US 2661387 A
Description (OCR text may contain errors)
Patented Dec. 1, 1953 UNITED STATES PATENT OFFICE POROUS ELECTRODE PLATES AND PROCESS FOR MAKING SUCH ARTICLES No Drawing. Application August 19, 1950, Serial No. 180,498
Claims priority, application Germany September 10, 1949 6 I Claims. (Cl. 136-25) The present invention relates to improvements in the production of porous shaped articles.
In the production of porous shaped articles by sintering finely divided metals it is often desirable to obtain sintered bodies having the highest possible porosity. The pore volume of the sintered body is dependent in particular on the piled-weight of the powderused for sintering.
It has already been proposed, for the purpose of reducing the piled-weight and increasing the 10 pore volume, to incorporate with the metal powder to be sintered, light metal oxide powders which are reduced to metal if the sintering is carried out in a reducing atmosphere, or to add substances which are volatilised when heated l5 and thus act as swelling means. These methods are not capable of general employment, however, because in many cases the substances used for loosening leave behind undesirable residues or have an otherwise injurious efiect.
We have now found that a loosening of the powder mass, in so far as it is magnetisable, can be obtained in a simple manner by subjecting the powder before or during the sintering to the action of a magnetic field. By this magnetic treatment, a metal powder having too high a piled-weight can be loosened to such an extent that it yields sufiiciently porous shaped articles. Thus by the method according to the invention it is no longer necessary to use specially light kinds of powder or to add the above-mentioned additional substances.
When a flat mould is filled with the magnetisable powder and the powder is covered with a cover consisting of non-magnetisable material and laid loosely thereon, and the mould is then brought in a horizontal position into a strong, vertically-acting magnetic field, the cover lifts by reason of the increase in volume of the powder mass brought about by the magnetic orientation of the powder particles. At the end of the magnetic action, the increase in volume of the powder mass reverts somewhat, but there still remains a considerable loosening so that, upon sintering, shaped articles having a substantially increased pore volume are obtained. The sintering of the powder may also be carried out under the action of the magnetic field; the magnetic field need only be maintained until the powder particles have been fixed in their position by being fritted together.
Our process is applicable not only to powders consisting entirely of magnetisable particles, such as the metals and metal oxides of the iron group, but in many cases mixtures of magnet- 2 isable and non-magnetisable powders may be successfully worked up into porous shaped articles.
The invention is especially suitable for the preparation of porous electrode plates consisting of metals of the iron group, for alkaline accumulators in which the highest possible pore volume is desirable. Moreover, the pores of plates produced according to our process show an orientation in the direction towards the plate surface, and also this structure makes the plates especially convenient to the employment for the said electrode purposes.
The following example will further illustrate the invention but the invention is not restricted to this example.
Example A fiat mould consisting of sheet chromiumnickel and having a base about 200 x 100 millimetres and a height of 18 millimetres is filled up to a height of 10 millimetres with a fine nickel powder prepared by decomposition of nickel carbonyl and the layer of powder is covered with a sheet chromium-nickel cover. The mould is brought in a horizontal position into the vertically directed field of an electromagnet so that the lines of magnetic force pass through the mould perpendicular thereto. Under the action of the magnetic field the powder mass extends in the direction of the lines of magnetic force and the applied cover is accordingly displaced upwards. The loosening of the powder remains to a great extent after the magnetic field has been switched off. The mould is then heated for 1 hours at a temperature of 950 C. The pore volume of the sinter body thus formed amounts to about 84;%, while a sinter body prepared without the aforesaid magnetic pretreatment of the powder but in otherwise an identical way has a pore volume of only The volume occupied by the nickel metal in the sinter body is thus reduced from 20% to 16% by the magnetic pretreatment. This represents a saving of nickel of 20%.
The thus obtained nickel plate is well suited as a porous electrode for alkaline accumulators.
What we claim is:
1. An improvement in producing porous, shaped articles by sintering magnetizable materials which comprises subjecting a mas of magnetizable particles to the flux lines of a magnetic field thereby causing alignment of said particles along the flux lines and then sintering the thus I if 2,661,387
' 3 ned particles thereby forming a 'sintered ped article of increased porosity. A process accordance with claim 1 wherethe particle mixture includes particles of a gnetizable metal and particles of a non-mag izable substance.
cularly thereto thereby causing the particles to align in the path of the lines of the magnetic force, switching off the magnetic flew and then sin-teririg the mass. 1
6. As a new article of manufacture, porous electro-plates for alkaline accumulators, the
. A process in accordance with claim 1 wherethe particle mixture irrciudesparticle's of a gnetizable metal oxide and particles "of a nongnetizable substance.
. An improvement in the'produ'ction of; porous tes by sintering powdersoi magnetizablema- .als which comprises arranging a' -inass of the vder in a flat mold, positioning the mold hori- .tally in a vertically directedii'eldof an elecmagnet so that the lines of magnetic force 15 through the mold perpendicularly thereto;
tching off the magnetic field and then si'ntei the mass to which an increased porosity has :n imparted by the aforesaid magnetic treatnt.
b. An improvement in producing porous plates sintering magnetizabl'e powdered materials .ich. comprises forming a flat mass of the rider. into a plate form, positioning. said plate m. horizontally in the vertically directed field an, electro-magnet so that the lines of magiic force pass through said form perpendipores of said plates being oriented in the directi'orr towards the plate surface, said orientation being effectuated by shaping a mass of magnetizable particles into' the form of a plate, positionLing the aforesaid. plate-shaped mass in a magnetic field; wherein the lines of magnetic flux pass transversely of said plate thereby to align the particles thereof and after said alignment sintering the same.
KARL ACKERMANN. LEO SCI-ILECHT.