Silicon nitride composite ceramic material for insulating support and preparation method thereof

Abstract

A silicon nitride composite ceramic material for insulating support and its preparation method belong to the technical field of silicon nitride composite ceramic materials, overcoming the defects of low toughness and insufficient temperature stability of volume resistivity of silicon nitride ceramic materials. The preparation method of the silicon nitride composite ceramic material for insulating support of the present invention comprises the following steps: Step 1, mixing raw materials to obtain a mixed powder; the silicon nitride powder comprises a first silicon nitride powder and a second silicon nitride powder; the average particle size D50 of the first silicon nitride powder is 0.1-0.5 μm; the average particle size D50 of the second silicon nitride powder is 0.7-1.2 μm; the mass ratio of the first silicon nitride powder to the second silicon nitride powder is (1-2):1; Step 2, pressing and forming a ceramic body; Step 3, in a nitrogen atmosphere, keeping the temperature at 1550-1650°C for 2-4 hours; keeping the temperature at 1780-1850°C for 2-4 hours; cooling to 1200-1400°C and keeping the temperature for 2-4 hours. The silicon nitride composite ceramic material has high toughness and temperature stability of resistivity.

Description

Technical Field

[0001] The present invention belongs to the technical field of silicon nitride composite ceramic materials, and in particular relates to a silicon nitride composite ceramic material for insulating support and a preparation method thereof. Background Art

[0002] Ultra-high voltage direct current (UHVDC) transmission is a key means of high-voltage, large-capacity, long-distance power transmission and grid interconnection in my country, and is of great significance to the development of my country's energy landscape. Gas-insulated metal-enclosed transmission lines have the advantages of large transmission capacity, small footprint, high operational stability, and environmental friendliness. Buried directly underground or in tunnels, they can solve transmission problems in special geographical environments and are an effective alternative to overhead transmission lines and cables. Pot-type and post insulators are the most critical insulating structures of gas-insulated equipment. Compared with the insulating gas, their insulation strength is relatively low, making them the insulation weak point of gas-insulated equipment. In recent years, surface flashover failures of pot-type and post insulators have frequently occurred under high pressure, strong electric fields, and large temperature gradients.

[0003] Silicon nitride ceramics have the advantages of excellent insulation properties, high hardness, high strength, and low thermal expansion coefficient. They have great potential for application in gas-insulated equipment. However, their toughness is relatively insufficient. In high-seismic intensity areas such as southeastern Tibet, there is a risk of fracture under the combined action of electric fields and temperature fields. In addition, their resistivity is unstable at the service temperature of gas-insulated equipment (60-100°C), which will cause electric field distortion. Therefore, there is an urgent need to develop silicon nitride ceramic materials with high toughness and low temperature drift for the service environment of ultra-high voltage gas-insulated equipment. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defects of low toughness and insufficient volume resistivity temperature stability of silicon nitride ceramic materials used in ultra-high voltage gas insulation equipment in the prior art, thereby providing a silicon nitride composite ceramic material for insulation support with high toughness, high resistivity and temperature stability and a preparation method thereof.

[0005] To this end, the present invention provides the following technical solutions.

[0006] In a first aspect, the present invention provides a method for preparing a silicon nitride composite ceramic material for insulating support, comprising the following steps:

[0007] Step 1: mixing silicon nitride powder, a sintering aid and a binder to obtain a mixed powder;

[0008] The silicon nitride powder includes a first silicon nitride powder and a second silicon nitride powder; the average particle size D50 of the first silicon nitride powder is 0.1 to 0.5 μm; the average particle size D50 of the second silicon nitride powder is 0.7 to 1.2 μm; the mass ratio of the first silicon nitride powder to the second silicon nitride powder is (1 to 2):1;

[0009] Step 2: pressing the mixed powder into a shape to obtain a ceramic body;

[0010] Step 3: Sintering in a protective atmosphere;

[0011] The step 3 comprises:

[0012] Step 1: In nitrogen atmosphere, keep the temperature at 1550-1650℃ for 2-4h;

[0013] Step 2: Heat to 1780-1850℃ and keep warm for 2-4h;

[0014] Step 3: Cool down to 1200-1400℃ and keep warm for 2-4h.

[0015] Furthermore, step 1 satisfies at least one of the following conditions:

[0016] (1) The mass ratio of the silicon nitride powder to the sintering aid is (84-94): (6-16);

[0017] (2) The binder is 1 to 2 wt% of the mass of the silicon nitride powder;

[0018] (3) The binder comprises at least one of polyvinyl butyral or polyvinyl alcohol;

[0019] (4) The α-phase content in the silicon nitride powder is ≥95wt%.

[0020] Furthermore, the sintering aid includes Y2O3, Al2O3 and SiO2;

[0021] The mass ratio of Y2O3, Al2O3 and SiO2 is (3-5): (3-5): 2.

[0022] Furthermore, at least one of the following conditions is met:

[0023] (1) The first step comprises: raising the temperature to 1200-1300°C at a rate of 10-15°C / min under a nitrogen atmosphere, then raising the temperature to 1550-1650°C at a rate of 3-5°C / min, and holding the temperature for 2-4 hours;

[0024] (2) The heating rate in the second step is 5-10°C / min;

[0025] (3) The cooling rate in the third step is 5-10°C / min;

[0026] (4) After the third step of heat preservation, cool down to room temperature at a rate of 10-15°C / min.

[0027] Furthermore, the pressing in step 2 includes dry pressing and cold isostatic pressing.

[0028] Furthermore, the dry pressing pressure is 50-100 MPa.

[0029] Furthermore, the pressure of the cold isostatic pressing is 200-250 MPa.

[0030] Furthermore, the step 2 further comprises the step of degreasing the ceramic body;

[0031] Preferably, the degreasing treatment is carried out at 450-550° C. for 8-10 hours.

[0032] Furthermore, the step 1 includes: mixing silicon nitride powder, a sintering aid, and a binder according to a ratio, and ball milling the mixture to obtain a mixed powder;

[0033] Optionally, the ball milling media for the ball milling treatment include silicon nitride balls and / or zirconium oxide balls;

[0034] Preferably, the size of the ball milling medium is 2-5 mm, and the ball-to-material ratio is controlled to be (3-4):1;

[0035] Optionally, the dispersion medium for ball milling is anhydrous ethanol;

[0036] Optionally, the ball milling speed is 200-400 r / min.

[0037] In a second aspect, the present invention provides a silicon nitride composite ceramic material for insulating support prepared according to the preparation method.

[0038] The technical solution of the present invention has the following advantages:

[0039] 1. The preparation method of the silicon nitride composite ceramic material for insulating support of the present invention comprises the following steps: Step 1, mixing silicon nitride powder, a sintering aid and a binder to obtain a mixed powder; the silicon nitride powder comprises a first silicon nitride powder and a second silicon nitride powder; the average particle size D50 of the first silicon nitride powder is 0.1-0.5 μm; the average particle size D50 of the second silicon nitride powder is 0.7-1.2 μm; the mass ratio of the first silicon nitride powder to the second silicon nitride powder is (1-2):1; Step 2, pressing the mixed powder into a shape to obtain a ceramic body; Step 3, sintering in a protective atmosphere; Step 3 comprises: Step 1, keeping the temperature at 1550-1650°C for 2-4 hours in a nitrogen atmosphere; Step 2, heating to 1780-1850°C and keeping the temperature for 2-4 hours; Step 3, cooling to 1200-1400°C and keeping the temperature for 2-4 hours.

[0040] The present invention uses silicon nitride powder as the main raw material and obtains a bimodal particle size distribution powder by grading powders of different particle sizes. During the high-temperature sintering process, the bimodal particle size powder is easy to rearrange the particles, and when the α-phase silicon nitride powder is transformed into the β-phase silicon nitride powder, it is easy to form self-toughening bimodal particle size β-phase columnar crystals, thereby improving the fracture toughness of the silicon nitride composite ceramic material.

[0041] After achieving initial densification at 1550-1650°C, the temperature is raised to 1780-1850°C and maintained to further promote the growth and densification of β-phase columnar crystals. The temperature is then lowered to 1200-1400°C and maintained to promote grain boundary phase recrystallization and improve the temperature stability of the resistivity of the silicon nitride composite ceramic. This ensures that the silicon nitride composite ceramic material of the present invention maintains a high resistivity at the service temperature of gas-insulated equipment (60-100°C), thus preventing electric field distortion at the service temperature.

[0042] 2. The sintering aid of the present invention comprises Y2O3, Al2O3, and SiO2 in a ratio of (3-5):(3-5):2. The addition of the Y2O3, Al2O3, and SiO2 ternary composite sintering aid forms a liquid phase during sintering that promotes the rearrangement and phase transformation of α-phase silicon nitride powder particles, lowers the sintering temperature, and achieves densification of the silicon nitride ceramic. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0044] Figure 1 This is a scanning electron microscope photograph of the product of Example 1;

[0045] Figure 2 This is a scanning electron microscope photograph of the product of Comparative Example 1;

[0046] Figure 3 The XRD patterns of the products of Example 1 and Comparative Example 3 are shown. DETAILED DESCRIPTION

[0047] The following examples are provided for a better understanding of the present invention and are not intended to limit the best mode of implementation. They do not limit the content and scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

[0048] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0049] The polyvinyl alcohol in the following examples and comparative examples was purchased from Kemp (Xiamen) New Materials Co., Ltd. with a purity of >99%; the first silicon nitride powder was SN-E10 from Ube, Japan; and the second silicon nitride powder was SN-E05 from Ube, Japan.

[0050] Example 1

[0051] This embodiment provides a method for preparing a silicon nitride composite ceramic material for insulating support, comprising the following steps:

[0052] Step 1: Mix 45 g of the first silicon nitride powder, 45 g of the second silicon nitride powder, 5 g of Y2O3, 3 g of Al2O3, 2 g of SiO2 and 1.8 g of polyvinyl alcohol, and ball-mill to obtain a mixed powder.

[0053] The α-phase content in the first silicon nitride powder and the second silicon nitride powder is ≥95 wt %. The average particle size D50 of the first silicon nitride powder is 0.3 μm, and the average particle size D50 of the second silicon nitride powder is 1.0 μm.

[0054] The ball milling medium is silicon nitride balls, which are 3 mm and 5 mm in size and are mixed in a mass ratio of 1:1. The ball-to-material ratio is controlled to be 3:1. The ball milling speed is 300 r / min, and the dispersion medium is anhydrous ethanol.

[0055] Step 2: dry-press the mixed powder obtained in step 1 at 50 MPa for 300 seconds, and then cold-isostatically press at 250 MPa for 300 seconds to obtain a ceramic body.

[0056] The ceramic body was degreased at 500°C for 10 h.

[0057] Step 3: Raise the temperature of the degreased ceramic body to 1200°C at a rate of 10°C / min under a nitrogen atmosphere, then raise the temperature to 1650°C at a rate of 5°C / min, and keep the temperature for 2 hours;

[0058] Then increase the temperature to 1825℃ at a rate of 5℃ / min and keep it at this temperature for 3h;

[0059] Then the temperature was lowered to 1300°C at 5°C / min and kept at this temperature for 3h;

[0060] Then the temperature was lowered to room temperature at 10°C / min.

[0061] Example 2

[0062] This embodiment provides a method for preparing a silicon nitride composite ceramic material for insulating support, comprising the following steps:

[0063] Step 1: Mix 42 g of the first silicon nitride powder, 42 g of the second silicon nitride powder, 8 g of Y2O3, 4.8 g of Al2O3, 3.2 g of SiO2 and 1.68 g of polyvinyl alcohol, and ball-mill them to obtain a mixed powder.

[0064] The α-phase content in the first silicon nitride powder and the second silicon nitride powder is ≥95 wt %. The average particle size D50 of the first silicon nitride powder is 0.3 μm, and the average particle size D50 of the second silicon nitride powder is 1.0 μm.

[0065] The ball milling medium is silicon nitride balls, which are 3 mm and 5 mm in size and are mixed in a mass ratio of 1:1. The ball-to-material ratio is controlled to be 3:1. The ball milling speed is 300 r / min, and the dispersion medium is anhydrous ethanol.

[0066] Step 2: dry-press the mixed powder obtained in step 1 at 80 MPa for 300 seconds, and then cold-isostatically press at 200 MPa for 300 seconds to obtain a ceramic body.

[0067] The ceramic body was degreased at 550°C for 8 hours.

[0068] Step 3: Raise the temperature of the degreased ceramic body to 1300°C at a rate of 15°C / min under a nitrogen atmosphere, then raise the temperature to 1600°C at a rate of 3°C / min, and keep the temperature for 3 hours;

[0069] Then increase the temperature to 1800℃ at a rate of 5℃ / min and keep it at this temperature for 4h;

[0070] Then the temperature was lowered to 1200°C at 5°C / min and kept at this temperature for 3h;

[0071] Then the temperature was lowered to room temperature at 10°C / min.

[0072] Example 3

[0073] This embodiment provides a method for preparing a silicon nitride composite ceramic material for insulating support, comprising the following steps:

[0074] Step 1: Mix 47 g of the first silicon nitride powder, 47 g of the second silicon nitride powder, 3 g of Y2O3, 1.8 g of Al2O3, 1.2 g of SiO2 and 1.88 g of polyvinyl alcohol, and ball-mill to obtain a mixed powder.

[0075] The α-phase content in the first silicon nitride powder and the second silicon nitride powder is ≥95 wt %. The average particle size D50 of the first silicon nitride powder is 0.3 μm, and the average particle size D50 of the second silicon nitride powder is 1.0 μm.

[0076] The ball milling medium is silicon nitride balls, which are 3 mm and 5 mm in size and are mixed in a mass ratio of 1:1. The ball-to-material ratio is controlled to be 3:1. The ball milling speed is 300 r / min, and the dispersion medium is anhydrous ethanol.

[0077] Step 2: dry-press the mixed powder obtained in step 1 at 50 MPa for 300 seconds, and then cold-isostatically press at 250 MPa for 300 seconds to obtain a ceramic body.

[0078] The ceramic body was degreased at 500°C for 10 h.

[0079] Step 3: Raise the temperature of the degreased ceramic body to 1200°C at a rate of 10°C / min under a nitrogen atmosphere, then raise the temperature to 1650°C at a rate of 5°C / min, and keep the temperature for 2 hours;

[0080] Then increase the temperature to 1825℃ at a rate of 5℃ / min and keep it at this temperature for 3h;

[0081] Then the temperature was lowered to 1300°C at 5°C / min and kept at this temperature for 3h;

[0082] Then the temperature was lowered to room temperature at 10°C / min.

[0083] Comparative Example 1

[0084] This comparative example is basically the same as Example 1, except that the silicon nitride powder used in this comparative example is all the first silicon nitride powder.

[0085] Comparative Example 2

[0086] This comparative example is basically the same as Example 1, except that the silicon nitride powder used in this comparative example is all the second silicon nitride powder.

[0087] Comparative Example 3

[0088] This comparative example provides a preparation method of a silicon nitride composite ceramic material, which is basically the same as Example 1, except that in step 3 of this comparative example, after cooling to 1300°C, no heat preservation is performed, and the temperature is directly cooled to room temperature at 10°C / min.

[0089] Test example

[0090] 1. Figure 1 and Figure 2 The scanning electron microscope images of the products of Example 1 and Comparative Example 1 are shown respectively. Figure 1 and Figure 2 It can be seen that the grading of powders with different particle sizes is conducive to the formation of uniformly distributed bimodal interlocking structure β-Si3N4 columnar crystals, which is beneficial to improving the fracture toughness of silicon nitride ceramics.

[0091] 2. Figure 3 The XRD patterns of the products of Example 1 and Comparative Example 3 are shown in FIG. Figure 3 It can be seen that keeping the temperature at 1300℃ can stabilize the Y2SiAlO5N phase, which is beneficial to improving the temperature stability of the volume resistivity of silicon nitride ceramics.

[0092] 3. The properties of the silicon nitride composite ceramic materials prepared in Examples 1-3 and Comparative Examples 1-3 were tested. The specific testing process was as follows:

[0093] Density: The silicon nitride composite ceramic material is ground and polished, and the bulk density is measured using the Archimedes drainage method. The density is then calculated using the theoretical density.

[0094] Fracture toughness: Fracture toughness is measured using the single-edge notched beam method (SENB). Samples are processed into a size of 3×6×30 mm. Then, cracks are introduced by artificial notching with a depth of approximately 3 mm and a width of approximately 0.2 mm. The fracture toughness of the samples is tested on a universal material testing machine.

[0095] Volume resistivity: The resistivity test is carried out according to the three-electrode method required by GB / T 1410 standard.

[0096] The test results are shown in Table 1.

[0097] Table 1 Properties of silicon nitride composite ceramic materials

[0098]

[0099] As can be seen from Table 1, the silicon nitride composite ceramic material of the present invention has excellent high fracture toughness, high density, and significantly improved resistivity stability, and has broad application scenarios in the field of high-voltage gas power insulation.

[0100] From the comparison between Example 1 and Comparative Example 3, it can be seen that the temperature stability of the resistivity can be further improved by maintaining the temperature after cooling in step 3.

[0101] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing a silicon nitride composite ceramic material for insulating support, characterized in that: The following steps are involved: Step 1: mixing silicon nitride powder, a sintering aid and a binder to obtain a mixed powder; The silicon nitride powder comprises a first silicon nitride powder and a second silicon nitride powder; the average particle size D50 of the first silicon nitride powder is 0.1-0.5 μm; the average particle size D50 of the second silicon nitride powder is 0.7-1.2 μm; the mass ratio of the first silicon nitride powder to the second silicon nitride powder is (1-2):1; Step 2: pressing the mixed powder into a shape to obtain a ceramic body; Step 3: Sintering in a protective atmosphere; The step 3 comprises: Step 1: In nitrogen atmosphere, keep the temperature at 1550~1650℃ for 2~4h; Step 2: Raise the temperature to 1780~1850℃ and keep warm for 2~4h; Step 3: Cool down to 1200~1400℃ and keep warm for 2~4h; In the silicon nitride powder, the α phase content is ≥95wt%; The sintering aids include Y2O3, Al2O3 and SiO2; The mass ratio of Y2O3, Al2O3 and SiO2 is (3~5): (3~5):

2.

2. The method for preparing the silicon nitride composite ceramic material for insulating support according to claim 1, characterized in that: Step 1 satisfies at least one of the following conditions: (1) The mass ratio of the silicon nitride powder to the sintering aid is (84-94): (6-16); (2) The binder is 1-2 wt% of the mass of the silicon nitride powder; (3) The binder includes at least one of polyvinyl butyral or polyvinyl alcohol.

3. The method for preparing the silicon nitride composite ceramic material for insulating support according to claim 1 or 2, characterized in that: At least one of the following conditions is met: (1) The first step includes: raising the temperature to 1200-1300°C at a rate of 10-15°C / min under nitrogen atmosphere, then raising the temperature to 1550-1650°C at a rate of 3-5°C / min, and keeping the temperature for 2-4 hours; (2) The heating rate in the second step is 5~10℃ / min; (3) The cooling rate in the third step is 5~10℃ / min; (4) After the third step of heat preservation, the temperature is lowered to room temperature at a rate of 10-15°C / min.

4. The method for preparing the silicon nitride composite ceramic material for insulating support according to claim 1 or 2, characterized in that: The pressing in step 2 includes dry pressing and cold isostatic pressing.

5. The method for preparing the silicon nitride composite ceramic material for insulating support according to claim 4, characterized in that: The dry pressing pressure is 50-100 MPa.

6. The method for preparing the silicon nitride composite ceramic material for insulating support according to claim 4, characterized in that: The cold isostatic pressing pressure is 200-250 MPa.

7. The method for preparing the silicon nitride composite ceramic material for insulating support according to claim 1 or 2, characterized in that: The step 2 also includes the step of degreasing the ceramic body.

8. The method for preparing the silicon nitride composite ceramic material for insulating support according to claim 7, characterized in that: The degreasing treatment is carried out by keeping the temperature at 450-550° C. for 8-10 hours.

9. A silicon nitride composite ceramic material for insulating support prepared according to the preparation method according to any one of claims 1 to 8.

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