DE1939794C3 - Negative magnesium electrode for galvanic elements - Google Patents

Description

The invention proposes magnesium alloys, which improved electrochemical Have properties when used as negative electrodes in galvanic elements.

The main types of battery systems or galvanic elements in which magnesium alloys are used are the magnesium seawater cells, which usually use silver chloride as the cathode (positive electrode) as well as the dry magnesium cells of the Leclanche type, in which Manganese dioxide or other materials can be used as a depolarizer. Magnesium alloy electrodes are usually in the form of sheets or foils with a thickness of 0.16-0.65 mm used With certain larger batteries, however, stronger electrodes can also be used in Form of cast or extruded sheets can be used. In cells of the Magnesium Leclanche type the electrode is usually in sheet metal form or in the form of extruded cylindrical cans before.

The magnesium alloy currently used extensively for magnesium seawater batteries is the alloy AZ61, which contains about 6% aluminum, 1% zinc and 0.2% manganese. It has been found that this alloy provides the best compromise of the properties required for the successful application of a magnesium seawater / cllc is required, namely a high electrode potential when at high discharge speeds is worked and the formation of a very fine granular reaction product, which from the Cell can be easily flushed out without clogging or occluding the cell to lead. A solution treatment extending over several hours at 400.degree. C. is essential in order to to produce a uniform single-phase structure, which this alloy has the required properties gives typical cell voltages for this alloy in the form of thin, roughened sheets,

κι if they work in a magnesium seawater silver chloride cell under flowing seawater with a salt content of 21 at 20 to 25'C and an electrode spacing of 0.5 to 0.58 mm at a current density of about 0.31 A / cm ² , are on the order of 1.0 volts

By adding further elements to the specified alloy composition, further alloys are created has been developed, which higher electrode potentials under discharge without a remarkable To result in deterioration in the shape of the reaction product. Such alloys 6% aluminum, 1% zinc, 0.2% manganese, up to 10% lead or 1 to 10% lead and 0.5 to 5% Contains mercury. Such alloys are in

2Ί of US Pat. No. 3,288,649.

A typical alloy containing about 7% aluminum, 1% zinc, 0.2% manganese and 0.5% lead, j: u was rolled out on a thin sheet and then subjected to a solution treatment to obtain a

ι «to give uniform single-phase structure, whereupon then the surface was roughened with a wire brush. When such an alloy in a magnesium-seawater-silver chloride cell with a flowing electrolyte and an electrode gap of

i) 0.5 to 0.58 mm was used at a current density of 0.31 A / cm ² , cell voltages of the order of magnitude of 1.15 volts were obtained.

Pure magnesium is unsuitable per se for these purposes, since during the use of the

-> <> cell the reaction product formed thick, flaky and is adhesive and tends to polarize the magnesium and clog the cell. In a similar way By adding lead or mercury to pure magnesium, the desired combination can be achieved.

4 ^r > nation of high potential and fine non-clogging reaction product cannot be achieved.

It has now been found that, by adding thallium, it becomes pure within certain limits

w Magnesium alloys can be produced, which have a very high electrode potential when discharged and which do not form a thick reaction product that easily clogs the cell. Magnesium alloys containing thallium can

«Can be pressed or rolled into thin sheets without difficulty.

The invention thus relates to a negative magnesium electrode for galvanic elements made from a magnesium alloy with the following alloy constituents

share bo:

Thallium I. until 15th Wt% aluminum 0 until 10 Wt% mercury 0 until 5 Wt .- "λ lead O until 5 Cicw .- "/ zinc 0 until 3 Wt% manganese 0 until 1 Weight% Calcium 0 until 1 Weight- "/"

cadmium
magnesium

0 to 1% by weight
at least 80% by weight

The following Table I shows typical electrode potential values and details of the resulting reaction product, as determined from experiments were using the magnesium alloys as anodes (negative electrodes) in an electrical

Table I.

Electric circuit were used to so the discharge ratios to mimic which occur in a seawater cell with a high energy density. The alloys were in the form of round cast rods which were solution-treated to give a uniform single phase structure.

alloy

Middle electrodes
potential (volts)
with reference to non-
polarized AgCl Condition of the electrode surfaces 1.57 thick adhering precipitate 1.55 pure 1.74 almost completely pure 2.00 voluminous precipitation 1.70 thick, sticky bodice 1.85 very fine powdery precipitate 1.98 medium-fine powdery low
blow

Pure Mg

Mg H- 6% Al + 1% Zn + 0.2% Mn

Mg Η- 6% Al + 1% Zn + 0.2% Mn + 5% Pb

Mg H- 5% Hg

Mg ■ «- 5% Pb

Mg + 7 '/ 2% TI

Mg ·! · 11% TI

The potential values are given in volts with respect to AgCl, with no drop in resistance within the Cell was present.

When an alloy consisting of manganese with 7 1/2% thallium was rolled into a thin sheet and then heat treated to obtain a uniform structure, and these sheets in a magnesium-seawater-silver chloride cell with flowing electrolyte and an electrode gap! 0.5 to 0.58 mm under a current density of about 0.31 A / cm ^{2 were} used, cell voltages of 1.4 volts were observed.

Because of the high solubility of thallium in magnesium, the possibility that the thallium forms a desired secondary phase in the metal during processing is very substantially reduced The solution treatment of the binary alloy is therefore only required for the reason to to achieve an even distribution of the thallium in the material.

The electrode potential of alloys containing thallium can be increased by increasing the thallium content by up to 15%, but no further advantage is obtained beyond this value. This can be seen from the figure of the drawings, which shows the change in the maximum and mean potential for a discharge lasting 5 minutes and also the evolution of hydrogen as a function of the thallium content. These values were obtained in an experiment in which the cross-section of a cast rod was used as the anode in a cell containing seawater, the other electrode being a platinum mesh. Current was passed through the cell to simulate a battery discharge of 0.31 A / cm ² , and the electrical potential at the magnesium surface was measured against a silver / silver chloride capillary electrode. During this experiment, the hydrogen evolving on the anode was collected.

For use in seawater bathing are the

«Ι optimal alloys those which during show the least amount of sludge formation during discharge, which also corresponds to the least amount of water generated. So these are those alloys which contain between 4 and 12% thallium and in particular

ii those between 5 and 10%, for example between Contains 6 and 9% thallium.

For magnesium dry cells and for batteries in which there is only a small flow of seawater, the shape of the reaction product is not so

4 »critical, as for pure seawater batteries, and as a result lower concentrations of thallium can be used for such purposes, which a result in larger electrode potential and with which during use thicker and more strongly adhesive

4i reaction products are formed.

If aluminum is added to magnesium alloys containing thallium, then during use a fluffier but less adhesive reaction product, which with increasing aluminum

") 0 content is getting finer and finer. Aluminum in a lot from 4 to 7% in the alloy results in a fine fluffy precipitate emerging from the surface the plate can be easily washed off, but it builds up with smaller amounts of aluminum

r> thick flaky precipitate on the material surface, which results in a potential drop Has.

If a 7 '/ 2% thallium and 5% aluminum containing alloy, for example, among the in

«> The conditions laid down in Table I are checked, this results in an electrode potential of 1.78VoIt with an almost completely clean surface, and an alloy containing 11% thallium and 5% aluminum gives an electrode potential of 1.83 volts

hi with just a loose powdery precipitate on the surface. Additions of up to 10% aluminum can be used in the alloys.
In Table II are the Snannuins and the

Sheep lamb formation properties for various alloys have been compiled, which were obtained in a single / cell test construction with flowing artificial seawater with a salt content of 21 at a temperature of 25 ° C. In this experiment, cells measuring 152 × 50 mm were assembled by juxtaposing a magnesium alloy sheet and a silver chloride foil between silver conductors. The electrolyte distance between the magnesium and the silver chloride was maintained by glass spheres which were embedded in the silver chloride. It was measured with an electrode gap of 0.6 mm and a linear electrolyte flow rate of 6 cm / sec. worked between the plates. The lines were constantly discharged at 0.31 A / cm ^{2 for up to 10 minutes.}

Table Il

Stress and sludge formation in various alloys

The addition of mercury or lead to the magnesium battery alloys increases the electrode polarity the alloy is enlarged. It has been found that by additions of lead and / or Queek- ". silver to the alloys containing thallium achieved a further increase in the electrode potential can be, but a somewhat larger sludge formation takes place. There can be additives up to 5%, for example 0.5 to 5%, can be made on each of these eggs. By adding Mercury to aluminum-containing thallium alloys are just about a profitable improvement the tension and a small improvement in the sludge properties. Examples of such leri alloys are compiled in table ü.

alloy % Al % Hg Typical Tension l '/ 2 after time in minutes 5 8th Mud sonication % TI % Pb '/ 2 1 1.16 2 4th 1.06 1.05 5 1.17 1.17 1.20 1.14 1.10 1.12 1.15 black down
hit metal 6th 1.20 1.20 1.23 1.19 1.15 1.24 1.14 low black
Precipitation on metal 7th 1.23 1.23 1.32 1.23 1.25 1.11 0.84 the same 7 '/ 2 1.26 1.28 1.37 1.41 1.36 1.05 0.71 adhere moderately
the black film 8th 1.35 1.35 1.29 1.39 1.30 1.19 1.00 strong black
Movie 9 2 1.25 1.28 U3 1.31 1.34 1.06 1.00 the same 7th 2 1.25 1.30 1.31 1.33 1.24 1.10 1.03 looser flaky
Precipitation V / 2 2 1.32 1.32 1.30 1.30 1.18 0.99 1.02 the same 8th 2 1.35 1.33 1.30 1.27 1.17 1.00 1.06 stronger flaky
Precipitation 9 5 1.36 1.33 1.10 1.28 1.17 0.96 0.94 the same 5 5 1.10 1.10 1.27 1.08 1.08 1.15 1.13 pure surface 7th 5 1.27 1.28 1.28 1.26 1.21 1.17 1.15 pretty pure
surface 7 '/ 2 5 1.28 1.29 1.28 1.27 1.22 1.15 1.12 the same 8th 5 1.30 1.30 1.30 1.26 1.21 1.15 1.10 less powdery
Precipitation 9 1 1.31 1.32 1.32 1.27 1.22 0.86 0.72 medium powdery
Precipitation 7 '/ 2 5 1 1.39 1.37 1.27 1.29 1.14 1.17 1.16 very strong
Precipitation 7 '/ 2 5 2 1.25 1.27 1.22 1.26 1.21 1.12 1.12 pure surface 7 '/ 2 5 1.21 1.22 1.26 1.21 1.18 1.17 1.12 pure surface 7 '/ 2 1 1.20 1.25 1.04 1.26 1.21 0.92 0.91 medium strength
Precipitation AZ 61 1.04 1.04 1.18 1.03 0.97 1.05 1.03 pure surface AP 65 1.15 1.18 1.17 1.11 low black
powdery down
blow

The alloys according to the invention can thus contain the following elements:

Preferred

optimum

IO

Thallium 1 to 15% by weight 4-10% 6-8%

Aluminum 0 to 10% by weight 0-7% 4-6%

(e.g. 1-7%) mercury 0 to 5% by weight

Lead 0 to 5% by weight

Zinc 0 to 3% by weight

Manganese 0 to 1% by weight Calcium 0 to 1% by weight

Cadmium 0 to 1% by weight

The water-activated battery can contain a cathode part using a silver chloride

or cuprous chloride plate in conjunction with a silver foil or other conductive material and an anode made of the magnesium alloy in the form of a thin-rolled sheet of 0.13 to 0.64 mm (e.g. 0.25 to 0.5 mm) spaced 0.5 to 2.5 mm from the chloride.

The heat treatment of the alloy can be carried out at temperatures of 350 to 450 ^° C. for 4 to 60 hours, and it is carried out, for example, at 380 to 420 ^° C. for 8 to 24 hours in the case of alloys which contain up to 12% thallium.

The alloys according to the invention contain at least 80% magnesium.

The subject matter of the invention can also be used in conjunction with an "air battric," as säe for example in British Patent 11 40 635 is described in that the anode consists of one of the alloys described here. the Anode can be rolled or pressed out to a thickness of 1.27 to 3.8 mm.

1 sheet of drawings

Claims (5)

Patent claims: I. Negative magnesium electrode for galvanic Magnesium alloy elements with the following alloy components: Thallium 1 to 15 wt% aluminum Obis 10% by weight mercury Obis 5% by weight lead Obis 5% by weight zinc Obis 3 wt% manganese Obis 1% by weight Calcium Obis 1% by weight cadmium Obis 1% by weight magnesium at least 80 C 2. Electrode according to claim 1, characterized in that the alloy is 4 to 10% thallium and contains 1 to 7% aluminum 3. Electrode according to claim 1 or 2, characterized in that the alloy is 6 to 8% thallium and contains 4 to 6% aluminum 4. Electrode according to claim 3, characterized in that the alloy 6 to 8% thallium, Contains 4 to 6% aluminum and 0.5 to 5% lead and / or mercury 5. A method for pretreating the electrode according to claims 1 to 4, characterized in that that the electrode is subjected to a heat treatment at 350 to 450 "C for 4 to 60 hours will.