US 3428543 A
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Description (OCR text may contain errors)
Feb. 18, 1969 "r. WEBER 3,428,543
COMPOSITE POWDERS AND APPARATUS FOR THE PRODUCTION OF THE SAME Filed May '7, 1965 United States Patent U.S. Cl. 204-273 Int. Cl. B01k 3/00 4 Claims ABSTRACT OF THE DISCLOSURE A composite powder consisting essentially of a core of tungsten, titanium or the carbides, borides, silicides, nitrides and oxides of tungsten or titanium and an envelope electrodeposited thereon, said envelope being nickel, cobalt, copper or silver; and an apparatus for preparing said composite powders.
This invention relates to composite powders and to processes and apparatus for the production of the same.
A composite powder within the meaning of the invention is a powder, the individual grains of which consist of two or more components which, without being chemically bonded, cannot be readily separated mechanically. Such is the case, more particularly, when one component completely surrounds the other component, in which arrangement one component is called the core, while the other one is called the envelope or jacket.
Such materials are used in powder metallurgy and in the field of flame-spraying.
An important advantage of such arrangements over similarly composed mixtures resides in the fact that they cannot separate into their different components when they are handled. The contact between the two phases (envelope/ core) is very intimate and the surfaces of contact are maximal. Another important advantage when compared with alloys resides in the fact that the heat of formation in the composite powder is preserved and becomes free and can be utilized only during subsequent thermal processing. Moreover, composite powders make it possible, for example, to overcome difficulties of wetting, to prevent agglomerations during dispersion and to obtain greater molding strengths.
In a known process for the production of composite powders, the envelope is applied to the core by hydrogen pressure reduction of the corresponding ammoniacal metallic salt solution.
It has now been found that it is possible to apply the envelopes to the cores electrolytically, i.e., by means of a process similar to the one which is used in galvanotechniques (electroplating) in the production of corresponding bulk goods.
The essential differences with respect to the last-named process reside in the fact that the individual particles are incomparably smaller than the bulk goods and need not necessarily be metals.
The envelope materials used according to the invention are all metals which can be electrolytically separated from aqueous solution, preferably Ni, Co, Cu, and Ag. The materials used for the core are preferably metallic powders, as well as powders of carbides, borides, silicides, and suitable oxides, which do not react with the electrolyte. Solutions similar to those used in galvanotechniques are used as electrolytes. The electrolytes are selected depending on the composition of the composite powder desired.
The anode material used is the material of the desired envelope. Insoluble anode material, such as, for example, platinized titanium, is also suitable as anode material; however, in this case the electrolyte must be constantly renewed.
It is essential for the process according to the invention that the material be constantly turned, either continuously or discontinuously, that it be possibly not in suspension during the current flow, and that the cathode surface remain covered with powder almost completely and uniformly during the electrolysis.
A tank with a cathodically connected metallic bottom, for example, nickel is used for the electrolysis. The anode comprises holes to allow the escape of possibly evolving gases and is suspended in the tank parallel to the bottom thereof.
The apparatus provided with an automatic turning device, comprises a plastic plate, which will be described below, between the anode and cathode. If the operation is a discontinuous one, the turning is effected in that the current is disconnected and the anode is lifted out, and then the material is turned by hand and is uniformly distributed over the bottom.
The operation proceeds as follows: the core material is uniformly distributed at the bottom, whereupon the automatic turning device is introduced, the anode being suspended thereabove. Suitable electrolyte solution is then added in an amount such that the anode is completely covered. After the automatic turning device has been connected, the voltage is applied to the cell.
The duration and intensity of the current flow depends on the desired composition of the composite powder and on the resistance of the bath.
After the electrolysis is terminated, the electrolyte is siphoned off, the composite powder is conveyed onto a suction filter and is washed in a suitable manner. After drying, the material obtained in this manner is, in general, the finished composite powder. If the composite powder is to have a specific grain size distribution, it must be screened in the usual manner. Oversized grain, caused partially by the natural increase of the diameter due to one layer being covered with another, and partially to the fact that several grains are covered together, can be ground to the desired grain or particle size.
In the case of some core materials, not every grain is covered. This difficulty can subsequently be overcome, for example, when nickel and cobalt are used as the envelope material, in that a subsequent magnetic separation and demagnetization is carried out.
The invention will be more readily understood from the following detailed description of a preferred embodiment as illustrated in the accompanying drawing in which:
FIGURE 1 is a side view partly in section of a cell provided in accordance with the invention; and
FIGURE 2 is a top plan view of one of the components of the cell.
The accompanying drawing shows an electrolyzing cell according to the invention with automatic turning device or apparatus. The inside diameter of the tank amounts, for example, to 40 cm.
The process is carried out in the following manner:
After the electrolyzing cell 1 has been charged, as -described above, the automatic turning device 5, which is a perforated plastic disc or plate, is caused to start to rotate slowly (for example, 0.5 to 6 revolutions per minute) by means of a motor 3 with gear 4 arranged adjustably on a vertical holding rod 2.
For this purpose, the disc is held in position by a drive rod 6 arranged in the center of the disc and extending perpendicularly to said disc. For insulating purposes the rod 6 is covered with a plastic layer or coating 7. The rod 6 can be connected to the motor shaft 9 by way of a coupling member 8.
In the manner of a Nipkow disc, non-conductive plastic pins 10, disposed along a figure S, are driven into the non-conductive plate 5. Said plate 5, provided with holes 18, is fitted with very little play in the tank 11 of the electrolyzing cell 1.
During the operation, the pins just contact the bottom 13 of the tank 11, said bottom being connected to the cathode 12. An insulating plastic plate 15 is arranged between the bottom 13 and a base plate 14.
Due to said arrangement, each increment of the bottom 13 is contacted once during each revolution and the material is turned.
Arranged above the plastic plate 5 is the anode 16 which, as already stated, is a perforated disc which is provided in its center with a bore 17, through which the rod 6 of the plastic disc is guided with play. The anode is suspended in the tank 11 by means of a suspension 19.
Example 1 The powder desired is a composite powder consisting of tungsten carbide and 12% Co having a grain size of 4080 The starting material is a tungsten carbide, grain size 37 to 70 of which 2.5 kg. are used. The electrolyte is a solution of 60 g. of cobalt sulfate per liter and 150 g. of ammonium sulfate per liter, which is adjusted to a pH of about 7 with ammonia. The amperage amounts to 48 amp the voltage will be approximately 2 volts. Electrolysis is carried out for 6.50 hours. After Washing and drying, about 2800 g. of composite powder are extracted. 2.5 kg. thereof pass through a suitable screen; the remaining 300 g. are ground in a ball mill for 15 minutes. After screening there remains a residue of about 100 g. of oversize grains. The material having the right grain size is separated magnetically. Magnetic separation shows 2,200 g. of strongly magnetic fractions with 12.3% C0, 120 g. of weakly magnetic fractions with 3.6% Co, and 360 g. of non-magnetic material. After demagnetization, the strongly magnetic fraction is the desired finished composite powder. The remainder is used again as starting material in subsequent operations.
Photomicrographs show that the tungsten carbide cores are almost 100% covered with cobalt.
Example 2 The powder desired is a composite powder consisting of a tungsten core having an average grain size of 6a with a 3.5% Ni and 1.5% Cu coating. 2.5 kg. of the desired core material are used as the starting material. First, electrolysis is carried out for two hours at 48 amp with a weakly ammonical nickel-chloride solution which contains 150 g. of ammonium chloride per liter. The material obtained in this manner passes 100% through the finest screen and contains no non-magnetic constituents. A mixture of 40 preparations had a nickel content of 3.4% determined analytically. The desired material is electrolyzed for 55 minutes at 48 amp with an ammonium-sulfate-containing copper sulfate solution neutralized to pH 7. The resulting material is screened through a 400 mesh screen; there remains a residue of about 2% of high-copper containing oversized grain. The screened material of 40 preparations is mixed and has a copper content of 1.6% The total amount of the 40 preparations amounts to 102 kg. of composite powder of the desired composition.
Example 3 The powder desired is a titanium/nickel composite powder of a grain size of 140+325 mesh with a titanium core and a nickel content of 60% Ni. 400 g. of titanium powder of the grain size .200+325 mesh are used. Electrolysis is carried out with an electrolytic solution, as described in Example 2, for 6 /2 hours at 48 amp.
The material is turned manually and discontinuously,
namely, about every twenty minutes, during the electrolysis. Since the light titanium powder tends to stick to the cathode, the latter is greased with Vaseline prior to use. The material is dried after the electrolysis and is screened through a 200 mesh screen. The constituent 200 consists mainly of titanium powder with a very small content of nickel. The coarse fraction is ground and is screened through a 140 mesh screen. passes through the screen and is the desired composite powder.
The great number of possible components for envelope and core allows a very large amount of combinations. Thus it is impossible to quote all conceivable practical examples. In all possible combinations the method according to the invention is the same. The method according to the invention is based on a system which is not restricted either by the nature or by the number of the combinations cited in the practical examples. Further examples will easily fit in this system.
What is claimed is:
1. Apparatus for electrolytically applying envelopes to cores to form composite powder grains, said apparatus comprising a tank adapted for containing an electrolyte and including a bottom adapted to constitute a cathode and to support said cores, anode means spaced from said bottom, perforated means between the bottom and anode means, a plurality of pins on the perforated means extending to said bottom and being arranged such that, on rotation of the perforated means substantially the entire bottom is traversed by the pin-s, and means connected to the perforated means for rotating the latter.
2. Apparatus for electrolytically applying envelopes to cores to form composite powder grains, said apparatus comprising a tank adapted for containing an electrolyte and including a bottom adapted to constitute a cathode and to support said cores, anode means spaced from said bottom, a perforated disc between the bottom and anode means, a plurality of pins arranged generally diametrically on the disc and disposed generally as to constitute a figure S, said pins extending to said bottom and being arranged such that, on rotation of the disc, substantially the entire bottom is contacted by the pins, and means extending through the plate and connected to the disc for rotating the latter.
3. Apparatus comprising a tank adapted for containing an electrolyte and including a bottom adapted to constitute a cathode and to support a material to be treated, a plate having an opening therein and arranged in parallel to said bottom, said plate being of a material insoluble in said electrolyte, electrically conductive means suspending the plate in the tank such that said plate constitutes an anode, a perforated disc between the bottom and plate, a plurality of pins arranged generally diametrically on the disc and disposed generally to constitute a figure S, said pins extending to said bottom and being arranged such that, on rotation of the disc, substantially the entire bottom is traversed by the pins, and means extending through the plate and connected to the disc for rotating the latter.
4. Apparatus for electrolytically applying envelopes to cores to form composite powder grains, said apparatus comprising a tank adapted for containing an electrolyte and including a bottom adapted to constitute a cathode and to support said cores, a plate having an opening therein and arranged in parallel to said bottom, said plate being of a material insoluble in said electrolyte, electrically conductive means suspending the plate in the tank such that said plate constitutes an anode, a perforated disc between the bottom and plate, a plurality of pins arranged generally diametrically on the disc and disposed genreally as to constitute a figure S, said pins extending to said bottom and being arranged such that, on rotation of the disc, substantially the entire bottom is traversed by the pins, and means extending through the plate and connected to the disc for rotating the latter whereby cores on the bottom are turned for complete processing, said means including a drive rod connected to the disc and an insulating coating on said rod.
References Cited UNITED STATES PATENTS Huber et a1. 204-10 Aylsworth 204-36 Crane 204-23 Taylor 204-36 Welch 204-23 Harshaw 204-23 Wulif 209-214 Matskawa 204-23 6 FOREIGN PATENTS 4/ 1952 Great Britain.
OTHER REFERENCES 5 Handbook of Practical Electroplating, Thomas M. Rodgers, Macmillan Company, New York, 1959, p. 237.
ROBERT K. MIHALEK, Primary Examiner.
10 T. TUFARIELLO, Assistant Examiner.