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 preparation method of the carbon composite ceramic linear resistor provided by the invention comprises the following steps: uniformly mixing bentonite, cordierite and nano carbon black to obtain powder, adding ethanol into the powder, uniformly mixing, adding a binder, and carrying out green body molding to obtain a green body; in a protective gas atmosphere, the green body is subjected to heat preservation at the temperature of 1100-1300 DEG C, and a sample is obtained; and polishing the sample, and spraying aluminum to obtain the carbon composite ceramic linear resistor. According to the invention, cordierite is used as an aggregate, bentonite is used as a sintering aid, and nano carbon black is used as a conductive filler to prepare the carbon ceramic resistance material. The cordierite coarse particles and the fine particle glass phase / carbon black are compounded, and the low thermal expansion coefficient of the cordierite is utilized, so that the thermal stress of the resistance material caused by temperature change is reduced, and the thermal shock resistance and the resistance stability are improved.

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] Overvoltages occur during the operation of high-voltage transmission and transformation systems. To protect the smooth operation of the power system, a closing resistor must be inserted into the line to absorb some of the electrical energy in the grid and convert it into heat, thereby weakening electromagnetic oscillations and limiting overvoltages. Therefore, a closing resistor must possess high-temperature resistance, stable and adjustable resistance, high-voltage resistance, and excellent mechanical properties. Traditional carbon-ceramic linear resistors are composite conductive materials made from aggregates such as bauxite, alumina, and mullite, along with clays such as bentonite and kaolin, and conductive carbon materials such as nanocarbon black and graphite. The materials are then mixed, molded, sintered, surface treated, and coated with electrodes. They offer numerous advantages, including high-temperature resistance, high-voltage resistance, corrosion resistance, zero inductance, a wide resistance range, and high stability. They are currently widely used as closing resistors in power systems.

[0003] With the development of ultra-high voltage (UHV) transmission and transformation systems, line voltages have increased, and the overvoltages experienced by closing resistors have increased. This generates more heat, causing them to rapidly rise to high temperatures and then cool down, subjecting them to extreme temperature fluctuations in a short period of time. However, current carbon ceramic resistors primarily use alumina as an aggregate. Due to alumina's high coefficient of thermal expansion, temperature fluctuations generate greater thermal stress. Excessive temperature fluctuations can lead to reduced strength and even fracture. Poor thermal shock resistance has hampered their further development and application.

[0004] Furthermore, existing ceramic linear resistor technology primarily focuses on improving density and resistivity, as well as increasing the resistor's energy tolerance. For example, Chinese invention patent application number CN202210706840.4, titled "A Carbon Ceramic Closing Resistor and Preparation Process," utilizes a combination of compression molding and cold isostatic pressing. By adjusting the compression and cold isostatic pressing pressures, the performance of the carbon ceramic closing resistor is improved. Chinese invention patent application number CN202110121871.9, titled "A Novel Carbon Composite Ceramic Linear Resistor and Preparation Method thereof," utilizes graphite (with excellent conductivity and positive temperature drift) as the conductive phase, carbon fiber as the conductive and reinforcing phase, and mullite (with a low thermal expansion coefficient) as the aggregate. The resulting carbon composite ceramic linear resistor exhibits zero bulk resistance, high operating temperature, and the ability to withstand higher surge currents and absorb more energy. Pulse energy density is a key quality indicator for carbon ceramic resistors. Instantaneous energy absorption causes the resistor's chip to heat up and crack, so the material requires excellent thermal shock resistance. The thermal shock resistance of a material can be expressed as R = σf (1-ν) / (Eα), where α is the material's thermal expansion coefficient. Therefore, by reducing the thermal expansion coefficient of the material, the thermal stress generated during thermal shock can be reduced, thereby improving thermal shock resistance. For example, in the Chinese invention patent application number CN202311750492.1, entitled "A high-strength, high-thermal-shock-resistant ceramic material, its preparation method, and application," cordierite is added to adjust the material's thermal expansion coefficient and promote sintering. In addition, an appropriate amount of pore-forming agent is added to form micropores to release thermal stress, ensuring crack resistance during water quenching at 200°C. However, the main phase of this ceramic is alumina, and the cordierite addition is only 0.5wt% to 2wt%. For example, in the Chinese invention patent with application number CN201710597667.8, entitled "A method for preparing a low-cost, high-performance, low-expansion ceramic blank and its ceramic products," cordierite is synthesized at high temperature, effectively reducing the thermal expansion coefficient of the ceramic. However, it can only withstand a single water quench at 450°C without cracking. However, its extreme thermal shock resistance is insufficient, and the cordierite content is difficult to accurately control. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention provides a carbon composite ceramic linear resistor and its preparation method. This material utilizes cordierite as the aggregate, bentonite as a sintering aid, and nanocarbon black as the conductive filler to produce the carbon ceramic resistor. Coarse cordierite particles are combined with fine glass phase / carbon black particles. The low thermal expansion coefficient of cordierite is utilized to reduce thermal stress generated by temperature fluctuations in the resistor material, thereby improving thermal shock resistance and resistance stability.

[0006] 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, cordierite, and nanocarbon black are uniformly mixed to obtain a powder. Ethanol is then added to the powder and mixed uniformly. A binder is then added and green compacts are formed to obtain a green compact. Ethanol is selected for its rapid volatilization by rotary evaporation. The powder is composed of the following components in the following volume percentages: 36% to 56% bentonite, 40% to 60% cordierite, and 4% to 7% nanocarbon black, for a total of 100%. For example, the volume percentages of bentonite are 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, and 56%.

[0007] The volume percentage of cordierite is 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, and 60%, but is not limited to the listed values. Other values not listed within the above numerical range are also applicable.

[0008] Under a protective gas atmosphere, the green body is held at 1100°C to 1300°C to obtain a sample; for example, the holding temperature is 1100°C, 1200°C, 1300°C, etc., but is not limited to the listed values, and other values not listed within the above numerical range are also applicable. When heating to the holding temperature, the heating rate from room temperature to 1100°C is 10°C / min, and the heating rate above 1100°C is 5°C / min. The reason for the holding treatment under a protective gas atmosphere in the present invention is that carbon black reacts with oxygen at high temperatures. To ensure stable resistivity, sintering must be carried out in an inert atmosphere, generally nitrogen or argon.

[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 holding time is 2 hours to 4 hours. For example, the holding time is 2 hours, 2.5 hours, 3 hours, 3.5 hours, or 4 hours, but the holding time is not limited to the listed values. Other values not listed within the above range are also applicable.

[0011] In a preferred embodiment of the present invention, the amount of binder added is 5% to 10% of the powder mass. For example, the amount of binder added is 5%, 6%, 7%, 8%, 9%, or 10% of the powder mass, but the amounts are not limited to these values, and other values not listed within the above range are also applicable.

[0012] In a preferred embodiment of the present invention, the binder is polyvinyl alcohol or polyvinyl acetal, for example, polyvinyl acetal is polyvinyl formal.

[0013] In a preferred embodiment of the present invention, the volume ratio of powder to ethanol is 1:3-4, for example, the volume ratio of powder to ethanol is 3:1, 3.2:1, 3.4:1, 3.6:1, 3.8:1, or 4:1.

[0014] In a preferred embodiment of the present invention, the spray thickness of aluminum is 10 μm to 15 μm. For example, the spray thickness of aluminum is 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, and 15 μm. Other values not listed within the above numerical range are also applicable.

[0015] In a preferred embodiment of the present invention, the pressure during the green body molding process is 75 MPa to 100 MPa. For example, the pressure of the green body molding is 75 MPa, 80 MPa, 85 MPa, 90 MPa, 95 MPa, 100 MPa, etc. Other values not listed in the above numerical range are also applicable.

[0016] In a preferred embodiment of the present invention, the mixing time is 10 to 16 hours, for example, the mixing time is 10 hours, 12 hours, 13 hours, 14 hours, 16 hours, etc., and other values not listed within the above numerical range are also applicable. During mixing, the ball-to-material mass ratio is 3:1, and the ball mill speed is 100 to 300 r / min.

[0017] The second object of the present invention is to provide a carbon composite ceramic linear resistor prepared by the above preparation method.

[0018] Compared with the prior art, the present invention has the following beneficial effects: In the present invention, cordierite is used as the aggregate of the ceramic resistor, and is mixed, molded, and sintered with a sintering aid, bentonite, and conductive phase nano-carbon black to form a carbon ceramic linear resistor. Selecting cordierite with a lower thermal expansion coefficient as the ceramic aggregate effectively reduces the thermal expansion coefficient of the carbon ceramic resistor, reduces the expansion deformation caused by heat, and reduces the thermal stress on the material, thereby effectively avoiding the formation of thermal stress cracks or instantaneous fractures in the resistor when it is powered on. It has the characteristics of non-inductive bulk resistance, high operating temperature, and effectively improved thermal shock resistance. In addition, during the preparation of the present invention, the conductive phase nano-carbon black itself hinders sintering and leaves pores, so there is no need to add additional pore-forming agents, and it effectively prevents crack propagation.

[0019] This method has the advantages of simple preparation process, low production cost, good thermal shock resistance, etc. It can meet the needs of modern electronic components for high-performance linear resistors. Compared with the existing technology, it solves the problem of poor thermal shock resistance of existing carbon ceramic linear resistors. DETAILED DESCRIPTION

[0020] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0021] The present invention selects cordierite as aggregate, bentonite as liquid phase, and carbon black as conductive material. Compared with traditional carbon ceramic resistors using alumina as aggregate, cordierite is more easily dissolved in the liquid phase at the same temperature due to its multi-component low melting point characteristics, and has a lower porosity. When the same amount of carbon black is added, the prepared resistor sample has a higher density, and the prepared carbon composite ceramic linear resistor material has a higher strength, which is about 100MPa~140MPa. In addition, due to the high bonding strength between cordierite and the liquid phase, when subjected to thermal shock, cracks appear in the glass phase, and the critical thermal shock temperature difference of cordierite is about 500°C or even higher. The thermal shock resistance of cordierite resistors is better. Cordierite can reduce the overall low thermal expansion coefficient of the material, carbon black acts as a conductive network to improve the thermal conductivity of the material, and carbon black itself hinders the liquid phase from shrinking to form pores, which together improve the thermal shock resistance of the carbon composite ceramic linear resistor material. The carbon composite ceramic linear resistor material prepared in this invention can be used in environments with a resistivity of 10Ω·cm to 200Ω·cm. Compared to conventional alumina ceramic resistors with a thermal shock temperature difference of around 300°C, the carbon composite ceramic linear resistor prepared in this invention has a thermal shock temperature difference of 400-500°C.

[0022] The particle size of the cordierite used in the present invention is 50 μm, the particle size of the nano carbon black is 27 nm, the polyvinyl alcohol is denoted as PVA, and the molecular weight of the polyvinyl alcohol is 1800.

[0023] Example 1 This embodiment provides a method for preparing a carbon composite ceramic linear resistor, which specifically includes the following steps: Step 1: Accurately weigh 60 vol.% cordierite powder, 36 vol.% bentonite, and 4 vol.% nanocarbon black, mix the cordierite, nanocarbon black, and bentonite to obtain a powder, weigh anhydrous ethanol according to a volume ratio of anhydrous ethanol to powder of 3:1, pour it into a ball mill and mix at a ball mill speed of 200 r / min for 12 hours, then dry and sieve to obtain a uniformly mixed powder.

[0024] Step 2: Add a PVA solution with a mass fraction of 5 wt.% to the evenly mixed powder, where the amount of PVA solution added is 10% of the mass of the evenly mixed powder. After grinding and sieving, press the green body using a compression molding method. Use a pressure of 75 MPa for bidirectional pressurization and hold the pressure for 60 seconds. Then place the green body in an oven and dry it at 100°C for 12 hours.

[0025] Step 3: Place the green body prepared in step 2 in a graphite crucible covered with graphite paper, 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.

[0026] Step 4: The sample obtained in step 3 was surface-polished using sandpaper of 200 mesh, 400 mesh, 600 mesh, and 800 mesh, and aluminum was sprayed on the upper and lower surfaces by a thermal sprayer with a thickness of 10 μm and dried in an oven at 100° C. to obtain a carbon composite ceramic linear resistor material.

[0027] Example 2 This embodiment provides a method for preparing a carbon composite ceramic linear resistor, which specifically includes the following steps: Step 1: Accurately weigh 50 vol.% cordierite powder, 46 vol.% bentonite, and 4 vol.% nano-carbon black, mix the cordierite, nano-carbon black, and bentonite to obtain a powder, weigh anhydrous ethanol according to a volume ratio of anhydrous ethanol to powder of 3:1, pour it into a ball mill and mix at a ball mill speed of 200 r / min for 12 hours, then dry and sieve to obtain a uniformly mixed powder.

[0028] Step 2: Add a PVA solution with a mass fraction of 5 wt.% to the evenly mixed powder, where the amount of PVA solution added is 10% of the mass of the evenly mixed powder. After grinding and sieving, press the green body using a compression molding method. Use a pressure of 75 MPa for bidirectional pressurization and hold the pressure for 60 seconds. Then place the green body in an oven and dry it at 100°C for 12 hours.

[0029] Step 3: Place the green body prepared in step 2 in a graphite crucible covered with graphite paper, 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.

[0030] Step 4: The sample obtained in step 3 was surface-polished using sandpaper of 200 mesh, 400 mesh, 600 mesh, and 800 mesh, and aluminum was sprayed on the upper and lower surfaces using a thermal sprayer with a thickness of 10 μm and dried in an oven at 100°C to obtain a carbon composite ceramic linear resistor material.

[0031] Example 3 This embodiment provides a method for preparing a carbon composite ceramic linear resistor, which specifically includes the following steps: Step 1: Accurately weigh 40 vol.% cordierite powder, 56 vol.% bentonite, and 4 vol.% nano-carbon black, mix the cordierite, nano-carbon black, and bentonite to obtain a powder, weigh anhydrous ethanol according to a volume ratio of anhydrous ethanol to powder of 3:1, pour it into a ball mill and mix at a ball mill speed of 200 r / min for 12 hours, then dry and sieve to obtain a uniformly mixed powder.

[0032] Step 2: Add a PVA solution with a mass fraction of 5 wt.% to the evenly mixed powder, where the amount of PVA solution added is 10% of the mass of the evenly mixed powder. After grinding and sieving, press the green body using a compression molding method. Use a pressure of 75 MPa for bidirectional pressurization and hold the pressure for 60 seconds. Then place the green body in an oven and dry it at 100°C for 12 hours.

[0033] Step 3: Place the green body prepared in step 2 in a graphite crucible covered with graphite paper, 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.

[0034] Step 4: The sample obtained in step 3 was surface-polished using sandpaper of 200 mesh, 400 mesh, 600 mesh, and 800 mesh, and aluminum was sprayed on the upper and lower surfaces using a thermal sprayer with a thickness of 10 μm and dried in an oven at 100°C to obtain a carbon composite ceramic linear resistor material.

[0035] Example 4 This embodiment provides a method for preparing a carbon composite ceramic linear resistor, which specifically includes the following steps: Step 1: Accurately weigh 60 vol.% cordierite powder, 36 vol.% bentonite, and 4 vol.% nanocarbon black, mix the cordierite, nanocarbon black, and bentonite to obtain a powder, weigh anhydrous ethanol according to a volume ratio of anhydrous ethanol to powder of 3:1, pour it into a ball mill and mix at a ball mill speed of 200 r / min for 12 hours, then dry and sieve to obtain a uniformly mixed powder.

[0036] Step 2: Add a PVA solution with a mass fraction of 5 wt.% to the evenly mixed powder, where the amount of PVA solution added is 10% of the mass of the evenly mixed powder. After grinding and sieving, press the green body using a compression molding method. Use a pressure of 75 MPa for bidirectional pressurization and hold the pressure for 60 seconds. Then place the green body in an oven and dry it at 100°C for 12 hours.

[0037] Step 3: Place the green body prepared in step 2 in a graphite crucible covered with graphite paper, 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 it from 1100°C to 1200°C at 5°C / min, keep warm for 2h, and finally cool it to room temperature with the furnace.

[0038] Step 4: The sample obtained in step 3 was surface-polished using sandpaper of 200 mesh, 400 mesh, 600 mesh, and 800 mesh, and aluminum was sprayed on the upper and lower surfaces by a thermal sprayer with a thickness of 10 μm. The sample was then dried in an oven at 100° C. to obtain a carbon composite ceramic linear resistor material.

[0039] Example 5 This embodiment provides a method for preparing a carbon composite ceramic linear resistor, which specifically includes the following steps: Step 1: Accurately weigh 60 vol.% cordierite powder, 36 vol.% bentonite, and 4 vol.% nanocarbon black, mix the cordierite, nanocarbon black, and bentonite to obtain a powder, weigh anhydrous ethanol according to a volume ratio of anhydrous ethanol to powder of 3:1, pour it into a ball mill and mix at a ball mill speed of 200 r / min for 12 hours, then dry and sieve to obtain a uniformly mixed powder.

[0040] Step 2: Add a PVA solution with a mass fraction of 5 wt.% to the evenly mixed powder, where the amount of PVA solution added is 10% of the mass of the evenly mixed powder. After grinding and sieving, press the green body using a compression molding method. Use a pressure of 75 MPa for bidirectional pressurization and hold the pressure for 60 seconds. Then place the green body in an oven and dry it at 100°C for 12 hours.

[0041] Step 3: Place the green body prepared in step 2 in a graphite crucible covered with graphite paper, 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 2 hours, and finally cool to room temperature with the furnace.

[0042] Step 4: The sample obtained in step 3 was surface-polished using sandpaper of 200 mesh, 400 mesh, 600 mesh, and 800 mesh, and aluminum was sprayed on the upper and lower surfaces by a thermal sprayer with a thickness of 10 μm and dried in an oven at 100° C. to obtain a carbon composite ceramic linear resistor material.

[0043] Example 6 This embodiment provides a method for preparing a carbon composite ceramic linear resistor, which specifically includes the following steps: Step 1: Accurately weigh 57 vol.% cordierite powder, 36 vol.% bentonite, and 7 vol.% nanocarbon black, mix the cordierite, nanocarbon black, and bentonite to obtain a powder, weigh anhydrous ethanol according to a volume ratio of anhydrous ethanol to powder of 4:1, pour it into a ball mill and mix at a ball mill speed of 200 r / min for 16 hours, then dry and sieve to obtain a uniformly mixed powder.

[0044] Step 2: Add a PVA solution with a mass fraction of 5 wt.% to the evenly mixed powder. The amount of PVA solution added is 5% of the mass of the evenly mixed powder. After grinding and screening, the green body is pressed by molding method. Bidirectional pressurization is performed using a pressure of 100 MPa and the pressure is maintained for 60 seconds. The green body is then placed in an oven and dried at 100°C for 12 hours.

[0045] Step 3: Place the green body prepared in step 2 in a graphite crucible covered with graphite paper, place the crucible in a multi-functional sintering furnace, fill it with nitrogen as a protective atmosphere, raise the temperature from room temperature to 1100°C at 10°C / min, keep it warm for 4 hours, and finally cool it to room temperature with the furnace.

[0046] Step 4: The sample obtained in step 3 was surface-polished using sandpaper of 200 mesh, 400 mesh, 600 mesh, and 800 mesh, and aluminum was sprayed on the upper and lower surfaces by a thermal sprayer with a thickness of 15 μm and dried in an oven at 100° C. to obtain a carbon composite ceramic linear resistor material.

[0047] Example 7 This embodiment provides a method for preparing a carbon composite ceramic linear resistor, which specifically includes the following steps: Step 1: Accurately weigh 57 vol.% cordierite powder, 38 vol.% bentonite, and 5 vol.% nanocarbon black, mix the cordierite, nanocarbon black, and bentonite to obtain a powder, weigh anhydrous ethanol according to a volume ratio of anhydrous ethanol to powder of 4:1, pour it into a ball mill and mix at a ball mill speed of 200 r / min for 10 hours, then dry and sieve to obtain a uniformly mixed powder.

[0048] Step 2: Add 5 wt.% PVA solution to the evenly mixed powder, where the amount of PVA solution added is 7% of the mass of the evenly mixed powder. After grinding and screening, press the green body using a compression molding method. Use a pressure of 80 MPa for bidirectional pressurization and hold the pressure for 60 seconds. Then, place the green body in an oven and dry it at 100°C for 12 hours.

[0049] Step 3: Place the green body prepared in step 2 in a graphite crucible covered with graphite paper, 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 it from 1100°C to 1300°C at 5°C / min, keep warm for 3 hours, and finally cool it to room temperature with the furnace.

[0050] Step 4: The sample obtained in step 3 was surface-polished using sandpaper of 200 mesh, 400 mesh, 600 mesh, and 800 mesh, and aluminum was sprayed on the upper and lower surfaces with a thickness of 12 μm using a thermal sprayer and dried in an oven at 100° C. to obtain a carbon composite ceramic linear resistor material.

[0051] Comparative Example 1 This embodiment provides a method for preparing a carbon composite ceramic linear resistor, which specifically includes the following steps: Step 1: Accurately weigh 60 vol.% alumina powder, 36 vol.% bentonite, and 4 vol.% nano-carbon black, mix the alumina, nano-carbon black, and bentonite to obtain a powder, weigh anhydrous ethanol according to a volume ratio of anhydrous ethanol to powder of 3:1, pour it into a ball mill and mix it at a ball mill speed of 200 r / min, mix for 12 hours, then dry and sieve to obtain a uniformly mixed powder.

[0052] Step 2: Add a PVA solution with a mass fraction of 5 wt.% to the evenly mixed powder, where the amount of PVA solution added is 10% of the mass of the evenly mixed powder. After grinding and sieving, press the green body using a compression molding method. Use a pressure of 75 MPa for bidirectional pressurization and hold the pressure for 60 seconds. Then place the green body in an oven and dry it at 100°C for 12 hours.

[0053] Step 3: Place the green body prepared in step 2 in a graphite crucible covered with graphite paper, 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.

[0054] Step 4: The sample obtained in step 3 was surface-polished using sandpaper of 200 mesh, 400 mesh, 600 mesh, and 800 mesh, and aluminum was sprayed on the upper and lower surfaces by a thermal sprayer with a thickness of 10 μm and dried in an oven at 100° C. to obtain a carbon composite ceramic linear resistor material.

[0055] Performance tests were conducted on the carbon composite ceramic linear resistors prepared in Examples 1 to 7 and Comparative Example 1. The flexural strength was measured using a three-point bending method, and the resistivity was measured using a four-probe method.

[0056] The thermal shock resistance of the sample was tested using the water quenching method: Heating was performed using a resistance wire furnace. Using the equipment's control program, the desired temperature was set between 200°C and 800°C. Specifically, the initial test temperature difference, ΔT, was 200°C. The sample was placed in the resistance wire furnace and heated to the desired temperature at a rate of 10°C / min and held at that temperature for 10 minutes. The furnace door was then opened, the sample removed, and quickly placed in deionized water at 20±3°C for 10 seconds to cool. The sample was then dried at 110°C for 2 hours and allowed to cool naturally to room temperature. The residual flexural strength of the sample was then tested. If the residual flexural strength of the sample after water quenching was higher than 70%, the test temperature difference, ΔT, was increased by 100°C. The above process was repeated until the residual flexural strength of the sample was lower than 70%. The next sample should be tested after the water temperature returned to room temperature. The critical thermal shock temperature difference is the temperature difference at which the residual flexural strength drops to 70% of the pre-thermal shock flexural strength. The resistor was then subjected to an energy injection test with an energy density of 300 J / cm. 3Measure the change in resistivity before and after the experiment. Perform energy injection test on the resistor to test the maximum pulse energy density of the resistor.

[0057] The test performance is shown in Table 1.

[0058] Table 1 Performance data of carbon composite ceramic linear resistors

[0059] Comparing Example 1 and Comparative Example 1, it can be seen that, at the same volume fraction of aggregate addition, the addition of cordierite significantly improves the thermal shock resistance and resistivity stability of the carbon ceramic linear resistor compared to alumina as an aggregate. This is because the thermal expansion coefficient of cordierite is much lower than that of alumina. Under the same temperature change, the thermal expansion difference between cordierite and the glass phase is smaller, resulting in lower thermal stress, reducing the risk of crack initiation and expansion, and improving the thermal shock resistance of the resistor. Cracks will destroy the internal conductive network of the resistor, reducing the number of conductive paths and increasing resistance. Therefore, by introducing cordierite, crack generation is reduced, thereby improving resistivity stability. In Examples 1 to 3, as the cordierite content increases, the critical thermal shock temperature difference of the carbon ceramic linear resistor increases, thermal shock resistance improves, and resistivity stability improves. This is because cordierite reduces the overall thermal expansion coefficient of the ceramic resistor, reducing the thermal stress generated by the material during thermal shock.

[0060] In Examples 3 to 5, as the sintering temperature increases, the liquid phase viscosity decreases, which promotes particle rearrangement, allows for better bonding between the liquid phase and cordierite, and improves both strength and thermal shock resistance.

[0061] In patent CN202311750492.1, cordierite is used as an auxiliary agent to produce a liquid phase to adjust the thermal expansion coefficient of the material and promote the densification of alumina ceramics. The main ceramic body is alumina. Since the strength of cordierite itself is lower than that of alumina, increasing the cordierite content will reduce the overall strength of the material, so the cordierite content is difficult to increase. However, too low a cordierite content will affect the thermal shock resistance, and the water quenching temperature can only reach 200°C, and a higher thermal shock temperature cannot be achieved. However, since the thermal shock resistance requirements for carbon ceramic resistors under actual service conditions are higher than the sample strength requirements, the present invention uses cordierite as a ceramic matrix and adds carbon black as a conductive filler and pore-forming agent while ensuring that the strength meets the service requirements, thereby significantly improving the thermal shock resistance and stability of ceramic resistors.

[0062] Extreme thermal shock resistance here refers to thermal shock temperatures exceeding 450°C, with the sample remaining crack-free after multiple thermal shocks. The ceramic blanks prepared in patent CN201710597667.8 lack extreme thermal shock resistance. In the present invention, carbon black acts as both a conductive material and a pore-forming agent during preparation. Using synthesized cordierite as the raw material and carbon black as a pore-forming agent effectively prevents crack propagation, thereby improving extreme thermal shock resistance.

[0063] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional 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.

[0064] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A method for preparing a carbon composite ceramic linear resistor, characterized in that: The following steps are involved: Bentonite, cordierite and nano carbon black are mixed evenly to obtain powder, ethanol is added to the powder and mixed evenly, a binder is added, and green body molding is performed to obtain a green body after molding; The powder is composed of the following components in volume percentage: bentonite 36% to 56%, cordierite 40% to 60%, nano carbon black 4% to 7%, totaling 100%; The green body was kept at 1100°C to 1300°C under a protective 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 insulation time is 2h~4h.

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

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

5. 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 1:3~4.

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

7. The method for preparing a carbon composite ceramic linear resistor according to claim 1, characterized in that: During the green body forming process, the pressure is 75MPa~100MPa.

8. The method for preparing a carbon composite ceramic linear resistor according to claim 1, characterized in that: The mixing time is 10h~16h.

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

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