A mixture for processing a body of polycrystalline diamond material

Abstract

An acid leaching mixture for removing residual solvent catalyst material from a body of polycrystalline diamond (PCD) material having a non-diamond phase including the solvent catalyst material. The mixture has a molar concentration of between 4M to 9M and comprises hydrofluoric (HF) acid, plus any one or more of hydrochloric (HCI) acid, nitric (HNO3) acid, sulfuric (H2SO,) acid, and / or phosphoric (H3PO2) acid and water. The molar concentration of the hydrofluoric (HF) acid and nitric (HNO3) acid may be at a molar concentration of 4M to 9M. The acid leaching mixture may comprise 13-20wt% hydrofluoric acid; 50-60wt% nitric acid and 20-40wt% water.

Description

This disclosure relates to a mixture for processing a body of polycrystalline diamond (PCD) material. BACKGROUND Cutter inserts for machining and other tools may typically comprise a layer of polycrystalline diamond (PCD) material bonded to a cemented carbide substrate. PCD is an example of a superhard material, also called a superabrasive material, which has a hardness value substantially greater than that of cemented tungsten carbide. 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 (interbonded) diamond grains forming a skeletal mass, which define interstices between the diamond grains. PCD material typically 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, typically about 5.5 GPa or more, and temperature of at least about 1200°C, typically about 1440°C, in the presence of a sintering aid, also referred to as a solvent catalyst material for diamond. Solvent catalyst materials for diamond are understood to be materials capable of promoting direct inter-growth of diamond grains at a pressure and temperature condition at which diamond is thermodynamically more stable than graphite. Examples of solvent catalyst materials for diamond are cobalt, iron, nickel and certain alloys including alloys of any of these elements. PCD may be formed, for example, on a cobalt-cemented tungsten carbide substrate, which may provide a source of cobalt catalyst material for the PCD. During sintering of the body of PCD material, a constituent of the cemented carbide substrate, such as cobalt from a cobalt cemented tungsten carbide substrate, liquefies and sweeps from a region adjacent the volume of diamond particles into interstitial regions between the diamond particles. In this example, the cobalt acts as a solvent catalyst to facilitate the formation of bonded diamond grains. Optionally, a metal-solvent catalyst may be mixed with diamond particles prior to subjecting the diamond particles and substrate to the HPHT process. The interstices within PCD material may at least partly be filled with the solvent catalyst material. The intergrown (inter-bonded) diamond structure therefore comprises original diamond grains as well as a newly precipitated or re-grown diamond phase, which bridges the original grains. In the final sintered structure, solvent catalyst material generally remains present within at least some of the interstices that exist between the sintered diamond grains. Sintered PCD typically has sufficient wear resistance and hardness for use in aggressive wear, cutting and drilling applications however a well-known problem experienced with this type of PCD compact or cutting element is that the presence of residual solvent catalyst material in the microstructural interstices may have a detrimental effect on the performance of the PCD compact at high temperatures as it is believed that the presence of the solvent catalyst in the diamond table reduces the thermal stability of the diamond table at these elevated temperatures. For example, the difference in thermal expansion coefficient between the diamond grains and the residual solvent catalyst is believed to lead to chipping or cracking in the PCD table of a cutting element during drilling or cutting operations where operating temperatures may reach 700 degrees C or more. The chipping or cracking in the PCD material may degrade the mechanical properties of the cutting element or lead to failure of the cutting element. Additionally, at high temperatures, diamond grains may undergo a chemical breakdown or back-conversion with the solvent catalyst. At extremely high temperatures, portions of diamond grains may transform to carbon monoxide, carbon dioxide, graphite, or combinations thereof, thereby degrading the mechanical properties of the PCD material. A potential solution to these problems is to remove residual catalyst solvent (also known as binder phase) from the body of PCD material. Chemical leaching is often used to remove metal solvent catalyst material, such as cobalt, from interstitial regions of a body of PCD material, such as from regions adjacent to the working surfaces of the PCD. It is typically extremely difficult and time consuming to remove effectively the bulk of a metallic solvent catalyst from a PCD table, particularly from the thicker PCD tables required by current applications. In general, current art is focused on achieving PCD of high diamond density and commensurately PCD that has an extremely fine distribution of metal solvent catalyst pools. This fine network typically resists penetration by the leaching agents, such that residual solvent catalyst often remains behind in the leached compact. Furthermore, achieving appreciable leaching depths can take so long as to be commercially unfeasible or require undesirable interventions such as extreme acid treatment or physical drilling of the PCD tables. There is therefore a need to overcome or substantially ameliorate the above-mentioned problems through an acid leach mixture for treating or processing a body of PCD material. SUMMARY Viewed from a first aspect there is provided an acid leaching mixture for removing residual solvent catalyst material from a body of polycrystalline diamond (PCD) material having a non-diamond phase comprising the solvent catalyst material, the acid leaching mixture having a molar concentration of between around 4M to around 9M and comprising: hydrofluoric (HF) acid; any one or more of hydrochloric (HCI) acid, nitric (HNO3) acid, sulfuric (H2SO4) acid, and / or phosphoric (H3PO4) acid; and water. In some examples, the acid leaching mixture comprises hydrofluoric acid at a molar concentration of between around 4M to around 9M; and nitric acid at a molar concentration of between around 4M to around 9M; and said water. In still further examples, the acid leaching mixture comprises hydrofluoric acid at a molar concentration of between around 5M to around 7M; and nitric acid at a molar concentration of between around 6.7M to around 8M; and said water. The water may be de-ionized water. In some examples, the acid leaching mixture is in aqueous form, and in other examples the acid leaching mixture is in vapour form having been heated to a temperature of between around 140 to around 300 degrees C to generate said vapour form. Viewed from a second aspect there is provided an acid leaching mixture for removing catalyst solvent material from a body of polycrystalline diamond (PCD) material having a non-diamond phase comprising the catalyst solvent material, the mixture being in vapour form derived from an aqueous solution of the acid leaching mixture defined above. Viewed from a third aspect there is provided an acid leaching mixture comprising between around 13wt% to around 20wt% hydrofluoric acid; between around 50wt% to around 60wt% nitric acid; and between around 20wt% to around 40wt% water, such as de-ionized water. BRIEF DESCRIPTION OF THE DRAWINGS Various versions will now be described in more detail, by way of example, with reference to the accompanying figures in which: Figure 1 is a schematic perspective view of a PCD cutter insert for a cutting drill bit for boring into the earth; Figure 2 is a schematic cross section view of a portion of the PCD cutter insert of Figure 1 showing the microstructure of the PCD material in the PCD cutter insert of Figure 1 prior to processing; and Figure 3 is a flow diagram of an exemplary method for processing a body of polycrystalline diamond (PCD) material of the cutter insert of Figure 1 using the example acid leach mixture. The same reference numbers refer to the same respective features in all drawings. DESCRIPTION The instant disclosure is directed to an acid leaching mixture for processing superabrasive articles, such as superabrasive cutting elements, superabrasive bearings, and superabrasive discs. The superabrasive articles disclosed herein may be used in a variety of applications, such as drilling tools (e.g. compacts, cutting elements, gage trimmers, etc.), machining equipment, bearing apparatuses, wire-drawing machinery, and other apparatuses. As used herein, a “superhard material” also known as a “superabrasive” material is a material having a Vickers hardness of at least about 28 GPa. Diamond and cubic boron nitride (cBN) materials are examples of superhard or superabrasive materials. As used herein, a “superhard construction” or “superabrasive construction” means a construction or compact comprising a body of polycrystalline superhard or superabrasive material. In such a construction, a substrate may be attached thereto or alternatively the body of polycrystalline material may be free-standing and unbacked. As used herein, polycrystalline diamond (PCD) is a type of polycrystalline superhard (PCS) material comprising 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 example of PCD material, interstices between the diamond grains may be at least partly filled with a binder material comprising a solvent catalyst for diamond. As used herein, “interstices” or “interstitial regions” are regions between the diamond grains of PCD material. In examples of PCD material, interstices or interstitial regions may be substantially or partially filled with a material other than diamond, or they may be substantially empty. PCD material may comprise at least a region from which catalyst material has been removed from the interstices, leaving interstitial voids between the diamond grains. A “catalyst material” for a superhard material is capable of promoting the growth or sintering of the superhard material. The term "substrate" as used herein means any substrate over which the superhard material layer is formed. For example, a "substrate" as used herein may be a transition layer formed over another substrate. As used herein, the term “integrally formed” regions or parts are produced contiguous with each other and are not separated by a different kind of material. The term "molar concentration" as used herein, may refer to a concentration in units of mol / L at a temperature of approximately 25[deg.] C. For example, a solution comprising solute A at a molar concentration of 1 M may comprise 1 mol of solute A per litre of solution. As used herein, the term "depth of leaching" or “leach depth” refers to the distance into the PCD cutter element, from the outer surface thereof, to which the leaching acid has penetrated during the leaching process to remove residual solvent catalyst therefrom. As shown in Figure 1, a cutting element 1 includes a substrate 10 with a body of PCD material 12 in the form of a layer formed on the substrate 10. The substrate 10 may be formed of a hard material such as cemented tungsten carbide. The cutting element 1 may be mounted into a bit body such as a drag bit body (not shown) and may be suitable, for example, for use as a cutter insert for a drill bit for boring into the earth. The exposed top surface of the superhard material opposite the substrate forms the cutting face 14, which is the surface which, along with its edge 16, performs the cutting in use. At one end of the substrate 10 is an interface surface 18 that forms an interface with the body of PCD material 12 which is attached thereto at this interface surface. As shown in the example of Figure 1, the substrate 10 is generally cylindrical and has a peripheral surface 22 and a peripheral top edge 20. As used herein, a PCD grade is a PCD material characterized in terms of the volume content and size of diamond grains, the volume content of interstitial regions between the diamond grains and composition of material that may be present within the interstitial regions. A grade of PCD material may be made by a process including providing an aggregate mass of diamond grains having a size distribution suitable for the grade, optionally introducing catalyst material or additive material into the aggregate mass, and subjecting the aggregated mass in the presence of a source of catalyst material for diamond to a pressure and temperature at which diamond is more thermodynamically stable than graphite and at which the catalyst material is molten. Under these conditions, molten catalyst material may infiltrate from the source into the aggregated mass and is likely to promote direct intergrowth between the diamond grains in a process of sintering, to form a PCD structure. The aggregate mass may comprise loose diamond grains or diamond grains held together by a binder material and said diamond grains may be natural or synthesized diamond grains. Different PCD grades may have different microstructures and different mechanical properties, such as elastic (or Young’s) modulus E, modulus of elasticity, transverse rupture strength (TRS), toughness (such as so-called KiC toughness), hardness, density and coefficient of thermal expansion (CTE). Different PCD grades may also perform differently in use. For example, the wear rate and fracture resistance of different PCD grades may be different. All of the PCD grades may comprise interstitial regions filled with material comprising cobalt metal, which is an example of solvent catalyst material for diamond. The PCD structure 12 may comprise one or more PCD grades. Figure 2 is a cross-section through a body of PCD material which may form the super hard layer 12 of Figure 1 in an example cutter element 1. During formation of a conventional polycrystalline diamond construction, the diamond grains 23 are directly interbonded to adjacent grains and the interstices 24 between the diamond grains 23 may be at least partly filled with a non-super hard phase material. This non-super hard phase material, also known as a filler material, may comprise residual solvent catalyst material, for example cobalt, nickel or iron. A sintered body of PCD material 12 is created having diamond to diamond bonding and having a second phase comprising solvent catalyst material dispersed through at least a portion of its microstructure. The body of PCD material 12 and attached substrate 10 which form the cutter element 1 may be formed according to standard methods, using HPHT conditions to produce a sintered compact. For example, a PCD layer 12 may formed by subjecting a plurality of diamond particles (e.g. diamond particles having an average particle size between approximately 0.5 pm and approximately 150 pm) to an HPHT sintering process in the presence of a metal solvent catalyst, such as cobalt, nickel, iron, and / or any other suitable group VIII element. During the HPHT sintering process, adjacent diamond grains in a mass of diamond particles may become bonded to one another, forming a PCD table (body of PCD material 12) comprising interbonded diamond grains. In one example, diamond grains in table 12 may have an average grain size of approximately 20 pm or less. Additionally, during an HPHT sintering process, diamond grains may become bonded to the adjacent substrate 10 at the interface 18. In various examples, the substrate 10 is formed of a cemented tungsten carbide material and after sintering, the resulting body of PCD material 12 may include tungsten and / or tungsten carbide in addition to the diamond grains and residual solvent catalyst material. For example, tungsten and / or tungsten carbide may be swept into the PCD layer 12 from the substrate 10 during HPHT sintering as liquefied solvent catalyst from the substrate 10 (e.g. cobalt from a cobalt-cemented tungsten carbide substrate) may dissolve and / or carry tungsten and / or tungsten carbide from the substrate 10 into the mass of diamond particles used to form the PCD table 12 during the HPHT sintering. In additional examples, tungsten and / or tungsten carbide particles may be intentionally mixed with diamond particles prior to forming the body of PCD material 12. It has been found that the removal of non-binder phase from within the PCD table, conventionally referred to as leaching, is desirable in various applications. One reason for this is that the presence of residual solvent catalyst material in the microstructural interstices is believed to have a detrimental effect on the performance of PCD compacts at high temperatures as it is believed that the presence of the solvent catalyst in the diamond table reduces the thermal stability of the diamond table at these elevated temperatures. To improve the performance and heat resistance of a surface region of the body of PCD material 12, at least a portion of the solvent catalyst, such as cobalt, is to be removed from the interstices 24 of at least a portion of the body of PCD material 12. Additionally, in some examples, tungsten and / or tungsten carbide may be removed from at least a portion of the body of PCD material 12. Chemical leaching is typically used to remove residual solvent catalyst from the body of PCD material 12 either up to a desired depth from an external surface of the body of PCD material or from substantially all of the PCD material 12. Following leaching, the body of PCD material 12 may therefore comprise a first volume that is substantially free of solvent catalyst material. However, small amounts of solvent catalyst material may remain within interstices that are inaccessible to the leaching process. Additionally, following leaching, the body of PCD material 12 may also comprise a volume or region that contains solvent catalyst material. In some examples, this further volume may be remote from one or more exposed surfaces of the body of PCD material 12. The interstitial material which may include, for example, the metal solvent catalyst and one or more additions in the form of carbide additions, may be leached from the interstices 24 in the body of PCD material 12 by exposing the PCD material to an example leaching mixture for example in liquid or vapour form. The PCD region 12 of the PCD compacts 1 to be leached by examples of the acid leaching mixture typically, but not exclusively, may have a thickness of about 1.5 mm to about 4 mm. Figure 3 is a flow diagram of a method 1000 for processing a body of PCD material 12 using the exemplary acid leaching mixture. As illustrated in this figure, and as indicated at 1002, at least a portion of the body of PCD material to be processed is exposed to the example acid leaching mixture having a molar concentration of between around 4M to around 9M, the mixture being for example in aqueous form, or in vapour form, and includes hydrofluoric (HF) acid, any one or more of nitric (HNO3) acid, hydrochloric (HCI) acid, sulfuric (H2SO4) acid, and / or phosphoric (H3PO4) acid, and water. In some examples, the leaching mixture includes hydrofluoric acid at a molar concentration of between around 4M to around 9M and optionally nitric acid at a molar concentration of between around 4M to around 9M, and the water. In one example the leaching mixture includes hydrofluoric acid at a molar concentration of between around 5 M to around 7M and nitric acid at a molar concentration of between around 6.7M to around 8M and water. In some examples, the hydrofluoric acid forms between around 10 vol% to around 30 vol% of the acid mixture, for example around 18 vol % for example at a concentration of around 5M. In some examples, the acid leaching mixture, in addition to including the hydrofluoric acid of the above examples, includes nitric acid forming between around 30 vol% to around 60 vol % of the acid mixture, for example around 44 vol% for example at a concentration of around 6.7M. In some examples, the water content of the acid mixture forms between around 20 to around 50 vol% of the mixture. In some examples, the acid leaching mixture is in vapour form derived from an aqueous solution of the acid leaching mixture described and claimed herein. Expressed differently in terms of the wt%, in some examples the leaching mixture may include between around 13wt% to around 20wt% hydrofluoric acid, between around 50wt% to around 60wt% nitric acid and between around 20wt% to around 40wt% water. The water may be de-ionized water. The body of PCD material 12 may be exposed to such an example acid leaching mixture in any suitable manner including, for example, during an aqueous leaching technique in which at least a portion of the body of PCD material 12 to be leached is immersed in the example leaching mixture for a period of time at an elevated temperature to leach the body of PCD material. In some examples a technique such as that described in U.S. patent no. 8,002,859 or U.S. patent no. 9,981,362, in which the PCD is exposed to the acid mixture at elevated temperature and pressure may be used to leach the body of PCD material. In other examples, a vapour leaching technique such as that described in U.S. patent no. 9,156,136 may be used to leach the body of PCD material using the example acid mixture and in such a technique the PCD cutter element to be leached is spaced from the liquid acid leaching mixture which is then heated to convert at least a portion of the liquid acid leaching mixture to vapour form, the PCD to be leached being exposed to the acid vapour and leached using the vapour form of the acid leaching mixture. The teachings of these aforementioned patents are hereby incorporated by reference in their entirety. According to some examples, in stage 1002, the body 12 of PCD material may be exposed to the leaching mixture at an elevated temperature, for example to a temperature at which the acid leaching mixture is boiling such as temperatures of between around 40 to around 70 degrees Celsius. According to other examples, the body 12 of PCD material may be exposed to the leaching mixture at a higher temperature, for example temperatures of between around 140 to around 300 degrees Celsius at which the example acid leaching mixture may at whole or in part be in vapour form, the vapour being used to leach the body of PCD material. Exposing the body of PCD material to an elevated temperature during leaching may increase the depth to which the body of PCD material may be leached and reduce the leaching time necessary to reach the desired leach depth. If only a portion of the body of PCD material 12 is to be leached and if it is still attached to the substrate 10, the substrate 10 may be at least partially surrounded by a protective layer or seal such as an o-ring seal to prevent the leaching mixture from chemically damaging certain portions of the body of PCD material and / or the substrate 10 attached thereto during the leaching process. Such a configuration may assist in selective leaching of the body of PCD material to create a desired leach profile in the PCD material, which may be beneficial and tailored to the desired end application. Following leaching, the protective layer or mask or seal is removed. Also, after exposure to the acid leaching mixture for the desired time, the body of PCD material is rinsed to remove residual acid leaching mixture therefrom, as illustrated in step 1200 in Figures. Additionally, in some examples, at least a portion of the body of PCD material and the leaching solution may be exposed to at least one of an electric current, microwave radiation, and / or ultrasonic energy to increase the rate at which the body of PCD material is leached. Some versions are described in more detail with reference to the following examples which are not intended to be limiting. The following examples provide further detail in connection with the examples described above. Example 1 Cutting elements, each comprising a body of PCD material 12 attached to a tungsten carbide substrate 10, were formed by HPHT sintering of diamond particles in the presence of cobalt. The sintered bodies of PCD material included cobalt within the interstitial regions between the inter-bonded diamond grains. Each body of PCD material 12 was leached using a leaching mixture including 44 vol% 6.7M nitric acid, 18 vol% 5M hydrofluoric acid and 38 vol% deionized water. The processing technique used was a vapour leaching technique in which the cutters were placed in individual leaching chambers and suspended above an amount of the example acid leaching mixture, the mixture filling around 50% of the volume of the leaching chamber. The chamber was sealed and heated to a temperature of around 180 degrees C to vaporize at least a portion of the acid leaching mixture. The bodies of PCD materials were leached by the acid vapour for 100 hours. At this time the leach depth of the body of PCD material was determined for various portions of the PCD table, through x-ray analysis. It was found that an average leach depth of between around 800 to around 1541 microns had been achieved after 100 hours. This is in contrast to an equivalent cutting element formed of an identical PCD table attached to a tungsten carbide substrate leached according to a conventional leaching mixture (comprising for example hydrofluroric acid (HF) and nitric acid diluted in water HF:HNOa (1:3)) and using conventional aqueous leaching techniques in which the body of PCD material to be leached is immersed in part in a conventional acid leaching mixture and heated to between around 40-70 degrees C for around 100 hours to leach the PCD material and, using such a technique, the bodies of PCD material so leached were found to have an average leach depth of around 345 microns after 100 hours. Example 2 Cutting elements, each comprising a body of PCD material 12 attached to a tungsten carbide substrate 10, were formed by HPHT sintering of diamond particles in the presence of cobalt. The sintered bodies of PCD material included cobalt within the interstitial regions between the inter-bonded diamond grains. Each body of PCD material 12 was leached using a leaching mixture including 44 vol% 6.7M nitric acid, 18 vol % 5M hydrofluoric acid and 38 vol % deionized water. The processing technique used was a vapour leaching technique in which the cutters were placed in individual leaching chambers and suspended above an amount of the example acid leaching mixture, the mixture filling around 50% of the volume of the leaching chamber. The chamber was sealed and heated to a temperature of around 200 degrees C to vaporize at least a portion of the acid leaching mixture. The bodies of PCD materials were leached by the acid vapour for 100 hours. At this time the leach depth of the body of PCD material was determined for various portions of the PCD table, through x-ray analysis. It was found that an average leach depth of between around 800 to around 1133 microns had been achieved after 100 hours. Example 3 Cutting elements, each comprising a body of PCD material 12 attached to a tungsten carbide substrate 10, were formed by HPHT sintering of diamond particles in the presence of cobalt. The sintered bodies of PCD material included cobalt within the interstitial regions between the inter-bonded diamond grains. Each body of PCD material 12 was leached using a leaching mixture including around 44 vol % 6.7M nitric acid, around 18 vol % 5M hydrofluoric acid and around 38 vol % deionized water. The processing technique used was a vapour leaching technique in which the cutters were placed in individual leaching chambers and suspended above an amount of the example acid leaching mixture, the mixture filling around 50% of the volume of the leaching chamber. The chamber was sealed and heated to a temperature of around 200 degrees C to vaporize at least a portion of the acid leaching mixture. The bodies of PCD materials were leached by the acid vapour for 100 hours. At this time the leach depth of the body of PCD material was determined for various portions of the PCD table, through x-ray analysis. It was found that an average leach depth of around 1023 microns had been achieved after 100 hours. Example 4 The same technique as described above in Examples 1 to 3 was applied to leach PCD cutters using each having a body of PCD material 12 to be leached, but in this example a leaching mixture including around 30-60 vol % 7.5M nitric acid, around 10-30 vol % 6.7M hydrofluoric acid and the remainder vol % being deionized water was used. The bodies of PCD materials were leached by the acid vapour for 100 hours. At this time the leach depth of the body of PCD material was determined for various portions of the PCD table, through x-ray analysis. It was found that an average leach depth of around 1029 microns had been achieved after 100 hours. Example 5 The same technique as described above in Examples 1 to 3 was applied to leach PCD cutters using each having a body of PCD material 12 to be leached, but in this example a leaching mixture including around 40-50 vol % 8.5M nitric acid, around 10-20 vol % 8M hydrofluoric acid and the remainder vol % being deionized water was used. The bodies of PCD materials were leached by the acid vapour for 100 hours. At this time the leach depth of the body of PCD material was determined for various portions of the PCD table, through x-ray analysis. It was found that an average leach depth of around 894 microns had been achieved after 100 hours. Example 6 The same technique as described above in Examples 1 to 3 was applied to leach PCD cutters using each having a body of PCD material 12 to be leached, but in this example a leaching mixture including around 30 - 60 vol % 9.2M nitric acid, around 10-30 vol % 9.6M hydrofluoric acid and the remainder vol % being deionized water was used. The bodies of PCD materials were leached by the acid vapour for 100 hours. At this time the leach depth of the body of PCD material was determined for various portions of the PCD table, through x-ray analysis. It was found that an average leach depth of around 762 microns had been achieved after 100 hours. Example 7 The same technique as described above in Examples 1 to 3 was applied to leach PCD cutters using each having a body of PCD material 12 to be leached, but in this example a leaching mixture including around 30-60 vol % 6.9M nitric acid, around 10-30 vol % 9.6M hydrofluoric acid and the remainder vol % being around 10-50 vol % deionized water was used. The bodies of PCD materials were leached by the acid vapour for 100 hours. At this time the leach depth of the body of PCD material was determined for various portions of the PCD table, through x-ray analysis. It was found that an average leach depth of around 824 microns had been achieved after 100 hours. When compared with the leach depths achievable using conventional leaching solutions, such as hydrofluroric acid (HF) and nitric acid diluted in water HF:HNOs (1:3), it has been determined that the examples including the above leaching mixtures may enable a greater leaching efficiency to be achieved with greater leach depths being achievable in a shorter period of time, in some cases enabling the desired leach depth to be achieved around 4 to around 6 times faster than using conventional acid leaching mixtures and processing techniques. The preceding description has been provided to enable others skilled the art to best utilize various aspects described by way of example herein. This description is not intended to be exhaustive or to be limited to any precise form disclosed. Many modifications and variations are possible. In particular, some example methods may be equally applicable to the effective leaching of PCD with other additives or interstitial material such as those in the form of other metal carbides including one or more of a carbide of tungsten, titanium, niobium, tantalum, zirconium, molybdenum, vanadium or chromium.

Claims

1. An acid leaching mixture for removing residual solvent catalyst material from a body of polycrystalline diamond (PCD) material having a non-diamond phase comprising the solvent catalyst material, the acid leaching mixture having a molar concentration of between around 4M to around 9M and comprising:hydrofluoric (HF) acid;any one or more of hydrochloric (HCI) acid, nitric (HNO3) acid, sulfuric (H2SO4) acid, and / or phosphoric (H3PO4) acid; andwater.

2. The acid leaching mixture of claim 1, wherein the leaching mixture comprises hydrofluoric acid at a molar concentration of between around 4M to around 9M.

3. The acid leaching mixture of any one of the preceding claims, wherein the leaching mixture comprises nitric acid at a molar concentration of between around 4M to around 9M.

4. The acid leaching mixture of claim 1, wherein the leaching mixture comprises hydrofluoric acid at a molar concentration of between around 5 M to around 7M; and nitric acid at a molar concentration of between around 6.7M to around 8M; and said water.

5. The acid leaching mixture of any one of the preceding claims, wherein the water is de-ionized water.

6. The acid leaching mixture of any one of the preceding claims, wherein the hydrofluoric acid comprises between around 10 vol% to around 30 vol% of the acid mixture.

7. The acid leaching mixture of claim 6, wherein the nitric acid comprises between around 30 vol % to around 60 vol % of the acid mixture.

8. The acid leaching mixture of any one of claims 6 or 7, comprising between around 20 to around 50 vol% water.

9. The acid leaching mixture of any one of the preceding claims, wherein the leaching mixture is in aqueous form.

10. The acid leaching mixture of any one of claims 1 to 8, wherein the leaching mixture is in vapour form.

11. An acid leaching mixture for removing catalyst solvent material from a body of polycrystalline diamond (PCD) material having a non-diamond phase comprising the catalyst solvent material, the mixture being in vapour form derived from an aqueous solution of the acid leaching mixture of any of claims 1 to 8.

12. An acid leaching mixture for removing catalyst solvent material from a body of polycrystalline diamond (PCD) material having a non-diamond phase comprising the catalyst solvent material, the mixture comprising:between around 13wt% to around 20wt% hydrofluoric acid;between around 50wt% to around 60wt%; nitric acid; and between around 20wt% to around 40wt% water.

13. The acid leaching mixture of claim 12, wherein:the hydrofluoric acid in the leaching mixture comprises around 14wt%, optionally around 13.8 wt%;the nitric acid in the leaching mixture comprises around 51 wt%, optionally around 51,6wt%; andthe water in the leaching mixture comprises around 35wt%, optionally around 34.6wt%, the water comprising de-ionized water.

14. The acid leaching mixture of claim 12, wherein:the hydrofluoric acid in the leaching mixture comprises around 13wt%, optionally around 13.5 wt%;the nitric acid in the leaching mixture comprises around 60 wt%, optionally around 59.8wt%; andthe water in the leaching mixture comprises around 27 wt%, optionally around 26.7wt%, the water comprising de-ionized water.

15. The acid leaching mixture of claim 12, wherein:the hydrofluoric acid in the leaching mixture comprises around 19 wt%, optionally around 19.2 wt%;the nitric acid in the leaching mixture comprises around 51 wt%, optionally around 51.1wt%; andthe water in the leaching mixture comprises around 30 wt%, optionally around 29.7wt%, the water comprising de-ionized water.

16. The acid leaching mixture of claim 12, wherein:the hydrofluoric acid in the leaching mixture comprises around 19 wt%, optionally around 18.7 wt%;the nitric acid in the leaching mixture comprises around 60 wt%, optionally around 59.3wt%; andthe water in the leaching mixture comprises around 21wt%, optionally around 20wt%, the water comprising de-ionized water.21

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