Novel cobalt removal method for diamond compact

Abstract

The invention provides a novel cobalt removal method for a diamond compact, and relates to the technical field of diamond compacts. The novel cobalt removal method for the diamond compact comprises the following steps: adding water into inorganic zinc-rich paint, copper powder, zinc oxide and mica powder, uniformly mixing, and stirring to obtain thin mucus; the method comprises the following steps: treating a diamond compact, coating dilute mucus by using a specific container, drying and grinding, sleeving a sealing ring, loading into a tool, putting into a high-temperature low-pressure reaction kettle, and removing cobalt by using a mixed reagent of hydrochloric acid, nitric acid and fluorine antimony sulfonic acid. According to the method, through double protection of physical barrier and chemical absorption, a sealing ring blocks a liquid reagent, a coating absorbs permeable gas, and a hard alloy matrix is protected; and meanwhile, the composite layer is in full contact with the reagent, and stirring and stepped heating are matched, so that the problems of difficult matrix protection and slow deep cobalt removal are solved, and safe, rapid and deep cobalt removal is realized.

Description

Technical Field

[0001] This invention relates to the field of diamond composite sheet technology, specifically a novel method for removing cobalt from diamond composite sheets. Background Technology

[0002] Diamond composite sheets are composite materials made of diamond and a cemented carbide matrix. Due to their ultra-high hardness and excellent wear resistance, they are widely used in oil drilling, geological exploration, coalfield drilling bits, and machining tools. During the synthesis process, metallic cobalt acts as a binder and catalyst, not only aiding in the regrowth of diamond but also promoting the formation of D-D bonds, playing a crucial role in the sintering of diamond composite sheets. However, in practical use, the difference in thermal expansion coefficients between metallic cobalt and diamond / cemented carbide, if not removed, can easily lead to cracking of the composite layer, severely affecting the service life of the diamond composite sheet.

[0003] Currently, the mainstream method for removing metallic cobalt from diamond composite sheets is the high-temperature, high-strength composite acid impregnation method. Compared with other cobalt removal methods, this method has advantages such as thorough removal, good timeliness, and rapid cobalt removal. However, protecting the cemented carbide matrix during the cobalt removal process has always been a challenge for the industry. Furthermore, the cobalt channels within the composite layer have a complex nanoscale structure, and due to capillary action, the cobalt removal rate slows down as the cobalt removal layer gradually moves downwards. Therefore, achieving safe, efficient, and rapid cobalt removal has become a crucial issue that urgently needs to be addressed in the development of the diamond composite sheet industry. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a novel method for removing cobalt from diamond composite sheets. This method solves the problems of difficulty in protecting the hard alloy substrate in traditional high-temperature strong composite acid impregnation methods, and the slow and uneven deep cobalt removal speed caused by the capillary effect of nanoscale cobalt channels within the composite layer, making it difficult to achieve safe, efficient, and deep cobalt removal.

[0005] To achieve the above objectives, the present invention provides a novel method for removing cobalt from diamond composite sheets, comprising the following steps: S1: Mix inorganic zinc-rich paint, copper powder, zinc oxide, and mica powder with water. The proportions of each component are as follows: inorganic zinc-rich paint 28-60%, copper powder 5-12%, zinc oxide 2-5%, mica powder 3-28%, and the remainder is water. S2: The raw materials are mixed by an electric mixer to obtain a uniform and consistent thin viscous liquid; S3: Machin the diamond composite sheet to the required size and remove surface rust; S4: Place the dilute viscous liquid in a container. The top cover of the container is made of a perforated, heat-soft material with a hole diameter 1-2 mm smaller than the diameter of the diamond composite sheet. Heat the top cover to 120-150℃ to soften it. Then, insert the composite layer of the diamond composite sheet into the hole of the top cover with the composite layer facing down. After cooling to room temperature, place the top cover containing the diamond composite sheet into the container for coating. Control the coating thickness by controlling the concentration of the dilute viscous liquid and the coating time (0.5-3 hours). S5: Place the coated diamond composite sheet and the top cover plate in an oven and heat them at 50-100℃ for 0.5-2 hours to remove volatile impurities such as dispersing solvent and water. After the coating is dry, take out the coated diamond composite sheet and grind the outer circle to a uniform diameter. S6: After the composite layer of the ground diamond composite sheet is fitted with a sealing ring, it is placed into the cobalt removal tooling and then placed in a high-temperature, low-pressure reactor with a stirring rod for cobalt removal.

[0006] Preferably, the copper powder, zinc oxide, and mica powder used in S1 are all powders of 1000 mesh or less.

[0007] Preferably, the inorganic zinc-rich paint in S1 contains 40% zinc.

[0008] Preferably, the inorganic zinc-rich paint in S1 includes paint, curing agent, and diluent, and the ratio of paint, curing agent, and diluent is 16:4:3.

[0009] Preferably, the cobalt removal process in S6 is as follows: the stirring rod is set to rotate at 20-45 rpm, the temperature is raised from room temperature to 80°C over 1 hour, kept at that temperature for 2 hours, and then raised to 120-160°C over another hour. The temperature is then kept constant for cobalt removal until the specified cobalt removal depth is reached.

[0010] Preferably, the cobalt removal reagent in S6 is composed of hydrochloric acid (concentration 30%-45%), nitric acid (concentration 40%-45%), and fluoroantimony sulfonic acid (concentration 15%-50%) in a volume ratio of 1:1:1.

[0011] This invention provides a novel method for removing cobalt from diamond composite sheets, which has the following beneficial effects: This process employs a dual protection mechanism of "physical barrier + chemical absorption". Through the synergistic effect of a coating with a specific ratio and a sealing ring, it can both prevent liquid cobalt removal reagent from directly contacting the hard alloy substrate and absorb the permeated reagent gas, thus completely solving the industry problem of easy corrosion of the substrate under high temperature and low pressure environment. This process optimizes the coating process (such as precise temperature control of the thermally flexible material cover, and adjustment of coating time and concentration) to ensure that the composite layer of the diamond composite sheet is completely exposed in the cobalt removal reagent. At the same time, the high-temperature and low-pressure reaction environment and stirring process enhance the contact efficiency and reactivity between the reagent and the composite layer, effectively overcome the capillary effect of the nanoscale cobalt channels, accelerate the cobalt removal speed, deepen the cobalt removal layer thickness, and ensure that the cobalt removal depth is uniform and stable, thereby improving the efficiency and thoroughness of cobalt removal. Attached Figure Description

[0012] Figure 1 This is a flowchart of a novel method for removing cobalt from diamond composite sheets; Figure 2 This is a cross-sectional schematic diagram of the coating container during the coating process; Figure 3 This is a front view of the perforated top cover; Figure 4 This is a detection image of the cobalt removal depth of a PDC that has undergone complete cobalt removal.

[0013] The components include: 1. Container; 2. Coated with a thin viscous liquid; 3. Top cover; 4. Diamond composite sheet; 5. Holes. Detailed Implementation

[0014] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0015] like Figure 1-3 As shown, this embodiment of the invention provides a novel method for removing cobalt from diamond composite sheets, comprising the following steps: S1: Mix inorganic zinc-rich paint, copper powder, zinc oxide, and mica powder with water. The proportions of each component are as follows: inorganic zinc-rich paint 28-60%, copper powder 5-12%, zinc oxide 2-5%, mica powder 3-28%, and the remainder is water. The inorganic zinc-rich paint serves as a base material, providing adhesion and reactivity. The zinc component can chemically react with the cobalt removal reagent gas to achieve gas absorption. Copper powder and zinc oxide serve as auxiliary reaction components, filling the nanoscale micropores formed after the coating reaction and enhancing the density of the protective layer. Mica powder, as a silicate mineral powder, increases friction through its particle shape, and its chemical stability helps resist reagent corrosion. Water serves as a dispersion medium to ensure uniform mixing of all components, forming a coatable system. S2: The raw materials are mixed by an electric mixer to obtain a uniform and consistent thin viscous liquid. This uniformity ensures that the composition of the protective layer is consistent during subsequent coating, avoiding uneven protective effect or impact on the cobalt removal reaction due to local component differences. S3: Machining the diamond composite sheet to the required size and removing surface rust. Machining to the specified size is to ensure that the composite sheet matches the subsequent tooling and sealing ring, and to avoid sealing failure due to dimensional deviation. Surface rust (mainly metal oxides) will affect the adhesion between the coating and the hard alloy substrate. After rust removal, the coating can adhere tightly to the substrate to form a continuous and complete protective layer, preventing the cobalt removal reagent from penetrating from the interface and corroding the substrate. S4: Place the dilute viscous liquid in container 1. The top cover 3 of container 1 is made of a heat-softening material with holes 5, the diameter of which is 1-2 mm smaller than the diameter of the diamond composite sheet. Heat the top cover 3 to 120-150℃ to soften it. Then, insert the composite layer of the diamond composite sheet downwards into the holes 5 of the top cover 3. After cooling to room temperature, place the top cover 3 containing the diamond composite sheet into container 1 for coating. The coating thickness is controlled by adjusting the concentration of the dilute viscous liquid and the coating time (0.5-3 hours). The heat-softening material... The material cover softens upon heating, facilitating the insertion of the diamond composite sheet into the pores. Upon cooling, the material hardens to achieve a tight fixation, ensuring stable positioning of the composite sheet during coating. The pore diameter is smaller than the composite sheet diameter, creating an interference fit that prevents the coating from contaminating the composite layer requiring cobalt removal (only the composite layer is exposed, while the protective layer only covers the alloy substrate). The coating thickness is controlled by concentration (affecting the solid content per unit volume) and time (affecting the adsorption amount), ensuring the protective layer effectively blocks reagent gases without causing difficulties in subsequent processing due to excessive thickness. S5: Place the coated diamond composite sheet and top cover plate in an oven and heat at 50-100℃ for 0.5-2 hours to remove volatile impurities such as dispersing solvent and water. After the coating is dry, remove the coated diamond composite sheet and grind its outer diameter to a uniform size. Heating in the oven at 50-100℃ slowly evaporates the moisture and dispersing solvent in the coating, preventing cracking due to rapid drying. The heat preservation process ensures that volatiles are fully removed, allowing the coating to solidify and form a protective film with certain strength and adhesion. Grinding the outer diameter to a uniform size ensures the fit accuracy between the composite sheet and the sealing ring and tooling, enhances the sealing effect, and prevents cobalt removal reagent from seeping in through gaps. S6: After the polished diamond composite sheet is fitted with a sealing ring, it is placed into a cobalt removal fixture and then placed in a high-temperature, low-pressure reactor with a stirring rod for cobalt removal. The sealing ring acts as the first physical barrier, using elastic deformation to fill the gap between the composite sheet and the fixture, preventing the liquid cobalt removal reagent from directly contacting the alloy matrix. The cobalt removal fixture fixes the position of the composite sheet, ensuring that the composite layer is completely exposed to the reagent. The high-temperature, low-pressure environment accelerates the volatilization of the cobalt removal reagent and enhances its reactivity, promoting the reaction between the reagent and the metallic cobalt in the composite layer. The stirring rod stirs the reagent to ensure uniform contact with the surface of the composite layer, avoiding a decrease in local reagent concentration that would lead to a decrease in the reaction rate, while accelerating the diffusion of reaction products to ensure uniform cobalt removal and achieving the required depth.

[0016] Specifically, the copper powder, zinc oxide, and mica powder used in S1 are all powders of 1000 mesh or less; among them, ultrafine powders of 1000 mesh or less have a larger specific surface area, which can improve the compatibility and dispersibility with the base material and ensure the fineness of the coating material; fine particles can fill the gaps inside the coating, enhance the density of the protective layer, and at the same time reduce mechanical damage to the surface of the composite sheet, ensuring that the substrate surface is smooth after coating. The inorganic zinc-rich paint in S1 contains 40% zinc. The 40% zinc content can balance the reactivity and coating stability. Too high a zinc content can easily lead to increased coating brittleness, while too low a content will not be able to fully absorb the infiltrated cobalt removal reagent gas. Zinc reacts with the cobalt removal reagent (acidic) to consume the infiltrated gas and form a "chemical barrier" to protect the substrate. The inorganic zinc-rich paint in S1 includes paint, curing agent, and thinner, with a ratio of 16:4:3. The paint provides the film-forming properties and adhesion of the coating. The curing agent cross-links the paint through a chemical reaction to form a three-dimensional network structure, enhancing the coating's hardness and corrosion resistance. The thinner adjusts the viscosity of the paint and, together with water, optimizes the coating performance of the thin viscous liquid. The 16:4:3 ratio ensures that the paint is fully cured, while avoiding coating embrittlement due to excessive curing agent or film quality issues due to excessive thinner. The cobalt removal process in S6 is as follows: the stirring rod is set to rotate at 20-45 rpm, the temperature is raised from room temperature to 80℃ over 1 hour, held for 2 hours, and then raised to 120-160℃ over another hour. The temperature is then maintained at a constant level for cobalt removal until the specified cobalt removal depth is reached. The required stirring speed of 20-45 rpm ensures uniform mixing of the reagents without causing vibration or sealing failure of the composite sheet due to excessive speed. The stepped heating (room temperature → 80℃ holding → 120-160℃ constant temperature) avoids excessive thermal stress on the composite sheet due to sudden temperature increases, which could lead to cracking. Simultaneously, the cobalt removal reaction is gradually activated: the surface cobalt is dissolved first in the low-temperature stage, and the diffusion and reaction of deep cobalt are accelerated in the high-temperature stage. Combined with the holding process, this ensures sufficient reaction at each stage. The cobalt removal reagent in S6 is composed of hydrochloric acid (concentration 30%-45%), nitric acid (concentration 40%-45%), and fluoroantimony sulfonic acid (concentration 15%-50%) in a volume ratio of 1:1:1. Hydrochloric acid provides hydrogen ions to dissolve metallic cobalt, while nitric acid, as a strong oxidant, oxidizes cobalt into soluble ions (Co²⁺→Co³⁺), enhancing its solubility. Fluoroantimony sulfonic acid, as a superacid, can break the cobalt bonds in the diamond composite layer and simultaneously penetrate nanoscale cobalt channels, solving the problem of deep cobalt removal caused by capillary action. The three reagents work synergistically in a 1:1:1 ratio, ensuring both strong corrosiveness for rapid cobalt removal and avoiding excessive erosion of the composite layer or protective layer by a single acid reagent.

[0017] In the cobalt removal process of this invention, the sealing ring and the coating form a "double protection": the sealing ring blocks liquid reagents, and the coating absorbs the permeated reagent gases. The combination of these two elements completely solves the problem of substrate corrosion caused by reagent volatilization under high temperature and low pressure. Simultaneously, the composite layer is completely exposed, maximizing the contact area between the reagent and cobalt. Combined with stirring and stepped heating processes, a balance between safe and efficient cobalt removal is achieved. (See the cobalt removal depth detection image of the completed PDC). Figure 4 As can be seen from the results, the cobalt removal depth reaches 1.22mm-1.5mm, and the cobalt removal depth in the vertical direction is uniform. This test result directly confirms that the "dual protection" mechanism did not hinder the cobalt removal reaction of the composite layer. The protective layer only acts on the alloy matrix, ensuring that the composite layer can fully contact and react with the cobalt removal reagent. At the same time, it avoids damage to the overall performance of the composite sheet due to matrix corrosion. This allows the composite sheet after cobalt removal to maintain the integrity of the matrix and achieve the expected cobalt removal depth requirement.

[0018] In summary, this invention utilizes a dual protection mechanism of "physical barrier + chemical absorption," employing a coating material with a specific ratio (containing inorganic zinc-rich paint, copper powder, etc.) to protect the cemented carbide substrate. Combined with a sealing ring to enhance the sealing effect, and utilizing a specific ratio of cobalt removal reagent in a high-temperature, low-pressure reactor, along with a stepped heating and stirring process, it efficiently breaks down the capillary effect of the nanoscale cobalt channels in the composite layer while avoiding substrate corrosion. This achieves safe, rapid, and deep cobalt removal from the diamond composite sheet, providing a reliable technical solution for its stable application in various high-intensity working conditions.

[0019] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A novel method for removing cobalt from diamond composite sheets, characterized in that, Includes the following steps: S1: Mix inorganic zinc-rich paint, copper powder, zinc oxide, and mica powder with water. The proportions of each component are as follows: inorganic zinc-rich paint 28-60%, copper powder 5-12%, zinc oxide 2-5%, mica powder 3-28%, and the remainder is water. S2: The raw materials are mixed by an electric mixer to obtain a uniform and consistent thin viscous liquid; S3: Machin the diamond composite sheet to the required size and remove surface rust; S4: Place the dilute viscous liquid in a container (1). The top cover (3) of the container (1) is a heat-soft material with holes (5). The diameter of the holes (5) is 1-2 mm smaller than the diameter of the diamond composite sheet. Heat the top cover (3) to 120-150°C to soften it. Then insert the composite layer of the diamond composite sheet downward into the holes (5) of the top cover (3). After cooling to room temperature, put the top cover (3) containing the diamond composite sheet into the container (1) for coating. Control the coating thickness by controlling the concentration of the dilute viscous liquid and the coating time (0.5-3 hours). S5: Place the coated diamond composite sheet and the top cover plate in an oven and heat them at 50-100℃ for 0.5-2 hours to remove volatile impurities such as dispersing solvent and water. After the coating is dry, take out the coated diamond composite sheet and grind the outer circle to a uniform diameter. S6: After the composite layer of the ground diamond composite sheet is fitted with a sealing ring, it is placed into the cobalt removal tooling and then placed in a high-temperature, low-pressure reactor with a stirring rod for cobalt removal.

2. The novel method for removing cobalt from diamond composite sheets according to claim 1, characterized in that: The copper powder, zinc oxide, and mica powder used in S1 are all powders of 1000 mesh or smaller.

3. The novel method for removing cobalt from diamond composite sheets according to claim 1, characterized in that: The inorganic zinc-rich paint in S1 contains 40% zinc.

4. The novel method for removing cobalt from diamond composite sheets according to claim 1, characterized in that: The inorganic zinc-rich paint in S1 includes paint, curing agent, and diluent, and the ratio of paint, curing agent, and diluent is 16:4:

3.

5. The novel method for removing cobalt from diamond composite sheets according to claim 1, characterized in that: The cobalt removal process in S6 is as follows: the stirring rod is set to rotate at 20-45 rpm, the temperature is raised from room temperature to 80°C in 1 hour, kept at that temperature for 2 hours, and then raised to 120-160°C in 1 hour. The temperature is then kept constant for cobalt removal until the specified cobalt removal depth is reached.

6. The novel method for removing cobalt from diamond composite sheets according to claim 1, characterized in that: The cobalt removal reagent in S6 is composed of hydrochloric acid (concentration 30%-45%), nitric acid (concentration 40%-45%), and fluoroantimony sulfonic acid (concentration 15%-50%) in a volume ratio of 1:1:1.

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