US3373013A

US3373013A - Process for producing finely divided metal products

Info

Publication number: US3373013A
Application number: US409410A
Authority: US
Inventors: John F Hardy; Merrill E Jordan
Original assignee: Cabot Corp
Current assignee: Cabot Corp
Priority date: 1964-11-06
Filing date: 1964-11-06
Publication date: 1968-03-12
Anticipated expiration: 1985-03-12

Description

March 12, 1968 J, HARDY ET AL PROCESS FOR PRODUCING FINELY DIVIDED METAL PRODUCTS Filed Nov. 6, 1964 INVENTOR. J. E HARDY, M. E. JORDAN United States Patent Ofiice 3,373,013 Patented Mar. 12, 1968 Walpole, Boston, Mass.,

This invention relates to a process for producing metallurgical materials. More precisely, the invention disclosed herein relates to an improved process for producing finely divided metallurgical powders of submicron dimensions.

Finely divided metallurgical powders including metal, metal oxide and metal carbide powders are well known products of commerce. Such products presently have many known specialized applications and their potential applications are regarded as especially promising. Many processes are known for producing such metallurgical powders and in general, the fineness and purity of the ultimate powder is primarily determined by the process utilized. For example, the most finely divided and purest powders are produced by elaborate and highly specialized ball milling techniques and also by vaporization or fuming techniques. Accordingly, the said powders are rather expensive because of the intricate processes involved in producing them. In view of the growing need for high purity metallurgical powders and especially those having average particle diameters below about one micron, any process whereby such powders can be produced consistently, easily and in a simple and inexpensive fashion would be indeed 'a notable contribution to the art.

A principal object of the present invention is to provide an improved process for making the foregoing contribution to the art.

A more specific object of the present invention is to produce finely divided metallurgical powders especially metal oxide powders in an extremely economical fashion.

Still another object of the present invention is to provide a simple process for producing powdered metals, or metal carbides in a finely divided form.

Another object of the present invention is to provide a process for producing powdered metals, metal oxides or metal carbides in a finely divided form in combination with varying amounts of carbon which combinations have specialized properties and are of particular utility 'as fillers and/or as pigments in elastomeric and plastomeric compositions.

Other objects and advantages of the present invention will in part be obvious to those well skilled in the art or will in part appear hereinafter.

In a very broad sense, the above-mentioned objects and advantages are realized in accordance with the practice of our invention by subdividing a slurry containing carbon black and at least one metal compound and introducing said subdivided slurry to a fluidized bed of solid materials maintained at a temperature sufliciently elevated to convert said compound to at least the corresponding oxide. Thus, the principles of our invention reside not only in the ingredients and the form thereof utilized but also in the specific manner of subsequently converting said compound in a surprisingly easy fashion to a metallurgical powder.

The operational features of the present invention will be better understood by reference to the attached drawing. Said drawing illustrates a view in elevation of an arrangement of apparatus with portions of said appa= ratus cut away to illustrate features thereof in more detail.

Referring now to the attached drawing, carbon black, preferably in slurry form, is fed to mixer 14 via line 16 while a slurry or solution of the metal compound(s) is fed to mixer 14 via line =12. Mixer 14 is provided with suitable agitation means (not shown) to produce an intimate mixture in slurry form of the carbon black 1 and metal compound. Said slurry is then conveyed preferably at a controlled rate and in any convenient manner, such as with the aid of gas from reservoir 20, from mixer 14 by way of line 16 to reactor 28. The terminal portion of line 16 should preferably be equipped with a fine spray nozzle 24 so that the slurry of black and metal compound is subdivided and introduced in aerosol form to reactor 28.

Reactor 28 is an enclosed, usually cylindrical, heated vertical chamber. Means for heating said chamber are not shown since many manners obvious to those skilled in the art of heating reactor 28 directly or indirectly are suitable for the practice of our invention. The major portion of the interior of reactor 28 is occupied by a plurality of heated particulate bodies 26 which are maintained in a fluidized state preferably by the gas from reservoir 20. In this respect, it is to be understood that auxiliary gas can also be introduced to reactor 28 through nozzle 24 or other entry ports to maintain bodies 26 in a fluidized state. It is to be also understood that the preferred fiuidizing action should normally be so adjusted as to maintain attrition of bodies 26 at a minimum.

The sub-divided carbon black/metal compound slurry which is sprayed into reactor 28 contacts heated bodies 26 and is converted to the desired metallurgical powder. After conversion, since the powder is considerably smaller in size than bodies 26, the powder is selectively conveyed by the fluidizing gas from reactor 28 to suitable collection means 32.

In the most preferred embodiment of our invention, bodies 26 are comprised of the same material as the metallurgical powder produced in reactor 28. That is to say, when the metal compound is to be converted in reactor 28 to the corresponding oxide, then bodies 26 should also be comprised of said oxide. This feature assures maximum purity of the powder produced in accordance with the practice of our invention. If purity is not a paramount consideration, said bodies can be comprised of any desired refractory and substantially inert material including metal, metal oxide, metal carbide and ceramics. It is to be understood that such features as the size of said bodies, the amount thereof in said reactor, the rate at which the slurry is introduced to the reactor and the rate of gas flow through the reactor will vary and be determined by factors such as the temperature in the ractor, the geometry thereof, the metallurgical powder desired, the particle size of the powder desired, etc. However, suitable operational conditions for any given system can be readily determined by those well skilled in the art. For example, helpful details on fluidized bed systems can be found in Perrys Chemical Engineers Handbook, 4th edition, Sections 2042 to 20-53.

We have found that carbon black is an essential ingredient in eifectuating the purposes of our process since even in those cases where carbon black is theoretically not required to produce the desired product, for example, in the production of metal oxides, the presence thereof normally permits the conversion of the metal compound to the desired corresponding metal powder to be achieved much more rapidly or at temperatures much lower than those normally required to accomplish said conversion in the absence of carbon black. Also, the use of carbon black permits one to conveniently apply the practice of our invention to the direct production of diverse metallurgical s powders since the amount of carbon black utilized can be selectively adjusted to conform to the stoichiometrtc amount required to directly convert the metal compound to such finely-divided metallurgical powders including powdered metal oxides, carbides and metals.

For the purposes of the present specification and the claims attached hereto, carbon black refers generally to products produced by the catalytic cracking and/or incomplete combustion of hydrocarbonaceous materials. Thus, for example, materials referred to in the art as acetylene blacks, lamp blacks, channel blacks, furnace blacks, thermal blacks, etc., are all included within the scope of the present invention.

Broadly, the metal compounds utilized in the practice of our invention include compounds of metals such as boron, silicon, barium, copper, aluminum, titanium, zirconium, tungsten, zinc, lead, tin, iron, cobalt, nickel, manganese, chromium, vanadium, thorium, molybdenum and mixtures of these. More specifically, however, the present invention relates to metal compounds which can be thermally decomposed or converted under suitable conditions to produce the corresponding metal, metal oxide or metal carbide. Representative preferred compounds include the sulfates, chlorides, bromides, iodides, fluorides, perchlorates, orthoarsenates, sulfides, acetates, citrates, oxalates, formates, benzoates, carbonates, oleates and tartrates of the above-mentioned metals. Especially preferred are the water soluble organic and inorganic compounds of the above-mentioned metals. The benefits which flow from the practice of our invention are especially apparent when compounds of the above-mentioned metals which can be converted to the desired metal powder at temperatures above about 500 F. but below about 2500 F. are utilized. Thus, such compounds constitute an especially preferred embodiment of our invention.

The exact amount of carbon black to be combined with any of the above-mentioned compounds will be determined primarily by the final metal powder desired. As stated, the practice of our invention can be applied to the production of diverse metallurgical powders. Such powders include powdered metals, metal oxides, metal carbides, mixtures of metal oxides, metal/metal oxide mixtures and metal/metal carbide mixtures. However, it is tobe understood that the practice of our invention does not necessarily require that any of the aforesaid powders except the metal oxides be produced directly. In other words, the practice of our invention is satisfied by merely converting metal compounds to the corresponding oxides. Said oxides can then be treated in any desired fashion to convert said oxides to the corresponding free metal or carbide or mixtures thereof.

The minimum amount of carbon black to be combined with the aforesaid compounds can readily be determined in practice. While some variations will occur, amounts of carbon black set forth in our copending US. Patent application 375,942 filed June 17, 1964, are generally entirely suitable for the practice of the present invention. When the practice of our invention is applied to the direct production of powdered metals, metal carbides, metal/metal oxide mixtures and metal/ metal carbide mixtures, the, minimum amount of carbon involved will normally be about equivalent to the stoichiometric amount requiredto produce the desired powder.

The amount of residual carbon black which can be tolerated in combination with the final metallurgical pow der is another factor which can affect the amount of carbon black to be combined with the aforesaid compounds. We consider our process most valuable when applied to the production of finely-divided metallurgical powders of high purity, that is to say, metallurgical powders in combination with very small quantities of carbon black, i.e. less than carbon black by weight of the total composition. Accordingly, in the most preferred embodiment, the amount of carbon black utilized will rarely exceed the amount required to produce compositions comprising about 10% by weight carbon black.

However, it is to be understood that our process can also be applied to the production of finely-divided metallurgical products in combination with larger amounts of carbon black. Such compositions can be utilized as fillers in elastomeric or plastorneric compositions and accordingly, can contain up to about 90% by weight of carbon black if desired. I

The temperature at which the metal compound in the carbon black/metal compound mixture can be converted to form the desired metallurgical product can vary over a wide range. In general, the range includes temperatures substantially below those normally required to convert the, metal compound as well as temperatures that can exceed said normal decomposition temperature by 400 or 500 F. and even more. Since our process is operated continuously, it is obviously normally desirable to reduce residence time to a minimum and thus the temperature of the con vension zone will be relatively high.

The environment in the conversion zone will also be determined primarily by the final metallurgical product desired and said environment can easily be selected by one well skilled in the art. For example, if the ultimate powder is to be a metal oxide of high purity (i.e. low carbon black content) then an oxidizing environment is definitely preferred. The oxidizing environment not only insures a rapid conversion of the metal compound to the corresponding oxide but also is effective in reducing the residual carbon content in combination with the final powder. Furthermore, when the conversion temperature utilized is higher than that normally required to convert the metal compound in the absence of any carbon black, and especially when larger amounts of carbon black are utilized, an oxidizing environment is also definitely preferred since reduction or carbide-forming reactions are thereby inhibited. An inert environment is often suitable for the production of metal oxides when the conversion temperature is closely controlled and maintained below or at about the temperature at which the compound normally decomposes to form the oxide unless, of course, the metal compound is one which cannot be decomposed to form the oxide in the absence of an oxidizing environment.

A reducing or inert environment is definitely preferred when the practice of our invention is applied to the direct production of powdered metals, metal/metal oxide mixtures and metal/metal carbide mixtures. Inert and reducing environments are also usually preferred when carbides are produced in accordance with our invention.

The following specific examples of particular embodiments of our invention are given for the purposes of providing a fuller and more complete understanding of some of the operating details of the invention together with many of the advantages to be obtained from practicing same. These examples should be considered as illustrative only and as in no sense limiting the scope of the present invention.

Example 1 In apparatus of the type set forth in the attached drawing, a slurry was prepared by mixing an, aqueous dispersion of carbon black and an aqueous solution of nickel sulfate. The concentrations of carbon black and nickel sulfate were adjusted so that the weight of carbon black in the final slurry represented 5% by weight of the total solids. Said slurry was then entrained in air under a pressure of about lbs/sq. in. and was continuously conveyed at a rate of about 10 lbs/hr. to an externally heated vertical chamber containing 20 lbs. fluidized nickel oxide pellets having an average particle diameter of about 500 microns. The average temperature of the fluidized mass was maintained at about 1500 F. The settled depth of the mass of nickel oxide pellets making up the bed was about 2 feet, the average velocity of the gas through said bed being about 5 ft./second. A finely-- divided composition comprising carbon black and nickel oxide was continuously collected in a cyclone communieating with the upper discharge end of said chamber.

lectron microscope examination of said composition revealed that the particle size of substantially all of said composition was in the sub micron particle range.

Example 2 In the same apparatus utilized in Example 1, a slurry was prepared by mixing an aqueous dispersion of carbon black and an aqueous solution of titanium sulfate. The concentrations of carbon black and titanium sulfate were adjusted so that the weight of carbon black in the final slurr represented 5% by weight of the total solids. Said Slurry was then entrained in air under a pressure of about 50 lbs/sq. in. and was continuously conveyed at a rate of about lbs/hr. to an externally heated vertical chamber containing about lbs. of fluidized titanium dioxide particles having an average particle diameter of about 300 microns. The average temperature of the fluidized mass Was maintained at about 2000 F. The settled bed depth of the mass of titanium dioxide particles was about 1.5 ft, average velocity of the gas through said bed being about 7 ft./second. A finely-divided composition comprising carbon black and titanium dioxide was collected in a cyclone communicating with the upper discharge end of said chamber.

Example 3 In the same apparatus utilized in Example 1, a slurry was prepared by mixing an aqueous dispersion of carbon black and an aqueous solution of iron sulfate. The concentrations of carbon black and nickel sulfate were adjusted so that the weight of carbon black in the final slurry represented about 10% by weight of the total solids therein. Said slurry was then entrained in carbon monoxide under a pressure of about 50 lbs/sq. in. and was conveyed to an externally heated vertical chamber containing lbs. of fluidized iron shot having an average particle diameter of about 500 microns. The average temperature of the fluidized mass was maintained at about l800 F. The average velocity of the gas through said bed was about 6 ft./second. A finely-divided composition comprising carbon black and iron metal was continuously collected in a cyclone communicating with the upper discharge end of said chamber.

Example 4 In the same apparatus utilized in Example 1, a slurry was prepared by mixing an aqueous dispersion of carbon black and an aqueous solution of ammonium paratungstate. The concentrations of carbon black and ammonium paratungstate were adjusted so that the weight of carbon black in the final slurry represented about by weight of the total solids therein. Said slurry was then entrained in argon gas under a pressure of about 50 lbs/sq. in. and was conveyed to an externally heated vertical chamber containing 50 lbs. of fluidized tungsten metal powder having an average particle diameter of about 250 microns. The average temperature of the fluidized mass was maintained at about 2200 F. The average velocity of the gas through said bed was about 15 ft./second. A finely-divided composition comprising carbon black and tungsten carbide was continuously collected in a cyclone communicating with the upper discharge end of said chamber.

It will be obvious from the preceding examples that the process of our invention is highly versatile and can be applied to the production of many finely-divided metal powders of commercial interest. Thus, many modifications in many of the incidental features utilized in illustrating our invention can be made without departing from the spirit and scope thereof. For example, while our discussion above has been limited to the term slurry, for the purposes of the present specification and the claims appended hereto, the term slurry includes within its scope the term dispersion.

Also, it is obvious that, if desired, flue gases, for example, from carbon black-producing units can be utilized in place of the fluidizing and/or entrainment media utilized above.

Having described our invention together with preferred embodiments thereof, what we declare as new and desire to secure by US. Letters Patent is as follows:

1. A process for producing finely-divided metallurgical powders comprising the steps of:

(a) uniformly mixing into a liquid medium (1) at least one metal compound which upon heating in an oxidizing atmosphere can be converted to the corresponding oxide, and

(2) carbon black,

(b) subdividing the resulting mixture into droplets and contacting said droplets with a plurality of fluidized particulate bodies heated to a temperature at least sufiicient to convert said metal compound to the corresponding oxide.

2. The process of claim 1 wherein said metal compound is chosen from the group consisting of compounds of boron, silicon, copper, barium, aluminum, titanium, zirconium, tungsten, zinc, lead, tin, iron, cobalt, nickel, manganese, chromium, vanadium, thorium, molybdemum and mixtures thereof.

3. The process of claim 1 wherein said metal pound is a compound of iron.

4. The process of claim 1 wherein said metal pound is a compound of nickel.

5. The process of claim 1 wherein said metal pound is a compound of tungsten.

6. The process of claim 1 wherein said metal pound is a compound of titanium.

7. The process of claim 1 wherein said metal pound is a compound of aluminum.

8. The process of claim 1 wherein said metal compound is soluble in said liquid medium.

9. The process of claim 1 wherein step (b) is accomplished in an oxidixing atmosphere.

10. The process of claim 1 wherein step (b) is accomplished in an inert atmosphere.

11. The process of claim 1 wherein step (b) is accomplished in a reducing atmosphere.

12. The process of claim 1 wherein step (b) is accomplished under oxidizing conditions such that the final product is substantially free of carbon black.

13. The process of claim 1 wherein the quantity of carbon black utilized is such that the resulting powder comprises less than about 10% by weight carbon black.

14. The process of claim 1 wherein step (b) is accomplished at temperatures between about 500 F. and about 2500 F.

15. The process of claim 1 wherein said particulate bodies comprise the same material to which said metal compound is converted.

16. The process of claim 1 wherein said metal compound is chosen from the group consisting of sulfates, nitrates, acetates and chlorides.

17. The process of claim 1 wherein a mixture of metal compounds is utilized.

18. The process of claim 1 wherein a metal oxide is produced.

19. The process of claim 1 wherein a free metal is produced.

20. The process of claim 1 wherein a metal carbide is produced.

com-

COIII- com- References Cited UNITED STATES PATENTS 1,984,380 12/1934 Odell 134-60 2,242,759 5/ 1941 Schlect et al. 7584 2,288,613 7/1942 Dill 7589 2,900,244 8/1959 Bradstreet et a1 75.5 3,305,349 2/1967 Bovarnick et al 750.5

DAVID L. RECK, Primary Examiner. W. STALLARD, Assistant Examiner.

Claims

1. A PROCESS OF PRODUCING FINELY-DIVIDED METALLURGICAL POWDERS COMPRISING THE STEPS OF: (A) UNIFORMLY MIXING INTO A LIQUID MEDIUM (1) AT LEAST ONE METAL COMPOUND WHICH UPON HEATING IN AN OXIDIZING ATMOSPHERE CAN BE CONVERTED TO THE CORRESPONDING OXIDE, AND (2) CARBON BLACK,