Carbon composite ceramic linear resistor and preparation method thereof

Abstract

The invention discloses a carbon composite ceramic linear resistor and a preparation method thereof, and belongs to the technical field of power electronic components. The 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 powder, uniformly mixing the powder and ethanol, drying, adding a binder solution, and carrying out green body forming to obtain a green body; carrying out heat preservation on the green body at 1150-1300 DEG C in a nitrogen-containing gas atmosphere to obtain a sample; and polishing the sample, and spraying aluminum to obtain the carbon composite ceramic linear resistor. According to the method for preparing the carbon composite ceramic linear resistor, the resistivity of the material can be reduced, and the thermal shock resistance of the ceramic resistor can be improved.

Description

Technical Field

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

[0002] Traditional carbon composite alumina ceramic linear resistors are made of alumina as aggregate, clay as sintering aid, and conductive carbon materials added for mixed molding and sintering. With the development of UHV, ceramic linear resistors are required to withstand more energy, which causes the resistor material to withstand a large temperature difference in a short period of time. The poor thermal shock resistance of traditional ceramic linear resistors makes it unable to withstand the thermal stress caused by the large temperature difference and breaks. As the application scope of carbon ceramic resistors becomes wider and wider, the demand for low resistivity gradually becomes prominent. Usually, the method of increasing the carbon content is used to reduce the resistivity of the material, but the excessive carbon content makes it difficult to sinter the ceramics and the resistivity is difficult to reduce. For example, the Chinese invention patent with application number CN202210706840.4 and invention name A carbon ceramic closing resistor and preparation process mentioned that the resistance value is reduced by modifying the highly conductive carbon black to improve the dispersion and using isostatic pressing, but the resistance value of the material remains almost unchanged by continuing to increase the carbon black content. In the preparation and properties of graphite / ceramic composite conductive materials published by Zheng Xin et al. in Volume 4, Issue 26 of Journal of Composite Materials in 2009, it was found that increasing the content of flake graphite to more than 15wt.% can produce ceramic resistors with a resistivity of 1Ω·cm~3Ω·cm, but excessive graphite content will cause the mechanical properties of the material to drop sharply and cannot meet the high-voltage service environment. At present, in addition to adjusting the carbon source to control the resistivity, the ceramic linear resistor technology also improves the sintering performance by adjusting the clay, such as the Chinese invention patent with application number CN202110120534.8 and the invention name of a low-temperature sintered carbon composite ceramic linear resistor and its preparation method, for improving the thermal shock resistance of ceramic linear resistors. Improving thermal conductivity can improve the thermal shock resistance of materials, but the thermal conductivity of traditional alumina aggregates is low, and the need for linear resistors to be porous also limits the improvement of thermal conductivity. According to the results of literature research, the current silicon carbide-based composite ceramic materials have both high thermal conductivity and certain electrical conductivity.

[0003] For example, in the Chinese invention patent with application number CN201610410680.3 and invention name A silicon carbide-based composite ceramic material and preparation method thereof, a pressureless sintering process is used to prepare silicon carbide / zirconium diboride dense ceramics. Zirconium diboride is added to silicon carbide as a second phase, and sintered in a normal pressure Ar atmosphere with a sintering temperature of 2100°C. At the same time, the content of the zirconium diboride second phase is controlled to adjust the resistivity. However, its nonlinear coefficient reaches 1.66 and cannot be used as a linear resistor.

[0004] In the Chinese invention patent with application number CN201610367998.8 and invention name "A silicon carbide / graphite composite material with low resistivity and linear resistance characteristics and its preparation method", silicon carbide / graphite ceramics are also prepared by pressureless sintering process, carbon is introduced using organic carbon source and amorphous carbon as carbon sources, and sintered at 2200℃ to transform the carbon phase into graphite phase. The resistivity is adjusted by controlling the graphite content and the material has linear volt-ampere characteristics. The carbon content is as high as 20wt.% at low resistivity, and the preparation process is complicated.

[0005] In summary, although silicon carbide-based composite ceramic materials have high thermal conductivity while achieving low resistivity and linear resistance characteristics, the linear characteristics and low resistivity of silicon carbide-based composite 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 high. In the composite system, the regulation of 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 resistivity regulation. The silicon carbide matrix mainly plays the role of building 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 method for preparing a carbon composite ceramic linear resistor to reduce the resistivity of the material and improve the thermal shock resistance of the ceramic resistor. The present invention uses silicon carbide as both an aggregate and a conductive phase, bentonite as a sintering aid, and nano carbon black as a conductive filler, and the raw materials are mixed, molded, and then sintered under high-temperature nitrogen to prepare a carbon ceramic resistor material. After nitrogen treatment, silicon carbide and bentonite / carbon black are composited, which can effectively reduce the resistivity of the material. On the other hand, silicon carbide has a low thermal expansion coefficient and good thermal conductivity, which can reduce the thermal stress generated by temperature changes in 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 method for preparing a carbon composite ceramic linear resistor, comprising the following steps: Bentonite, silicon carbide and nano carbon black are mixed evenly to obtain powder, the powder and ethanol are mixed evenly, a binder solution is added, and green body molding is performed to obtain a green body after molding.

[0008] In a nitrogen-containing gas atmosphere, the green body is kept warm at 1150°C-1300°C to obtain a sample; it should be noted that when the temperature is raised to a temperature above 1100°C, the heating rate is reduced in order to ensure a uniform furnace chamber temperature.

[0009] The sample was polished and then sprayed with aluminum to obtain a carbon composite ceramic linear resistor.

[0010] In a preferred embodiment of the present invention, the powder is composed of the following components in volume percentage: 33% to 56% bentonite, 40% to 60% silicon carbide, and 1% to 7% nano carbon black, which totals 100%.

[0011] For example, the volume percentage of bentonite is 33%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, and 56%.

[0012] The volume percentages of silicon carbide are 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, and 60%.

[0013] Nano carbon black 1%, 2%, 3%, 4%, 5%, 6%, 7%. However, it is not limited to the listed values, and other values ​​not listed in the above range are also applicable.

[0014] In a preferred embodiment of the present invention, the insulation time is 2h~4h, for example, the insulation time is 2h, 2.5h, 3h, 3.5h, 4h.

[0015] The heating rate is 5°C / min~10°C / min, for example, the heating rate is 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0016] In a preferred embodiment of the present invention, the pressure of green body molding is 75 MPa-100 MPa, for example, the pressure of green body molding is 75 MPa, 80 MPa, 85 MPa, 90 MPa, 95 MPa, 100 MPa, etc.

[0017] In a preferred embodiment of the present invention, the amount of the binder solution added is 5% to 10% of the mass of the powder, and the mass concentration of the binder in the binder solution is 5%.

[0018] For example, the addition amount of the binder solution is 5%, 6%, 7%, 8%, 9%, and 10% of the powder mass, but it is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0019] In a preferred embodiment of the present invention, the binder is polyvinyl alcohol.

[0020] In a preferred embodiment of the present invention, the volume ratio of the powder to ethanol is 3-3.5:1, for example, the volume ratio of the powder to ethanol is 3:1, 3.1:1, 3.2:1, 3.3:1, 3.4:1, 3.5:1.

[0021] In a preferred embodiment of the present invention, the powder and ethanol are mixed at a ball milling speed of 100 r / min to 300 r / min for 10 h to 16 h.

[0022] For example, the ball milling speed is 100 r / min, 150 r / min, 200 r / min, 250 r / min, 300 r / min, and the mixing time is 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, etc., but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0023] 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, or 15 μm.

[0024] The second object of the present invention is to provide a carbon composite ceramic linear resistor prepared by the above preparation method.

[0025] Compared with the prior art, the present invention has the following advantages: The present invention uses bentonite, silicon carbide and nano carbon black as raw materials, and silicon carbide is used as both a ceramic aggregate and a conductive phase. Both silicon carbide and nano carbon black have good electrical conductivity, and silicon carbide has excellent thermal conductivity, a low thermal expansion coefficient and stable physical and chemical properties. Silicon carbide and bentonite are easy to obtain and constitute porous ceramics. The carbon ceramic resistor prepared thereby has a lower resistivity, a high operating temperature and strong thermal shock resistance. Bentonite forms a liquid phase above 1000°C, and silicon carbide is combined with glass to form a conductive path, which does not require a high density. The preparation process time is significantly shortened, and sintering is performed at 1150°C to 1300°C, which effectively reduces the total sintering time. And the green body in the present invention does not need to be debonded, which reduces time.

[0026] The resistivity of silicon carbide itself is about 10 5 Ω·cm. In the prior art, the regulation of resistivity and the volt-ampere characteristics are achieved by increasing the content of the highly conductive second phase. At this time, silicon carbide contributes little to the change in resistivity. However, the present invention treats the silicon carbide semiconductor with a high-temperature nitrogen-containing gas atmosphere to perform N-type doping, which can effectively reduce the resistivity of silicon carbide itself. The doped silicon carbide itself and between silicon carbide and carbon black can form a conductive path like between carbon black particles, and at this time, silicon carbide plays the role of a conductive phase.

[0027] Compared with the prior art, the manufacturing method of the carbon ceramic linear resistor of the present invention has simple process, readily available raw materials, low production cost, low resistivity of the resistor, wide operating temperature range and strong thermal shock resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a graph showing the volt-ampere characteristic curve of the carbon-ceramic linear resistor material in Example 1. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions 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.

[0030] The particle sizes of 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. The present invention selects silicon carbide of 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 sintering.

[0031] The molecular weight of the polyvinyl alcohol used in the present invention is 9000-10000.

[0032] The particle size of nano carbon black is 27nm, and the particle size of bentonite is 5μm.

[0033] In the present invention, vol.% represents volume percentage, and wt.% represents mass concentration.

[0034] Example 1 This embodiment provides a method for preparing a carbon composite ceramic linear resistor, which specifically includes the following steps: 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 hours.

[0035] Step 2: Accurately weigh 60 vol.% silicon carbide powder, 36 vol.% bentonite, and 4 vol.% nano carbon black, mix silicon carbide, nano carbon black and bentonite to obtain 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, the ball mill speed is 200 r / min, mix for 12 hours, and then dry and sieve to obtain a uniformly mixed powder.

[0036] Step 3: Add 5wt.% polyvinyl alcohol solution to the evenly mixed powder, where the amount of polyvinyl alcohol solution added is 10% of the powder mass. After grinding and sieving, use a compression molding method to press the green body. Use a pressure of 75MPa for bidirectional pressurization, hold the pressure for 60s, and then put the green body into an oven and dry it at 100°C for 12h.

[0037] 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, increase the temperature from room temperature to 1100°C at 10°C / min, then increase the temperature from 1100°C to 1150°C at 5°C / min, keep warm for 2h, and finally cool to room temperature with the furnace to obtain a sample.

[0038] Step 5: The sample obtained in step 4 was surface-grinded using sandpaper of 200 mesh, 400 mesh, 600 mesh and 800 mesh, respectively. A thermal sprayer was used to spray aluminum on the upper and lower surfaces with a thickness of 10 μm and dried in an oven at 100° C. to obtain a carbon-ceramic linear resistor material.

[0039] Example 2 This embodiment provides a method for preparing a carbon composite ceramic linear resistor, which specifically includes the following steps: 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 hours.

[0040] Step 2: Accurately weigh 50 vol.% silicon carbide powder, 46 vol.% bentonite, and 4 vol.% nano carbon black, mix silicon carbide, nano carbon black and bentonite to obtain 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, the ball mill speed is 200 r / min, mix for 12 hours, and then dry and sieve.

[0041] Step 3: Add 5wt.% polyvinyl alcohol solution to the evenly mixed powder, where the amount of polyvinyl alcohol solution added is 10% of the powder mass. After grinding and sieving, use a compression molding method to press the green body. Use a pressure of 75MPa for bidirectional pressurization, hold the pressure for 60s, and then put the green body into an oven and dry it at 100°C for 12h.

[0042] 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, increase the temperature from room temperature to 1100°C at 10°C / min, then increase the temperature from 1100°C to 1150°C at 5°C / min, keep warm for 2h, and finally cool to room temperature with the furnace.

[0043] Step 5: The sample obtained in step 4 was surface-grinded using sandpaper of 200 mesh, 400 mesh, 600 mesh and 800 mesh, respectively. A thermal sprayer was used to spray aluminum on the upper and lower surfaces with a thickness of 10 μm, and the samples were dried in an oven at 100° C. to obtain a carbon-ceramic linear resistor material.

[0044] Example 3 This embodiment provides a method for preparing a carbon composite ceramic linear resistor, which specifically includes the following steps: 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 hours.

[0045] Step 2: Accurately weigh 40 vol.% silicon carbide powder, 56 vol.% bentonite, and 4 vol.% nano carbon black, mix silicon carbide, nano carbon black and bentonite to obtain 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, the ball mill speed is 200 r / min, mix for 12 hours, and then dry and sieve.

[0046] Step 3: Add 5wt.% polyvinyl alcohol solution to the evenly mixed powder, where the amount of polyvinyl alcohol solution added is 10% of the powder mass. After grinding and sieving, use a compression molding method to press the green body. Use a pressure of 75MPa for bidirectional pressurization, hold the pressure for 60s, and then put the green body into an oven and dry it at 100°C for 12h.

[0047] 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, increase the temperature from room temperature to 1100°C at 10°C / min, then increase the temperature from 1100°C to 1150°C at 5°C / min, keep warm for 2h, and finally cool to room temperature with the furnace.

[0048] Step 5: The sample obtained in step 4 was surface-grinded using sandpaper of 200 mesh, 400 mesh, 600 mesh and 800 mesh, respectively. A thermal sprayer was used to spray aluminum on the upper and lower surfaces with a thickness of 10 μm and dried in an oven at 100° C. to obtain a carbon-ceramic linear resistor material.

[0049] Example 4 This embodiment provides a method for preparing a carbon composite ceramic linear resistor, which specifically includes the following steps: 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 hours.

[0050] Step 2: Accurately weigh 60 vol.% silicon carbide powder, 33 vol.% bentonite, and 7 vol.% nano carbon black, mix silicon carbide, nano carbon black and bentonite to obtain 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, the ball mill speed is 200 r / min, mix for 12 hours, and then dry and sieve.

[0051] Step 3: Add 5wt.% polyvinyl alcohol solution to the evenly mixed powder, where the amount of polyvinyl alcohol solution added is 10% of the powder mass. After grinding and sieving, use a compression molding method to press the green body. Use a pressure of 75MPa for bidirectional pressurization, hold the pressure for 60s, and then put the green body into an oven and dry it at 100°C for 12h.

[0052] 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, increase the temperature from room temperature to 1100°C at 10°C / min, then increase the temperature from 1100°C to 1150°C at 5°C / min, keep warm for 2h, and finally cool to room temperature with the furnace.

[0053] Step 5: The sample obtained in step 4 was surface-grinded using sandpaper of 200 mesh, 400 mesh, 600 mesh and 800 mesh, respectively. A thermal sprayer was used to spray aluminum on the upper and lower surfaces with a thickness of 10 μm, and the samples were dried in an oven at 100° C. to obtain a carbon-ceramic linear resistor material.

[0054] Example 5 This embodiment provides a method for preparing a carbon composite ceramic linear resistor, which specifically includes the following steps: 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 hours.

[0055] Step 2: Accurately weigh 60 vol.% silicon carbide powder, 39 vol.% bentonite, and 1 vol.% nano carbon black, mix silicon carbide, nano carbon black and bentonite to obtain 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, the ball mill speed is 200 r / min, mix for 12 hours, and then dry and sieve.

[0056] Step 3: Add 5wt.% polyvinyl alcohol solution to the evenly mixed powder, where the amount of polyvinyl alcohol solution added is 10% of the powder mass. After grinding and sieving, use a compression molding method to press the green body. Use a pressure of 75MPa for bidirectional pressurization, hold the pressure for 60s, and then put the green body into an oven and dry it at 100°C for 12h.

[0057] 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, increase the temperature from room temperature to 1100°C at 10°C / min, then increase the temperature from 1100°C to 1150°C at 5°C / min, keep warm for 2h, and finally cool to room temperature with the furnace.

[0058] Step 5: The sample obtained in step 4 was surface-grinded using sandpaper of 200 mesh, 400 mesh, 600 mesh and 800 mesh, respectively. A thermal sprayer was used to spray aluminum on the upper and lower surfaces with a thickness of 10 μm, and the samples were dried in an oven at 100° C. to obtain a carbon-ceramic linear resistor material.

[0059] Example 6 This embodiment provides a method for preparing a carbon composite ceramic linear resistor, which specifically includes the following steps: 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 hours.

[0060] Step 2: Accurately weigh 60 vol.% silicon carbide powder, 36 vol.% bentonite, and 4 vol.% nano carbon black, mix silicon carbide, nano carbon black and bentonite to obtain 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, the ball mill speed is 200 r / min, mix for 12 hours, and then dry and sieve.

[0061] Step 3: Add 5wt.% polyvinyl alcohol solution to the evenly mixed powder, where the amount of polyvinyl alcohol solution added is 10% of the powder mass. After grinding and sieving, use a compression molding method to press the green body. Use a pressure of 75MPa for bidirectional pressurization, hold the pressure for 60s, and then put the green body into an oven and dry it at 100°C for 12h.

[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, increase the temperature from room temperature to 1100°C at 10°C / min, then increase the temperature from 1100°C to 1200°C at 5°C / min, keep warm for 2h, and finally cool to room temperature with the furnace.

[0063] Step 5: The sample obtained in step 4 was surface-grinded using sandpaper of 200 mesh, 400 mesh, 600 mesh and 800 mesh, respectively. A thermal sprayer was used to spray aluminum on the upper and lower surfaces with a thickness of 10 μm, and the samples were dried in an oven at 100° C. to obtain a carbon-ceramic linear resistor material.

[0064] Example 7 This embodiment provides a method for preparing a carbon composite ceramic linear resistor, which specifically includes the following steps: 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 hours.

[0065] Step 2: Accurately weigh 60 vol.% silicon carbide powder, 36 vol.% bentonite, and 4 vol.% nano carbon black, mix silicon carbide, nano carbon black and bentonite to obtain 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, the ball mill speed is 200 r / min, mix for 12 hours, and then dry and sieve.

[0066] Step 3: Add 5wt.% polyvinyl alcohol solution to the evenly mixed powder, where the amount of polyvinyl alcohol solution added is 10% of the powder mass. After grinding and sieving, use a compression molding method to press the green body. Use a pressure of 75MPa for bidirectional pressurization, hold the pressure for 60s, and then put the green body into an oven and dry it at 100°C for 12h.

[0067] 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, increase the temperature from room temperature to 1100°C at 10°C / min, then increase the temperature from 1100°C to 1250°C at 5°C / min, keep warm for 2h, and finally cool to room temperature with the furnace.

[0068] Step 5: The sample obtained in step 4 was surface-grinded using sandpaper of 200 mesh, 400 mesh, 600 mesh and 800 mesh, respectively. A thermal sprayer was used to spray aluminum on the upper and lower surfaces with a thickness of 10 μm and dried in an oven at 100° C. to obtain a carbon-ceramic linear resistor material.

[0069] Example 8 This embodiment provides a method for preparing a carbon composite ceramic linear resistor, which specifically includes the following steps: 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 hours.

[0070] Step 2: Accurately weigh 60 vol.% silicon carbide powder, 36 vol.% bentonite, and 4 vol.% nano carbon black, mix silicon carbide, nano carbon black and bentonite to obtain 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, the ball mill speed is 200 r / min, mix for 12 hours, and then dry and sieve.

[0071] Step 3: Add 5wt.% polyvinyl alcohol solution to the evenly mixed powder, where the amount of polyvinyl alcohol solution added is 10% of the powder mass. After grinding and sieving, use a compression molding method to press the green body. Use a pressure of 75MPa for bidirectional pressurization, hold the pressure for 60s, and then put the green body into an oven and dry it at 100°C for 12h.

[0072] 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, increase the temperature from room temperature to 1100°C at 10°C / min, then increase the temperature from 1100°C to 1300°C at 5°C / min, keep warm for 2h, and finally cool to room temperature with the furnace.

[0073] Step 5: The sample obtained in step 4 was surface-grinded using sandpaper of 200 mesh, 400 mesh, 600 mesh and 800 mesh, respectively. A thermal sprayer was used to spray aluminum on the upper and lower surfaces with a thickness of 10 μm, and the samples were dried in an oven at 100° C. to obtain a carbon-ceramic linear resistor material.

[0074] Example 9 This embodiment provides a method for preparing a carbon composite ceramic linear resistor, which specifically includes the following steps: 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 hours.

[0075] Step 2: Accurately weigh 60 vol.% silicon carbide powder, 36 vol.% bentonite, and 4 vol.% nano carbon black, mix silicon carbide, nano carbon black and bentonite to obtain powder, measure anhydrous ethanol according to the volume ratio of powder to anhydrous ethanol of 3.2:1, put the powder and anhydrous ethanol into a ball mill, the ball mill speed is 100 r / min, mix for 16 hours, and then dry and sieve to obtain a uniformly mixed powder.

[0076] Step 3: Add 5wt.% polyvinyl alcohol solution to the evenly mixed powder, the amount of polyvinyl alcohol solution added is 5% of the powder mass, and after grinding and sieving, use the molding method to press the green body, use 80MPa pressure for bidirectional pressurization, hold the pressure for 60s, and then put the green body into an oven at 100℃ and dry it for 12h.

[0077] 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, increase the temperature from room temperature to 1100°C at 10°C / min, then increase the temperature from 1100°C to 1300°C at 5°C / min, keep warm for 3h, and finally cool to room temperature with the furnace to obtain a sample.

[0078] Step 5: The sample obtained in step 4 was surface-grinded using sandpaper of 200 mesh, 400 mesh, 600 mesh and 800 mesh, respectively. A thermal sprayer was used to spray aluminum on the upper and lower surfaces with a thickness of 12 μm and dried in an oven at 100° C. to obtain a carbon-ceramic linear resistor material.

[0079] Example 10 This embodiment provides a method for preparing a carbon composite ceramic linear resistor, which specifically includes the following steps: 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 hours.

[0080] Step 2: Accurately weigh 60 vol.% silicon carbide powder, 36 vol.% bentonite, and 4 vol.% nano carbon black, mix silicon carbide, nano carbon black and bentonite to obtain powder, measure anhydrous ethanol according to the volume ratio of powder to anhydrous ethanol of 3.5:1, put the powder and anhydrous ethanol into a ball mill, the ball mill speed is 300 r / min, mix for 10 hours, and then dry and sieve to obtain a uniformly mixed powder.

[0081] Step 3: Add 5wt.% polyvinyl alcohol solution to the evenly mixed powder, the amount of polyvinyl alcohol solution added is 7% of the powder mass, and after grinding and sieving, use the molding method to press the green body, use 100MPa pressure for bidirectional pressurization, hold the pressure for 60s, and then put the green body into an oven at 100℃ and dry it for 12h.

[0082] 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, increase the temperature from room temperature to 1100°C at 10°C / min, then increase the temperature from 1100°C to 1200°C at 5°C / min, keep warm for 4 hours, and finally cool to room temperature with the furnace to obtain a sample.

[0083] Step 5: The sample obtained in step 4 was surface-grinded using sandpaper of 200 mesh, 400 mesh, 600 mesh and 800 mesh, respectively. A thermal sprayer was used to spray aluminum on the upper and lower surfaces with a thickness of 15 μm and dried in an oven at 100° C. to obtain a carbon-ceramic linear resistor material.

[0084] Comparative Example 1 This comparative example provides a method for preparing a carbon composite ceramic linear resistor, which specifically includes the following steps: Step 1: Pretreatment of raw materials: Place alumina powder, bentonite and nano carbon black in an oven and dry at 80°C for 2 hours.

[0085] 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 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, the ball mill speed is 200 r / min, mix for 12 hours, and then dry and sieve to obtain a uniformly mixed powder.

[0086] Step 3: Add 5wt.% polyvinyl alcohol solution to the evenly mixed powder, where the amount of polyvinyl alcohol solution added is 10% of the powder mass. After grinding and sieving, use a compression molding method to press the green body. Use a pressure of 75MPa for bidirectional pressurization, hold the pressure for 60s, and then put the green body into an oven and dry it at 100°C for 12h.

[0087] Step 4: Place the green body prepared in step 3 in an ink crucible, place the crucible in a multi-functional sintering furnace, fill it with nitrogen as a protective atmosphere, increase the temperature from room temperature to 1100°C at 10°C / min, then increase the temperature from 1100°C to 1150°C at 5°C / min, keep warm for 2h, and finally cool to room temperature with the furnace to obtain a sample.

[0088] Step 5: The sample obtained in step 4 was surface-grinded using sandpaper of 200 mesh, 400 mesh, 600 mesh and 800 mesh, respectively. A thermal sprayer was used to spray aluminum on the upper and lower surfaces with a thickness of 10 μm, and the aluminum was dried in an oven at 100° C. to obtain a carbon-ceramic linear resistor material.

[0089] Comparative Example 2 This comparative example provides a method for preparing a carbon composite ceramic linear resistor, which specifically includes the following steps: Step 1: Pretreatment of raw materials: Place alumina powder, bentonite and nano carbon black in an oven and dry at 80°C for 2 hours.

[0090] Step 2: Accurately weigh 60 vol.% alumina, 33 vol.% bentonite, and 7 vol.% nano carbon black, mix the alumina, 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, the ball mill speed is 200 r / min, mix for 12 hours, and then dry and sieve to obtain a uniformly mixed powder.

[0091] Step 3: Add 5wt.% polyvinyl alcohol solution to the evenly mixed powder, where the amount of polyvinyl alcohol solution added is 10% of the powder mass. After grinding and sieving, use a compression molding method to press the green body. Use a pressure of 75MPa for bidirectional pressurization, hold the pressure for 60s, and then put the green body into an oven and dry it at 100°C for 12h.

[0092] 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, increase the temperature from room temperature to 1100°C at 10°C / min, then increase the temperature from 1100°C to 1150°C at 5°C / min, keep warm for 2h, and finally cool to room temperature with the furnace to obtain a sample.

[0093] Step 5: The sample obtained in step 4 was surface-grinded using sandpaper of 200 mesh, 400 mesh, 600 mesh and 800 mesh, respectively. A thermal sprayer was used to spray aluminum on the upper and lower surfaces with a thickness of 10 μm, and the aluminum was dried in an oven at 100° C. to obtain a carbon-ceramic linear resistor material.

[0094] Comparative Example 3 This comparative example provides a method for preparing a carbon composite ceramic linear resistor, which specifically includes the following steps: Step 1: Pretreatment of raw materials: Place alumina powder, bentonite and nano carbon black in an oven and dry at 80°C for 2 hours.

[0095] Step 2: Accurately weigh 60 vol.% alumina, 30 vol.% bentonite, and 10 vol.% nano carbon black, mix the alumina, 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, the ball mill speed is 200 r / min, mix for 12 hours, and then dry and sieve to obtain a uniformly mixed powder.

[0096] Step 3: Add 5wt.% polyvinyl alcohol solution to the evenly mixed powder, where the amount of polyvinyl alcohol solution added is 10% of the powder mass. After grinding and sieving, use a compression molding method to press the green body. Use a pressure of 75MPa for bidirectional pressurization, hold the pressure for 60s, and then put the green body into an oven and dry it at 100°C for 12h.

[0097] 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, increase the temperature from room temperature to 1100°C at 10°C / min, then increase the temperature from 1100°C to 1150°C at 5°C / min, keep warm for 2h, and finally cool to room temperature with the furnace to obtain a sample.

[0098] Step 5: The sample obtained in step 4 was surface-grinded using sandpaper of 200 mesh, 400 mesh, 600 mesh and 800 mesh, respectively. A thermal sprayer was used to spray aluminum on the upper and lower surfaces with a thickness of 10 μm, and the aluminum was dried in an oven at 100° C. to obtain a carbon-ceramic linear resistor material.

[0099] Comparative Example 4 This comparative example provides a method for preparing a carbon composite ceramic linear resistor, which specifically includes the following steps: Step 1: Pretreatment of raw materials: Place alumina powder, bentonite, and flake graphite in an oven and dry at 80°C for 2 hours.

[0100] Step 2: Accurately weigh 60 vol.% alumina, 26 vol.% bentonite, and 14 vol.% flake graphite, mix the alumina, flake graphite, 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, rotate the ball mill at 200 r / min, mix for 12 hours, and then dry and sieve to obtain a uniformly mixed powder.

[0101] Step 3: Add 5wt.% polyvinyl alcohol solution to the evenly mixed powder, where the amount of polyvinyl alcohol solution added is 10% of the powder mass. After grinding and sieving, use a compression molding method to press the green body. Use a pressure of 75MPa for bidirectional pressurization, hold the pressure for 60s, and then put the green body into an oven and dry it at 100°C for 12h.

[0102] 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, increase the temperature from room temperature to 1100°C at 10°C / min, then increase the temperature from 1100°C to 1150°C at 5°C / min, keep warm for 2h, and finally cool to room temperature with the furnace to obtain a sample.

[0103] Step 5: The sample obtained in step 4 was surface-grinded using sandpaper of 200 mesh, 400 mesh, 600 mesh and 800 mesh, respectively. A thermal sprayer was used to spray aluminum on the upper and lower surfaces with a thickness of 10 μm, and the aluminum was dried in an oven at 100° C. to obtain a carbon-ceramic linear resistor material.

[0104] The volume density and porosity of the carbon ceramic linear resistors prepared in this embodiment and the comparative example are measured by the Archimedes drainage method, the resistivity is measured by the four-probe method, and the thermal conductivity of the sample is measured by the laser flash method. The thermal shock resistance of the sample is tested by the water quenching method: the sample is placed in an electric furnace and heated to 200°C~800°C respectively, and the initial test temperature difference is 200°C. The sample to be tested is placed in a resistance wire furnace and heated to a predetermined temperature at a rate of 10°C / min and kept warm for 10 minutes. Then the furnace door is opened to take out the sample and quickly put it into 20±3°C deionized water to cool for 10s. The sample is taken out and dried at 110°C for 2 hours and then naturally cooled to room temperature. Then the residual bending strength of the sample is tested. If the residual bending strength rate of the sample after water quenching is higher than 70%, the test temperature difference is increased by 100°C, and the above process is repeated until the residual bending strength rate of the sample is lower than 70%. Note that the next sample to be tested should be tested after the water temperature changes to room temperature. The residual bending strength is measured by the three-point bending method. The temperature difference corresponding to the residual bending strength dropping to 70% of the bending strength before thermal shock is the critical thermal shock temperature difference. The test performance is shown in Table 1.

[0105] Table 1 Performance of carbon ceramic linear resistors of the embodiments of the present invention and the comparative examples

[0106] Example 1 The volt-ampere characteristic curve of the carbon ceramic resistor material prepared using silicon carbide as aggregate is as follows Figure 1 As shown, from Figure 1 It can be seen that the voltage and current of the carbon ceramic resistor material prepared using silicon carbide are in a linear relationship, indicating that the carbon ceramic resistor material of the present invention is a linear resistor.

[0107] By comparing Example 1 and Comparative Example 1, it can be seen that under the same volume fraction of aggregate addition, compared with alumina as aggregate, the substitution of silicon carbide has a significant improvement effect on the conductivity and thermal shock resistance of the obtained carbon ceramic linear resistor. This is because the introduction of silicon carbide increases the number of conductive paths in the material and reduces the resistivity. At the same time, the thermal conductivity is significantly improved, which alleviates the internal and external temperature difference during water quenching and reduces the generated thermal stress.

[0108] Comparative Examples 1, 2 and 3 show that, in a system with alumina as aggregate, although the resistivity can be reduced by increasing the content of nano-carbon black, excessively high carbon content will make the material difficult to sinter. At the same time, carbon black will undergo a carbon thermal reduction reaction with iron oxide impurities in bentonite to release gas, which will eventually cause the sample to expand. The contact resistance between carbon black particles increases, causing the resistivity of the sample to increase instead of decrease. 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.

[0109] By comparing Example 1 with Comparative Examples 2 and 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, reduces the thermal conductivity, and increases the thermal stress during water quenching.

[0110] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0111] 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 equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing a carbon composite ceramic linear resistor, characterized in that: The following steps are involved: The bentonite, silicon carbide and nano carbon black are mixed evenly to obtain a powder, the powder is mixed evenly with ethanol and then dried, a binder solution is added, and a green body is formed to obtain a green body after forming; The green body is kept at 1150°C to 1300°C in a nitrogen-containing gas atmosphere to obtain a sample; The sample was polished and then sprayed with aluminum to obtain a carbon composite ceramic linear resistor.

2. The method for preparing a carbon composite ceramic linear resistor according to claim 1, characterized in that: The powder is composed of the following components in volume percentage: bentonite 33%~56%, silicon carbide 40%~60%, nano carbon black 1%~7%, totaling 100%.

3. The method for preparing a carbon composite ceramic linear resistor according to claim 1, characterized in that: The insulation time is 2h~4h.

4. The method for preparing a carbon composite ceramic linear resistor according to claim 1, characterized in that: The pressure of green body molding is 75MPa~100MPa.

5. The method for preparing a carbon composite ceramic linear resistor according to claim 1, characterized in that: The amount of binder solution added is 5% to 10% of the powder mass, and the mass concentration of the binder is 5%.

6. The method for preparing a carbon composite ceramic linear resistor according to claim 1, characterized in that: The binder is polyvinyl alcohol.

7. The method for preparing a carbon composite ceramic linear resistor according to claim 1, characterized in that: The volume ratio of powder to ethanol is 3~3.5:

1.

8. The method for preparing a carbon composite ceramic linear resistor according to claim 1, characterized in that: When the powder and ethanol are mixed, they are mixed at a ball mill speed of 100 r / min~300 r / min for 10 h~16 h.

9. The method for preparing a carbon composite ceramic linear resistor according to claim 1, characterized in that: The thickness of sprayed aluminum is 10μm~15μm.

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

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