Press machine, pressing method

Abstract

The present invention provides a press machine and a pressing method that can apply a desired pressure to a sample without increasing its size and while reducing the wobble of the pressurizing axis. [Solution] The press machine is a press machine 10 that pressurizes a sample while heating it. It comprises a frame 14 composed of an upper frame 11, a bottom frame 12, and side frames 13 connecting the upper frame 11 and the bottom frame 12; a wire 15 that applies compressive stress to the side frames 13 by being wound around the outer circumference of the frame 14; a pressurizing section 16 provided on the bottom frame; a container 17 placed on the top surface 16a of the pressurizing section 16; a chamber 18 that is housed in the container 17 and has an anvil that holds a pressure medium containing the sample; and at least the chamber 18 and a heating section for heating the sample.

Description

Technical Field

[0001] The present invention relates to a press machine and a pressing method for performing high-pressure pressing at high temperatures.

Background Art

[0002] Conventionally, a high-temperature and high-pressure method is known as a method for producing synthetic diamond. The high-temperature and high-pressure method is a method for synthesizing diamond by exposing a carbon material as a carbon source to high temperature and high pressure together with a metal catalyst.

[0003] The synthesis conditions employed in the high-temperature and high-pressure method are determined by the carbon equilibrium phase diagram with temperature on the horizontal axis and pressure on the vertical axis. The carbon-diamond equilibrium line obtained from the carbon equilibrium phase diagram serves as a reference for producing synthetic diamond. The pressure and temperature employed in the high-temperature and high-pressure method are selected from pressures on the high-pressure side and temperatures on the high-temperature side with respect to the carbon-diamond equilibrium line.

[0004] The pressure employed in the high-temperature and high-pressure method is usually about 5.0 to 10 GPa. In order to synthesize large diamonds, it is required to apply an extremely high pressing force to the press machine. Here, when pressing exceeding GPa is performed, when a compressive stress is applied to the sample, a tensile stress is generated in the frame of the press machine due to the reaction force. When a tensile stress is applied to the frame, the compressive stress applied to the sample may be relaxed, and it may not be possible to apply a sufficient pressing force to the sample.

[0005] Therefore, for example, Patent Document 1 discloses a technique of winding a wire around the outer periphery of a frame and applying a compressive stress to the frame in advance. According to this technique, it is said that the reaction force generated in the frame when the sample is pressed cancels out the compressive stress applied in advance, and a desired pressure can be applied to the sample.

[0006] Furthermore, the press described in Patent Document 1 consists of an upper yoke and a lower yoke fixed to a frame, a die mold fixed to the lower yoke, and a ram fixed to the upper yoke. For example, when compressing powder, powder is generally filled into a sample introduction hole provided in the die mold indirectly fixed to the frame, and the powder is compressed by an upper punch. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 48-63372 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] Patent Document 1 describes 25-75 kp / mm 2 A certain level of pressure is expected. Normally, the anvil is indirectly fixed to the frame with bolts or similar fasteners. Furthermore, when bolts are used to fix the anvil to the machine, a clearance is provided between the press machine's mounting base and the anvil. Thus, assuming a pressing pressure of around 500 MPa and press operation at room temperature, even with a clearance, the damping caused by misalignment of the press axis due to gaskets between the anvil and chamber does not pose a significant problem during pressing.

[0009] However, when applying high pressures of 5.5 to 10 GPa, the pressure used in diamond synthesis, at temperatures exceeding 1000°C, the pressure applied to the sample is attenuated due to misalignment of the press axis. Therefore, in the case of the invention described in Patent Document 1, where the wire is wound around the frame, although the attenuation of the applied pressure due to the reaction force of the frame can be avoided, the desired pressure may not be applied to the sample due to misalignment of the press axis.

[0010] One possible way to avoid the reduction in press force due to misalignment of the press axis is to increase the size of the press machine. However, even with a larger press machine, the press force will still be reduced, and a significant increase in costs is unavoidable.

[0011] Therefore, the object of the present invention is to provide a press machine and a pressing method that can apply a desired pressure to a sample without increasing its size and while reducing the wobble of the pressurizing axis. [Means for solving the problem]

[0012] The inventors decided to first use a device in which a wire is wound around a frame, as described in Patent Document 1, in order to apply high pressure to a sample at high temperature. Then, they investigated a configuration that would prevent wobble of the press axis due to clearance.

[0013] Typically, when employing the high-temperature, high-pressure method, the sample is inserted into a predetermined position, then pressurized and heated by applying electricity to the sample. However, if the anvil is fixed with a fixing jig such as a bolt, the clearance between the fixing jig and the anvil can cause the pressurizing axis to shift. Furthermore, in order to synthesize large diamonds, it is unavoidable to use a larger jig for gripping the sample. In addition, as the number of presses increases, distortion occurs in the jig and the press device itself, making fine adjustment of the pressurizing axis even more difficult.

[0014] Furthermore, when pressing is performed with a pressure of 5.5 GPa or higher and a heating temperature exceeding 1000°C, it is not possible to fine-tune the misalignment of the pressurizing axis using mechanical adjustment devices or software, as is possible when pressing with a pressure of around MPa. Moreover, if wire is wound around the frame, it is thought that the wobble of the pressurizing axis will be suppressed to some extent. However, as mentioned above, when a pressurizing force of GPa is applied to the sample, the anvil itself is thick and heavy, making fine adjustment difficult after it has been fixed with bolts or the like. Even if the position is finely adjusted before being fixed with bolts, slight misalignment of the anvil that occurs when the bolts are fastened is unavoidable.

[0015] Therefore, unlike conventional methods, the inventors deliberately placed the chamber equipped with the anvil only on the top surface of the pressurizing part, such as a hydraulic press. Furthermore, the inventors conceived the idea of ​​performing the press without fixing it to a frame with bolts or the like. As a result, it was found that the position of the anvil spontaneously makes fine adjustments during pressurization, thereby mitigating the wobble of the pressurizing axis and allowing the desired pressurizing force to be applied to the sample. This is presumed to be because, when the tensile stress on the frame is offset by the compressive stress applied beforehand by winding the wire, equilibrium is achieved between the frame and the chamber because the chamber equipped with the anvil is not fixed to the frame, and the sample can be pressurized by hydrostatic pressure.

[0016] In addition to the above, the inventors conceived of housing the anvil in a container to maintain a high pressurizing force applied to the sample, in addition to the spontaneous fine adjustment function of the pressurizing axis during pressurization. As a result, even if the pressure medium held between the anvil and the chamber is crushed during pressurization, the crushed pieces of the pressure medium and other crushed parts are not allowed to escape to the outside by the side walls of the container, and a high pressurizing force is maintained. The present invention, derived from this finding, is as follows:

[0017] (1) A press machine that heats and pressurizes a sample, A frame consisting of an upper frame, a bottom frame, and side frames connecting the upper frame and the bottom frame, A wire that applies compressive stress to the side frame by being wound around the outer circumference of the frame, A pressurizing section is provided on the bottom frame, A container placed on the top surface of the pressurized section, A chamber that is housed in a container and has an anvil that holds a pressure medium containing a sample, At least a chamber and a heating unit that heats the sample by applying an electric current, A press machine characterized by being equipped with the following features.

[0018] (2) The shape of the anvil is of the Chebyshev type or the toroidal type, and the press machine according to (1) above.

[0019] (3) The inner diameter of the container is larger than the outer shape of the chamber, and the press machine according to (1) or (2) above.

[0020] (4) The container is composed of an upper container and a bottom container, the upper container is fixed to the upper frame, and the bottom container is fixed to the top surface of the pressurizing part, and the press machine according to (3) above.

[0021] (5) Further, the press machine according to any one of (1) to (4) above, comprising a measuring part for measuring the current value and voltage value of the current flowing through the chamber.

[0022] (6) Further comprising a control part, the control part, a resistance value acquisition part for acquiring the resistance value from the measuring part at predetermined time intervals, a resistance difference calculation part for calculating a resistance difference obtained by subtracting the resistance value immediately before obtaining the latest resistance value from the latest resistance value among the resistance values obtained by the resistance value acquisition part, a resistance difference sign confirmation part for confirming the sign of the resistance difference calculated by the resistance difference calculation part, a resistance difference second or more negative value confirmation part for confirming whether the resistance difference is a second or more negative value when the sign of the resistance difference is confirmed to be negative by the resistance difference sign confirmation part, a heating end signal transmission part for transmitting a heating end signal to the heating part when the resistance difference second or more negative value confirmation part confirms that the negative value is a second or more negative value, a pressurization end signal transmission part for transmitting a pressurization end signal to the pressurizing part after the heating end signal transmission part transmits the heating end signal and the press machine according to (5) above.

[0023] (7) The press machine according to (6) above, further comprising a resistance difference two consecutive negative value confirmation unit that confirms whether the second or subsequent negative value confirmed by the resistance difference two or more times negative value confirmation unit is the same negative value calculated immediately after the negative value calculated by the resistance difference calculation unit immediately before the calculation of the said negative value.

[0024] (8) If the resistance difference sign verification unit confirms that the sign of the resistance difference is negative, the threshold calculation unit calculates a threshold value of 1% or more of the resistance value immediately before obtaining the latest resistance value used to calculate the resistance difference with a negative sign, A threshold-above-negative-value-checking unit checks whether the absolute value of a resistance value whose sign has been confirmed to be negative by the resistance difference sign confirmation unit, or the absolute value of a negative value confirmed by the resistance difference second or more times negative value confirmation unit or the resistance difference two consecutive times negative value confirmation unit, is greater than or equal to the threshold calculated by the threshold calculation unit. A press machine as described in (7) above, comprising the above.

[0025] (9) A pressing method using a press machine as described in any one of the above items (1) to (8), The pressure medium containing the sample is held between the anvils provided in the chamber. The chamber holding the pressure medium is housed in a container. Place the container on the top surface of the pressurized section. Apply the desired pressure to the container. After applying pressure, at least the chamber and the sample are heated. A pressing method characterized by the following features. [Brief explanation of the drawing]

[0026] [Figure 1] Figure 1 is a schematic perspective view showing an example of a press machine according to this embodiment. [Figure 2] Figure 2 is a perspective view of the container that houses the chamber. [Figure 3] Figure 3 is a partial cross-sectional view showing an example of a press machine according to this embodiment. [Figure 4] Figure 4 is a perspective view showing an anvil that can be used in the press machine according to this embodiment and a pressure medium held between the anvils, where Figure 4(a) is a chechevita type and Figure 4(b) is a toroidal type. [Figure 5] Figure 5 is a phase equilibrium diagram of carbon. [Figure 6] Figure 6 is a block diagram showing an example of a hardware configuration of a control unit used in a press machine according to this embodiment. [Figure 7] Figure 7 is a block diagram showing the functional configuration of a control unit, an example of one used in a press machine according to this embodiment. [Figure 8] Figure 8 is a flowchart of a control unit, showing an example used in a press machine according to this embodiment. [Figure 9] Figure 9 is a block diagram showing the functional configuration of another example of a control unit used in the press machine according to this embodiment. [Figure 10] Figure 10 is a flowchart of another example of a control unit used in the press machine according to this embodiment. [Figure 11] Figure 11 is a graph showing the time evolution of pressure, temperature, and resistance in a diamond generation (synthesis) program generated or synthesized by another example control unit used in the press machine according to this embodiment. [Figure 12] Figure 12 is a block diagram showing the functional configuration of another example of a control unit used in the press machine according to this embodiment. [Figure 13] Figure 13 is a flowchart of another example of a control unit used in the press machine according to this embodiment. [Figure 14] Figure 14 is a partial cross-sectional view showing an example of a press machine using a convex anvil. [Modes for carrying out the invention]

[0027] Embodiments of the present invention will be described in detail with reference to the drawings. The following embodiments are examples of the present invention, and the present invention is not limited to these embodiments. Furthermore, combinations of each embodiment can also be implemented.

[0028] 1. Press machine Figure 1 is a schematic perspective view showing an example of a press machine according to this embodiment. The press machine 10 according to this embodiment includes a frame 14 composed of an upper frame 11, a bottom frame 12, and side frames 13 connecting the upper frame 11 and the bottom frame 12. The frame 14 also includes a wire 15 that applies compressive stress to the side frame 13 by winding a wire around a recess provided on the outer circumference of the frame 14. The press machine also includes a press section 16 provided on the bottom frame 12, a container 17 placed on the top surface 16a of the press section 16, and a chamber 18 that houses the container 17 and includes an anvil for holding a pressure medium containing a sample. Furthermore, the press machine includes a heating section (not shown) for heating the container 17, the chamber 18, the pressure medium, and the sample.

[0029] As shown in Figure 1, the frame 14 is formed by connecting an upper frame 11 and a bottom frame 12 via a pair of side frames 13. The upper frame 11, the bottom frame 12, and the side frames 13 may be separate components or may be a single integrated unit.

[0030] The shapes of the upper frame 11 and the bottom frame 12 are not particularly limited, but it is preferable that they be semicircular or semi-elliptical when viewed from the front, as shown in Figure 1 for the upper frame 11. The bottom frame 12 shown in Figure 1 is rectangular when viewed from the front, but the portion between the two bases 12a and 12b that make up the bottom frame 12, that is, the portion around which the wire 15 is wound, may be semicircular or semi-elliptical when viewed from the front, as shown by the dotted line portion 12c. With such a shape, compressive stress from the wire 15 can be efficiently applied to the side frame 13.

[0031] A recess is provided on the side of the frame 14, and a wire 15 is wound around the recess. The wire 15 applies compressive stress to a pair of side frames 13 via the upper frame 11 and the bottom frame 12.

[0032] The compressive stress applied to the frame 14 by the wire 15 is offset by the reaction force generated in the side frame 13 when the chamber 18 is pressurized via the container 17. As a result, the desired pressure can be applied to the sample without pressure attenuation.

[0033] In this embodiment, when the press machine 10 presses the container 17 with the upper frame 11 and bottom frame 12 as the pressurizing section 16 rises, a reaction force is applied to the frame 14. This reaction force is generated in the opposite direction to the pressurizing direction. Therefore, if the compressive stress previously applied to the frame 14 by the wire 15 balances the reaction force, the pressurizing force is applied to the sample contained in the anvil, which is held by the chamber 18, without attenuation.

[0034] The compressive stress caused by winding the wire 15 can be determined, for example, as follows: First, with the wire 15 not yet wound, the pressure applied to the dummy sample is set on the apparatus side and applied. Then, the difference between the pressure actually applied to the sample and the pressure set on the apparatus side is calculated as the reaction force. The frame 14 can be wound with the wire 15 so that this reaction force is equal to the compressive stress.

[0035] Since the reaction force changes depending on the rigidity of the frame 14, it is necessary to measure the reaction force in advance before winding the wire 15. Because the reaction force is approximately equal to the pressure applied to the sample, the compressive stress can be estimated and adjusted using the wire 15.

[0036] The pressurizing unit 16 is provided on the bottom frame 12, as shown in Figure 1. The pressurizing unit 16 can raise the container 17 that houses the chamber 18, for example, by a hydraulic cylinder. This operation pressurizes the sample contained in the pressure medium via the container 17 and chamber 18 by the anvil. The hydraulic cylinder can have the same configuration as conventional ones.

[0037] The applied pressure should be around 100 to 10,000 tons, and a press capable of applying even greater pressure is also acceptable. Depending on the press pressure of the press machine, the size of the sample should be determined so that a pressure of approximately 5.5 to 10 GPa is applied to the sample, which is above the graphite-diamond equilibrium line.

[0038] Figure 2 is a perspective view of the container 17 that houses the chamber 18. The container 17 consists of a bottom container 17a and an upper container 17b. Preferably, the inner diameter D1 of the container 17 is larger than the outer diameter D2 of the chamber 18.

[0039] Due to this relationship between D1 and D2, the chamber 18 is not fixed as in conventional designs, and the outward pushing of the chamber crushed pieces perpendicular to the press axis during crushing can be suppressed to some extent. Therefore, the attenuation of pressure on the sample contained in the anvil of the chamber 18 can be suppressed as much as possible. Furthermore, the attenuation of pressure applied to the sample can be suppressed as long as D1 is not too large than D2. A more preferable range for D2 is 0.70 × D1 to 0.99 D1.

[0040] Furthermore, it is preferable that the container 17 is fixed to the frame 14 from the viewpoint of improving the positioning accuracy of the chamber 18 during pressing. For example, the bottom container 17a may be fixed to the top surface 16a of the pressurizing section 16, and the upper container 17b may be fixed to the surface of the upper frame 11 that contacts the upper container 17b. The fixing method is not particularly limited and can be fixed with bolts or the like.

[0041] The heating unit (not shown) in the press machines 10 and 30 shown in Figures 1 and 3 is a device that heats the space between the bottom container 17a and the upper container 17b, the space between the bottom chamber 18a and the upper chamber 18b, and the sample by applying electric current. In order to apply electric current to the sample, the heating unit may be electrically connected to the container 17, or at least to the chamber 18. The heating device constituting the heating unit can be any conventionally used power supply. The general configuration of the heating device includes an electrical signal control unit (not shown) connected to the container 17 or the chamber 18. The output should be controlled based on information from the electrical signal control unit.

[0042] As will be described later, when observing the state of sample 22 by observing its resistance, it is preferable to keep the output of the heating unit constant. The output of the heating unit can be set to the output at which diamond is synthesized or generated from a dummy sample, for example. The heating temperature should be 1000°C or higher, and should be above the graphite-diamond equilibrium line.

[0043] Figure 3 is a partial cross-sectional view showing an example of a press machine 30 according to this embodiment. In Figure 3, the side frame 13 shown in Figure 1 is omitted. Also, parts of the upper frame 11 and bottom frame 12 are omitted. As shown in Figure 3, the pressurizing section 16 is provided on the bottom frame 12, and a container 17 that houses the chamber 18 is placed on the top surface 16a of the pressurizing section 16.

[0044] Chamber 18 consists of a bottom chamber 18a and an upper chamber 18b. The bottom chamber 18a and the upper chamber 18b are each equipped with anvils 19a and 19b. The anvils 19a and 19b may be made of cemented carbide or the like, and each may be fitted into the bottom chamber 18a and the upper chamber 18b, respectively. As shown in Figure 3, it is preferable that the anvils 19a and 19b that come into contact with the sample 22 are concave. With concave anvils 19a and 19b, as shown in Figure 3, the concave part is a curved surface such as a substantially spherical shape, so that pressure can be applied quickly and uniformly to the entire sample 22.

[0045] On the other hand, it is not impossible to pressurize the sample 32 even with a convex anvil. Figure 14 is a partial cross-sectional view showing an example of a press machine using convex anvils 29a and 29b. In Figure 14, the frame and pressurizing section are omitted, and a cross-sectional view of the pressure medium 33 containing the anvils 29a and 29b, the chamber 28, and the sample 32 is shown. The convex anvils 29a and 29b shown in Figure 14 are frustoconical in shape and pressurize the sample 32 contained in the pressure medium 33 from above and below with a surface. However, since the sample 32 is pressed with a surface on the anvils 29a and 29b, it is susceptible to the effects of axial wobble, and it takes time for the desired pressure to be applied uniformly to the sample 32. For this reason, it is not necessary to use a convex anvil in this embodiment.

[0046] As shown in Figure 3, a pressure medium 23 containing the sample 22 is sandwiched between the bottom chamber 18a and the upper chamber 18b. The pressure medium is not particularly limited as long as it is molded from oxide powder or the like. The shape of the pressure medium 23 is preferably spherical so as not to attenuate the pressurizing force, for example, a checevica type or a toroidal type. The toroidal type shown in Figure 3 is particularly preferred.

[0047] Figure 4 is a perspective view showing an anvil and a pressure medium held between the anvils that can be used in the press machine according to this embodiment. Figure 4(a) is a Chechevita type, and Figure 4(b) is a toroidal type. As shown in Figure 4(a), in the Chechevita type, the pressure medium 70 is sandwiched between the upper and lower anvils 72 and 73 in the central recess 71. When high pressure is applied, the pressure medium is appropriately compressed within the recess, preventing a reduction in the pressure applied to the raw material. Note that the sample contained in the pressure medium 70 is omitted in Figure 4(a).

[0048] As shown in Figure 4(b), in the toroidal type, an annular recess 82 is provided around the central recess 81. The annular recess 82 is formed in an annular shape when viewed from above in the drawing. When the pressure medium 80 is compressed, it tries to leak out from the recess 81 in the left-right direction in Figure 4(b), but the annular recess 82 prevents the flow of the compressed pressure medium, thus suppressing pressure reduction even after pressurization time has elapsed. In Figure 4(b), one annular recess 82 is provided, but other annular recesses may be provided around it. Note that in Figure 4(b), the sample contained in the pressure medium 80 is omitted.

[0049] The sample 22 shown in Figure 3 is not particularly limited and is not limited in any way as long as it is used to manufacture a material that requires high temperature and high pressure processing. For example, HPHT single crystal diamond can be obtained by using a sample that is a mixture of predetermined amounts of amorphous carbon such as carbon black and a carbon compound such as pentaerythritol. When using these samples, high temperature and high pressure synthesis in a short time is required. For this reason, it is preferable to use concave anvils 19a and 19b, as shown in Figure 3.

[0050] Alternatively, a sample mixed with graphite and various metal catalysts may be used. For example, resin-type NiMn or metal-type NiFe(Co) may be used as the metal catalyst. When using these samples, it is preferable to use convex anvils 29a and 29b, as shown in Figure 14. HPHT single-crystal diamond can also be obtained using these samples.

[0051] The timing of the start and end of heating, and the start and end of pressurization, is preferably controlled by the control unit 24. The control unit 24 sends a signal to the pressurization unit 16 to pressurize to a preset pressure, and after the pressure reaches the graphite-diamond equilibrium line or higher, it sends a signal to the heating unit to heat. In particular, after starting pressurization and heating in that order, it is preferable that the timing of ending heating be controlled by the control unit 24 based on predetermined information, as will be described later. Details will be described later. The pressurization rate is preferably 0.5 to 1.5 GPa / second, and the heating rate is preferably 500 to 1000 °C / second.

[0052] Considering these pressurization and heating rates, it is preferable that the heating start time be 5 to 100 seconds after the start of pressurization. This is because the pressurized force reaches the desired pressure after 5 to 100 seconds from the start of pressurization. Thereafter, for example, heating is performed for a heating time in the range of 1 to 1800 seconds, and after the heating is completed, the temperature is cooled to below the graphite re-transposition temperature, and then pressurization is terminated. The cooling means are not particularly limited, but various means such as air cooling and cooling with a cooling medium may be used.

[0053] The pressurizing section 16 continues pressurizing after the start of pressurization and reaching the desired pressure by maintaining the hydraulic cylinder in the same raised position for several tens of seconds to several minutes. Subsequently, by heating to a temperature above the graphite-diamond equilibrium line, the appropriate pressurizing and heating conditions are achieved, and diamond is synthesized from the sample, causing the applied pressure to decrease slightly. However, since the press machines 10 and 30 according to this embodiment are primarily devices for generating or synthesizing diamond, a slight decrease in applied pressure is acceptable. For example, a decrease of about 1 to 10% from the maximum applied pressure is acceptable. Naturally, it is necessary to maintain a pressure above the graphite-diamond equilibrium line obtained from the graphite phase equilibrium diagram shown in Figure 5.

[0054] Furthermore, it is preferable that the bottom chamber 18a and the upper chamber 18b are depressurized after heating by the heating unit for a predetermined time has been completed. In other words, it is preferable that the heating and cooling of the sample be performed while pressurized. By performing pressurization and heating at this timing, carbonization of the sample can be suppressed more reliably.

[0055] The timing of depressurization is preferably after heating is complete and after the chamber 18 has cooled to a temperature at which re-dislocation to graphite does not occur. For example, depressurization can be performed 5 to 30 seconds after heating is complete. Furthermore, the pressurization and heating described above may be carried out in the atmosphere.

[0056] In light of the above, a comprehensive evaluation of the press machine can be performed by considering axial runout, pressurizing speed, pressure relief, and sample volume for the press machine according to this embodiment and for press machines outside the scope of this embodiment. As the press machine, the press machine 10 shown in Figure 1, with a maximum pressurizing capacity of 1500 tons, is used. The outer recess of the frame 14 is wrapped with wire, and compressive stress is applied to the side frame 13. Then, the sample is subjected to high-temperature and high-pressure treatment with a pressurizing pressure and heating temperature equal to or greater than the graphite-diamond equilibrium line shown in Figure 5, with the anvil shape, pressure medium shape, presence or absence of anvil chamber fixing, and presence or absence of a container as shown in Table 1.

[0057] [Table 1]

[0058] In Table 1, axial runout is evaluated to confirm the effect of whether or not the chamber 18 is fixed. The pressurization rate is evaluated to confirm the effect of the shape of the anvil 19 and the presence or absence of the container 17. The pressure release is evaluated to confirm the effect of whether or not the chamber 18 is fixed, the presence or absence of the container 17, and the shape of the pressure medium (shape of the anvil). The sample volume is evaluated to confirm the effect of the presence or absence of the container and the shape of the pressure medium (shape of the anvil).

[0059] To confirm the above Table 1, in addition to the concave anvils 19a and 19b shown in Figure 3, an configuration using the convex anvils 29a and 29b shown in Figure 14 is assumed. Furthermore, when a container 17 is used as shown in Figure 3, an configuration in which the bottom container 17a is fixed to the top surface 16a of the pressurizing section 16 and the upper container 17b is fixed to the upper frame 11 is assumed. In addition, when no container is used, or when a container 17 cannot be used, an configuration in which the anvils 29a and 29b are fixed to the pressurizing section is assumed in Figure 14, and an configuration in which the chamber is directly fixed to the pressurizing section is assumed in Figure 3.

[0060] In Table 1, "convex," "frustum of a cone," "fixed," and "yes (×)" indicate that containers cannot be used because anvils 29a and 29b, shown in Figure 14, are fixed to the top surface of the frame and pressurizing section, respectively. Similarly, "concave," "chechevitsa," or "toroid," "fixed," and "yes (×)" indicate that containers cannot be used because the bottom chamber, shown in Figure 3, is fixed to the top surface of the pressurizing section with bolts or the like. These cannot be implemented and are therefore indicated with "-" in Table 1.

[0061] In this embodiment, the combination of "concave," "chechevita," or "toroid," "free," and "present" excels in all evaluations, resulting in an overall rating of "9" or "10." On the other hand, in other examples that deviate from this embodiment, the highest overall rating is "6," falling short of this embodiment. Furthermore, it is believed that a similar trend will be observed regardless of which of the aforementioned samples is used.

[0062] As mentioned above, the heating section is energized with an output that reaches a temperature above the graphite-diamond equilibrium line. Here, when diamond is formed or synthesized, the area where diamond appears is almost insulated, and the resistance between the upper chamber 18b and the bottom chamber 18a increases as the amount of diamond synthesized or formed increases. Also, although the current flows through the sample, it does not flow through the pressure medium, so the resistance value is approximately the resistance value of the sample. For this reason, by monitoring the resistance value, the status of diamond formation or synthesis can be grasped in real time.

[0063] Thus, it is preferable to monitor the state of the sample by determining the resistance value from the current and voltage values ​​between the bottom chamber 18a and the upper chamber 18b.

[0064] To confirm that diamond is being synthesized, it is preferable to have a measuring unit 20 that measures the current and voltage values ​​between the upper chamber 18b and the bottom chamber 18a at predetermined intervals, as shown in the press machine 30 in Figure 3. The measuring unit 20 may also include a pressure gauge 21 for measuring the pressure of the pressurizing unit 16. The resistance value can be obtained from the current and voltage values ​​measured by the measuring unit 20. Even if the output from the heating unit is constant, the resistance value changes when the sample is synthesized or generated as diamond, or when it undergoes re-transposition to graphite. For this reason, in the press machine 30 shown in Figure 3, it is possible to observe the change in the resistance value of the sample while energizing the sample with the output from the heating unit.

[0065] Furthermore, the press machine 30 shown in Figure 3 may also include a control unit 24 that receives measurement values ​​from the measuring unit 20 and the pressure gauge 21, and controls the depressurization timing of the pressurizing unit 16 and the heating termination timing of the heating unit (not shown). The control unit 24 that monitors changes in the sample will be described in detail below.

[0066] Figure 6 is a block diagram showing an example of the hardware configuration of a control unit 24 used in a press machine according to this embodiment. The control unit 24 includes a CPU (Central Processing Unit) 51 that performs various processing, a memory 52, a non-volatile storage device 53, an input means 54, a monitor 55, and an input / output interface 56.

[0067] The CPU 51 loads the program stored in the storage device 53 into memory 52 and executes it. The functions described later are executed by the CPU 51. In addition to the program, the storage device 53 stores various data. The storage device 53 is a non-volatile memory such as ROM (Random Access Memory) or an externally connectable HDD. Alternatively, any medium capable of storing a program, such as a floppy disk, hard disk, optical disk, CD-ROM, DVD-ROM, or ROM, which stores data magnetically or optically, is acceptable.

[0068] The recording medium on which the program is stored can be any medium capable of storing a program, such as a floppy disk, hard disk, optical disk, CD-ROM, DVD-ROM, ROM, etc., which store data magnetically or optically. The recording medium can then be made functional by the computer 50 when connected to the input / output interface 56 of the control unit 24.

[0069] The program according to this embodiment, stored in the storage device 53, is loaded into the memory 52. ​​The input means 54 is a device for inputting information. The execution results of the CPU 51, etc., are displayed on the monitor 55. The input / output interface 56 is an interface for sending and receiving data and signals with external devices such as the measuring unit, heating unit, and pressurizing unit.

[0070] The input means 54 is a keyboard or mouse, and it is used to select various options displayed on the monitor 55, or to input the output of the heating unit or the pressure applied by the pressurizing unit into the input fields.

[0071] Figure 7 is a block diagram showing the functional configuration of a control unit 24, an example used in a press machine according to this embodiment. The control unit 24 can be operated by a computer using the program according to this embodiment. The same applies to the control units 34 and 44, which will be described in detail below.

[0072] The control unit 24 includes a resistance value acquisition unit 24a, a resistance difference calculation unit 24b, a resistance difference sign confirmation unit 24c, a resistance difference negative value confirmation unit 24d, a heating completion signal transmission unit 24e, and a pressurization completion signal transmission unit 24f. These functions will be explained using Figure 8. Figure 8 is a flowchart of the control unit 24, showing an example used in a press machine according to this embodiment. In the following explanation, the hardware configurations shown in Figures 3 and 6 will be used as appropriate.

[0073] First, when a predetermined pressure is applied to the sample and current is supplied from the heating unit to the sample, the resistance value acquisition unit 24a acquires a resistance value from the resistance meter 20a of the measurement unit 20 shown in Figure 3 at predetermined intervals (S20). This resistance value is calculated by current × voltage at predetermined intervals. The predetermined interval can be approximately 0.1 to 1 second. The resistance difference calculation unit 24b calculates the resistance difference between the latest resistance value and the resistance value immediately before acquiring the latest resistance value among the resistance values ​​acquired by the resistance value acquisition unit 24a (S21), and stores the calculation result in the storage device 53 and / or memory 52 shown in Figure 6. Immediately after the current is supplied, diamond is synthesized or generated by the current supplied to the sample, so the sign of the resistance difference remains positive.

[0074] Next, the resistance difference sign verification unit 24c checks the sign of the resistance difference calculated by the resistance difference calculation unit 24b (S22). If the sign of the resistance difference is not negative, that is, if the resistance difference is zero or a positive value (S22, no), the process returns to S11.

[0075] On the other hand, if the sign of the resistance difference is negative (S22, yes), the second or subsequent negative value verification unit 24d reads the resistance difference calculation result stored in the storage device 53 or memory 52 in Figure 6 and checks whether the negative value confirmed by the resistance difference sign verification unit 24c is the second negative value (S23). Specifically, it checks whether there is a calculation result showing a negative value among the resistance difference calculation results read from the storage device 53 or memory 52 in Figure 6. If the negative value is the first negative value (S23, no), the process returns to S11.

[0076] On the other hand, if the negative value is the second negative value (S23, yes), the heating termination signal transmitting unit 24e transmits a signal to the heating unit to terminate heating (S24). Subsequently, the pressurization termination signal transmitting unit 24f transmits a pressurization termination signal to the pressurization unit 16 after the heating termination signal has been transmitted by the heating termination signal transmitting unit 24e and a predetermined time has elapsed (S25).

[0077] In this embodiment, when the resistance difference sign confirmation unit 24c confirms a resistance difference with a positive sign, it indicates that diamond synthesis or generation has begun. Therefore, according to this embodiment, the diamond synthesis or generation process can be monitored in situ, leading to further improvements in diamond synthesis or generation. Furthermore, if the start of re-dislocation to graphite is determined by only one negative value, it may be incorrectly determined that re-dislocation to graphite has started if a negative value is obtained by chance for some reason. In this case, diamond synthesis or generation will stop midway. However, as in this embodiment, by terminating heating when a second negative value is calculated, it is possible to accurately determine re-dislocation to graphite.

[0078] Figure 9 is a block diagram showing the functional configuration of another example of a control unit 34 used in a press machine according to this embodiment. Compared to the control unit 24 shown in Figure 7, the control unit 34 shown in Figure 9 includes a resistance difference two consecutive negative value confirmation unit 34g. This function will be explained using Figure 10.

[0079] Figure 10 is a flowchart of the control unit 34 of another example used in the press machine according to this embodiment. Steps S30 to S33, S35, and S36 in Figure 10 are the same as steps S20 to S25 in Figure 8, respectively, so their explanation is omitted. As shown in Figure 10, if the resistance difference is a second negative value as determined by the second negative value confirmation unit 34d (S33, yes), the second consecutive negative value confirmation unit 34g checks whether the resistance difference is a second consecutive negative value (S34). If the resistance difference is not a second consecutive negative value (S34, no), the process returns to S31. On the other hand, if the resistance value is a second consecutive negative value (S34, yes), steps S35 and S36 are performed.

[0080] Thus, the control unit 34 checks whether the resistance difference shows a second negative value and whether the second negative value occurs twice in a row. This allows for more accurate monitoring of the timing of the end of diamond synthesis or diamond generation, as well as the timing of re-dislocation to graphite.

[0081] The operation of the control unit 34 will be described in detail with reference to Figure 11. Figure 11 is a graph showing the time changes of pressure, temperature, and resistance value in a diamond generation (synthesis) program generated or synthesized by another example of the control unit 34 used in the press machine according to this embodiment. The elapsed time rate represents the elapsed time rate (%) when the time from the start of pressurization to the end of pressurization is set to 100%. In Figure 11, the pressure and temperature are constant, but some fluctuations are permissible as long as they are within the range above the graphite-diamond equilibrium line.

[0082] As shown in Figure 11, after the pressure reaches the desired value, starting heating when the elapsed time rate is around 40% causes the resistance value to rise sharply from 39% to 50%. The resistance difference at this elapsed time rate is positive. It is presumed that diamond is being generated or synthesized from the sample during this period.

[0083] Furthermore, since the resistance value decreases significantly between 50% and 51% of the elapsed time, the resistance difference between 50% and 51% of the elapsed time is calculated to be a negative value. This negative value is the first occurrence. In other words, S32 in Figure 10 is yes. It is presumed that during this period, some of the diamond begins to re-transpose into graphite.

[0084] Since the resistance value does not change from 51% to 55% of the elapsed time, the resistance difference is zero. In other words, between 51% and 55% of the elapsed time, the resistance difference does not show a negative value, so S32 in Figure 10 is no. During this period, it is presumed that diamond formation or synthesis continues, and that re-dislocation to graphite is also occurring in parallel.

[0085] When the elapsed time rate is 55-56%, the resistance value decreases, resulting in a negative resistance difference. This corresponds to the second negative value, so S32 in Figure 10 is yes, and S33 in Figure 10 is also yes. However, although this negative value is the second negative value, it is not continuous with the first negative value. Therefore, S34 in Figure 10 is no.

[0086] Even at an elapsed time of 56-57%, the resistance decreases, resulting in a negative resistance difference. This is the third negative value, so S32 and S33 in Figure 10 are yes. Furthermore, since this is the second consecutive negative value, S34 is also yes. The process then immediately proceeds to S35 and S36 in Figure 10, where heating and pressurization are completed. This completes the diamond generation or synthesis process.

[0087] Thus, the control unit 34 terminates heating and pressurization when the resistance difference shows a continuous negative value, allowing for a more accurate determination of the timing to terminate heating. Consequently, diamond synthesis and production can be carried out until the very last moment, thereby improving the diamond yield.

[0088] Furthermore, as shown in Figure 11, even for samples where it takes time to calculate consecutive negative resistance differences, the resistance value can be continuously monitored until two consecutive negative resistance differences are confirmed. Therefore, it is possible to confirm two consecutive negative values ​​in various samples with different redislocation behaviors to graphite.

[0089] In the case of the control unit 24 shown in Figures 7 and 8, the elapsed time rate in Figure 11 shows a second negative value at 55-56%, so the process immediately proceeds to S24 and S25 in Figure 8, and heating and pressurization are completed. This completes the diamond generation or diamond synthesis.

[0090] Figure 12 is a block diagram showing the functional configuration of another example of a control unit 44 used in a press machine according to this embodiment. Compared to the control unit 34 shown in Figure 9, the control unit 44 shown in Figure 12 includes a threshold calculation unit 44h and a threshold-above / below negative value confirmation unit 44i. This function will be explained using Figure 13.

[0091] Figure 13 is a flowchart of the control unit 44 of another example used in the press machine according to this embodiment. Since steps S40-S42 and S45-48 are the same as steps S30-S36 in Figure 11, their explanation is omitted.

[0092] If the resistance difference sign confirmation unit 44c confirms that the sign of the resistance difference is negative (S42, yes), the threshold calculation unit 44h calculates a threshold value of 1% or more of the resistance value immediately before obtaining the latest resistance value used to calculate the resistance difference with a negative sign (S43). Then, the threshold-greater-than-negative value confirmation unit 44i checks whether the absolute value of the resistance difference with a negative sign confirmed by the resistance difference sign confirmation unit 44c is greater than or equal to the threshold value calculated by the threshold calculation unit 44h (S44). If the absolute value is less than the threshold (S44, no), the process returns to S41. On the other hand, if the absolute value is greater than or equal to the threshold (S44, yes), S45 to S48 are executed.

[0093] Thus, in the control unit 44, if the resistance difference sign verification unit 44c confirms that the sign of the resistance difference is negative, the control unit 44 compares the resistance difference with a threshold. Therefore, if the two consecutive negative resistance difference verification unit 44g confirms that there are two consecutive negative resistance differences, the absolute value of at least the second consecutive negative value among the calculated negative values ​​will be greater than or equal to the threshold. Consequently, the timing of the end of diamond generation or diamond synthesis can be monitored with even greater accuracy.

[0094] For example, if the first negative value is less than the threshold, S44 in Figure 13 is "no". If the second consecutive negative value immediately following is greater than or equal to the threshold, S42, S44-S46 are "yes".

[0095] If the first negative value is greater than or equal to the threshold, S42 and S44 are yes, but S45 is no. If the subsequent consecutive negative values ​​are greater than or equal to the threshold, S42, S44-S46 are yes. In addition, as shown in Figure 11, for example, if the second negative value after some time has passed since the first negative value is either greater than or equal to the threshold or less than the threshold, if the subsequent third consecutive negative value is greater than or equal to the threshold, S42 and S44-S46 are yes.

[0096] Therefore, although S43 and S44 are placed after S42 in Figure 13, the same result can be obtained by moving S43 and S44 after S45 or after S46. Also, the same result can be obtained by moving them after S45 or after S46 instead of after S42. In other words, the threshold-above-negative value confirmation unit 44i may check whether the absolute value of the resistance difference whose sign has been confirmed to be negative by the resistance difference sign confirmation unit 44c, or the absolute value of the negative value of the resistance difference confirmed by the second or more negative value confirmation unit 44d or the two consecutive negative value confirmation unit 44g of the resistance difference, is greater than or equal to the threshold value.

[0097] By comparing the resistance difference with a threshold value, minute negative values ​​due to noise and other factors can be excluded, allowing for a more accurate determination of re-transposition to graphite. When calculating the threshold value, it is recommended to use a value of 1% or more of the resistance value immediately preceding the acquisition of the latest resistance value used to calculate the resistance difference. This is because if a negative value is calculated, the previous resistance value is greater than the latest resistance value, allowing for a larger threshold value to be used to determine the resistance difference. Preferably, this percentage should be calculated as a threshold value of 2% or more, and even more preferably as a threshold value of 3% or more, as needed.

[0098] 2. Pressing method The pressing method according to this embodiment is a pressing method using the aforementioned press machine. It will be explained with reference to Figure 3.

[0099] First, the pressure medium 23 containing the sample 22 is clamped by the anvil 19 provided in the chamber 18. The chamber 18, which clamps the pressure medium 23, is placed in the container 17. The container 17 containing the chamber 18 is placed on the top surface 16a of the pressurizing section 16. As the pressurizing section 16 rises, the container 17 is pressurized. Consequently, the chamber 18, the pressure medium 23, and the sample 22 are also pressurized. The applied pressure should be at or above the graphite-diamond equilibrium line.

[0100] After applying pressure and a predetermined time has elapsed, at least the chamber 18 and the sample 22 are heated by applying an electric current. The heating temperature should be above the graphite-diamond equilibrium line. In Figure 3, the container 17, chamber, and sample are heated by applying an electric current. After a predetermined time has elapsed since the start of heating, the heating is terminated. After the temperature of the container 17 has cooled to a temperature at which the generated or synthesized diamond does not re-transpose into graphite, the pressure is terminated. The temperature at which re-transposition into graphite does not occur is in the temperature range below the graphite-diamond equilibrium line shown in Figure 5.

[0101] In the pressing method according to this embodiment, the chamber 18 is housed in the container 17 without being fixed. This prevents the crushing of the pressure medium, etc., from being pushed out to the sides during pressurization, thus maintaining the pressurizing force on the sample.

[0102] Furthermore, in the pressing method according to this embodiment, the control unit described above can be used to employ, for example, the following pressing method. First, when a predetermined pressure is applied to the sample and current is supplied to the sample from the heating unit, the resistance value is acquired at predetermined time intervals. Among the acquired resistance values, the resistance difference is calculated by subtracting the resistance value immediately before acquiring the latest resistance value from the latest resistance value.

[0103] Next, the system checks whether the calculated resistance difference has a negative sign. If the sign is negative, it reads out the previous calculation results and checks whether the resistance difference is a negative value for the second time or more. If it is confirmed that the negative value is a negative value for the second time or more, it sends a heating termination signal to the heating unit, sends a heating termination signal, waits for a predetermined time to elapse, and after the predetermined time has elapsed, sends a pressurization termination signal to the pressurization unit.

[0104] This manufacturing method allows for precise timing of redislocation from single-crystal diamond to graphite during single-crystal diamond production through in-situ monitoring. This enables high yields of single-crystal diamond. Furthermore, because redislocation to graphite can be determined regardless of the sample, it eliminates the need to pre-measure reference data, as was previously required, and can accommodate variations between samples and various types of samples. [Explanation of Symbols]

[0105] 10,30 Press machine, 14 Frame, 15 Wire, 16 Pressurization section, 17 Container, 18 Chamber, 19 Anvil, 20 Measurement section, 21 Pressure gauge, 22,32 Sample, 23,33 Pressure medium, 24,34,44 Control section

Claims

1. A press machine that heats and pressurizes a sample, A frame comprising an upper frame, a bottom frame, and side frames connecting the upper frame and the bottom frame, A wire that is wound around the outer circumference of the frame to apply compressive stress to the side frame, The bottom frame has a pressurizing section, A container placed on the top surface of the pressurizing section, A chamber housed in the aforementioned container and comprising an anvil that holds a pressure medium containing the sample, At least the chamber and the heating unit that heats the sample by passing an electric current through them, A press machine characterized by being equipped with the following features.

2. The press machine according to claim 1, wherein the shape of the anvil is either chechevita type or toroidal type.

3. The press machine according to claim 1 or 2, wherein the inner diameter of the container is larger than the outer diameter of the chamber.

4. The container consists of an upper container and a bottom container. The press machine according to claim 3, wherein the upper container is fixed to the upper frame and the bottom container is fixed to the top surface of the pressurizing section.

5. Furthermore, the press machine according to any one of claims 1 to 4, further comprising a measuring unit for measuring the current value and voltage value of the current flowing through the chamber.

6. Furthermore, it is equipped with a control unit, The control unit, A resistance value acquisition unit that acquires resistance values ​​from the measurement unit at predetermined intervals, A resistance difference calculation unit calculates the resistance difference obtained by subtracting the resistance value immediately before obtaining the latest resistance value from the latest resistance value among the resistance values ​​obtained by the resistance value acquisition unit, A resistance difference sign confirmation unit confirms the sign of the resistance difference calculated by the resistance difference calculation unit, If the resistance difference sign confirmation unit confirms that the sign of the resistance difference is negative, the resistance difference second or later negative value confirmation unit confirms whether the resistance difference is a negative value for the second time or more, When the resistance difference negative value confirmation unit confirms that the negative value is the second or subsequent negative value, the heating termination signal transmission unit transmits a heating termination signal to the heating unit. After the heating termination signal is transmitted by the heating termination signal transmitting unit, the pressurization termination signal transmitting unit transmits a pressurization termination signal to the pressurization unit. The press machine according to claim 5, comprising:

7. The press machine according to claim 6, further comprising a resistance difference two consecutive negative value confirmation unit that confirms whether the second or subsequent negative value confirmed by the resistance difference two or more negative value confirmation unit is the same negative value calculated immediately after the negative value calculated by the resistance difference calculation unit immediately before the calculation of the said negative value.

8. If the resistance difference sign verification unit confirms that the sign of the resistance difference is negative, the threshold calculation unit calculates a threshold value of 1% or more of the resistance value immediately before obtaining the latest resistance value used to calculate the resistance difference with a negative sign. A threshold-or-exceeding negative value confirmation unit confirms whether the absolute value of the resistance value confirmed to be negative by the resistance difference sign confirmation unit, or the absolute value of the negative value confirmed by the resistance difference second or more negative value confirmation unit or the resistance difference two consecutive negative value confirmation unit, is greater than or equal to the threshold calculated by the threshold calculation unit. The press machine according to claim 7, comprising:

9. A pressing method using a press machine according to any one of claims 1 to 8, The anvil provided in the chamber holds the pressure medium containing the sample, The chamber holding the pressure medium is housed in the container. The container is placed on the top surface of the pressurizing section, A desired pressure is applied to the container. After applying the aforementioned pressure, at least the chamber and the sample are heated. A pressing method characterized by the following features.

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