U.S. patent application number 13/880255 was filed with the patent office on 2013-12-12 for polycrystalline diamond material.
This patent application is currently assigned to ELEMENT SIX ABRASIVES S.A.. The applicant listed for this patent is Charles Stephan Montross, Kaveshini Naidoo. Invention is credited to Charles Stephan Montross, Kaveshini Naidoo.
Application Number | 20130326963 13/880255 |
Document ID | / |
Family ID | 43334291 |
Filed Date | 2013-12-12 |
United States Patent
Application |
20130326963 |
Kind Code |
A1 |
Montross; Charles Stephan ;
et al. |
December 12, 2013 |
POLYCRYSTALLINE DIAMOND MATERIAL
Abstract
A polycrystalline diamond material comprising a mass of diamond
particles or grains exhibiting inter-granular bonding and a binder
material comprises a non-metallic catalyst material for diamond,
the non-metallic catalyst material for diamond comprising at least
one nitrogen compound derived from an ammonium compound and/or at
least one halide compound.
Inventors: |
Montross; Charles Stephan;
(Springs, ZA) ; Naidoo; Kaveshini; (Springs,
ZA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Montross; Charles Stephan
Naidoo; Kaveshini |
Springs
Springs |
|
ZA
ZA |
|
|
Assignee: |
ELEMENT SIX ABRASIVES S.A.
Luxembourg
LU
|
Family ID: |
43334291 |
Appl. No.: |
13/880255 |
Filed: |
October 20, 2011 |
PCT Filed: |
October 20, 2011 |
PCT NO: |
PCT/EP2011/068305 |
371 Date: |
September 2, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61405726 |
Oct 22, 2010 |
|
|
|
Current U.S.
Class: |
51/308 ;
51/307 |
Current CPC
Class: |
C04B 2235/3225 20130101;
C04B 35/6306 20130101; C04B 2235/5436 20130101; C04B 2235/3244
20130101; C04B 2235/3206 20130101; C04B 35/645 20130101; C04B
2235/3201 20130101; C04B 2235/3205 20130101; B24D 3/04 20130101;
C04B 2235/3427 20130101; C04B 2235/3251 20130101; C04B 2235/77
20130101; C04B 2235/442 20130101; C04B 2235/96 20130101; C04B
2235/448 20130101; C04B 2235/3234 20130101; C04B 2235/3213
20130101; C04B 2235/44 20130101; C04B 2235/3284 20130101; C04B
2235/5454 20130101; C04B 2235/3215 20130101; C04B 2235/447
20130101; C04B 2235/3203 20130101; C04B 2235/6567 20130101; C04B
2235/444 20130101; C04B 2235/3208 20130101; B82Y 30/00 20130101;
C04B 35/6303 20130101; C04B 35/52 20130101; C04B 2235/3409
20130101; C04B 35/6316 20130101; C04B 2235/427 20130101 |
Class at
Publication: |
51/308 ;
51/307 |
International
Class: |
B24D 3/04 20060101
B24D003/04 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 22, 2010 |
GB |
1017924.0 |
Claims
1. A polycrystalline diamond material comprising a mass of diamond
particles or grains exhibiting inter-granular bonding and a binder
material comprising a non-metallic catalyst material for diamond,
the non-metallic catalyst material for diamond comprising at least
one nitrogen compound derived from an ammonium compound and/or at
least one halide compound.
2. A polycrystalline diamond material according to claim 1, wherein
the ammonium compound comprises an anion selected from the group
comprising the carbonates, phosphates, hydroxides, oxides,
sulphates, borates, titanates, silicates, halides, and combinations
thereof.
3. A polycrystalline diamond material according to claim 1, wherein
the halide compound comprises a cation selected from the group
comprising the alkali metals, alkali earth metals, transition
metals, ammonium, and combinations thereof.
4. A polycrystalline diamond material according to claim 3, wherein
the non-metallic catalyst material for diamond comprises one or
more of lithium chloride, sodium chloride, potassium chloride,
rubidium chloride, caesium chloride, magnesium chloride, calcium
chloride, strontium chloride, barium chloride, yttrium chloride,
zirconium chloride, zinc chloride, niobium chloride, oxidation
states thereof, and/or mixtures thereof.
5. A polycrystalline diamond material according to claim 1, wherein
the diamond particles or grains have an average particle or grain
size of from about 5 nanometres to about 50 microns.
6. A polycrystalline diamond material according to claim 1, wherein
the diamond content of the polycrystalline diamond material is at
least 80 percent and at most 98 percent of the volume of the
polycrystalline diamond material.
7. A polycrystalline diamond material according to claim 1, wherein
the polycrystalline diamond material comprises at most 20 volume
percent of the non-metallic catalyst material for diamond.
8. A method for making polycrystalline diamond material, the method
including providing a mass of diamond particles or grains,
contacting the diamond particles or grains with a binder material
comprising a non-metallic catalyst material for diamond, the
non-metallic catalyst material for diamond comprising at least one
ammonium compound and/or at least one halide compound,
consolidating the diamond particles or grains and binder material
to form a green body, and subjecting the green body to a
temperature and pressure at which diamond is thermodynamically
stable, sintering and forming polycrystalline diamond material.
9. A method according to claim 8, wherein the ammonium compound
comprises an anion selected from the group comprising the
carbonates, phosphates, hydroxides, oxides, sulphates, borates,
titanates, silicates, halides, and combinations thereof.
10. A method according to claim 8, wherein the halide compound
comprises a cation selected from the group comprising the alkali
metals, alkali earth metals, transition metals, ammonium, and
combinations thereof.
11. A method according to claim 10, wherein the non-metallic
catalyst material for diamond comprises any one or more of lithium
chloride, sodium chloride, potassium chloride, rubidium chloride,
caesium chloride, magnesium chloride, calcium chloride, strontium
chloride, barium chloride, yttrium chloride, zirconium chloride,
zinc chloride, niobium chloride, all oxidation states thereof,
and/or mixtures thereof.
12. A method according to claim 8, wherein the method includes
subjecting the green body in the presence of the non-metallic
catalyst material for diamond to a pressure and temperature at
which diamond is more thermodynamically stable than graphite.
13. A method according to claim 12, wherein the pressure is at
least about 4 GPa and the temperature is at least about
1000.degree. C.
14. A method according to claim 12, wherein the pressure is at most
about 8 GPa and the temperature is at most about 2300.degree.
C.
15. A wear element comprising a polycrystalline diamond material
according to claim 1.
Description
FIELD
[0001] This disclosure relates to polycrystalline diamond (PCD)
material, and to a method of making such material.
BACKGROUND
[0002] Cutter inserts for machine and other tools may comprise a
layer of polycrystalline diamond (PCD) bonded to a cemented carbide
substrate. PCD is an example of a superhard material, also called
superabrasive material, which has a hardness value substantially
greater than that of cemented tungsten carbide.
[0003] Components comprising PCD are used in a wide variety of
tools for cutting, machining, drilling or degrading hard or
abrasive materials such as rock, metal, ceramics, composites and
wood-containing materials. PCD comprises a mass of substantially
inter-grown diamond grains forming a skeletal mass, which defines
interstices between the diamond grains. PCD material comprises at
least about 80 volume % of diamond and may be made by subjecting an
aggregated mass of diamond grains to an ultra-high pressure of
greater than about 5 GPa and temperature of at least about 1,200
degrees centigrade in the presence of a sintering aid, also
referred to as a catalyst material for diamond. Catalyst material
for diamond is understood to be material that is capable of
promoting direct inter-growth of diamond grains at a pressure and
temperature condition at which diamond is thermodynamically more
stable than graphite. Some catalyst materials for diamond may
promote the conversion of diamond to graphite at ambient pressure,
particularly at elevated temperatures. Examples of catalyst
materials for diamond are cobalt, iron, nickel and certain alloys
including any of these. PCD may be formed on a cobalt-cemented
tungsten carbide substrate, which may provide a source of cobalt
catalyst material for the PCD. The interstices within PCD material
may at least partly be filled with the catalyst material.
[0004] A well-known problem experienced with this type of PCD
material, however, is that the residual presence of the catalyst
material for diamond, in particular a metallic catalyst material
for diamond, for example Co, Ni or Fe, in the interstices has a
detrimental effect on the performance of the PCD material at high
temperatures. During application, the PCD material heats up and
thermally degrades, largely due to the presence of the metallic
catalyst material that catalyses graphitisation of the diamond and
also causes stresses in the PCD material due to the large
difference in thermal expansion between the metallic catalyst
material and the diamond microstructure.
[0005] One approach to addressing this problem is to remove,
typically by leaching, the catalyst material, also referred to as a
catalyst/solvent in the art, from the PCD material.
[0006] U.S. Pat. No. 3,745,623 and U.S. Pat. No. 4,636,253 teach
the use of heated acid mixtures in the leaching process in which
mixtures of HF, HCl, and HNO.sub.3 and HNO.sub.3 and HF,
respectively, are used.
[0007] U.S. Pat. No. 4,288,248 and U.S. Pat. No. 4,224,380 describe
removal of the catalyst/solvent by leaching the PCD tables in a hot
medium comprising HNO.sub.3--HF (nitric acid and hydrofluoric
acid), alone or in combination with a second hot medium comprising
HCl--HNO.sub.3 (hydrochloric acid and nitric acid).
[0008] US 2007/0169419 describes a method of leaching a portion or
all of the catalyst/solvent from a PCD table by shielding the
portion of the PCD table not to be leached and immersing the
shielded PCD table in corrosive solution to dissolve the
catalyst/solvent in water and aqua regia. The leaching process is
accelerated by the use of sonic energy, which agitates the
interface between the PCD table and the corrosive solution to
accelerate the dissolution rate of the catalyst/solvent.
[0009] U.S. Pat. No. 4,572,722 discloses a leaching process that is
accelerated by forming a hole in the PCD table by laser cutting or
spark emission prior to or during the leaching process. The PCD
table is then leached by using conventional acid leaching
techniques, electrolytic leaching and liquid zinc extraction.
[0010] An alternative approach to addressing the problem is to use
a non-metallic catalyst material for diamond that produces a more
thermally stable PCD material.
[0011] JP2795738 (B2) describes sintering a mixture of diamond
powder and metal carbonates at pressures of 6-12 GPa and
temperatures of 1700-2500.degree. C. to give sintered
polycrystalline material consisting of 0.1-15 vol % non-metallic
binder in a sintered diamond layer.
[0012] JP4114966 describes the use of carbon powder added as a
sintering aid to diamond powder and an alkali earth carbonate, in
order to improve the sinterability of the non-metallic system.
[0013] JP2003226578 also addresses the problem of poor
sinterability, which describes the use of oxalic acid dihydrate as
a sintering aid in a carbonate-based non-metallic solvent/catalyst
system.
[0014] JP2002187775 describes the addition of other organic
compounds to achieve a sintered carbonate-based non-metallic PCD,
and similarly the addition of metal carbides is described in
JP6009271.
SUMMARY
[0015] In general terms, this disclosure relates to comprises a
polycrystalline diamond material having a non-metallic catalyst
material for diamond.
[0016] Viewed from a first aspect there is provided a
polycrystalline diamond material comprising a mass of diamond
particles or grains exhibiting inter-granular bonding and a binder
material comprising a non-metallic catalyst material for diamond,
the non-metallic catalyst material for diamond comprising at least
one nitrogen compound derived from an ammonium compound and/or at
least one halide compound.
[0017] The ammonium compound may comprise an anion selected from
the group comprising the carbonates, phosphates, hydroxides,
oxides, sulphates, borates, titanates, silicates, halides, and
combinations thereof.
[0018] The halide compound may comprise a cation selected from the
group comprising the alkali metals, alkali earth metals, transition
metals, ammonium, and combinations thereof.
[0019] In some embodiments, the non-metallic catalyst material for
diamond may comprise one or more of lithium chloride, sodium
chloride, potassium chloride, rubidium chloride, caesium chloride,
magnesium chloride, calcium chloride, strontium chloride, barium
chloride, yttrium chloride, zirconium chloride, zinc chloride,
niobium chloride, all oxidation states thereof, and mixtures
thereof.
[0020] In some embodiments, the average particle size of the
diamond particles or grains may be from about 5 nanometres to about
50 microns, or from about 20 nanometres to about 20 microns, or
from about 50 nanometres to about 10 microns.
[0021] In some embodiments, the diamond content of the
polycrystalline diamond material may be at least about 80 percent,
at least about 88 percent, at least about 90 percent, at least
about 92 percent or even at least about 96 percent of the volume of
the polycrystalline diamond material. In one or more embodiments,
the diamond content of the polycrystalline diamond material may be
at most about 98 percent of the volume of the polycrystalline
diamond material.
[0022] The content of the non-metallic catalyst material for
diamond may, for example, be at most about 20 volume percent, at
most about 10 volume percent, at most about 8 volume percent, or
even at most about 4 volume percent of the PCD material.
[0023] Viewed from a further aspect there is provided a method for
making polycrystalline diamond material, the method including
providing a mass of diamond particles or grains, contacting the
diamond particles or grains with a binder material comprising a
non-metallic catalyst material for diamond, the non-metallic
catalyst material for diamond comprising at least one ammonium
compound and/or at least one halide compound, consolidating the
diamond particles or grains and binder material to form a green
body, and subjecting the green body to a temperature and pressure
at which diamond is thermodynamically stable, sintering and forming
polycrystalline diamond material.
[0024] In some embodiments, the salts may be combined with the
diamond particles or grains via infiltration, mixing, milling,
chemical vapour deposition, colloidal (sol-gel) deposition, atomic
layer deposition, physical vapour deposition, and the like.
[0025] In some embodiments, the diamond particles or grains and the
binder material may be mixed in powder form with appropriate
binding aids.
[0026] The diamond particles or grains may be suspended in a liquid
medium, the non-metallic catalyst material for diamond
precipitating in situ onto the surfaces of respective diamond
particles or grains in the liquid medium in order to coat the
diamond particles or grains.
[0027] In some embodiments, the diamond particles or grains prior
to contact with the binder material may have an average particle or
grain size of from about 5 nanometres to about 50 microns, or from
about 20 nanometres to about 20 microns, or from about 50
nanometres to about 10 microns.
[0028] In some embodiments, a multimodal mixture of diamond
particles or grains of varying average particle or grain size may
be provided.
[0029] The polycrystalline diamond material may be a stand-alone
compact or may be attached to a substrate, such as a metal carbide
substrate, for example.
[0030] Sintering may be carried out at pressures of 4 GPa or more,
or 7 GPa or more, and temperatures of 1000.degree. C. or more, or
1700.degree. C. or more, for sintering times of 10 minutes or
longer, or sintering times of 30 seconds or longer, or one minute
or longer.
[0031] In some embodiments, sintering may be carried out at
pressures of 7 GPa or less and temperatures of 1800.degree. C. or
less.
[0032] According to another aspect, there is provided a wear
element comprising a polycrystalline diamond material as defined
above.
[0033] Enhanced thermal stability of the polycrystalline diamond
material over conventional metal catalysed polycrystalline material
and lower sintering temperatures and pressures than for other
non-metallic catalyst materials for diamond may be obtained through
one or more embodiments.
DETAILED DESCRIPTION OF EMBODIMENTS
[0034] As used herein, "polycrystalline diamond" (PCD) material
comprises a mass of diamond grains, a substantial portion of which
are directly inter-bonded with each other and in which the content
of diamond is at least about 80 volume percent of the material. In
one embodiment of PCD material, interstices between the diamond
grains may at least partly be filled with a binder material
comprising a non-metallic catalyst for diamond.
[0035] As used herein, "non-metallic catalyst material for diamond"
is a material that is capable of catalysing intergrowth of
polycrystalline diamond particles or grains under conditions of
temperature and pressure at which diamond is more thermodynamically
stable than graphite.
[0036] As used herein, "interstices" or "interstitial regions" are
regions between the diamond grains of PCD material.
[0037] A multi-modal size distribution of a mass of grains is
understood to mean that the grains have a size distribution with
more than one peak, each peak corresponding to a respective "mode".
Multimodal polycrystalline bodies are typically made by providing
more than one source of a plurality of grains, each source
comprising grains having a substantially different average size,
and blending together the grains or particles from the sources.
Measurement of the size distribution of the blended grains
typically reveals distinct peaks corresponding to distinct modes.
When the grains are sintered together to form the polycrystalline
body, their size distribution is further altered as the grains are
compacted against one another and fractured, resulting in the
overall decrease in the sizes of the grains. Nevertheless, the
multimodality of the grains is usually still clearly evident from
image analysis of the sintered article.
[0038] As used herein, a green body is an article that is intended
to be sintered or which has been partially sintered, but which has
not yet been fully sintered to form an end product. It may
generally be self-supporting and may have the general form of the
intended finished article.
[0039] As used herein, a superhard wear element is an element
comprising a superhard material and is for use in a wear
application, such as degrading, boring into, cutting or machining a
workpiece or body comprising a hard or abrasive material.
[0040] A polycrystalline diamond material according to some
embodiments comprises diamond having increased thermal stability
over conventional solvent/catalyst sintered diamond composite
materials. In some embodiments, the polycrystalline diamond
material includes a binder comprising a non-metallic catalyst
material for diamond. The non-metallic catalyst material for
diamond comprises at least one nitrogen compound derived from an
ammonium compound and/or at least one halide containing
compound.
[0041] A method for making polycrystalline diamond material, in
some embodiments, includes contacting a mass of diamond particles
or grains with a binder material comprising a non-metallic catalyst
material for diamond. The non-metallic catalyst material for
diamond is at least one ammonium compound and/or at least one
halide compound.
[0042] The salts may be combined with diamond by, for example,
infiltration, mixing, milling, chemical vapour deposition,
colloidal (sol-gel) deposition, atomic layer deposition, physical
vapour deposition and other similar processes that would be
appreciated by those skilled in the art.
[0043] The non-metallic binder material may be combined with the
diamond particles or grains in powder form. It can be mixed in a
conventional mixing process such as, for example, a planetary ball
milling process, typically in the presence of a milling aid such as
methanol, for example. Milling balls, such as Co-WC milling balls,
may be used to mill the binder and diamond powders together. The
binder and diamond mixture may then typically be dried at a
temperature of 50 to 100.degree. C. to remove the methanol and
other volatile residues and then consolidated into a green body
ready for sintering.
[0044] In an alternative embodiment, the non-metallic binder
material may be combined with the diamond particles or grains in a
sol-gel process. Diamond powder is suspended in a liquid under
vigorous stirring to form a diamond suspension. The liquid is
typically water although the person skilled in the art will
appreciate that any appropriate liquid medium can be used. A first
salt of the desired ammonium cation and/or halide anion may be
chosen such that it is soluble in a solvent, but forms an insoluble
salt with a chosen anion/cation, as the case may be, in the diamond
suspension. A second salt of the desired anion/cation may be chosen
such that it is soluble in a solvent, but the anion/cation forms an
insoluble salt respectively with the ammonium cation and/or halide
anion of the first salt.
[0045] The two salt containing solutions are added concomitantly
drop wise to the diamond suspension such that an insoluble
precipitate consisting of the non-metallic catalyst material for
diamond forms on the surface of the respective diamond particles or
grains.
[0046] The liquid containing the suspended diamond particles or
grains is stirred during the drop wise addition. This stirring may
be accomplished by a heater-stirrer and magnetic stirrer, or by an
overhead stirrer, or by ultrasonication, or any other suitable
method that is able effectively to disperse the diamond particles
in the liquid.
[0047] The diamond powder with precipitated salt may be removed
from suspension and dried at a temperature suitable for removing
any residual suspension medium or solvents that may be present. The
drying temperature may typically be around 50 to 100.degree. C., or
a temperature that does not volatise the ammonium or halide
compound. Alternatively, the diamond with precipitated salt may be
dried under vacuum at a moderate temperature or room temperature.
The diamond with precipitated salt may be stationary during drying,
or may be agitated, tossed or moved in a way that increases the
efficiency or rate of drying. The diamond particles and binder
material are consolidated to form a green body.
[0048] Prior to contact with the binder material, the diamond
particles may have an average particle size ranging from about 5
nanometres to about 50 microns.
[0049] The green body, once formed, is placed in a suitable
container and introduced into a high pressure and high temperature
press. Pressure and heat are applied in order to sinter the diamond
particles together, typically at pressures of around 4 to 7 GPa or
more and temperatures of around 1000 to 1700.degree. C. or
more.
[0050] In some embodiments, the grain boundaries of the diamond
particles or grains may contain reduced levels of contaminants that
originate from residues of the starting salts, thereby enabling
stronger diamond-diamond bonding and improved material properties.
In the case of ammonium cations, the lower concentration of
contaminants is expected because the ammonium cations will
dissociate under sintering conditions to form hydrogen and
nitrogen, which are liberated as gases.
[0051] In some embodiments, the sintered PCD may contain an amount
of dissolved nitrogen or hydrogen gas. The hydrogen gas liberated
during HPHT is expected to have the beneficial effect of helping to
reduce the carbon monoxide or carbon dioxide intermediate to
diamond, thereby enabling the use of lower pressures and
temperatures.
[0052] In other embodiments, for example where halides are used,
lower pressures and temperatures may also be used to sinter the
PCD. For example, 7 GPa or less and 1800.degree. C. or less, as
opposed to the more conventional 8 GPa or more and 2300.degree. C.
or more for more conventional non-metallic catalyst systems, may be
used. Although wishing not to be bound by theory, it is believed
that the disruption of the C--O bonds by the chloride ion reduces
the temperature at which the potassium carbonate becomes
catalytically active.
[0053] In some embodiments where, for example, compounds containing
an ammonium cation are used, the anion may be any one or more of
the following: carbonates, phosphates, hydroxides, oxides,
sulphates, borates, titanates, silicates, halides and the like.
[0054] In some embodiments where, for example, compounds containing
halide anions are used, the cation may be any one or more of the
following: alkali metals, alkali earth metals, and transition
metals. Examples of such compounds may include lithium chloride,
sodium chloride, potassium chloride, rubidium chloride, caesium
chloride, magnesium chloride, calcium chloride, strontium chloride,
barium chloride, yttrium chloride, zirconium chloride, zinc
chloride, niobium chloride, all oxidation states thereof, and
mixtures thereof.
[0055] In some embodiments, mixtures of ammonium and halide
compounds may be used.
[0056] The diamond grain sizes in the sintered PCD may range from
about 5 nanometres to about 50 microns, or from about 20 nanometres
to about 20 microns, or from about 50 nanometres to about 10
microns. The diamond size distributions may be monomodal or
multimodal.
[0057] The non-metallic PCD may be monolithic, or may be attached
to a suitable substrate, for example a Co-WC substrate. The
interface between the PCD and the substrate may be planar or
non-planar.
[0058] The non-metallic PCD may be leached partly or fully, using
any appropriate leaching process that would be understood by a
person skilled in the art.
EXAMPLES
[0059] A number of embodiments are described in more detail with
reference to the examples below, which are not intended to be
limiting.
Example 1
[0060] An approximate eutectic mixture of CaCO.sub.3 and
Ca(OH).sub.2 was mixed with NH.sub.4Cl in the ratio of 0.4 moles
CaCO.sub.3 with 0.4 moles Ca(OH).sub.2 and 0.2 moles NH.sub.4Cl.
This binder mixture was mixed with diamond in a ratio of 4.5 g
diamond to 0.5 g binder mixture. This combined mixture was densely
packed into an air tight metal container suitable for HPHT
processing. This container was then subjected to HPHT processing to
temperatures above 1500.degree. C. and pressures above 6.8 GPa and
held for times ranging from 10 minutes to 60 minutes. It was
expected that there would be an intergrown diamond compact after
HPHT processing.
Example 2
[0061] An equimolar mixture of MgCO.sub.3 and Mg(OH).sub.2 (in the
absence of phase diagrams in the available literature for this
system, it was assumed that an equimolar mixture would be
sufficiently close to an eutectic composition) was mixed with
NH.sub.4Cl in the ratio of 0.4 moles MgCO.sub.3 with 0.4 moles
Mg(OH).sub.2 and 0.2 moles NH.sub.4Cl. This binder mixture was
mixed with diamond in a ratio of 4.5 g diamond to 0.5 g binder
mixture. This combined mixture was densely packed into an air tight
metal container suitable for HPHT processing. This container was
then subjected to HPHT processing to temperatures at 1500.degree.
C. and pressures above 6.8 GPa and held for times ranging from 10
minutes to 60 minutes. It was expected that there would be an
intergrown diamond compact after HPHT processing.
Example 3
[0062] An approximate eutectic mixture of CaCO.sub.3 and
Ca(OH).sub.2 was mixed with NH.sub.4Cl in the ratio of 0.4 moles
CaCO.sub.3 with 0.4 moles Ca(OH).sub.2 and 0.2 moles NH.sub.4Cl.
This binder mixture was mixed with diamond in a ratio of 9 g
diamond to 1 g binder mixture. This combined mixture was densely
packed into an air tight metal container suitable for HPHT
processing. This container was then subjected to HPHT processing to
the following temperatures: 1600.degree. C., 1800.degree. C., and
2000.degree. C. and a pressure of 8 GPa and held for a time of 10
minutes. It was expected that there would be an intergrown diamond
compact after HPHT processing under all of these conditions.
Example 4
[0063] An equimolar mixture of MgCO.sub.3 and NH.sub.4 Oxalate was
mixed as a binder with diamond in a ratio of 4.5 g diamond to 0.5 g
binder mixture. This combined mixture was densely packed into an
air tight metal container suitable for
[0064] HPHT processing. This container was then subjected to HPHT
processing to temperatures above 1500.degree. C. and pressures
above 6.8 GPa and held for times ranging from 10 minutes to 60
minutes. It was expected that there would be an intergrown diamond
compact after HPHT processing.
Example 5
[0065] NH.sub.4 Oxalate was mixed as a binder with diamond in a
ratio of 4.5 g diamond to 0.5 g binder mixture. This combined
mixture was densely packed into an air tight metal container
suitable for HPHT processing. This container was then subjected to
HPHT processing to temperatures above 1500.degree. C. and pressures
above 6.8 GPa and held for times ranging from 10 minutes to 60
minutes. It was expected that there would be an intergrown diamond
compact after HPHT processing.
Example 6
[0066] K.sub.2CO.sub.3 and KCl were dried at 50.degree. C. for 24
hours, then were planetary ball milled separately for 45 minutes at
90 rpm, then combined in a molar ratio of 70:30. This mix was
combined with diamond powder of average particle size 10 micron in
an amount of 5 vol % mix to 95 vol % diamond. Being very
hygroscopic, the salt mix was dried between steps as well as stored
when necessary in a vacuum oven. Practical difficulties with
pressure generation were experienced, so that no sintering was
achieved in the experiments. However, it is expected that sintering
at greater than 1000.degree. C. and greater than 7 GPa for more
than 5 minutes will cause sintering, with 1260.degree. C., 7.7 GPa
and 1 hour expected to result in well sintered non-metallic PCD
with very good thermal stability and wear behaviour. These
temperatures are unusually low for sintering PCD, and this benefit
is thought to be due to the presence of the chloride ions which may
destabilise the carbonate anions and increase their reactivity as a
catalyst material for diamond.
* * * * *