NZ199844A - Preparing lead/lead oxide particulate material for use in lead-acid batteries - Google Patents

Description

1 99 Priority Date(c): CompSsto SpscfBcaticn Filed: Class: CoI (Q%Hp.' M jojob ■ .

Publication Deis: ... 2 4- AUG .19B4.

P.O. Journal, fide: .. J^k(. tePATWc^, 2&FEB1982 N.Z. NO.

NEW ZEALAND Patents Act 1953 COMPLETE SPECIFICATION 'NOVEL LEADY OXIDE PRODUCTS AND METHOD FOR PREPARING SAME." We, GOULD INC., a corporation of the State of Delaware of 10 Gould Center, Rolling Meadows, Illinois 60008, United States of America do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- ~ 1 ~ (Followed by 1A.) 199844 •M-MET-81rfr2- -1A- This invention relates to the manufacture of leady oxide for use, for example, in the preparation of active materials for lead-acid batteries and, more particularly, to an improved method and product.

The active materials in lead-acid batteries are prepared, as is well known, frcm a mixture of lead and lead oxide in the form of finely divided lead oxide particles with a residual core of lead. There are two main processes being used commercially at the present time. The first utilizes an attrition mill in which blocks of solid lead are ground by self-attrition in a rotating steel drum. The resulting lead powder is partially oxidized by air, and the powder is then removed frcm the drum either by air or through screens. The powder is then generally classified, and the oversize particles are returned for further milling while the under-size particles are collected for use.

In the second process, molten lead is fed into a reaction vessel, e.g. - a Barton pot, and is agitated by a rotating paddle. This breaks the molten lead into droplets and exposes a large surface area 199844 to incoming air for oxidation. The powder is conveyed from the reaction pot by air flow and is then classified or further ground. The use of reaction pots are generally thought to have advantages over 5 attrition mills in terms of lower capital and operating costs per unit output of lead oxide. The material produced typically has a different particle shape in relation to that resulting from the use of attrition mills, i.e. - spherical as opposed 10 to relatively flat or leaf-like, and possesses a somewhat higher lead oxide content. However, processes using reaction pots tend to be more difficult to control in comparison to attrition mills in terms of the ability to produce oxide of a consis-15 tent quality.

Thus, in a reaction-pot type of process, the temperature is basically controlled by the rate at which lead is introduced into the reaction pot. The air throughput together with the residence time 20 in the reaction pot control the amount of free lead in the product as well as the average particle size. Regardless of attempts at satisfactory control temperature, it is sometimes difficult in practice to avoid undesirable "hot spots" in localized areas 25 which can adversely affect product consistency, e.g. - leading to higher orthorhonbic lead oxide contents. Further, while longer than normally used residence times can reduce the average product particle size somewhat, this may result in undesirably low lead 30 contents. Typically, it is desired to maintain a lead content of about 18 to 25 percent by weight to avoid undesirably low exothermic characteristics which hamper further processing, e.g. - curing of active material paste using such leady oxide pro- i 99344 * ducts for lead-acid batteries.

It has been suggested to add water to a reaction pot to provide improvements in the manufacture of leady oxide. However, insofar as is known, 5 these efforts have been plagued by explosion and blowback problems. More particularly, these difficulties appear to have resulted fran the buildup of moist oxide which hang up in the reaction pot and then drop back into the pot, causing steam expansion 10 or the like which then spews leady oxide out of the reaction pot and into the immediate area. In short, insofar as is known, prior attempts to use water injection in processes for forming leady oxide have been singularly unsuccessful.

Further, it has been suggested to incorporate various additives into the active neterials of lead-acid batteries to enhance various performance characteristics. Materials suggested include various lead compounds such as PbtOH)^, Pb0.H20 and Pb(C03)2-20 In addition, it has been suggested to add to a battery a variety of metallic sulfates such as sodium or potassium in various ways for a multitude of purposes.

Still further, it is known that substantial advantage is achieved by injecting controlled amounts of water in atomized form into the reaction pot employed.

It is accordingly an object of the present invention to provide a more facile method for preparing leady oxide.

A further object lies in the provision of leady oxide characterized by a relatively low average particle size. 199844 4 Yet another object of this invention is. to provide leady oxide characterized by a relatively higher content of tetragonal lead oxide in relation to the orthorhombic lead oxide content in comparison to conventional leady oxide produced in reaction pots.

A still further object provides leady oxide characterized by relatively high acid absorption capabilities.

Another object lies in the provision of a method of preparing leady oxide with superior efficiency. A related preparing leady oxide which allows the achievement of higher production rates than in conventional reaction pot processes.

Accordingly the present invention provides a method 15 for preparing leady oxide for use in making active materials for lead-acid batteries which comprises feeding molten lead into a reaction pot, dispersing the molten lead into droplets, partially oxidizing the lead droplets in the reaction pot by contact with a stream of air containing 20 water in atomized form at a pH of from about 8 to ahout 12, removing the oxidized lead droplets from the reaction pot in the air stream, and thereafter collecting the oxidized lead droplets. will become apparent from the following detailed description and from the drawing, in which: The sole figure is a schematic view showing illustrative apparatus in accordance with the present invention. modifications and alternative forms, there will herein be described in detail the preferred embodiments. It is to be understood, however, that it is not intended to limit the invention to the specific forms disclosed. On the contrary, it is intended to cover all modifications and 35 alternative forms falling within the spirit and scope of the invention as expressed in the appended claims. For example, while the invention will be described in conjunction with the use of a Barton pot as the reaction pot, it should be appreciated that this invention is equally applicable 40 to the use of other types of reaction pots employed for an(3 more specific object is to provide a method for Other objects and advantages of the present invention While the invention is susceptible to various I 99844 making leady oxide.

As previously noted, it is known that a more facile preparation of improved leady oxide products is achieved by 5 introducing controlled amounts of water in atanized form into the reaction pot. Introduction of water in this fashion and in such amounts eliminates explosion and blowback problems while providing improved products. In accordance with the present 10 invention, the benefits of such preparation are retained while further and significant improvements are achieved by adjusting the pH of the water added to about 8 to about 12.

Turning now to the sole Figure, means are pro-15 vided for introducing lead in molten form into a reaction pot. To this end, such means includes a pig feeder 10 which introduces the lead into a melting pot 12, equipped with an exhaust vent 14. The molten lead produced is then transported using a 20 pump 16 through an inclined trough 18 into a Barton pot 20. Alternatively, and more typically molten lead may be fed into the Barton pot by gravity feed, using air as a displacement medium, as is known.

The Barton pot incorporates means for dis-25 persing the molten lead into a droplet form whereby the droplets formed are then partially oxidized by incoming air. Typically, and as is shown, the Barton pot 20 is eguipped with a rotating paddle 22, driven by motor 24. Ambient air for oxidizing the 30 lead droplets is drawn in through intake 26. The resulting product exits from the Barton pot 20 through exit port 28.

The conditions which may be used in commercial Barton pots can vary widely. Conceptually, the '8 MAY 1934° I 99844 amount of air drawn into the reaction pot should be more than sufficient to both carry out oxidization of the lead as well as to serve as a carrier for the oxidized lead droplets into whatever collecting 5 or classifying means are employed. Illustrative parameters include the introduction into a Barton pot of about 1600 to 2200 or 2300 pounds of molten lead per hour with an air throughput of about 1500 to 2500 cubic feet per minute. 10 In accordance with the present invention, a means of introducing water in atomized form with the incoming air into the Barton pot is provided in controlled amounts and at a pH in the range of from about 8 to about 12. To this end, water is provided 15 from a source not shown through a rotameter 30 and a conventional pneumatic spray nozzle 32, which is positioned within the air intake 26.

The desired pH can be achieved by adding to the water sodium or potassium hydroxide by using any suitable means such as (not shown) a conventional displacement pump. The amounts needed will, 25 of course, depend upon the pH of the untreated water, which typically will be about 5 or 6. It should be appreciated that, while sodium or potassium hydroxide are preferred, any other material could be on-ployed so long as this does not result in the pre-30 sence of materials that would significantly adversely affect either the further processing of the leady oxide or the resulting battery performance.

It has been found that the addition of water at such controlled pH enhances production rates per 1^-8 MAY 1984 99844 7 - unit weight of lead in relation to conventional processes. Indeed, it is believed that the increased production of leady oxide provided per pound of lead feed will offer substantial economic benefits.

Typically, the leady oxide product exits through 10 exit port 28 and is then collected by any appropriate means. As is illustrated, this can suitably comprise a settling chamber 34, a cyclone precipitator 36 and a bag filter 38. The product frcn each can be transported via a screw conveyor 4 0 for storage, shipment or the like. Air throughput in the system may be provided by a fan 42 vtfiich draws ambient air into the Barton pot and then through the system, as is known.

Overly coarse product fran the collection 20 means, particularly from the settling chamber where at least half of the product will generally be obtained, can be recycled into the reaction pot, if desired. Moreover, if further reduction in the average particle size of the leady oxide is desi-25 rable, this can be achieved by employing a hammer-mill or the like, as is often used in commercial practice. However, as will be discussed in greater detail hereinafter, the leady oxide products produced by this invention typically possess a relatively small average particle size.

As has been alluded to previously, the leady oxide produced in the present invention possesses characteristics which are, in some respects, quite different from those obtained in conventional re- TV* *r«MAY 1984^1 1 99 action pot processes. It should be appreciated, of course, that the particular process parameters employed may well alter the specific process parameters actually achieved. However, typically, the leady oxide 5 obtained in the present invention will usually have a relatively smaller particle size than that achieved in conventional processes. As an illustrative example, the average particle size of leady oxide products obtained in accordance with the present invention may 10 vary in the range from about 1.5 microns to about 17 microns (prior to any hammermilling or the like). Further, the leady oxide products of this invention tend to have lesser amounts of orthorhombic lead oxide in comparison to the level obtained in conventional 15 Barton pot leady oxide preparation.

The leady oxide of this invention also achieves somewhat higher acid absorption characteristics in relation to conventional products. While this is speculation, it may well be that, at least at some 20 stage in the processing, the leady oxide produced using the method of this invention may contain minor amounts of other compounds, e.g. - about 1/2 to 1% or even more by weight of PbCOH^- Indeed, the controlled pH is believed to enhance the weight gains 25 obtained in the processing over that achieved by the use of untreated water (viz. - unadjusted pH), presumably by increasing the amount of PbtOH^ or other compounds obtained. Regardless of the mechanism involved, it appears that improved oxide 30 efficiencies are obtained, possibly due to increased acid absorption characteristics.

The leady oxide of the present invention may be used in conventional active material paste pre- 1 99844 paration without any necessity for change in formulation or processing techniques. Similarly, pasted grids for both positive and negative electrodes can then be formed into the active materials by any 5 of the presently known techniques.

Moreover, when the leady oxide products of the present invention are utilized to prepare active materials for lead-acid batteries, no adverse effects have been seen. Indeed, it appears for some reason 10 that the use of the present invention results in somewhat higher oxide efficiency in the sense that the reserve capacity of batteries utilizing such leady oxide appears to be slightly enhanced in relation to reserve capacities achieved with active 15 matericil formed frcm leady oxide made in conventional reaction pot processes.

The following Example is merely illustrative of the present invention and is not intended as a limitation upon the scope thereof.

EXAMPLE To illustrate the performance of the present invention, test cells were made which incorporated active materials made frcm the leady oxide of this 25 invention and were conqpared to a control cell having active materials made frcm leady oxide made in a conventional reaction pot process.

Two cells were made utilizing leady oxide in which controlled amounts of water were introduced 30 in atomized form into a Barton pot as is generally shown in the sole Figure, the amount of water being , about 1-1/2% by weight based upon the weight of molten lead being introduced, the pH being adjusted to 8 by addition of sodium hydroxide. As a control, a t99844 cell was made in which the active materials were prepared using similar leady oxide product from a Barton pot process, except that no water addition was utilized. Each cell had six positive and seven 5 negative electrodes. Each grid for the electrodes was pasted with approximately the same amount of active material, and the pasted grids were similarly cured. The cells were then assembled and subjected to the same formation technique.

Each cell was then subjected to a discharge- charge regime for 3 2 cycles. The discharge regime involved a current discharge of 2 0 amps until a cut-off voltage of 1.75 was reached. The charge regime involved a recharge to provide about 110 to 15 about 115% of the Ampere-Hour capacity removed in the discharge regime.

The time in minutes before the voltage cut-off was reached is set forth in the Table below: Control Cell Test Cells Cycle Number 1 142 146 144 2 151 153 155 3 160 163 167 4 171 173 175 176 174 179 6 174 179 181 7 179 182 184 8 180 186 188 9 179 182 184 179 183 186 11 177 183 185 12 172 177 179 13 171 176 178 t 199844 14 167 178 180 173 180 182 16 167 173 177 17 157 167 169 5 18 162 167 170 19 159 165 169 155 162 167 21 163 170 176 22 159 165 171 10 23 165 .. 167 174 24 158 162 170 153 155 161 26 149 152 159 27 153 159 165 15 28 149 155 163 29 147 151 159 145 149 153 31 160 162 165 32 165 167 172 As can be seen from the Table, the performance of the test cells using the leady oxide of the present invention consistently provided somewhat improved product performance.

Thus, as has been seen, the present invention provides an improved method for preparing leady oxide. The product obtained is also characterized by improved properties, including improved acid absorption properties. 199844 12

Claims (4)

WHAT WE CLAIM IS:

1. A method for preparing leady oxide for use in making active materials for lead-acid batteries which comprises feeding molten lead into a reaction pot^dispersing the V: molten lead into droplets, partially oxidizing the lead droplets in the reaction pot by contact with a stream of air containing water in atomized form at a pH of from substantially 8 to substantially 12, removing the oxidized lead droplets from the reaction pot in the air stream, and thereafter collecting the oxidized lead droplets.

2. The method of claim 1 in which the pH is maintained by adding to the water a hydroxide selected from the group consisting of sodium hydroxide^ potassium hydroxide and mixtures thereof.

3. A method according to claim 1 substantially as hereinbefore described.

4. Leady oxide when prepared by a method according to any one of the preceding claims. GOULD INC By Their Attorneys HENRY HUGHES LIMITED