured in this way with regard to the durability of the lead-acid battery, that they do not release these metals into the electrolyte solution. To avoid the Bringing in any corrosive foreign metals with the electrolyte liquid It is advisable to observe the values for accumulator acid over the maximum permissible VDE regulations applicable to impurities.

Used the process of corrosion inhibition by indium on other zinc systems containing electrode material, for example the customary ones Primary batteries of the carbon-manganese dioxide-ammonium chloride-zinc system are used which have just been specified with regard to interfering foreign substances for the Pb 02 H2S O4 Zn element To transfer points of view in a corresponding manner. That said, it's in order to be a longer one To achieve service life, expediently, to increase the self-discharge of the Zn electrode serving purity regulations for the materials and chemicals to be observed in each individual case, unless you want the advantages of In-Protection perceive in a modified sense, namely in the following: The application of the In-Protection not only offers the possibility of delaying the self-discharge all other things being equal; the process also allows the same self-discharge speeds to be achieved with less pure materials. This is also a significant advantage of the process, as it is well known that the purity requirements are often considerable and are difficult to fulfill.

The exact in-amounts required to achieve the optimal inhibitory effect are necessary, depending on the type of element and zinc quality subject to certain fluctuations. In this respect, the above percentages are to be understood as guidelines, from which deviated upwards or downwards in individual cases can be. Neutral or weakly acidic electrolytes require less indium additions to the electrolyte liquid as strongly acidic. The exact amount of the optimal amount leaves determine yourself through trial and error.

The following are some experimental examples with acidic electrolyte solutions the measurements carried out and their results are listed; the observed weight losses as a result of the (electroless) dissolution of the zinc in acid are in each case in milligrams specified and based on 1 cm2 and 1 day; so they represent corrosion rates.

With a chemically pure, according to spectral analysis Cd-free, about 0.005% Zinc containing Pb 0.001% Fe could be applied to the cast and amalgamated Electrodes when lying in sulfuric acid with a density of 1.25 for 6 to 9 weeks Corrosion loads of 6.0 to 6.5 mg / cm2 and day due to previous alloying of 0.01 In to 3 to 3.3 mg / cm2 and day, by adding 0.01% Cd to about 4.0 lower mg / cm2 and day.

In the case of a sheet other than soft fine zinc sheet of quality class 99.99511 / o Related zinc type with a spectroscopically determined iron content of 0.002% (in addition to 0.002% Pb and 0.0001% Cd) the rate of dissolution was from 7 to 9 mg / cm2 and day of unalloyed zinc reduced to 6.1 or 5.3 mg / cm2 and day, if 0.01% In or 0.01% In -1-0.010 / a Cd was added beforehand.

In other series of tests it was found that the above-mentioned corrosion losses drop to about 1 mg / cm2 and day and below when the cell is working. For example, in a series of experiments over 153 days with cells in which an approximately 20 cm2 Pb 02 grid electrode (soft lead grid) was opposed to an approximately 20 cm2 cast and amalgamated zinc electrode, with a continuous current consumption of 3.5 mA during the first 50 days the following corrosion losses were measured: 1. In 0.01%. . . . . . . . . . . . . . 1.2 mg / cm2 and day 2. In -f- Cd 0.010 / 0 ...... 1.0 mg / cm2 and day each 3. In -I- Mg per 0.01% ...... 0.7 mg / cm2 and day 4. In -I- Cd -f- Mg per 0.01% 1.1 mg / cm2 and day 5. In 0.10 / 0. . . . . . . . . . . . . . . 4.0 mg / cm2 and day 6. In + Cd each 0.10% ....... 6.8 mg / cm2 and day 7. In -I- Mg per 0.5% ....... 2.1 mg / cm2 and day Tests 5, 6 and 7 were discontinued after 50 days because of the relatively severe corrosion. It is noteworthy that a comparison test to 5, in which an equal amount of Cd was added instead of In, had to be eliminated after 9 days because of the occurrence of pitting corrosion; for the same reason a parallel attempt to 7; in which an additional 0.5% Cd had been added, precipitate after 12 days. Trials 1 to 4 were continued for a total of 153 days. The corrosion losses, which were measured on average over the last 75 days, were consistently below the values given above. Pitting did not occur here in any case. The above-mentioned chemically pure zinc (with 0.001% Fe) was used as the starting material for the alloys.

The effect of adding an indium salt to the acid is shown as follows Experiment demonstrated: a cell made up of a 20 cm2 Pb 02 soft lead electrode and an approximately 30 cm2 sheet zinc electrode (soft fine zinc sheet 99.995% Zn 0.002% Fe, amalgamated), immersed in sulfuric acid (density 1.25) containing 0.1% In contains dissolved as indium sulfate (0.23% In2 (S O4) 3), showed during a 20 day If there is no current consumption, there is a corrosion loss of the zinc of 3.1 mg / cm2 and day, after a further 20 days of standing. with current consumption (approx. 30 mA) such a one of 0.33 mg / cm2 and day and finally after standing for another 20 days without drawing any current a loss of only 0.18 mg / cm2 per day. From comparative experiments with acid, which only contained 0.01% In ions, it is evident that indium ions also in this concentration are still clearly effective.

Seat of the effect of as a metallic alloy component or as the salt-like electrolyte component supplied indium is in any case the interface Zinc electrolyte fluid. How and in what form the inhibiting metal is brought there is of minor importance. So can the indium for example, bring it into effect in such a way that it is previously in a suitable manner thin layer on the pure zinc precipitates, namely before, after or during amalgamation, e.g. B. in such a way that the amalgamation liquid (Mercury chloride solution) an indium salt is added during the amalgamation. The type of indium salt that is added to the electrolyte solution is in itself immaterial, but the selection must of course be made from the point of view that with the In-salt, no anions that would damage the positive electrode in the electrolyte solution may be brought. In the case of strongly acidic solutions, you can simply use a corresponding Amount of indium oxide, oxide hydrate or metal can dissolve, in the case of strongly alkaline Solutions Oxide hydrate, which dissolves in it to form indates.

It is also possible to have a supply of a sparingly soluble compound; for example, annealed indium (III) oxide, to be added to the cell to create a depot To create indium compounds., Compared to organic inhibitors, according to the invention inorganic protective substance called the advantage of unlimited chemical durability also in the working element and not influencing the potential setting on the electrodes.

Claims (6)

PATENT CLAIMS: 1. Process for the production of a galvanic primary or secondary element with a solution electrode which is produced using fine zinc of preferably more than 99.99% zinc, and with an acidic, neutral or alkaline electrolyte, characterized in that the electrolyte Indium compounds are added and / or indium metal is alloyed to the fine zinc. 2. The method according to claim 1, characterized in that 0.001 up to 0.03% indium can be added to zinc. 3. The method according to claims 1 and 2, characterized in that the electrolyte liquid contains a sparingly soluble, Indium compound present as soil or a preparation containing indium is added. 4. The method according to claims 1 to 3, characterized in that that the electrolyte liquid 0.1 to 1 g per liter of indium as indum salt, for. B. Indium sulfate, is added and, in this case, the electrolyte from diluted Sulfuric acid. 5. Process according to claims 1 to 4, characterized in that that the active mass of the positive electrode is made of antimony-free lead dioxide will. 6. The method according to claims 1 to 5, characterized in that the positive electrode as active mass lead dioxide - contains and their carrier is made from a lead-indium alloy. Considered publications: U.S. Patent No. 2,683,184; Gmelin's Handbook of Inorganic Chemistry; "Indium" (1936), pp. 6 and 48; "Zinc" (1956), pp. 703/704; Victor Tafel, "Textbook of Metallurgy", 11: 556 (1953); Ziegenberg, "Trockenelemente und -batterien" (1934), p. 279.