US3181933A

US3181933A - Radioactive diamond and process for the preparation thereof

Info

Publication number: US3181933A
Application number: US92357A
Authority: US
Inventors: Jr Robert H Wentorf
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1961-02-28
Filing date: 1961-02-28
Publication date: 1965-05-04
Anticipated expiration: 1982-05-04

Description

M y 1965 R. H. WENTORF, JR 3, 1,

RADIOACTIVE DIAMOND AND PROCESS FOR THE PREPARATION THEREOF Filed Feb. 28. 1961 zv/crrsz E/VD o/s/r N/C/(EL rues S? GkAPH/TE E PYROPl/VL ure- Tues HEATER SAMPLE/901.051?

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United States Patent 3,181,933 RADIQACTIVE DEAMQND AND PRO'CESS F63 THE PREPARATEQN THEREGF Robert H. Wentorf, J12, Schenectady, N.Y., assignor to GeneralEleetrie Company, a corporation of New York Filed Feb. 28, 196i, Ser. No. 92,357 Claims. (Cl. 23-=-29.l)

This invention relates to radioactive diamond material and to. the preparation thereof. More particularly, this invention is concerned with diamonds having a radioactivity extending through the diamond matrix as well as being present on the surface thereof obtained by heating at elevated temperatures and pressures in the diamond-forming region a radioactive carbonaceous material in combination with a catalyst for making diamonds.

As is Well known in the art, natural diamonds, particularly natural diamonds of the industrial variety, readily acquire and retain a charge of static electricity. This generally occurs when natural industrial diamonds come into contact with each other or with some other surface. The static charge on industrial diamonds results in a number of problems in their use. Thus, when an attempt is made to sort industrial diamonds, it is found that the static charge seriously interferes with the segregation of the diamonds into various size groups and interferes with the moving of the diamonds from one location to another. In addition, when natural diamonds are employed in bearings or in grinding tools, the charge on the surface of the diamond tends to attract dust or other undesirable particles of matter to the surface of the diamond. When diamonds are used as bearing materials such as in timepieces and other delicate mechanisms the dust or other particles attracted by the static charge by the bearing and, therefore, reduces or destroy the efiicie'ncy of the bearing. Where diamonds are used in industrial grinding tools, it is found that the static charge on the diamond surface causes particles of dust and of metal to adhere to the surface of the diamond and interfere with proper and accurate grinding.

One method for making radioactive diamonds is disclosed and claimed in my copending application Serial No. 562,585, filed January 31, 1956, and assigned to the same assignee as the present invention, now US. Patent 2,996,763, issued August 22, 1961. In accordance with this method, diamonds having radioactivity are prepared by heating at elevated temperatures and pressures, a mixture comprising a carbonaceou material, for instance, a non-diamond form or carbon, in the presence of a radioactive material, preferably a radioactive metal, and in the further presence of a metal of the type capable of forming diamond from the carbonaceous material. It was found that when employing a radioactive metal for making the above-described radioactive diamonds, the radioactivity appeared only on the surface layer of the diamond and apparently was not present in the core of the diamond. For many applications this may be sufiicient, but in a large number of applications, particularly Where testing of abrasives is important to determine the efficiency of the abrasive, there is a need for the radioactivity to be not only on the surface layer but also to be present in the matrix of the diamond and advantageously permeate the entire diamond.

Unexpectedly, I have discovered that I am able to make radioactive diamonds in which the radioactivity of the diamonds extends throughout the entire diamond, including the surface layer and matrix thereof, subjecting a radioactive carbonaceous material, such a radioactive non-diamond carbon, to elevated temperatures and pressures in the diamond-forming region in the presence Patented May 4-, 1&65

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of a metal or alloy conducive to the formulation of diamonds.

It is accordingly an object of the present invention to provide a diamond material which does not retain a charge of static electricity of any substantial period of time.

Another object of the present invention is to prepare diamond material of the type described having a radioactivity exceeding that of known diamond from a radioactive carbonaceous material such as radioactive nondiamond carbon.

It is a further object of the present invention to provide a radioactive diamond whose radioactivity is present not only on the surface layer thereof, but also permeates the entire matrix of the diamond as a result of radioactive carbon atoms introduced during production thereof.

The term radioactive carbonaceous material is used in the present application to refer to a carbonaceous material, for instance, non-diamond carbon, such as graphite, which has the property of spontaneously emitting alpha, beta, or gamma rays, or neutrons by the disintegration of the nuclei of the atoms of the carbonaceous material. As is well known, the radiation emitted by radioactive elements causes ionization of the medium surrounding in the radioactive material or the medium through which the alpha, beta, gamma rays, or neutrons pass. It is further understood that when, for example, air is ionized by rays from a radioactive material, the ionized air becomes, to some extent, a conductor of electricity. Thus, Where the diamond material of the present invention acquires a static charge, the radioactivity of the diamond material causes ionization of the air or other medium surrounding'the diamond material and this ionized air or other medium carries away the static charge from the surface of the diamond material, rendering the diamond material electrically neutral.

As can be seen from the description of the ionization of the medium surrounding the diamond materials of the present invention and the discharging of the static charge on the diamond material, the diamond material of the present invention is free from the problems associated with natural diamonds. Thus, since the diamonds of the present invention do not retain a static charge, they may be sorted without the difficulty caused by any static charge on the material. In addition, when the diamonds of the present invention are used as bearings, they will have no tendency to attract dust or other abrasive particles to their surface. Furthermore, when the diamond material of the present invention is employed as abrasive material in abrasive wheels, there is again no tendency for any static charge to accumulate on the diamonds and therefore there is no tendency for the grinding wheel to attract particles of metal which may interfere with the accurate use of the grinding wheel.

Various catalysts may be employed in the preparation of the radioactive diamonds of the present invention. Generally, these catalysts comprise metals or alloys of metals which have been found to besignificantly eifective in converting carbonaceous materials to diamond. Included among the metals which may be employed as a catalyst for making the radioactive diamonds may be 7 mentioned, for instance, iron, cobalt, nickel, rhodium,

of converting the carbonaceous material to diamond. lneluded among such alloys may be alloys of metals selected from the class consisting of the above metals, many examples of such alloys being given in Strong Patent 2,947,- 609, issued August 2, 1960.

The pressure at which the radioactive diamonds may be made will depend upon various considerations, such as temperature, the particular radioactive carbonaceous material which may be used, the catalyst employed, and whether the catalyst and alloy are individual metal, etc. Since it is known that the measurement of pressures in the high ranges required for making diamonds is relatively difilcult, it will be apparent that no exact standard for effecting these measurements can be stated. However, prior art workers have attempted to rely on such pressure measurements by determining the phase changes which occur in such metals as bismuth, thallium, cesium, and barium. If one employs as standards the phase changes which result in these metals by determination of changes of electrical resistance, it will be found that pressures on the order of from 40,000 to 100,000 atmospheres or more ordinarily are found to be the range of pressure useful in making of the diamonds in the present invention. Regardless of the standards which are used for measuring the pressures under which the radioactive carbonaceous material undergoes transformation to diamond, the pressure range will be within the limits recited above and advantageously within the range of about 42,000 to about 75,000 atmospheres.

The temperatures at which diamonds of the present invention may be formed can also be varied widely in accordancewith the factors which will cause variation in the pressures. the range of about 1200 C. toabout 2200 C. or higher. Caution should be exercised that in making diamonds, the actual temperature and pressure is that required for operating within the diamond-forming region and that any changes of temperature or pressure will not be used which in any Way adversely affect the desired result.

The process of the present invention may be carried out in any type of apparatus capable of producing the pressures required at the temperature required. However, I prefer to employ apparatus of the type described in the patent of H. T. Hall, US. 2,941,248, issued June 21, 1960, and assigned to the same assignee as the present invention. The apparatus disclosed in the aforementioned Hall patent is a high pressure device for insertion between the platens of a hydraulic press. The high pressure device consists of an annular member defining a substantially cylindrical reaction area, and two conical, piston-type members designed to fit into the substantially cylindrical portion of the annular member from either side of said annular member. A reaction vessel which fits into the annular member may be compressed by the two piston members to reach the pressures required in the practice of the present invention. The temperature required is obtained by any suitable means, such as, for example, by induction heating, by passing an electrical current through the reaction vessel, or by winding heating coils around the reaction vessel.

The reaction vessel or cylinder described in the above Hall patent may be formed of any of the conventional materials of construction or of graphite. Where the reaction vessel is constructed of a metal, it is convenient to employ one of the metals which acts as a catalyst in the present invention. This vessel may then be filled with the radioactive non-diamond carbon and compressed so that the metal present in the vessel will serve as a catalyst for the transformation to diamond. Where the reaction chamber or vessel is formed of radioactive graphite, it may be filled with the catalyst material and the compression of the graphite vessel with the catalyst at the pressures and temperatures required by the present invention results in the transformation of the radioactive non-diamond carbon into the radioactive diamond of the Generally, I employ temperatures within &

present invention. Regardless of the material of construction of the reaction vessel, the radioactive non-diamond carbon and the catalyst may be admixed inside the vessel. Thus, mixtures of powdered radioactive graphite and powdered catalyst may be employed as a charge in the reaction vessel and the compression of the vessel and charge at the required temperature effects transformation to radioactive diamond material.

In the preferred embodiment of my invention, l employ a reaction vessel comprising a cylinder of graphite (which may or may not be radioactive) having a hollowedout cylindrical center portion, the axis of the center portion being coaxial with the axis of the reaction vessel. Into this graphite reaction vessel are placed cylinders or disks of radioactive graphite and the catalyst. This reaction vessel is sealed at its end by metallic disks which may be formed of any material of construction inert under the conditions of the reaction or it may be formed of a catalyst metal. This reaction vessel is then placed in the apparatus described in the above-mentioned Hall patent and subjected to the elevated temperature and pressure required to effect the transformation to radioactive diamond material. Alternatively, instead of employing a reaction vessel, a cylinder of radioactive carbonaceous material, such as radioactive graphite, may be sandwiched between two disks formed of a metal which acts as a catalyst for the transformation. The sandwich is then placed in the high pressure apparatus and subjected to the conditions required to cause the transformation to radioactive diamond material. As a further alternative, a metallic reaction vessel may be filled with a radioactive carbonaceous material in powder or solid form and the catalyst for the reactionmay be supplied by admixing it with the powdered radioactive carbonaceous material or by forming end disks of either of the catalyst materials to seal the reaction vessel. This assembly is then subjected to the pressures and temperatures required. A reaction vessel may also be formed by compressing a mixture of radioactive non-diamond carbon and catalyst until a cylinder is formed which fits into the substantially cylindrical aperture described in the above-mentioned Hall patent.

Again, this latter apparatus may be employed in the usual manner at elevated temperatures and pressures to effect the transformation to radioactive diamond material.

The annexed drawing illustrates a preferred embodiment of the invention.

In carrying out the process of the present invention, the temperature in the reaction vessel may be measured by a thermocouple located adjacent the reaction vessel previously mentioned. In carrying out this process, the time of reaction required to convert the reaction mixture into radioactive diamond material may vary from a few seconds up to several minutes or more depending on the particular charge to the reaction vessel. However, regardless of the charge to the reaction vessel, I have found that the radioactive diamond material of the present invention is formed within two to seven minutes. instead of observing the time which the reaction vessel is maintained at the reaction temperature, I may alternatively observe the progress of the reaction by the method described in the patent of H. T. Hall, U.S. 2,947,608, issued August 2, 1960, and assigned to the same assignee as the present invention. By the process of this Hall patent, the mixture of radioactive non-diamond carbon and catalyst is first subjected to a pressure of at least about 40,000 to 60,000 atmospheres (depending on the catalyst used) and subsequently sufiicient heat is applied to the mixture for a suflicient time to cause an inflection in the electrical resistance of the mixture. When the inflection in the electrical resistance of the mixture occurs, the transformation of the mixture to the radioactive diamond material of the present invention has begun to occur.

The radioactive carbonaceous materialswhich may be employed in the practice of the present invention include all of the man-produced radioactive isotopes of carbonaceous materials, such as carbon 14, radioactive graphite (made radioactive by bombardment, for instance, in an atomic reactor, with neutrons, with energetic particles or with high energy radiation).

In preparing the radioactive diamond material of the present invention, the proportions of the ingredients employed are not critical, and I have found that suitable radioactive diamond material can be formed regardless of the relative concentrations of the radioactive non-diamond carbon and the catalyst. The presence of nonradioactive carbonaceous material is not precluded as long as the amount of such material does not adversely affect obtaining the radioactive diamond. In the preferred embodiment of this invention, it is preferred to have the ingredients present, on a weight basis, in the proportions of about 0.1 to parts or more of catalyst per part of radioactive non-diamond carbon. Regardless of the proportions of ingredients and the physical location of the various ingredients in the reaction vessel, it has been found that the resulting product comprises diamond having a radioactivity extending throughout its mass as well as on its surface.

Since the radioactive materials of the present invention are similar to other radioactive materials, some degree of care is necessary in handling the products of the present invention. The degree of care required in handling the radioactive diamond materials is similar to that degree required in handling the radioactive corbonaceous material itself.

The following examples are illustrative of the practice of my invention and are not intended for purposes of limitation.

Example 1 In this example, a solid cylinder of radioactive graphite (machined from a block of graphite which had been made radioactive by being subjected to the radiation flux in an atomic pile at Oak Ridge, Tennessee, US. Atomic Installation) 0.295 inch in diameter and 0.75 inch long, was encased in a thin walled nickel tube (as catalyst) which was in turn encased in an alumina insulating sheath which was enclosed in a carbon tube heater. This assembly, which is more particularly illustrated in the attached drawing, was placed in the usual pyrophyllite sample holder as shown in the above-mentioned Hall Patent 2,941,248, and subjected to a pressure of about 65,000 to 75,000 atmospheres at a temperature of about 1500 C. for 27 minutes. The capsule was cooled, and removed from the press. Excess carbon and nickel were dissolved from the pressed slug by the use of hot sulfuric acid to which KNO had been added, and thereafter the mass was dissolved in aqua regia leaving behind crystals of diamondwhich were identified as such by their refractive index and cubic or octahedral crystal habit. The radioactive diamonds thus obtained were tested for radioactivity (by measurement with a Geiger counter) and found to be radioactive not only on their surface but also throughout the mass of the diamonds. Most of the radioactivity was in the form of gamma rays. Repeated treatments with acids did not diminish the radioactivity. This established clearly that the radioactivity was being released from inside the diamonds. Even when the diamonds were crushed to a powder, the radioactivity could readily be determined throughout the powdered mass.

Example 2 0.45 inch. Into this tube was charged a mixture of radioactive graphite powder (made from the same source as used in Example 1 and the powder was confined within the tube by end plugs made of an alloy of nickel and chromium (80 percent nickel and 20 percent chromium) having a diameter of-0.09 inch and about 0.125 inch in height. These nickel-chromium alloy plugs were the catalyst for conversion of the radioactive graphite to diamond. The capsule was pressed at a pressure of about 55,000 to 56,000 atmospheres at a temperature between 1250 to 1350 C. for about 6 minutes. The slug thus obtained was dissolved in acids and cleaned up similarly as was done in Example 1 to yield a good quantity of diamonds which exhibited a perceptable degree of radioactivity. Employing a scintillation counter, it was found that the background average was about 257 counts per minute while the diamond plus background average was about 382 counts per minute.

Although the catalyst materials which may be employed in the practice of the present invention have been described only in terms of pure metals, or alloys of these metals, it should be understood that compounds of these metals which decompose under the conditions of the reaction may also be employed. Thus, compounds of the catalyst which decompose into pure metal under the condition of the reaction include, for example, the carbides, sulfides, carbonyls, cyanides, ferrotungstates, ferritungstates, oxides, nitrides, nitrates, hydrides, chlorides, mo lybdates, arsenates, acetates, oxalates, carbonates, borates, chromates, phosphates, phosphides, permanganates, silicates sulfates, tungstates, etc. Specific examples of decomposable compounds usable as catalysts in the present invention include ferrous sulfide, iron carbonyls, palladium chloride, chromium carbide, tantalum hydride, sodium fluoride, nickel permanganate, cobalt acetate, nickel sulfate, etc. Obviously other catalysts, both metal and alloy may be employed, many examples of which have been given above, without departing from the scope of the invention.

Although the above examples have described the reaction of the present invention only at certain pressures and temperatures, it should be understood that any pressure in excess of 40,000 atmospheres is satisfactory for the practice of this invention. My preferred pressure range is from about 46,000 to 85,000 atmospheres. Similarly, my temperature range may vary from 1200 C. to 2000 C., and preferably from about 1400 C. to 1800 C. Other examples of catalyst, temperature, and pressure which may be employed can be found in the foregoing US. Patents 2,947,610, 2,947,609, and 2,947,611.

The radioactive diamond material or" the present invention is useful for all of those uses to which diamonds are commonly put. In addition, this radioactive diamond material is particularly useful as the abrasive medium in an abrasive wheel. In addition, the radioactive diamond material of the present invention is particularly suitable for use as a bearing surface in applications where the bearing must withstand an extremely high load and where the dust which would be attracted by an ordinary diamond bearing would ruin the effectiveness of the bearing action. Thus, the radioactive diamond materials of the present invention are particularly suitable as jewels for use in clocks, timers, and the like where dust might interfere with the accuracy of the device.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A process for making man-produced radioactive diamonds having a radioactivity which is both (1) coextensive with the mass of the diamond and (2) exceeds that of known diamond, which process comprises heating at a temperature in excess of 1200 C. and at a pressure in excess of 40,000 atmospheres in the diamond-forming region, a man-produced carbonaceous material rendered radioactive by bombardment with high energy radiation in combination with a catalyst for diamond formation.

2. The process as in claim 1 in which the man-produced radioactive isotope is graphite made radioactive by subjectingthe graphite to the radiation flux in an atomic pile.

- 3. The process as in claim 1 in which the catalyst is an alloy of nickel and chromium.

4. The process as in claim 1 in which the catalyst is nickel.

5. Man-produced diamond having a radioactivity both on its surface and throughout its mass in which radioactive carbon atoms have been introduced during the production of said diamond, the said radioactivity being substantiaily greater than that of known diamond.

References Cited by the Examiner UNETED STATES PATENTS 2,315,845 4/43 Ferris 252301.1

0 3 2,947,610 8/60 Ha1ieta1. 23- 209.1

FOREIGN PATENTS 1,009,251 3/52 France.

5 OTHER REFERENCES Freedman: J. Chem. Physics, 20, 1040 (1952). Bradford: Radioisotopes in Industry, pp. 24, 84, 279, Reinhold Publ. Co., N.Y., 1953.

10 MAURICE A. BRINDISI, Primary Examiner.

Claims

1. A PROCESS FOR MAKING MAN-PRODUCED RADIOACTIVE DIAMONDS HAVING A RADIOACTIVITY WHICH IS BOTH (1) COEXTENSIVE WITH THE MASS OF THE DIAMOND AND (2) EXCEEDS THAT OF KNOWN DIAMOND, WHICH PROCESS COMPRISES HEATING AT A TEMPERATURE IN EXCESS OF 1200*C. AND AT A PRESSURE IN EXCESS OF 40,000 ATMOSPHERES IN THE DIAMOND-FORMING REGION, A MAN-PRODUCED CARBONACEOUS MATERIAL RENDERED RADIOACTIVE BY BOMBARDMENT WITH HIGH ENERGY RADIATION IN COMBINATION WITH A CATALYST FOR DIAMOND FORMATION.