WO1983000038A1

WO1983000038A1 - Production of ultra-hard particles

Info

Publication number: WO1983000038A1
Application number: PCT/US1981/000866
Authority: WO
Inventors: Frederic A French; Douglas A French
Original assignee: French, Frederic, A.; French, Douglas, A.
Priority date: 1981-06-22
Filing date: 1981-06-22
Publication date: 1983-01-06
Also published as: JPS58501430A; EP0081487A4; EP0081487A1

Abstract

The production of an ultra-hard particle composed substantially of carbon as the dominant element is taught. The ultra-hard particle is the product of the reaction of a metal carbide selected from the group consisting of Al4C3 and Be2C with a member selected from the group consisting of CHnXAY(4-n)-A, C2Hn'XA'Y(6-n')-A', C2Hn''XA''Y(4-n'')-A'' and X2 wherein X and Y are different halogens selected from the group consisting of chlorine, bromine, iodine and fluorine, and wherein A is an integer from 0 to 4, A' is an integer from 0 to 6 and A'' is an integer from 0 to 4, and wherein n is an integer from 0 to 4, n' is an integer from 0 to 6 and n'' is an integer from 0 to 4, wherein A, A', A'', n, n' or n'' is the same integer in any particular member selected and wherein n + A = 4, n' + A' = 6 and n'' + A'' = 4.

Description

Production of Ultra-Hard Particles

Technical Field

This invention relates to the production of ultra-hard particles composed substantially of carbon as the dominant element.

Background Art

Numerous attempts were made prior to 1955 to convert various forms of carbon, including graphite, into its diamond form or other ultra-hard carbonaceous forms. None of these attempts have been adequately substantiated. A valid diamond synthesis was reported in 1955 but details were not revealed until 1959 (Nature 184:1094-8, 1959). At temperatures of 1200° to 2400^βC and pressures ranging from 55,000 to 100,000 atmospheres or^* more, carbon is converted into its diamond form in the presence of transition metals (chromium, manganese, iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium and platinum) or tantalum. Higher pressures are required at higher temperatures.

- Rather esoteric means were also investigated in the quest for a more convenient graphite to diamond conversion. As reported in Phys. Rev. Letters _7:367 (1961), it was taught that diamond might be obtained in less than a microsecond by the action of extremely high pressure explosive shock waves on graphite. In fact, diamonds were actually recovered from carbon subjected to an explosive shock. Epitaxial methods have also been reported where the decomposition of gases, such as methane, ethane and propane in contact with diamond powder was found to

MPI promote diamond growth. However, in performing epi¬ taxial techniques, temperatures in the vicinity of 1300°K. and pressures on the order of 10~ to 10^~ atmospheres were found to be required. It is obvious that the prior techniques employed in the fabrication of synthetic diamonds and other ultra-hard carbonaceous materials are at best cumber¬ some and expensive to carry out. The maintenance of any extremes in temperature and pressure requires enormous energy and sophisticated equipment, which in turn detracts from the widespread commercialization of synthetic diamond fabrication.

Disclosure of Invention

It is an object of the present invention to produce ultra-hard carbonaceous particles while elimi¬ nating the drawbacks experienced in prior art produc¬ tion techniques.

It is a further object of the present invention to produce ultra-hard carbonaceous particles without the necessity for employing extreme temperatures and pressures which are required by the prior art.

It is yet a further object of the present inven¬ tion to produce ultra-hard carbonaceous particles from sources other than graphite or amorphous carbon. It is yet a further object of the present inven¬ tion to produce ultra-hard carbonaceous particles by means of high thermodynamic drive carbon yielding reactions.

It has been found that ultra-hard carbonaceous particles can be produced from the reaction of a metal carbide such as aluminum carbide (Al.C.) or beryllium carbide (Be-C) when reacted with halogens and related halocompounds. Care has been exercised to minimize or eliminate the presence of substances which would react parasitically with carbon or the reactants, such as oxygen and oxygenated compounds with oxidizing power. The reactions have tended to produce very hard and strong, covalently bonded lattice structures under highly exothermic conditions at moderate temperatures. The reactions have been accomplished at relatively low temperatures (a few hundred degrees C) and at low pressures (a few atmospheres or less). It has also been an objective to employ a system having no solvency capability for carbon while carrying out the reactions of the present invention at favorable (spontaneous) energies on the order of 100 times as great or greater, per gram atom, as the diamond-graphite interconversion energy. Under proper conditions, the metal carbides are quite reactive having carbon atoms that are indi¬ vidually isolated. In actual reactions which have been carried out, the reaction energy has been found to be enormously favorable and more than 100 times as great per cartfcm atom as the graphite-carbon inter- conversion energy.

Best Mode for Carrying Out the Invention

It has been found that the aluminum carbide or the beryllium carbide used in the invention must be rela¬ tively free of impurities, particularly carbon. If free carbon is present in the metal carbide, graphite nucleation may occur and this greatly diminishes the yield of ultra-hard carbon particles. For this reason, aluminum carbide or beryllium carbide starting materials are selected which possess slightly greater stoichiometric aluminum or beryllium to carbon ratios than are indicated by the formulae A1.C-. or Be₂C. The physical forms of the aluminum carbide or beryllium carbide are not absolutely critical in carrying out the present invention. However, the various reactions

OM?l occur more rapidly with finely divided particles in the 50-500 mesh range.

The reaction is carried out in a hot melt system. The melt system is comprised of a molten solution of more than one metal halide wherein the metals are selected from the group consisting of Groups I, II and III of the periodic table and the halides are selected from the group consisting of chlorine, bromine, iodine and fluorine. The presence of oxidizing anions such as sulfates, nitrates and carbonates and hydrogen contain¬ ing anions such as hydroxides should be avoided in the melt system.

The melt system performs several valuable func¬ tions in carrying out the present invention. Firstly, it provides for a reaction medium at a temperature substantially below temperatures at which diamond to graphite reversion occurs at a measurable rate. Secondly, it acts as a heat sink. For example, a melt system comprised of lithium chloride (LiCl) combined with aluminum chloride (AlCl^) is fluid at a temperature as low as 150^CC. Ideally, the melt system can be composed of an aluminum halide (A1X.,, where X represents Cl, Br or I although some F may also be present), complexed with one or more metallic halides such as alkaline halides and alkaline earth halides.

When lithium chloride is used with aluminum chloride at a molar ratio LiClrAlCl-, greater than one, the predomi- nant melt species are L —i , A1C1.—, and Cl-. If the ratio is high, a solid LiCl phase or Li^AlCl_^ may be present. If the molar ratio of LiCl:AlCl-. is less than 1:1, including as high as approximately 1:2, the pre¬ dominant melt species are Li^""^", A1C1, , and Al-Cl., . Br may be substituted wholly or partially for Cl. Some fluorine, iodide or iodine may be present in free form or in the aluminum-containing anions in either the

OMPI initial melt or the final melt system. Such a melt system also exhibits substantial solvent and penetrant capability for A1₂0₃ and hydroxy aluminous complexes which naturally form on the surface of aluminum or aluminum carbide in the presence of oxygen or water. A coating of A1_0₃, or bound aluminum atoms bearing OH groups, is extremely tenacious and provides a substantial barrier to the carrying out of the present invention. Thus, the melt system, to function in the present invention, must have solvency capability for aluminum oxide, aluminum oxygen complexes and hydrogen- containing aluminum oxygen complexes. The melt system must also have the ability to wet the metal carbide surface and must have the ability not to destroy the carbon halide reactants or the metal carbide. It must also be substantially anhydrous and substantially free of hydroxyl groups.

The present invention can be carried out at pressures betvfeen approximately 0.1 to 100 atmospheres. As an upper limit, the reaction should take place at a pressure less than the pressure where diamond would be the stable form of carbon if the reaction was allowed to reach equilibrium, approximately 20,000 atmospheres. However, above 100 atmospheres, there is little benefit to the reaction while rather sophisticated equipment is necessary to maintain such high pressures. The optimum temperature range would depend upon the actual compounds used to make up the melt and as primary reactants. As a general rule, temperatures between approximately 100" to 700°C are to be used in carrying out the reaction noting that the temperature must be high enough to at least maintain the melt system in a liquid state.

The following examples demonstrate a number of specific embodiments of the invention.

OMPI Example 1 The melt system is formed by the preparation of a solution of mixed halides which are heated for a suf¬ ficient time to insure that substantially all hydrogen and hydrogen chloride have been purged from the system. In this example, 24.5 g of anhydrous LiCl was heated in a 500 ml flask at approximately 130-140°C for two days. Approximately 67 g of anhydrous A1C1-. was then added under an argon blanket, the temperature elevated to approximately 250°C and the mixture stirred for 35 minutes at which time very little HC1 was evident.

After the melt system was formed, the metal carbide was added. In this example, 2.9 g of Al.C, as added and held briefly. The halogen-containing reactant can then be added to the solution fay stepwise additions until an excess is present. In this example, 1 ml portions of CC1. were added every ten minutes to a total of 10 is followed by further 2 ml additions at ten minute intervals. The temperature was main- tained at approximately 265°C throughout the CCL. additions and the suspension allowed to cool slightly thereafter.

The melt suspension which was formed according to the following reaction: ^A14^C3 ^{÷ 3CC1}4 ^^{6C + 4Al :ι}-3 was washed by incorporating the suspension in 10 is of concentrated HC1 and 200 mis H_?0. The suspension was boiled for 50 minutes. Alternatively, this suspension could have been incorporated in aqueous solutions of non-oxidizing acids such as H-SO. or CH_,S0_,H or even nonaqueous systems such as nitrobenzene. The suspension was then filtered and the solids washed in 100 mis of 1:10 HC1 followed by three 100 ml water additions, two 40 ml isopropyl alcohol washes, and concluding by four 25 ml acetone washes. The product was dried, resulting in ultra-hard carbonaceous particles.

OMPI Exa ple 2 To the same melt system as developed in Example 1 was added, in addition to the aluminum carbide, approx¬ imately 2 g of KBr. CC1. remained as the halogen reactant and was added in a stepwise fashion much, as was done in Example 1. The final ultra-hard carbon¬ aceous product was washed and dried, again, as was done in Example 1.

Example 3 The melt system was the same as Example 1 while the reactants included aluminum carbide and CBr 4■ . More specifically, after the l₄C₃ was added to the hot melt, 1 g of CBr. was added followed by 10 is of CC1₄ in 0.5 ml portions every five minutes. The ultra-hard carbonaceous product was washed as done in Example 1.

Example 4

The melt 'system was prepared as in Example 1 and aluminum carbide was chosen as a first reactant. The remaining reactants included 1 g of CBr₄ and a total of 13.6 g of C-Cl.- added in 1.7 g portions every five minutes. The ultra-hard carbonaceous particles were washed and dried as in Example 1 producing the final product according to the following reaction:

2C₂Clg + 1₄C₃ > 4A1C1₃ + 7C.

Example 5

To the melt system prepared as in Example 1 was added 2.9 g of Al.C, and 2 g of FeS in 18 mg of NaCl as a nucleating agent. These latter ingredients were mixed in the melt system for approximately ten minutes followed by the addition of 1 g of CBr₄ and

7 g of C₂Cl_fi while allowing the fluid reaction mixture to reflux for approximately 65 minutes at 240°C. Three

MPI more additions of C₂Cl_g were made over the next 10 minutes and the suspension was refluxed again for 20 minutes. A final 3 g of C₂Cl_fi was added over a 20 minute interval and the suspension again heated for 30 minutes. The ultra-hard carbonaceous particles were then washed and dried as in Example 1.

Example 6

The melt system was prepared as in Example 1 to which was added 2.9 g of 1₄C₃ and 20 rag of ten percent FeS in NaCl as a nucleating agent. The fluid reaction mixture was stirred at approximately 240^βC for 15 minutes after which a total of 24 g of CBr₄ was added in 2 g portions every 5 minutes. The reaction proceeded according to the following equation: ^A14^C3 ^{+ 3CBr} > 4AlBr₃ + 6C and the ultra-hard carbonaceous particles were filtered, washed and dried according to the manner employed in Example 1. *

Example 7 The melt system was formed by mixing 10 g of powdered KBr, 21 g of LiCl and approximately 67 g of A1C1₃. The mixture was heated to approximately 240°C and stirred for 1 hour under argon. To the melt system was added 20 mg of HgCl₂ as a possible catalyst to which 2.9 g of Al₄C₃ was added. After waiting 5 minutes, ' ap -p mroximatelJy 1 ml of C2,C14, was added to the hot melt. The solution was allowed to reflux and, after 10 minutes, 1 g of CBr₄ was added. Then, at 10 minute intervals, 1 ml p ^**■ortions of C2.C14. were added until a total of 9 ml were in the system. The reactants were heated for 45 minutes, filtered, washed and dried as in Example 1. The reaction proceeded according to the following equation:

OMPI A1₄C₃ + 3C₂C1₄ 4A1C1₃ + 9C forming ultra-hard carbonaceous particles.

Example 8

The melt system of Example 1 was prepared and to it was added 2.9 g of Al₄C₃ and 20 g of ten percent

FeS in NaCl as a nucleating agent. The second reactant was made up of 8 ml Br₂ which was added in 0.4 ml portions at 5 minute intervals. The reaction products were filtered, washed and dried as in Example 1 produc- ing a product according to the following equation:

A1 4.C3-, + 6Br2 ■ '> 4AlBr3-, + 3C.

Example 9 A melt system was prepared according to Example 1 with the addition of 5 g of KI. To this was added approximately 2.88 g of 1 ., at 250°C which was reacted with CC1₄ added to the system every five minutes in 0.5^* ml amounts totaling 20 additions. The reaction produced ultra-hard particles which were filtered, washed and dried according to the procedure of Example 1.

Example 10 A melt system was prepared according to Example 1 with the addition of 5 g of NaF. To the melt system was added approximately 2.88 g of finely ground Al₄C₃ to which was added CC1₄ in 1 ml amounts every ten minutes totaling 12 additions. The reaction product was filtered, washed and dried according to.Example 1 producing the ultra-hard carbonaceous materials of this invention. Example 11 A melt system comprised of 42 g of LiCl and 134 g of A1C1₃ was prepared as per Example 1 to which 5.76 g of 1₄C₃ having a -270 mesh size was added. At a starting temperature of approximately 236^βC, Freon 11 (CC1₃F) was added in 1 ml amounts every five minutes totaling 23 additions. The reaction product was fil¬ tered, washed and dried according to Example 1 produc¬ ing the ultra-hard carbonaceous materials of the present invention.

Example 12 The melt system of Example 1 was prepared to which approximately 2.88 g of A1₄C₃ was added having a -270 mesh at 242°C. Chlorine gas was then bubbled into the hot melt system at a rate of 0.05 cubic feet per hour for 1/2 hour. The rate was then increased to 0.1 cubic feet per hour for the next 2-1/2 hours amounting to a total chϊOrine addition of 10.7 liters. The reac¬ tion product was filtered, washed and dried as was shown in Example 1 producing ultra-hard carbonaceous particles according to the present invention.

Example 13 A new melt system was prepared by placing 29.2 g of NaCl in a flask which was heated to 180°C under vacuum for 2 hours and which was allowed to stand overnight under full vacuum. With mechanical stirring under an argon blanket, 67 g of A1C1-. was added to complete the melt system. To this melt was added

2.88 g of l₄C₃ and, as a second reactant, 1 ml of CC1₄ was added every 10 minutes to a total of 13 additions. The temperature was maintained above 300°C producing a reaction product which was filtered, washed and dried according to Example 1 producing the ultra- hard carbonaceous particles of the present invention.

Example 14 A new melt system was prepared by placing 37.3 g of KC1 in a flask which was heated at full vacuum to 180°C for 2 hours. The KC1 was maintained at full vacuum overnight and, under mechanical stirring, 67 g of A1C1-. was then added to complete the melt. Approxi¬ mately 2.88 g of Al₄C₃ was then added, which was reacted with CC1₄ which was in turn added in 1 cc amounts every 10 minutes to a total of 13 additions. As in Example 13, the temperature was maintained above 300°C producing a reaction product which was filtered, washed and dried according to Example 1. The reaction produced ultra-hard carbonaceous particles according to the present invention.

Example 15

To the melt system prepared according to Example 1 was added 2.88 g ³ of A14.C3- which was reacted with CC12_F2„ at a rate of 0".1 cubic feet per hour. The temperature was maintained between 230°-245°C while the CC1_F₂ was bubbled into the system for 2 hours. At the end of these additions, the reaction product was filtered, washed and dried according to Example 1 yielding ^'ultra- hard carbonaceous particles according to the present invention.

Example 16

A melt system according to Example 1 was prepared. At a temperature of approximately 247^βC, 2.88 g of Al₄C, was added and reacted with CC1_F_ which was introduced into the hot melt system at a rate of 0.1 cubic feet per hour for 4 hours. The temperature was maintained at approximately 238°C producing a reaction product which was filtered, washed and dried and which was in the nature of ultra-hard carbonaceous particles. Example 17 A melt system according to Example 1 was prepared. To this was added approximately 2.9 g of A1₄C, and 20 mg of 10 percent FeS in NaCl, which was heated for an additional 15 minutes. A second reactant comprising CHBr₃ was added in 0,5 ml intervals every five minutes to a total of 7.0 ml. The reaction product was fil¬ tered, washed and dried producing ultra-hard carbona¬ ceous particles according to the following equation: Al 4.C3, + 4CHBr3-, λ ' 4AlBr3_, + 6C + CH4.

Example 18 To the melt prepared according to Example 1 was added 1.5 g of 1₄C₃ and 20 mg of FeS in NaCl. A second reactant comprising CH-I- was added every five minutes in 0.5 ml amounts with refluxing until a total of 5 ml had been added. The product was then washed and dried producing ultra-hard carbonaceous particles according to tfhe following reaction:

6CH₂I₂ + 1₄C₃ 4A1I₃ + 3CH₄ -_- 6C As can be seen from the above working examples, ultra-hard carbonaceous particles can be produced as the product of a reaction of a metal carbide selected from the group consisting of l₄C₃ and Be~C with a member selected from the group consisting of ^CHn^XA^Z(4-n)-A' ^C2^Hn^{,X ,Y}(6-n' )-A- ' ^C2^Hn"^XA"^Y (4-n^π}-A^π and X₂ wherein X and Y are different halogens selected from the group consisting of chlorine, bromine, iodine and fluorine, and wherein A is an integer from 0 to 4,

A^* is an integer from 0 to 6 and A" is an integer from 0 to 4, and wherein n is an integer from 0 to 4, n' is an integer from 0 to 6 and n" is an integer from 0 to

4, wherein A, A', A", n, n' or n^π is the same integer in any particular member selected and wherein n + A = 4,

OMPI n' + A' = 6 and n" + A" = 4. In actual reactions which were carried out, the reaction energy was found to be enormously favorable and more than 100 times as great per carbon atom as the graphite-carbon interconversion energy. The need for extremes in either temperature or pressure, conditions which were employed by synthetic diamond and other hard carbonaceous particle fabrica¬ tors, have been completely eliminated in practicing the present invention. The reaction was carried out in a hot melt system comprised of a molten solution of more than one metal halide wherein the metals are seldcted from the group consisting of Group I, Group II and Group III metals of the periodic table and the halides are selected from the group consisting of chlorine, bromine, iodine and fluorine. The present invention also contemplates the use of nucleating agents with lattice constants as close to that of diamond. For example, very fine particles of FeS, Cu, of diamond itself may be employed. The present invention also contemplates the use of a catalyst such as I₂.

Each of the ultra-hard carbonaceous products produced according to the above-recited examples was tested for hardness and corresponding abrasiveness. The commonly used Moh's Scale from 1-10, where 1 is talc, 7 is quartz, 9 is corundum and 10 is diamond, is purely a ranking by scratch ability and has no relative quantitative significance. In some grinding tests, diamond is at least 100 times as hard as corundum. When one places a small amount of powdered abrasive on a glass slide, moistens the powder, rubs this against another glass slide for a few seconds, washes the slide and then observes the results under a microscope by reflective light, marked quantitative and qualitative differences between abrasive materials are notable.

OMPI Corundum or carborundum as fine grits or powders yield, at most, short grooves. These abrasives crumble relatively rapidly and the glass slide quickly assumes a frosted appearance. Fine diamond grits and the carbonaceous powders of the present invention behave totally differently and yield long, highly character¬ istic, meteoric grooves. Each of the hard carbonaceous products of the above-recited examples displayed at least some tendency to yield these characteristic meteoric grooves when tested.

Claims

1. Ultra-hard particles composed largely of carbon on an atomic basis comprising the product of the reaction of a metal carbide selected from the group consisting of Al₄C₃ and Be₂C with a member selected from the g³roup consisting³ of CHnXA,Y(,4,,-n).-A,,

^C2^Hn'^XA'^Y(6-n-)-A" ^C2^Hn"^XA^»Y{4-n" )-A^{» and X}2 ^{wherein X} and Y are different halogens selected from the group consisting of chlorine bromine, iodine and fluorine, and wherein A is an integer from 0 to 4, A' is an integer from 0 to 6 and A" is an integer from 0 to 4, and wherein n is an integer from 0 to 4, n¹ is an integer from 0 to 6 and n^π is an integer from 0 to 4, wherein A, A', A", n, n¹ or n" is the same integer in any particular member selected and wherein n + A = 4, n^* + A' = 6 and n" + A" = 4.

2. The ultra-hard particles of claim 1 wherein said reaction^•'is carried out in a hot melt system.

3. The ultra-hard particles of claim 2 wherein said hot melt system is comprised of a molten solution of more than one metal halide wherein the metals are selected from the group consisting of Group I, Group II and Group III metals of the periodic table and the halides are selected from the group consisting of chlorine, bromine, iodine and fluorine.

4. The ultra-hard particles of claim 1, 2, or 3 wherein the hot melt system is substantially free of oxidizing anions and hydrogen containing anions.

5. The ultra-hard particles of claim 1 wherein the metal carbide is Al 4.C3,.

6. The ultra-hard particles of claim 2 wherein the hot melt system exhibits substantial solvent capability for A1₂0₃

7. The ultra-hard particles of claim 2 wherein the hot melt system is substantially anhydrous and substantially free of hydroxyl groups.

8. The ultra-hard particles of claim 1 wherein a crystal nucleating agent is included in the reactants.

9. The ultra-hard particles of claim 8 wherein the crystal nucleating agent is a member of the group consisting of FeS, Cu and diamond.

10. The ultra-hard particles of claim 3 wherein one of the metal halides comprises A1X₃, wherein X is selected from the group consisting of Cl, Br, I and F.

11. The ultra-hard particles of claim 10 wherein the metallic halide is selected from the group consist¬ ing of alkaline halides and alkaline earth halides.

12. The ultra-hard particles of claim 11 wherein said hot melt comprises a molten solution of A1C1- and LiCl.