US1804924A - Method of producing metallic powders - Google Patents

Description

Patented May 12, 1931 UNITED STATES PATENT oFnc-c EUGENE rITzPATRIoK, F woonnnvnir, enemies w. CLARK, or IBELLEROSE, an!) PETER A. T ERNAN, on Leeann HILL, NEW YORK, ASSIGNOBS T0 NICHOLS 0019mm COMPANY, on NEW YORK, N. Y., A CORPORATION or NEW YOR-K METHOD OF PRODUCING METALLIC POWDERS No Drawing. Application filed June 20,

This invention relates to method of making metallic powders, and more particularly relatively pure fine metallic powders. H

The invention has proven to be of-great merit more specifically in the production of copper powder and has produced fine copper powder of a'hig'h degree of urity.

Many uses are well known to those skilled in this art for metallic powders, and more particularly for relatively pure fine metallic powders.

By Way of example, the use of fine copper powder is well known to those skilled in the art, for example as in paints, lacquers, for

plating, for copper carbon .brushes, and other uses. In-many of these uses it is desirable to have a product of the highest degree of purity compatible with its economical production, and which will contain no extraneous or altered coating as a protecting medium or as oxidation. One of the great difiiculties experienced in making such a product has been in producing a copper pow- 'der free from oxidation and other impurities.

An object of the present invention is to produce fine metallic powders of an extremely high degree of purity, and in. a highly satisfactory commercial manner. More specifically an object of the invention is to produce fine metallic'copper of a very high degree of purity.

Further objects of the invention will more ,fully appear from the following description.

lyte, and (3) drying. Sincesuitable apparatus well known inthe art may be adapted for carrying out theimethod, and since such apparatus per se forms no part of the presentinvention, it is believed that the method will be clearly understood, by those skilled 1928 Serial No. 237,033.

in the art, without showing the apparatus,"

and hence the apparatus will' not be illustrated.

i "The production of fine metallic powders is well known in the art, and it has long been desired to produce such powders in as pure a state as possible. The present method is an improvement over prior processes, and by its use metallic powders, such for example as" scribed in detail; it being understood that.

the invention is not thereby to be limited to this specific material.

Formationa'n electrolytic cell I A suitable electrolyte, suchas copper sulphate, is placed in an electrolyte tank, such for example as a wooden tank. lined with sheet lead. An anode of copper, preferably 99.75% purity have been proin plate form, is suitably suspended in the j electrolyte, and a cathode of copper, preferably in rod or bar form, is similarly suspended in the electrolyte; and the anode and cathode are respectively connected to the plus and'minus sides of a suitable source of electric current. The relative size of the electrodesare so proportioned-with respect to the current used, that. the current density at the cathode will be high; the purpose being to use such a'current density that the copper particles deposited on the cathode will be of the desired degree of fineness and will form thereon in a loose flufiy mass, suchas in the form of a metal sponge or slime, which will be easily dislodged from the cathode and in which the separate particles remain only loosely adherent. The metal sponge or slime is freed from the cathodes as by rapping or jarring the cathodes at frequent intervals-to thereby dislodge the sponge or slime and preclpitate the same in the bottom of the tank.

Washing} free from electrolyte.

- The precipitatev is now removed from the electrolyte in a suitable manner, together to prevent oxidation, and is freed of the electrolyte, such for example as by means of a gravity filter and circulating water, during which time the copper particles are always kept submerged, or substantially protected by the liquid, to prevent oxidation. During the washing or cleansing of the particles the temperature of the liquid should be so regulated or limited that the washing liquid never exceeds about 120 F. The washing should be done preferably with boiled water, condensate, or suitable liquid of a non-oxidizing character; in order that the particles will not be oxidized thereby or their purity in any way affected.

' Drying boiling point of the liquid. This method of powder is then removed, and screened to the protecting the particles against oxidation or impurities is very important, if not essential. The cop er particles are left in the dryer until su stantially entirely dried. The

desired fineness.

In order that those skilled in the art may more fully appreciate the invention, and the beneficial results obtained thereby, we will giye following a brief example of a run actually carriedon under practical commercial conditionsin' connection with producing copper powder. While this is not to be takenin a limiting sense, nevertheless it is thought thatit may be of assistance in understanding the invention and in serving as an illustration. of one preferred embodiment of the invention.

EmampZe.The tank used was constructed of wood lined with sheet lead. The inside dimensions were 36" by 18".by 36 depth at one end and 40 depth at'the other end.

4 outlet was placed at the lower end for removal of the precipitate. The anodes consisted of six copper plates each 12 wide and submerged 24 below the surface of the electrolyte; thereby providing an anode surface.

of 12 square feet. The cathodes consisted of 12 copper rods each in diameter and submerged 24 in the electrolyte; thereby providing a cathode surface of approximately 2.356 square feet. The anodes and the cathodes were connected respectively in multiple; and were connected to a suitable source of electric current. The electrolyte varied in composition from 2.29% to 2.45% of copper.

with water standing above it.

(as copper sulphate) and from 11.32% to 11.43% sulphuric acid. The cell was operated for 90 hours, and the average current used was 893.75 amperes at 1.50 volts, with the average electrolyte temperature at 129.3 F. The current density at the anodes averaged approximately 74.48 amperes Per square foot; while the current density at the cathodes averaged approximately 379.35 amperes per square foot. No artificial circulation was used in the cell; the only circulation being that caused by gas sing at the electrodes. The cathodes were rapped every 15 minutes to dislodge the cop per sponge or slime and the cell was shut down once each day to clean out the precipitate from the bottom of the tank.

The copper slime o'r sponge thus removed was placed in a gravity filter and washed free from the electrolyte by circulating water through it: care being taken to keep the finely divided copper particles submerged to prevent oxidation. The washing was continued until the water showed no trace of sulphates, this being determined by testing with barium chloride.

It has been found to be highly desirable, if not essential, that the temperature of the water used for washing should be kept below 120 F.. as above this temperature consider- I able oxidation takes place; and likewise it has'been found that boiled water or condensate should be used for washing.

The washed material was placed in copper pans, in a layer of thickness and The pans were then placed in a cold vacuum dryer, the dryer closed and the vacuum brought up to about 26" of mercury. After this vacuum had been reached, the steam was turned on and the temperature of the dryer was brought to the boiling point of the water, which at this pressure was about 125 F. This method of keeping the material covered with water before drying is likewise deemed to be very desirable, if not essentiah In order to prevent oxidation extreme care was taken to keep the material at all times free from contact with air above F.; and therefore for this and other reasons the dryer was evacuated before thetemperature of the material was raised. By noting when the formation ,of condensate stopped in the vacuum dryer condensers it was determined when the material was completely dried. v

The material was then removed from the vacuum dryer and the finely divided copper powder thus produced was screened through a- 160 mesh screen. The material Which passed the screen amounted to 175 lbs. The resultant product averaged 99.56% purity, and in some. instances was as high as 99.75% pure. The resulting product of pure finely divided copper particles is not easily susceptible to' atmospheric oxidation when in dry form and is therefore quite stable; being also free from any extraneous substance.

The theoretical amount of finely divided copper in pounds which can be produced by the ampere hours used is:

The ampere efficiency for this run, based on good production, was,

The powder. used in this run in kilowatt days was,

pounds well understood by those skilled in the art;

nevertheless, it might be pointed out that, in addition to the features of importance enumerated heretofore, there are certain factors which are believed to be of importance, and

such of these factors as we deem of importance at this time will be pointed out following. It would appear that the metal sponge or slime produced should be taken from the metallic anode of the correspiondin metal, and that the cathode should be of t e same metal; to preclude any opportunity of impurities enteringinto the product. We have found that it is desirable to keep the copper content of the electrolyte substantially within 1% variation, and theacid content of the electrolyte within 5% variation. We hate further found that although the current density heretofore disclosed is satisfactory, nevertheless much higher current densities may be successfully employed. The electrolyte and anode should be free from harmful impurities, such for example as arsenic, antimony, bismuth and lead.

Having thus described our invention with particularity with reference to the preferred method of carrying out the same,-it will be obvious to those skilled in the art, after understanding our invention, that various changes and modifications may be made therein without departing from the spirit and scope of our invention, and we aim in the appended claims to cover such. changes and modifications as are within the scope of the invention. 3

WW] at we claim is:

-1. Method of producing metal powder, which comprisesdisintegrating a' metal by electrolysisto produce relatively fine metallic particles, removing the metallic particle precipitate from the electrolyte while preventing oxidation, washing said precipitatev free from said electrolyte, and introducing metallic particles, maintaining said particles free from atmospheric contact and while so U maintained washing them free from the electrolyte and submerging in a non-oxidizing medium, placing said submerged particles-in vacu'oand evaporating said mediui'n'while i'naintaining sufficient vacuum to rapidly'remove all volatile matter and until saidparticles are dry, to thereby prevent oxidation of said particles.

3. Method of producing copper powder, which comprises electrolytically disintegratproduce relatively fine copper .particlcs, maintaining said particles free from atm'os submerging in water, placing said submerged particles in vacuo and evaporating said water while maintaining suflicient vacuum' to rapidly remove all volatile matter and until saidparticles are dry, to thereby said electrolyte to provide substantially pure metal particles, covering said particles with viiig substantially pure metallic copper to pheric contact and while so maintained washing them free from the electrolyte and a non-oxidizing liquid, placing saidparticles thus protected in vacuo, and evaporating said liquid to thereby dry said particles substantially free from oxidation and exti'a neousmatter. I I I I 5. Method of producing metal powder. which consists in forming metal sponge in an electrolyte, precipitating said sponge,

washing said precipitate free from said .electrolyte to provide substantially pure metal particles, covering said particles with water,

placing said particles thus protected in vacuo, and evaporating said water tothereby dry said particles substantially free from oxidation.

6. Method of produc ng metal powder, which consists-in forming metal sponge in an electrolyte, washing said .sponge free from said electrolyte in water to provide substantially pure'metal particles, keeping said particlesfree from oxidation duringsaid washing. and atthe'end of. said washing leaving said particles covered with water, placing said particles thus'protected in vacuo, and

was

der tree from extraneous matter.

8. Method of producing metal powder, which consists in forming fine metal particles by disintegrating a mass of metal by electrolysis in an electrolyte of the same metal, removing said particles, washing the particles and placing said particles in vacno while always maintaining said particles submerged in a liquid preventing substantial oxidation, and drying said particles while in'vacuo, to thereby eliminate said liquid and produce a substantially non-oxidized pure finemetal powder. v

9. Method of producing copper powder, which consists in placing a copper anode and a suitable cathode in a copper sulphate electrolyte, passing a relatively high density electric current of relatively low potential between said electrodes to produce fine particles of copper in said electrolyte, removing and washing said particles free from said electrolyte 'while keeping said particles submerged to prevent oxidaton, and'after washing and while still submerged placing sa1d particles in a vacuum dryer, producing a vacuum therein while keeping the temperature below about 120 F., and after said vacuum has been brought up to about 26 inches of mercury increasing the temperature of the dryer to the boiling point of the submerg ng liquid at the pressure employed and drying said particles in vacuo.

10. Method of producing non-oxidized substantially pure copper powder, which comprises forming copper sponge in an electrolyte, removing said sponge while preventing itsexposure to'air of a temperature greater than approximately 110 F., washing said sponge free of said electrolytewith water below approximately 120 F., placing sa1d copper submerged in Water in suitable receptacles, placing said receptacles in a substantially cool vacuum dryer, creating a vacuum" therein of approximately 26 inches ofmercury, and thereafter raising the'temperature of said dryer up to approximately 125 F.,

to thereby dry said copper particles and produce copper powder in pure non-oxidized form.

11. Method of producing copper powder of a degree of purity between 99% and 100%, which comprises electrolytically disintegrating copper in a copper sulphate electrolyte to produce fine copper particles, washing sa1d particles free from said electrolyte with water, covering sa1d particles with water, placing sa1d covered particles in a relatively cool vacuum dryer, evacuating said dryer, and

12. Method of producing fine copper powder of a degree of purity between 99% and 100%, which comprises electrolytically disintegrating copper in a copper sulphate electrolyte with a relatively low anode current density and a relatively high cathode current density, washing said disintegration particles free from said electrolyte with water,

covering said particles with water, placing said covered particles in a relatively cool vacuum dryer, evacuating said dryer to approximately 20 inches of mercury, and heating said dryer to approximately 125 F. and drying said particlesin vacuo, said particles being kept free from contact with air above F. and water above F. at atmospheric pressure from the time of removal from said electrolyte until placed in vacuo. In testimony whereof we have signed our names to this specification.

EUGENE FITZPATRICK. CHARLES W. CLARK. PETER A. TIERNAN.