Cobalt removal method for polycrystalline diamond

Abstract

The invention relates to a cobalt removal method for polycrystalline diamond, and belongs to the technical field of polycrystalline diamond processing. The cobalt removal method of the polycrystalline diamond comprises the following steps: immersing the polycrystalline diamond in cobalt removal liquid for ultrasonic treatment; the cobalt removal liquid is mainly composed of an acidic compound, water-soluble hydrochloride and water. According to the cobalt removal method for the polycrystalline diamond, cobalt, tungsten and other metals in the polycrystalline diamond are preliminarily dissolved by utilizing the permeation and immersion effect of the acidic compound, and meanwhile, the dissolving capacity of metal ions is improved by utilizing the metal coordination effect of the water-soluble hydrochloride; besides, energy (high-frequency vibration and high radiation pressure) of ultrasonic waves acts on the cobalt removal liquid and the polycrystalline diamond, the collision frequency of the cobalt removal liquid and the polycrystalline diamond can be increased, metal dissolution is accelerated, the metal removal effect is improved, and rapid and deep cobalt removal can be achieved.

Description

Technical Field

[0001] This invention relates to a method for removing cobalt from polycrystalline diamond, belonging to the field of polycrystalline diamond processing technology. Background Technology

[0002] Polycrystalline diamond composite sheets, often referred to as the "teeth of industry," are abbreviated as PDC. They are made by sintering a cemented carbide matrix with diamond micropowder or a small amount of cobalt powder under high temperature and high pressure (HTHP) with cobalt as a catalyst. They possess excellent performance and are primarily used in drilling and extraction of oil and natural gas. Cobalt plays a role in promoting the formation of DD bonds between diamond microparticles during PDC synthesis. However, cobalt has a strong affinity for carbon under high temperature and low pressure, which can cause diamond to transform into graphite, leading to reduced wear resistance of the composite sheet. Furthermore, the significant difference in thermal expansion coefficients between cobalt and diamond can easily lead to increased stress during the high temperatures of drilling, causing internal cracks in the PDC and resulting in failures such as wear, chipping, and tooth breakage.

[0003] To mitigate the negative impacts (thermal expansion, thermal catalysis, thermal oxidation, etc.) of cobalt binder on the polycrystalline diamond layer after synthesis, composite sheet manufacturers often employ acid leaching or electrolysis to remove cobalt or partially remove cobalt from the polycrystalline diamond layer after synthesis, thereby improving the thermal stability of the composite sheet. While electrolysis has drawbacks such as high equipment requirements, complex processes, and the need for large quantities of electrolyte, acid leaching is relatively cheaper and easier to scale up.

[0004] Chinese invention patent application CN115768925A, published on March 7, 2023, discloses a cobalt removal solution composed of nitric acid and hydrofluoric acid. The cobalt removal depth of polycrystalline diamond composite sheets can reach 1200μm after immersing them in the solution at 70°C for 900 hours. However, the solution uses hydrofluoric acid, which is harmful to the human body, and is therefore quite hazardous.

[0005] Chinese invention patent application CN111911082A, published on November 10, 2020, discloses a method for removing cobalt from polycrystalline diamond composite sheets by immersing them in a cobalt-removing solution. The solution comprises a first cobalt-removing solution mainly composed of Lewis acid, ferric chloride, and hydrochloric acid, and a second cobalt-removing solution mainly composed of nitric acid, hydrofluoric acid, and hydrogen peroxide. Alternating between these two solutions can improve the strengthening effect. However, this cobalt-removing method is cumbersome and complex to operate. Summary of the Invention

[0006] The purpose of this invention is to provide a method for removing cobalt from polycrystalline diamond, which can solve the problems of the high hazard of the cobalt removal solution or the complexity of the cobalt removal process when using acid leaching to remove metal from polycrystalline diamond.

[0007] To achieve the above objectives, the technical solution adopted by the cobalt removal method for polycrystalline diamond of the present invention is as follows: A method for removing cobalt from polycrystalline diamond includes the following steps: immersing the polycrystalline diamond in a cobalt removal solution for intermittent ultrasonic treatment; the cobalt removal solution mainly consists of an acidic compound, a water-soluble hydrochloride, and water; the acidic compound includes HCl and HNO3; the mass fraction of the acidic compound in the cobalt removal solution is not less than 20%; the concentration of the water-soluble hydrochloride in the cobalt removal solution is 0.1~17 mol / L.

[0008] The cobalt removal method for polycrystalline diamond of this invention utilizes the penetration of acidic compounds to initially dissolve metals such as cobalt and tungsten in the polycrystalline diamond. Simultaneously, the metal coordination effect of water-soluble hydrochloride enhances the solubility of metal ions. Furthermore, the energy of ultrasound (high-frequency vibration and high radiation pressure) acts on the decobalt removal solution and polycrystalline diamond, increasing the collision frequency between them, accelerating metal dissolution, and improving the metal removal effect, enabling rapid and deep cobalt removal. This method allows for a cobalt removal depth of 1000-1300 μm in polycrystalline diamond products, significantly greater than the commonly used cobalt removal depth (below 800 μm) in the market. This effectively improves the thermal stability and wear resistance of the decobalt-removed polycrystalline diamond composite sheet, increases its service life, and reduces drilling and extraction costs for oil, natural gas, and other resources.

[0009] Preferably, the intermittent ultrasound treatment is repeated in units of 1-2 hours of ultrasound followed by 30-60 minutes of intermittent ultrasound, with a total treatment time of 5-30 days. To further enhance the ultrasonic effect and facilitate the dissolution of metals in polycrystalline diamond into the cobalt removal solution, in some preferred embodiments, the ultrasonic frequency during treatment is 35-45 kHz, and the power density is 0.5-1.2 W / cm³. 2 .

[0010] Preferably, the mass fraction of acidic compounds in the cobalt removal solution is 20-68%. More preferably, the mass fraction of acidic compounds in the cobalt removal solution is 20-45%.

[0011] Preferably, the mass ratio of HCl to HNO3 is (1~9):(1~9). More preferably, the mass ratio of HCl to HNO3 is (1.2~1.4):1. For example, the mass ratio of HCl to HNO3 is 1.3:1.

[0012] Preferably, the water-soluble hydrochloride is selected from one or any combination of sodium chloride, potassium chloride, magnesium chloride, calcium chloride, ferric chloride, and ammonium chloride. More preferably, the concentration of the water-soluble hydrochloride in the cobalt removal solution is 0.1~0.5 mol / L.

[0013] Preferably, the temperature of the cobalt removal solution is 20~90°C. More preferably, the temperature of the cobalt removal solution is 65~75°C. For example, the temperature of the cobalt removal solution is 70°C. Detailed Implementation

[0014] (I) Description of preferred embodiments of the method for removing cobalt from polycrystalline diamond according to the present invention This invention utilizes the penetrating effect of acidic compounds to initially dissolve metals such as cobalt and tungsten in polycrystalline diamond. Simultaneously, it utilizes the metal coordination effect of water-soluble hydrochloride to enhance the solubility of metal ions. In addition, the energy of ultrasound (high-frequency vibration and high radiation pressure) acts on the decobalt removal solution and polycrystalline diamond, which can increase the collision frequency between the decobalt removal solution and polycrystalline diamond, accelerate the dissolution of metals, improve the metal removal effect, and achieve rapid and deep decobalt removal.

[0015] The cobalt removal method for polycrystalline diamond of the present invention can achieve a cobalt removal depth of 1000~1300μm for polycrystalline diamond products, which is significantly greater than the cobalt removal depth of commonly used polycrystalline diamond products on the market (below 800μm). This can effectively improve the thermal stability and wear resistance of the polycrystalline diamond composite sheet after cobalt removal, increase the service life of the diamond composite sheet, and reduce the drilling and mining costs of oil, natural gas, etc.

[0016] The method for removing cobalt from polycrystalline diamond according to the present invention includes the following steps: immersing polycrystalline diamond in a cobalt removal solution for ultrasonic treatment; the cobalt removal solution mainly consists of an acidic compound, a water-soluble hydrochloride, and water; the acidic compound includes HCl and HNO3.

[0017] Using HCl and HNO3 as acidic compounds can effectively enhance their ability to penetrate the interior of polycrystalline diamond and dissolve metals, thereby improving the cobalt removal effect. The mass ratio of HCl to HNO3 can be (1~9):(1~9), more preferably (1.2~1.4):1. The mass fraction of acidic compounds in the cobalt removal solution can be 20~68%, and in some more preferred embodiments, the mass fraction of acidic compounds in the cobalt removal solution is 20~45%. If the mass fraction of acidic compounds in the cobalt removal solution is too low, the cobalt removal effect will be unsatisfactory; if the mass fraction of acidic compounds in the cobalt removal solution is too high, there will be less hydrogen ion ionization, which is not conducive to increasing the acidity of the cobalt removal solution and affects the cobalt removal effect.

[0018] The water-soluble hydrochloride is selected from one or any combination of sodium chloride, potassium chloride, magnesium chloride, calcium chloride, ferric chloride, and ammonium chloride. The chloride ions in the water-soluble hydrochloride have a strong coordination ability and can form stable soluble coordination ions with cobalt ions, thereby accelerating the dissolution of cobalt and improving the cobalt removal effect of polycrystalline diamond.

[0019] To better leverage the synergistic effect with acidic compounds, and to optimally utilize the corrosive and penetrating properties of the acidic compounds as well as the coordination effect of the water-soluble hydrochloride salt to achieve a synergistic metal removal effect and good cobalt removal efficiency, the concentration of water-soluble hydrochloride salt in the cobalt removal solution can be 0.1~17 mol / L. In some more preferred embodiments, the concentration of water-soluble hydrochloride salt in the cobalt removal solution is 0.1~0.5 mol / L.

[0020] To improve the cobalt removal effect and to avoid harm to human health from the volatilization of acidic compounds in the cobalt removal solution, in some preferred embodiments, the temperature of the cobalt removal solution is 20~90°C. In some more preferred embodiments, the temperature of the cobalt removal solution is 65~75°C. For example, the temperature of the cobalt removal solution is 70°C.

[0021] The polycrystalline diamond suitable for use in this invention can be a polycrystalline diamond composite sheet. To protect the metal alloy substrate in the polycrystalline diamond composite sheet from corrosion by the cobalt removal solution during ultrasonic treatment, the alloy substrate in the polycrystalline diamond composite sheet is sealed before ultrasonic treatment. The material used to seal the alloy substrate is an acid- and corrosion-resistant material, such as PVDF, PVC, PP, or PE.

[0022] To further improve the cobalt removal effect, in some preferred embodiments, the cobalt removal method for polycrystalline diamond further includes the following steps: cleaning the polycrystalline diamond with a solvent, drying it, and then performing the ultrasonic treatment. In some preferred embodiments, the solvent is selected from acetone, water, and alcohol, or any combination thereof. In some preferred embodiments, the cleaning involves sequentially cleaning the polycrystalline diamond with acetone, water, and alcohol.

[0023] In some preferred embodiments, the method for removing cobalt from polycrystalline diamond further includes the following step: after ultrasonic treatment, cleaning the ultrasonically treated polycrystalline diamond. Cleaning the ultrasonically treated polycrystalline diamond can remove the cobalt removal solution and metal ions remaining on and inside the polycrystalline diamond, thereby improving the cobalt removal effect.

[0024] The technical solution of the present invention will be further described below with reference to specific embodiments. In the following embodiments, unless otherwise specified, all raw materials are commercially available conventional raw materials, and the processing methods involved are conventional methods. Unless otherwise specified, "%" refers to mass fraction.

[0025] Example 1 The method for removing cobalt from polycrystalline diamond in this embodiment specifically adopts the following steps: (1) The polycrystalline diamond composite sheet of model 1613 was cleaned with acetone, water and alcohol in sequence to remove oil stains and dirt on the surface of the polycrystalline diamond composite sheet, and then dried.

[0026] (2) Use acid-resistant and corrosion-resistant material (PVDF) to seal the polycrystalline diamond composite sheet to ensure that the alloy substrate is in a sealed state and expose the polycrystalline diamond layer, so as to reduce the corrosion of the alloy substrate by the decobalt removal liquid during decobalt removal.

[0027] (3) Place the sealed polycrystalline diamond composite sheet into the reactor, and then add the cobalt removal solution to the reactor to ensure that the polycrystalline diamond layer in the sealed polycrystalline diamond composite sheet is completely immersed in the cobalt removal solution. Then place the reactor in an ultrasonic constant temperature chamber and control the temperature of the cobalt removal solution in the reactor to 70°C. Then turn on the ultrasonic treatment and use intermittent ultrasonic treatment to ultrasonically treat the polycrystalline diamond layer immersed in the cobalt removal solution. Ultrasonic treatment is performed for 1 hour, followed by a 30-minute interval, and this cycle is repeated until the intermittent ultrasonic treatment time reaches 15 days. After ultrasonic treatment, the polycrystalline diamond composite sheet is taken out and cleaned to obtain the cobalt-removed polycrystalline diamond composite sheet. In this embodiment, the ultrasonic frequency during ultrasonic treatment is 42KHz and the power is 0.8W / cm. 2 .

[0028] The cobalt removal solution used in this embodiment consists of an acidic compound, hydrochloride, and water. The acidic compound is composed of HCl and HNO3 in a mass ratio of 1.3:1. The hydrochloride is potassium chloride. The mass fraction of the acidic compound in the cobalt removal solution is 45%, and the concentration of the hydrochloride in the cobalt removal solution is 0.1 mol / L.

[0029] The cobalt removal solution used in this embodiment is prepared by a method including the following steps: concentrated hydrochloric acid and concentrated nitric acid are stirred evenly to obtain an acidic compound solution, and then potassium chloride is added to the acidic compound solution and stirred until the potassium chloride is completely dissolved to obtain the cobalt removal solution.

[0030] Based on this embodiment, cobalt removal is carried out under the process parameters defined in this invention. For example, sodium chloride is selected as the water-soluble hydrochloride, and the concentration of the water-soluble hydrochloride is controlled at 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, and 0.5 mol / L, which can achieve the corresponding improvement effect of cobalt removal.

[0031] Example 2 The method for removing cobalt from polycrystalline diamond in this embodiment differs from the method in Example 1 only in that, in this embodiment, during intermittent ultrasonication, there is a 60-minute interval between every 1 hour of ultrasonication. The specific steps are as follows: (1) The polycrystalline diamond composite sheet of model 1613 was cleaned with acetone, water and alcohol in sequence to remove oil stains and dirt on the surface of the polycrystalline diamond composite sheet, and then dried.

[0032] (2) Use acid-resistant and corrosion-resistant material (PVDF) to seal the polycrystalline diamond composite sheet to ensure that the alloy substrate is in a sealed state and expose the polycrystalline diamond layer, so as to reduce the corrosion of the alloy substrate by the decobalt removal liquid during decobalt removal.

[0033] (3) Place the sealed polycrystalline diamond composite sheet into the reactor, and then add the cobalt removal solution to the reactor to ensure that the polycrystalline diamond layer in the sealed polycrystalline diamond composite sheet is completely immersed in the cobalt removal solution. Then place the reactor in an ultrasonic constant temperature chamber and control the temperature of the cobalt removal solution in the reactor to 70°C. Then turn on the ultrasonic treatment and use intermittent ultrasonic treatment to ultrasonically treat the polycrystalline diamond layer immersed in the cobalt removal solution. Ultrasonic treatment is performed for 1 hour, followed by a 60-minute interval, and this cycle is repeated until the intermittent ultrasonic treatment time reaches 15 days. After ultrasonic treatment, the polycrystalline diamond composite sheet is taken out and cleaned to obtain the cobalt-removed polycrystalline diamond composite sheet. In this embodiment, the ultrasonic frequency during ultrasonic treatment is 42KHz and the power is 0.8W / cm. 2 .

[0034] The cobalt removal solution used in this embodiment consists of an acidic compound, hydrochloride, and water. The acidic compound is composed of HCl and HNO3 in a mass ratio of 1.3:1. The hydrochloride is potassium chloride. The mass fraction of the acidic compound in the cobalt removal solution is 45%, and the concentration of the hydrochloride in the cobalt removal solution is 0.1 mol / L.

[0035] Example 3 The method for removing cobalt from polycrystalline diamond in this embodiment differs from the method for removing cobalt from polycrystalline diamond in Example 1 only in that the mass fraction of the acidic compound in the cobalt removal solution used in this embodiment is 20%. The specific steps are as follows: (1) The polycrystalline diamond composite sheet of model 1613 was cleaned with acetone, water and alcohol in sequence to remove oil stains and dirt on the surface of the polycrystalline diamond composite sheet, and then dried.

[0036] (2) Use acid-resistant and corrosion-resistant material (PVDF) to seal the polycrystalline diamond composite sheet to ensure that the alloy substrate is in a sealed state and expose the polycrystalline diamond layer, so as to reduce the corrosion of the alloy substrate by the decobalt removal liquid during decobalt removal.

[0037] (3) Place the sealed polycrystalline diamond composite sheet into the reactor, and then add the cobalt removal solution to the reactor to ensure that the polycrystalline diamond layer in the sealed polycrystalline diamond composite sheet is completely immersed in the cobalt removal solution. Then place the reactor in an ultrasonic constant temperature chamber and control the temperature of the cobalt removal solution in the reactor to 70°C. Then turn on the ultrasonic treatment and use intermittent ultrasonic treatment to ultrasonically treat the polycrystalline diamond layer immersed in the cobalt removal solution. Ultrasonic treatment is performed for 1 hour, followed by a 30-minute interval, and this cycle is repeated until the intermittent ultrasonic treatment time reaches 15 days. After ultrasonic treatment, the polycrystalline diamond composite sheet is taken out and cleaned to obtain the cobalt-removed polycrystalline diamond composite sheet. In this embodiment, the ultrasonic frequency during ultrasonic treatment is 42KHz and the power is 0.8W / cm. 2 .

[0038] The cobalt removal solution used in this embodiment consists of an acidic compound, hydrochloride, and water. The acidic compound consists of HCl and HNO3 in a mass ratio of 1.3:1. The hydrochloride is potassium chloride. The mass fraction of the acidic compound in the cobalt removal solution is 20%, and the concentration of the hydrochloride in the cobalt removal solution is 0.1 mol / L.

[0039] (ii) Comparative Example Comparative Example 1 The difference between the cobalt removal method of polycrystalline diamond in this comparative example and the cobalt removal method of polycrystalline diamond in Example 1 is that the acidic compound in the cobalt removal solution used in the cobalt removal method of polycrystalline diamond in this comparative example is HCl, and the mass fraction of the acidic compound is 45%.

[0040] Comparative Example 2 The difference between the cobalt removal method of polycrystalline diamond in this comparative example and the cobalt removal method of polycrystalline diamond in Example 1 is that the acidic compound in the cobalt removal solution used in the cobalt removal method of polycrystalline diamond in this comparative example is HNO3, and the mass fraction of the acidic compound is 45%.

[0041] Comparative Example 3 The only difference between the cobalt removal method of polycrystalline diamond in this comparative example and the cobalt removal method of polycrystalline diamond in Example 1 is that hydrochloric acid is not added to the cobalt removal solution.

[0042] (III) Experimental Examples To evaluate the cobalt removal effect of different polycrystalline diamond removal methods, the metal removal depth in the polycrystalline diamond layer of the polycrystalline diamond composite sheets treated in Examples 1-3 and Comparative Examples 1-3 was non-destructively tested using X-ray machine. The results are shown in Table 1. During the test, for different samples, five tests were performed by axial rotation five times, and then the numerical range of the tested metal removal depth was statistically analyzed (the two endpoints of the numerical range are the maximum and minimum values ​​of the metal removal depth obtained at the five locations, respectively).

[0043] Table 1. Metal removal depth of polycrystalline diamond layer in polycrystalline diamond composite sheets of various embodiments and comparative examples.

[0044] As shown in Table 1, the cobalt removal method of this invention can effectively remove metals such as Co, achieving a cobalt removal depth of 1000~1300 μm within the same time frame. The experimental results also demonstrate that, for the same required cobalt removal depth, this method offers a faster overall cobalt removal speed, which is beneficial for rapidly achieving deep cobalt removal.

[0045] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for removing cobalt from polycrystalline diamond, characterized in that, Includes the following steps: Polycrystalline diamond is immersed in a cobalt removal solution and subjected to intermittent ultrasonic treatment; the cobalt removal solution is mainly composed of acidic compounds, water-soluble hydrochloride and water; the acidic compounds include HCl and HNO3; the mass fraction of acidic compounds in the cobalt removal solution is not less than 20%; the concentration of water-soluble hydrochloride in the cobalt removal solution is 0.1~17 mol / L.

2. The method for removing cobalt from polycrystalline diamond as described in claim 1, characterized in that, The intermittent ultrasound is repeated in one ultrasound processing unit, with an ultrasound session of 1-2 hours followed by an interval of 30-60 minutes. The total processing time for the intermittent ultrasound is 5-30 days.

3. The method for removing cobalt from polycrystalline diamond as described in claim 1, characterized in that, The mass fraction of acidic compounds in the cobalt removal solution is 20-68%.

4. The method for removing cobalt from polycrystalline diamond as described in claim 3, characterized in that, The mass fraction of acidic compounds in the cobalt removal solution is 20-45%.

5. The method for removing cobalt from polycrystalline diamond as described in claim 1, characterized in that, The mass ratio of HCl to HNO3 is (1~9):(1~9).

6. The method for removing cobalt from polycrystalline diamond as described in claim 5, characterized in that, The mass ratio of HCl to HNO3 is (1.2~1.4):

1.

7. The method for removing cobalt from polycrystalline diamond as described in claim 1, characterized in that, The water-soluble hydrochloride is selected from one or any combination of sodium chloride, potassium chloride, magnesium chloride, calcium chloride, ferric chloride, and ammonium chloride.

8. The method for removing cobalt from polycrystalline diamond as described in claim 7, characterized in that, The concentration of water-soluble hydrochloride in the cobalt removal solution is 0.1~0.5 mol / L.

9. The method for removing cobalt from polycrystalline diamond as described in any one of claims 1 to 8, characterized in that, The temperature of the cobalt removal solution is 20~90℃.

10. The method for removing cobalt from polycrystalline diamond as described in claim 9, characterized in that, The temperature of the cobalt removal solution is 65~75℃.

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