US2037672A - Method of producing metal powders - Google Patents

Description

Patenterl' Apr.- 14, 1936 UNITED STATES METHOD OF PRODUCING METAL POWDERS Walter Zeiss, Berlin-Charlottenburg, Germany No Drawing. Application November 1, 1934,

Serial No. 751,035 1933 1': Claims. (01. -22) This invention relates to the production of metal powders, more particularly to .a new and more economical method of producing such powders.

Metal powders have been prodiced in such a manner that the corresponding metals are vaporized and that the metal powder was precipitated from the vapor by rapid cooling. This process, however, showed a great number of disadvantages among which especially the necessary high temperature caused difficulties in technical operation.

According to the present invention these disadvantages are avoided whereby metal powders of excellent qualities are obtained in a simple manner. The process consists inintimately mixing the molten metal with a fine-grained, solid and hard material, for instance, sand, at the same time taking care by introducing inert gases, such as nitrogen and the like that no oxidation of the metal takes place.

The dispersion. thus produced from the molten metal and the grainy hard material, thereupon, is cooled while intimately and continuously mixing and the mixture obtained thereby is used either as such or the metal powder is separated from the dispersing agent. This separation may be carried out, for instance, by physical methods, as by sifting, sieving, elutriating, and the like.

The pure metal is especially suitable as starting material, but also metal alloys and, when working, for instance, in the presence of a reducing gas, also fusible metal compounds capable of reduction can be used. As dispersing agent there may be employed those materials which do not exhibit any change of form (deformation) at the temperature of the fused metal, such as, for instance, fine-grained sand or other minerals, various other kinds of rocks or even artificially produced solid materials, such as glass, porcelain, carbides and the like. Even metals or metal compounds, insofar as they do not react with the metal to be pulverized, can be used for this purpose. In case metal compounds which are dispersed in a reducing atmosphere are used as starting material, as dispersing agent there may be employed a catalytically acting agent which accelerates the reduction, for instance, hard but still porous pieces of porcelain which are impregnated with a catalyst capable of accelerating the reaction.

It is advisable to select as a dispersing agent a material the size of the separate grains of which varies between 2 and 3 mm. in diameter; for therewith the best results are achieved. But the In Germany November 1,

use of a dispersing agent of coarser grain has the advantage that the separation of the metal powder from the dispersing agent in an air separator and even in a sieving device can be carried out with a better effect and more readily than with a dispersing agent of finer grain.

Furthermore it has been found that the size of the grains of the metal powder can be varied depending upon the use of larger or smaller amounts of the dispersing agent with respect to the metal. Extremely fine-grained powders are obtained on employing larger quantities of the dispersing agent. Such metal powders possess a high setting and pouring volume. On decreasing the amount of the dispersing agent in the mixture, more coarse-grained products are obtained which possess a low setting and pouring volume.

When starting with metal compounds and converting the same into metals by reduction, it is frequently of advantage first to produce the oxides from said compounds by treating the same with oxidizing gases, and then to convert the oxides into the metals by further treatment with reducing gases. It has been found that in some cases it is of advantage to incompletely reduce the metal oxide. Thereby the very bothersome sticking of the metal to the dispersing agent is avoided. In order to produce therefrom the oxide-free metal, the small quantities of oxide present in the powderafter such a treatment and the separation from the dispersing agent can be readily removed by treatment with hydrogen.

' The observation that the presence of small quantities of the oxide prevents the sticking to the dispersing agent can also be made use of by mixing small amounts of oxygen orgases containing oxygen to the inert gases on dispersing the molten metal. It has been found that the metal powders obtained thereby which contain metal oxide, are especially suitable for the purposes of the accumulator or storage battery industry. The same result is achieved by exposing the molten metal in contact with the dispersing agent for a brief period of time to a stream of air in such a manner that complete oxidation of the metal cannot take place.

The temperature on dispersing the liquid metal is preferably about 50 to above, the melting.

point of the starting material to be transformed into a powder. When producing themetal pow-j der by reducing the metal compoundsit rnay sometimes be. of advantage to operate under pressure. The solidification of the dispersion .canbe effected by simplecooling or by the ,acjztidn}ota cold gas or air current. The separation of the dispersing agent from the metal powder can be carried out by any chemical or physical method. The air separation process has proved to be especially advantageous, but also other methods, such as sieving, centrifuging, elutriating or even dissolving the dispersing agent may be employed.

Example 1 200 kg. of sand and 200 kg. of metallic lead are heated above the melting point of the lead in a container provided with a stirring device. When the lead is molten, the stirring device is caused to operate. Thereupon an air current is passed for A to hour through the apparatus at a temperature of about 440 C. The mixture is allowed to cool while stirring and the slightly oxidizedJead powder is separated from the sand by air separation. The lead powder obtained thereby represents an excellent material for the purposes of the storage battery industry. On suitable selection of the reaction conditions and corresponding proportioning of the oxygen supply a lead powder containing varying amounts of lead oxide, as required, can be obtained.

In order to produce lead powder itself, the process is preferably carried out in the atmosphere of an inert gas, such as nitrogen to which small amounts of oxygen or air are admixed in order to prevent the sticking of the lead to the sand. In order to obtain a pure metal powder the reaction product is subjected to a treatment with hydrogen at a temperature below the melting point of the lead before or after separation of the sand.

Of course, one may also proceed in such a manner that the sand is stirred into the molten lead or that the molten lead is allowed to trickle into the sand heated to about 400-600 C., while stirring the sand.

When using about 300 kg. of sand for 200 kg. of metallic lead in this example, a finer grained product than described is obtained, while by using only 100 kg. of sand for 200 kg. of lead a coarser grained powder results.

Example 2 Antimony sulfide is mixed with the same amount by weight of unglazed porous stoneware grit and is stirred in the presence of air at about 700 C. Antimony oxide of the melting point 656 C. is formed whereby sulfur dioxide is evolved. Thereupon, while maintaining the same temperature, hydrogen is passed over the mixture of antimony oxide and stoneware grit until the reduction to antimony is completed. The antimony is separated from the grit by sieving off the former. Thereby an antimony powder of dark color is obtained. The air or the oxygen in the first reaction step and the hydrogen in the second reaction step can be introduced also under pressure. The stoneware grit can furthermore be impregnated with materials which are capable of catalytically accelerating the oxidation as well as the reduction.

Example 3 Molten zinc is intimately dispersed with granulated iron in the presence of an inert gas, such as nitrogen, until it is transformed into a finely divided, extremely reactive zinc powder which can be used either in mixture with the iron or after separation from the latter.

Other metals than those mentioned in the examples, such as tin, bismuth, cadmium andthe like, can also be converted very readily, and in a simple and convenient manner into powder.

While. I have described my invention setting forth several embodiments thereof, it is not limited thereto as variations in the procedure may be used within the spirit of the invention. Other metals than those named are amenable to the treatment. The time and temperature of treating may be varied at will, the character of the dispersing agent may be changed, the means for stirring the metal and dispersing agent may be of any suitable type and the separating means may be other than those specifically described above. These and other variations, which will be apparent to those skilled in the art, may be made in my invention, the scope of which is defined in the claims appended hereto.

What I claim is- 1. A method of producing metal powders which comprises providing a mixture of a molten metal and a solid dispersing agent which is not deformed at the temperature of operation, stirring said mixture, and cooling the same to solidify the metal into powder form during said stirring.

2. A method of producing metal powders which comprises providing a mixture of a molten metal and a solid dispersing agent which is not deformed at the temperature of operation, stirring said mixture, and cooling the same to solidify the metal into powder form during said stirring and separating said powder from said dispersing agent.

3. A method of producing metal powders which comprises providing a mixture of a molten metal and a solid dispersing agent which is not deformed at the temperature of operation, stirring said mixture in the presence of an indifferent gas, and cooling the same to solidify the metal into powder form during said stirring.

4. A method of producing metal powders which comprises providing a mixture of a molten metal and a solid dispersing agent which is not deformed at the temperature of operation, stirring said mixture in the presence of an amount of oxygen capable of partially oxidizing said metal, and cooling the same to solidify the metal into powder form during said stirring.

5. A method of producing metal powders which comprises providing a mixture of a molten metal and a solid dispersing agent which is not deformed at the temperature of operation, stirring said mixture in the presence of an indifferent gas containing oxygen.

6. A method of producing metal powders which comprises providing a mixture of a molten metal and a solid dispersing agent which is not deformed at the temperature of operation, stirring said mixture in the presence of an amount of oxygen capable of partially oxidizing said metal, and cooling the same to solidify the metal into powder form during said stirring, separating said powder from said dispersing agent and subjecting said powder to reduction.

7. A method of producing metal powders which comprises providing a mixture of a molten metal containing metal oxide and a solid dispersing agent which is not deformed at the temperature of operation, stirring said mixture, and cooling the same to solidify the metal into powder form during said stirring.

8. A method of producing metal powders which comprises providing a mixture of a molten metal and a solid dispersing agent which is not deformed at the temperature of operation and having a diameter of about 2-3 mm., stirring said mixture, and cooling the same to solidify the metal into powder form during said stirring.

9. A method of producing metal powders which comprises providing a mixture of a molten metal at a temperature about 50-100 C. above its melting point and a solid dispersing agent which is not deformed at the temperature of operation, stirring said mixture, cooling the same to solidify the metal into powder form during said stirring.

10. A method of producing metal powders which comprises providing a mixture ofa molten metal and a solid dispersing agent which is not deformed at the temperature of operation, stirring said mixture, and cooling the same to solidify the metal into powder form during said stirring, and varying the amount of said agent, whereby the diameter of the resulting powder is inversely varied.

11. A method of producing metal powders which comprises providing a mixture of a metal oxide and a solid dispersing agent which is not deformed at the temperature of operation, heating the same to a temperature above the melting point of the metal in the presence of a reducing agent, stirring said mixture, and cooling the same to solidify the metal into powder during said stirring.

12. A method of producing metal powders which comprises providing a mixture of a metal oxide and a solid dispersing agent which is not deformed at the temperature of operation, heating the same to a temperature above the melting point of the metal in the presence of a reducing agent under pressure, stirring said mixture, and cooling the same to solidify the metal into powder during said stirring.

13. A method of producing metal powders which comprises providing a mixture of a metal compound and a solid dispersing agent which is not deformed at the temperature of operation, heating the same under oxidizing conditions to form the metal oxide, heating under reducing conditions to form the metal, the temperature being above the melting point thereof, stirring said mixture, and cooling the same to solidify the metal into powder during said stirring.

14. A method of producing metal powders which comprises providing a mixture 01' a metal compound and a solid dispersing agent which is not deformed at the temperature of operation, heating the same under oxidizing conditions'to form the metal oxide, heating under reducing conditions to incompletely reduce the oxide into the metal, the temperature being above the melting point thereof, stirring said mixture, and cooling the same to solidify the metal into powder during said stirring.

15. A method of producing metal powders which comprises providing a mixture of a metal compound and a solid dispersing agent which is not deformed at the temperature of operation, heating the same under oxidizing conditions to form the metal oxide, heating under reducing conditions to incompletely reduce the oxide into the metal, the temperature being above the melting point thereof, stirring said mixture and cooling the same to solidify the metal into powder during said stirring, separating the powder and completing the reduction of oxide to metal.

16. A method of producing metal powders which comprises providing a mixture of a molten metal and a. solid dispersing agent which is not deformed at a temperature of operation, the amount of said agent being sumcient to render the resulting mass non-liquid, stirringsaid mixture to coat said agent with a film of, said metal and cooling said mixture to solidify said metal.

17. A method of producing metal powders which comprises providing a mixture of a molten metal and a solid dispersing agent which is not deformed at the temperature of operation, the amount of said agentbeing suflicient to render the resulting mass non-liquid, stirring said mixture to coat said agent with a film of said metal and cooling said mixture to solidify said metal, the shrinkage of said metal during said solidification causing the film to crack ofi of said agent and to form a powder.

WALTER ZEISS.