Discharge plasma sintering device and sintering method for producing large-size advanced ceramics

Abstract

The invention discloses a spark plasma sintering device for producing large-size advanced ceramics. The spark plasma sintering device comprises a vacuum cavity, a discharge assembly and a control assembly. The discharge assembly is formed by splicing a plurality of discharge modules, an insulating layer is arranged between the adjacent discharge modules, and the adjacent discharge modules are isolated through the insulating layer; according to the invention, an advanced ceramic sample to be sintered is effectively partitioned, and a control assembly controls a plurality of discharge modules to circularly discharge / cut off power repeatedly in an extremely short time according to a set sequence, so that the partitioned regions of a material are circularly conducted to release heat / cut off to stop heat release repeatedly in the extremely short time according to the sequence; plasma sintering of large-size advanced ceramics under the condition of current with conventional magnitude is realized. According to the sintering method disclosed by the invention, the treatment such as granulation on the advanced ceramic powder is not needed, the treatment procedures such as degumming with very long time consumption on the forming additive are also not needed, and the rapid production of the advanced ceramic can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of advanced ceramic production, and more specifically, to a spark plasma sintering device and a sintering method for producing large-size advanced ceramics. Background Art

[0002] Advanced ceramics have the advantages of high hardness, good wear resistance, and stable chemical properties, and are widely used in semiconductor, photovoltaic, medical and other industries. There are many sintering methods for advanced ceramics, including pressureless sintering, hot pressing sintering and other process methods. Generally, the specific sintering method is selected based on the material type, product shape, performance requirements, etc. of the product.

[0003] Spark Plasma Sintering (SPS) is a new ceramic sintering method. Different from traditional hot pressing sintering, SPS sintering equipment can release pulse current through electrodes to cause spark discharge between powder particles, thereby generating a large amount of plasma between powders. The plasma produces a large amount of heat in the mold and material, and finally completes the rapid sintering process. In the process of spark plasma sintering, a low voltage and high current parameter combination mode is usually adopted. The large amount of plasma excited by the SPS equipment can have a multifunctional effect on the material powder, release a large amount of heat while removing the inert substances on the surface of the powder, and promote the bonding between powders. At the same time, the induced magnetic field generated by the pulse current can cause the powder surface to deform to a certain extent, increase its surface area, and further increase the rate of particle bonding. Therefore, SPS spark plasma sintering has the characteristics of fast heating rate, short sintering time, energy saving and environmental protection, and the resulting sintered body has uniform grains, high density and good mechanical properties. At the same time, spark plasma sintering can produce a wide variety of materials and is widely used in the preparation of nanomaterials, gradient functional materials, metal materials, magnetic materials, composite materials, ceramics and other materials.

[0004] Since SPS plasma sintering requires the power generator of the device to generate low-voltage, high-current pulse current, the production process of SPS plasma sintering will be limited by the power of the power generator, which has certain limitations on the cross-sectional area of ​​sintered ceramic products. For large-sized ceramic products with large cross-sectional areas, in order to ensure the current density required for sintering, it is necessary to increase the power of the power generator accordingly and improve the specifications of the controllers, components, wires, etc. in the device. This will quickly increase the preparation cost of the equipment on the one hand, and also put forward very high requirements on the supporting power supply system on the other hand.

[0005] Therefore, how to effectively increase the size of sinterable products of spark plasma sintering equipment without significantly increasing the manufacturing cost of the equipment and the burden on the power supply system, and produce large-sized advanced ceramics in a more economical way, has become an important problem that technicians in this field need to solve. Summary of the invention

[0006] The present invention discloses a spark plasma sintering device for producing large-size advanced ceramics, comprising a vacuum chamber, a discharge component and a control component; the vacuum chamber comprises a left chamber and a right chamber, the left chamber and the right chamber are arranged opposite to each other, and the discharge component is installed between the left chamber and the right chamber; the discharge component is composed of a plurality of discharge modules, and an insulating layer is arranged between adjacent discharge modules and isolated by the insulating layer; the discharge module comprises an upper electrode, an upper pressure head, an upper mold, a lower mold, a lower pressure head and a lower electrode arranged in sequence from top to bottom; the bottom end of the upper electrode is conductively connected to the top end of the upper pressure head; the upper mold comprises an upper conductive part and an upper insulating part, and the bottom end of the upper pressure head is connected to the top end of the conductive part; the lower mold comprises a lower conductive part and a lower insulating part, and the upper insulating part is connected to the lower insulating part; a discharge cavity capable of accommodating materials is arranged between the upper mold and the lower mold; the bottom end of the lower conductive part is conductively connected to the top end of the lower pressure head; the bottom end of the lower pressure head is conductively connected to the top end of the lower electrode;

[0007] The control component includes a PLC control system, a current sensor, a temperature sensor, a pressure sensor and a pulse current generator; the current sensor is connected to the discharge module and is used to detect the working current of the discharge module; the temperature sensor is used to detect the temperature of the material; the pressure sensor is connected to the upper pressure head and the lower pressure head and is used to detect the pressure of the upper pressure head and the lower pressure head; the pulse current generator is connected to the upper electrode and the lower electrode and is used to emit a pulse current; the PLC control system is respectively connected to the current sensor, the temperature sensor, the pressure sensor and the pulse current generator, and the PLC control system is used to control the discharge sequence and parameters.

[0008] Preferably, it also includes a switch assembly connected to the PLC control system, the switch assembly includes a first single-pole double-throw switch, a second single-pole double-throw switch and a third single-pole double-throw switch; the first single-pole double-throw switch includes a fixed end A1, a fixed end A2 and a movable end A3, the second single-pole double-throw switch includes a fixed end B1, a fixed end B2 and a movable end B3, the third single-pole double-throw switch includes a fixed end C1, a fixed end C2 and a movable end C3; the discharge assembly is composed of four discharge modules, the four discharge modules are module A, module B, module C and module D; one end of the module A, one end of the module B, one end of the module C and one end of the module D are respectively connected in parallel to the pulse current generator; the other end of the module A is connected in series with the fixed end A1, the other end of the module B is connected in series with the fixed end A2, the other end of the module C is connected in series with the fixed end B1, the other end of the module D is connected in series with the fixed end B2, the moving end A3 is connected in series with the fixed end C1, the moving end B3 is connected in series with the fixed end C2, and the moving end C3 is connected to the pulse current generator.

[0009] Preferably, the upper electrode has the same structure as the lower electrode, and the upper electrode is made of copper or copper alloy material, and its electrical conductivity is 50-56.5MS / m, and its compressive strength is 200-300MPa; the upper pressure head has the same structure as the lower pressure head, and the upper pressure head is made of stainless steel or manganese alloy steel material, and its electrical conductivity is 1.25-1.43MS / m, and its compressive strength is 300-500MPa; the upper mold has the same structure as the lower mold, and the upper conductive part and the lower conductive part are both made of high-strength graphite material with a compressive strength of 100-150MPa, a resistivity of 7-8μΩ·m, and a melting point of 3850±50°C.

[0010] Preferably, the insulating layer is an insulating coating, which is respectively coated on the upper electrode, the upper pressure head, the upper mold, the lower mold, the lower pressure head and the lower electrode; the insulating coating is aluminum oxide or aluminum oxide or titanium oxide composite ceramic with a room temperature dielectric constant of 12, and the insulating strength of the insulating coating is 1069V / 0.1mm and the resistivity is 1014Ω·cm.

[0011] Preferably, the cross section of the discharge assembly is rectangular; the four upper electrodes form an electrode group A1 of a rectangular structure, and the adjacent upper electrodes are isolated by the insulating layer; the four lower electrodes form an electrode group B1 of a rectangular structure, and the adjacent lower electrodes are isolated by the insulating layer; the four upper pressure heads form a pressure head group A1 of a rectangular structure, and the adjacent upper pressure heads are isolated by the insulating layer; the four lower pressure heads form a pressure head group B1 of a rectangular structure, and the adjacent lower pressure heads are isolated by the insulating layer; the four upper molds form a top and bottom with grooves respectively. A rectangular mold A1, adjacent upper molds are isolated by the insulating layer; four lower molds form a rectangular mold B1 with grooves on the top and bottom respectively, and adjacent lower molds are isolated by the insulating layer; the electrode group A1 is docked with the pressure head group A1, the pressure head group A1 is inserted into the groove on the top of the rectangular mold A1, the groove at the bottom of the rectangular mold A1 is docked with the groove at the top of the rectangular mold B1, the groove at the bottom of the rectangular mold B1 is sleeved on the top of the pressure head group B1, and the pressure head group B1 is docked with the electrode group B1.

[0012] Preferably, the cross section of the discharge assembly is rhombus-shaped; the four upper electrodes form an electrode group A2 of a quadrangular prism structure, and the adjacent upper electrodes are isolated by the insulating layer; the four lower electrodes form an electrode group B2 of a quadrangular prism structure, and the adjacent lower electrodes are isolated by the insulating layer; the four upper pressure heads form a pressure head group A2 of a quadrangular prism structure, and the adjacent upper pressure heads are isolated by the insulating layer; the four lower pressure heads form a pressure head group B2 of a quadrangular prism structure, and the adjacent lower pressure heads are isolated by the insulating layer; the four upper molds form a quadrangular prism structure with grooves on the top and bottom, respectively. The body mold A2, adjacent upper molds are isolated by the insulating layer; four lower molds form a quadrangular prism mold B2 with grooves on the top and bottom respectively, and adjacent lower molds are isolated by the insulating layer; the electrode group A2 is docked with the pressure head group A2, the pressure head group A2 is inserted into the groove on the top of the quadrangular prism mold A2, the groove at the bottom of the quadrangular prism mold A2 is docked with the groove at the top of the quadrangular prism mold B2, the groove at the bottom of the quadrangular prism mold B2 is sleeved on the top of the pressure head group B2, and the pressure head group B2 is docked with the electrode group B2.

[0013] Preferably, the cross section of the discharge assembly is triangular; the four upper electrodes form an electrode group A3 of a triangular prism structure, and the adjacent upper electrodes are isolated by the insulating layer; the four lower electrodes form an electrode group B3 of a triangular prism structure, and the adjacent lower electrodes are isolated by the insulating layer; the four upper pressure heads form a pressure head group A3 of a triangular prism structure, and the adjacent upper pressure heads are isolated by the insulating layer; the four lower pressure heads form a pressure head group B3 of a triangular prism structure, and the adjacent lower pressure heads are isolated by the insulating layer; the four upper molds form a triangular prism structure with grooves on the top and bottom, respectively. The cylindrical mold A3, adjacent upper molds are isolated by the insulating layer; four lower molds form a triangular prism mold B3 with grooves on the top and bottom respectively, and adjacent lower molds are isolated by the insulating layer; the electrode group A3 is docked with the pressure head group A3, the pressure head group A3 is inserted into the groove on the top of the triangular prism mold A3, the groove at the bottom of the triangular prism mold A3 is docked with the groove at the top of the triangular prism mold B3, the groove at the bottom of the triangular prism mold B3 is sleeved on the top of the pressure head group B3, and the pressure head group B3 is docked with the electrode group B3.

[0014] A sintering method of a spark plasma sintering device for producing large-size advanced ceramics comprises the following steps:

[0015] Step S1: ball milling; placing alumina powder, alumina grinding balls toughened by zirconium oxide and ethanol into a polytetrafluoroethylene ball milling jar for wet ball milling;

[0016] Step S2: ultrasonic treatment; the fully ball-milled alumina slurry is ultrasonically treated for 35 to 45 minutes, and stirring is maintained during the ultrasonic treatment to remove agglomerates in the powder;

[0017] Step S3: sieving; placing the alumina slurry in a drying oven, keeping it at 100° C. for 12 hours for drying, and then sieving it with a 200-mesh sieve to obtain alumina powder of target fineness;

[0018] Step S4: setting up a spark plasma sintering device, placing the treated alumina powder into a graphite mold, and then placing the graphite mold into a spark plasma sintering furnace, evacuating to 4-6 Pa, and applying a pressure of 25 MPa for pre-pressing in an argon atmosphere;

[0019] Step S5: heating to the sintering temperature; passing a pulse current to raise the pressure to 40 MPa, and the control device controls the four discharge modules to perform multiple cycles of discharge / power-off in the order of discharge module A, discharge module B, discharge module C, and discharge module D. Under the action of the pulse current, discharge is generated between the particles of the aluminum oxide powder, plasma is excited, and the temperature of the aluminum oxide powder is quickly raised to the sintering temperature;

[0020] Step S6: constant temperature sintering; the PLC control system controls the pulse current to decrease to 750-850A and keeps the temperature for 5 minutes;

[0021] Step S7: After sintering is completed, the PLC control system controls the upper electrode and the lower electrode to stop discharging, allowing the material to cool naturally; after the temperature inside the furnace body drops to room temperature, the applied pressure is gradually reduced; after the pressure drops to 0, the material is taken out of the graphite mold to obtain a sintered product.

[0022] Preferably, in step S5, the current of the DC pulse output by the pulse current generator is 3650-3750A, the pulse frequency is 40Hz, and the single discharge time is 0.25-0.75s.

[0023] Preferably, in step S1, the rotation speed of the ball mill is 185-200 r / min, the forward and reverse switching frequency is 10 min / time, the ball milling time is 10-13 h, and the ball-to-material ratio is 3-5:1.

[0024] The spark plasma sintering device for producing large-sized advanced ceramics provided by the present invention is to put the alumina powder after ball milling, supercharging and sieving into the discharge assembly, utilize the splicing structure of the discharge module and isolate it through the insulating layer to realize the effective partitioning of the material to be sintered, and the control assembly controls several discharge modules to cycle the discharge / power-off process in a very short time in a set order for many times, so that the areas into which the material is divided cycle the process of conducting heat release / power-off to stop heat release in a very short time in sequence for many times, so that the temperature difference of each part of the material at the same time is small, and the purpose of plasma sintering large-sized products under the condition of passing a conventional current is achieved. The sintering method adopted by the present invention does not need to granulate the powder of advanced ceramics, nor does it need to carry out very time-consuming degumming and other processing procedures for molding additives, so that rapid production can be realized, and the industry pain point problem of long production cycle of large-sized ceramic products by traditional methods can be eliminated. In addition, the production process is carried out under the control of the PLC control system, and only the furnace needs to be switched on and off once to produce a large-sized product, and the operation process is simple, which can effectively reduce the manufacturing cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0026] Figure 1 It is a schematic structural diagram of a spark plasma sintering device for producing large-size advanced ceramics according to the present invention;

[0027] Figure 2 A partial exploded view of a vacuum chamber and a discharge assembly of a spark plasma sintering device for producing large-size advanced ceramics according to the present invention;

[0028] Figure 3 It is a schematic diagram of the splicing effect of the discharge modules of the spark plasma sintering device for producing large-size advanced ceramics of the present invention;

[0029] Figure 4 A schematic diagram of electric field lines generated by a discharge module of a spark plasma sintering device for producing large-size advanced ceramics according to the present invention;

[0030] Figure 5 The structure diagram of the electrode group A1 of the spark plasma sintering device for producing large-size advanced ceramics of the present invention;

[0031] Figure 6 A top view of an electrode group A1 of a spark plasma sintering device for producing large-size advanced ceramics according to the present invention;

[0032] Figure 7 The structure diagram of the head group A1 of the spark plasma sintering device for producing large-size advanced ceramics of the present invention;

[0033] Figure 8 A top view of a press head assembly A1 of a spark plasma sintering device for producing large-size advanced ceramics according to the present invention;

[0034] Fig. 9 It is a structural diagram of a rectangular parallelepiped mold A1 of a spark plasma sintering device for producing large-size advanced ceramics of the present invention;

[0035] Fig.10 A top view of a rectangular parallelepiped mold A1 of a spark plasma sintering device for producing large-size advanced ceramics according to the present invention;

[0036] Fig.11 It is a schematic diagram of the structure of the opening group of the spark plasma sintering device for producing large-size advanced ceramics of the present invention;

[0037] Fig.12 It is a schematic structural diagram of an electrode group A2 of another embodiment of a spark plasma sintering device for producing large-size advanced ceramics of the present invention;

[0038] Fig.13 It is a schematic structural diagram of a press head group B2 of another embodiment of the spark plasma sintering device for producing large-size advanced ceramics of the present invention;

[0039] Fig.14A schematic structural diagram of a quadrangular prism mold A2 of another embodiment of a spark plasma sintering device for producing large-size advanced ceramics according to the present invention;

[0040] Fig.15 It is a schematic structural diagram of an electrode group A3 of another embodiment of a spark plasma sintering device for producing large-size advanced ceramics of the present invention;

[0041] Fig.16 It is a schematic structural diagram of a press head group B3 of another embodiment of the spark plasma sintering device for producing large-size advanced ceramics of the present invention;

[0042] Fig.17 A schematic structural diagram of a triangular prism mold A3 of another embodiment of a spark plasma sintering device for producing large-size advanced ceramics according to the present invention;

[0043] The marks in the drawings are as follows:

[0044] 1--Vacuum chamber, 11--Left chamber, 12--Right chamber, 2--Discharge assembly, 21--Discharge module, 211--Upper electrode, 212--Upper pressure head, 213--Upper mold, 2131--Upper conductive part, 2132--Upper insulating part, 214--Lower mold, 2141--Lower conductive part, 2142--Lower insulating part, 215--Lower pressure head, 216--Lower electrode, 22--Insulating layer, 23--Module A, 24--Module B, 25--Module C, 26--Module D, 3--Control Components, 31--PLC control system, 32--current sensor, 33--temperature sensor, 34--pressure sensor, 35--pulse current generator, 36--switch component, 361--first single-pole double-throw switch, 3611--fixed end A1, 3612--fixed end A2, 3613--moving end A3, 362--second single-pole double-throw switch, 3621--fixed end B1, 3622--fixed end B2, 3623--moving end B3, 363--third single-pole double-throw switch, 4--materials. DETAILED DESCRIPTION

[0045] The present invention discloses a spark plasma sintering device and a sintering method for producing large-sized advanced ceramics. The advanced ceramic samples to be sintered are effectively divided into zones, and a control component controls a plurality of discharge modules to cycle the discharge / power-off process in a set sequence for multiple times in a very short time, so that the zones into which the material is divided cycle the process of conducting and releasing heat / powering off and stopping heat release in sequence for multiple times in a very short time, so that the temperature difference of each part of the material is small at the same time, thereby achieving the purpose of plasma sintering large-sized products under the condition of passing a conventional current.

[0046] The following is a clear and detailed description of the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] See also Figures 1 to 17 The present invention provides a spark plasma sintering device for producing large-size advanced ceramics, comprising a vacuum chamber 1, a discharge component 2 and a control component 3; the vacuum chamber 1 comprises a left chamber 11 and a right chamber 12, the left chamber 11 and the right chamber 12 are arranged opposite to each other, and the discharge component 2 is installed between the left chamber 11 and the right chamber 12; the discharge component 2 is composed of a plurality of discharge modules 21, and an insulating layer 22 is provided between adjacent discharge modules 21 and isolated by the insulating layer 22; the discharge module 21 comprises an upper electrode 211, an upper pressure head 212, an upper mold 213, a lower mold 214, a lower pressure head 215 and a lower electrode 211 arranged in sequence from top to bottom 216; the bottom end of the upper electrode 211 is conductively connected to the top end of the upper pressure head 212; the upper mold 213 includes an upper conductive part 2131 and an upper insulating part 2132, and the bottom end of the upper pressure head 212 is connected to the top end of the conductive part; the lower mold 214 includes a lower conductive part 2141 and a lower insulating part 2142, and the upper insulating part 2132 is connected to the lower insulating part 2142; a discharge cavity for accommodating the material 4 is provided between the upper mold 213 and the lower mold 214; the bottom end of the lower conductive part 2141 is conductively connected to the top end of the lower pressure head 215; the bottom end of the lower pressure head 215 is conductively connected to the top end of the lower electrode 216;

[0048] The control component 3 includes a PLC control system 31, a current sensor 32, a temperature sensor 33, a pressure sensor 34 and a pulse current generator 35; the current sensor 32 is connected to the discharge module 21, and is used to detect the working current of the discharge module 21; the temperature sensor 33 is used to detect the temperature of the material 4; the pressure sensor 34 is connected to the upper pressure head 212 and the lower pressure head 215, and is used to detect the pressure of the upper pressure head 212 and the lower pressure head 215; the pulse current generator 35 is connected to the upper electrode 211 and the lower electrode 216, and is used to emit a pulse current; the PLC control system 31 is respectively connected to the current sensor 32, the temperature sensor 33, the pressure sensor 34 and the pulse current generator 35, and the PLC control system 31 is used to control the discharge sequence and parameters.

[0049] In the embodiment of the present invention, the function of the vacuum cavity 1 is to wrap the discharge component 2 so that it is in a vacuum environment for discharge operation, which is conducive to eliminating the obstruction of gas molecules to electrons, so as to improve the performance and stability of electronic devices. The vacuum cavity 1 is composed of a left cavity 11 and a right cavity 12. The left and right cavities can be spliced ​​with each other. When opened, the discharge component 2 can be easily taken out and the material 4 can be taken and placed. When closed, the discharge operation area of ​​the discharge component 2 can be wrapped. In addition, an observation window is also provided on the right cavity 12, through which the discharge component 2 operating inside can be intuitively seen.

[0050] The discharge assembly 2 in this embodiment adopts a block structure design, the purpose of which is to divide the material 4 into multiple areas to achieve fine operation. Specifically, the discharge assembly 2 is composed of multiple discharge modules 21 with the same structure, and the discharge modules 21 are isolated by an insulating layer 22, that is, adjacent discharge modules 21 are not conductive to each other.

[0051] The discharge module 21 includes an upper electrode 211, an upper pressure head 212, an upper mold 213, a lower mold 214, a lower pressure head 215 and a lower electrode 216, which are arranged in sequence from top to bottom. The shapes of the upper electrode 211 and the lower electrode 216 are determined according to the shape of the material 4 to be produced. The upper and lower electrodes in relative positions are called electrode pairs. The upper electrode 211 and the lower electrode 216 are respectively connected to the control component 3. The control component 3 controls the electrode pair to realize the discharge operation, and an electric field can be generated in the powder material 4 during the discharge process. The upper pressure head 212 and the lower pressure head 215 have the same function, which are used to extrude the upper mold 213 and the lower mold 214 respectively, and also play the role of current conduction; the upper pressure head 212 and the lower pressure head 215 are respectively provided with a conductive area and an insulating area, and the conductive area has the characteristics of being able to conduct electricity, high compressive strength and economical cost. The insulating area is covered by the insulating layer 22, so that the conductive area and the insulating area are separated, the conductive area of ​​the upper press head 212 corresponds to the adjacent upper electrode 211, and the conductive area of ​​the lower press head 215 corresponds to the adjacent lower electrode 216. The upper mold 213 and the lower mold 214 are also designed in pairs, the upper conductive part 2131 of the upper mold 213 is connected to the conductive area of ​​the upper press head 212, and the lower conductive part 2141 of the lower mold 214 is connected to the conductive area of ​​the lower press head 215. Through the above-mentioned structural setting, after the material 4 is placed in the discharge cavity between the upper mold 213 and the lower mold 214, the current can flow between the upper electrode 211, the upper press head 212, the upper mold 213, the material 4, the lower mold 214, the lower press head 215 and the lower electrode 216. Since each discharge module 21 is insulated, when one of the discharge modules 21 is energized, the remaining discharge modules 21 are non-conductive, thereby realizing the partitioning operation of the material 4. It should be noted that the thickness of the insulating layer 22 can be made very thin, and during the plasma sintering process of a certain block of material 4, a portion of the plasma will escape to a small area outside the edge so that these areas are also plasma sintered at the same time, so that the produced material 4 is uniform and dense. In the specific discharge operation process, the current sensor 32 is connected to the electrode pair and the PLC control system 31 to detect the working current of the electrode. The temperature sensor 33 is connected to the inner wall of the mold and the PLC control system 31 to detect the temperature of the material 4. The pressure sensor 34 is respectively connected to the upper pressure head 212, the lower pressure head 215 and the PLC control system 31 to detect the pressure of the pressure head. The PLC control system 31 is connected to each sensor, the pulse current generator 35, the upper electrode 211 and the lower electrode 216 to control the order of discharge and the size of each parameter.

[0052] Furthermore, the pulse current generator 35 is used to emit pulse current, the voltage emitted is 0-10V, the current is 0-30kA, the current frequency is 0-5000Hz, and the maximum power is 300KW. These parameters can be adjusted by the PLC control system 31. The time for a single discharge of the electrode pair is selected to be 0.25-0.75s. Under the current of conventional size, the material 4 is heated by about 0.2°C each time the electrode discharges, and the pulse current passes through a certain area at a heating rate of about 400°C / min without interruption. In order to make the temperature difference of each area of ​​the material not exceed 10°C, the number of times the electrode discharges in a certain area in each cycle cannot exceed 50 times. Since the frequency of the current used is 40-45Hz, 0.25-0.75s can meet this condition.

[0053] The working process of this embodiment is as follows: the material 4 is placed in the discharge component 2, and then the vacuum chamber 1 is closed. The control component 3 applies a pulse current to one of the discharge modules 21 through the pulse current generator 35. The current only passes between the upper electrode 211, the upper pressure head 212, the upper mold 213, the material 4, the lower mold 214, the lower pressure head 215 and the lower electrode 216 in the discharge module 21. When the discharge starts, charge accumulation is formed on the inner surface of the upper and lower molds 214, and a uniform local electric field with the same cross-sectional area as the block is generated in the corresponding area of ​​the powder material 4, as shown in the attached figure. Figure 4 . This electric field can induce the powder particles on the upper and lower sides of the gap to produce positive and negative electrodes respectively, and with the application of pulse current, the powder particles in the gap will be broken down by the pulse electric field generated by the accumulation of positive and negative charges to produce electric spark discharge, and a large amount of plasma will be continuously generated. Under the action of the electric field, the plasma forms a channel in the gap between the powder particles and forms a loop in the powder material 4. Since it can move in the gaps between the powder particles, the current carrying efficiency of the charged particles in the plasma is much greater than the original carriers of the material. Therefore, the plasma generated in the local columnar electric field greatly improves the conductivity of part of the powder in the electric field, and most of the current in the loop will pass through this part, and the current density passing through can meet the needs of plasma sintering. Most of the charged particles in the plasma generated by the material 4 in this area move in the direction of the electric field lines perpendicular to the cross section, and almost do not escape into the material 4 in other areas, and interact with the surface of the powder particles in the working area of ​​the material 4, generating a large amount of heat and rapidly increasing the temperature in the area. Under the dual effects of the electric heat of the mold and the self-heating of the material 4, rapid plasma sintering of the target part of the material 4 is achieved. At the same time, the plasma is no longer generated after the power is turned off, and the conductivity of the power-off area returns to the original level. When the discharge group in other areas discharges, almost no current passes. Through the regional division of the discharge device combination, the material 4 is separated into a separate part for plasma sintering, so that the pulse current is maintained within the acceptable range of the device while ensuring the current density of the sintered part.

[0054] In addition to controlling the size of each parameter through the control device, the present invention can also control the multiple discharge modules 21 through the control component 3 to cycle the discharge / power-off process in a set order for multiple times within a time of 0.25 to 0.75 seconds, so that the areas into which the material 4 is divided can cycle the process of conducting heat release / power-off to stop heat release in a very short time in sequence for multiple times. In one cycle, the material 4 is sintered in different areas, but because the time of one cycle is very short, the temperature of the material 4 as a whole remains the same at the same time. Therefore, the present invention can complete the plasma sintering of large-sized materials 4 under conventional current through the linkage use of the discharge component 2 and the control device, and can avoid the hidden dangers of uneven local heating.

[0055] In actual production, the appropriate combination of discharge components 2 can be flexibly selected according to the shape and size of the material 4. Generally, the principle of equal division of regions is adopted for comprehensive design according to the actual conditions such as the power of the equipment and the cross-sectional area required by the material to be sintered, the sintering temperature, etc. Therefore, products of different shapes and sizes can be produced by this plasma sintering device.

[0056] In addition, the present invention is not limited by the cross-sectional area of ​​the product to be sintered, and large-sized products can be sintered at one time without destructive splitting and assembly of the product itself. There is almost no difference between the various parts of the plasma sintering, and because the insulating layer 22 of the upper pressure head 212, the lower pressure head 215, the upper mold 213 and the lower mold 214 is very thin, during the plasma sintering of a certain block of material 4, part of the plasma will escape to a small area outside the edge, so that these areas are also plasma sintered at the same time. These make the material 4 produced using the method of the present invention uniform and dense.

[0057] Preferably, it also includes a switch assembly 36 connected to the PLC control system 31, the switch assembly 36 includes a first single-pole double-throw switch 361, a second single-pole double-throw switch 362 and a third single-pole double-throw switch 363; the first single-pole double-throw switch 361 includes a fixed end A13611, a fixed end A23612 and a movable end A33613, the second single-pole double-throw switch 362 includes a fixed end B13621, a fixed end B23622 and a movable end B33623, the third single-pole double-throw switch 363 includes a fixed end C1, a fixed end C2 and a movable end C3; the discharge assembly 2 is composed of four discharge modules 21, and the four discharge modules 21 are module A23, module B2 4. Module C25 and module D26; one end of the module A23, one end of the module B24, one end of the module C25 and one end of the module D26 are respectively connected in parallel to the pulse current generator 35; the other end of the module A23 is connected in series with the fixed end A13611, the other end of the module B24 is connected in series with the fixed end A23612, the other end of the module C25 is connected in series with the fixed end B13621, the other end of the module D26 is connected in series with the fixed end B23622, the moving end A33613 is connected in series with the fixed end C1, the moving end B33623 is connected in series with the fixed end C2, and the moving end C3 is connected to the pulse current generator 35.

[0058] In order to better associate the discharge module 21 and the PLC control system 31, the present embodiment adopts the method of connecting the discharge module 21 in parallel with another identical unit and in series with a single-pole double-throw switch, and then in parallel with another identical unit and in series with another single-pole double-throw switch, and so on. Each switch is connected to the PLC control system 31. When a certain partition needs to pass current during the sintering process, the PLC control system 31 will control each switch to the appropriate position to achieve the target discharge module 21 while the other discharge modules 21 are powered off. The PLC control system 31 controls the changes in the positions of each switch to rotate the current of each partition, thereby achieving the purpose of rotating the heating / stopping the heating of each partition in a cycle. For example, as shown in the attached figure Fig.11As shown, in one cycle, module A23, module B24, module C25 and module D26 need to be discharged separately one after another, and the PLC control system 31 controls the first single-pole double-throw switch 361 to the 1-1 position, the second single-pole double-throw switch 362 to be disconnected, and the third single-pole double-throw switch 363 to the 3-1 position to discharge module A23; then the first single-pole double-throw switch 361 is turned to the 1-2 position to discharge module B24; then the PLC control system 31 controls the first single-pole double-throw switch 361 to be disconnected, the second single-pole double-throw switch 362 to be turned to the 2-1 position, and the third single-pole double-throw switch 363 to be turned to the 3-2 position to discharge module C25; finally, the second single-pole double-throw switch 362 is turned to the 2-2 position to discharge module D26. The PLC control system 31 installs the above logic and method to achieve the purpose of rotating the current of each partition in one cycle.

[0059] Preferably, the upper electrode 211 has the same structure as the lower electrode 216, and the upper electrode 211 is made of copper or copper alloy material, and its electrical conductivity is 50-56.5MS / m, and its compressive strength is 200-300MPa; the upper pressure head 212 has the same structure as the lower pressure head 215, and the upper pressure head 212 is made of stainless steel or manganese alloy steel material, and its electrical conductivity is 1.25-1.43MS / m, and its compressive strength is 300-500MPa; the upper mold 213 has the same structure as the lower mold 214, and the upper conductive part 2131 and the lower conductive part 2141 are both made of high-strength graphite material with a compressive strength of 100-150MPa, a resistivity of 7-8μΩ·m, and a melting point of 3850±50℃. In this embodiment, the upper electrode 211 and the lower electrode 216 are made of copper or copper alloy material, with an electrical conductivity of 50 to 56.5 MS / m and a compressive strength of 200 to 300 MPa, and have the advantages of high electrical conductivity, high compressive strength, and economical cost. The shape of the electrode is determined according to the shape of the material 4 to be produced. The insulating layer 22 between the electrodes is used to insulate and fix the electrodes to form an electrode group. The upper pressure head 212 and the lower pressure head 215 are used to transmit the pressure applied to the material 4 and conduct current. They are made of conductive materials such as stainless steel, manganese alloy steel, etc., with an electrical conductivity of 1.25 to 1.43 MS / m and a compressive strength of 300 to 500 MPa, and have the advantages of being able to conduct electricity, high compressive strength, and economical cost. The upper conductive part 2131 of the upper mold 213 and the lower conductive part 2141 of the lower mold 214 are respectively made of conductive materials such as high-strength graphite, etc., and the high-strength graphite material with a compressive strength of 100-150 MPa, a resistivity of 7-8 μΩ·m, and a melting point of 3850±50°C is adopted; the upper insulating part 2132 and the lower insulating part 2142 can be made of insulating materials such as ceramic materials, the upper conductive part 2131 is separated by the upper insulating part 2132, and the lower conductive part 2141 is separated by the lower insulating part 2142, and each part corresponds to each other.

[0060] Preferably, the insulating layer 22 is an insulating coating, which is coated on the upper electrode 211, the upper pressure head 212, the upper mold 213, the lower mold 214, the lower pressure head 215 and the lower electrode 216 respectively; the insulating coating is aluminum oxide or aluminum oxide or titanium oxide composite ceramic with a room temperature dielectric constant of 12, and the insulating strength of the insulating coating is 1069V / 0.1mm, and the resistivity is 1014Ω·cm. In this embodiment, all insulating coatings are made of aluminum oxide or aluminum oxide / titanium oxide composite ceramics with a room temperature dielectric constant of 12, with a maximum insulation strength of 1069V / 0.1mm and a resistivity of 1014Ω·cm. Furthermore, each component of the present invention is dip-coated with a precursor glaze slurry and then heated to 1200-1300°C and cured for 0.5-1h to obtain an insulating coating with a thickness of 0.2-0.3mm.

[0061] Preferably, the cross section of the discharge assembly 2 is rectangular; the four upper electrodes 211 form an electrode group A1 of a rectangular structure, and the adjacent upper electrodes 211 are isolated by the insulating layer 22; the four lower electrodes 216 form an electrode group B1 of a rectangular structure, and the adjacent lower electrodes 216 are isolated by the insulating layer 22; the four upper pressing heads 212 form a pressing head group A1 of a rectangular structure, and the adjacent upper pressing heads 212 are isolated by the insulating layer 22; the four lower pressing heads 215 form a pressing head group B1 of a rectangular structure, and the adjacent lower pressing heads 215 are isolated by the insulating layer 22; the four upper molds 213 form a A rectangular mold A1 is provided with grooves on the top and bottom, and adjacent upper molds 213 are isolated by the insulating layer 22; four lower molds 214 form a rectangular mold B1 with grooves on the top and bottom, and adjacent lower molds 214 are isolated by the insulating layer 22; the electrode group A1 is connected with the pressure head group A1, the pressure head group A1 is inserted into the groove on the top of the rectangular mold A1, the groove at the bottom of the rectangular mold A1 is connected with the groove at the top of the rectangular mold B1, the groove at the bottom of the rectangular mold B1 is sleeved on the top of the pressure head group B1, and the pressure head group B1 is connected with the electrode group B1.

[0062] Please refer to Figures 5 to 10As shown in the figure, the discharge assembly 2 of the present invention adopts the method of electrode grouping, pressure head partitioning, and mold partitioning to achieve the purpose of product partition block sintering; specifically, the number of discharge modules 21 is four, that is, the number of upper electrodes 211, lower electrodes 216, upper pressure heads 212, lower pressure heads 215, upper molds 213 and lower molds 214 are four respectively. In the horizontal direction, the four upper electrodes 211 form an electrode group A1 with a rectangular structure, and similarly, the four lower electrodes 216 form an electrode group B1. In contrast, the four upper pressure heads 212 form a pressure head group A1 with a rectangular structure, the four lower pressure heads 215 form a pressure head group B1, the four upper molds 213 form a rectangular mold A1, and the four lower molds 214 form a rectangular mold B1. Then the electrode group A1, the pressure head group A1, the rectangular parallelepiped mold A1, the rectangular parallelepiped mold B1, the pressure head group B1 and the electrode group B1 are arranged in order from top to bottom, and then the material 4 is loaded between the rectangular parallelepiped mold A1 and the rectangular parallelepiped mold B1. The discharge assembly 2 of this embodiment adopts a structure similar to a rectangular parallelepiped, which is convenient for processing advanced ceramics with a rectangular parallelepiped structure.

[0063] Preferably, the cross section of the discharge assembly 2 is a rhombus; the four upper electrodes 211 form an electrode group A2 of a quadrangular prism structure, and the adjacent upper electrodes 211 are isolated by the insulating layer 22; the four lower electrodes 216 form an electrode group B2 of a quadrangular prism structure, and the adjacent lower electrodes 216 are isolated by the insulating layer 22; the four upper pressing heads 212 form a pressing head group A2 of a quadrangular prism structure, and the adjacent upper pressing heads 212 are isolated by the insulating layer 22; the four lower pressing heads 215 form a pressing head group B2 of a quadrangular prism structure, and the adjacent lower pressing heads 215 are isolated by the insulating layer 22; the four upper molds 213 form a top and A quadrangular prism mold A2 with grooves at the bottom, and adjacent upper molds 213 are isolated by the insulating layer 22; four lower molds 214 form a quadrangular prism mold B2 with grooves at the top and bottom, and adjacent lower molds 214 are isolated by the insulating layer 22; the electrode group A2 is docked with the pressure head group A2, the pressure head group A2 is inserted into the groove at the top of the quadrangular prism mold A2, the groove at the bottom of the quadrangular prism mold A2 is docked with the groove at the top of the quadrangular prism mold B2, the groove at the bottom of the quadrangular prism mold B2 is sleeved on the top of the pressure head group B2, and the pressure head group B2 is docked with the electrode group B2. Please refer to Figure 12 to Figure 14 Through the above-mentioned structural setting, a quadrangular prism space is formed between the rectangular parallelepiped mold A2 and the rectangular parallelepiped mold B2, which can process advanced ceramics with a quadrangular prism structure.

[0064] Preferably, the cross section of the discharge assembly 2 is triangular; the four upper electrodes 211 form an electrode group A3 of a triangular prism structure, and the adjacent upper electrodes 211 are isolated by the insulating layer 22; the four lower electrodes 216 form an electrode group B3 of a triangular prism structure, and the adjacent lower electrodes 216 are isolated by the insulating layer 22; the four upper pressing heads 212 form a pressing head group A3 of a triangular prism structure, and the adjacent upper pressing heads 212 are isolated by the insulating layer 22; the four lower pressing heads 215 form a pressing head group B3 of a triangular prism structure, and the adjacent lower pressing heads 215 are isolated by the insulating layer 22; the four upper molds 213 form a top and The triangular prism mold A3 is provided with grooves at the bottom, and the adjacent upper molds 213 are isolated by the insulating layer 22; the four lower molds 214 form a triangular prism mold B3 with grooves at the top and bottom, and the adjacent lower molds 214 are isolated by the insulating layer 22; the electrode group A3 is connected with the pressure head group A3, the pressure head group A3 is inserted into the groove at the top of the triangular prism mold A3, the groove at the bottom of the triangular prism mold A3 is connected with the groove at the top of the triangular prism mold B3, the groove at the bottom of the triangular prism mold B3 is connected to the top of the pressure head group B3, and the pressure head group B3 is connected with the electrode group B3. Please refer to Figures 15 to 17 Through the above-mentioned structural setting, a triangular prism space is formed between the rectangular parallelepiped mold A3 and the rectangular parallelepiped mold B3, which can process advanced ceramics with a triangular prism structure.

[0065] The spark plasma sintering device of the present invention performs local focusing and discharge of pulse current on the to-be-sintered product in the designated partition by reasonably partitioning the material 4, and utilizes the PLC control system 31. After the designated discharge time is completed, the control circuit rotates the discharge area to the next designated partition, and the control component 3 controls the multiple discharge modules 21 to cycle the discharge / power-off process in a very short time in a set sequence for many times, so that the areas into which the material 4 is divided cycle the process of conducting heat release / power-off to stop heat release in a very short time in sequence for many times, so that the temperature of the material 4 as a whole remains consistent at the same time, and finally the whole piece of material 4 can be plasma sintered. Through the spark plasma sintering device of the present invention, the pulse current can be focused on the designated partition without increasing the power of the plasma SPS sintering equipment, so that the current density of the sintering part can be guaranteed, and it is ensured that the powder in the designated area can generate enough plasma, and the sintering effect in the area is guaranteed, and finally the purpose of plasma rapid sintering of large-sized products is achieved, and the cost of the equipment is effectively reduced.

[0066] A sintering method of a spark plasma sintering device for producing large-size advanced ceramics comprises the following steps:

[0067] Step S1: ball milling; placing alumina powder, alumina grinding balls toughened by zirconium oxide and ethanol into a polytetrafluoroethylene ball milling jar for wet ball milling;

[0068] Step S2: ultrasonic treatment; the fully ball-milled alumina slurry is ultrasonically treated for 35 to 45 minutes, and stirring is maintained during the ultrasonic treatment to remove agglomerates in the powder;

[0069] Step S3: sieving; placing the alumina slurry in a drying oven, keeping it at 100° C. for 12 hours for drying, and then sieving it with a 200-mesh sieve to obtain alumina powder of target fineness;

[0070] Step S4: setting up a spark plasma sintering device, placing the treated alumina powder into a graphite mold, and then placing the graphite mold into a spark plasma sintering furnace, evacuating to 4-6 Pa, and applying a pressure of 25 MPa for pre-pressing in an argon atmosphere;

[0071] Step S5: heating to the sintering temperature; passing a pulse current to raise the pressure to 40 MPa, and the control device controls the four discharge modules to perform multiple cycles of discharge / power-off in the order of discharge module A, discharge module B, discharge module C, and discharge module D. Under the action of the pulse current, discharge is generated between the particles of the aluminum oxide powder, plasma is excited, and the temperature of the aluminum oxide powder is quickly raised to the sintering temperature;

[0072] Step S6: constant temperature sintering; the PLC control system controls the pulse current to decrease to 750-850A and keeps the temperature for 5 minutes;

[0073] Step S7: After sintering is completed, the PLC control system controls the upper electrode and the lower electrode to stop discharging, allowing the material to cool naturally; after the temperature inside the furnace body drops to room temperature, the applied pressure is gradually reduced; after the pressure drops to 0, the material is taken out of the graphite mold to obtain a sintered product.

[0074] Preferably, in step S5, the current of the pulse current generator for DC pulse output is 3650-3750A, the pulse frequency is 40Hz, and the time of a single discharge is 0.25-0.75s. In this step, discharge is generated between particles under the action of the pulse current, plasma is excited, and the temperature of the powder material rises rapidly, and the temperature rises rapidly to 1500°C at a heating rate of 100°C / min. When a current of about 8000A continues to pass through a certain part, the heating rate of this part is about 1000°C / min. Since the present invention adopts four-electrode cyclic intermittent discharge, in order to make the heating rate of the material 100°C / min, the pulse current used should satisfy the heating rate of 400°C / min when continuously passing through a certain area. When the power supply voltage remains unchanged, the insulation power is 10% of the input power when the temperature rises at 1000℃ / min, then the insulation current is 10% of 8000A, that is, 800A. The current required for heating at 400℃ / min is 8000A minus 40% of the insulation current, that is, 2880A. Therefore, the required pulse current is the sum of the two, about 3700A.

[0075] Preferably, in step S1, the rotation speed of the ball mill is 185-200 r / min, the forward and reverse switching frequency is 10 min / time, the ball milling time is 10-13 h, and the ball-to-material ratio is 3-5:1.

[0076] By adopting this sintering method, the following advantages are achieved: there is no need to granulate the powder of advanced ceramics, nor is there a need to perform very time-consuming degumming and other processing steps for molding additives, which can achieve very fast production and get rid of the industry pain point of the long production cycle of large-size ceramic products by traditional methods. Moreover, the production process is carried out under the control of the control device, and the production of a large-size product only requires the furnace to be turned on and off once, which is a simple operation process and can effectively reduce manufacturing costs.

[0077] The following is described through three embodiments:

[0078] Embodiment 1:

[0079] Step S1: ball milling; alumina powder, alumina grinding balls toughened by zirconia and ethanol are placed in a polytetrafluoroethylene ball mill for wet ball milling; the speed of the ball mill is 200 r / min, the forward and reverse exchange frequency is 10 min / time, the ball milling time is 10 h, and the ball-to-material ratio is 3:1;

[0080] Step S2: ultrasonic treatment; the fully ball-milled alumina slurry is ultrasonically treated for 40 min, and stirring is maintained during the ultrasonic treatment to remove agglomerates in the powder;

[0081] Step S3: sieving; placing the alumina slurry in a drying oven, keeping it at 100° C. for 12 hours for drying, and then sieving it with a 200-mesh sieve to obtain alumina powder of target fineness;

[0082] Step S4: setting up a spark plasma sintering device, placing the treated alumina powder into a graphite mold, and then placing the graphite mold into a spark plasma sintering furnace, evacuating to 4-6 Pa, and applying a pressure of 25 MPa for pre-pressing in an argon atmosphere;

[0083] Step S5: heating to the sintering temperature; passing a pulse current to increase the pressure to 40MPa, the control device controls the four discharge modules, and the discharge module A, discharge module B, discharge module C, and discharge module D are repeatedly discharged / power-off in the order of multiple cycles. Under the action of the pulse current, discharge is generated between the particles of the aluminum oxide powder, plasma is excited, and the temperature of the aluminum oxide powder is quickly raised to the sintering temperature; the pulse current generator outputs a DC pulse current of 3700A, a pulse frequency of 40Hz, and a single discharge time of 0.25 to 0.75s;

[0084] Step S6: constant temperature sintering; the PLC control system controls the pulse current to be reduced to 800A and keeps the temperature for 5 minutes;

[0085] Step S7: After sintering is completed, the PLC control system controls the upper electrode and the lower electrode to stop discharging, allowing the material to cool naturally; after the temperature inside the furnace body drops to room temperature, the applied pressure is gradually reduced; after the pressure drops to 0, the material is taken out of the graphite mold to obtain a sintered product.

[0086] Embodiment 2:

[0087] Step S1: ball milling; alumina powder, alumina grinding balls toughened by zirconium oxide and ethanol are placed in a polytetrafluoroethylene ball mill for wet ball milling; the speed of the ball mill is 190 r / min, the forward and reverse exchange frequency is 10 min / time, the ball milling time is 11 h, and the ball-to-material ratio is 4:1;

[0088] Step S2: ultrasonic treatment; the fully ball-milled alumina slurry is ultrasonically treated for 35 min, and stirring is maintained during the ultrasonic treatment to remove agglomerates in the powder;

[0089] Step S3: sieving; placing the alumina slurry in a drying oven, keeping it at 100° C. for 12 hours for drying, and then sieving it with a 200-mesh sieve to obtain alumina powder of target fineness;

[0090] Step S4: setting up a spark plasma sintering device, placing the treated alumina powder into a graphite mold, and then placing the graphite mold into a spark plasma sintering furnace, evacuating to 4-6 Pa, and applying a pressure of 25 MPa for pre-pressing in an argon atmosphere;

[0091] Step S5: heating to the sintering temperature; passing a pulse current to increase the pressure to 40MPa, the control device controls the four discharge modules, and the discharge module A, discharge module B, discharge module C, and discharge module D are repeatedly discharged / power-off in the order of multiple cycles. Under the action of the pulse current, discharge is generated between the particles of the aluminum oxide powder, plasma is excited, and the temperature of the aluminum oxide powder is quickly raised to the sintering temperature; the pulse current generator outputs a DC pulse current of 3700A, a pulse frequency of 40Hz, and a single discharge time of 0.25 to 0.75s;

[0092] Step S6: constant temperature sintering; the PLC control system controls the pulse current to be reduced to 800A and keeps the temperature for 5 minutes;

[0093] Step S7: After sintering is completed, the PLC control system controls the upper electrode and the lower electrode to stop discharging, allowing the material to cool naturally; after the temperature inside the furnace body drops to room temperature, the applied pressure is gradually reduced; after the pressure drops to 0, the material is taken out of the graphite mold to obtain a sintered product.

[0094] Embodiment 3:

[0095] Step S1: ball milling; alumina powder, alumina grinding balls toughened by zirconium oxide and ethanol are placed in a polytetrafluoroethylene ball mill for wet ball milling; the speed of the ball mill is 185 r / min, the forward and reverse exchange frequency is 10 min / time, the ball milling time is 13 h, and the ball-to-material ratio is 5:1;

[0096] Step S2: ultrasonic treatment; the fully ball-milled alumina slurry is ultrasonically treated for 45 min, and stirring is maintained during the ultrasonic treatment to remove agglomerates in the powder;

[0097] Step S3: sieving; placing the alumina slurry in a drying oven, keeping it at 100° C. for 12 hours for drying, and then sieving it with a 200-mesh sieve to obtain alumina powder of target fineness;

[0098] Step S4: setting up a spark plasma sintering device, placing the treated alumina powder into a graphite mold, and then placing the graphite mold into a spark plasma sintering furnace, evacuating to 4-6 Pa, and applying a pressure of 25 MPa for pre-pressing in an argon atmosphere;

[0099] Step S5: heating to the sintering temperature; passing a pulse current to increase the pressure to 40MPa, the control device controls the four discharge modules, and the discharge module A, discharge module B, discharge module C, and discharge module D are repeatedly discharged / power-off in the order of multiple cycles. Under the action of the pulse current, discharge is generated between the particles of the aluminum oxide powder, plasma is excited, and the temperature of the aluminum oxide powder is quickly raised to the sintering temperature; the pulse current generator outputs a DC pulse current of 3700A, a pulse frequency of 40Hz, and a single discharge time of 0.25 to 0.75s;

[0100] Step S6: constant temperature sintering; the PLC control system controls the pulse current to be reduced to 800A and keeps the temperature for 5 minutes;

[0101] Step S7: After sintering is completed, the PLC control system controls the upper electrode and the lower electrode to stop discharging, allowing the material to cool naturally; after the temperature inside the furnace body drops to room temperature, the applied pressure is gradually reduced; after the pressure drops to 0, the material is taken out of the graphite mold to obtain a sintered product.

[0102] The spark plasma sintering device for producing large-sized advanced ceramics provided by the present invention is to put the alumina powder after ball milling, supercharging and sieving into the discharge assembly, utilize the splicing structure of the discharge module and isolate it through the insulating layer to realize the effective partitioning of the material to be sintered, and the control assembly controls several discharge modules to cycle the discharge / power-off process in a very short time in a set order for many times, so that the areas into which the material is divided cycle the process of conducting heat release / power-off to stop heat release in a very short time in sequence for many times, so that the temperature difference of each part of the material at the same time is small, and the purpose of plasma sintering large-sized products under the condition of passing a conventional current is achieved. The sintering method adopted by the present invention does not need to granulate the powder of advanced ceramics, nor does it need to carry out very time-consuming degumming and other processing procedures for molding additives, so that rapid production can be realized, and the industry pain point problem of long production cycle of large-sized ceramic products by traditional methods can be eliminated. In addition, the production process is carried out under the control of the PLC control system, and only the furnace needs to be switched on and off once to produce a large-sized product, and the operation process is simple, which can effectively reduce the manufacturing cost.

[0103] The above is a detailed introduction to the spark plasma sintering device for producing large-size advanced ceramics provided by the present invention. For those skilled in the art, according to the ideas of the embodiments of the present invention, there may be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A spark plasma sintering device for producing large-size advanced ceramics, characterized in that: The invention comprises a vacuum chamber (1), a discharge component (2) and a control component (3); the vacuum chamber comprises a left chamber (11) and a right chamber (12), the left chamber and the right chamber are arranged opposite to each other, and the discharge component is installed between the left chamber and the right chamber; the discharge component is composed of a plurality of discharge modules (21) spliced ​​together, and an insulating layer (22) is provided between adjacent discharge modules and isolated by the insulating layer; the discharge module comprises an upper electrode (211), an upper pressure head (212), an upper mold (213), a lower mold (214), and a lower pressure head (215) which are arranged in sequence from top to bottom. and a lower electrode (216); the bottom end of the upper electrode is conductively connected to the top end of the upper pressure head; the upper mold comprises an upper conductive portion (2131) and an upper insulating portion (2132), the bottom end of the upper pressure head is connected to the top end of the conductive portion; the lower mold comprises a lower conductive portion (2141) and a lower insulating portion (2142), the upper insulating portion is in contact with the lower insulating portion; a discharge cavity capable of accommodating a material (4) is provided between the upper mold and the lower mold; the bottom end of the lower conductive portion is conductively connected to the top end of the lower pressure head; the bottom end of the lower pressure head is conductively connected to the top end of the lower electrode; The control component comprises a PLC control system (31), a current sensor (32), a temperature sensor (33), a pressure sensor (34) and a pulse current generator (35); the current sensor is connected to the discharge module and is used to detect the working current of the discharge module; the temperature sensor is used to detect the temperature of the material; the pressure sensor is connected to the upper pressure head and the lower pressure head and is used to detect the pressure of the upper pressure head and the lower pressure head; the pulse current generator is connected to the upper electrode and the lower electrode and is used to emit a pulse current; the PLC control system is respectively connected to the current sensor, the temperature sensor, the pressure sensor and the pulse current generator, and the PLC control system is used to control the discharge sequence and parameters.

2. The spark plasma sintering device for producing large-size advanced ceramics according to claim 1, characterized in that: It also includes a switch assembly (36) connected to the PLC control system, the switch assembly includes a first single-pole double-throw switch (361), a second single-pole double-throw switch (362) and a third single-pole double-throw switch (363); the first single-pole double-throw switch includes a fixed end A1 (3611), a fixed end A2 (3612) and a movable end A3 (3613), the second single-pole double-throw switch includes a fixed end B1 (3621), a fixed end B2 (3622) and a movable end B3 (3623), and the third single-pole double-throw switch includes a fixed end C1, a fixed end C2 and a movable end C3; the discharge assembly is composed of four discharge modules spliced ​​together, the four The discharge modules are module A (23), module B (24), module C (25) and module D (26); one end of module A, one end of module B, one end of module C and one end of module D are respectively connected in parallel to the pulse current generator; the other end of module A is connected in series with the fixed end A1, the other end of module B is connected in series with the fixed end A2, the other end of module C is connected in series with the fixed end B1, the other end of module D is connected in series with the fixed end B2, the moving end A3 is connected in series with the fixed end C1, the moving end B3 is connected in series with the fixed end C2, and the moving end C3 is connected to the pulse current generator.

3. The spark plasma sintering device for producing large-size advanced ceramics according to claim 2, characterized in that: The upper electrode has the same structure as the lower electrode, and is made of copper or copper alloy material, with an electrical conductivity of 50 to 56.5 MS / m and a compressive strength of 200 to 300 MPa; the upper pressure head has the same structure as the lower pressure head, and is made of stainless steel or manganese alloy steel material, with an electrical conductivity of 1.25 to 1.43 MS / m and a compressive strength of 300 to 500 MPa; the upper mold has the same structure as the lower mold, and both the upper conductive part and the lower conductive part are made of high-strength graphite material with a compressive strength of 100 to 150 MPa, a resistivity of 7 to 8 μΩ·m, and a melting point of 3850±50°C.

4. The spark plasma sintering device for producing large-size advanced ceramics according to claim 3, characterized in that: The insulating layer is an insulating coating, which is respectively coated on the upper electrode, the upper pressure head, the upper mold, the lower mold, the lower pressure head and the lower electrode; the insulating coating is aluminum oxide or aluminum oxide or titanium oxide composite ceramic with a room temperature dielectric constant of 12, and the insulating strength of the insulating coating is 1069V / 0.1mm and the resistivity is 1014Ω·cm.

5. The spark plasma sintering device for producing large-size advanced ceramics according to claim 2, characterized in that: The cross section of the discharge assembly is rectangular; the four upper electrodes form an electrode group A1 of a rectangular structure, and the adjacent upper electrodes are isolated by the insulating layer; the four lower electrodes form an electrode group B1 of a rectangular structure, and the adjacent lower electrodes are isolated by the insulating layer; the four upper pressure heads form a pressure head group A1 of a rectangular structure, and the adjacent upper pressure heads are isolated by the insulating layer; the four lower pressure heads form a pressure head group B1 of a rectangular structure, and the adjacent lower pressure heads are isolated by the insulating layer; the four upper molds form a rectangular structure with grooves on the top and bottom respectively. The upper mold A1 is a rectangular mold, and the adjacent upper molds are isolated by the insulating layer; the four lower molds form a rectangular mold B1 with grooves on the top and bottom respectively, and the adjacent lower molds are isolated by the insulating layer; the electrode group A1 is docked with the pressure head group A1, the pressure head group A1 is inserted into the groove on the top of the rectangular mold A1, the groove at the bottom of the rectangular mold A1 is docked with the groove at the top of the rectangular mold B1, the groove at the bottom of the rectangular mold B1 is sleeved on the top of the pressure head group B1, and the pressure head group B1 is docked with the electrode group B1.

6. The spark plasma sintering device for producing large-size advanced ceramics according to claim 2, characterized in that: The cross section of the discharge assembly is a rhombus; the four upper electrodes form an electrode group A2 of a quadrangular prism structure, and the adjacent upper electrodes are isolated by the insulating layer; the four lower electrodes form an electrode group B2 of a quadrangular prism structure, and the adjacent lower electrodes are isolated by the insulating layer; the four upper pressure heads form a pressure head group A2 of a quadrangular prism structure, and the adjacent upper pressure heads are isolated by the insulating layer; the four lower pressure heads form a pressure head group B2 of a quadrangular prism structure, and the adjacent lower pressure heads are isolated by the insulating layer; the four upper molds form a quadrangular prism body mold with grooves on the top and bottom respectively. Tool A2, adjacent upper molds are isolated by the insulating layer; four lower molds form a quadrangular prism mold B2 with grooves on the top and bottom respectively, and adjacent lower molds are isolated by the insulating layer; the electrode group A2 is docked with the pressure head group A2, the pressure head group A2 is inserted into the groove on the top of the quadrangular prism mold A2, the groove at the bottom of the quadrangular prism mold A2 is docked with the groove at the top of the quadrangular prism mold B2, the groove at the bottom of the quadrangular prism mold B2 is sleeved on the top of the pressure head group B2, and the pressure head group B2 is docked with the electrode group B2.

7. The spark plasma sintering device for producing large-size advanced ceramics according to claim 2, characterized in that: The cross section of the discharge assembly is triangular; four upper electrodes form an electrode group A3 of a triangular prism structure, and adjacent upper electrodes are isolated by the insulating layer; four lower electrodes form an electrode group B3 of a triangular prism structure, and adjacent lower electrodes are isolated by the insulating layer; The four upper pressing heads form a pressing head group A3 of a triangular prism structure, and the adjacent upper pressing heads are isolated by the insulating layer; the four lower pressing heads form a pressing head group B3 of a triangular prism structure, and the adjacent lower pressing heads are isolated by the insulating layer; The four upper molds form a triangular prism mold A3 with grooves on the top and bottom, respectively, and the adjacent upper molds are isolated by the insulating layer; the four lower molds form a triangular prism mold B3 with grooves on the top and bottom, respectively, and the adjacent lower molds are isolated by the insulating layer; the electrode group A3 is connected with the pressure head group A3, the pressure head group A3 is inserted into the groove on the top of the triangular prism mold A3, the groove at the bottom of the triangular prism mold A3 is connected with the groove on the top of the triangular prism mold B3, the groove at the bottom of the triangular prism mold B3 is connected to the top of the pressure head group B3, and the pressure head group B3 is connected with the electrode group B3.

8. A sintering method for a spark plasma sintering device for producing large-size advanced ceramics according to any one of claims 1 to 7, characterized in that: The following steps are included: Step S1: ball milling; placing alumina powder, alumina grinding balls toughened by zirconium oxide and ethanol into a polytetrafluoroethylene ball milling jar for wet ball milling; Step S2: ultrasonic treatment; the fully ball-milled alumina slurry is ultrasonically treated for 35 to 45 minutes, and stirring is maintained during the ultrasonic treatment to remove agglomerates in the powder; Step S3: sieving; placing the alumina slurry in a drying oven, keeping it at 100° C. for 12 hours for drying, and then sieving it with a 200-mesh sieve to obtain alumina powder of target fineness; Step S4: setting up a spark plasma sintering device, placing the treated alumina powder into a graphite mold, and then placing the graphite mold into a spark plasma sintering furnace, evacuating to 4-6 Pa, and applying a pressure of 25 MPa for pre-pressing in an argon atmosphere; Step S5: heating to sintering temperature; A pulse current is introduced to increase the pressure to 40 MPa. The control device controls the four discharge modules to perform multiple cycles of discharge / power-off in the order of discharge module A, discharge module B, discharge module C, and discharge module D. Under the action of the pulse current, discharge is generated between the particles of the alumina powder, plasma is excited, and the temperature of the alumina powder is quickly raised to the sintering temperature. Step S6: constant temperature sintering; The PLC control system reduces the pulse current to 750-850A and keeps the temperature for 5 minutes. Step S7: After sintering is completed, the PLC control system controls the upper electrode and the lower electrode to stop discharging, allowing the material to cool naturally; after the temperature inside the furnace body drops to room temperature, the applied pressure is gradually reduced; after the pressure drops to 0, the material is taken out of the graphite mold to obtain a sintered product.

9. The sintering method of the spark plasma sintering device for producing large-size advanced ceramics according to claim 8, characterized in that: In step S5, the pulse current generator outputs a DC pulse with a current of 3650-3750A, a pulse frequency of 40Hz, and a single discharge time of 0.25-0.75s.

10. The sintering method of the spark plasma sintering device for producing large-size advanced ceramics according to claim 8, characterized in that: In step S1, the rotation speed of the ball mill is 185-200 r / min, the forward and reverse switching frequency is 10 min / time, the ball milling time is 10-13 h, and the ball-to-material ratio is 3-5:1.

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