GB2465175A

GB2465175A - Method of leaching a polycrystalline diamond (PCD) table

Info

Publication number: GB2465175A
Application number: GB0820371A
Authority: GB
Inventors: Richard Bodkin; Iain Patrick Goudemond; Mehmet Serdar Ozbayraktar; John Liversage
Original assignee: Element Six Ltd
Current assignee: Element Six Ltd
Priority date: 2008-11-07
Filing date: 2008-11-07
Publication date: 2010-05-12
Also published as: GB0820371D0

Abstract

A method of leaching a polycrystalline diamond (PCD) table is disclosed where the polycrystalline diamond (PCD) table has a second phase which contains a diamond catalyst/solvent and WC (tungsten carbide). The method includes the steps of: (a) contacting the PCD table with a mineral acid selected from the group comprising HCl (hydrochloric acid), H2SO4(sulphuric acid), H3PO4(phosphoric acid), HNO3(nitric acid), HBr (hydrobromic acid), and HClO4(perchloric acid), for a time sufficient for the catalyst/solvent to be removed substantially from the PCD table to form a porous PCD table; and (b) contacting the porous PCD table with an HF-containing acid mixture, such as HF-HNO3(hydrofluoric acid and nitric acid), for a time sufficient to remove substantially all of any residual catalyst/solvent and the majority of the WC present in the porous PCD table. Step (a) may be carried out under reflux conditions or under HPHT conditions.

Description

METHOD OF LEACHING A POLYCRYSTALLINE DIAMOND (PCD) TABLE

BACKGROUND OF THE INVENTION

This invention relates to a method of leaching a polycrystalline diamond (PCD)

table.

Polycrystalline diamond, also known as a diamond abrasive compact, comprises a mass of diamond particles containing a substantial amount of direct diamond-to-diamond bonding. Polycrystalline diamond will generally have a second phase which contains a diamond catalyst/solvent such as cobalt, nickel, iron or an alloy containing one or more such metals.

When diamond particles are combined with a suitable metallic catalyst/solvent, this catalyst/solvent promotes diamond-to-diamond bonding between the diamond grains, resulting in an intergrown or sintered structure. This intergrown diamond structure therefore comprises original diamond grains as well as newly precipitated or re-grown diamond phase, which bridges these original grains. In the final sintered structure, catalyst/solvent material remains present within the interstices that exist between the sintered diamond grains. The sintered POD has sufficient wear resistance and hardness for use in aggressive wear, cutting and drilling applications.

A well-known problem experienced with this type of PCD compact, however, is that the residual presence of solvent/catalyst material in the microstructural interstices has a detrimental effect on the performance of the compact at high temperatures.

A potential solution to this problem is to remove the catalyst/solvent or binder phase from the POD material.

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 POD 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 POD table and the corrosive solution to accelerate the dissolution rate of the catalyst/solvent.

US 4,572,722 discloses a leaching process which is accelerated by forming a hole in the POD table by laser cutting or spark emission prior to or during the leaching process. The POD table is then leached by using conventional acid leaching techniques, electrolytic leaching and liquid zinc extraction. In particular, this reference discloses leaching the POD table by using HOl and HF in the presence of a Platinum Group metal catalyst.

US 3,745,623 and US 4,636,253 teach the use of acid mixtures in the leaching process in which mixtures of HF, HOl, and HNO3 and HNO3 and HF, respectively, are used. In such cases heat is used to accelerate the rate of leaching.

US 4,288,248 and us 4,224,380 describe removal of the catalyst/solvent by using a two step leaching process in which the POD tables are alternatively placed in a first hot medium comprising HNO3-HF (nitric acid and hydrofluoric acid) and in a second hot medium comprising HOI-HNO3 (hydrochloric acid and nitric acid). The patents describe leaching coarse POD grain plates having a thickness of 0.5mm. The leaching process is again accelerated by using hot acids.

As outlined above it is, typically, extremely difficult and time consuming to effectively remove the bulk of a metallic catalyst/solvent from a POD table, particularly from the thicker POD tables required by current applications. In general, the current art is focussed on achieving POD of high diamond density and commensurately POD that has an extremely fine distribution of metal catalyst/solvent pools. This fine network resists penetration by the leaching agents, such that residual catalyst/solvent 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.

SUMMARY OF THE INVENTION

According to the invention a method of leaching a polycrystalline diamond (POD) table having a second phase which contains a diamond catalyst/solvent and WO (tungsten carbide) includes the steps of: (a) contacting the POD table with a mineral acid selected from the group comprising HOI (hydrochloric acid), H2S04 (sulphuric acid), H3P04 (phosphoric acid), HNO3 (nitric acid), HBr (hydrobromic acid), and HOIO4 (perchloric acid), in particular HOI, for a time sufficient for the catalyst/solvent to be removed substantially from the POD table to form a porous POD table; and (b) contacting the porous POD table with an Hf-containing acid mixture, in particular Hf-HNO3 (hydrofluoric acid and nitric acid), for a time sufficient to remove substantially all of any residual catalyst/solvent and the majority of the WO present in the porous POD table.

Preferably, at least 80 wt%, more preferably at least 85 wt%, of the catalyst/solvent, such as cobalt, nickel, iron or an alloy containing one or more such metals, in particular cobalt, is removed by the mineral acid in step (a).

Typically, about 65 wt% or more, preferably at least 80 wt%, of the WO is removed by the Hf-containing acid mixture in step (b).

Although the first step (a) of removing the catalyst/solvent may be carried out under reflux conditions (for example 11 6 °O and room pressure for HOl), the removal thereof under high temperature and high pressure conditions is preferred. Where high temperature and high pressure conditions are used, temperatures of from about 90 to about 350°O, in particular about 220°O, and pressures of from about 5 to about 345 bar, in particular about 20 bar, may be applied to the PCD table.

The PCD table is contacted with the mineral acid in step (a) for a period of between 80 hours and 500 hours, which is the time typically required for the catalyst/solvent to be removed substantially from the POD table.

During the second step (b) of the method, the HF-containing acid mixture preferably removes substantially all remaining or residual catalyst/solvent material and substantially all tungsten carbide from the POD table.

The thickness of the POD table to be leached may be in the region of about 1.5mm to about 3.0mm.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail, by way of example only, with reference to the accompanying figures in which: Figure 1 shows a graph of the reaction rate of a typical HF:HNO3 (1:3) leaching method and the % weight loss of the POD table over time; Figure 2 shows a graph of comparative results of a one step HF-HNO3 process and the method of the present invention; and Figure 3 shows a graph of comparative results of one step HF-HNO3 and HCI processes and the method of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

This invention concerns a method of leaching a polycrystalline diamond (POD)

table.

In accordance with the method of the invention, a sintered POD table having diamond to diamond bonding and having a second phase comprising catalyst/solvent and WC (tungsten carbide) dispersed through its microstructure is provided. The POD table is typically formed in the presence of conventional diamond catalyst/solvent according to standard methods using HpHT conditions to produce a sintered POD table. The POD tables to be leached by the method of the invention typically have a thickness of about 1.5 mm to about 3.0 mm.

It has been found that the removal of WC within the POD table is necessary where it is desired to reattach the polycrystalline diamond disk to a carbide post, which is typically accompanied by re-infiltration of, for example, a binder material in order for such re-attachment to be successful. The carbide grains can potentially block the pathways along which re-infiltration occurs. These blockages prevent the complete re-infiltration of the binder material during the reattachment cycle, which in turn has deleterious consequences for the reattachment process.

For instance, the tables crack across the length of the reattached piece with the crack contained within the POD material. It is believed that these cracks are associated with a poorer strength material that is formed as a result of the partial re-infiltration that has been achieved by the presence of the carbide grains.

The reaction rate regarding leaching is considered to be dominated by the chemical rate initially as acid contacts a surface of the PCD table and later by the diffusion rate as the acid diffuses through the pores of the PCD table.

HF-HNO3 has been shown to be the most effective media for the removal of tungsten carbide (WC) in the sintered POD table. The problem with HF-HNO3 is that it is volatile arid when heating this acid specific technology, for example, gas sealing technology, is required. If such technology is not provided then the application of temperature will reduce the efficacy of HF-HNO3 due to evaporation of the HF (poisonous) and formation of NO species, which are usually gaseous, and thus frequent replenishment of the acid media is required. Furthermore, as outlined above heat would ordinarily be required to accelerate the leaching process in order to render the process commercially feasible. Another problem is that HF-HNO3 is corrosive to most containment vessels making the reaction difficult to perform.

HCI and other similar mineral acids are easier to work with at high temperatures than HF-HNO3 and are aggressive towards the catalyst/solvent, particularly cobalt (Go). HGI, for example, removes the bulk of the catalyst/solvent from the PCD table in a reasonable time period, depending on the temperature, typically in the region of 80 hours, although it does not remove WO.

By providing a two step approach of contacting the POD table with a mineral acid such as HCI to form a porous POD table and then by contacting the porous POD table with HF-HNO3, the method of the present invention improves the diffusion rate of the reaction to accelerate the rate of leaching.

In order substantially to remove the catalystlsolvent and WC present in the POD table, the POD table is initially contacted with a mineral acid selected from the group comprising HOI (hydrochloric acid), H2S04 (sulphuric acid), H3P04 (phosphoric acid), HNO3 (nitric acid), HBr (hydrobromic acid), and H0104 (perchloric acid), in particular HOl, under reflux conditions, or more preferably at a temperature of from about 90 to about 350°O, in particular about 220°O, and a pressure of from about 5 to about 345 bar, in particular about 20 bar.

It is preferable to leach the POD table in such a manner as to remove the catalyst/solvent as fully as possible and to form a porous POD table. However, a certain amount of residual catalyst/solvent material may persist, either adhering to surfaces within the leached pores, or bound up by the POD table microstructure, particularly of the central volume of the POD table.

By creating a porous structure in step one of the method, the diffusion controlled regime is improved as the HF-containing acid mixture, in particular Hf-HNO3, penetrates the pores to remove the residual catalyst/solvent and in particular any The leaching reaction rate of a typical HF:H NO3 (1:3) leaching method is illustrated in Figure 1 of the drawings. Referring to Figure 1, from 0 to 100 hours the reaction rate is considered to be dominated by the chemical rate as the acid contacts a surface of the POD table or pore within the POD table. At approximately 100 hours the reaction rate flattens and is then dominated by the diffusion rate as the acid diffuses through the pores of the POD table. The mass that is lost during the acid treatment, as illustrated in Figure 1, is considered to be the catalyst/solvent and tungsten carbide (WO).

The improvement in the rate of leaching is illustrated in Figure 2, which compares a one step HF-HNO3 leaching process with an exemplary method of the present invention. The results labelled as 70°O and 90°O refer to a one step HF-HNO3 treatment. The two-step process illustrates a preferred embodiment of the present invention and refers to the initial acid treatment having been achieved in which the catalyst/solvent, in this case Oo, has substantially been removed from the POD table with HOl, whereafter it is contacted with HF:HNO3.

The comparison shows that the rate at which catalyst/solvent and WO can be removed from the POD table will be accelerated by utilising the two step process of the present invention.

As is evident from accompanying Figure 3, the two step process fully treats the disk after 96 hours, which compares favourably with an HOl treatment at 220 00, particularly as the HOI treatment does not remove any WO. The favourable leaching of catalyst/solvent and WO was achieved by firstly treating the table in HOl under reflux, although it could be achieved by treating the table under elevated pressure and temperature. The HOl does not fully treat the table since it leaves behind the WO material, hence the table is subsequently subjected to room pressure boiling HF-HNO3 (96°O) in Teflon beakers. With the Oo material having been removed substantially by the HOl treatment step, the capillaries have largely been opened and the HF-HNO3 is able to diffuse into the structure much more efficiently, allowing for complete leaching within 96 hours (less than hours).

Claims

CLAIMS1. A method of leaching a polycrystalline diamond (PCD) table having a second phase which contains a diamond catalyst/solvent and WC (tungsten carbide), the method including the steps of: (a) contacting the POD table with a mineral acid selected from the group comprising HCI (hydrochloric acid), H2S04 (sulphuric acid), H3P04 (phosphoric acid), HNO3 (nitric acid), HBr (hydrobromic acid), and HCIO4 (perchloric acid) for a time sufficient for the catalyst/solvent to be removed substantially from the POD table to form a porous POD table; and (b) contacting the porous POD table with an Hf-containing acid mixture for a time sufficient to remove substantially all of any residual catalyst/solvent and the majority of the WO present in the porous POD table.
2. A method according to Claim 1, wherein the mineral acid in step (a) is HCI.
3. A method according to Olaim 1 or Olaim 2, wherein the Hf-containing acid mixture in step (b) is Hf-H NO3.
4. A method according to any one of Claims 1 to 3, wherein in step (a) contacting of the PCD table with the mineral acid is carried out under reflux conditions.
5. A method according to any one of Claims 1 to 3, wherein in step (a) contacting of the POD table with the mineral acid is carried out under conditions of high temperature and high pressure.
6. A method according to Olaim 5, wherein the temperature is from about 90 to about 35000 and the pressure from about 5 to about 345 bar.
7. A method according to Claim 6, wherein the temperature is about 220°C and the pressure about 20 bar.
8. A method according to any one of Claims 1 to 7, wherein the POD table has a thickness of from about 1.5mm to about 3.0mm.