U.S. patent application number 13/880289 was filed with the patent office on 2013-12-19 for polycrystalline diamond material.
This patent application is currently assigned to Element Six Abrasives S.A.. The applicant listed for this patent is Kaveshini Naidoo. Invention is credited to Kaveshini Naidoo.
Application Number | 20130333300 13/880289 |
Document ID | / |
Family ID | 43334290 |
Filed Date | 2013-12-19 |
United States Patent
Application |
20130333300 |
Kind Code |
A1 |
Naidoo; Kaveshini |
December 19, 2013 |
POLYCRYSTALLINE DIAMOND MATERIAL
Abstract
A polycrystalline diamond material comprises 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 being a metal
oxoanion, the oxoanion being selected from the group comprising
molybdates, tungstates, vanadates, phosphates and mixtures
thereof.
Inventors: |
Naidoo; Kaveshini; (Springs,
ZA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Naidoo; Kaveshini |
Springs |
|
ZA |
|
|
Assignee: |
Element Six Abrasives S.A.
Luxembourg
LU
|
Family ID: |
43334290 |
Appl. No.: |
13/880289 |
Filed: |
October 20, 2011 |
PCT Filed: |
October 20, 2011 |
PCT NO: |
PCT/EP2011/068306 |
371 Date: |
September 2, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61405733 |
Oct 22, 2010 |
|
|
|
Current U.S.
Class: |
51/309 |
Current CPC
Class: |
C04B 2235/5454 20130101;
C04B 2237/36 20130101; C04B 2235/3291 20130101; C04B 35/6261
20130101; C04B 35/62805 20130101; C04B 35/624 20130101; C04B
35/62886 20130101; C04B 35/645 20130101; C04B 2235/427 20130101;
C04B 2237/525 20130101; C04B 2237/02 20130101; C04B 2237/55
20130101; C04B 2235/9684 20130101; C04B 2235/326 20130101; C04B
2235/5445 20130101; C04B 2237/401 20130101; C04B 35/6303 20130101;
C04B 35/6306 20130101; C04B 2235/3281 20130101; C04B 2235/3275
20130101; C04B 2237/122 20130101; C04B 2235/3224 20130101; C04B
35/62818 20130101; C04B 2235/656 20130101; C04B 2235/3205 20130101;
C04B 2235/3244 20130101; C04B 2235/447 20130101; C04B 2235/6567
20130101; C22C 26/00 20130101; C04B 2235/80 20130101; C04B
2235/3201 20130101; C04B 37/006 20130101; C04B 2235/3227 20130101;
C04B 2237/61 20130101; C04B 2235/3256 20130101; C04B 2235/5472
20130101; C04B 2237/363 20130101; B82Y 30/00 20130101; C04B
2235/3298 20130101; C04B 35/52 20130101; B24D 3/16 20130101; C04B
37/026 20130101; C04B 2235/5436 20130101; C04B 2235/3239
20130101 |
Class at
Publication: |
51/309 |
International
Class: |
B24D 3/16 20060101
B24D003/16 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 22, 2010 |
GB |
1017923.2 |
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 being a metal
oxoanion, the oxoanion being selected from the group comprising
molybdates, tungstates, vanadates, phosphates and mixtures
thereof.
2. A polycrystalline diamond material according to claim 1, wherein
the metal oxoanion is selected from the group of compounds of the
general formula A(M.sub.xO.sub.y).sub.z or
AB(M.sub.xO.sub.y).sub.z, where A and B are alkali metals, alkali
earth metals, transition metals, lanthanides, actinides, or
monovalent, divalent or trivalent metals, M is tungsten,
molybdenum, vanadium or phosphorous, and 0.67.ltoreq.x.ltoreq.4,
3.ltoreq.y.ltoreq.12, and 1.ltoreq.z.ltoreq.3.
3. A polycrystalline diamond material according to claim 1, wherein
the metal oxoanion is selected from the group comprising sodium
molybdate, cobalt molybdate, zirconium tungstate, potassium
vanadate, KBi(WO.sub.4).sub.2, La.sub.4Cu.sub.3MoO.sub.12,
ZrMo.sub.2O.sub.8, HfW.sub.2O.sub.8, La.sub.2Mo.sub.3O.sub.12,
Eu.sub.2Mo.sub.3O.sub.12, Sc.sub.0.67WO.sub.4,
Eu.sub.0.67MoO.sub.4, Zr.sub.2(WO.sub.4)(PO.sub.4).sub.2 and
LnAg(WO.sub.4)(MoO.sub.4).
4. A polycrystalline diamond material according to claim 1, wherein
the metal oxoanion is sodium molybdate.
5. A polycrystalline diamond material according to claim 1, wherein
the diamond particles have an average particle or grain size of
from about 10 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 being a metal oxoanion,
the oxoanion being selected from the group comprising the
molybdates, tungstates, vanadates, phosphates and mixtures thereof,
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 metal oxoanion is
selected from the group of compounds of the general formula
A(M.sub.xO.sub.y).sub.z or AB(M.sub.xO.sub.y).sub.z, where A and B
are alkali metals, alkali earth metals, transition metals,
lanthanides, actinides, or monovalent, divalent or trivalent
metals, M is tungsten, molybdenum, vanadium or phosphorous, and
0.67.ltoreq.x.ltoreq.4, 3.ltoreq.y.ltoreq.12, and
1.ltoreq.z.ltoreq.3.
10. A method according to claim 8, wherein the metal oxoanion is
selected from the group comprising sodium molybdate, cobalt
molybdate, zirconium tungstate, potassium vanadate,
KBi(WO.sub.4).sub.2, La.sub.4Cu.sub.3MoO.sub.12, ZrMo.sub.2O.sub.8,
HfW.sub.2O.sub.8, La.sub.2Mo.sub.3O.sub.12,
Eu.sub.2Mo.sub.3O.sub.12, Sc.sub.0.67WO.sub.4,
Eu.sub.0.67MoO.sub.4, Zr.sub.2(WO.sub.4)(PO.sub.4).sub.2 and
LnAg(WO.sub.4)(MoO.sub.4).
11. A method according to claim 8, wherein the metal oxoanion is
sodium molybdate.
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 6.8 GPa and the temperature is at least about 1500
degrees centigrade.
14. A method according to claim 8, wherein the formed
polycrystalline diamond material defines an attachment surface, the
method including reducing non-metallic catalyst material for
diamond adjacent the attachment surface to its metallic form and
attaching a substrate or other supporting material to the
attachment surface of the polycrystalline diamond material.
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 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 being a metal
oxoanion, the oxoanion being selected from the group comprising
molybdates, tungstates, vanadates, phosphates and mixtures
thereof.
[0017] The metal oxoanion may be selected from the group of
compounds of the general formula A(M.sub.xO.sub.y).sub.z or
AB(M.sub.xO.sub.y).sub.z, where A and B are alkali metals, alkali
earth metals, transition metals, lanthanides, actinides, or
monovalent, divalent or trivalent metals, M is tungsten,
molybdenum, vanadium or phosphorous, and 0.67.ltoreq.x.ltoreq.4,
3.ltoreq.y.ltoreq.12, and 1.ltoreq.z.ltoreq.3.
[0018] In one or more embodiments the metal oxoanion may be
selected from the group consisting of sodium molybdate, cobalt
molybdate, zirconium tungstate, potassium vanadate,
KBi(WO.sub.4).sub.2, La.sub.4Cu.sub.3MoO.sub.12, ZrMo.sub.2O.sub.8,
HfW.sub.2O.sub.8, La.sub.2Mo.sub.3O.sub.12,
Eu.sub.2Mo.sub.3O.sub.12, Sc.sub.0.67WO.sub.4,
Eu.sub.0.67MoO.sub.4, Zr.sub.2(WO.sub.4)(PO.sub.4).sub.2 and
LnAg(WO.sub.4)(MoO.sub.4).
[0019] In one embodiment, the metal oxoanion is sodium
molybdate.
[0020] The average particle size of the diamond particles or grains
may be from about 10 nanometres to about 50 microns.
[0021] In one or more embodiments, the polycrystalline diamond
material comprises residues of the binder material in the form of
its oxygen- and/or nitrogen-containing compounds.
[0022] 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 some embodiments, the diamond content of the
polycrystalline diamond material is at most about 98 percent of the
volume of the polycrystalline diamond material.
[0023] In some embodiments, the content of the non-metallic
catalyst material for diamond is 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.
[0024] A further aspect provides 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 being a metal oxoanion, the oxoanion
being selected from the group comprising molybdates, tungstates,
vanadates, phosphates and mixtures thereof, 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.
[0025] 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 and the binder material may
be provided as respective adjacent layers, the non-metallic
catalyst material melting and infiltrating into the layer of
diamond particles or grains under suitable pressure and temperature
conditions.
[0027] 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.
[0028] Prior to contact with the binder material, the diamond
particles or grains may have an average particle or grain size of
from about 10 nanometres to about 50 microns.
[0029] In some embodiments, a multimodal mixture of diamond
particles or grains of varying average particle or grain size are
provided.
[0030] The polycrystalline diamond material may be a stand-alone
compact. In other embodiments, the polycrystalline diamond material
may be attached to a substrate, such as a metal carbide substrate,
for example.
[0031] In one or more embodiments, the polycrystalline diamond
material defines an attachment surface, and the method may include
reducing non-metallic catalyst material for diamond adjacent the
attachment surface to its metallic form and attaching a substrate
or other supporting material to the attachment surface of the
polycrystalline diamond material.
[0032] Sintering may be carried out at pressures of 6.8 GPa or
more, or 7.7 GPa or more, and temperatures of 1500 degrees
centigrade or more, or 2250 degrees centigrade or more, for
sintering times of 3 minutes or less, or 3 minutes or longer.
[0033] Organic compounds, for example organic anhydride complexes,
and/or water may also be added to aid sintering.
[0034] The non-metallic catalyst material for diamond may be
removed from interstices in one or more regions of the
polycrystalline diamond material to provide a polycrystalline
diamond material having one or more regions substantially free of
the non-metallic catalyst material for diamond.
[0035] A replacement material may be introduced into the one or
more regions substantially free of the non-metallic catalyst
material for diamond.
[0036] The one or more regions substantially free of the
non-metallic catalyst material for diamond may be located adjacent
one or more working surfaces of the polycrystalline diamond
material.
[0037] Viewed from another aspect there is provided a wear element
comprising a polycrystalline diamond material as described
above.
[0038] Some embodiments may assist in providing one or more of
enhanced thermal stability of the polycrystalline diamond material
over conventional metal catalysed polycrystalline material,
improved wear resistance of the polycrystalline diamond material
due to precipitation hardening caused by partial decomposition of
the non-metallic catalyst to form non-catalysing oxide
precipitates, and improved brazing to a metal substrate by reducing
the metal salt to metal at the attachment surface.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] Non-limiting embodiments will now be described with
reference to the accompanying FIG. 1 which shows an XRD analysis of
a sample of an embodiment of a polycrystalline diamond
material.
DETAILED DESCRIPTION OF EMBODIMENTS
[0040] 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
some embodiments of PCD material, interstices between the diamond
grains may at least partly be filled with a binder material
comprising a non-metallic catalyst material for diamond.
[0041] 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.
[0042] As used herein, "interstices" or "interstitial regions" are
regions between the diamond grains of PCD material.
[0043] 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.
[0044] 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.
[0045] 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.
[0046] 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 may be a metal oxoanion, wherein the oxoanion is selected
from the group comprising the molybdates, tungstates, vanadates,
phosphates and mixtures thereof.
[0047] In some embodiments, the metal oxoanions include compounds
of the general formula A(M.sub.xO.sub.y).sub.z or
AB(M.sub.xO.sub.y).sub.z, where A and B are alkali metals, alkali
earth metals, transition metals, lanthanides, actinides, or
monovalent, divalent or trivalent metals, M is tungsten,
molybdenum, vanadium or phosphorous, and 0.67.ltoreq.x.ltoreq.4,
3.ltoreq.y.ltoreq.12, and 1.ltoreq.z.ltoreq.3.
[0048] Although not an exhaustive list, exemplary metal oxoanions
may include sodium molybdate, cobalt molybdate, zirconium
tungstate, potassium vanadate, KBi(WO.sub.4).sub.2,
La.sub.4Cu.sub.3MoO.sub.12, ZrMo.sub.2O.sub.8, HfW.sub.2O.sub.8,
La.sub.2Mo.sub.3O.sub.12, Eu.sub.2Mo.sub.3O.sub.12,
Sc.sub.0.67WO.sub.4, Eu.sub.0.67MoO.sub.4,
Zr.sub.2(WO.sub.4)(PO.sub.4).sub.2 and
LnAg(WO.sub.4)(MoO.sub.4).
[0049] 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 may be a metal oxoanion, the oxoanion being selected from
the group comprising the molybdates, tungstates, vanadates,
phosphates and mixtures thereof. The diamond particles or grains
and binder material may be consolidated into a green body, which
green body is then subjected to a temperature and pressure at which
diamond is more thermodynamically stable than graphite in order to
sinter it and form polycrystalline diamond material.
[0050] In some embodiments, the non-metallic binder material is
combined with the diamond particles or grains in powder form and
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, are used to mill the binder and diamond
powders together. The binder and diamond mixture is then typically
dried at a temperature of 50 to 100.degree. C. to remove the
methanol and other volatile residues. It is then consolidated into
a green body ready for sintering. Alternatively, the diamond powder
and binder material may be provided in layer form, the non-metallic
catalyst material for diamond melting and infiltrating into the
diamond powder layer under suitable temperature and pressure
conditions, as would be appreciated by a person skilled in the
art.
[0051] In an alternative embodiment, the non-metallic binder
material is 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 may be used. A first
salt of the desired oxoanion is chosen such that it is soluble in a
solvent, but forms an insoluble salt with a chosen cation in the
diamond suspension. A second salt of the desired cation is chosen
such that it is soluble in a solvent, but the cation forms an
insoluble salt with the oxoanion of the first salt.
[0052] The two salt containing solutions are added concomitantly
drop wise to the diamond suspension such that an insoluble
precipitate comprising a molybdate, tungstate, vanadate, phosphate,
or mixture thereof, forms on the surface of the respective diamond
particles or grains.
[0053] 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.
[0054] 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 is typically 50 to 100.degree. C. 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.
[0055] Prior to contact with the binder material, the diamond
particles may have an average particle size ranging from about 10
nanometres to about 50 microns.
[0056] The green body, once formed is placed in a suitable
container and introduced into a high pressure high temperature
press. Pressure and heat are applied in order to sinter the diamond
particles together, typically at pressures of 6.8 to 7.7 GPa or
more and temperatures of 1500 to 2200.degree. C. or more.
[0057] In one embodiment, the metal salt adjacent a surface of the
polycrystalline diamond material is reduced to its metal, by for
example reacting with dry hydrogen at elevated temperature, which
is expected to facilitate brazing of the polycrystalline diamond
material onto a metal carbide substrate, for example.
EXAMPLES
[0058] Some embodiments are described in more detail with reference
to the examples below, which are not intended to be limiting.
Example 1
Fine Diamond with Sodium Molybdate Admixed by Planetary Ball
Milling
[0059] 25 g of diamond powder of approximate average particle size
20 microns was added to 125 g of Co--WC milling balls in a
polypropylene milling jar of approximate volume 600 ml. 2.5 g of
anhydrous sodium molybdate and 100 ml of methanol were added, the
jar was sealed and placed in a planetary ball mill and milled for
15 minutes at 90 rpm. The milling jar was opened, and a further 25
g of the diamond powder was added along with a further 125 g of
milling balls, a further 2.5 g of sodium molybdate and 100 ml of
methanol. The jar was sealed and milled for a further 15 minutes at
90 rpm. The milling jar was removed from the mill, opened and left
in an oven at 50 degrees centigrade overnight for the methanol to
evaporate and the diamond-salt powder mix to dry.
[0060] The diamond-salt mix was separated from the milling balls by
screening, then 2 g of the mix was placed in a metal canister and
sintered at 7.7 GPa and 2250 degrees centigrade for 3 minutes. SEM
analysis of the sintered PCD material showed intergrowth between
the diamond grains. XRD analysis of the sintered PCD material, as
depicted in FIG. 1, showed the presence of MoO.sub.2 and
Na.sub.0.9Mo.sub.2O.sub.4, with traces of NaWO.sub.3, the tungsten
having been introduced due to contamination by the Co--WC milling
balls during the milling step. A wear test showed an improvement of
approximately 20% over similar metallic PCD containing Co--WC
binder. Thermogravimetric analysis showed an increase in the
temperature of oxidation from 750 degrees centigrade for the
standard metallic PCD to 940 degrees centigrade for the
non-metallic PCD, indicating a significant improvement in the
thermal stability of the latter.
Example 2
Fine Diamond with Colloidally Deposited Cobalt Molybdate
[0061] 65 g of diamond powder of average particle size 2 micron may
be suspended in 2.5 litres of deionised water. An aqueous solution
of cobalt nitrate, Co(NO.sub.3).sub.2, and an aqueous solution of
sodium molybdate, NaMoO.sub.4, may be added simultaneously and
dropwise to the suspension while vigorously stirring the
suspension. The cobalt nitrate solution may be made by dissolving
35 g of Co(NO.sub.3).sub.2.6H.sub.2O in 200 ml of deionised water.
The sodium molybdate solution may be made by dissolving 30 g of
NaMoO.sub.4 in 200 ml of deionised water. The cobalt nitrate and
sodium molybdate may be reacted to form a precipitate of cobalt
molybdate on the surfaces of the suspended diamond particles. The
diamond powder with cobalt molybdate precipitate may be washed,
typically twice with deionised water, to remove the soluble sodium
nitrate by-product of the reaction.
[0062] The coated diamond may be washed in ethanol, and dried in an
oven overnight at 50 degrees centigrade. A 2 g sample of the dried
coated diamond may be placed in a metal canister and sintered at
7.7 GPa and 2250 degrees centigrade for 3 minutes. SEM analysis of
the sintered PCD is expected to show diamond intergrowth, with a
more homogeneous microstructure than was obtained in Example 1 by
milling. Similar benefits with respect to wear behaviour and
thermal stability as obtained in Example 1 are expected.
Example 3
Fine Diamond with Colloidally Deposited Zirconium Tungstate
[0063] 65 g of diamond powder of average particle size 2 micron may
be suspended in 2.5 litres of deionised water. An aqueous solution
of zirconium nitrate, Zr(NO.sub.3).sub.4.5H.sub.2O, and an aqueous
solution of potassium tungstate, K.sub.2WO.sub.4, may be added
simultaneously and dropwise to the suspension while vigorously
stirring the suspension. The zirconium nitrate solution may be made
by dissolving 54 g of Zr(NO.sub.3).sub.4.5H.sub.2O in 200 ml of
deionised water. The potassium tungstate solution may be made by
dissolving 52 g of K.sub.2WO.sub.4 in 200 ml of deionised water.
The zirconium nitrate and potassium tungstate may be reacted to
form a precipitate of zirconium tungstate on the surfaces of the
suspended diamond particles. The diamond powder with zirconium
tungstate precipitate may be washed, typically twice with deionised
water, to remove the soluble potassium nitrate by-product of the
reaction.
[0064] The coated diamond may be washed in ethanol, and dried in an
oven overnight at 50 degrees centigrade. A 2 g sample of the dried
coated diamond may be placed in a metal canister and sintered at
7.7 GPa and 2250 degrees centigrade for 3 minutes. SEM analysis of
the sintered PCD is expected to show diamond intergrowth, with a
more homogeneous microstructure than was obtained in Example 1 by
milling. Similar benefits with respect to wear behaviour and
thermal stability as obtained in Example 1 are expected.
Example 4
Fine Diamond With Potassium Vanadate Admixed by Planetary Ball
Milling
[0065] 25 g of diamond powder of approximate average particle size
20 microns may be added to 125 g of Co--WC milling balls in a
polypropylene milling jar of approximate volume 600 ml. 3 g of
tripotassium vanadate, K.sub.3VO.sub.4, and 100 ml of methanol may
be added, the jar sealed and placed in a planetary ball mill and
milled for 15 minutes at 90 rpm. On opening the milling jar, a
further 25 g of the diamond powder may be added along with a
further 125 g of milling balls, a further 3 g of tripotassium
vanadate and 100 ml of methanol, followed by sealing the jar and
milling for a further 15 minutes at 90 rpm. Drying may be achieved
by removing the milling jar from the mill, opening and leaving in
an oven at 50 degrees centigrade overnight for the methanol to
evaporate and the diamond-salt powder mix to dry.
[0066] The diamond-salt mix may be separated from the milling balls
by screening, then 2 g of the mix may be placed in a metal canister
and sintered at 7.7 GPa and 2250 degrees centigrade for 3 minutes.
A wear test is expected to show an improvement over similar
metallic PCD containing Co--WC binder.
* * * * *