US2286237A - Copper powder - Google Patents

Description

Patented June 16, 1942 Search mum COPPER POWDER John D. Shaw, Glen Rock, and Walter N. Revock,

Hillside, N. J., assignors to Metals Disintegrating Company, Inc., Elizabeth, N. J a corporation of New Jersey No Drawing; Application June 15, 1940, Serial No. 340,836

1 Claim.

This invention relates to the production of copper powder and has for its object the enhancement of the keeping qualities thereof, especially in the presence of moisture.

We have discovered that if the exposed surfaces of copper contain small amounts of metal more electro-positive than copper and having a melting point between 200 and 500 0., the powder keeps its luster much longer than it will if such metal is absent, this probably because of a resulting inhibition of oxidation.

The principal metals in this group and their melting points are as follows:

Zinc 419 Lead 327 Cadmium 321 Bismuth 2'71 Tin 232 One of these addition metals or a mixture of two or more of them effectively added to copper powder as hereinafter set forth, in an amount suflicient to produce a surface alloy on the particles, containing as a whole around 0.5% of alloying metal, gives good results. It will be clear that the concentration of the added metal will be over 0.5% in the surface layers. Below 0.10% total the effect is feeble. Beyond 5 total the keeping qualities do not increase materially with further additions of the alloying element. Further, the amount of alloying element should not be so great as to substantially change the physical and working qualities of the copper, as for example to mask the color of the copper. The usual limits are 0.25 to 1.0%.

It has also been found that while, used alone, bismuth and tin are more effective than the other metals, best results are obtained by the use of either lead or zinc in conjunction with either bismuth or tin or both these latter metals. When we speak in the claims of other metal more electropositive than copper melting between 200 and 500 0., we mean any one or combination of the addition metals.

It is advantageous to obtain the desired results by heating the copper powder to temperatures well below its melting point (1083 C.), in contact with the added metal in powder form under surface alloying conditions. That is, the temperature should be such that surface alloying can take place. Surface alloying usually occurs readily and rapidly if the temperature is above the melting point of the alloying metal, e. g., 500 C. Another alloying condition isthat the surface of the copper particles at the time the surface-alloying takes place, should be clean and reasonably free from oxide film, which film would pervent actual contact between the copper metal and the alloying metal. That means that the heating of the copper powder and alloying element should take place in a reducing atmosphere.

The greater efficiency of surface alloying over complete homogeneous alloying, such as results from actually melting copper with the addition agents, is believed to be due to the greater concentration of such agents in the surface layers when surface alloying is the method used, so that less of the added metal is required to give equal surface concentration; and of course because while the coating produced by our method is of minimum thickness to inhibit oxidation, etc., of the mass of the copper metal of the particle, it is thin enough so that for practical purposes the physical and working qualities of the particle are substantially those of copper metal. For example, there is no masking of the color of the copper.

While the particles of copper should be free of oxide film at the time of alloying that does not mean that the process must start with copper powder. In fact, best result appear to be obtained where the process starts with a mixture of oxide of copper and finely divided alloying metal. The reducing atmosphere converts the copper oxide into metal and permits the alloying to take place thereafter. As the reduction is not instantaneous in all parts, reduction and alloying take place simultaneously.

Oxides of the added metals may be used and give as satisfactory products as the powdered metals themselves, but the necessary reactions take longer to accomplish. The term metal as applied to the added metals is to be interpreted as including the metal content of the oxides thereof. The same also applies to the use of the names of the individual metals.

For various reasons it is advantageous to produce copper powder by first converting bulk copper into oxide and then reducing the comminuated oxides to metal by heating it in a reducing atmosphere. That being the case, the simplest as well as the best procedure is to add the alloying metals or their oxides to the copper oxide, thereby carrying out two process steps simultaneously. And obviously, for the purposes of this invention, copper powder comprehends copper oxide, to the extent that the basic copper content is made available and subject to the surface alloying operation herein set forth.

Best results are obtained, so far as keeping qualities are concerned, when the starting material for the present process, so far as the copper is concerned, is cuprous oxide rather than cupric oxide. Complete absence of cupric oxide is not important. However, it is advisable not to have very much more than 10 to 15% of cupric oxide. The reason for the superiority of cuprous oxide is believed to be the fact that the reduced metal is less porous and hence more readily completely surface-alloyed with the added metal.

The added alloying metal powder should be relatively much more finely divided than the copper to give maximum contact with the copper powder and to hold the amount of addition agent to a minimum.

We claim:

Copper powder, the particles whereof have a surface alloy coating of the copper with other metal more electropositive than copper melting between 200 and 500 C., the proportion of such other metal to the copper being of the order of about 0.25% to 1.00%.

JOHN D. SHAW. WALTER N. REVOCK.