DE1907326A1 - Manufacture of porous nickel electrodes - of uniform fine porosity - Google Patents

Abstract

Process comprises sintering a mixture of nickel powder and a pore-builder such as ammonium carbonate, bicarbonate, nitrite etc. The pore builder is finely ground in a closed mill to a size of 5 to 25 mu and the nickel powder added to the mill immediately on completion of grinding.

Description

Method of Making Porous Nicel Electrodes The invention relates to the production of porous nickel electrodes from a mixture of nickel powder and a pore former, such as ammonium carbonate, bicarbonate, nitrite, urea or the like., which is driven out after the shaping during sintering, and has a particularly special purpose Method of the object, by means of which a uniformly distributed fine pore structure is achieved.

There are several methods of making porous nickel electrodes known. In one of these processes, the nail powder is loosely placed on a sintered bed poured and then carried out the sintering process.

Another method is to make a slurry using a Cellulose solution, which is driven out during sintering, used. When roller compaction either carbonyl nickel powder is used alone, but only one with which Porosity of bo yO can be achieved, or one also adds an filler, which is then driven out during sintering. What is known is ammonium carbonate or bicarbonate as FU toft, which after expulsion by the Sintering leave the pore space.

The use of mixtures of nickel powder with pore-forming agents par excellence However, it presents the problem that a uniform pore structure is hardly obtainable is. Rather, the pores often have a different shape and size. they are also very unevenly over the surface and the cross section of the electrode plates distributed. The formation of the porosity of sintered electrodes therefore depends very dependent on chance, and uniform conditions, such as those for series production are of great importance can practically not be complied with.

The invention is based on these disadvantages and difficulties to eliminate and to develop a process for the production of porous nickel electrodes, through which a uniform fine pore structure is achieved.

According to the invention, this object is achieved in that the pore-forming agent is in the form of ammonium carbonate, bicarbonate, nitrite, urea or the like. in a ball mill initially crushed to a particle size of about 5-25Xt and immediately then the nickel powder is mixed in in the ball mill.

This procedure has the advantage that it is a very fine pore former is used, which is intimately mixed with the nickel powder. Pore builder of this type, such as ammonium salts or the like., So far, have been in a much coarser one Particle size used and also have the disadvantage that they change when standing on Air; unite relatively quickly to form larger crystal units. Through the immediate Mixing in the nickel powder after the grinding process creates this difficulty but switched off and there is an intimate mixture between nickel powder and a very fine pore former.

To the powder mixture, which in this state strongly for bridging tends to be able to process well and evenly, according to the invention it becomes before Granulated shape. This happens because the powder mixture is an organic one Wetting agents, e.g., a methyl cellulose solution admitted and the whole is made into a paste. This paste is then after drying crushed to a grain size of less than 0.2 mm by means of a crusher mill. That Granules can then be introduced into the sintering mold in a simple manner. E.g.

compacted in the usual way by pressing or rolling, whereby optionally wire frames or the like. can be stored.

During sintering, the pore former evaporates, so that a uniform distributed, fine pore structure is retained, with the pores almost exclusively are open, and can later be filled with an electrochemically active mass.

Commercially available ammonil carbonate is typically of a particle size of about 0.2 mm. By grinding according to the invention in the ball mill, it becomes comminuted to a particle size of about 5 to 25 6. As pore formers are all suitable for grindable substances, which are completely volatilized during the sintering process and leave corresponding pores in the electrode body.

The nickel powder should have a low bulk density. Come for this E.g. the powder types 255, 270 and 287 from Mond Nickel Comp. in question.

The object of the invention is based on the following exemplary embodiment explained in more detail: In a porcelain egg mill with a capacity of 5 liters, approximately 250 g ammonium carbonate with porcelain balls down to a fineness of about 5 to 25 # £ t ground. The grinding time is about an hour. Immediately afterwards 500 g of type 287 nickel powder are added. Then the ball becomes hollow put back into operation until an even distribution of the mixed components is reached.

This is usually the case after an hour or two.

The powder mixture of NicKelpowder and ammonium carbonate is under Avoid the ingress of moisture through a sieve with a mesh size of 0.1s and should then be processed further immediately. Either it will be immediate fed to the pressing or rolling treatment or with the aim of particularly good further processing granulated. This is done by mixing the powder with a methyl cellulose solution is processed into a paste. This is then dried and using crushed in a crusher mill.

The material is then subsequently reduced to a suitable particle size of o, lo mm sieved. Small, solidified agglomerates are formed, especially those are easy to pour and are particularly suitable for further processing.

The shaping of the powder mixture or the granulate made from it happens in a manner known per se. For example, a shaping take place with the help of a stainless steel plate. To this is first a nickel wire mesh with a wire thickness of 0.1 to 0.15 mm and a Mesh size of 0.8 to 1.2 mm applied. The nickel wire mesh is secured by fastening brought at the ends in a completely plane-parallel position to the auxiliary board. That Powder mixture or granulate is sprinkled on and doctored off. Then will the board with the wire mesh and the powder mixture passed through a rolling mill, which connects the powder mixture firmly with the nickel mesh foil, so that an easy plate body to be handled arises. However, the wire network can also focus on that initially placed on a board and scraped off powder mixture and while rolling be pressed in. The solidification process can also be done by pressing.

It is of particular importance that the powder mixture after grinding and mixing is immediately further processed, so that ammonium carbonate evaporates the mixing ratio does not change or.

the distribution of the pore former becomes uneven.

After shaping, the sintering treatment takes place at temperatures of preferably 850 to 900 ° C under a protective gas, e.g. split ammonia, exogas, Forming gas or the like. instead of. The sintering can be carried out continuously in a manner known per se or in flocks.

The nickel electrodes created in this way have treatment after sintering despite their high porosity due to the even distribution of the very fine pores such a strength that it is a bending stress around a radius from the Endure five to six times the thickness of the material without being destroyed.

The invention is not limited to the exemplary embodiment numerous changes can be made without departing from the scope of the invention is exceeded For example, instead of the mentioned Pore formers other grindable and volatilized at the sintering temperatures Substances to use. Any other closed ball mill can also be used instead of a ball mill Grinding system are used, in which the action of air humidity, which affects the grindability of the pore formers, is excluded.

Claims (2)

Patent claims: Process for making porous nickel electrodes from a mixture made of nickel powder and a pore-forming agent such as ammonium carbonate, bicarbonate, nitrite, Urea or the like, which is expelled after shaping during sintering, thereby characterized in that the pore former in a closed mill, e.g. a ball mill, ground to a particle size of about 5 to 25 / t and immediately thereafter the nickel powder is mixed in in the mill. 2. Method according to claim 1, characterized in that the mixture from nickel powder and pore former is granulated by adding to this mixture an organic wetting agent such as a methyl cellulose solution to a paste processed and the latter after drying by means of a crusher mill to a grain size is crushed below about 0.2 mm.