Silicon nitride composite ceramic with high dielectric property and preparation method thereof

Abstract

A high-dielectric-performance silicon nitride composite ceramic and its preparation method are disclosed, belonging to the field of electrical insulating ceramics technology, overcoming the shortcomings of poor dielectric properties in existing insulating support materials. The preparation method of the high-dielectric-performance silicon nitride composite ceramic of this invention includes the following steps: Step 1, mixing silicon nitride powder, sintering aid, dispersant, binder, and water to prepare a slurry; the sintering aid includes Y2O3, Al2O3, and Bi2O3, with a mass ratio of Y2O3:Al2O3:Bi2O3:silicon nitride powder of (0.01-0.15):(0.01-0.13):(0.01-0.08):1; Step 2, preparing granulated powder; Step 3, pressing and molding; Step 4, debinding; Step 5, performing the first sintering under negative pressure, followed by the second sintering under nitrogen pressure. The silicon nitride composite ceramic of this invention exhibits excellent dielectric properties.

Description

Technical Field

[0001] This invention belongs to the field of electrical insulating ceramics technology, specifically relating to a high dielectric silicon nitride composite ceramic and its preparation method. Background Technology

[0002] Silicon nitride ceramics possess high strength, high toughness, high thermal conductivity, and excellent resistance to oxidation, creep, and high resistivity, making them one of the most widely used structural ceramics. With the continuous development of powder metallurgy technology, silicon nitride, as a structural-functional integrated ceramic material with superior comprehensive performance, has received increasing attention. The combination of high strength, high resistivity, high dielectric constant, and low dielectric loss in silicon nitride ceramics makes them potentially valuable for applications in ultra-high voltage power transmission.

[0003] DC through-wall bushings are crucial equipment in ultra-high voltage (UHVDC) transmission systems. Post insulators and basin insulators are the core components of the gas-insulated through-wall bushings, playing a key role in supporting the conductor rods. Currently, UHVDC gas-insulated posts commonly use composite materials of alumina and epoxy resin, which are prone to flashover accidents at high voltage levels, posing a significant threat to line safety. Therefore, higher requirements are placed on the dielectric properties of the materials. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defect of poor dielectric properties of insulating pillar materials in the prior art, thereby providing a silicon nitride composite ceramic with high dielectric properties and its preparation method.

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

[0006] In a first aspect, the present invention provides a method for preparing silicon nitride composite ceramics with high dielectric properties, comprising the following steps:

[0007] Step 1: Prepare a slurry by mixing silicon nitride powder, sintering aid, dispersant, binder and water;

[0008] The sintering aids include Y2O3, Al2O3, and Bi2O3, with a mass ratio of Y2O3:Al2O3:Bi2O3:silicon nitride powder of (0.01-0.15):(0.01-0.13):(0.01-0.08):1.

[0009] Step 2: Prepare granulated powder from the slurry using spray granulation;

[0010] Step 3: Press the granulated powder into shape to obtain a ceramic green body;

[0011] Step 4: Remove the adhesive from the ceramic green body;

[0012] Step 5: The ceramic green body after debinding is sintered under negative pressure for the first step, and then sintered under nitrogen pressure for the second step.

[0013] Furthermore, step 5 includes:

[0014] First, heat the material to 1100–1500℃ under a pressure of 70–95 kPa and hold it for 1–5 hours; then, purge it with nitrogen, pressurize it to 0.1–5 MPa, heat it to 1750–1900℃, and hold it for 1–5 hours.

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

[0016] (1) The silicon nitride powder is silicon nitride micron powder; preferably, the average particle size of the silicon nitride micron powder is 0.4-1.0 microns;

[0017] (2) The silicon nitride powder is α-Si3N4;

[0018] (3) The dispersant includes one or more of polyacrylamide, sodium hydroxymethyl cellulose, or Darvan CN;

[0019] (4) The adhesive includes one or more of polyvinyl alcohol, polyacrylic acid or polyethylene glycol;

[0020] (5) The mass ratio of the dispersant to silicon nitride powder is (0.01-0.25):1;

[0021] (6) The mass ratio of the binder to the silicon nitride powder is (0.03-0.26):1;

[0022] (7) The solid content of the slurry is 43-55 wt.%.

[0023] Furthermore, step 1 includes:

[0024] Silicon nitride powder, sintering aid, dispersant and water are premixed in a sand mill;

[0025] Then transfer the premixed material to a mixing tank, add the binder, and continue mixing;

[0026] Preferably, the mixture is premixed in a sand mill for 1 to 10 hours;

[0027] Preferably, the mixture is stirred in a mixing tank for 0.5 to 6 hours.

[0028] Furthermore, spray granulation also includes drying and sieving steps.

[0029] Furthermore, the drying conditions are drying at 110–150°C for 1–20 hours;

[0030] and / or

[0031] The sieving process involves passing the material through a 60-120 mesh sieve, and the material passing through the sieve is used as granulation powder.

[0032] Furthermore, in step 3, the pressing process includes at least one of dry pressing and cold isostatic pressing.

[0033] Furthermore, the pressure for dry pressing is 70–120 MPa, and the pressure is held for 5–10 minutes;

[0034] and / or

[0035] The pressure for cold isostatic pressing is 100-300 MPa, and the pressure is maintained for 5-10 minutes.

[0036] Furthermore, step 4 satisfies at least one of the following conditions:

[0037] (1) The ceramic green body is debinded in flowing air; preferably, the air flow rate is 0.5-4 L / min;

[0038] (2) The degreasing process includes: raising the temperature from room temperature to 300-450°C for 1-5 hours, holding the temperature for 1-6 hours, raising the temperature to 550-650°C for another 1-5 hours, holding the temperature for 0.5-5 hours, and then raising the temperature to 750-850°C for another 1-3 hours.

[0039] Secondly, the present invention provides a silicon nitride composite ceramic with high dielectric properties prepared according to the preparation method described above.

[0040] Nitrogen pressure refers to the positive pressure under a nitrogen atmosphere.

[0041] The technical solution of this invention has the following advantages:

[0042] 1. The preparation method of the high dielectric silicon nitride composite ceramic of the present invention includes the following steps: Step 1, mixing silicon nitride powder, sintering aid, dispersant, binder and water to prepare a slurry; the sintering aid includes Y2O3, Al2O3 and Bi2O3, and the mass ratio of Y2O3:Al2O3:Bi2O3:silicon nitride powder is (0.01-0.15):(0.01-0.13):(0.01-0.08):1; Step 2, spray granulating the slurry to prepare granulated powder; Step 3, pressing the granulated powder into a ceramic green body; Step 4, removing the binder from the ceramic green body; Step 5, performing a first sintering under negative pressure on the debinded ceramic green body, followed by a second sintering under nitrogen pressure.

[0043] This invention employs a Y-Al-Bi ternary composite sintering aid. The Y2O3 sintering aid reduces the electrical conductivity barrier and improves temperature stability; the Bi2O3 sintering aid introduces interfacial energy levels and increases the trapping charge. In addition, the low-melting-point oxides Bi2O3 and Al2O3 can also reduce the sintering temperature.

[0044] A sintering process combining micro-negative pressure and gas pressure is adopted. First, internal defects are reduced by sintering at low temperature under micro-negative pressure. Then, the temperature is increased under nitrogen pressure to increase the density, thereby improving the dielectric properties.

[0045] This method has a simple preparation process, strong controllability, and produces silicon nitride composite materials with high density and excellent dielectric properties.

[0046] The silicon nitride composite ceramic prepared by this invention has a density greater than 98%, a dielectric constant between 7.6 and 8.5 at 50 Hz (20℃), and a dielectric loss of less than 0.01 (20℃), exhibiting excellent dielectric properties. Attached Figure Description

[0047] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0048] Figure 1 This is an SEM image of the high dielectric silicon nitride composite ceramic prepared in Example 1. Detailed Implementation

[0049] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0050] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0051] Example 1

[0052] This embodiment provides a method for preparing silicon nitride composite ceramics with high dielectric properties, including the following steps:

[0053] (1) Take 10 kg of α-Si3N4 powder with an average particle size of 0.9 μm, 0.5 kg of yttrium oxide, 0.3 kg of alumina, 0.15 kg of bismuth oxide sintering aids, and 0.15 kg of polyacrylamide (average Mn 150000) dispersant and put them into a sand mill. Use deionized water as the ball milling medium and premix for 2 hours. Then transfer the mixed slurry to a mixing tank, add 0.5 kg of polyethylene glycol (average Mn 8000) binder, adjust the solid content to 53 wt.%, and continue stirring for 1 hour.

[0054] (2) The slurry was granulated by spray drying and then dried at 130°C for 8 hours. After drying, it was passed through a 60-mesh sieve and the sieve material was taken as granulation powder.

[0055] (3) The granulated powder was dry-pressed at 100MPa for 10 minutes and then further cold isostatically pressed at 250MPa for 10 minutes to obtain a ceramic green body.

[0056] (4) Remove the glue from the ceramic green body under flowing air: the air flow rate is 3L / min, the temperature is raised from room temperature to 400℃ in 3 hours, held for 5 hours, then raised to 600℃ in another 3 hours, held for 3 hours, and then raised to 800℃ in another hour without holding.

[0057] (5) The ceramic green body after debinding is sintered in a gas pressure sintering furnace: first, the temperature is raised to 1300℃ under a pressure of 90KPa and held for 4 hours. Then, nitrogen is introduced, the pressure is increased to 1MPa, the temperature is raised to 1850℃, and held for 5 hours.

[0058] Figure 1 This is a SEM image of the silicon nitride composite ceramic prepared in Example 1. Figure 1 It can be seen that the silicon nitride composite ceramics prepared by the present invention have uniform microstructure and high density.

[0059] Example 2

[0060] This embodiment provides a method for preparing silicon nitride composite ceramics with high dielectric properties, including the following steps:

[0061] (1) Take 10 kg of α-Si3N4 powder with an average particle size of 0.7 μm, 0.53 kg of yttrium oxide sintering aid, 0.25 kg of alumina, 0.12 kg of bismuth oxide, and 0.15 kg of polyacrylamide (average Mn 150000) dispersant and put them into a sand mill. Use deionized water as the ball milling medium and premix for 2 hours. Then transfer the mixed slurry to a mixing tank, add 0.55 kg of polyethylene glycol (average Mn 8000) binder, adjust the solid content to 55 wt.%, and continue stirring for 1 hour.

[0062] (2) The slurry was granulated by spray drying and then dried at 130°C for 8 hours. After drying, it was passed through a 60-mesh sieve and the sieve material was taken as granulation powder.

[0063] (3) The granulated powder was dry-pressed at 100MPa for 8 minutes and then further cold isostatically pressed at 250MPa for 8 minutes to obtain a ceramic green body.

[0064] (4) Remove the glue from the ceramic green body under flowing air: the air flow rate is 2L / min, the temperature is raised from room temperature to 400℃ in 3 hours, held for 5 hours, then raised to 600℃ in another 3 hours, held for 4 hours, and then raised to 800℃ in another hour without holding.

[0065] (5) The green body after debinding is sintered in a pressure sintering furnace: first, the temperature is raised to 1400℃ under a pressure of 85KPa and held for 4 hours. Then, nitrogen is introduced, the pressure is increased to 1MPa, the temperature is raised to 1850℃ and held for 3 hours.

[0066] Example 3

[0067] This embodiment provides a method for preparing silicon nitride composite ceramics with high dielectric properties, including the following steps:

[0068] (1) Take 10 kg of α-Si3N4 powder with an average particle size of 0.4 μm, 0.5 kg of yttrium oxide sintering aid, 0.35 kg of alumina, 0.15 kg of bismuth oxide, and 0.15 kg of polyacrylamide (average Mn 150000) dispersant and put them into a sand mill. Use deionized water as the ball milling medium and premix for 2 hours. Then transfer the mixed slurry to a mixing tank, add 0.5 kg of polyethylene glycol (average Mn 8000) binder, adjust the solid content to 50 wt.%, and continue stirring for 1 hour.

[0069] (2) The slurry was granulated by spray drying and then dried at 130°C for 8 hours. After drying, it was passed through a 60-mesh sieve and the sieve material was taken as granulation powder.

[0070] (3) The granulated powder is dry-pressed at 100MPa for 10min and then further cold isostatically pressed at 250MPa for 10min.

[0071] (4) Remove the glue from the ceramic green body under flowing air: the air flow rate is 2.5L / min, the temperature is raised from room temperature to 400℃ in 3 hours, held for 5 hours, then raised to 600℃ in another 3 hours, held for 2 hours, and then raised to 800℃ in another hour without holding.

[0072] (5) The green body after debinding is sintered in a gas pressure sintering furnace: first, the temperature is raised to 1400℃ under a pressure of 90KPa and held for 4 hours. Then, nitrogen is introduced, the pressure is increased to 1MPa, the temperature is raised to 1850℃ and held for 5 hours.

[0073] Comparative Example 1

[0074] This comparative example is basically the same as Example 1, except that bismuth oxide sintering aid was not used. The selected sintering aids were 0.5 kg of yttrium oxide and 0.3 kg of alumina.

[0075] Comparative Example 2

[0076] This comparative example is basically the same as Example 1, except that the amount of bismuth oxide sintering aid used is 0.9 kg.

[0077] Comparative Example 3

[0078] This comparative example is basically the same as Example 1, except that the two-step sintering process combining micro-negative pressure and gas pressure was not used. Only gas pressure sintering was used: nitrogen was introduced, pressurized to 1MPa, heated to 1300°C, and held for 4 hours, then heated to 1850°C and held for 5 hours.

[0079] Test case

[0080] The silicon nitride composite ceramics prepared in Examples 1-3 and Comparative Examples 1-3 were thinned to 5 mm on both sides, polished on both sides, and then subjected to dielectric property testing. The test was conducted in accordance with GB / T 5594.4-2015, and the test results are shown in Table 1.

[0081] Table 1 Properties of Silicon Nitride Composite Ceramics

[0082]

[0083] As shown in Table 1, the silicon nitride composite ceramic of the present invention has improved density and dielectric constant compared with the comparative example, and the dielectric loss is also significantly reduced.

[0084] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a silicon nitride composite ceramic with high dielectric properties, characterized in that, Includes the following steps: Step 1: Prepare a slurry by mixing silicon nitride powder, sintering aid, dispersant, binder and water; The sintering aids include Y2O3, Al2O3, and Bi2O3, with a mass ratio of Y2O3:Al2O3:Bi2O3:silicon nitride powder of (0.01-0.15):(0.01-0.13):(0.01-0.08):

1. Step 2: Prepare granulated powder from the slurry by spray granulation; Step 3: Press the granulated powder into shape to obtain a ceramic green body; Step 4: Remove the adhesive from the ceramic green body; Step 5: The ceramic green body after debinding is sintered under negative pressure for the first step, and then sintered under nitrogen pressure for the second step. Step 5 includes: First, raise the temperature to 1100~1500℃ under a pressure of 70-95 kPa, and hold for 1~5 hours; Then nitrogen gas is introduced, pressurized to 0.1~5MPa, heated to 1750~1900℃, and held at that temperature for 1~5 hours; The high dielectric silicon nitride composite ceramic obtained has a dielectric constant between 7.6 and 8.5 at 50 Hz and 20 °C, and a dielectric loss of less than 0.01 at 20 °C.

2. The method for preparing high-dielectric-performance silicon nitride composite ceramics according to claim 1, characterized in that, Step 1 satisfies at least one of the following conditions: (1) The silicon nitride powder is silicon nitride micron powder; (2) The silicon nitride powder is α-Si3N4; (3) The dispersant includes one or more of polyacrylamide, sodium hydroxymethyl cellulose, or Darvan CN; (4) The adhesive includes one or more of polyvinyl alcohol, polyacrylic acid, or polyethylene glycol; (5) The mass ratio of the dispersant to silicon nitride powder is (0.01-0.25):1; (6) The mass ratio of the binder to the silicon nitride powder is (0.03-0.26):1; (7) The slurry has a solid content of 43~55 wt.%.

3. The method for preparing silicon nitride composite ceramics with dielectric properties according to claim 2, characterized in that, The average particle size of the silicon nitride micron powder is 0.4-1.0 micrometers.

4. The method for preparing high-dielectric-performance silicon nitride composite ceramics according to claim 1, characterized in that, Step 1 includes: Silicon nitride powder, sintering aid, dispersant and water are premixed in a sand mill; The premixed material is then transferred to a mixing tank, the binder is added, and mixing continues.

5. The method for preparing high-dielectric-performance silicon nitride composite ceramics according to claim 4, characterized in that, Premix in a sand mill for 1-10 hours; and / or Mix in a mixing tank for 0.5 to 6 hours.

6. The method for preparing high-dielectric-performance silicon nitride composite ceramics according to claim 1, characterized in that, Spray granulation also includes drying and sieving steps.

7. The method for preparing high-dielectric-performance silicon nitride composite ceramics according to claim 6, characterized in that, The drying conditions are as follows: drying at 110~150℃ for 1~20 hours; and / or The sieving process involves passing the material through a 60-120 mesh sieve, and the material passing through the sieve is used as granulation powder.

8. The method for preparing high dielectric silicon nitride composite ceramics according to claim 1, characterized in that, In step 3, the pressing process includes at least one of dry pressing and cold isostatic pressing.

9. The method for preparing high dielectric silicon nitride composite ceramics according to claim 8, characterized in that, The pressure for dry pressing is 70~120MPa, and the pressure is held for 5~10 minutes; and / or The pressure for cold isostatic pressing is 100~300MPa, and the pressure is maintained for 5~10 minutes.

10. The method for preparing high-dielectric-performance silicon nitride composite ceramics according to claim 1, characterized in that, Step 4 must satisfy at least one of the following conditions: (1) The ceramic green body is debonded in flowing air; (2) The degreasing process includes: raising the temperature from room temperature to 300-450°C for 1-5 hours, holding the temperature for 1-6 hours, raising the temperature to 550-650°C for another 1-5 hours, holding the temperature for 0.5-5 hours, and then raising the temperature to 750-850°C for another 1-3 hours.

11. The method for preparing high-dielectric-performance silicon nitride composite ceramics according to claim 10, characterized in that, The ceramic green body is debinded in flowing air at a flow rate of 0.5-4 L / min.

12. A silicon nitride composite ceramic with high dielectric properties prepared by the preparation method according to any one of claims 1-11.

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