US2170814A - Method of preparing copper powder - Google Patents

Description

Patented- Aa 29, 1939 Z,l70,814 PATENT OFFICE amsu mo 0]" PREPARING 00m POWDER Joseph E. Drapcau, In, cam City, 111., aaclgnur company, Cleveland, 0

to'lilcGiidden oorporationelohio uNo Drawing.

This invention relates to the production of copper powder, and has particular reference to a new form oi pure copper powder. which combines low.- apparent density, a porous structure under the microscope, and a good degree of resistance to atmospheric influences. It further relates to a process for producing this new copper powder.

.Powdered copper is a raw material that is used extensively in several industries, including the paint, electrical and bearing industries. In the paint field, color and leaflng properties in paint tween 50 and 150 amperes per square inchof cathvehicles are important; in the electrical fleld. conductivity, and mechanical strength 01' molded products made from the powder, are the prime considerations: while in the bearing field; inechanical strength of the bearings produced is, of

course, by far the most important property. In all cases, maximum resistance to atmospheric corrosion is likewise desirable.

Copper powder has been produced bythe elec-' trical method, which consists of electrolytic deposition, employing current densities (cathodic) be- ,ode deposition surface, in the presenceof suit able addition reagents (colloids), causing the copper to be plated out of solution in a loose, sponge-like mass. This sponge-like copper product is washed as Ireeas possible or the electrolyte solution and dried under non-oxidizing conditions. The outstanding disadvantage of this type of copper powder is its high cost, and its marked tendency to reoxidize when exposed to atmospheric conditions. The traces of electrolyte salts increase the rate of oxidation or the copper pow- Another'method of making copper powder has been to stamp it out of thin sheets or copper alloy metal, using a lubricant. The resultant powder, when examined under the microscope, is in the form of flat sheets, coated with lubricant. While excellent color and leaflng are obtained in paintvehicles, the lubricant results in poor mechanical strength and electrical conductivity. Such flake powder is' dense, has no mobility, does not weld, and is not suitable for bearings, and only in special cases for brushes. The excellent color is'due to the alloying ofsmall percentages of zinc or aluminum with copper.

It has also been proposed'to obtain copper powder by reducing cupric or cuprous oxide powder, in a furnace, by the use-oi various reducing to electrical bid, a

Application Deoember a 1931. Serial No. new

serum. (or. is-r-vs) tivity, and may be usedin bearings with fair results.

According to the present invention, a process is provided whereby a new form of copper powder is produced having superior properties as conductivity and mechanical strength, and is characterized by its low apparent gravity (below 2.5 grams per c. c.) its porous structure under a microscope, and its ability to withstand atmospheric conditions without blackening.

The invention comprises the conversion of cop-' per wire or other pieces of copper metal such as punchings, shot, etc., into copper powder. The steps comprise first. oxidizing the copper to 'copper oxide, preferably cuprous oxide, breaking up this oxide, and then reducing the powdered oxide to copper. ,By this procedure, a pyrometallurgical method is provided for the production of copper powder from copper, which powderhas the properties and advantages enumerated above.

My process comprises first, roasting of pieces a core of metal. An oxidizing atmosphere is maintained, and I have found that the presence of water vapor accelerates the reaction. The

charge is pulled, and allowed to cool in air; a

thin film of cupric oxide forms oni the surface only. The oxide is separated from the metal core by grinding in a rod or ball mill, and screening or air classifying; The resultant product is a cuprous oxide which contains 2% or lessor cupric, andat least 98% of cuprous oxide. The temperature is preferably between 800 and 1780 F., as

at these temperatures cuprous oxide is formed.

As an example, a charge 01' 2,000 poundsof 10 gaugepure copper wire was placed in a hand rabbled furnace, and heated at 1650 F. in an oxidizing atmosphere in the presence. of water vapor for 48 hours. The charge was rabbled from time to time. A 79.0% conversion to cuprous oxide was Using the same charge, without adding water vapor, the same percentage conversiontookGB hours.

Thecharge is drawn from the-furnace, and

cooled in A thin film of cupric oxide forms onthe surface 0! the pieces; but this film prevents oxidation below it. 'Thecooled charge is the oxide is powdery, the metal malleable, so that separation is easily eil'ected. The metal may be screened. out, or the mixture may be air classified. The resultant powdered cuprous oxide then ground, p'reierably'in a rod or ball mill; 7

is 98% or more pure; the impurity is largely the fllm oi cupric oxide. formed during cooling.

The oxide powder, which is substantially free from any occluded saltspis then subjected to a reducing action. For most economical results, it is preferred to use a cuprous oxide powder which is substantially pure, as it has only-half as much oxygen to remove as cupric oxide. However, it will be understood by those skilled in the art, that a copper oxide powder containing varying proportions of cuprous and cupric oxide may be used in the reduction. The important thing to be kept in mind is that the oxide be free of occluded salts, and it is' preferable that the oxide be substantially a pure, uniform cuprous may be used which keeps the particles broken up,

oxide, as will be produced by the above described oxidation of copper wire, etc.

The reduction and heating of the oxide is conducted in a furnace, and I'may use anyof. the common reducing gases-hydrogen, carbon monoxide, artificial or natural illuminating gas, methane, ethylene, etc.

Temperatures may vary over aconsiderable range. Below 350 F., the reaction proceeds too slowly to be economically feasible; and in no case should the temperature exceed 700 F.,. at which point the materials tend to sinter. However, much superior results asto low apparent density are obtained by keeping the temperature at a. minimum; and I prefer tooperatein the range of 350-500 F. for optimum results. Higher temperatures may be used, up to 700 F.; but as the temperature increases, the apparent density likewise increases.

An important feature of my process is the continuous motion imparted to the powder during the reducing, whereby the tendency to sinter is minimized. While any method of rabbling it is of course necessary that air be excluded. A rotating drum, provided with attached 'rabbles, provides the most simple, effective apparatus for the purpose. A mechanical rabble, on a furnace .bed designed, to exclude air, might do as well, as

continuous rabbling is not essential to good results, although frequent rabbling is; but such a rabble is much more difllcult to operate than a rotating drum. r V

In place of the attached rabbles, I have obtained satisfactory results by the use of irregular shaped light weight metal pieces in the drum. In this connection, it is important that any milling action in the drum be minimized, as such action increases apparent density and reduces porosity;v and the rabbling, must be carried out in a manner which will not atthe same time introduce a ball or hammer milling effect,

Another important item in regard to thlsstep of the process is the time required for 'reduction. The reaction should preferably be carried on rapidly, in order to reduce the milling action due to the attrition of the particles on each other.

Reaction times of over 18 hours should be avoided where low density is desired.

. After the oxide powder has all been reduced. the powder is. allowed to cool in a reducing at'-, mosphere until room temperature is reached in order to prevent reoxidation of the copper. This is most easily accomplished bysealing up the drum containing the cooper powder and reducing gases fromthe airuntil the; powder has cooled to approximately-roomjtemperature;

The cooled copper powder maythen'be treated'in a ball mill or other mill to break up the agglomerated material. v v The'product obtained by the process as outlined diners from conventional prior art copper powders in many importantrespects. In the ticle ,size. The nodule powder of the prior art will weigh, in all cases, more than 2.5 grams per c. c., and may range up to 3,5; my powders run below.2.5 in apparent density, and ordinarily will run about 2.0, although with extreme care they may be kept below 2.0. For powder of 100 mesh or finer, particle size seems to have no eilect on apparent density. The electrolytic coppers may be made in apparent density of from 0.5 to '2.0,

while the flaked stamped powders may vary from 1.0 to 3.5; these apparent densities, however, depend largely on particle size, and on the distribution of the various sizes of particle in the mass.

A third distinction lies in the ability of my products to withstand atmospheric corrosion. Ordinary electrolytic copper powder will be substantially black. after 60 days exposure-to the air, while my powder retains its'color. It is true that both stamped and nodule powders will retain their color; but the stamped product is coated with lubricant, and the nodule powder has decidedly less reactive surface as compared with my porous powders.

In the electrical field, my powder gives results superior to prior art powders. When incorporated into brushes by mixing with carbon or graphite, tests indicate that equivalent .con-,

tests were made, using my new powder and an ordinary prior art powder commonly used in the bearing industry. The following table shows the results obtained in a typical test run:

High density 00 per g g splow er b g I so s angist: tinny porous Apparent density in gram per cubic centi- I meter. 3. 2 2. 00 Flow or mobility relation (relative weight through standardoriiice in given time) percent, 100, 87 Screen analysis: V

On 150 mesh .-do 0.0 0. 0 On 325 mesh --.do 45.0 46.0 Through 325 mesh-.. do" 55. 0 54. 0 Slntering data:

Unsintered weight. gralns. 14. 53 14. 56 Unsintered length .mches 0. 679 0. 688 Unsintered width do 0. 818 0.817 Sintered length" d0 0. 733 0. 736 .Sintered dth do 0.839 0.833 Radial strength. sq. 147 189 Radial strength ratio .pereent 100 128. 5 Oil absorption. .-peroent by weight 3. 42 3. 87 Oil absorption ratioi peroenL- 100. 0 110. 4

The hearings were produced with a compres- 3 -sion of the above weights. of copper powder in it is possible to make fairly goodcopper powden extent.

By my method it is now possible to make for, the first time a copper powder of porous structure witlra large reactive surface, and with low ap-' parent density, which at the same time will resist atmospheric corrosion. The copper powder 'of my process is a low cost productpslpable of replacing high cost electric copper powder in the bearing and electrical fields and having the added advantage of resistance to atmospheric corrosion and freedom from occluded salts.

This applicatiomis a continuation in part of applications Serial No. 729,443, flied June I, 1934,

' and Serial No. 3,499,-flled January 125, 1935.

I claim: r

1. The method of producing copper powder which comprises roasting pieces oi substantially pure copper presenting a larse surface area to to produce a surface oxidation to cuprous oxide, stopping the oxidation while a core of metal remains unoxidized, to maintain the cuprous state or the oxide, milling the copper oxide, separating the powdered oxide reducing atmosphere at a temperature below that at which substantial sinterlng occurs. 2. The process of producing copper powder which comprises ieces of substantially purecopper of substantially uniform cross section presenting a large surface area to oxidation in an oxidizing atmosphere at temperatures be-v tween 800 and 1780" F., to produce a surface oxidation of cuprous oxide, stoppin the oxida-- tion while a coreioi metallic copper remains unoxidized, to maintain the cuprous state of the oxide, milling the resulting material to powder the cuprous oxide, from the metallic copper core, and reducing the milled cuprous oxide by roasting in a reducing atmosphere at a temperature between 350 and 700 E, and cooling the reducing atmosphere,

JOSEPH DRAPEAU. JEL- rrom the copper, and reducing 'the oxide to metallic copper by roasting in a separating the cuprous oxide reduced material in a m