Mixture of basic lead sulfates

Abstract

A microporous lead-containing solid material is produced, which can serve as a carrier for desired materials into a reaction for various desired purposes. For example, if the microporous solid is impregnated with borax it tends to inhibit the growth of unduly large crystals of tetrabasic lead, which is useful in producing batteries having improved functional qualities.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application claims priority from provisional application Ser. No. 61 / 272,490, filed Sep. 29, 2009.FIELD OF THE INVENTION[0002]The present invention relates to a novel, low density, high porosity chemical mixture of, primarily, basic lead sulfate salts which is useful as a carrier to convey other materials into a chemical process, to processes for its use, and to products made thereby. For example, the material of the invention can be used as a carrier for other materials which act to inhibit excessive crystal growth in lead-acid battery paste, which yields improved battery performance.BACKGROUND OF THE INVENTION[0003]Significant background material on the manufacture of lead-acid batteries can be found in the inventor's prior U.S. patent application Ser. No. 11 / 234,077 and corresponding PCT application PCT / US2005 / 034214, published as WO 2006 / 034466 and incorporated herein by this reference. Some of this material is reproduced below.[0...

AI Technical Summary

Benefits of technology

[0035]Assuming that borax or perhaps some other material would be useful in limiting 4BS crystal growth, the next concern is to find a way to convey such a crystal growth-modifying ingredient into a workable paste mix. Any organic carrier can degrade ultimately to acetic acid, which undesirably corrodes the positive grids. Any inorganic carrier would need to be extremely porous, such that the additive, e.g. borax, would slowly dissolve and diffuse from the carrier to the 4BS growth plane, would also need to be extremely inexpensive, and would also need to be inert so as not to interfere with the battery operating conditions. This precludes use of most materials except titania, that is, TiO2, and lead compounds. Titania, used widely as a white paint pigment, is much cheaper than various nonstoichiometric titanium oxides, which have rough surfaces, but has no significant internal porosity. Titania, if used, would remain inert within each plate, that is, would not participate in charge or discharge, and would thus add undesired weight. Therefore, no titanium-oxygen material is particularly suitable as a carrier.

[0038]The improvements and advantages provided by using such a combination of borax with the novel Fluff microporous lead sulfate mixture carrier (the combination hereinafter being referred to as “BF”) include that it has no effect on the processing characteristics of battery paste containing this material, and that its use, like PCA, limits the size of the 4BS crystals formed to 40 to 60 microns, presumably by causing more crystals to form and thereby reduce their size. Other crystals of large surface area and fine crystal structure are also formed, as shown by SEM, also providing improved high rate battery performance. XRD analysis shows the crystal mixture consists of 4BS and some various lead borate salts. The greater alkalinity of paste containing a BF combination due to the presence of the sodium ion also improved grid-paste adhesion, as shown by pellet-puncture mechanical tests. Initial tests of experimental plates made with a paste containing 4BS nucleant seeds plus BF showed a 10% improvement in moderately fast discharges (20 minute, the “reserve capacity”) versus controls which did not include BF. The inventor extrapolated, based on the well-known Peukert law, that cranking performance should have been improved by at least 10%, but because of the design of the battery test cells, this was not tested in the intial experiments.

[0041]The ability of the Fluff to convey a material that might otherwise be deleterious into a process so as to be gradually diffused or dispersed may be useful in other applications. For example, the Fluff might be useful to convey colorants into glasses and ceramics. The Fluff might also be useful to convey catalysts for fuel cells or other applications. In another possible battery application, the Fluff might carry barium into plates to act as an “expander” which enhances discharge capacity. In this application, the Fluff could be expected to disperse Ba slowly, during curing, so that any BaSO4 produced would be minimal in size and would not undesirably enhance shedding. This might allow use of barium as an expander within positive as well as negative plates.

Problems solved by technology

As mentioned, finely powdered 4BS seeds, such as are described in U.S. Pat. Nos. 7,118,830 and 7,517,370, are costly to make and difficult to handle.

In order to prevent or limit growth of over-large crystals of 4BS, one could drastically change the curing conditions, but this would preferentially affect the outsides of each plate, and, worse, perhaps affect only the outside plates of a stack of pasted plates stacked up for curing in an oven.

Neither borate ion nor sodium is deleterious to battery operation, but unfortunately even as little as 0.1% borax can make battery paste soupy and unprocessable.

Other salts have various other problems.