DE2407030A1 - METHOD OF MANUFACTURING POROESE NICKEL PLATES - Google Patents

Description

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SHERRIO ?! GORDON MINES LIMITED, Toronto, Ontario, Canada

Process for making porous nickel plates.

The invention relates to a method for the production of porous nickel plates, in particular of those nickel plates which are used in electrochemical facilities.

Sintered plates are commonly used as the basis for battery electrodes used, wherein the active electrode material is embedded in the sintered plates. In general, the electrochemical activity depends on the amount of active material embedded in the electrode, which in turn is the Amount of active material that can be installed per unit volume of the plate, on the porosity of which depends. By Increasing the plate porosity can therefore increase the capacity for the active material. The degree of porosity finds in practice, however, its limit is the required strength of the plate. This must be sufficiently high

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during manufacture and during the service life to withstand occurring forces.

Various methods have been used to produce high strength porous electrode plates. One of the procedures involves the shaping of a laminar structure, which is composed of a layer that is highly porous but relatively soft material, which is bound to one or more layers of a less permeable but solid support grid is. The resulting plate has sufficient strength, but has only a relatively low average porosity and therefore only a limited capacity for active substances Material.

Another method is to create a powder dispersion by adding a volatile solid powder to one further powder, which can be sintered into a high-strength plate. At sintering temperature, the mostly the volatile powder and leaves cavities or pores in the sintered material. The porosity of such plates however, it is not high because the pores after volatilization are due to the high levels required for the sintering process Temperature contract largely.

The object of the invention is therefore to provide a better, namely simpler and more effective method of production more porous. To propose fuckel plates which are highly porous

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and have high strength. This is according to the invention achieved by using nickel powder with a fineness of below about 270 mesh (Tyler sieve) as the starting material of Mckeloxide content adjusted to about 0.7 to 1.4 percent by weight and the raw material thus obtained in a volatile Liquid is slurried that then the slurry to a below sintering temperature, but a temperature sufficient to evaporate the volatile liquid fraction is heated and that the heated slurry is then sintered under a reducing atmosphere to give a finished sintered plate.

It has been shown that in this surprisingly simple manner, high-strength and highly porous ffickel plates are effectively produced can be. The panels have a uniform tensile strength and a continuous porosity and require no reinforcement by a support grid or the like.

During the sintering process, the reducing agent decomposes Atmosphere to the mckeloxide in the powder composition Nickel. It is believed that this freshly reduced crochet activates the sintering process, thereby accelerating the bonding of the individual Nxckelteilchen to each other. As a result from this, the sintering process can be carried out relatively quickly, so that shrinkage and loss of porosity are kept to a minimum is lowered and no reduction in the tensile strength of the finished panel has to be accepted.

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The starting material for the method according to the invention consists of largely pure metallic nickel powder. Preferably a powder is used, the particles of which are irregular in shape and have a low bulk density and only shrinks slightly during sintering. Such a powder can namely be very high to sintered plates Process porosity. The size of those present in the source material Nickel particles have a significant influence on the strength of the finished product using the process according to the invention manufactured panels. The particles should have a particle size below about -270 mesh (Tyler sieve). Plates that are made from larger particles have only a low strength and are used as accumulator or battery plates are unsuitable if they are not reinforced by carrier grids or other stiffeners. the The strength of the plates decreases as the size of the nickel particles decreases in the starting material, with the result that these nickel particles in the starting material are as small as possible should, the higher the strength requirements placed on the panels will. However, it should again be noted that the particles forming the starting material sinter together the faster and consequently the smaller the particles, the less porous the panels made therefrom. It must therefore a compromise between high strength and high porosity can be found. In general, therefore, nickel particles become having a particle size of about 400 mesh is preferred since panels made from such particles have both a

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have high strength as well as satisfactory porosity.

Highly pure kickel powder of the required particle size is currently commercially available. Particularly suitable nickel powders can be made by the process described in Canadian Patent 77% - 036.

The kickeloxide content in the starting Mickel powder is limited to a range of about 0.? up to 1.4 percent by weight (based on the total weight of fuck powder plus nickel oxide). The Hiekeloxide content can be adjusted in several ways. Material can also be added to the BFickelpulver, which decomposes to Sickeloxide. Such material includes nickel hydroxide and an oxidizable nickel powder such as nickel graphite. After the material has been added to the gelatinous powder, it is decomposed by heating under controlled oxidizing conditions in order to ensure the formation of the required proportion of hickel oxide.

Alternatively, the kickeloxide content can also be adjusted by adding a precisely measured amount of oxidizing agent to the slurry. The oxidizing gown reacts with the stoichiometric equivalent of wrapping powder in the slurry . generates the desired kenge of kickeloxide. Ammonium nitrate is "for example a suitable oxidation

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funds for this purpose.

Another possibility for adjusting the nickel oxide content of the slurry provides for controlled heating of the nickel powder before it is slurried in the liquid medium in order to convert the desired proportion of nickel to nickel oxide. Oxidation of the nickel powder can also be effected by treating the nickel in a warm aerated saline solution. Suitable salts for this purpose include ammonium sulfate, ammonium chloride, ammonium acetate, ammonium carbonate, ammonium nitrate, sodium chloride, sodium nitrate and potassium chloride. Ammonium hydroxide is also suitable for this purpose.

The preferred procedure for adjusting the nickel oxide content consists in adding a controlled amount of freshly precipitated nickel hydroxide. The nickel hydroxide can by adding sodium hydroxide to a solution of nickel nitrate.

As previously indicated, it is of importance to the powdery Mix just enough to add nickel oxide generating substance so that the nickel oxide content of the mixture before Sintering is in the range of 0.7 to 1.4 percent by weight. The tensile strength of the sintered nickel plates drops sharply when the nickel oxide content of the slurry prior to sintering drops to below 0.7%. On the other hand, if the nickel oxide content rises over $ 1.4, then a drop does not occur with the train

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strength of the finished board but also its porosity on.

Subsequently, the setting of the nickel oxide content is the powder mixture is dispersed in a liquid to form a slurry. The liquid must be at sintering temperature volatilize and must not react with the powder mixture. Water is the most useful and economical for this purpose Liquid.

The liquid used for slurrying should be sufficiently viscous so that the powder mixture does not settle out. Around In order to give the slurry a sufficient viscosity in this regard, it is desirable to use an organic substance to be added, such as halogenated gelatins or starch-soluble derivatives of cellulose, e.g. alkali or ammonium salts of Carboxy-methyl celluloses, hydroxy-alkyl celluloses, hydroxy-ethyl cellulose and hydroxy propyl cellulose. In particular, the cellulose derivatives only need to be used in very small quantities to keep the slurry highly viscous. In addition, these derivatives act as binders for the slurry.

In general, the slurry should contain from about 25 to about 75 weight percent solids. When the solids content is below 25%, there is insufficient contact between the particles to create a self-supporting metal plate 2U.

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generate while in the presence of metal particles in a lot over 75 percent by weight generally the addition of a sufficient amount Binder amount is not possible to ensure the formation of a self-supporting plate.

The resulting slurry becomes panels with the desired ones Dimensions shaped and then subjected to a heating process at a temperature and sufficient is carried out for a long time in order to ensure a largely complete elimination of the volatile! fraction of the slurry and eliminate water of hydration if nickel hydroxide is present in the slurry. In most cases For example, the heating process can be carried out by raising the temperature of the slurry to about 650 ° C., with the Slurry held at this temperature for about ten minutes will.

The plates heated in this way are then subjected to a sintering process fed, in which they are heated to a temperature in the range of 816 to 927 C. 'The sintering process will be completed once the nickel particles have grown into finished panels with the required strength and porosity have connected. Usually 20 to 30 minutes is sufficient for this purpose. The sintering process should be longer than necessary not be carried out, as a longer sintering to plates is less Porosity leads.

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During the sintering process, the powder mixture must be in contact with a reducing gas (preferably hydrogen). At the sintering temperature, any organic substances which were added with the powder mixture, expelled in the Eegel without noticeable residue. As a result The result is largely pure porous nickel plates, which, as required, are coated with active material, e.g. nickel hydroxide for a positive Electrode or zinc or cadmium hydroxide for a negative electrode, can be impregnated.

The nickel plates ultimately obtained have an unusually high porosity and capacity to contain active material and also high mechanical strength.

The invention is explained in more detail below using non-limiting examples:

EXAMPLE 1

This example illustrates the importance of careful adjustment the nickel oxide content of the powder mixture before the sintering process illustrated. The nickel oxide content of the test mixture was adjusted by using nickel hydroxide, which was freshly taken from a solution by adding sodium hydroxide a nickel nitrate solution had been precipitated. Of the. Precipitate was washed until the conductivity of the Wash water reached a low level; then was

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de it processed into a pulp with water, which is 2 percent by weight Contained methyl cellulose. A number of slurry samples were prepared in such a way that the pulp has been combined with various amounts of nickel powder. The individual quantities contained over 99% nickel and the best cobalt, Copper, iron, sulfur and carbon.

The slurry samples were on one for ten minutes Preheated to a temperature of 690 ° G to decompose the nickel hydroxide. They were then made into plates in a graphite mold molded and sintered for 20 minutes in the presence of dry hydrogen at a temperature of 899 ° C. The tensile strength and the porosity of the resulting sintered plates are shown in the following table.

TABLE I.

Nickel oxide from the
Decomposition of added nickel hydroxide in% by weight

Tensile strength of

Sintered plates

(kp / cm ² )

Porosity of the sintered plate (%)

0.32
0.64

0.95
1.4-1.8
3.3

2.95 4.29 6.33 7.38 2.11 2.11

91 89 90 89 89 87

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The table shows that 0.95% nickel oxide resulting from the decomposition of the nickel hydroxide is produced, the strength of the sintered plate can more than double, with only a slight one Reduction in porosity occurs. Nickel oxide, which is added in an amount of over 1.4 percent by weight however, has an adverse effect on the strength of the plate.

EXAMPLE 2

This example illustrates the effect of the particle size of the starting material nickel powder. Samples were prepared by using different particle sizes of the nickel powder of the same composition as in Example 1. The nickel powder was slurried in water containing 2% methocel and ammonium nitrate (weight ratio of ammonium nitrate to nickel = 0.5 s 100). The slurry samples were dried at a temperature of 100 ⁰ C, then placed in graphite molds at a temperature of 899 ° C for 20 minutes under hydrogen atmosphere sintered. The finished panels were then rotated on a turntable under a stiff brush approximately 12.5 mm wide, the bristles of which were cut to about 3 "to 6 mm in length. The weight on the brush was 344 grams and the brush was able to cover an area Sweep approximately 6.45 cm of the surface of the panels.

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Each plate was rotated 240 times at a rotation speed of Rotated 250 revolutions per minute. The abrasion resistance the panels were determined by measuring their 3 weight loss. The porosity of the plates was also measured. the The results can be found in the following table:

TABLE II Porosity (%) Particle size of the Loss through Starting hick- Removal powder (Tyler sieve) 91.8 over (mg) 91.9 - 200 + 270 15th 90.5 - 270 + 325 15th 87.5 325-400 1 - 400 0

The results listed in Table II show that the particle size of the starting material has a significant influence on the strength of the finished sintered plates. Plates made from particles with a particle size of over 200mesh are generally too weak for use in accumulators. The porosity of the finished panels decreases as the particle size in the starting material decreases. For most applications a porosity of. 85% satisfactory, from which it can be seen that useful battery plates be made from a starting material

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can whose nickel particles have a particle size of 400 mesh.

The main advantages of the method according to the invention are thus justified by the following:

A starting material in the form of a nickel powder is used, whose particles are below 270 mesh (Tyler sieve) particle size own. The nickel oxide content of the starting material is adjusted to 0.7 to 1.4 percent by weight and then the powder is slurried in a volatile liquid which, if necessary, contains an organic binder can. The slurry is heated to a temperature below the sintering temperature to remove the volatile liquid to evaporate. The slurry is then heated to sintering temperature under a reducing atmosphere.

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Claims (7)

Claims 1. A method for producing porous nickel plates, characterized in that in nickel powder with a fineness below about 270 mesh (Tyler sieve) as the starting material the content of nickel oxide to about 0.7 "to 1.4 percent by weight is adjusted and the starting material thus obtained is slurried in a volatile liquid is that then the slurry to a below sintering temperature, but for evaporation the volatile liquid fraction is heated to a sufficient temperature and that the heated slurry is then sintered under a reducing atmosphere to give a finished sintered plate. 2. The method according to claim 1, characterized in that an organic binder is added to the slurry will. 3 »The method according to claim 2, characterized in that the slurry is formed into a plate and this Plate is then subjected to the heating and sintering process. 4. The method according to any one of claims 1 to 3, characterized in that that the particle size of the starting material, is over 400 mesh (Tyler sieve size). 4098 3 5/0760 5. The method according to any one of claims 1 to 4-, characterized in that that the nickel oxide content of the starting material is achieved by adding freshly precipitated nickel hydroxide, which is followed by heating for the purpose of decomposition of the nickel hydroxide connects to nickel oxide, is set. 6. The method according to any one of claims 1 to 5}, characterized in that that the sintering process is carried out under a hydrogen atmosphere. 7. The method according to claim 2 or 3, characterized in that that the organic binder is an alkali salt of carboxy-methyl Cellulose or an ammonium al ζ the carboxy-ethyl cellulose, Hydroxy-alkyl cellulose, hydroxy-ethyl cellulose or is hydroxy-Iropyl cellulose. 409835/0760