IE48165B1 - Method of preparing alloys for making electrode supports in lead accumulators - Google Patents

Abstract

Low antimony alloys of lead are used for casting electrode supports in lead accumulators. They include less than 4% antimony by weight to avoid various poisoning effects of antimony on the electrochemical processes involved. Such alloys tend to have grains of excessive size which can lead to brittle castings. To reduce the grain size the present invention includes an additive constituted by a rare earth or a mixture of rare earths, e.g. misch metal at between 0.001% and 1% by weight, and preferably at 0.2%. The invention also provides an electrode support cast from the alloy, an electrode including such a support and a lead acid battery including such electrodes.

Description

The present invention relates to low antimony alloys for making electrode supports for use in lead accumulators. The main constituent of such alloys is lead and they include less than 4% antimony by weight, together with various other additives, e.g. 0.2% tin. These other additives are generally included in small percentages for various well known specific purposes, and the combined total weight of such additives rarely exceeds 2%. In the present invention they are limited to not more than 2% by weight.

Antimony is often included in lead alloys for elect rodes since it tends to improve the use made of the active materials, particularly during cycling. However, its concentration is kept below 4% in order to avoid problems with self discharging and low hydrogen overpressure.

The Applicant has observed that a problem with electrode supports cast from low antimony alloys, and parti cularly those in the form of grids, is that they may be brittle due to cracking. This cracking seems to be due to 2G the large grain size of low antimony alloys.

Attempts have been made to reduce the grain size by introducing sulphur, selenium or tellurium in these alloys. But the results obtained have not been conclusive, since the addition of such materials is difficult even though they do provide a degree of fining. They are difficult to 4816S - 3 introduce partially because of their low solubility in the lead-antimony alloys concerned, but especially because they give rise to substantial irregularities in the shapes and sizes of the grains, thereby still leading to cracking phenomena.

Furthermore, the use of temperatures in the region of 450°C during the making of such alloys, particularly when using sulphur, leads to the emission of polluting lead vapour.

Preferred implementations of the present invention provide other means of reducing grain size in an attempt to mitigate the problem of brittle electrode supports and support grids.

The present invention provides a method of preparing a lead-antimony alloy containing a balance of lead and including antimony at less than 4% by weight together with other additives at not more than 2% by weight, said alloy being intended for use in manufacturing supports for the electrodes of lead accumulators, the method including a step of introducing an additional additive into the lead at a temperature of less than 45O°C and before the antimony is added to the alloy, said additional additive being constituted by a mixture of rare earths, the concentration of the rare earth additive lying between 0.001 and 1% by weight of the final composition.

The invention supposes that the other usual additives are added in the usual manner as required.

Preferably said mixture of rare earths is misch metal, comprising a mixture of cerium, lanthanum, neodymium and praseodymium, e.g. 50% cerium, 25% lanthanum, 20% neodymium, and 5% praseodymium.

The concentration of misch metal may be about 0.2%.

The use of such an additive makes it possible to multiply the number of domains or grains per unit area by about 400, whereas sulphur can only obtain a multiplication - 4 48165 factor of about 50.

The rare earth mixture may be used in conjunction with sulphur, selenium or tellurium, but preferably it is used without sulphur since it is then possible to obtain such lead-antimony-rare earth alloys at temperatures of around 400°C, which, in comparison with sulphur, leads both to an energy saving and to a reduction in pollution.

Naturally the invention also provides lead alloys produced by the method, electrode supports constituted by the above-defined alloys, electrodes comprising such supports, and lead accumulators comprising such electrodes.

Claims (9)

1. CLAIMS;

1. A method of preparing a lead-antimony alloy containing a balance of lead and including antimony at less than 4% by weight together with other additives at not more than 2% by weight, said alloy being intended for use in manufacturing supports for the electrodes of lead accumulators, the method including a step of introducing an additional additive into the lead at a temperature of less than 45O°C, and before the antimony is added to the alloy, said additional additive being constituted by a mixture of rare earths, the concentration of the rare earth additive lying between 0.001 and 1% by weight of the final composition.

2. A method according to claim 1, wherein the said mixture of rare earths is misch metal.

3. A method according to claim 2, wherein the concentration of misch metal is about 0.2% by weight.

4. A method according to any preceding claim, wherein the lead is at a temperature of about 400°C when the rare earth additive is introduced.

5. A method of producing a lead-antimony alloy containing a mixture of rare earths as an additive substantially as herein described.

6. A lead-antimony alloy produced by the method of any preceding claim.

7. An electrode support constituted by an alloy according to claim 6.

8. An electrode including supports according to claim 7.

9. An accumulator including electrodes according to claim 8.