Transition metal element doped metamaterial structure SiOC ceramic as well as preparation method and application thereof

Abstract

The invention discloses transition metal element doped metamaterial structure SiOC ceramic as well as a preparation method and application thereof, and relates to the technical field of ceramic. The method comprises the following steps: preparing a SiOC ceramic precursor solution; uniformly dispersing a transition metal element compound in the SiOC ceramic precursor solution to obtain a doped solution; the SiOC precursor polymer is sequentially subjected to room-temperature stirring, curing, heat treatment, ball milling, screening, tabletting and pyrolysis operation, and the transition metal element doped structured SiOC ceramic is obtained. The conductivity of the SiOC ceramic is regulated and controlled by changing the concentration of the doped transition metal compound, the conductivity with the semiconductor level is obtained, the high piezoresistive coefficient is obtained, and therefore the pressure change can be well monitored.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramics, and in particular to a transition metal element-doped metamaterial structure SiOC ceramic, a preparation method thereof, and applications thereof. Background Art

[0002] Mechanization and intelligentization play an indispensable role in industrial production and manufacturing. Sensors play a crucial role in this area, monitoring signals, monitoring data, and alerting to dangers. Typically, sensors based on flexible materials can be used for everyday applications, including pressure monitoring, blood pressure measurement, and low-temperature measurement. However, these sensors still have limitations in stability, mechanical properties, and sensitivity, making them unsuitable for industrial production. Pressure monitoring is crucial in applications such as aerospace, transportation, and energy development. Aerospace sensors require custom materials with oxidation resistance, high temperature resistance, and excellent mechanical properties. These sensors often need to operate in extreme environments, such as high temperature, high pressure, or high-flow media. Pressure sensors with high load capacity, high sensitivity, and environmental tolerance remain scarce. Among various sensor transmission mechanisms, the piezoresistive effect is based on the change in sensor resistance in response to externally applied mechanical stress. This phenomenon has a wide range of sensing applications, including the measurement of pressure, acceleration, and vibration fields. Traditional piezoresistive materials, such as silicon semiconductors, diamond, and germanium, have low sensitivity and operating temperatures below 500°C.

[0003] Functionalized polymer-derived ceramics have excellent oxidation resistance, mechanical properties, and improved electromagnetic properties, and therefore have the potential to become good sensors, such as SiCN, SiC, Si3N4, BN, AlN, SiOC, BCN, etc. Polymer-derived ceramics have the ability to operate for a long time in harsh environments and are expected to be used in temperature, gas, and pressure sensing applications. In addition, the structure can be customized according to different application requirements. Their anti-deformation structure can ensure the integrity and connectivity of the sensing layer and maintain regular sensing capabilities under pressure loads. However, the machinability of ceramic structures is poor. Hard processing usually leads to unnecessary quality degradation. Therefore, it is necessary to explore a feasible, simple, and non-destructive method to prepare customized ceramics. Summary of the Invention

[0004] In view of the deficiencies in the above-mentioned background technology, the present invention mainly solves the technical problems that traditional ceramic sensors are easily damaged during processing, cannot operate stably in harsh environments such as high temperature, have low mechanical strength and poor piezoresistive performance, and at the same time solves the problems of low piezoresistive coefficient and long-term stable cyclic operation of ceramic pressure sensors. The present invention provides a transition metal element doped SiOC ceramic and its preparation method and application. The method regulates the conductivity of SiOC ceramics by changing the concentration of doped transition metal compounds to obtain semiconductor-level conductivity and a higher piezoresistive coefficient, thereby being able to monitor pressure changes well. The conductivity can be increased by 2 to 5 times by regulating the doping concentration and sintering process; the present invention adopts room temperature stirring, curing, heat treatment, ball milling and screening, tableting and pyrolysis operations to prepare ceramic sensors, which are simple to manufacture and have good repeatability.

[0005] The first object of the present invention is to provide a method for preparing a transition metal element-doped structured SiOC ceramic, comprising the following steps: preparing a SiOC ceramic precursor solution; uniformly dispersing a transition metal element compound in a SiOC ceramic precursor solution to obtain a doping solution; The SiOC precursor polymer is sequentially subjected to room temperature stirring, curing, heat treatment, ball milling and screening, tableting, and pyrolysis to obtain transition metal element-doped structured SiOC ceramics; The curing step is to cure the mixture at 130°C to 160°C for 15 to 20 hours and then cool it to room temperature. The heat treatment is carried out at 330-360°C in ultra-high purity argon for 4-6 hours; The pyrolysis operation is to pyrolyze the green body after tableting at 1200-1300°C under argon conditions for 2-4 hours; The transition metal element in the transition metal element compound includes one or more of manganese, chromium, zinc, molybdenum, palladium, cadmium and platinum.

[0006] Preferably, the stirring at room temperature is stirring the doping solution at a rate of 800-1000 rpm / min for 5-10 h.

[0007] Preferably, the ball milling and sieving require grinding the heat-treated sample into powder particles with a size of 0.5-1.5 μm, and then separating the powder and the grinding balls by sieving, wherein the rotation speed during the grinding process is 2500-3000 rpm / min and the time is 12-15 hours.

[0008] Preferably, the tableting is performed by compressing the sieved powder under a uniaxial pressure of 20 MPa and then under a cold isostatic pressure of 200 MPa to form a green body.

[0009] Preferably, during the heat treatment, the heating rate is 1-2°C / min, and the cooling rate is 2-3°C / min.

[0010] Preferably, the transition metal element compound includes one or more of manganese acetylacetonate, chromium nitrate, chromium acetylacetonate, zinc nitrate, zinc acetylacetonate, molybdenum pentachloride, palladium acetylacetonate, cadmium acetylacetonate, and platinum acetylacetonate.

[0011] Preferably, the SiOC ceramic precursor solution is prepared by uniformly dispersing a silicone resin solution in anhydrous ethanol.

[0012] Preferably, the mass ratio of the silicone resin solution to anhydrous ethanol is 2:1.

[0013] The second object of the present invention is to provide a transition metal element doped structured SiOC ceramic.

[0014] The third object of the present invention is to provide a transition metal element doped structured SiOC ceramic for use in a pressure sensor.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a transition metal-doped metamaterial SiOC ceramic, its preparation method, and its application. By doping with transition metal compounds, the present invention dramatically increases the electrical conductivity of SiOC ceramics, reaching semiconductor levels. When subjected to pressure, the semiconductor material within the SiOC ceramic further contacts the conductive phase. When the concentration exceeds the tunneling threshold, a tunneling effect occurs, causing a change in resistance. Therefore, the SiOC ceramic semiconductor material can be used for pressure detection.

[0016] The preparation method provided by the present invention has simple process for preparing SiOC ceramics, good repeatability and low cost.

[0017] The transition metal element-doped SiOC ceramics of the present invention are suitable for large-area preparation.

[0018] The transition metal element-doped structured SiOC ceramics prepared by the present invention are resistant to high temperatures exceeding 1300°C and have good compressive strength. The manufactured polymer precursor ceramics have stable piezoresistive properties. The piezoresistivity of the SiOC ceramics containing transition metal elements is 3 to 5 times that of SiOC ceramics. The ceramics doped with chromium acetylacetonate have a maximum piezoresistive rate of 78.12%.

[0019] This invention can control the conductivity of SiOC ceramics by varying the concentration of doped transition metal compounds, achieving semiconductor-level conductivity and a high piezoresistance coefficient, enabling effective monitoring of pressure changes. By adjusting the doping concentration and sintering process, the conductivity can be increased by 2-5 times.

[0020] The present invention enables the pressure sensor to simultaneously obtain better temperature detection function by doping SiOC ceramics with some transition metal element compounds. For example, manganese acetylacetonate and molybdenum pentachloride have a large resistance change with temperature and a negative temperature coefficient characteristic, indicating that they can be used for temperature detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The resistance change under pressure of SiOC doped with transition metal compounds manganese acetylacetonate, chromium acetylacetonate, and zinc acetylacetonate in Examples 1 to 3; Figure 2 The resistance change under pressure of SiOC after doping with molybdenum pentachloride, a transition metal compound, in Example 4 and Example 8; Figure 3 The resistance change of SiOC doped with calcium acetylacetonate, a non-transition metal compound, under pressure in Comparative Example 1; Figure 4 The resistance change under pressure after SiOC is doped with strontium acetylacetonate, a non-transition metal element compound in Comparative Example 2; Figure 5 The resistance change of SiOC doped with manganese acetylacetonate, a transition metal compound, in Example 1 and cycled 100 times under a pressure of 150N; Figure 6 The compressive strength changes of SiOC ceramics doped with 2% manganese acetylacetonate, chromium acetylacetonate, and zinc acetylacetonate, respectively, provided in Example 1; Figure 7 This is the resistance versus temperature curve of the manganese acetylacetonate-doped SiOC ceramic prepared in Example 4; Figure 8 These are the experimental data of ln(R)-1 / T of the manganese acetylacetonate-doped SiOC ceramics prepared in Example 4 and the data results fitted according to the Steinhart-Hart equation. DETAILED DESCRIPTION

[0022] In order to enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention is further described below with reference to specific embodiments and drawings, but the embodiments are not intended to limit the present invention.

[0023] The present invention is mainly based on structured SiOC ceramics prepared by doping liquid silicone resin with transition metal elements. The process is simple, repeatable and low-cost. Among functional ceramics, PDC has good application prospects. The silicon polymer precursor contained in its main chain can be transformed, so the precursor can be modified to achieve different functions and applications. Functional PDC has high stability, good environmental tolerance and mechanical properties, can maintain its function in harsh environments, avoid catastrophic rupture, and ensure long-term operation safety. The present invention further improves the mechanical properties and piezoresistive properties of SiOC pressure sensors by using transition metal elements to dope SiOC polymer-derived ceramics.

[0024] The purpose of the present invention is to provide a transition metal element-doped metamaterial structure SiOC ceramic and its preparation method and application, so as to solve the technical problems of traditional ceramic sensors such as easy damage during processing, inability to operate stably in harsh environments such as high temperature, low mechanical strength and poor piezoresistive performance, and at the same time solve the problems of low piezoresistive coefficient and long-term stable cyclic operation of ceramic pressure sensors.

[0025] In order to achieve the above object, a first aspect provides a method for preparing a transition metal element-doped structured SiOC ceramic, comprising the following steps: preparing a SiOC ceramic precursor solution; uniformly dispersing a transition metal element compound in a SiOC ceramic precursor solution to obtain a doping solution; The SiOC precursor polymer is sequentially subjected to room temperature stirring, curing, heat treatment, ball milling and screening, tableting, and pyrolysis to obtain transition metal element-doped structured SiOC ceramics; The curing step is to cure the mixture at 130°C to 160°C for 15 to 20 hours and then cool it to room temperature. The heat treatment is carried out at 330-360°C in ultra-high purity argon for 4-6 hours; The pyrolysis operation is to pyrolyze the green body after tableting at 1200-1300°C under argon conditions for 2-4 hours; The transition metal element in the transition metal element compound includes one or more of manganese, chromium, zinc, molybdenum, palladium, cadmium and platinum.

[0026] The SiOC ceramic precursor solution is prepared by uniformly dispersing a silicone resin solution in anhydrous ethanol, wherein the mass ratio of the silicone resin solution to the anhydrous ethanol is 2:1.

[0027] Preparation method of silicone resin solution: 712g of methyltriethoxysilane is used as the starting material, 234g of water, 2.2g of 0.1N hydrochloric acid and 900g of toluene are added, and the temperature is raised to 74~78℃ while stirring, and reflux is maintained for 6 hours. Then, about 1.28g of hexamethyldisilazane is added. The heating is stopped and the stirring is continued for about half an hour, and then the temperature is raised to 75~89℃ to evaporate the ethanol and part of the solvent. After aging for 1.5 hours, the reaction is stopped and cooled to obtain 565g of colorless and transparent silicone resin solution with a resin R / Si value of 1.0.

[0028] The present invention dopes the transition metal compound at a concentration of 2% to 5% by mass relative to the liquid silicone resin. Lower doping levels prevent the formation of an effective conductive phase network after sintering, resulting in lower piezoresistivity. Excessive doping levels can lead to severe phase separation after sintering, reducing the compressive strength and piezoresistivity of the structural ceramic. Therefore, the optimal doping range for the transition metal compound is 2% to 5% by mass of the liquid silicone resin.

[0029] The present invention uses a tabletting method to prepare SiOC ceramics doped with transition metal elements, making the sintered ceramic sheets compact and dense, avoiding damage to the SiOC ceramics caused by other physical processing methods, resulting in defects and low mechanical strength, and the inability to operate stably in harsh environments such as high temperatures.

[0030] The precursor solution prepared by the sol-gel method in the present invention needs to be further solidified after being stirred evenly, which is achieved by silanol condensation to form silicon-oxygen chains. When the condensation reaction is in progress, the silanol concentration gradually decreases, which increases steric hindrance and poor fluidity, resulting in a decrease in the reaction rate. At the same time, this process allows the transition metal element compound and the silicone resin to fully undergo polymerization reaction, thereby adding the metal element to the R chain. Among them, the heat treatment is mainly to degrade, unzip and rearrange the silicone resin side chain. Ball milling and screening are to refine and powder the block sample in preparation for pressing sheet shape testing. The two-step tableting of uniaxial compression and cold isostatic pressing is to ensure full contact between the powders and reduce the atomic distance. The last step of pyrolysis is to allow SiOC to undergo SiOC→SiO2+C+SiC phase transformation under high temperature and non-oxygen conditions, precipitate a conductive phase, improve conductivity, and enhance its piezoresistive rate and responsiveness. Each step in the experiment is mutually connected and paves the way for the next step, and none of them can be missing.

[0031] The room temperature stirring is to stir the doping solution at a rate of 800-1000 rpm / min for 5-10 h.

[0032] The ball milling and sieving process requires grinding the heat-treated sample into powder particles with a size of 0.5-1.5 μm, and then separating the powder and the grinding balls by sieving. During the grinding process, the rotation speed is 2500-3000 rpm / min and the time is 12-15 hours.

[0033] Tableting was performed by compressing the sieved powder under a uniaxial pressure of 20 MPa and then under a cold isostatic pressure of 200 MPa to form a green compact.

[0034] During heat treatment, the heating rate is 1~2℃ / min and the cooling rate is 2~3℃ / min.

[0035] The transition metal element compound includes one or more of manganese acetylacetonate, chromium nitrate, chromium acetylacetonate, zinc nitrate, zinc acetylacetonate, molybdenum pentachloride, palladium acetylacetonate, cadmium acetylacetonate, and platinum acetylacetonate.

[0036] It should be noted that transition metal doping of SiOC ceramics forms a large network of conductive phases within the ceramic, significantly increasing the sample's conductivity to semiconductor levels. Under pressure, the distance between the conductive phases decreases, allowing electrons to further penetrate the barriers and conduct electricity due to quantum tunneling, further reducing the resistance. This decreases nonlinearly with pressure, and when the distance between the conductive phases cannot be further reduced, the resistance stops decreasing. Transition metal doping creates a pinning effect within the SiOC ceramic, significantly increasing its compressive strength and Young's modulus.

[0037] The present invention proposes to prepare SiOC ceramics by using room temperature stirring, curing, heat treatment, ball milling and screening, tableting, and pyrolysis operations, combined with transition metal element doping. The excellent mechanical strength and piezoresistive properties of SiOC ceramics overcome the shortcomings of pure SiOC, such as low mechanical strength and poor piezoresistive properties. In addition, the use of a secondary tableting method to prepare SiOC ceramics doped with transition metal elements makes the sintered ceramic sheets compact and dense, which overcomes the shortcomings of traditional ceramic preparation methods and makes the preparation simple and reproducible. The temperature resistance of the transition metal element-containing SiOC ceramics prepared in the present invention is further improved, which solves the high temperature resistance shortcomings of traditional sensors and makes the conductivity of SiOC ceramics easy to adjust. During the use of the transition metal element-doped SiOC ceramics in pressure sensors, some transition metal element compounds doped SiOC ceramics can enable the pressure sensor to simultaneously obtain better temperature detection function. For example, manganese acetylacetonate and molybdenum pentachloride have a large resistance change with temperature and have a negative temperature coefficient characteristic.

[0038] During the preparation process of the SiOC ceramic precursor solution, it is necessary to prepare the SiOC polymer-derived ceramic precursor solution through organic solvent dissolution and doping methods; thereby obtaining a highly sensitive modified SiOC ceramic pressure sensor with extreme environmental tolerance.

[0039] It is necessary to prepare a SiOC polymer-derived ceramic precursor solution through organic solvent dissolution and doping methods; thereby obtaining a highly sensitive modified SiOC ceramic pressure sensor with extreme environmental tolerance.

[0040] Compounds that can be dissolved in the SiOC precursor solution include chlorides, nitric acid compounds and acetylacetone compounds of manganese, chromium, zinc, molybdenum, palladium, cadmium and platinum.

[0041] The SiOC ceramic precursor solution in the present invention is a polymer-derived ceramic precursor solution; The polymer-derived ceramic precursor solution can be: A SiOC-derived ceramic polymer precursor solution doped with manganese acetylacetonate, chromium nitrate, and chromium acetylacetonate, wherein the mass of the doped manganese acetylacetonate, chromium nitrate, and chromium acetylacetonate is 2% to 5% of the mass of the liquid silicone resin.

[0042] Alternatively, a SiOC-derived ceramic polymer precursor solution is doped with zinc nitrate, zinc acetylacetonate, and molybdenum pentachloride, wherein the weight of the doped zinc nitrate, zinc acetylacetonate, and molybdenum pentachloride is 2% to 5% of the weight of the liquid silicone resin.

[0043] Alternatively, a SiOC-derived ceramic polymer precursor solution is doped with palladium acetylacetonate, cadmium acetylacetonate, or platinum acetylacetonate, wherein the mass of the doped palladium acetylacetonate, cadmium acetylacetonate, or platinum acetylacetonate is 2% to 5% of the mass of the liquid silicone resin.

[0044] In order to completely dissolve the added transition metal element compound, the polymer-derived ceramic precursor solution was stirred for 6 hours after doping.

[0045] The undoped SiOC preform prepared after pyrolysis treatment yields an undoped SiOC sample. However, its inherent electrical conductivity is poor, and the concentration of conductive phases, such as free carbon, is low, resulting in a small change in resistance under pressure and a small piezoresistive coefficient. By doping the SiOC ceramic with 2% to 5% of the liquid silicone resin content in transition metal compounds, the phase transformation is promoted, increasing the concentration of the conductive phase. Its conductivity is raised to the semiconductor level, resulting in a large change in resistance under pressure and a large piezoresistive coefficient. However, if the concentration of the doped transition metal compound is too high, its conductivity is high, approaching the conductor level, and the resistance change under pressure is small or unchanged. Therefore, doping with a certain concentration of transition metal compounds to achieve semiconductor conductivity is the key to preparing SiOC pressure sensors.

[0046] The SiOC preform doped with a transition metal element compound is pyrolyzed at 1200-1300° C. in argon for 2-4 hours, and then cooled to room temperature in the furnace to obtain a SiOC ceramic doped with the transition metal element.

[0047] The figures in the present specification illustrate only the resistance change under pressure after doping SiOC with some non-transition metal compounds and transition metal compounds, the changes in compressive strength and conductivity of SiOC doped with different proportions of chromium acetylacetonate, and the resistance change with temperature after doping SiOC with some transition metal compounds, as well as the fitting results, to illustrate the practical effects of the present invention.

[0048] A second aspect of the present invention provides a transition metal element-doped structured SiOC ceramic.

[0049] A third aspect of the present invention provides a transition metal element-doped structured SiOC ceramic for use in a pressure sensor.

[0050] It should be noted that the experimental methods used in the present invention are conventional methods unless otherwise specified, and the reagents and materials used are commercially available unless otherwise specified. Among them, the silicone resin solution was purchased from Hubei Xinsihai Chemical Co., Ltd.

[0051] Example 1 A method for preparing transition metal element-doped SiOC ceramics comprises the following steps: 1. Take 50g of silicone resin solution and add it to a beaker. Then add 25g of anhydrous ethanol according to the mass ratio of silicone resin solution to anhydrous ethanol of 2:1. Stir at room temperature for 2h to obtain SiOC ceramic precursor solution.

[0052] 2. Add 1 g of manganese acetylacetonate transition metal compound to the SiOC ceramic precursor solution, and then stir at a rate of 1000 rpm / min for 6 h to allow the precursor solution to fully undergo polymerization reaction.

[0053] 3. Curing the mixture at 150°C for 15 h, and then cooling it to room temperature.

[0054] 4. Heat treatment was performed at 350°C in ultra-high purity argon for 4 hours, with a heating rate of 1°C / min and a cooling rate of 2°C / min.

[0055] 5. Grind the heat-treated solid into powder particles of about 1 μm at a speed of 3000 rpm / min for 12 h; separate the powder and grinding balls by sieving.

[0056] 6. The ball-milled and sieved powders were compressed under a uniaxial pressure of 20 MPa and then under a cold isostatic pressure of 200 MPa to form green compacts.

[0057] 7. The pressed green body is pyrolyzed at 1300°C under argon for 2 hours to convert the green body into SiOC ceramics doped with transition metal elements.

[0058] According to the method provided in this embodiment, SiOC ceramics doped with the corresponding transition metal elements were prepared by adding 2% of manganese acetylacetonate relative to the mass of the liquid resin.

[0059] Example 2 A method for preparing transition metal element-doped SiOC ceramics comprises the following steps: 1. Take 60g of silicone resin solution and add it to a beaker. Then add 30g of anhydrous ethanol according to the mass ratio of silicone resin solution to anhydrous ethanol of 2:1. Stir at room temperature for 2h to obtain SiOC ceramic precursor solution.

[0060] 2. Add 1.2 g of chromium acetylacetonate transition metal compound to the SiOC ceramic precursor solution, and then stir at 900 rpm / min for 6 h to allow the precursor solution to fully undergo polymerization reaction.

[0061] 3. Curing the mixture at 160°C for 18 h, and then cooling to room temperature.

[0062] 4. Heat treatment was performed at 330°C in ultra-high purity argon for 5 hours, with a heating rate of 2°C / min and a cooling rate of 3°C / min.

[0063] 5. Grind the heat-treated solid into powder particles of about 1 μm at a speed of 2500 rpm / min for 15 h; separate the powder and grinding balls by sieving.

[0064] 6. The ball-milled and sieved powders were compressed under a uniaxial pressure of 20 MPa and then under a cold isostatic pressure of 200 MPa to form green compacts.

[0065] 7. The pressed green body is pyrolyzed at 1300°C under argon for 2 hours to convert the green body into SiOC ceramics doped with transition metal elements.

[0066] According to the method provided in this embodiment, SiOC ceramics doped with the corresponding transition metal elements were prepared by adding 2% of chromium acetylacetonate relative to the mass of the liquid resin.

[0067] Example 3 A method for preparing a transition metal element-doped structured SiOC ceramic comprises the following steps: 1. Take 80g of silicone resin solution and add it to a beaker. Then add 40g of anhydrous ethanol according to the mass ratio of silicone resin solution to anhydrous ethanol of 2:1. Stir at room temperature for 2h to obtain SiOC ceramic precursor solution.

[0068] 2. Add 1.6 g of zinc acetylacetonate transition metal compound to the SiOC ceramic precursor solution, and then stir at a rate of 1000 rpm / min for 6 h to allow the precursor solution to fully undergo polymerization reaction.

[0069] 3. Curing the mixture at 140 °C for 20 h, and then cooling it to room temperature.

[0070] 4. Heat treatment was performed at 360°C in ultra-high purity argon for 6 hours, with a heating rate of 1°C / min and a cooling rate of 3°C / min.

[0071] 5. Grind the heat-treated solid into powder particles of about 1 μm at a speed of 2800 rpm / min for 13 h; separate the powder and grinding balls by sieving.

[0072] 6. The ball-milled and sieved powders were compressed under a uniaxial pressure of 20 MPa and then under a cold isostatic pressure of 200 MPa to form green compacts.

[0073] 7. The pressed green body is pyrolyzed at 1300°C under argon for 3 hours to convert the green body into SiOC ceramics doped with transition metal elements.

[0074] According to the method provided in this embodiment, by adding 2% of zinc acetylacetonate relative to the mass of the liquid resin, the corresponding transition metal element-doped SiOC ceramics were prepared.

[0075] Example 4 A method for preparing a transition metal element-doped structured SiOC ceramic comprises the following steps: 1. Take 70g of silicone resin solution and add it to a beaker. Then add 35g of anhydrous ethanol according to the mass ratio of silicone resin solution to anhydrous ethanol of 2:1. Stir at room temperature for 2h to obtain SiOC ceramic precursor solution.

[0076] 2. Add 2.1 g of molybdenum pentachloride transition metal compound to the SiOC ceramic precursor solution, and then stir at 800 rpm / min for 6 h to allow the precursor solution to fully undergo polymerization reaction.

[0077] 3. Curing the mixture at 130 °C for 20 h, and then cooling to room temperature.

[0078] 4. Heat treatment was performed at 340°C in ultra-high purity argon for 6 hours, with a heating rate of 2°C / min and a cooling rate of 2°C / min.

[0079] 5. Grind the heat-treated solid into powder particles of about 1 μm at a speed of 2900 rpm / min for 14 h; separate the powder and grinding balls by sieving.

[0080] 6. The ball-milled and sieved powders were compressed under a uniaxial pressure of 20 MPa and then under a cold isostatic pressure of 200 MPa to form green compacts.

[0081] 7. The pressed green body is pyrolyzed at 1200°C under argon for 4 hours to convert the green body into SiOC ceramics doped with transition metal elements.

[0082] According to the method provided in this embodiment, SiOC ceramics doped with corresponding transition metal elements were prepared by adding 3% of molybdenum pentachloride relative to the mass of the liquid resin.

[0083] Example 5 A method for preparing a transition metal element-doped structured SiOC ceramic comprises the following steps: 1. Take 60g of silicone resin solution and add it to a beaker. Then add 30g of anhydrous ethanol according to the mass ratio of silicone resin solution to anhydrous ethanol of 2:1. Stir at room temperature for 2h to obtain SiOC ceramic precursor solution.

[0084] 2. Add 2.4 g of cadmium acetylacetonate transition metal compound to the SiOC ceramic precursor solution, and then stir at a rate of 1000 rpm / min for 6 h to allow the precursor solution to fully undergo polymerization reaction.

[0085] 3. Curing the mixture at 150 °C for 18 h, and then cooling to room temperature.

[0086] 4. Heat treatment was performed at 350°C in ultra-high purity argon for 5 hours, with a heating rate of 2°C / min and a cooling rate of 3°C / min.

[0087] 5. Grind the heat-treated solid into powder particles of about 1 μm at a speed of 3000 rpm / min for 15 h; separate the powder and grinding balls by sieving.

[0088] 6. The ball-milled and sieved powders were compressed under a uniaxial pressure of 20 MPa and then under a cold isostatic pressure of 200 MPa to form green compacts.

[0089] 7. The pressed green body is pyrolyzed at 1250°C under argon for 2 hours to convert the green body into SiOC ceramics doped with transition metal elements.

[0090] According to the method provided in this embodiment, SiOC ceramics doped with corresponding transition metal elements were prepared by adding cadmium acetylacetonate in an amount of 4% relative to the mass of the liquid resin.

[0091] Example 8 The same as Example 4, except that 2.8 g of molybdenum pentachloride transition metal element compound is added to the SiOC ceramic precursor solution.

[0092] Comparative Example 1 The same as Example 1, except that calcium acetylacetonate is used instead of manganese acetylacetonate.

[0093] Comparative Example 2 The same as Example 1, except that strontium acetylacetonate is used instead of chromium acetylacetonate.

[0094] In order to illustrate the relevant properties of the transition metal element doped SiOC ceramic provided by the present invention, it is described in conjunction with the accompanying drawings.

[0095] Figure 1 The resistance change under pressure after SiOC is doped with the transition metal element compound manganese acetylacetonate in Example 1; Figure 1 The resistance change under pressure after doping SiOC with the transition metal element compound chromium acetylacetonate in Example 2; Figure 1 The resistance change under pressure after the transition metal element compound zinc acetylacetonate is doped with SiOC in Example 3; wherein 2h and 8h represent the thermal decomposition holding time of the transition metal element compounds manganese acetylacetonate, chromium acetylacetonate and zinc acetylacetonate at 1300°C.

[0096] Figure 2 The resistance changes under pressures of 0-800N are shown in Example 4, where 3% of the transition metal compound of molybdenum pentachloride is doped with SiOC, and in Example 8, where 4% of the transition metal compound of molybdenum pentachloride is doped with SiOC.

[0097] Figure 3 The resistance change of SiOC doped with calcium acetylacetonate, a non-transition metal element compound, under pressure in Comparative Example 1; Figure 4 The resistance change under pressure after SiOC is doped with strontium acetylacetonate, a non-transition metal element compound in Comparative Example 2; from Figures 1 to 4The results show that the piezoresistivity of SiOC doped with transition metal compounds manganese acetylacetonate and chromium acetylacetonate reaches 84.62% and 49.43%, respectively. The piezoresistivity of SiOC doped with zinc acetylacetonate and molybdenum pentachloride reaches 34.66% and 74.15%, respectively. In contrast, the piezoresistivity of SiOC doped with calcium acetylacetonate and strontium acetylacetonate, both non-transition metal compounds, is 5.57% and 8.68%, respectively. The piezoresistivity of SiOC doped with transition metal compounds is 6 to 15 times that of non-transition metal compound-doped SiOC, fully demonstrating the beneficial effect of transition metal compound-doped SiOC on improving piezoresistivity.

[0098] Figure 5 The resistance change of the SiOC ceramic doped with 2% manganese acetylacetonate provided in Example 1 after 100 stable operations at 150N fully demonstrates the beneficial effect of transition metal element compounds on improving the piezoresistive performance of the SiOC pressure sensor and maintaining long-term stable operating performance.

[0099] Figure 6 Compressive strength changes of SiOC ceramics doped with 2% manganese acetylacetonate, chromium acetylacetonate, and zinc acetylacetonate, respectively, provided in Examples 1, 2, and 3. Wherein, 2h and 8h represent the pyrolysis holding time of transition metal element compounds manganese acetylacetonate, chromium acetylacetonate, and zinc acetylacetonate at 1300°C.

[0100] from Figure 6 It can be seen that under the same doping content and pyrolysis holding time, the sample doped with chromium acetylacetonate has the highest compressive strength, exceeding 40 MPa, while the sample doped with manganese acetylacetonate has the lowest compressive strength. At the same doping content, the strength of the samples doped with the three transition metal elements after 2 hours of pyrolysis holding exceeds that after 8 hours of pyrolysis holding. There is no direct correlation between compressive strength and piezoresistivity, but it is mainly related to phase transformation and conductivity.

[0101] Figure 7 This is the resistance variation curve of the SiOC ceramic doped with manganese acetylacetonate prepared in Example 1; Figure 8 The experimental data of ln(R)-1 / T of the manganese acetylacetonate-doped SiOC ceramic prepared in Example 1 and the data results fitted according to the Steinhart-Hart equation; Figure 7 and Figure 8 It is fully demonstrated that doping with transition metal element compounds can make SiOC have negative temperature coefficient characteristics, which can be used for temperature detection.

[0102] The present invention describes preferred embodiments and their effects. However, those skilled in the art, once informed of the basic inventive concept, may make additional changes and modifications to these embodiments. Therefore, it is intended that the appended claims be interpreted to include the preferred embodiments as well as all changes and modifications that fall within the scope of the invention.

[0103] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing structured SiOC ceramics doped with transition metal elements, characterized in that: The following steps are involved: preparing a SiOC ceramic precursor solution; uniformly dispersing a transition metal element compound in a SiOC ceramic precursor solution to obtain a doping solution; The SiOC precursor polymer is sequentially subjected to room temperature stirring, curing, heat treatment, ball milling and screening, tableting, and pyrolysis to obtain transition metal element-doped structured SiOC ceramics; The curing step is to cure the mixture at 130°C to 160°C for 15 to 20 hours and then cool it to room temperature. The heat treatment is carried out at 330-360°C in ultra-high purity argon for 4-6 hours; The pyrolysis operation is to pyrolyze the green body after tableting at 1200-1300°C under argon conditions for 2-4 hours; The transition metal element in the transition metal element compound includes one or more of manganese, chromium, zinc, molybdenum, palladium, cadmium and platinum.

2. The method for preparing the transition metal element-doped structured SiOC ceramic according to claim 1, characterized in that: The room temperature stirring is to stir the doping solution at a rate of 800-1000 rpm / min for 5-10 h.

3. The method for preparing the transition metal element-doped structured SiOC ceramic according to claim 1, characterized in that: The ball milling and sieving process requires grinding the heat-treated sample into powder particles with a size of 0.5-1.5 μm, and then separating the powder and the grinding balls by sieving. During the grinding process, the rotation speed is 2500-3000 rpm / min and the time is 12-15 hours.

4. The method for preparing the transition metal element-doped structured SiOC ceramic according to claim 1, characterized in that: Tableting was performed by compressing the sieved powder under a uniaxial pressure of 20 MPa and then under a cold isostatic pressure of 200 MPa to form a green compact.

5. The method for preparing the transition metal element-doped structured SiOC ceramic according to claim 1, characterized in that: During heat treatment, the heating rate is 1~2℃ / min and the cooling rate is 2~3℃ / min.

6. The method for preparing the transition metal element-doped structured SiOC ceramic according to claim 1, characterized in that: The transition metal element compound includes one or more of manganese acetylacetonate, chromium nitrate, chromium acetylacetonate, zinc nitrate, zinc acetylacetonate, molybdenum pentachloride, palladium acetylacetonate, cadmium acetylacetonate, and platinum acetylacetonate.

7. The method for preparing the transition metal element-doped structured SiOC ceramic according to claim 1, characterized in that: The SiOC ceramic precursor solution is prepared by uniformly dispersing a silicone resin solution in anhydrous ethanol.

8. The method for preparing the transition metal element-doped structured SiOC ceramic according to claim 7, characterized in that: The mass ratio of silicone resin solution to anhydrous ethanol is 2:

1.

9. A transition metal element-doped structured SiOC ceramic prepared by the method according to any one of claims 1 to 8.

10. Use of the transition metal element-doped structured SiOC ceramic according to claim 9 in a pressure sensor.

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