A carbon composite ceramic linear resistor and its preparation method

Abstract

The present invention discloses a carbon composite ceramic linear resistor and a preparation method thereof, belonging to the technical field of power electronic components. The present invention provides a preparation method of a carbon composite ceramic linear resistor, which comprises the following steps: uniformly mixing bentonite, silicon carbide and nano carbon black to obtain a powder material, uniformly mixing the powder material and ethanol, drying, adding a binder solution, and performing green body forming to obtain a green body after forming; under the atmosphere of a nitrogen element-containing gas, keeping the green body at 1150 °C to 1300 °C to obtain a specimen; after polishing the specimen, spraying aluminum to obtain a carbon composite ceramic linear resistor. The method for preparing the carbon composite ceramic linear resistor of the present invention can reduce the resistivity of the material and improve the thermal shock resistance of the ceramic resistor.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic components, and more particularly to a carbon composite ceramic linear resistor and a preparation method thereof. Background Art

[0002] Traditional carbon composite alumina ceramic linear resistors are formed by mixing alumina as the aggregate, clay as the sintering aid, and adding conductive carbon materials for molding and sintering. With the development of ultra-high voltage, ceramic linear resistors are required to withstand more energy, which causes the resistance material to bear a huge temperature difference in a short time. The poor thermal shock resistance of traditional ceramic linear resistors makes them unable to withstand the thermal stress caused by the huge temperature difference and break. As the application range of carbon ceramic resistors becomes wider and wider, the demand for low resistivity gradually becomes prominent. Usually, the resistivity of the material is reduced by increasing the carbon content. However, too high a carbon content makes it difficult to sinter the ceramic and the resistivity is difficult to decrease. For example, in the Chinese invention patent with the application number CN202210706840.4 and the invention name of a carbon ceramic closing resistor and its preparation process, the resistance value is reduced by improving the dispersion of highly conductive carbon black through modification and using isostatic pressing molding. However, when the carbon black content is further increased, the resistance value of the material hardly changes. In the article "Preparation and Properties of Graphite / Ceramic Composite Conductive Materials" published by Zheng Xin et al. in the 4th volume of the 26th issue of Acta Materiae Compositae Sinica in 2009, when the content of flake graphite is increased to more than 15wt.%, a ceramic resistor with a resistivity of 1Ω·cm to 3Ω·cm can be prepared. However, too high a graphite content will cause a sharp decline in the mechanical properties of the material and cannot meet the high-voltage service environment. At present, in addition to adjusting the carbon source to control the resistivity in ceramic linear resistor technology, the sintering performance is also improved by adjusting the clay. For example, in the Chinese invention patent with the application number CN202110120534.8 and the invention name of a low-temperature sintering carbon composite ceramic linear resistor and its preparation method, for improving the thermal shock resistance of ceramic linear resistors. Improving the thermal conductivity can improve the thermal shock resistance of the material, but the traditional alumina aggregate has a low thermal conductivity, and the demand for porosity in linear resistors also limits the improvement of the thermal conductivity. According to the results of literature research, at present, silicon carbide-based multiphase ceramic materials have both high thermal conductivity and certain electrical conductivity.

[0003] For example, in the Chinese invention patent with the application number CN201610410680.3 and the invention name of a silicon carbide-based multiphase ceramic material and its preparation method, a silicon carbide / zirconium diboride dense ceramic is prepared by a pressureless sintering process. By adding zirconium diboride as the second phase to silicon carbide and sintering in an atmospheric pressure Ar atmosphere at a sintering temperature of 2100°C, the resistivity is adjusted by controlling the content of the zirconium diboride second phase. However, its non-linear coefficient reaches 1.66 and it cannot be used as a linear resistor.

[0004] In the Chinese invention patent with the application number CN201610367998.8 and the invention title of "A silicon carbide / graphite composite material with low resistivity and linear resistance characteristics and its preparation method", the silicon carbide / graphite ceramic is also prepared by the pressureless sintering process. Organic carbon sources and amorphous carbon are used as carbon sources to introduce carbon, and sintering is carried out at 2200 °C to transform the carbon phase into the graphite phase. By controlling the graphite content, the resistivity is adjusted and the material has linear volt-ampere characteristics. When the resistivity is low, the carbon content is as high as 20 wt.%, and at the same time, the preparation process is complex.

[0005] To sum up, although the silicon carbide-based multiphase ceramic materials have high thermal conductivity while achieving low resistivity and linear resistance characteristics, the linear characteristics and low resistivity of the silicon carbide-based multiphase ceramics are inseparable from their high density, and they cannot be used as high-power linear resistors. At the same time, the sintering temperature is high, the preparation process is complex, and the production cost is relatively high. In the composite system, the adjustment of the resistivity is achieved by adjusting the content of the second phase with high conductivity. The resistivity of silicon carbide itself is as high as 10 5 Ω·cm, which makes little contribution to the regulation of resistivity. The silicon carbide matrix mainly plays the role of constructing the skeleton in the composite system. Summary of the Invention

[0006] In order to overcome the defects of the above-mentioned prior art, the purpose of the present invention is to provide a preparation method of a carbon composite ceramic linear resistor to reduce the resistivity of the material and improve the thermal shock resistance of the ceramic resistor. In the present invention, silicon carbide is used as both the aggregate and the conductive phase, bentonite is used as the sintering aid, and nano carbon black is used as the conductive filler. The raw materials are mixed, molded by pressing, and then sintered under high-temperature nitrogen to obtain the carbon ceramic resistor material. After nitrogen treatment, the silicon carbide is combined with bentonite / carbon black, which can effectively reduce the resistivity of the material. On the other hand, silicon carbide has a low coefficient of thermal expansion and good thermal conductivity, which can reduce the thermal stress generated by the temperature change of the resistor material and improve the thermal shock resistance of the carbon ceramic resistor material.

[0007] The first object of the present invention is to provide a preparation method of a carbon composite ceramic linear resistor, including the following steps:

[0008] Mix bentonite, silicon carbide and nano carbon black evenly to obtain a powder. After mixing the powder and ethanol evenly, add a binder solution and carry out green body forming to obtain a green body after forming.

[0009] Under an atmosphere of a nitrogen element-containing gas, keep the green body at 1150 °C to 1300 °C to obtain a specimen; it should be noted that when the temperature is raised to a temperature above 1100 °C, the heating rate is reduced to ensure the uniformity of the furnace chamber temperature.

[0010] After grinding and processing the specimen, spray aluminum to obtain a carbon composite ceramic linear resistor.

[0011] In a preferred embodiment of the present invention, the powder material is composed of the following components by volume percentage: bentonite 33% - 56%, silicon carbide 40% - 60%, nano carbon black 1% - 7%, with a total of 100%.

[0012] For example, the volume percentage of bentonite is 33%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%.

[0013] The volume percentage of silicon carbide is 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%.

[0014] The nano carbon black is 1%, 2%, 3%, 4%, 5%, 6%, 7%. However, it is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0015] In a preferred embodiment of the present invention, the heat preservation time is 2h - 4h. For example, the heat preservation time is 2h, 2.5h, 3h, 3.5h, 4h.

[0016] The heating rate is 5℃ / min - 10℃ / min. For example, the heating rate is 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min. However, it is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0017] In a preferred embodiment of the present invention, the pressure for green body forming is 75MPa - 100MPa. For example, the pressure for green body forming is 75MPa, 80MPa, 85MPa, 90MPa, 95MPa, 100MPa, etc.

[0018] In a preferred embodiment of the present invention, the addition amount of the binder solution is 5% - 10% of the powder mass, and in the binder solution, the mass concentration of the binder is 5%.

[0019] For example, the addition amount of the binder solution is 5%, 6%, 7%, 8%, 9%, 10% of the powder mass. However, it is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0020] In a preferred embodiment of the present invention, the binder is polyvinyl alcohol.

[0021] In a preferred embodiment of the present invention, the volume ratio of the powder material to ethanol is 3 - 3.5:1. For example, the volume ratio of the powder material to ethanol is 3:1, 3.1:1, 3.2:1, 3.3:1, 3.4:1, 3.5:1.

[0022] In a preferred embodiment of the present invention, when the powder material and ethanol are mixed, the ball milling speed is 100 r / min to 300 r / min, and the mixing time is 10 h to 16 h.

[0023] For example, the ball milling speeds are 100 r / min, 150 r / min, 200 r / min, 250 r / min, 300 r / min, and the mixing times are 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, etc., but not limited to the listed values. Other unlisted values within the above value ranges are also applicable.

[0024] In a preferred embodiment of the present invention, the thickness of the sprayed aluminum is 10 μm to 15 μm. For example, the thickness of the sprayed aluminum is 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm.

[0025] The second object of the present invention is to provide a carbon composite ceramic linear resistor prepared by the above preparation method.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] The present invention uses bentonite, silicon carbide, and nano carbon black as raw materials. Silicon carbide serves as both a ceramic aggregate and a conductive phase. Both silicon carbide and nano carbon black have good electrical conductivity. At the same time, silicon carbide has excellent thermal conductivity, a low coefficient of thermal expansion, and stable physical and chemical properties. Silicon carbide and bentonite are easily obtained and form a porous ceramic. Therefore, the carbon ceramic resistor prepared has a lower resistivity, a high use temperature, and strong thermal shock resistance. Bentonite forms a liquid phase above 1000 °C, combining silicon carbide with glass, thereby forming a conductive path, and does not require a high density. The preparation process time is significantly shortened, and sintering is carried out at 1150 °C to 1300 °C, effectively reducing the total sintering time. And the green body in the present invention does not need to be debonded, reducing time.

[0028] The resistivity of silicon carbide itself is about 10 5 Ω·cm. In the prior art, the regulation of resistivity and volt-ampere characteristics are both achieved by increasing the content of the highly conductive second phase. At this time, silicon carbide contributes little to the change in resistivity. However, in the present invention, through the treatment in a high-temperature nitrogen-containing gas atmosphere, N-type doping of silicon carbide semiconductors can effectively reduce the resistivity of silicon carbide itself. After doping, both silicon carbide itself and between silicon carbide and carbon black can form conductive paths like between carbon black particles. At this time, silicon carbide plays the role of a conductive phase.

[0029] Compared with the prior art, the manufacturing method of the carbon ceramic linear resistor of the present invention has a simple process, easily available raw materials, low production costs, a low resistivity of the prepared resistor, a wide use temperature range, and strong thermal shock resistance. Brief Description of the Drawings

[0030] Figure 1 It is the volt-ampere characteristic curve diagram of the carbon-ceramic linear resistance material in Example 1. Specific Embodiments

[0031] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0032] The particle sizes of the silicon carbide used in the present invention are 62.5 μm and 10 μm respectively, and the volume ratio of 62.5-μm silicon carbide to 10-μm silicon carbide is 2:1. By selecting silicon carbide with different particle sizes and through particle size grading, the density of the green body can be improved, thereby reducing the shrinkage rate of the green body during sintering.

[0033] The molecular weight of the polyvinyl alcohol used in the present invention is 9000-10000.

[0034] The particle size of the nano carbon black is 27 nm, and the particle size of the bentonite is 5 μm.

[0035] In the present invention, vol.% represents volume percentage, and wt.% represents mass concentration.

[0036] Example 1

[0037] This example provides a preparation method of a carbon composite ceramic linear resistor, which specifically includes the following steps:

[0038] Step 1: Pretreatment of raw materials: Place the silicon carbide powder, bentonite, and nano carbon black in an oven and dry them at 80 °C for 2 h.

[0039] Step 2: Accurately weigh 60 vol.% of silicon carbide powder, 36 vol.% of bentonite, and 4 vol.% of nano carbon black. Mix the silicon carbide, nano carbon black, and bentonite to obtain a powder. Measure anhydrous ethanol according to the volume ratio of the powder to anhydrous ethanol of 3:1. Put the powder and anhydrous ethanol into a ball milling tank, the rotation speed of the ball mill is 200 r / min, mix the materials for 12 h, and then dry and screen to obtain a uniformly mixed powder.

[0040] Step 3: Add a 5 wt.% polyvinyl alcohol solution to the uniformly mixed powder. The addition amount of the polyvinyl alcohol solution is 10% of the mass of the powder. After grinding and screening, use the die pressing method to press a green body, apply a two-way pressure of 75 MPa, and keep the pressure for 60 s. Then put the green body into an oven and dry it at 100 °C for 12 h.

[0041] Step 4: Place the green body prepared in Step 3 in a graphite crucible, place the crucible in a multi-functional sintering furnace, fill it with nitrogen as a protective atmosphere, heat it from room temperature to 1100 °C at a rate of 10 °C / min, then heat it from 1100 °C to 1150 °C at a rate of 5 °C / min, hold for 2 h, and finally cool it to room temperature in the furnace to obtain a specimen.

[0042] Step 5: Perform surface grinding on the specimen obtained in Step 4. The sandpapers are 200 mesh, 400 mesh, 600 mesh, and 800 mesh in sequence. Spray aluminum on the upper and lower surfaces using a thermal spraying machine with a thickness of 10 μm and dry it in an oven at 100 °C to obtain a carbon-ceramic linear resistance material.

[0043] Example 2

[0044] This example provides a method for preparing a carbon composite ceramic linear resistor, which specifically includes the following steps:

[0045] Step 1: Pretreatment of raw materials: Place silicon carbide powder, bentonite, and nano carbon black in an oven and dry them at 80 °C for 2 h.

[0046] Step 2: Accurately weigh 50 vol.% silicon carbide powder, 46 vol.% bentonite, and 4 vol.% nano carbon black. Mix the silicon carbide, nano carbon black, and bentonite to obtain a powder. Measure absolute ethanol according to the volume ratio of the powder to absolute ethanol being 3:1. Put the powder and absolute ethanol into a ball milling tank, set the rotation speed of the ball mill to 200 r / min, mix for 12 h, then dry and screen.

[0047] Step 3: Add a 5 wt.% polyvinyl alcohol solution to the uniformly mixed powder. The addition amount of the polyvinyl alcohol solution is 10% of the powder mass. After grinding and screening, use a die pressing method to press a green body, apply a two-way pressure of 75 MPa, hold the pressure for 60 s, and then place the green body in an oven and dry it at 100 °C for 12 h.

[0048] Step 4: Place the green body prepared in Step 3 in a graphite crucible, place the crucible in a multi-functional sintering furnace, fill it with nitrogen as a protective atmosphere, heat it from room temperature to 1100 °C at a rate of 10 °C / min, then heat it from 1100 °C to 1150 °C at a rate of 5 °C / min, hold for 2 h, and finally cool it to room temperature.

[0049] Step 5: Perform surface grinding on the sample obtained in Step 4. The sandpapers are 200 mesh, 400 mesh, 600 mesh, and 800 mesh in sequence. Spray aluminum on the upper and lower surfaces using a thermal spraying machine with a thickness of 10 μm and dry it in an oven at 100 °C to obtain a carbon-ceramic linear resistance material.

[0050] Example 3

[0051] This embodiment provides a method for preparing a carbon composite ceramic linear resistor, which specifically includes the following steps:

[0052] Step 1: Pretreatment of raw materials: Place silicon carbide powder, bentonite, and nano-carbon black in an oven and dry them at 80°C for 2 hours.

[0053] Step 2: Accurately weigh 40 vol.% silicon carbide powder, 56 vol.% bentonite, and 4 vol.% nano-carbon black. Mix the silicon carbide, nano-carbon black, and bentonite to obtain a powder. Measure anhydrous ethanol according to a volume ratio of powder to anhydrous ethanol of 3:1. Put the powder and anhydrous ethanol into a ball mill jar, set the ball mill speed at 200 r / min, mix for 12 hours, then dry and screen.

[0054] Step 3: Add a 5 wt.% polyvinyl alcohol solution to the uniformly mixed powder. The addition amount of the polyvinyl alcohol solution is 10% of the powder mass. After grinding and screening, use the die pressing method to press a green body, apply a two-way pressure of 75 MPa, keep the pressure for 60 s, and then place the green body in an oven and dry it at 100°C for 12 hours.

[0055] Step 4: Place the green body prepared in Step 3 in a graphite crucible, place the crucible in a multi-functional sintering furnace, fill it with nitrogen as a protective atmosphere, heat it from room temperature to 1100°C at a rate of 10°C / min, then heat it from 1100°C to 1150°C at a rate of 5°C / min, keep it warm for 2 hours, and finally cool it to room temperature with the furnace.

[0056] Step 5: Perform surface grinding on the sample obtained in Step 4. The sandpapers are 200 mesh, 400 mesh, 600 mesh, and 800 mesh in sequence. Spray aluminum on the upper and lower surfaces using a thermal spray machine with a thickness of 10 μm and dry it in an oven at 100°C to obtain a carbon-ceramic linear resistor material.

[0057] Example 4

[0058] This embodiment provides a method for preparing a carbon composite ceramic linear resistor, which specifically includes the following steps:

[0059] Step 1: Pretreatment of raw materials: Place silicon carbide powder, bentonite, and nano-carbon black in an oven and dry them at 80°C for 2 hours.

[0060] Step 2: Accurately weigh 60 vol.% silicon carbide powder, 33 vol.% bentonite, and 7 vol.% nano-carbon black. Mix the silicon carbide, nano-carbon black, and bentonite to obtain a powder. Measure anhydrous ethanol according to a volume ratio of powder to anhydrous ethanol of 3:1. Put the powder and anhydrous ethanol into a ball mill jar, set the ball mill speed at 200 r / min, mix for 12 hours, then dry and screen.

[0061] Step 3: Add a polyvinyl alcohol solution with a concentration of 5 wt.% to the uniformly mixed powder. The addition amount of the polyvinyl alcohol solution is 10% of the mass of the powder. After grinding and sieving, use the die pressing method to press the green body. Apply a two-way pressure of 75 MPa for a holding time of 60 s. Subsequently, place the green body in an oven and dry it at 100 °C for 12 h.

[0062] Step 4: Place the green body prepared in Step 3 in a graphite crucible, place the crucible in a multi-functional sintering furnace, fill it with nitrogen as a protective atmosphere, heat it from room temperature to 1100 °C at a rate of 10 °C / min, then heat it from 1100 °C to 1150 °C at a rate of 5 °C / min, hold for 2 h, and finally cool it to room temperature with the furnace.

[0063] Step 5: Perform surface grinding treatment on the sample obtained in Step 4. The sandpapers are 200 mesh, 400 mesh, 600 mesh, and 800 mesh in sequence. Spray aluminum on the upper and lower surfaces using a thermal spraying machine with a thickness of 10 μm, and dry it in an oven at 100 °C to obtain a carbon-ceramic linear resistance material.

[0064] Example 5

[0065] This example provides a preparation method for a carbon composite ceramic linear resistor, which specifically includes the following steps:

[0066] Step 1: Pretreatment of raw materials: Place silicon carbide powder, bentonite, and nano-carbon black in an oven and dry them at 80 °C for 2 h.

[0067] Step 2: Accurately weigh 60 vol.% silicon carbide powder, 39 vol.% bentonite, and 1 vol.% nano-carbon black. Mix the silicon carbide, nano-carbon black, and bentonite to obtain a powder. Measure anhydrous ethanol according to the volume ratio of powder to anhydrous ethanol of 3:1. Put the powder and anhydrous ethanol into a ball mill tank, set the ball mill speed at 200 r / min, mix for 12 h, and then dry and sieve.

[0068] Step 3: Add a polyvinyl alcohol solution with a concentration of 5 wt.% to the uniformly mixed powder. The addition amount of the polyvinyl alcohol solution is 10% of the mass of the powder. After grinding and sieving, use the die pressing method to press the green body. Apply a two-way pressure of 75 MPa for a holding time of 60 s. Subsequently, place the green body in an oven and dry it at 100 °C for 12 h.

[0069] Step 4: Place the green body prepared in Step 3 in a graphite crucible, place the crucible in a multi-functional sintering furnace, fill it with nitrogen as a protective atmosphere, heat it from room temperature to 1100 °C at a rate of 10 °C / min, then heat it from 1100 °C to 1150 °C at a rate of 5 °C / min, hold for 2 h, and finally cool it to room temperature with the furnace.

[0070] Step 5: Perform surface grinding on the sample obtained in Step 4. Use sandpapers of 200 mesh, 400 mesh, 600 mesh, and 800 mesh in sequence. Spray aluminum on the upper and lower surfaces using a thermal spraying machine with a thickness of 10 μm, and dry it in an oven at 100 °C to obtain a carbon-ceramic linear resistance material.

[0071] Example 6

[0072] This example provides a preparation method for a carbon composite ceramic linear resistor, which specifically includes the following steps:

[0073] Step 1: Pretreatment of raw materials: Place silicon carbide powder, bentonite, and nano carbon black in an oven and dry at 80 °C for 2 h.

[0074] Step 2: Accurately weigh 60 vol.% silicon carbide powder, 36 vol.% bentonite, and 4 vol.% nano carbon black. Mix the silicon carbide, nano carbon black, and bentonite to obtain a powder. Measure absolute ethanol according to the volume ratio of powder to absolute ethanol of 3:1. Put the powder and absolute ethanol into a ball milling tank, set the rotation speed of the ball mill to 200 r / min, mix for 12 h, then dry and sieve.

[0075] Step 3: Add a 5 wt.% polyvinyl alcohol solution to the uniformly mixed powder. The addition amount of the polyvinyl alcohol solution is 10% of the powder mass. After grinding and sieving, use a die pressing method to press a green body, apply a two-way pressure of 75 MPa, keep the pressure for 60 s, and then put the green body into an oven and dry at 100 °C for 12 h.

[0076] Step 4: Place the green body prepared in Step 3 in a graphite crucible, place the crucible in a multi-functional sintering furnace, fill it with nitrogen as a protective atmosphere, heat from room temperature to 1100 °C at a rate of 10 °C / min, then heat from 1100 °C to 1200 °C at a rate of 5 °C / min, hold for 2 h, and finally cool to room temperature with the furnace.

[0077] Step 5: Perform surface grinding on the sample obtained in Step 4. Use sandpapers of 200 mesh, 400 mesh, 600 mesh, and 800 mesh in sequence. Spray aluminum on the upper and lower surfaces using a thermal spraying machine with a thickness of 10 μm, and dry it in an oven at 100 °C to obtain a carbon-ceramic linear resistance material.

[0078] Example 7

[0079] This example provides a preparation method for a carbon composite ceramic linear resistor, which specifically includes the following steps:

[0080] Step 1: Pretreatment of raw materials: Place silicon carbide powder, bentonite, and nano carbon black in an oven and dry at 80 °C for 2 h.

[0081] Step 2: Accurately weigh 60 vol.% silicon carbide powder, 36 vol.% bentonite, and 4 vol.% nano carbon black. Mix the silicon carbide, nano carbon black, and bentonite to obtain a powder. Measure absolute ethanol according to the volume ratio of powder to absolute ethanol being 3:1. Put the powder and absolute ethanol into a ball milling tank, set the ball mill rotation speed at 200 r / min, mix for 12 h, then dry and screen.

[0082] Step 3: Add a 5 wt.% polyvinyl alcohol solution to the uniformly mixed powder. The addition amount of the polyvinyl alcohol solution is 10% of the powder mass. After grinding and screening, use the die pressing method to press a green body, perform two-way pressing with a pressure of 75 MPa, keep the pressure for 60 s, and then put the green body into an oven and dry at 100 °C for 12 h.

[0083] Step 4: Place the green body prepared in Step 3 in a graphite crucible, put the crucible in a multi-functional sintering furnace, fill it with nitrogen as a protective atmosphere, heat from room temperature to 1100 °C at a rate of 10 °C / min, then heat from 1100 °C to 1250 °C at a rate of 5 °C / min, hold for 2 h, and finally cool to room temperature with the furnace.

[0084] Step 5: Perform surface grinding treatment on the sample obtained in Step 4. The sandpapers are 200 mesh, 400 mesh, 600 mesh, and 800 mesh in sequence. Spray aluminum on the upper and lower surfaces using a thermal spraying machine with a thickness of 10 μm and dry in an oven at 100 °C to obtain a carbon-ceramic linear resistance material.

[0085] Example 8

[0086] This example provides a preparation method for a carbon composite ceramic linear resistor, which specifically includes the following steps:

[0087] Step 1: Pretreatment of raw materials: Place the silicon carbide powder, bentonite, and nano carbon black in an oven and dry at 80 °C for 2 h.

[0088] Step 2: Accurately weigh 60 vol.% silicon carbide powder, 36 vol.% bentonite, and 4 vol.% nano carbon black. Mix the silicon carbide, nano carbon black, and bentonite to obtain a powder. Measure absolute ethanol according to the volume ratio of powder to absolute ethanol being 3:1. Put the powder and absolute ethanol into a ball milling tank, set the ball mill rotation speed at 200 r / min, mix for 12 h, then dry and screen.

[0089] Step 3: Add a 5 wt.% polyvinyl alcohol solution to the uniformly mixed powder. The addition amount of the polyvinyl alcohol solution is 10% of the powder mass. After grinding and screening, use the die pressing method to press a green body, perform two-way pressing with a pressure of 75 MPa, keep the pressure for 60 s, and then put the green body into an oven and dry at 100 °C for 12 h.

[0090] Step 4: Place the green body prepared in Step 3 into a graphite crucible, place the crucible in a multi-functional sintering furnace, fill it with nitrogen as a protective atmosphere, heat it from room temperature to 1100 °C at a rate of 10 °C / min, then heat it from 1100 °C to 1300 °C at a rate of 5 °C / min, hold for 2 h, and finally cool it to room temperature with the furnace.

[0091] Step 5: Perform surface grinding on the sample obtained in Step 4. The sandpapers are 200 mesh, 400 mesh, 600 mesh, and 800 mesh in sequence. Spray aluminum on the upper and lower surfaces using a thermal spraying machine with a thickness of 10 μm, and dry it in an oven at 100 °C to obtain a carbon-ceramic linear resistance material.

[0092] Example 9

[0093] This example provides a preparation method of a carbon composite ceramic linear resistor, which specifically includes the following steps:

[0094] Step 1: Pretreatment of raw materials: Place silicon carbide powder, bentonite, and nano-carbon black in an oven and dry them at 80 °C for 2 h.

[0095] Step 2: Accurately weigh 60 vol.% silicon carbide powder, 36 vol.% bentonite, and 4 vol.% nano-carbon black. Mix the silicon carbide, nano-carbon black, and bentonite to obtain a powder. Measure absolute ethanol according to the volume ratio of the powder to absolute ethanol of 3.2:1. Put the powder and absolute ethanol into a ball milling tank, the rotation speed of the ball mill is 100 r / min, mix for 16 h, then dry and screen to obtain a uniformly mixed powder.

[0096] Step 3: Add a polyvinyl alcohol solution with a concentration of 5 wt.% to the uniformly mixed powder. The addition amount of the polyvinyl alcohol solution is 5% of the powder mass. After grinding and screening, use a die pressing method to press a green body, perform two-way pressing with a pressure of 80 MPa, and keep the pressure for 60 s. Then put the green body into an oven and dry it at 100 °C for 12 h.

[0097] Step 4: Place the green body prepared in Step 3 into a graphite crucible, place the crucible in a multi-functional sintering furnace, fill it with nitrogen as a protective atmosphere, heat it from room temperature to 1100 °C at a rate of 10 °C / min, then heat it from 1100 °C to 1300 °C at a rate of 5 °C / min, hold for 3 h, and finally cool it to room temperature with the furnace to obtain a specimen.

[0098] Step 5: Perform surface grinding on the specimen obtained in Step 4. The sandpapers are 200 mesh, 400 mesh, 600 mesh, and 800 mesh in sequence. Spray aluminum on the upper and lower surfaces using a thermal spraying machine with a thickness of 12 μm and dry it in an oven at 100 °C to obtain a carbon-ceramic linear resistance material.

[0099] Example 10

[0100] This embodiment provides a method for preparing a carbon composite ceramic linear resistor, which specifically includes the following steps:

[0101] Step 1: Pretreatment of raw materials: Place silicon carbide powder, bentonite, and nano carbon black in an oven and dry at 80°C for 2 h.

[0102] Step 2: Accurately weigh 60 vol.% silicon carbide powder, 36 vol.% bentonite, and 4 vol.% nano carbon black. Mix the silicon carbide, nano carbon black, and bentonite to obtain a powder. Measure absolute ethanol according to the volume ratio of powder to absolute ethanol of 3.5:1. Put the powder and absolute ethanol into a ball milling tank, with the ball mill rotating at 300 r / min and mixing for 10 h. Then dry and screen to obtain a uniformly mixed powder.

[0103] Step 3: Add a 5 wt.% polyvinyl alcohol solution to the uniformly mixed powder. The addition amount of the polyvinyl alcohol solution is 7% of the powder mass. After grinding and screening, use a die pressing method to press a green body, apply a two-way pressure of 100 MPa, keep the pressure for 60 s, and then place the green body in an oven and dry at 100°C for 12 h.

[0104] Step 4: Place the green body prepared in Step 3 in a graphite crucible, place the crucible in a multi-functional sintering furnace, fill it with nitrogen as a protective atmosphere, heat from room temperature to 1100°C at a rate of 10°C / min, then heat from 1100°C to 1200°C at a rate of 5°C / min, hold for 4 h, and finally cool to room temperature in the furnace to obtain a specimen.

[0105] Step 5: Polish the surface of the specimen obtained in Step 4 successively with sandpapers of 200 mesh, 400 mesh, 600 mesh, and 800 mesh. Spray aluminum on the upper and lower surfaces using a thermal spraying machine with a thickness of 15 μm and dry in an oven at 100°C to obtain a carbon-ceramic linear resistor material.

[0106] Comparative Example 1

[0107] This comparative example provides a method for preparing a carbon composite ceramic linear resistor, which specifically includes the following steps:

[0108] Step 1: Pretreatment of raw materials: Place alumina powder, bentonite, and nano carbon black in an oven and dry at 80°C for 2 h.

[0109] Step 2: Accurately weigh 60 vol.% alumina, 36 vol.% bentonite, and 4 vol.% nano carbon black. Mix the alumina, nano carbon black, and bentonite to obtain a powder. Measure absolute ethanol according to the volume ratio of powder to absolute ethanol of 3:1. Put the powder and absolute ethanol into a ball milling tank, with the ball mill rotating at 200 r / min and mixing for 12 h. Then dry and screen to obtain a uniformly mixed powder.

[0110] Step 3: Add a polyvinyl alcohol solution with a concentration of 5 wt.% to the uniformly mixed powder. The addition amount of the polyvinyl alcohol solution is 10% of the powder mass. After grinding and sieving, use the die pressing method to press the green body, perform two-way pressing with a pressure of 75 MPa, and keep the pressure for 60 s. Subsequently, place the green body in an oven and dry it at 100 °C for 12 h.

[0111] Step 4: Place the green body prepared in Step 3 in a graphite crucible, place the crucible in a multi-functional sintering furnace, fill it with nitrogen as a protective atmosphere, heat it from room temperature to 1100 °C at a rate of 10 °C / min, then heat it from 1100 °C to 1150 °C at a rate of 5 °C / min, keep it warm for 2 h, and finally cool it to room temperature with the furnace to obtain the sample.

[0112] Step 5: Perform surface grinding treatment on the sample obtained in Step 4. The sandpapers are 200 mesh, 400 mesh, 600 mesh, and 800 mesh in sequence. Spray aluminum on the upper and lower surfaces using a thermal spraying machine with a thickness of 10 μm, and dry it in an oven at 100 °C to obtain the carbon-ceramic linear resistance material.

[0113] Comparative Example 2

[0114] This comparative example provides a preparation method of carbon composite ceramic linear resistance, which specifically includes the following steps:

[0115] Step 1: Pretreatment of raw materials: Place alumina powder, bentonite, and nano carbon black in an oven and dry them at 80 °C for 2 h.

[0116] Step 2: Accurately weigh 60 vol.% alumina, 33 vol.% bentonite, and 7 vol.% nano carbon black. Mix alumina, nano carbon black, and bentonite to obtain a powder. Measure anhydrous ethanol according to the volume ratio of powder to anhydrous ethanol of 3:1. Put the powder and anhydrous ethanol into a ball milling tank, set the rotation speed of the ball mill to 200 r / min, mix the materials for 12 h, then dry and sieve them to obtain a uniformly mixed powder.

[0117] Step 3: Add a polyvinyl alcohol solution with a concentration of 5 wt.% to the uniformly mixed powder. The addition amount of the polyvinyl alcohol solution is 10% of the powder mass. After grinding and sieving, use the die pressing method to press the green body, perform two-way pressing with a pressure of 75 MPa, and keep the pressure for 60 s. Subsequently, place the green body in an oven and dry it at 100 °C for 12 h.

[0118] Step 4: Place the green body prepared in Step 3 in a graphite crucible, place the crucible in a multi-functional sintering furnace, fill it with nitrogen as a protective atmosphere, heat it from room temperature to 1100 °C at a rate of 10 °C / min, then heat it from 1100 °C to 1150 °C at a rate of 5 °C / min, keep it warm for 2 h, and finally cool it to room temperature with the furnace to obtain the sample.

[0119] Step 5: Perform surface grinding on the specimen obtained in Step 4. The sandpapers used are 200 mesh, 400 mesh, 600 mesh, and 800 mesh in sequence. Spray aluminum on the upper and lower surfaces using a thermal spraying machine with a thickness of 10 μm, and dry it in an oven at 100 °C to obtain a carbon-ceramic linear resistance material.

[0120] Comparative Example 3

[0121] This comparative example provides a preparation method for a carbon composite ceramic linear resistor, which specifically includes the following steps:

[0122] Step 1: Pretreatment of raw materials: Place alumina powder, bentonite, and nano carbon black in an oven and dry them at 80 °C for 2 h.

[0123] Step 2: Accurately weigh 60 vol.% alumina, 30 vol.% bentonite, and 10 vol.% nano carbon black. Mix alumina, nano carbon black, and bentonite to obtain a powder. Measure absolute ethanol according to the volume ratio of the powder to absolute ethanol being 3:1. Put the powder and absolute ethanol into a ball milling tank, set the rotation speed of the ball mill to 200 r / min, mix the materials for 12 h, then dry and sieve them to obtain a uniformly mixed powder.

[0124] Step 3: Add a polyvinyl alcohol solution with a concentration of 5 wt.% to the uniformly mixed powder. The addition amount of the polyvinyl alcohol solution is 10% of the powder mass. After grinding and sieving, use a die pressing method to press a green body, apply a two-way pressure of 75 MPa, keep the pressure for 60 s, and then put the green body into an oven and dry it at 100 °C for 12 h.

[0125] Step 4: Place the green body prepared in Step 3 in a graphite crucible, place the crucible in a multi-functional sintering furnace, fill it with nitrogen as a protective atmosphere, heat it from room temperature to 1100 °C at a rate of 10 °C / min, then heat it from 1100 °C to 1150 °C at a rate of 5 °C / min, hold the temperature for 2 h, and finally cool it to room temperature in the furnace to obtain a specimen.

[0126] Step 5: Perform surface grinding on the specimen obtained in Step 4. The sandpapers used are 200 mesh, 400 mesh, 600 mesh, and 800 mesh in sequence. Spray aluminum on the upper and lower surfaces using a thermal spraying machine with a thickness of 10 μm, and dry it in an oven at 100 °C to obtain a carbon-ceramic linear resistance material.

[0127] Comparative Example 4

[0128] This comparative example provides a preparation method for a carbon composite ceramic linear resistor, which specifically includes the following steps:

[0129] Step 1: Pretreatment of raw materials: Place alumina powder, bentonite, and flake graphite in an oven and dry them at 80 °C for 2 h.

[0130] Step 2: Accurately weigh 60 vol.% alumina, 26 vol.% bentonite, and 14 vol.% flake graphite. Mix alumina, flake graphite, and bentonite to obtain a powder. Measure absolute ethanol according to the volume ratio of the powder to absolute ethanol being 3:1. Put the powder and absolute ethanol into a ball milling jar, with the ball mill rotating at 200 r / min and mixing for 12 h. Then dry and screen to obtain a uniformly mixed powder.

[0131] Step 3: Add a polyvinyl alcohol solution with a concentration of 5 wt.% to the uniformly mixed powder. The addition amount of the polyvinyl alcohol solution is 10% of the mass of the powder. After grinding and screening, use a die pressing method to press a green body, apply a two-way pressure of 75 MPa, and keep the pressure for 60 s. Subsequently, put the green body into an oven and dry it at 100 °C for 12 h.

[0132] Step 4: Place the green body prepared in Step 3 in a graphite crucible, put the crucible in a multi-functional sintering furnace, fill it with nitrogen as a protective atmosphere, heat from room temperature to 1100 °C at a rate of 10 °C / min, then heat from 1100 °C to 1150 °C at a rate of 5 °C / min, keep the temperature for 2 h, and finally cool to room temperature with the furnace to obtain a specimen.

[0133] Step 5: Perform surface grinding treatment on the specimen obtained in Step 4. The sandpapers are 200 mesh, 400 mesh, 600 mesh, and 800 mesh in sequence. Spray aluminum on the upper and lower surfaces using a thermal spraying machine with a thickness of 10 μm, and dry it in an oven at 100 °C to obtain a carbon-ceramic linear resistance material.

[0134] For the carbon-ceramic linear resistors prepared in this example and the comparative example, use the Archimedes drainage method to measure their bulk density and porosity, use the four-probe method to measure their resistivity, and use the laser flash method to measure the thermal conductivity of the specimen. Use the water quenching method to test the thermal shock resistance of the specimen: Put the specimen into an electric furnace and heat it to 200 °C - 800 °C respectively. The initial test temperature difference is 200 °C. Put the sample to be tested into a resistance wire furnace and heat it to the predetermined temperature at a rate of 10 °C / min and keep the temperature for 10 min. Then open the furnace door, take out the sample and quickly put it into deionized water at 20 ± 3 °C to cool for 10 s. Take out the sample, dry it at 110 °C for 2 h, and then naturally cool to room temperature. Then test the residual flexural strength of the sample. If the residual flexural strength ratio of the sample after water quenching is higher than 70%, increase the test temperature difference by 100 °C, and continue to repeat the above process until the residual flexural strength ratio of the sample is lower than 70%. Note that the next sample to be tested should be tested after the water temperature returns to room temperature. Use the three-point bending method to measure its remaining flexural strength. The temperature difference corresponding to when the remaining flexural strength drops to 70% of the flexural strength before thermal shock is the critical thermal shock temperature difference. The test results are shown in Table 1.

[0135] Table 1 Performance of the carbon-ceramic linear resistors of the embodiments and comparative examples of the present invention

[0136]

[0137] The volt-ampere characteristic curve of the carbon ceramic resistor material prepared using silicon carbide as the aggregate in Example 1 is as shown in Figure 1 shown. It can be seen from Figure 1 that for the carbon ceramic resistor material prepared using silicon carbide, the voltage and current show a linear relationship, indicating that the carbon ceramic resistor material of the present invention is a linear resistor.

[0138] Comparing Example 1 and Comparative Example 1, it can be seen that under the condition of the same volume fraction of aggregate addition, compared with alumina as the aggregate, the substitution of silicon carbide significantly improves the conductivity and thermal shock resistance of the prepared carbon ceramic linear resistor. This is because the introduction of silicon carbide increases the number of conductive paths in the material and decreases the resistivity. At the same time, the thermal conductivity is significantly improved, alleviating the internal and external temperature difference during water quenching and reducing the generated thermal stress.

[0139] Comparative Example 1, Comparative Example 2 and Comparative Example 3 show that in the system with alumina as the aggregate, although the resistivity can be reduced by increasing the content of nano carbon black, too high carbon content will make the material difficult to sinter. At the same time, since carbon black will undergo a carbothermal reduction reaction with iron oxide impurities in bentonite to release gas, ultimately causing the sample to expand and the contact resistance between carbon black particles to increase, resulting in the resistivity of the sample increasing instead of decreasing. Based on this, the present invention introduces silicon carbide and uses it in combination with bentonite and nano carbon black to effectively reduce the resistivity.

[0140] Comparing Example 1 and Comparative Example 2 and Comparative Example 4, it can be seen that although the resistivity can be reduced by increasing the content of flake graphite, the thermal shock resistance is lower than that of the sample using silicon carbide. This is because adding too much graphite reduces the density of the sample, decreases the thermal conductivity, and increases the thermal stress suffered during water quenching.

[0141] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications once they learn the basic creative concepts. Therefore, the appended claims are intended to be construed to include the preferred embodiments as well as all changes and modifications falling within the scope of the present invention.

[0142] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations.

Claims

1. A preparation method of a carbon composite ceramic linear resistor, characterized in that, It includes the following steps: Mix bentonite, silicon carbide and nano carbon black evenly to obtain a powder material. Mix the powder material and ethanol evenly and then dry it. Add a binder solution and carry out green body forming to obtain a green body after forming; The powder material is composed of the following components by volume percentage: 33% - 56% of bentonite, 40% - 60% of silicon carbide, 1% - 7% of nano carbon black, with a total of 100%; Under the atmosphere of a nitrogen element-containing gas, keep the green body at 1150°C - 1300°C for heat preservation to obtain a specimen; After grinding and processing the specimen, spray aluminum to obtain a carbon composite ceramic linear resistor.

2. The preparation method of a carbon composite ceramic linear resistor according to claim 1, wherein The heat preservation time is 2h - 4h.

3. The preparation method of a carbon composite ceramic linear resistor according to claim 1, characterized in that, The pressure for green body forming is 75MPa - 100MPa.

4. The preparation method of a carbon composite ceramic linear resistor according to claim 1, characterized in that, The addition amount of the binder solution is 5% - 10% of the powder mass, and the mass concentration of the binder is 5%.

5. The preparation method of a carbon composite ceramic linear resistor according to claim 1, characterized in that, The binder is polyvinyl alcohol.

6. The preparation method of a carbon composite ceramic linear resistor according to claim 1, characterized in that, The volume ratio of the powder material to ethanol is 3 - 3.5:

1.

7. The preparation method of a carbon composite ceramic linear resistor according to claim 1, characterized in that, When the powder material and ethanol are mixed, at a ball milling speed of 100r / min - 300r / min, mix for 10h - 16h.

8. The preparation method of a carbon composite ceramic linear resistor according to claim 1, characterized in that, The thickness of the sprayed aluminum is 10μm - 15μm.

9. A carbon composite ceramic linear resistor prepared by the preparation method according to any one of claims 1 - 8.

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