Manufacturing methods for ceramic components, especially synthetic diamonds.

Abstract

The present invention relates to a method for manufacturing ceramic components from a sample of ceramic powder. This method comprises the steps of heating a sample to a predetermined minimum heating temperature using a heating device, and generating and radiating multiple elastic waves toward a focusing system using multiple elastic wave generators, wherein the elastic waves have an elastic wave intensity of I at the input of the focusing system. e The process includes a step of generating a [specific component] and a step of focusing the elastic wave to a focal region within a sample, wherein the focusing system defines a multiplication coefficient M. The focused elastic wave has at least M × I in at least a portion of the focal region. e This generates a minimum elastic wave intensity. This elastic wave intensity, when combined with the minimum heating temperature applied to the sample, is sufficient to sinter the ceramic powder in a portion of the focal region.

Description

[Technical Field]

[0001] This invention relates to a method for producing ceramic components, particularly synthetic diamonds.

[0002] The present invention relates in particular to a method for manufacturing ceramic components by sintering, preferably a method for manufacturing synthetic diamonds, and an apparatus for carrying out this method. [Background technology]

[0003] Ceramic components manufactured by sintering are increasingly used in industry due to their electronic, mechanical, optical, thermal, or chemical properties.

[0004] Conventional sintering is a method that involves heating powder of a material selected to be used as a ceramic substrate (e.g., alumina or zirconia). Heating causes the powder particles to form chemical bonds with each other, thereby creating the ceramic. The required temperature generally exceeds 1500°C, and the heating time is approximately several hours (about 10°C per minute at the center). The main drawback of conventional sintering is that when producing ceramic parts with particle sizes of 10-100 μm, while hardness is high, mechanical strength is low. In fact, particle size is one of the parameters that determine the mechanical strength of a mechanical part. The smaller the particle size, the higher the mechanical strength of the part.

[0005] During the 20th century, conventional sintering techniques were improved, allowing for faster heating of the powder, reaching temperatures of up to 200°C per minute at the core. This is known as "flash sintering" (or "spark plasma sintering"). In flash sintering, ceramic powder is placed in a mold, usually made of graphite, and if the material is conductive, a high-intensity DC or AC current is passed through the mold and powder. This innovation has made it possible to reduce sintering time to about 10 minutes, suppress the growth of powder particles, and promote the formation of chemical bonds between particles. This advantage makes it possible to manufacture mechanical parts with particle sizes of approximately 1 μm by heating to temperatures exceeding 1200°C.

[0006] One of the drawbacks of flash sintering is that it requires relatively high heating temperatures. This limits the use of materials that are metastable at room temperature and pressure in the manufacture of machine parts. For example, diamond is stable at room temperature and pressure, but reverts to graphite form above 800°C in an oxygen atmosphere, and above 1700°C in an inert atmosphere or vacuum.

[0007] In the early 21st century, flash sintering technology was further improved, enabling the compression of powder under pressures exceeding several hundred MPa. Applying such pressure to flash sintering not only makes it possible to sinter materials that are metastable at atmospheric pressure, but also lowers the temperature required for powder sintering in the range of 500 to 1000°C depending on the material, further suppressing grain growth during sintering. Mechanical parts with particle sizes of less than 100 nm can be obtained in approximately 10 minutes. Furthermore, it is possible to sinter nanometer-sized diamond powder at 5 GPa and 1500°C to obtain polycrystalline diamond mechanical parts with particle sizes in the range of 10 to 100 nm.

[0008] One of the main drawbacks of high-pressure flash sintering is the inability to create complex shapes during the sintering process. In fact, the equipment currently used to achieve pressures exceeding GPa severely limits the shape of the sintering mold.

[0009] To manufacture ceramic components using synthetic diamonds, technologies other than high-pressure flash sintering of diamond powder can also be used.

[0010] One such technique is the High Pressure High Temperature (HPHT) method. In this technique, a carbon sample, such as graphite, is placed in a container and exposed to a high temperature of approximately 1500°C and a high pressure of approximately 15 GPa. By adding a transition metal such as nickel or cobalt as a catalyst to the sample, the temperature can be reduced to 1000°C and the pressure to 6 GPa. Similarly, HPHT technology makes it possible to sinter diamond pellets using graphite powder instead of diamond powder. In this case, the graphite powder is compressed at a pressure exceeding 7 GPa and heated at a temperature exceeding 2000°C. The powder then undergoes sequential phase changes and sintering processes to form diamond pellets.

[0011] Another technique is chemical vapor deposition (CVD). The diamond sample is placed inside a vacuum chamber.

[0012] A gas containing hydrogen is introduced into the chamber. This gas is ionized by microwave discharge, generating plasma. The chemical species generated by the plasma are gradually adsorbed onto the substrate, forming the target object.

[0013] The main drawbacks of these first two techniques are as follows: it is difficult or impossible to precisely control the spatial location where conditions suitable for diamond formation are obtained, and there are limitations on the direction of diamond growth. In the case of HPHT technology, the direction is determined by the compression pattern, while in the case of CVD technology, the direction is perpendicular to the substrate.

[0014] Another technology is based on the principle of dynamic compression to convert graphite into diamond, producing only synthetic diamond powder.

[0015] In the dynamic compression technique for converting graphite to diamond, the conversion is not diffusive, as in the HPHT technique. That is, it is not due to temperature-induced atomic diffusion. The conversion is martensitic, meaning it is induced by local deformation of the crystal lattice. This point was described by Christian et al. in the December 1995 issue of Journal de Physique IV (Vol. 5, No. C8), and has been further demonstrated by numerous experiments conducted since the early 1990s, specifically by Erskine et al. (1992, Journal of Applied Physics, Vol. 71, No. 10), Kraus et al. (2016, Nature Communications, Vol. 7, No. 10970), and Volt et al. (2019, Journal of Applied Physics, Vol. 125, No. 245902).

[0016] This technique is based, for example, on the use of shock waves. Shock waves are generated by projecting, for example, a metal foil onto a graphite sample. In the literature, shock waves generated by explosions are generally referred to. Shock waves can also be generated by laser ablation. This technique has several drawbacks, in particular, that the graphite sample is partially destroyed when generating these shocks, and that the duration of these shocks is very short, approximately microseconds. The resulting diamond is limited to the form of nanocrystalline or microcrystalline materials. [Prior art documents] [Non-patent literature]

[0017] [Non-Patent Document 1] Journal de Physique IV (Vol. 5, No. C8) [Non-Patent Document 2] Erskine et al. (1992, Journal of Applied Physics, Vol. 71, No. 10) [Non-Patent Document 3] Kraus et al. (2016, Nature Communications, Vol. 7, No. 10970) [Non-Patent Document 4] Volt et al. (2019, Journal of Applied Physics, Vol. 125, No. 245902) [Overview of the project] [Means for solving the problem]

[0018] The present invention aims to overcome the shortcomings of solutions proposed by the prior art, particularly those described above.

[0019] To achieve this objective, the present invention proposes a method for manufacturing ceramic parts from a sample of ceramic powder. The method comprises the steps of heating the ceramic powder sample to a predetermined minimum heating temperature using a heating device, and then generating and radiating multiple elastic waves toward a focusing system using multiple elastic wave generators, each of which is configured to radiate elastic waves with a frequency f in the range of 1 MHz to 100 MHz, and the elastic waves have an elastic wave intensity of I at the input of the focusing system. e The method includes a step of generating a [specific component] and a step of focusing the elastic wave to a focal region within a ceramic powder sample using a focusing system, wherein the focusing system is characterized by defining a multiplication coefficient M.

[0020] The focused elastic wave, in at least a portion of the focal region, is at least M×I e This generates a minimum elastic wave intensity, and when combined with the application of a minimum heating temperature to the ceramic powder sample, it has sufficient elastic wave intensity to sinter the ceramic powder in a portion of the focal region.

[0021] The term "ceramics" refers to so-called technical ceramics. Technical ceramics include the following: • Ceramic oxides: These are mainly composed of metal oxides such as zirconium oxide and alumina. • Non-oxide ceramics: Materials based on carbon, nitrides, and silicon compounds (e.g., silicon carbide, tungsten carbide, aluminum nitride). • Silicate ceramics: These are made primarily from raw materials combined with alumina (e.g., aluminum silicate).

[0022] The method according to the present invention allows for the sintering of ceramic powder by locally compressing it while heating it to a predetermined minimum temperature.

[0023] As is clear from this method, the sample is heated before the generation and emission of elastic waves by multiple elastic wave generators. The sample is not heated by the elastic waves emitted by the multiple elastic wave generators.

[0024] The predetermined minimum temperature is preferably higher than the sintering temperature of the selected ceramic powder. The sintering temperature corresponds to the minimum temperature required to sinter the powder under a predetermined pressure. The higher the applied pressure, the lower the sintering temperature.

[0025] It is well known that elastic wave pressure can be expressed as a function of elastic wave intensity. When a material is initially in a normal temperature and pressure state, the pressure is obtained corresponding to each elastic wave intensity value. Therefore, if the function of elastic wave intensity with respect to pressure and the function of the minimum temperature required for sintering with respect to pressure are known for the same powder, the minimum temperature required for sintering can be determined as a function of elastic wave intensity. Accordingly, depending on the ceramic powder used in the method according to the present invention, a heating temperature that is advantageous for enabling the powder to be sintered in at least a portion of the focal region can be applied.

[0026] In other words, the sintering temperature of a ceramic powder is a function of the elastic wave intensity generated in at least a portion of the focal region. The elastic wave intensity and sintering temperature required to sinter the ceramic powder depend on the ceramic powder used.

[0027] The sintering temperature can be derived from known information regarding the elastic wave intensity that can be generated by elastic waves focused in at least a portion of the focal region. Therefore, the method according to the present invention can be carried out for a particular ceramic powder using a set of values ​​(elastic wave intensity, heating temperature) to be applied in order to perform sintering in at least a portion of the focal region.

[0028] Therefore, the method according to the present invention offers the advantage of enabling the sintering of ceramic powder in a portion of the focal region. Furthermore, this method also offers the advantage of precisely controlling the spatial position in which the conditions for enabling the sintering of ceramic powder are met.

[0029] As an example, the method according to the present invention produces an elastic wave intensity of 5.10 11 W / m 2 Diamond can also be obtained by sintering diamond powder, starting from a minimum heating temperature of 1360°C.

[0030] In certain embodiments, the present invention includes the following features, which may be implemented individually or in a technically functional combination.

[0031] In a particular embodiment of the present invention, the ceramic powder is selected from diamond powder, tungsten carbide powder, silicon nitride powder, fully stabilized zirconia powder, α-alumina powder, γ-alumina powder, and titanium oxide powder.

[0032] In a particular embodiment of the present invention, the method includes the movement of the focal region within the sample during the emission of elastic waves.

[0033] By shifting the focal region within the sample in this way, it becomes possible to sinter the sample in a selected area, which offers the advantage of being able to manufacture parts with a predetermined shape from powder.

[0034] The present invention also relates to an apparatus for carrying out a method according to at least one embodiment thereof. The apparatus comprises a heating device for heating a sample, a plurality of elastic wave generators configured to generate elastic waves, and a focusing system for focusing the elastic waves in a focal region within the sample, the focusing system defining a multiplication coefficient M. The plurality of elastic wave generators and the heating device for heating the sample are separate elements within the apparatus.

[0035] Each elastic wave generator in the apparatus is preferably configured to emit elastic waves of frequency f, preferably in the range of 1 MHz to 100 MHz.

[0036] In a preferred embodiment, all elastic wave generators in the apparatus emit elastic waves at the same frequency.

[0037] The focusing system is designed and dimensionally determined to receive all elastic waves emitted by the elastic wave generator.

[0038] In certain embodiments, the present invention further satisfies the following features, which are implemented individually or in each technically functional combination.

[0039] In certain embodiments, the heating device enables heating of the sample by the Joule effect or induction effect.

[0040] In certain embodiments, each elastic wave generator is a piezoelectric actuator.

[0041] In certain embodiments, the apparatus includes a member for moving a focal region within the sample in order to sinter the entire sample.

[0042] As an example of an embodiment of a focal region shifting member, the member that shifts the focal region within a sample is a member that shifts the elastic wave focusing system, and / or a member that shifts the sample, and / or a member that shifts the elastic wave generator, and / or a member that changes the phase of the elastic wave generator.

[0043] The present invention also relates to a method for producing diamond from a sample containing graphite powder. The method includes a step of heating a graphite powder sample to a predetermined minimum temperature by a heating device, and then a step of generating and radiating a plurality of elastic waves toward a focusing system by a plurality of elastic wave generators, wherein each elastic wave generator is configured to radiate an elastic wave having a frequency f in the range of 1 MHz to 100 MHz, and the elastic waves generate an elastic wave intensity I e at an input portion of the focusing system. The method further includes a step of focusing the elastic waves by the focusing system to a focal region within the graphite powder sample, wherein the focusing system is characterized by defining a multiplication factor M. The focused elastic waves generate an elastic wave intensity that is at least M×I e =1.10 12 W / m 2 at least in a part of the focal region. The elastic wave intensity corresponds to a minimum elastic wave intensity sufficient to perform a process of achieving a phase change from graphite powder to diamond powder in a first stage and then a process of sintering the obtained diamond powder in combination with the minimum heating temperature applied to the sample in a second stage.

[0044] To achieve a phase conversion from graphite to diamond, the elastic wave intensity in the focal region needs to exceed a minimum pressure at which the arriving elastic wave pressure is sufficiently low, diamond becomes more stable than graphite, and the atomic kinetic energy is sufficient to break the metastability of graphite during the duration of elastic wave radiation.

[0045] When the elastic wave intensity generated in the focal region is at least 1.10 12 W / m 2 the duration of elastic wave intensity radiation determines the conversion rate from graphite to diamond in the focal region. In other words, when the elastic wave intensity radiated in the focal region is constant, the longer the duration of elastic wave intensity radiation, the greater the conversion rate from graphite to diamond in the focal region. Further, to obtain a desired conversion rate from graphite to diamond, the greater the elastic wave intensity radiated, the shorter the duration of elastic wave intensity radiation in the focal region.

[0046] Therefore, depending on the elastic wave intensity generated in the focal region, it is preferable to radiate elastic waves for a duration longer than the minimum duration sufficient to obtain a desired predetermined conversion rate from graphite to diamond in the focal region.

[0047] As is evident from this method, the sample is heated before elastic waves are generated and emitted by multiple elastic wave generators. The sample is not heated by the elastic waves emitted by the multiple elastic wave generators. By heating the sample in parallel at a predetermined minimum temperature, the elastic wave intensity is increased to 1.10 12 W / m 2 In the focal region where it reaches a certain point, the advantage is that the resulting diamond powder is denser due to sintering.

[0048] The sintering temperature of graphite powder depends on the intensity of elastic waves generated in at least a portion of the focal region.

[0049] The sintering temperature can be derived from known information regarding the elastic wave intensity that can be generated by elastic waves focused in at least a portion of the focal region. Therefore, the method according to the present invention can be performed on graphite powder using a set of values ​​to be applied (elastic wave intensity, heating temperature) to carry out sintering of the graphite powder in at least a portion of the focal region.

[0050] The present invention also relates to a method for producing diamond from a sample containing amorphous carbon powder. The method comprises the steps of heating a sample of amorphous carbon powder to a predetermined minimum temperature using a heating device, and then generating and radiating multiple elastic waves toward a focusing system using multiple elastic wave generators, each elastic wave generator configured to radiate elastic waves with a frequency f in the range of 1 MHz to 100 MHz, and the elastic waves have an elastic wave intensity of I at the input of the focusing system. eThe process includes a step of generating a [specific component] and a step of focusing the elastic wave to a focal region in an amorphous carbon powder sample using a focusing system, wherein the focusing system defines a multiplication coefficient M. The focused elastic wave is at least M × I in at least a portion of the focal region. e = 2.1 × 10 12 W / m 2 This generates an elastic wave intensity equal to [a certain value]. This elastic wave intensity corresponds to the minimum elastic wave intensity sufficient to perform a process in which a phase change from amorphous carbon powder to diamond powder is achieved in the first step, and then a process in which the obtained diamond powder is sintered in combination with the minimum heating temperature applied to the sample in the second step.

[0051] "Amorphous carbon" refers to sp 2 Atomic bonding (the same type of bonding as in graphite) and sp 3 This refers to allotropic forms of carbon that contain a mixture of atomic bonds (the same type of bonds as in diamond) and may also contain hydrogen atoms. The distribution of these different bond types is random, and this distribution is not necessarily regular, whether on a small or large scale.

[0052] Preferably, amorphous carbon that does not contain hydrogen atoms generally has sp in the range of 40% to 90% 3 It has a mixing ratio.

[0053] For a phase transition from amorphous carbon to diamond to occur in the focal region, the following conditions must be met: the elastic wave intensity must exceed the minimum pressure sufficient to make diamond more stable than graphite; and the kinetic energy of the atoms must be sufficient to break the metastability of graphite during the duration of the elastic wave emission.

[0054] The elastic wave intensity generated in the focal region is at least 2.1.10 12 W / m 2When equal to , the duration of the elastic wave intensity radiation determines the conversion rate from amorphous carbon to diamond in the focal region. In other words, if the elastic wave intensity emitted in the focal region is constant, the longer the duration of the elastic wave intensity radiation, the greater the conversion rate from amorphous carbon to diamond in the focal region. Furthermore, to obtain the desired conversion rate from amorphous carbon to diamond, the greater the emitted elastic wave intensity, the shorter the duration of the elastic wave intensity radiation in the focal region.

[0055] Therefore, depending on the elastic wave intensity generated in the focal region, it is preferable to radiate elastic waves for a duration longer than the minimum duration sufficient to obtain a desired predetermined conversion rate from amorphous carbon to diamond in the focal region.

[0056] As is evident from this method, the sample is heated before elastic waves are generated and emitted by multiple elastic wave generators. The sample is not heated by the elastic waves emitted by the multiple elastic wave generators.

[0057] By heating the sample in parallel at a predetermined minimum temperature, the elastic wave intensity is 2.1.10 12 W / m 2 In the focal region that reaches [a certain point], the obtained diamond powder is densely densified by sintering.

[0058] The sintering temperature of amorphous carbon powder depends on the intensity of elastic waves generated in at least a portion of the focal region.

[0059] The sintering temperature can be derived from known information regarding the elastic wave intensity that can be generated by elastic waves focused in at least a portion of the focal region. Therefore, the method according to the present invention can be performed on amorphous carbon powder using a set of values ​​to be applied (elastic wave intensity, heating temperature) to carry out sintering in at least a portion of the focal region.

[0060] The present invention also relates to an apparatus for carrying out a method for producing diamond from a sample containing graphite powder or a sample containing amorphous carbon powder. The apparatus comprises a heating device for heating the sample, a plurality of elastic wave generators configured to generate elastic waves, and a focusing system for focusing the elastic waves in a focal region within the sample, the focusing system defining a multiplication coefficient M. The plurality of elastic wave generators and the heating device for heating the sample are separate elements within the apparatus.

[0061] Each elastic wave generator in the apparatus is preferably configured to emit elastic waves of frequency f, preferably in the range of 1 MHz to 100 MHz.

[0062] In a preferred embodiment, all elastic wave generators in the apparatus emit elastic waves at the same frequency.

[0063] The focusing system is designed and dimensionally determined to receive all elastic waves emitted by the elastic wave generator.

[0064] In certain embodiments, the present invention further satisfies the following features, which are implemented individually or in each technically functional combination.

[0065] In certain embodiments, the heating device enables heating of the sample by the Joule effect or induction effect.

[0066] In certain embodiments, each elastic wave generator is a piezoelectric actuator.

[0067] In certain embodiments, the apparatus includes a component for moving a focal region within a sample in order to form a diamond within the sample.

[0068] As an example of an embodiment of a focal region shifting member, the member that shifts the focal region within a sample is a member that shifts the elastic wave focusing system, and / or a member that shifts the sample, and / or a member that shifts the elastic wave generator, and / or a member that changes the phase of the elastic wave generator. [Brief explanation of the drawing]

[0069] The present invention will be described illustratively with reference to the following drawings, which are not intended to limit the present invention.

[0070] [Figure 1] Figure 1 is a perspective view of an apparatus particularly suited to the ceramic manufacturing method according to the present invention. [Figure 2] Figure 2 is a perspective view of one half of the device shown in Figure 1. [Figure 3] Figure 3 is a cross-sectional view of the device shown in Figure 2. [Figure 4] Figure 4 is an enlarged view of region III in Figure 3, and shows an example of a piezoelectric actuator. [Figure 5] Figure 5 is a graph showing the sintering temperature as a function of pressure for different types of ceramic powders. [Figure 6] Figure 6 is a graph showing the sintering temperature as a function of elastic wave intensity for different types of ceramic powders. [Figure 7] Figure 7 shows model curves illustrating the relationship between elastic wave intensity and induced pressure for graphite and amorphous carbon. [Figure 8] Figure 8 shows model curves illustrating the kinetic energy as a function of elastic wave intensity for graphite and amorphous carbon. [Figure 9] Figure 9 is a graph showing the time required to emit elastic waves as a function of the intensity of the elastic waves, in order to reproduce conditions sufficient to achieve 99% phase change in the diamond graphite sample and the diamond amorphous carbon sample.

[0071] In these figures, the same symbols common to each figure indicate the same or similar elements. Furthermore, for ease of understanding, unless otherwise specified, the drawings are not depicted to scale. [Modes for carrying out the invention]

[0072] The apparatus 100 shown in Figures 1 to 4 is adapted to perform both of the following methods: a method for producing ceramic parts from a sample 50 of ceramic powder (hereinafter referred to as the "first method"), and a method for producing diamond from a sample 50 containing graphite powder or amorphous carbon powder (hereinafter referred to as the "second method").

[0073] In the first method, sample 50 contains only ceramic powder.

[0074] The ceramic powder is preferably selected from tungsten carbide, silicon nitride, fully stabilized zirconia (FSZ), α-alumina, γ-alumina, titanium oxide, and diamond.

[0075] In the second method, sample 50 may contain a diamond core and graphite powder or amorphous carbon powder. Preferably, sample 50 contains only graphite powder or amorphous carbon powder.

[0076] Preferably, the ceramic powder, graphite powder, or amorphous carbon powder consists of nanometer-sized particles. These particles are separated from each other.

[0077] In the following description, “particle” means a particle whose ratio of maximum to minimum dimension is preferably 5 or less. The particles may have a spherical, cubic, or other geometric shape.

[0078] When the term "size" is applied to particles, it refers to the maximum dimensions of those particles.

[0079] The term "nanometer size" also refers to dimensions between 1 nanometer and less than 1,000 nanometers.

[0080] As shown in Figures 1 to 4, the apparatus 100 comprises a plurality of elastic wave generators 10 and a focusing system 20 for focusing the elastic waves into a focal region within the sample 50.

[0081] Preferably, as shown in Figures 3 and 4, the elastic wave generator 10 is attached to the focusing system 20.

[0082] The sample 50, positioned downstream of the focusing system 20, is placed within a medium called the propagation medium 40. The sample 50 is held within the propagation medium 40. For example, a container 70 placed within the propagation medium 40 is used to hold the sample 50.

[0083] In one embodiment, the container 70 has a tubular shape, with at least one end of both ends closed, preferably both ends closed.

[0084] Each elastic wave generator 10 of the apparatus 100 is configured to generate and emit elastic waves of frequency f, preferably in the range of 1 MHz to 100 MHz.

[0085] In a preferred embodiment, all elastic wave generators 10 of the apparatus 100 emit elastic waves at the same frequency.

[0086] Preferably, the elastic waves emitted by the elastic wave generator 10 are synchronized.

[0087] As another non-limiting example, some, for example, half of the elastic wave generators 10 of the device 100 may radiate at the same frequency f1, while the remaining elastic wave generators 10 of the device 100 may radiate at the same frequency f2, but different from f1.

[0088] Each elastic wave generator 10 of the device 100 is configured to generate elastic waves and transmit them at an output P.

[0089] Preferably, the elastic wave generators 10 have the same or similar structures.

[0090] In a preferred embodiment, the elastic wave generator 10 is a piezoelectric actuator. The piezoelectric actuator converts an electrical signal into an elastic wave signal at a predetermined output.

[0091] In a preferred embodiment of the piezoelectric actuator, the piezoelectric actuator has a configuration in which at least one impedance mismatch layer 11, at least one piezoelectric element 12, and at least one impedance matching layer 13 are sequentially stacked.

[0092] At least one piezoelectric element 12 is interposed between at least one impedance mismatch layer 11 and at least one impedance matching layer 13. On the other hand, at least one impedance matching layer 13 is interposed between at least one piezoelectric element 12 and the focusing system 20.

[0093] In the non-limiting example shown in Figure 4, the piezoelectric actuator 10 comprises two impedance mismatch layers 11, one piezoelectric element 12, and one impedance matching layer 13.

[0094] The frequency of the electrical signal applied between the terminals of at least one piezoelectric element 12 determines the frequency of the generated elastic wave. This frequency may, for example, correspond to the resonant frequency of at least one piezoelectric element 12, maximizing the conversion efficiency from electrical signal to elastic wave.

[0095] Preferably, at least one impedance matching layer 13 is configured to maximize the transmission of elastic waves from at least one piezoelectric element 12 to the focusing system 20.

[0096] Preferably, at least one impedance mismatch layer 11 is configured to minimize the transmission of elastic waves to the outside of the apparatus 100.

[0097] The piezoelectric actuator 10 is preferably disposed within a member referred to as a barrel 15 and is fixedly held in place.

[0098] The barrel 15 has a plurality of openings 151, each opening designed to accommodate one piezoelectric actuator. The openings extend through the thickness direction of the barrel.

[0099] Each piezoelectric actuator 10 is positioned within a hole 151 in the barrel 15, and at least one impedance matching layer 13 is positioned facing the focusing system 20.

[0100] The openings of the barrel 15 are preferably arranged parallel to each other. By arranging the piezoelectric actuators 10 parallel to each other, the elastic waves emitted from the piezoelectric actuators propagate in the same direction.

[0101] The opening is preferably arranged such that the piezoelectric actuators 10 are equally spaced from one another within the barrel 15.

[0102] The components of the piezoelectric actuator 10 are, for example, cylindrical, and the hole 151 in the barrel 15 is also cylindrical.

[0103] Preferably, the prestress bolts 16 are configured to hold and compress the piezoelectric actuator 10 within the opening 151 of the barrel 15. Such compression of the piezoelectric actuator advantageously maximizes the efficiency of converting electrical energy into elastic wave energy. Each prestress bolt 16 preferably abuts against an impedance mismatch layer 11.

[0104] The device 100 is equipped with a number of prestress bolts 16 corresponding to the number of piezoelectric actuators 10.

[0105] Preferably, the device 100 includes a member called a cover 17, which is fixed to the barrel 15. The cover 17 has a screw hole 171 into which a prestress bolt 16 is screwed.

[0106] The apparatus 100 preferably includes a control unit (not shown) for managing the elastic wave generator 10.

[0107] The apparatus 100, preferably a control unit, is configured to control the timing of elastic wave emission by a plurality of elastic wave generators 10.

[0108] In one embodiment (not shown), the management unit includes a power supply and a synchronization unit.

[0109] This power supply is configured to provide power to each elastic wave generator 10 in the form of a DC signal.

[0110] This synchronization unit is configured to drive the elastic wave generator 10 in a synchronous manner.

[0111] As a non-limiting example, if the elastic wave generator 10 is a piezoelectric actuator, the control unit includes a power supply configured to supply the required power to each piezoelectric actuator in the form of a DC signal, and a synchronization unit. The synchronization unit includes a primary clock that drives the piezoelectric actuators from a single time reference, a cascaded clock that controls the power circuits of each piezoelectric actuator with in-phase signals, and a power circuit consisting of a half-H bridge for charging and discharging the piezoelectric actuators.

[0112] As mentioned above, the device 100 also includes a focusing system 20.

[0113] This focusing system 20 is configured to receive elastic waves emitted by multiple elastic wave generators 10 and focus them into a focal region within the sample 50.

[0114] The "focal region" refers to a region of reduced size where all elastic waves converge.

[0115] The focal region is preferably smaller than sample 50.

[0116] Preferably, the sample is contained within a tubular container 70 with a diameter of 50 mm and a length of 50 mm. The sample completely fills the container.

[0117] The focal area is preferably smaller than 1 mm × 1 mm × 1 mm.

[0118] The dimensions of the focal region are determined by the frequency of the elastic wave, the propagation speed of the elastic wave within the sample 50, the diameter of the cross-section of the focusing system 20, and the focal length of the focusing system 20. Here, "cross-section" refers to a cross-section perpendicular to the axis of symmetry of the focusing system.

[0119] The focal region is generally approximated as an ellipsoid with a circular cross-section. The cross-section of the focal region refers to the cross-section perpendicular to the direction of propagation of elastic waves located on the axis of symmetry of the focusing system. This ellipsoid is defined by a major semi-axis and a minor semi-axis. The major semi-axis corresponds to half the length of the ellipsoid in the direction of propagation of elastic waves located on the axis of symmetry of the focusing system. The minor semi-axis corresponds to the radius of the largest cross-section.

[0120] Preferably, the focal region is an ellipsoid with a circular cross-section, with the major semi-axis in the range of 0.2 mm to 2 mm and the minor semi-axis in the range of 0.05 mm to 1 mm, and more preferably in the range of 0.07 mm to 0.75 mm. The upper limit is applied to powders with high elastic wave propagation velocities (e.g., diamond powder), and the lower limit is applied to powders with low elastic wave propagation velocities (e.g., graphite powder).

[0121] Preferably, the sample is initially positioned so that the focal region is located in the center of the sample. In other words, the ellipsoid is positioned so that its center coincides with the center of the sample.

[0122] The focal plane of a focal region is defined as the cross-section of the focal region that passes through the center of the ellipsoid. In other words, the largest cross-section of the ellipsoid is contained within the focal plane.

[0123] Therefore, the sample 50 is preferably initially positioned such that the focal plane of the focal region passes through the center of the sample.

[0124] The focusing system 20 defines a multiplication coefficient M. This multiplication coefficient M is defined as the ratio of the input cross-section (area) of the focusing system to the cross-section (area) of the focal region in the focal plane. The cross-section of the focal region in the focal plane is defined as the cross-section passing through the center of the ellipsoid.

[0125] The focusing system 20 is designed and dimensionally set to receive all elastic waves radiated by the elastic wave generator 10.

[0126] The focusing system 20 is configured to have a minimum focal length. Having a minimum focal length allows for the advantageous minimization of the volume in the focal region, and therefore the maximum elastic wave intensity achieved in the focal region. As a preferred example, regardless of the type of powder used, the focal length is approximately 100 mm for a focusing system 20 with a diameter of 15 cm. The focal length increases as the diameter of the focusing system 20 increases.

[0127] Advantageously, the focusing system 20 has a shape that matches the elastic wave velocity of the propagation medium 40 and its own elastic wave velocity.

[0128] In one embodiment of the focusing system 20, the focusing system is a focusing lens. This focusing lens is provided to face the elastic wave generator 10 and comprises a first surface 21 having a planar support surface for the elastic wave generator 10, and a second surface 22 provided to face the sample 50 and having a shape corresponding to the elastic wave velocity of the propagation medium 40 and the elastic wave velocity of the focusing lens itself.

[0129] In this example, the dimensions of the focal region, and therefore its volume, are determined by the frequency f of the elastic wave, the propagation speed of the elastic wave in the selected powder, the diameter of the focusing lens, and the focal length of the focusing lens.

[0130] As a non-limiting example, if the frequency of the elastic wave is 20 MHz, and the elastic wave propagates through sample 50 in graphite powder, and a focusing system with a diameter of 150 mm and a focal length of 100 mm is used, the focal region can be approximated as an ellipsoid with a circular cross-section, with a major axis of 0.5 mm and a minor axis of 0.18 mm.

[0131] As another non-limiting example, if the frequency of the elastic wave is 20 MHz, and the elastic wave propagates through diamond powder, and a focusing system with a diameter of 450 mm and a focal length of 300 mm is used, the focal region can be approximated as an ellipsoid with a circular cross-section, with a major semi-axis of 1.0 mm and a minor semi-axis of 0.35 mm.

[0132] In the example shown in Figure 1, the focusing system 20 is a plano-concave spherical lens. That is, the first surface 21 is flat, and the second surface 22 is concave.

[0133] The multiplication coefficient M for this plano-concave spherical lens is defined as the ratio of the cross-sectional area of ​​the first surface 21 to the cross-sectional area of ​​the focal region in the focal plane.

[0134] In one embodiment, the focusing system 20 is located and fixed inside the cylinder 19. The barrel 15 housing the elastic wave generator 10 is located at the first end 191 of the cylinder. The cover plate 18 is located at the second end 192 of the cylinder. A propagation medium 40 is interposed between the focusing system 20 and the cover 18.

[0135] In the non-limiting example shown in Figure 1, the cylinder 19 has a circular cross-section.

[0136] Preferably, the propagation medium 40 is selected so that the elastic waves emitted from the focusing system 20 propagate easily toward the sample 50. The propagation medium 40 is preferably a solid or liquid medium.

[0137] The propagation medium 40 is, for example, water or liquid gallium.

[0138] Preferably, the focusing system 20 is made of a material having a much higher elastic wave propagation velocity than the propagation medium 40, thereby minimizing the focal length of the focusing system and thus the dimensions of the focal region. The focusing system 20 is made of a material having an elastic wave impedance close to that of the propagation medium 40 in order to maximize the transmission of elastic waves from the focusing system 20 to the propagation medium 40.

[0139] In a preferred embodiment, the focusing system 20 is made of aluminum. The propagation speed of elastic waves in aluminum is approximately 6400 m / s, and the propagation speed of elastic waves in gallium is 2850 m / s. The elastic wave impedance of aluminum is approximately 17 M rail, and the elastic wave impedance of gallium is also approximately the same, so the transmission rate of elastic waves from the focusing system 20 to the propagation medium 40 is 100%.

[0140] The apparatus 100 also includes a heating device (not shown) for heating the sample 50. This heating device is configured to maintain a uniform heating temperature for the sample 50.

[0141] As is clear from this explanation, the heating device for sample 50 is an additional element within the apparatus 100, and is a separate and independent element from the multiple elastic wave generators.

[0142] In the first embodiment, the heating device enables heating by Joule heating. For example, the heating device comprises two electrical cables, each connected to a container 70 containing the sample 50. Preferably, the two electrical cables are spaced apart from each other. A high current of direct current or alternating current with a voltage of several volts flows through the container. The applied current is approximately several kiloamperes. As the current passes through the container, the sample 50 is heated.

[0143] Preferably, the container 70 is made of a conductive material such as graphite.

[0144] When using a graphite container, sample 50 can be heated up to a maximum of 3000°C.

[0145] In a second embodiment, the heating device is designed for induction heating. This heating device includes, for example, an induction coil wound around a container 70. The container is preferably tubular in shape. By supplying an alternating current to the induction coil, an induction current is generated within the container 70, thereby heating the container and the sample 50.

[0146] Preferably, the container 70 is made of a conductive material such as metal.

[0147] Depending on the type of metal used, the sample 50 can be heated to 1000°C to 1500°C.

[0148] For reference, diamond is stable at room temperature and pressure, but it reverts to graphite above 800°C in an oxygen atmosphere, and to graphite above 1700°C in an inert atmosphere or vacuum.

[0149] Preferably, if the sample 50 is diamond powder, the sample 50 is placed in an inert atmosphere or a vacuum atmosphere. More broadly, the entire apparatus 100 is placed in an inert atmosphere or a vacuum atmosphere.

[0150] For other ceramics, there are no particular restrictions on the atmosphere in which the sample is placed.

[0151] In a preferred embodiment (not shown), the apparatus 100 includes a moving member (not shown) for moving a focal region within the sample 50. Such a moving member advantageously enables the formation of a ceramic component by moving the focal region within the sample.

[0152] In one embodiment of the moving member, the moving member is configured to move the sample 50.

[0153] In another embodiment, the moving member is configured to move the focusing system 20.

[0154] In yet another embodiment, the moving member is configured to move the elastic wave generator 10.

[0155] In yet another embodiment, the moving member is configured to change the phase of the elastic wave generator 10.

[0156] The first method is described below.

[0157] The first method is based on the principle of high-pressure flash sintering. In other words, the first method involves heating ceramic powder to a predetermined temperature while applying sufficient pressure to locally compress the powder and cause sintering.

[0158] As is generally known, the higher the applied pressure, the lower the sintering temperature. For reference, sintering temperature refers to the minimum temperature required to sinter a powder under a given pressure.

[0159] As an example, Figure 5 shows seven curves indicating the minimum temperature required to sinter a powder for different pressure values ​​(in GPa). Each curve corresponds to a different type of ceramic powder. Figure 5 shows diamond powder, tungsten carbide powder, silicon nitride powder, fully stabilized zirconia powder, α-alumina powder, γ-alumina powder, and titanium oxide powder.

[0160] In the first method, the sample 50 is heated to a predetermined temperature.

[0161] The sample is heated to a predetermined minimum temperature. This minimum temperature is preferably higher than the sintering temperature of the selected ceramic powder. The sintering temperature is a function of the pressure applied to the focal region of the sample 50.

[0162] As an example, as shown in Figure 5, in the case of diamond powder, the sintering temperature is 1400°C when the applied pressure is 4 GPa, and 1300°C when the applied pressure is 5 GPa.

[0163] Heating is preferably performed by the heating device of apparatus 100.

[0164] In one embodiment, heating is performed by the Joule effect, which is achieved by passing an electric current through an electrical cable to the container 70.

[0165] In another embodiment, heating is performed by induction, which is achieved by generating an induced current in the container 70 via an induction coil.

[0166] When the sample 50 reaches a predetermined minimum temperature, the first method performs the step of generating and emitting multiple elastic waves.

[0167] As is clear from this explanation, the process of generating and emitting multiple elastic waves is performed after the heating process. The process of generating and emitting multiple elastic waves is performed only when the sample 50 has reached a predetermined minimum temperature.

[0168] Elastic waves are emitted simultaneously for a predetermined period. Preferably, they are emitted for the same period.

[0169] For example, each elastic wave is radiated over a period of approximately one hour.

[0170] Elastic waves are generated and emitted by elastic wave generators 10, which are preferably controlled by a control unit. The emission time of each elastic wave is controlled by the control unit. Each elastic wave generator 10 generates and emits elastic waves at a predetermined output. Preferably, the output generated by all elastic wave generators 10 is the same.

[0171] These elastic waves together produce an elastic wave intensity I at the input of the focusing system 20. e Generates.

[0172] For reference, the elastic wave intensity I generated at the input of the focusing system is... e This is determined by the ratio of the output injected into the focusing system 20 to the input cross-section of the focusing system 20. The output injected into the focusing system 20 is determined by multiplying the number of elastic wave generators 10 used by the output generated by one elastic wave generator 10 (assuming all elastic wave generators produce the same output).

[0173] The emitted elastic waves are then focused at a focal region located within the sample 50. The elastic waves are emitted in the direction of the focusing system 20, pass through the focusing system, and all converge toward the focal region within the sample 50.

[0174] In the focal region, the focused elastic wave has an elastic wave intensity I at the input of the focusing system. e It is easy to understand that this generates elastic wave intensity equivalent to the value obtained by multiplying by the focusing system's multiplication coefficient M. This multiplication coefficient M is the elastic wave intensity I induced by focusing. e This is the multiplication coefficient.

[0175] Elastic wave intensity is not uniform within the focal region.

[0176] More precisely, the spatial distribution of elastic wave intensity at the focal plane is not uniform, but is known to take the shape of an Airy spot. Therefore, within the focal plane, the elastic wave intensity forms a central (circular) spot and a series of concentric rings surrounding it. 85% of the elastic wave power is concentrated at the central spot. The remaining elastic wave power is distributed in the series of concentric rings, decreasing as you move outwards. The average elastic wave intensity within the central spot is 0.85 × M × I e The elastic wave intensity at 80% of the maximum value of the central spot is 2.9 × M × I. e The maximum elastic wave intensity within the central spot is 3.7 × M × I. e Therefore, the maximum elastic wave intensity within this central spot is localized. The spatial distribution of elastic wave intensity in a plane perpendicular to the focal plane is also not uniform. Elastic wave intensity gradually decreases as you move away from the focal plane.

[0177] In this invention, the focal region corresponds to the central spot within the focal plane. Therefore, the maximum elastic wave intensity within the focal region is greatest within the focal plane, and thus the maximum elastic wave intensity within the focal region is 3.7 × M × I e That is the case.

[0178] According to the present invention, the focused elastic wave is at least M×I in at least a portion of the focal region. e It generates elastic wave intensity equal to [a certain value].

[0179] According to the present invention, the elastic wave intensity generated in at least a portion of the focal region must be equal to or greater than the minimum elastic wave intensity sufficient to cause sintering of the ceramic powder in at least a portion of the focal region, in combination with the heating temperature applied to the ceramic powder sample 50.

[0180] As is well known to those skilled in the art, elastic wave pressure can be expressed as a function of elastic wave intensity. For certain materials under normal temperature and pressure conditions, each elastic wave intensity value gives a corresponding pressure value. These elastic wave intensity values ​​have been characterized in detail by the study of the so-called Hugoniot curves described in the "LASL Shock Hugoniot Data," published by the University of California Press in 1980.

[0181] Therefore, if the pressure as a function of elastic wave intensity and the minimum temperature required for sintering as a function of pressure for the same powder are known, it is possible to determine the minimum temperature required for sintering as a function of elastic wave intensity.

[0182] Figure 6 shows different elastic wave intensity values ​​(unit: W / m). 2 Four curves are shown that indicate the minimum temperature required to sinter the powders. Each curve corresponds to a different type of ceramic powder. In the non-limiting example shown in Figure 6, the powders shown are diamond powder, tungsten carbide powder, silicon nitride powder, and α-alumina powder.

[0183] Therefore, as shown in Figure 6, for the diamond powder sample 50 heated to a minimum temperature of 1375°C, 4.7 × 10 11 W / m 2 By applying the elastic wave intensity of , diamond powder can be sintered. In contrast, to sinter the same powder without pressure, temperatures exceeding 2000°C are required. Similarly, for a sample 50 of α-alumina powder heated to a minimum temperature of 840°C, 4.9 × 10⁻⁶ 10 W / m 2By applying elastic wave intensity, α-alumina powder can be sintered; however, to sinter the same powder without pressure, a temperature of 1100°C is required.

[0184] Depending on the type of ceramic powder used in the first method, a pair of values ​​(elastic wave intensity and heating temperature) to be applied can be associated, thereby advantageously sintering the powder in at least a portion of the focal region.

[0185] According to the first method of the present invention, 5 × 10 11 W / m 2 Starting from the elastic wave intensity and a minimum heating temperature of 1360°C, diamond can be obtained by sintering diamond powder.

[0186] According to the first method of the present invention, diamond can be obtained by sintering diamond powder under the following conditions. • Elastic wave intensity 1 × 10⁻⁶ 11 W / m 2 and a minimum heating temperature of 1700°C, • Elastic wave intensity 5 × 10⁻⁶ 13 W / m 2 And a minimum heating temperature of 1000°C.

[0187] Generally, diamonds can be obtained from diamond powder, and the elastic wave intensity is 1 × 10⁻⁶. 11 W / m 2 From 5x10 13 W / m 2 The temperature can vary, with the minimum heating temperature ranging from 1700°C to 1000°C.

[0188] To prevent the graphitization of diamond, the minimum heating temperature must not exceed 1700°C under an inert atmosphere or vacuum.

[0189] Furthermore, non-restrictive examples are explained below.

[0190] According to the first step of the present invention, oxide powder can be sintered under the following conditions to obtain an oxide. · Elastic wave intensity 5×10 8 W / m 2 and a minimum heating temperature of 1700 °C, · Elastic wave intensity 1×10 12 W / m 2 and a minimum heating temperature of 500 °C.

[0191] Generally, in order to sinter oxide powder to obtain an oxide, the elastic wave intensity can vary from 5×10 8 W / m 2 to 1×10 12 W / m 2 and the minimum heating temperature can vary from 1700 °C to 500 °C respectively.

[0192] Examples of the oxide include aluminum oxide (alumina), silicon oxide, titanium oxide, zinc oxide, zirconium oxide (zirconia), molybdenum oxide, or tungsten oxide.

[0193] According to the first method of the present invention, carbide powder can be sintered under the following conditions to obtain a carbide. · Elastic wave intensity 5×10 8 W / m 2 and a minimum heating temperature of 2200 °C, · Elastic wave intensity 5×10 12 W / m 2 and a minimum heating temperature of 1000 °C.

[0194] Generally, in order to sinter carbide powder to obtain a carbide, the elastic wave intensity can vary from 5×10 8 W / m 2 to 5×10 12 W / m 2 and the minimum heating temperature can vary from 2200 °C to 1000 °C respectively.

[0195] Examples of the carbide include boron carbide, silicon carbide, titanium carbide, zirconium carbide, molybdenum carbide, and tungsten carbide.

[0196] According to the first method of the present invention, nitrides, borides, or silicides can be obtained by sintering powders of nitrides, borides, or silicides respectively under the following conditions. · Elastic wave intensity 5×10 8 W / m 2 and minimum heating temperature 2000 °C, · Elastic wave intensity 5×10 12 W / m 2 and minimum heating temperature 700 °C.

[0197] Generally, in order to sinter powders of nitrides, borides or silicides to obtain the corresponding compounds, the elastic wave intensity can vary from 5×10 8 W / m 2 to 5×10 12 W / m 2 and the minimum heating temperature can vary from 2000 °C to 700 °C respectively.

[0198] These compounds include hexagonal or cubic boron nitride, aluminum nitride, silicon nitride, titanium nitride, zirconium nitride, molybdenum nitride, tungsten nitride, aluminum boride, titanium boride, zirconium boride, molybdenum silicide, etc.

Example

[0199] The apparatus 100 was reproduced on a small scale and simulations were carried out to determine the desired volume of the focal region.

[0200] In this simulation, the focusing system 20 is a plano-concave spherical lens. The plano-concave spherical lens has the following dimensions. That is, the diameter of the first surface 21 is 7.5 mm, the thickness at the center is 2 mm, and the radius of curvature of the second surface 22 is 4 mm. The plano-concave spherical lens is made of aluminum.

[0201] 190 piezoelectric actuators, each with a diameter of 0.5 mm, are evenly arranged opposite the first surface 21 of a plano-concave spherical lens. These 190 piezoelectric actuators are bonded to the first surface 21 of the plano-concave spherical lens. Each piezoelectric actuator emits elastic waves at a frequency of 20 MHz. Each piezoelectric actuator generates an output of 1 W.

[0202] The values ​​shown below correspond to the diamond powder sample. For comparison, the values ​​in parentheses correspond to the α-alumina powder sample.

[0203] The simulation results show that the volume of the focal region can be approximated as an ellipsoid with a circular cross-section, with a semi-major axis of 0.92 mm (0.87 mm) and a semi-minor axis of 0.33 mm (0.31 mm).

[0204] From this simulation, the magnification coefficient M of a plano-concave spherical lens can be determined. In this case, the magnification coefficient M is defined as the ratio of the incident cross-sectional area of ​​the plano-concave spherical lens to the cross-sectional area of ​​the focal region within the focal plane. Therefore, the magnification coefficient M is 1.3 × 10⁻⁶. 2 (1.4 × 10 2 )

[0205] It is known that increasing the dimensions of a plano-concave spherical lens does not affect the dimensions of the focal region, as long as the same angular aperture is maintained. The angular aperture is proportional to the ratio of the diameter of the first surface to the radius of curvature of the second surface of the plano-concave spherical lens.

[0206] Therefore, the dimensions of the focal region obtained in the simulation can be maintained by a plano-concave spherical lens with a first surface diameter of 450 mm (150 mm) and a second surface radius of curvature of 240 mm (80 mm). It is well known that the thickness of the lens does not affect the angular aperture. The thickness of the lens is set to 1 cm in order to maintain the strength of the lens while minimizing the propagation distance of elastic waves.

[0207] At these dimensions, the magnification coefficient M of the plano-concave spherical lens is 4.7 × 10⁻⁶. 5 (5.7 × 10 4 )

[0208] To cover the first surface of this plano-concave spherical lens, for example, 1600 (150) piezoelectric actuators with a diameter of 10 mm, or 10000 (940) piezoelectric actuators with a diameter of 4 mm, or 100 (10) piezoelectric actuators with a diameter of 40 mm can be used.

[0209] If 1600 (150) piezoelectric actuators with a diameter of 10 mm are used, and each piezoelectric actuator generates a 100 W elastic wave, then these elastic waves will total 1.0 × 10⁻⁶ at the lens input. 6 W / m 2 (8.5×10 5 W / m 2 ) Elastic wave intensity I e Generates.

[0210] Note that elastic wave intensity I e It should be noted that this corresponds to the ratio of the total output injected into the plano-concave spherical lens to the cross-sectional area of ​​the first surface of the plano-concave spherical lens. The output injected into the lens is equivalent to the product of the number of piezoelectric actuators used and the output generated by each piezoelectric actuator.

[0211] Furthermore, the elastic wave intensity at the same plano-concave spherical lens input section can also be obtained, for example, by using 10,000 (940) piezoelectric actuators with a diameter of 4 mm, each generating 15.90 W, or by using 100 (10) piezoelectric actuators with a diameter of 40 mm, each generating 1590 W.

[0212] In a configuration with 1600 (150) piezoelectric actuators, the average elastic wave intensity within the focal plane of the focal region is 4.0 × 10⁻¹⁰. 11 W / m 2 (0.85 × 4.7 × 10 5 ×1.0×10 6 W / m 2 (equivalent to) (4.1 × 10 10 W / m 2) and the maximum elastic wave intensity within the focal region is 1.7×10 12 W / m 2 (equivalent to 3.7×4.7×10 5 ×1.0×10 6 W / m 2 ; in the case of α-alumina, it is 1.8×10 11 W / m 2 ).

[0213] Therefore, at least a part of the focal region can obtain a minimum elastic wave intensity of 4.7×10 11 W / m 2 (equivalent to 1.6×10 6 ×1.0×10 6 W / m 2 ; 4.9×10 10 W / m 2 ).

[0214] In the part of the focal region where the elastic wave intensity reaches 4.7×10 11 W / m 2 (4.9×10 10 W / m 2 ), by heating the sample 50 to a minimum temperature of 1375 °C (840 °C), diamond powder (α-alumina powder) is densified by sintering.

[0215] According to the first method of the present invention, ceramic powder can be sintered within the focal region. Furthermore, according to this method, there is an advantage that the spatial position where the sintering conditions of this ceramic powder are satisfied can be precisely controlled.

[0216] In one aspect of the first method, while radiating elastic waves, the focal region is moved within the sample.

[0217] By moving the focal region within the sample, ceramic powder can be sintered in different regions of the sample, and finally a sintered ceramic part with a desired size and shape can be obtained.

[0218] As an example, to shift the focal region relative to the sample, the sample is moved by a moving member.

[0219] In other embodiments, the focusing system is moved by a moving member in order to move the focal region relative to the sample.

[0220] In further embodiments, the elastic wave generator is simultaneously moved by a moving member in order to move the focal region relative to the sample.

[0221] In yet another embodiment, the elastic wave generators are phase-shifted relative to each other to shift the focal region relative to the sample, thereby moving the focal region within the sample.

[0222] The second method is described below. The second method is configured to produce diamond from a sample containing graphite powder or amorphous carbon powder.

[0223] Amorphous carbon is sp 2 and sp 3 This refers to a mixture of atomic bonds, and a mixture that may contain concentrations of hydrogen atoms.

[0224] Advantageously, amorphous carbon that does not contain hydrogen atoms generally has sp(s) in the range of 40% to 90%. 3 It has a mixing ratio.

[0225] The second method is based on the principle of dynamic compression, which will be described later, in the first stage, and on the principle of high-pressure flash sintering in the subsequent second stage.

[0226] In the first stage, graphite powder is converted into diamond powder, and in the second stage, the diamond powder is densified by sintering to form diamond.

[0227] The second method yields high-density diamond with improved mechanical strength.

[0228] In the second method, the sample 50 is heated to a predetermined temperature.

[0229] The sample is heated to a predetermined minimum temperature. This minimum temperature is preferably higher than the sintering temperature of the diamond powder, and the sintering temperature is determined by the pressure applied to the sample 50.

[0230] In the case of diamond powder, the sintering temperature is 1400°C under a pressure of 5 GPa.

[0231] Heating is preferably performed by the heating device of apparatus 100.

[0232] In one embodiment, heating is performed by the Joule effect. That is, heating is performed by passing an electric current through an electrical cable to the container 70.

[0233] In other embodiments, heating is performed by induction. That is, heating is performed by generating an induced current in the container 70 via an induction coil.

[0234] In the second method, after the sample reaches a predetermined minimum temperature, multiple elastic waves are generated and emitted.

[0235] It is clear that the process of generating and emitting multiple elastic waves is performed after the heating process. The process of generating and emitting multiple elastic waves is initiated only when the sample 50 reaches a predetermined minimum temperature.

[0236] Elastic waves are emitted simultaneously for a predetermined period of time, preferably at the same time.

[0237] For example, each elastic wave is emitted for approximately one hour.

[0238] The elastic waves are preferably generated and emitted by an elastic wave generator 10 controlled by a control unit. The emission time of each elastic wave is controlled by the control unit. Each elastic wave generator 10 generates and emits elastic waves at a predetermined output. The outputs generated by the elastic wave generators 10 are preferably identical.

[0239] The elastic wave as a whole has an elastic wave intensity I at the input of the focusing system 20. e Generates.

[0240] Similar to the first step, the elastic wave intensity I generated at the input of the focusing system is determined by the ratio of the output injected into the focusing system 20 to the input cross-sectional area of ​​the focusing system 20. The output injected into the focusing system 20 is obtained by multiplying the number of elastic wave generators 10 used by the output generated by each elastic wave generator 10 (assuming that all elastic wave generators produce the same output).

[0241] The emitted elastic waves are focused to a focal region located within the sample 50. The elastic waves are emitted in the direction of the focusing system 20, pass through the focusing system, and all converge to the focal region within the sample 50.

[0242] Similar to the first method, in the focal region, the focused elastic wave is equal to the elastic wave intensity I at the input of the focusing system. e This generates an elastic wave intensity equivalent to multiplying by the focusing system's multiplication coefficient M. This multiplication coefficient M is the elastic wave intensity I generated by focusing. e This is the multiplication coefficient.

[0243] Similar to the first method, the elastic wave intensity in the focal region is not uniform. More specifically, the spatial distribution of elastic wave intensity at the focal plane is not uniform and is known to take the shape of an Airy spot. Therefore, within the focal plane, the elastic wave intensity forms a central (circular) spot and a series of concentric rings located around it. 85% of the elastic wave output is concentrated at the central spot. The remaining elastic wave output is distributed in the series of concentric rings, decreasing towards the outside. The average elastic wave intensity within the central spot is 0.85 × M × I e The elastic wave intensity at 80% of the maximum value of the central spot is 2.9 × M × I. e The maximum elastic wave intensity within the central spot is 3.7 × M × I. e Therefore, the maximum elastic wave intensity within this central spot is localized. The spatial distribution of elastic wave intensity in a plane perpendicular to the focal plane is also not uniform. Elastic wave intensity gradually decreases as you move away from the focal plane.

[0244] In this invention, the focal region corresponds to the central spot on the focal plane. Therefore, the maximum intensity within the focal region is greatest on the focal plane, and the maximum elastic wave intensity within the focal region is 3.7 × M × I e That is the case.

[0245] According to the present invention, in the case of graphite powder, the focused elastic wave has an elastic wave intensity of at least 1.0 × 10 in at least a portion of the focal region. 12 W / m 2 It must be generated in such a way that this intensity corresponds to the minimum elastic wave intensity sufficient to achieve the phase transition from graphite to diamond.

[0246] According to the present invention, sp 3 For amorphous carbon powder with a blending ratio of 40% to 90%, the focused elastic wave has an elastic wave intensity of at least 2.1 × 10⁻¹⁰ in at least a portion of the focal region. 12 W / m 2 It must be generated in such a way that this intensity corresponds to the minimum elastic wave intensity sufficient to achieve the phase transition from amorphous carbon to diamond.

[0247] More specifically, sp 3 In the case of amorphous carbon powder with a type admixture of 40%, the focused elastic wave has an elastic wave intensity of at least 1.4 × 10⁻¹⁰ in at least a portion of the focal region. 12 W / m 2 It must be produced in such a way that this intensity corresponds to the minimum elastic wave intensity sufficient to cause a phase change of the amorphous carbon into diamond. 3 In the case of amorphous carbon powder with a type blending ratio of 90%, the focused elastic wave has an elastic wave intensity of at least 2.1 × 10⁻¹⁰ in at least a portion of the focal region. 12 W / m 2 It must be produced in such a way that this intensity corresponds to the minimum elastic wave intensity sufficient to cause a phase change of the amorphous carbon into diamond.

[0248] The following descriptions and numerical values ​​in this specification are based on examples of graphite powder samples. To avoid duplication with descriptions relating to amorphous carbon powder samples, values ​​corresponding to amorphous carbon powder samples are shown in parentheses.

[0249] In at least a portion of the focal region, the elastic wave intensity is 1.0 × 10⁻⁶. 12 W / m 2 (sp 3 Depending on the mixing ratio, 1.4 × 10 12 W / m 2 ~2.1×10 12 W / m 2 To obtain the elastic wave intensity I, the elastic wave intensity I generated at the input of the focusing system is required. e Both the wave output and the magnification coefficient M of the focusing system can be adjusted. By adjusting several parameters within the device, namely the number of elastic wave generators, the output generated by these elastic wave generators, the incident cross-sectional area of ​​the focusing system, and the magnification coefficient M of the focusing system, it is possible to achieve a 1.0 × 10⁻¹⁶ beam in at least a portion of the focal region. 12 W / m 2 (sp 3 Depending on the mixing ratio, 1.4 × 10 12 W / m 2 ~2.1×10 12 W / m 2) can be achieved in elastic wave intensity.

[0250] As described above, the second method according to the present invention is based on the principle of dynamic compression for converting graphite (amorphous carbon) into diamond.

[0251] Those skilled in the art know that in order to transform graphite (amorphous carbon) into diamond by dynamic compression, the following two conditions must be met. • The diamond (amorphous carbon) is under sufficient pressure to be more stable than graphite (amorphous carbon). • To impart sufficient kinetic energy to the carbon atoms to break the metastability of graphite (amorphous carbon) due to the double bond between carbon atoms.

[0252] In other words, applying sufficient pressure to graphite (amorphous carbon) causes diamond to become a stable phase, and then imparting sufficient kinetic energy causes a phase change.

[0253] In conventional dynamic compression using shock waves, pressure and kinetic energy are supplied by the shock. In the case of shock waves, pressure and kinetic energy can be expressed as functions of shock intensity. In this case, the shock intensity must be sufficient to satisfy the following conditions. The pressure reached must exceed the minimum pressure sufficient for diamond (amorphous carbon) to be more stable than graphite (amorphous carbon), for example, at least 5 GPa (the stable pressure of diamond under static compression). • During the shock wave irradiation time, the kinetic energy of the carbon atoms must be sufficient to break the metastable nature of the graphite (the amorphous carbon).

[0254] For example, Erskine et al. have shown that dynamic compression using shock waves can convert graphite samples to diamond in several hundred nanoseconds at 6 GPa and complete in less than 10 nanoseconds at 20 GPa.

[0255] Similarly, in compression by elastic waves, pressure and kinetic energy can be expressed as functions of elastic wave intensity.

[0256] The elastic wave intensity must be sufficient to satisfy the following conditions: • The pressure reached exceeds the minimum pressure sufficient to make diamond more stable than graphite (amorphous carbon). The kinetic energy of the atoms is sufficient to break the metastable nature of the graphite (or amorphous carbon) during the period of elastic wave emission.

[0257] When a given material is initially in a normal temperature and pressure state, each elastic wave intensity value corresponds to a unique pair of pressure and kinetic energy. These elastic wave intensity values ​​are characterized in detail by the study of so-called Hugoniot curves, described in the "LASL Shock Hugoniot Data" published by the University of California Press in 1980.

[0258] The influence of kinetic energy on the conversion of graphite (amorphous carbon) to diamond can be modeled by the "kinetic" Arrhenius law, which is analogous to the influence of temperature. This model considers the role that kinetic energy plays in dynamic compression, rather than thermal energy in static compression, in enabling the transition of graphite (amorphous carbon) to diamond. For example, graphite (sp 3 The elastic wave intensity of amorphous carbon with a hybridization ratio of 40% to 90% is approximately 2 × 10⁻⁶. 13 W / m 2 (In the case of amorphous carbon powder, sp 3 When the mixing ratio is 40%, 2.7 × 10 13 W / m 2 , sp 3 When the mixing ratio is 90%, 4.0 × 10 13 W / m 2 Dynamic compression, which is ) at a pressure of 25 GPa (in the case of amorphous carbon powder, sp 3 With a 40% blend ratio, the concentration was 34 GPa, sp. 3At a 90% hybridization ratio, it induces kinetic energy of 49 GPa and 0.16 eV, which corresponds to the thermal kinetic energy induced at a temperature of approximately 1500°C.

[0259] Figure 7 shows a model curve illustrating the induced pressure with respect to elastic wave intensity, with graphite powder (solid line) and sp 3 Amorphous carbon powder with a 40% blending ratio (dashed line), and sp 3 The diagrams show the amorphous carbon powder with a 90% blending ratio (dotted line).

[0260] Figure 8 is a model curve showing kinetic energy as a function of elastic wave intensity, with graphite powder (solid line) and sp 3 Amorphous carbon powder with a 40% blending ratio (dashed line), and sp 3 The figures are shown for amorphous carbon powder with a 90% blending ratio (dotted line). When the elastic wave intensity is sufficient, the radiation time of the elastic wave intensity determines the phase change rate, i.e., the conversion rate of graphite (amorphous carbon) to diamond. In other words, for a given elastic wave intensity, the conversion rate of graphite (amorphous carbon) to diamond is a function of the radiation time of that elastic wave intensity. More specifically, the longer the radiation time of the elastic wave intensity, the higher the conversion rate of graphite (amorphous carbon) to diamond. Also, to obtain a given conversion rate, the higher the emitted elastic wave intensity, the shorter the required radiation time.

[0261] Based on the Arrhenius rule, the reaction rate k can be approximated by the following equation.

[0262]

number

[0263] Here, E a A is the activation energy in the conversion from graphite to diamond, i.e., the energy required for a carbon atom to break the metastable state of graphite, and A is a constant that is essentially dependent on the mechanism involved in the phase change (thermal diffusion, martensitic transformation, etc.).

[0264] E aAccording to the literature by Xie et al. (2017, Journal of the American Chemical Society, Vol. 139, No. 7, pp. 2545-2548), the value is approximately 0.2 eV. Furthermore, based on previous experimental results by Erskine et al., the constant A is approximately 2.3 × 10⁻⁶. 9 It is / s.

[0265] Therefore, graphite powder (sp 3 In dynamic compression of amorphous carbon powder with a blending ratio of 40% to 90%, the elastic wave intensity is approximately 1.1 × 10⁻⁶. 12 W / m 2 (In the case of amorphous carbon powder, sp 3 With a mixing ratio of 40%, 1.4 × 10 12 W / m 2 , sp 3 2.1 × 10 with a mixing ratio of 90% 12 W / m 2 When this is the case, the pressure is approximately 5 GPa (equivalent to the stable pressure of diamond) (in the case of amorphous carbon powder, sp 3 With a 40% blend ratio, the concentration was 6.5 GPa, sp. 3 With a hybridization ratio of 90%, the energy is 9.5 GPa, and the kinetic energy is approximately 0.012 eV (sp). 3 This value is the same for amorphous carbon with a hybridization ratio of 40% to 90%. This kinetic energy is approximately 4 × 10 / s (sp) with respect to the phase change rate k. 3 It is induced (equivalent values) with amorphous carbon with a hybridization ratio of 40% to 90%.

[0266] The phase change rate is expressed by the following formula.

[0267]

number

[0268] Here, t is time.

[0269] In other words, 95% conversion is achieved in 3 / k seconds, and 99% conversion is achieved in 5 / k seconds. Therefore, in the region under dynamic compression, it is possible to achieve 99% conversion in approximately 0.01 seconds (sp 3(The same value applies to amorphous carbon with a hybridization ratio of 40% to 90%).

[0270] For example, Figure 9 shows a graphite sample (solid line), sp 3 Amorphous carbon sample with a 40% hybridization ratio (dashed line), and sp 3 This graph shows the radiation time of elastic waves required to reproduce the conditions sufficient to achieve a 99% phase change to diamond in an amorphous carbon sample with a 40% hybridization ratio (dotted line), as a function of the intensity of those elastic waves.

[0271] As shown in Figure 9, in the case of graphite powder, the elastic wave intensity is approximately 1.4 × 10⁻⁶. 13 W / m 2 Therefore, when a pressure of 20 GPa (a pressure exceeding the minimum pressure necessary for diamond to become stable) can be reached, the kinetic energy imparted to the carbon atoms is sufficient to convert at least 99% of the graphite sample into diamond in about 10 ns. On the other hand, when the elastic wave intensity is approximately 1.6 × 10⁻⁶ 12 W / m 2 Therefore, when a pressure of 6 GPa (a pressure exceeding the minimum pressure sufficient for diamond to become stable) can be reached, the kinetic energy imparted to the carbon atoms is 0.017 eV, and at least 99% of the graphite sample is converted to diamond in about 1 ms. In contrast, the elastic wave intensity is 5 × 10⁻¹⁰ 11 W / m 2 If the pressure is less than 100, and assuming that the pressure remains within the diamond's stable region, the phase change will take more than 100 hours to occur.

[0272] Returning to the second method of the present invention, the focused elastic wave generates elastic wave pressure and kinetic energy in the focal region due to the elastic wave intensity as described above.

[0273] Graphite (sp 3 For amorphous carbon (with a hybridization ratio of 40% to 90%) to undergo a phase change into diamond in the focal region, the generated elastic wave intensity must be at least the minimum elastic wave intensity sufficient for the phase change, i.e., 1.0 × 10⁻¹⁶, in at least a portion of the focal region. 12 W / m 2(In the case of amorphous carbon powder, sp 3 With a mixing ratio of 40%, 1.4 × 10 12 W / m 2 , sp 3 2.1 × 10 with a mixing ratio of 90% 12 W / m 2 It must be equal to or greater than ).

[0274] As mentioned above, if the elastic wave intensity obtained in the focal region is sufficient to cause a phase change from graphite (amorphous carbon) to diamond, the emission time of that elastic wave intensity determines the rate of phase change from graphite (amorphous carbon) to diamond in the focal region. In other words, if a constant elastic wave intensity is obtained in the focal region, the conversion rate of graphite (amorphous carbon) to diamond within the focal region is a function of the elastic wave emission time. More specifically, when the elastic wave intensity is constant, the longer the elastic wave emission time, the higher the conversion rate of graphite (amorphous carbon) to diamond.

[0275] In the second step of this method, after the graphite (amorphous carbon) is converted into diamond powder or extremely low-density diamond, the conditions for sintering and increasing the density of the diamond are suitably met by combining pressure and the heating temperature of the sample 50.

[0276] The second method according to the present invention provides an elastic wave intensity of 1.0 × 10 12 W / m 2 (In the case of amorphous carbon powder, sp 3 With a mixing ratio of 40%, 1.4 × 10 12 W / m 2 , sp 3 2.1 × 10 with a mixing ratio of 90% 12 W / m 2 ) or higher, and the minimum heating temperature is 1300°C (in the case of amorphous carbon powder, sp 3 Mixing ratio 40%, 1250℃, sp 3 Under conditions of a 90% mixture ratio and 1100°C, graphite powder (sp 3 It makes it possible to obtain diamond from graphite (amorphous carbon with a hybridization ratio of 40% to 90%). 3Diamond can be obtained by converting amorphous carbon (with a composition ratio of 40% to 90%) into diamond, and then sintering it.

[0277] To prevent the graphitization of diamond, the heating temperature must not exceed 1700°C. Furthermore, this heating must be performed in an inert atmosphere or vacuum. [Examples]

[0278] The apparatus 100 was reproduced on a smaller scale, and simulations were performed to determine the desired volume of the focal region.

[0279] In this simulation, the focusing system 20 is a plano-concave spherical lens. The plano-concave spherical lens has the following dimensions: the diameter of the first surface 21 is 7.5 mm, the thickness of the central part is 2 mm, and the radius of curvature of the second surface 22 is 4 mm. The plano-concave spherical lens is made of aluminum.

[0280] 190 piezoelectric actuators, each with a diameter of 0.5 mm, are evenly arranged opposite the first surface 21 of a plano-concave spherical lens. These 190 piezoelectric actuators are bonded to the first surface 21 of the plano-concave spherical lens. Each piezoelectric actuator emits elastic waves at a frequency of 20 MHz. Each piezoelectric actuator generates an output of 1 W.

[0281] The following values ​​correspond to graphite powder samples. For comparison, the values ​​shown in parentheses are sp 3 This product is suitable for amorphous carbon powder samples with a blending ratio of 40% to 90%.

[0282] The results of this simulation show that the volume of the focal region can be considered as an ellipsoid with a circular cross-section, and its semi-major axis is 0.5 mm (sp 3 For amorphous carbon powder with a 40% blending ratio, the particle size is 0.66 mm, sp. 3 For amorphous carbon powder with a type admixture ratio of 90%, the diameter is 0.87 mm, and the minor radius is 0.18 mm (sp). 3 For amorphous carbon powder with a 40% blending ratio, the particle size is 0.24 mm, sp. 3For amorphous carbon powder with a mold composition ratio of 90%, the thickness is 0.32 mm.

[0283] From this simulation, the magnification coefficient M of a plano-concave spherical lens can be derived. In this case, the magnification coefficient M is defined as the ratio of the incident cross-sectional area of ​​the plano-concave spherical lens to the cross-sectional area of ​​the focal region at the focal plane. Therefore, the magnification coefficient M is 4.3 × 10⁻⁶. 2 (sp 3 For amorphous carbon powder with a 40% blending ratio, the result is 2.4 × 10 2 , sp 3 For amorphous carbon powder with a type admixture ratio of 90%, the ratio is 1.3 × 10⁻⁶. 2 )

[0284] It is known that increasing the dimensions of a plano-concave spherical lens does not affect the dimensions of the focal region, as long as the same angular aperture is maintained. The angular aperture is proportional to the ratio of the diameter of the first surface to the radius of curvature of the second surface of the plano-concave spherical lens.

[0285] Therefore, a plano-concave spherical lens with a first surface diameter of 450 mm and a second surface radius of curvature of 240 mm can maintain the dimensions of the focal region obtained in the simulation. It is known that the lens thickness does not affect the angular aperture. The lens thickness is set to 1 cm in order to maintain the strength of the lens while favorably minimizing the propagation distance of elastic waves.

[0286] At these dimensions, the magnification coefficient M of the plano-concave spherical lens is 1.6 × 10⁻⁶. 6 (sp 3 For amorphous carbon powder with a 40% blending ratio, the result is 8.9 × 10⁻⁶. 5 , sp 3 For amorphous carbon powder with a type admixture ratio of 90%, the result is 4.7 × 10⁻⁶. 5 )

[0287] To cover the first surface of this plano-concave spherical lens, for example, 1600 piezoelectric actuators with a diameter of 10 mm, or 10000 piezoelectric actuators with a diameter of 4 mm, or 100 piezoelectric actuators with a diameter of 40 mm can be used.

[0288] If we select an example using 1600 piezoelectric actuators with a diameter of 10 mm, where each actuator generates elastic waves with an output of 100 W (200 W each), these elastic waves will cause 1.0 × 10⁻¹⁶ vibrations at the lens input. 6 W / m 2 (2.0 × 10 6 W / m 2 ) Elastic wave intensity I e This is generated.

[0289] Note that elastic wave intensity I e This is defined as the ratio of the power input to the plano-concave spherical lens to the cross-sectional area of ​​the first surface of the plano-concave spherical lens. The power input to the lens is determined by the product of the number of piezoelectric actuators used and the output generated by each piezoelectric actuator.

[0290] The elastic wave intensity at the incident portion of the same plano-concave spherical lens can also be obtained using a configuration with 10,000 piezoelectric actuators with a diameter of 4 mm, each generating an output of 15.90 W, or a configuration with 100 piezoelectric actuators with a diameter of 40 mm, each generating an output of 1590 W.

[0291] In a configuration using 1600 piezoelectric actuators, the average elastic wave intensity within the focal region at the focal plane is 1.3 × 10⁻⁶. 12 W / m 2 (0.85 × 1.6 × 10 6 ×1.0×10 6 W / m 2 )(sp 3 For amorphous carbon powder with a type admixture ratio of 40%, the ratio is 1.5 × 10⁻⁶. 12 W / m 2 , sp 3 For amorphous carbon powder with a type admixture ratio of 90%, the ratio is 0.8 × 10⁻⁶. 12 W / m 2 ) and the maximum elastic wave intensity in the focal region is 5.4 × 10⁻¹⁰. 12 W / m 2 (3.7×1.6×10 6 ×1.0×10 6 W / m 2 )(each, sp3 For amorphous carbon powder with a 40% blending ratio, the result is 6.6 × 10⁻⁶. 12 W / m 2 , sp 3 For amorphous carbon powder with a type admixture ratio of 90%, the result is 3.6 × 10⁻⁶. 12 W / m 2 )

[0292] Therefore, in a part of the focal region, 10 12 W / m 2 (each, sp 3 For amorphous carbon powder with a 40% blending ratio, the ratio is 1.4 × 10⁻⁶. 12 W / m 2 , sp 3 For amorphous carbon powder with a type admixture ratio of 90%, the ratio is 2.1 × 10⁻⁶. 12 W / m 2 This allows for obtaining elastic wave intensity exceeding ) in graphite powder (each, sp 3 The strength is sufficient to produce diamond powder from amorphous carbon powder with a composition ratio of 40% to 90%.

[0293] Sample 50 was heated to 1300°C (each at sp 3 For amorphous carbon powder with a 40% blending ratio, 1250°C, sp 3 For amorphous carbon powder with a type admixture ratio of 90%, parallel heating is performed at the lowest temperature of 1100°C, and the elastic wave intensity in the focal region is 1.0 × 10⁻⁶. 12 W / m 2 (each, sp 3 For amorphous carbon powder with a 40% blending ratio, the ratio is 1.4 × 10⁻⁶. 12 W / m 2 , sp 3 For amorphous carbon powder with a type admixture ratio of 90%, the ratio is 2.1 × 10⁻⁶. 12 W / m 2 In the portion reaching ), the generated diamond powder is densely densified by sintering.

[0294] According to the second step of the present invention, it becomes advantageous to generate diamond nuclei in the focal region or to grow nuclei already present in the sample.

[0295] Furthermore, the second step allows for precise control of the spatial location where the conditions for diamond formation are met. According to the second step of the present invention, unlike shock wave technology, it is also possible to generate diamonds without destroying the sample.

[0296] According to the second step of the present invention, the emission time of elastic waves can also be controlled.

[0297] In a specific embodiment of the second step, the focal region is moved within the sample while the elastic wave is being emitted.

[0298] This particular embodiment of the second step is carried out when elastic waves are emitted for a longer duration than the radiation time required to convert a desired proportion of graphite (amorphous carbon) into diamond within the focal region.

[0299] By moving the focal region within the sample, a diamond nucleus can be grown to a desired size and shape. The direction of movement of the focal region within the sample is used to control the direction of diamond growth and obtain the desired shape.

[0300] The velocity of the focal region within a sample is favorably related to the elastic wave emission time required to convert a desired proportion of graphite (amorphous carbon) into diamond within that focal region. That is, the velocity of the focal region within a sample is a function of the elastic wave intensity within that focal region. This is because the elastic wave intensity determines the emission time required to convert a desired proportion of graphite (amorphous carbon) into diamond.

[0301] Preferably, the radiation time required to convert all or part of the graphite (amorphous carbon) into diamond is very short, generally less than one second, so the focal area can be continuously moved while adjusting the movement speed.

[0302] In one embodiment, the sample is moved by a moving member in order to move the focal region relative to the sample.

[0303] In other embodiments, the focusing system is moved by a moving member in order to move the focal region relative to the sample.

[0304] In further embodiments, the elastic wave generator is simultaneously moved by a moving member in order to move the focal region relative to the sample.

[0305] In yet another embodiment, the elastic wave generators are phase-shifted relative to each other to shift the focal region relative to the sample, thereby moving the focal region within the sample.

[0306] As is clear from the above description, the present invention achieves its intended purpose through its various features and advantages. In particular, the present invention provides two methods for producing diamonds without destroying a sample, and further has the advantage of allowing precise control over the direction of diamond growth.

Claims

1. A method for manufacturing ceramic parts from a sample of ceramic powder (50), The process involves heating the ceramic powder sample (50) to a predetermined minimum heating temperature using a heating device, Subsequently, a process is performed in which multiple elastic wave generators generate and radiate multiple elastic waves toward a focusing system (20), wherein each elastic wave generator is configured to radiate elastic waves with a frequency f in the range of 1 MHz to 100 MHz, and the elastic waves are generated at the input of the focusing system, with an elastic wave intensity of I ｅ A process characterized by generating, A step of focusing the elastic wave onto a focal region within the ceramic powder sample (50) using the focusing system (20), wherein the focusing system is characterized by defining a multiplication coefficient M. Includes, The focused elastic wave, in at least a portion of the focal region, is at least M × I ｅ A minimum elastic wave intensity is generated, and in combination with the application of the minimum heating temperature to the ceramic powder sample (50), the elastic wave intensity is sufficient to sinter the ceramic powder in the part of the focal region. A method characterized by the following features.

2. The minimum heating temperature of the ceramic powder sample (50) is higher than the sintering temperature of the ceramic powder. The method according to claim 1, characterized in that

3. The ceramic powder is selected from diamond powder, tungsten carbide powder, silicon nitride powder, fully stabilized zirconia powder, α-alumina powder, γ-alumina powder, and titanium oxide powder. The method according to claim 1 or 2, characterized in that

4. The emission of the elastic wave further includes the movement of the focal region within the sample (50), The method according to any one of claims 1 to 3, characterized in that

5. An apparatus (100) for carrying out the method described in any one of claims 1 to 4, A heating device for heating the sample (50), Multiple elastic wave generators (10) configured to generate elastic waves with a frequency f in the range of 1 MHz to 100 MHz, A focusing system (20) for focusing the elastic wave in the focal region within the sample (50), comprising a focusing system (20) that defines a multiplication coefficient M, Equipped with, The plurality of elastic wave generators (10) and the heating device for heating the sample (50) are separate elements within the apparatus (100). Apparatus (100) characterized by the following.

6. Each of the elastic wave generators (10) is a piezoelectric actuator. The apparatus (100) according to claim 5, characterized in that...

7. The device further comprises a member for moving the focal region within the sample (50). The apparatus (100) according to claim 5 or 6, characterized in that

8. The member for moving the focal region within the sample (50) is a member for moving the elastic wave focusing system, and / or a member for moving the sample, and / or a member for moving the elastic wave generator, and / or a member for changing the phase of the elastic wave generator. The apparatus (100) according to claim 7, characterized in that...

9. A method for producing a diamond from a sample (50) containing graphite powder, The process involves heating the graphite powder sample (50) to a predetermined minimum temperature using the heating device, Subsequently, a process is performed in which multiple elastic wave generators generate and radiate multiple elastic waves toward a focusing system (20), wherein each elastic wave generator is configured to radiate elastic waves with a frequency f in the range of 1 MHz to 100 MHz, and the elastic waves are generated at the input of the focusing system, with an elastic wave intensity of I ｅ A process characterized by generating, A step of focusing the elastic wave into a focal region within the graphite powder sample (50) using the focusing system (20), wherein the focusing system is characterized by defining a multiplication coefficient M. Includes, The focused elastic wave, in at least a portion of the focal region, at least M × I ｅ = 1.10 １２ W / m ２ It generates elastic wave intensity equal to, The elastic wave intensity is, In the first stage, a process is performed to achieve a phase change from the graphite powder to the diamond powder, Next, in the second stage, the obtained diamond powder is sintered in combination with the minimum heating temperature applied to the sample (50), Corresponding to the minimum elastic wave intensity sufficient to perform, A method characterized by the following features.

10. The minimum heating temperature of the sample (50) containing the graphite powder is higher than the sintering temperature of the graphite powder. The method according to claim 9, characterized in that

11. A method for producing diamond from a sample (50) containing amorphous carbon powder, The heating device is used to heat the amorphous carbon powder sample (50) to a predetermined minimum temperature, Subsequently, a process is performed in which multiple elastic wave generators generate and radiate multiple elastic waves toward a focusing system (20), wherein each elastic wave generator is configured to radiate elastic waves with a frequency f in the range of 1 MHz to 100 MHz, and the elastic waves are generated at the input of the focusing system, with an elastic wave intensity of I ｅ A process characterized by generating, A step of focusing the elastic wave onto a focal region within the amorphous carbon powder sample (50) using the focusing system (20), wherein the focusing system is characterized by defining a multiplication coefficient M. Includes, The focused elastic wave generates an elastic wave intensity equal to at least M×I ｅ = 2.1×10 １２ W / m ２ in at least a part of the focal region. The elastic wave intensity is, In the first stage, a process is performed to achieve a phase change from the amorphous carbon powder to diamond powder, Next, in the second stage, the obtained diamond powder is sintered in combination with the minimum heating temperature applied to the sample (50), Corresponding to the minimum elastic wave intensity sufficient to perform, A method characterized by the following features.

12. The minimum heating temperature of the sample (50) containing the amorphous carbon powder is higher than the sintering temperature of the amorphous carbon powder. The method according to claim 11, characterized in that

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