Note: Descriptions are shown in the official language in which they were submitted.
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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 2400C and pressures ranging from 55,000 to 100,000
atmospheres or more, carbon is converted into its
diamond ~orm 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
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promote diamond growth. However, in performing epi-
taxial techniques, temperatures in the vicinity of
1300K. and pressures on the order of 10 3 to 10 4
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 (Al4C3) or beryllium
carbide (Be2C) when reacted with halogens and related
halocompounds. Care has been exercised to minimize or
eliminate the presence of substances which would rèact
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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 carbon atom as the graphite-carbon inter-
conversion energy.
Best Mode for Carr in Out the Invention
Y 9
It has been found that the aluminum carbide or theberyllium 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 Al4C3 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
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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 (AlCl3) is fluid at a
temperature as low as 150C. Ideally, the melt system
can be composed of an aluminum halide (AlX3, 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 LiCl:AlCl3 greater than one, the predomi-
nant melt species are Li+, AlCl4 , and Cl . If the
ratio is high, a solid LiCl phase or Li3~lCl6 may be
present. If the molar ratio of LiCl:AlCl3 is less than
1:1, including as high as approximately 1:2, the pre-
dominant melt species are Li+, AlCl4 , and Al2Cl7 .
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
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initial melt or the final melt system. Such a melt
system also exhibits substantial solvent and penetrant
capability for Al2O3 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 Al2O3, 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 between 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 700C 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.
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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 130-140C for two days.
Approximately 67 g of anhydrous AlC13 was then added
under an argon blanket, the temperature elevated to
approximately 250C and the mixture stirred for 35
minutes at which time very little HCl was evident.
After the melt system was formed, the metal
carbide was added. In this example, 2.9 9 of Al4C3
as added and held briefly. The halogen-containing
reactant can then be added to the solution by stepwise
additions until an excess is present. In this example,
1 ml portions of CCl4 were added every ten minutes to
a total of 10 mls followed by further 2 ml additions at
ten minute intervals. The temperature was main-
tained at approximately 265C throughout the CCL4
additions and the suspension allowed to cool slightly
thereafter.
The melt suspension which was formed according to
the following reaction:
A14C3 + 3CC14 >6C + 4AlCl3
was washed by incorporating the suspension in 10 mls of
concentrated HCl and 200 mls H2O. The suspension was
boiled for 50 minutes. Alt~rnatively, this suspension
could have been incorporated in ~queous solutions of
non-oxidizing acids such as H2SO4 or CH3SO3H or even
nonaqueous systems such as nitrobenzene. The suspension
was then filtered and the solids washed in 100 mls of
1:10 HCl 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.
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Example 2
To the same melt system as developed in Example 1
was added, in addition to the aluminum carbide, approx-
imately 2 g of XBr. CC14 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 CBr4. More
specifically, after the A14C3 was added to the hot melt,
1 g of CBr4 was added followed by 10 mls 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 C2C16 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:
2C2C16 ~ A14C3 ~4A~C13 + 7C.
Example 5
To the melt system prepared as in Example 1 was
added 2.9 g of A14C3 and 2 mg 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 C2C16 while allowing the fluid reaction mixture
to reflux for approximately 65 minutes at 240C. Three
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more additions of C2C16 were made over the next 10
minutes and the suspension was refluxed again for 20
minutes. A final 3 g of C2Cl6 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 Al4C3 and 20 mg of ten
percent FeS in NaCl as a nucleating agent. The fluid
reaction mixture was stirred at approximately 240C 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:
Al C + 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
AlCl3. The mixture was heated to approximately 240C
and stirred for 1 hour under argon. To the melt system
was added 20 mg of HgCl2 as a possible catalyst to
25 which 2.9 g of A14C3 was added. After waiting 5
minutes, approximately 1 ml of C2Cl4 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 portions of C2Cl4 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: -
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g
Al4C3 + 3C2cl4 ~ 4AlCl3 + 9C
forming ultra-hard carbonaceou's particles.
Example 8
The melt system of Example 1 was prepared and to
it was added 2.9 g of Al4C3 and 20 mg 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:
Al C + 6Br - - > 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 Al4C3 at 250C which was
reacted with CCl4 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 systém
was added approximately 2.88 g of finely ground Al4C3
to which was added CCl4 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.
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Example 11
A melt system comprised of 42 g of LiCl and 134 g
of AlCl3 was prepared as per Example 1 to which 5.76
g of Al4C3 having a -270 mesh size was added. At a
starting temperature of approximately 236C, Freon 11
~CCl3F) was added in 1 ml amounts every five minutes
totaling 23 additions. The reaction product was fil-
tered, washed and drièd 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 242C. 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 chlorine 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 NaC1 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 AlCl3 was added to
complete the melt system. To this melt was added
2.88 g of Al4C3 and, as a second reactant, 1 ml of
CCl4 was added every 10 minutes to a total of 13
additions. The temperature was maintained above 300C
producing a reaction product which was filtered, washed
and dried according to Example 1 producing the ultra-
hard carbonaceous particles of the present invention.
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Example 14
A new melt system was prepared by placing 37.3 g
of KCl in a flask which was heated at full vacuum to
180C for 2 hours. The KCl was maintained at full
vacuum overnight and, under mechanical stirring, 67 g
of AlCl3 was then added to complete the melt. Approxi-
mately 2.88 g of Al4C3 was then added, which was
reacted with CCl4 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
300C 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 of A14C3 which was reacted with CC12F2
at a rate of 0.1 cubic feet per hour. The temperature
was maintained between 230-245C while the CCl2F2 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 247C, 2.88 g of Al4C3
was added and reacted with CC12F2 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 238C producing a reaction product
which was filtered, washed and dried and which was in
the nature of ultra-hard carbonaceous particles.
;
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Example 17
A melt system according to Example 1 was prepared.
To this was added approximately 2.9 g of Al4C3 and
20 mg of tO 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:
A14C3 + 4CHBr3 )4AlBr3 + 6C + CH4
Example 18
To the melt prepared according to Example 1 was
added 1.5 g of Al4C3 and 20 mg of FeS in NaCl. A
s~econd reactant comprising CH2I2 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 the following reaction:
6CH2I2 + Al4C3 ~4AlI3 + 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 Al4C3 and Be2C
with a member selected from the group consisting of
n A (4-n)-A~ C2Hn,xA.Y(6-n~)-A~ C2Hn"XA"Y (4
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" i5 an integer from
0 to 4, and wherein n is an integer from 0 to 4, n' i9
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 selecteA and wherein n + A = 4,
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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, or 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.
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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.
