Method for producing superhard material

Abstract

To provide a method for monitoring the temperature of a metal catalyst in a process for producing a superhard material.SOLUTION: A method for monitoring the temperature of a metal catalyst, comprising the step of continuously measuring the electrical resistance of a heater during the heating of a high-pressure cell (HP C), the HP C having a housing in which said heater is placed, locked from above and below by means of current-carrying washers, An insulating sleeve having an insulating washer at an end thereof is disposed inside the heater, and at least a carbon source and a metal catalyst are disposed inside the sleeve; detecting a rapid increase in the electrical resistance of the heater; and identifying a time of the detected rapid increase in the electrical resistance of the heater as corresponding to melting of the metal catalyst.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to the field of producing ultra-hard materials, in particular diamond, by High Pressure / High Temperature (HPHT) methods. [Background technology]

[0002] The HPHT method has traditionally been used to synthesize single crystal diamond, polycrystalline diamond, diamond powder, and cubic boron nitride. For this purpose, HPHT presses, such as cubic (or cube) presses, belt presses, toroidal presses, non-pressing devices such as "split sphere" presses, and others, are used.

[0003] In particular, one well-known method for producing diamond involves treating carbon, for example in the form of graphite, at high pressure and high temperature in the presence of a metal solvent catalyst in a high-pressure cell, as disclosed in patents US4340576 and US4617181. The solvent catalyst is usually made of iron, cobalt, nickel, or manganese, a mixture of these metals, or a mixture of these metals with the addition of any other suitable elements. The treatment is carried out at a pressure and temperature that is within the diamond stability region (or field) on the carbon phase diagram.

[0004] In this method, it is very important to accurately measure the process temperature, since deviation from the required temperature can result in the failure to obtain the desired product. In particular, if the actual temperature is lower than the required temperature, the melting point of the metal catalyst cannot be reached, and as a result, the subsequent graphite-to-diamond phase transition does not occur. On the other hand, if the actual temperature exceeds the required temperature, the process will exceed the diamond stability region, resulting in graphite as the output. When growing crystals on a seed, exceeding the required temperature can result in an increased temperature difference between the carbon source and the growing crystal, which can result in increased mass transfer, increased growth rate, crystal defects, etc. Conversely, lowering the actual temperature below the required temperature can reduce the temperature difference between the carbon source and the growing crystal, but this can lead to a slower rate or even a complete cessation of crystal growth.

[0005] One way to measure temperature is to incorporate a thermocouple into the high-pressure cell, as described in SU636515, SU1137779, and SU1302505. However, integrating a thermocouple into the high-pressure cell significantly complicates the cell design and can significantly increase the cost of diamond production.

[0006] Due to the complexity of temperature measurement, determining the temperature during diamond production typically uses electrical heating power as a guide, as described in Patent RU2192511. In this case, the temperature is calculated according to the electrical heating power supplied to the electric heater placed inside the high-pressure cell. This approach has several drawbacks. In particular, the temperature calculated based on the electrical heating power may differ from the actual temperature. This is thought to be due to calculation errors, for example, due to the possibility of changes in the environmental conditions of the device for producing ultra-hard materials. Furthermore, because high-pressure cells have complex structures, errors in temperature calculations may occur, especially since they consist of many components. When cells are pre-compressed during the production of ultra-hard materials, the thermal field generated in each cell will differ to some extent from the thermal fields generated in other cells. The difference between the calculated temperature and the actual temperature may lead to uncontrollable production results. In particular, in such cases, the resulting diamond may lack the desired properties, or such a temperature difference may lead to situations where diamonds cannot be obtained in principle.

[0007] When using the HPHT method, after the melting point of the metal catalyst is reached, the temperature in the high-pressure cell typically needs to be increased by no more than a few tens of degrees, typically no more than 30-70 degrees, as set forth in Patent No. RU 2320404. In this case, when the calculated and actual temperatures are distinguished, it can be difficult to determine when the actual temperature in the high-pressure cell reaches the melting point of the metal catalyst before the graphite-to-diamond phase transition occurs.

[0008] The closest prior art to the claimed invention is a method for monitoring the temperature of a metal catalyst in a process for producing an ultra-hard material described in SU1788700.

[0009] The known method comprises monitoring the temperature of a metal catalyst in a process for producing an ultra-hard material during heating of a high-pressure cell (HPC) comprising a housing in which a tubular heater, an additional heat source, a carbon source, a metal catalyst and diamond seeds are placed, said monitoring being carried out using thermocouples measuring the temperature of a hotter part of the metal catalyst and the temperature of a cooler part thereof, according to a compiled algorithm for the power of the additional heat source to maintain a constant temperature difference between the carbon source and the surface of the growing single crystal. DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0010] The problem that the present invention aims to solve is thus to provide an improved method for the production of ultrahard materials, which method offers the possibility of reliably controlling the ultrahard material production process, in particular the possibility of determining with high precision in real time the moment (or time point) of melting of the metal catalyst and of the phase transition from graphite to diamond. [Means for solving the problem]

[0011] According to the present invention, a method for producing ultrahard materials, particularly diamond, is proposed, according to which a high-pressure cell (HPC) is provided. The HPC includes a housing in which a heater is disposed. An insulating washer, with an insulating sleeve disposed on its end, is disposed within the heater. A carbon source and a metal catalyst are located inside the sleeve. The heater is locked from above and below by a current-carrying washer. The HPC is placed in a high-pressure apparatus, and the required pressure is created within it. Then, current is passed through the heater to heat it. Once the required temperature is reached, the power increase process is stopped, and the HPC is maintained at the specified temperature for a specific time. The current supply to the heater is then terminated, the pressure is released, and the HPC is removed. The electrical resistance of the heater is continuously measured during heating to detect a sudden change in resistance, indicating the melting of the metal catalyst and the phase transformation of the carbon source to diamond.

[0012] This method simplifies the process of producing ultrahard materials, since expensive upgrades to the HPC are not required to provide the possibility of directly measuring the temperature in the cell. Furthermore, the present invention allows for the real-time determination of the melting moment of the metal catalyst located in the HPC and the subsequent phase transition of graphite to diamond, thereby increasing the accuracy of determining the actual temperature in the HPC and eliminating the need to rely solely on approximate calculations based on the current supplied to the heater when determining the temperature in the HPC. Another technical result of the present invention is ensuring repeatability of diamond crystal synthesis conditions, which is achieved by accurately determining the melting moment of the metal catalyst and the phase transition of graphite to diamond. [Brief explanation of the drawings]

[0013] The drawing (FIG. 1) shows an exemplary diagram, where the solid line shows the change in resistance versus time and the dotted line shows the change in power supplied to the heater versus time. DETAILED DESCRIPTION OF THE INVENTION

[0014] Although the following examples of the present invention will be described in relation to the production of diamond, it will be apparent to those skilled in the art that the present invention is also applicable to the production of other ultra-hard materials.

[0015] According to the present invention, the HPHT process for producing diamonds involves fabricating a high-pressure cell (HPC) containing a ceramic or other suitable material body. The cell body has a tubular or other suitable shape and includes a heater, typically made from graphite or a mixture of graphite and other materials. The heater can also be made from any other suitable material. An insulating sleeve with an insulating washer is placed inside the heater, forming a reaction zone. The carbon source is typically a form of graphite or another diamond or non-diamond form of carbon, and a metal catalyst is placed inside the reaction zone. The metal catalyst can be made from iron, cobalt, nickel, or manganese, or a mixture of these metals with the addition of any other suitable elements.

[0016] The HPC is then placed in a high-pressure apparatus, which can be any apparatus suitable for preparing ultrahard materials. High pressures, typically exceeding 4.5 GPa, are generated in the HPC. Generally, the pressure can range from 4.5 to 10 GPa. The reaction zone is then heated by passing an electric current through a heater.

[0017] The reaction zone is heated gradually, with a smooth increase in power. The heater's electrical resistance is continuously measured during heating. In some embodiments, the current and voltage in the electrical circuit near the heater are continuously measured during heating, and the heater's electrical resistance is calculated from the measurements. Note that in preferred embodiments, the current and voltage in the electrical circuit are measured as close to the heater as possible or directly at the heater itself to obtain a more accurate heater resistance value. In accordance with this method, a diagram of the heater's resistance is created. Note that as the applied power increases, the resistance generally decreases smoothly. Typically, the power increases substantially linearly during diamond production, and the resistance correspondingly decreases linearly depending on the power.

[0018] In the illustrated diagram, the solid line represents resistance versus time, and the dotted line represents power supplied to the heater versus time. The present authors have discovered that deformation of the HPC adjacent to the metal catalyst and carbon source occurs at the time of metal catalyst melting and during the subsequent phase transformation of the carbon source (e.g., graphite) into diamond within the HPC. In particular, in some implementations, deformation of the insulating sleeve occurs, which results in deformation of the heater. This deformation results in a noticeable change in the heater's electrical resistance. In particular, during the period when the metal catalyst melts and the carbon source transforms into diamond, a sharp increase in resistance can be observed, followed by a decrease in resistance, as shown in the diagram. In this way, by monitoring the resistance of the heater's electrical circuit during the temperature increase, it is possible to accurately determine the moment of metal catalyst melting and the subsequent phase transformation of the carbon source into diamond in real time.

[0019] According to this method, after detecting that the carbon source has completed its diamond transformation process, heating of the HPC is continued for a period of time to the required temperature, which typically ranges from 1100 to 2300°C, depending on the needs of the specific type of manufacturing process. However, it will be clear to those skilled in the art that the lower limit of the temperature range typically depends on the melting temperature of the metal catalyst, and therefore both the upper and lower limits can be varied, while the upper limit depends on the pressure generated in the HPC, i.e., the upper limit temperature can increase with increasing pressure. The process of increasing the heating power is then stopped. It should be noted that, according to the example shown in the drawings, the power supplied to the heater continues to increase for a certain period of time after the carbon source has completed its diamond transformation process. However, in other embodiments, depending on the manufacturing technology, the power increase process can be stopped before or simultaneously with the completion of the carbon source's diamond transformation process.

[0020] The HPC is then maintained at the given temperature for the time required by the process. Typically, this time can be from 15 minutes to 500 hours, depending on the specific process. However, it will be apparent to those skilled in the art that the specific time is not necessarily limited to the above values ​​and may, in some cases, exceed certain limits if necessary. The supply of current to the heater is then terminated, the pressure is released, and the HPC is removed.

[0021] Various specific examples of the method for producing an ultra-hard material according to the present invention will be described below.

[0022] Example 1 The high-pressure cell (HPC) contains a ceramic shell and a cylindrical graphite heater, which is locked from above and below by current-carrying washers. An insulating sleeve with insulating washers on its ends is placed inside the heater, and a mixture of graphite and a metal catalyst is placed inside the sleeve. The HPC is placed in a toroidal press. Pressures exceeding 4.5 GPa are generated within the cell by the press.

[0023] A current is applied to the current-carrying part of the cell. The heating power is increased at a rate of 30 W per minute. The resistance of the heater circuit is measured simultaneously with heating. When the heating power reaches 6.10 kW, a sudden increase of 10% in the heater circuit resistance is observed, indicating the melting of the metal catalyst and the diamond phase transformation of the carbon source.

[0024] When the power value reaches 6.5 kW, the operator stops the power increase process. After 10 minutes of exposure, the operator turns off the heating. After the pressure is released, the HPC is removed from the toroidal press. Inside the cell is a sintered mass of fine-crystalline diamond.

[0025] Example 2 The high-pressure cell (HPC) contains a ceramic shell and a cylindrical graphite heater, which is locked from above and below by current-carrying washers. An insulating bushing with insulating washers at its ends is placed inside the heater. A substrate with a diamond crystal seed pressed into it is placed at the bottom of the bushing, a metal catalyst is placed above the substrate, and a carbon source in the form of graphite is placed above the catalyst. The HPC is then placed in a cubic press. Pressures exceeding 4.5 GPa are generated within the cell by the press. Electric current is passed through the current-carrying portion of the cell. The heating power is increased at a rate of 30 W per minute. The resistance of the heater circuit is measured simultaneously. When the heating power reaches 6.50 kW, a sudden 10% increase in the heater circuit resistance is observed, indicating the melting of the metal catalyst and the diamond phase transformation of the carbon source. When the power value reaches 6.7 kW, the operator stops the power increase process. After 300 hours of exposure, the operator turns off the heating. After the pressure is released, the HPC is removed from the cubic press. Inside the cell is a single diamond crystal weighing 55 carats.

Claims

1. A method for monitoring the temperature of a metal catalyst in a process for producing an ultrahard material made of diamond from a carbon source in the form of graphite, or another diamond or non-diamond form; A step of continuously measuring the electrical resistance of a heater while heating a high-voltage cell (HPC), wherein the HPC has a housing in which a heater made of graphite having a tubular shape is arranged, locked from above and below by energizing washers, and an insulating sleeve having insulating washers at its end is arranged inside the heater, and at least the carbon source and metal catalyst are arranged inside the sleeve, the catalyst containing iron, cobalt, nickel or manganese, and A step of detecting a sudden increase in the electrical resistance of the heater due to deformation of the heater, Steps to identify the point in time when the electrical resistance of the heater increases sharply due to the detected deformation of the heater, as corresponding to the melting of the metal catalyst and the subsequent phase transition of the carbon source to diamond. A method characterized by including the following.

2. A method for producing an ultrahard material made of diamond from a source of carbon in the form of graphite, or another diamond or non-diamond form, A step of providing a high-pressure cell (HPC) comprising a housing in which a tubular heater made of graphite is arranged, locked from above and below by energizing washers, an insulating sleeve having insulating washers at its ends is arranged inside the heater, and at least the carbon source and metal catalyst are arranged inside the sleeve, wherein the catalyst contains iron, cobalt, nickel or manganese, and The steps include: placing the high-voltage cell inside the high-voltage device; The steps include supplying the necessary pressure into the high-pressure cell, The steps include heating the high-voltage cell by supplying increased power to the heater, The steps include stopping the increase in power when the required temperature is reached, The steps include maintaining the high-pressure cell at the required temperature for a predetermined time, The steps include: ending the power supply to the heater and releasing the pressure; The steps include removing the high-voltage cell from the high-voltage device, The method has, The steps include: continuously measuring the electrical resistance of the heater during heating; A step of detecting a sudden increase in the electrical resistance of the heater due to deformation of the heater, The step of identifying the point in time when the electrical resistance of the heater increases sharply due to the detected deformation of the heater corresponds to the melting of the metal catalyst and the subsequent phase transition of the carbon source to diamond. A method characterized by including

3. The method according to claim 2, wherein a substrate with a diamond crystal seed pressed inside is also arranged inside the sleeve.

Images