A method for preparing silicon nitride composite refractory material

Abstract

The present invention relates to the field of refractory materials, and specifically to a method for preparing silicon nitride composite refractory materials. A method for preparing silicon nitride composite refractory materials, comprising the following steps: magnetization treatment of investment casting waste sand; preparation of refractory premix; nitrogen sintering of the refractory premix; and directional pressing and sintering of magnetized refractory blanks. The present invention adds nano-barium ferrite magnetic particles to investment casting waste sand, and subsequently nitrogen sinters the refractory premix so that the nano-barium ferrite magnetic particles are uniformly dispersed in the silicon nitride crystals. The obtained refractory blank is then magnetized and directionally pressed in a magnetic field, so that the silicon nitride crystals combined with the nano-barium ferrite magnetic particles are oriented, thereby reducing the internal stress of the silicon nitride composite refractory material during thermal expansion, lowering its thermal expansion coefficient, and effectively improving the thermal conductivity of the silicon nitride composite refractory material, thereby improving its refractory performance.

Description

Technical Field

[0001] The present invention relates to the field of refractory materials, in particular to a method for preparing a silicon nitride multiphase refractory material. Background Art

[0002] High-purity silicon nitride has excellent properties such as high strength, high hardness, high fracture toughness, as well as high temperature resistance, wear resistance, corrosion resistance, and good thermal shock resistance. For refractory materials in my country's high-temperature industry, these excellent properties of silicon nitride can greatly improve the performance of refractory materials, thereby helping to expand the application scenarios of my country's refractory materials and increase their service life.

[0003] However, the existing high-purity silicon nitride production process not only has high requirements on the quality of raw materials, but also usually needs to go through multiple steps such as high-temperature synthesis, gas phase reaction and hot pressing sintering for production. In these production steps, not only the material requirements of the production equipment are high, but also the control accuracy requirements of the process in each step are very high, which leads to high production costs of high-purity silicon nitride, greatly limiting the wide application of silicon nitride in the field of refractory materials. To address this problem, some researchers have tried to use industrial waste to produce silicon nitride refractory materials to reduce costs. However, due to the presence of a large amount of impurities in industrial waste and the disordered composition structure of the waste, the performance of the produced refractory materials is poor. Summary of the Invention

[0004] In order to solve the above technical defects, the present invention has developed a method for preparing a silicon nitride composite refractory material with low cost, simple preparation method and excellent refractory performance.

[0005] A method for preparing a silicon nitride composite refractory material comprises the following steps:

[0006] S1: Magnetic treatment of investment casting waste sand

[0007] The investment casting waste sand is added into a mixer and dry-mixed, and then a water-based polyurethane resin is added and mixed and rolled to obtain water-based polyurethane resin-coated waste sand. The water-based polyurethane resin-coated waste sand and nano-barium ferrite magnetic particles are placed in a drum mixer and dry-mixed, and then placed in a mixer and continued to be mixed and rolled, and then placed in a molding machine for compression molding to obtain a waste sand blank. The waste sand blank is heat-treated and then naturally cooled to room temperature to obtain a magnetic waste sand casting.

[0008] S2: Preparation of refractory premix

[0009] Crushing the magnetic waste sand casting to obtain casting particles, placing the casting particles, silicon powder and zirconia balls into a ball mill, adding deionized water and ball milling to obtain ball milling slurry, spray drying the ball milling slurry to obtain a refractory premix;

[0010] S3: Nitrogen sintering of refractory premix

[0011] The refractory premix is placed in a reactor, the reactor is evacuated and nitrogen is introduced, and then the refractory premix is heated at a high temperature to obtain a refractory blank, and the refractory blank is placed in a pulse magnetic field magnetizer for magnetization to obtain a magnetized refractory blank;

[0012] S4: Directional pressing and sintering of magnetized refractory blanks

[0013] The magnetized refractory blank is filled into a mold, and then the mold is placed in a molding machine, and uniform speed pressurization is performed in a magnetic field to obtain a blank. The blank is placed in a flowing atmosphere sintering furnace, and nitrogen is continuously introduced and sintered. After natural cooling, a silicon nitride composite refractory material is obtained.

[0014] Furthermore, step S1 of magnetizing investment casting waste sand comprises the following steps:

[0015] S1.1: Add 8-10 parts by weight of investment casting waste sand to a mixer and dry mix at a mixing speed of 100-120 rpm for 15-20 minutes. Then, add 1.5-2 parts by weight of a 65-75% aqueous polyurethane resin to the mixer and continue mixing at a speed of 100-120 rpm for 15-20 minutes to obtain aqueous polyurethane resin-coated waste sand.

[0016] S1.2: The waterborne polyurethane resin-coated waste sand prepared in step S1.1 and 1-2 parts by weight of nano-barium ferrite magnetic particles are dry-mixed in a drum mixer at a speed of 120-150 rpm for 20-25 minutes, then added to a mixer and continuously mixed for 15-20 minutes. The mixture is then pressed in a molding press at a pressure of 80-100 MPa to obtain a waste sand blank.

[0017] S1.3: Place the waste sand blank in a box furnace, heat it from room temperature to 250-300°C at a heating rate of 4-5°C / min, hold it for 30-40 minutes, then heat it to 350-400°C at a heating rate of 2-3°C / min, hold it for 55-60 minutes, and then cool it naturally to room temperature to obtain a magnetic waste sand casting.

[0018] Furthermore, the preparation of the refractory premix in step S2 comprises the following steps:

[0019] S2.1: The magnetic waste sand casting obtained in step S1.3 is crushed in a crusher to a particle size of 20-30 mm to obtain casting particles. The casting particles, silicon powder, and zirconium oxide balls are mixed in a mass ratio of 1:(2-3):(3-3.5) and added to a ball mill. After adding deionized water, the ball mill is started and the speed is adjusted to 250-300 rpm. The ball mill is milled for 1-1.5 hours to obtain a ball-milled slurry.

[0020] S2.2: Place the ball-milled slurry in a spray dryer, adjust the feed temperature to 250-300°C, the nozzle angle to 40-60°, and the discharge temperature to 80-90°C, and spray dry the ball-milled slurry to obtain a refractory premix with a particle size of 10-100 μm.

[0021] Furthermore, step S3 of nitrogen sintering of the refractory premix comprises the following steps:

[0022] S3.1: Place the refractory premix prepared in step S2.2 into a reactor, seal the reactor, and then evacuate the reactor to a vacuum. Then, introduce nitrogen to bring the pressure in the reactor to 1.5-2.5 MPa. Then, heat the refractory premix at 1250-1300°C for 2-3 hours to obtain a refractory billet.

[0023] S3.2: placing the refractory blank in a pulse magnetic field magnetizer, adjusting the magnetic field of the pulse magnetic field magnetizer to 1-1.5 T to magnetize the refractory blank to obtain a magnetized refractory blank.

[0024] Furthermore, step S4 of directional pressing and sintering the magnetized refractory blank comprises the following steps:

[0025] S4.1: Place the magnetized refractory blank into a mold, then place the mold in a molding press. Set a 2-2.5T magnetic field around the mold. Adjust the pressure of the molding press to 100-120MPa at a rate of 18-20MPa / min. Continue pressing for 1-2 minutes to obtain a blank.

[0026] S4.2: Place the green body in a flowing atmosphere sintering furnace, continuously introduce nitrogen, and heat it to 1000-1050°C at a heating rate of 5-6°C / min in a nitrogen atmosphere, then heat it to 1250-1300°C at a heating rate of 2-3°C / min, keep it at that temperature for 2-3 hours, and naturally cool it to room temperature to obtain a silicon nitride composite refractory material.

[0027] Furthermore, the mesh size of the investment casting waste sand in step S1.1 is 80-120 mesh, and the composition is 50-55wt% SiO2, 35-40wt% Al2O3, 6-8wt% ZrO2, 1.5-2wt% Fe2O3, and the rest is a small amount of CaO, MgO, K2O and Na2O metal oxides.

[0028] Furthermore, the particle size of the zirconia balls in step S2.1 is 1-2 mm.

[0029] Furthermore, after adding deionized water in step S2.1, the solid content of the slurry in the ball mill is 60-65%.

[0030] Furthermore, the mold in step S4.1 is a strip mold of 40 mm×40 mm×160 mm.

[0031] Furthermore, the magnetic field in step S4.1 is generated by placing electromagnets around the mold and energizing the electromagnets.

[0032] The beneficial effects are: 1. The present invention magnetizes the refractory blank and performs magnetic field-oriented pressing, so that the silicon nitride crystals combined with nano-barium ferrite magnetic particles are oriented under the action of the magnetic field, thereby reducing the internal stress of the silicon nitride composite refractory material during thermal expansion and lowering its thermal expansion coefficient. At the same time, it can effectively improve the thermal conductivity of the silicon nitride composite refractory material, reduce local overheating caused by heat accumulation, and thus improve its refractory performance.

[0033] 2. The present invention adds nano-barium ferrite magnetic particles to investment casting waste sand, and then performs mixing, grinding and heat treatment, so that SiO2 in the investment casting waste sand adsorbs the nano-barium ferrite magnetic particles. In the subsequent nitrogen sintering of the refractory premix, silicon powder and nitrogen generate silicon nitride under high temperature conditions, so that the barium ferrite magnetic particles are evenly dispersed in the silicon nitride crystals and tightly combined with the silicon nitride crystals, thereby avoiding uneven distribution of structural components of the silicon nitride composite refractory material during the subsequent sintering process, thereby improving the refractory performance of the refractory material.

[0034] 3. The present invention first coats investment casting waste sand with an aqueous polyurethane resin, and then mixes and grinds the obtained aqueous polyurethane resin-coated waste sand with nano-barium ferrite magnetic particles, so that the nano-barium ferrite magnetic particles are evenly distributed and bonded in the waste sand blank, thereby improving the adsorption of the barium ferrite magnetic particles by the investment casting waste sand during a subsequent heat treatment process, and introducing C and N elements into the magnetic waste sand casting. During the subsequent nitrogen sintering process of the refractory premix, a ceramic-bonded carbon network is formed with silicon nitride, thereby improving the refractory performance of the silicon nitride composite refractory material.

[0035] 4. The present invention prepares silicon nitride composite refractory materials by utilizing silicon powder and investment casting waste sand as main materials, wherein the main components of the investment casting waste sand are SiO2 and Al2O3. After being mixed with silicon powder, the materials are placed in a nitrogen atmosphere and sintered to obtain silicon nitride composite refractory materials with silicon nitride phase, silicon oxynitride phase and Sialon phase as main components. The preparation method is simple, which fills the defect of single performance of silicon nitride in refractory materials. In addition, the content of other heavy metal elements in the investment casting waste sand can be reduced to the standard after high-temperature sintering treatment, which reduces the preparation cost of silicon nitride composite refractory materials under the premise of safety and environmental protection, and opens up an innovative situation for the application of silicon nitride composite materials in refractory materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1This is a flow chart of a method for preparing a silicon nitride composite refractory material used in an embodiment of the present invention.

[0037] Figure 2 A typical microstructure diagram of a silicon nitride composite material produced according to an embodiment of the present invention. DETAILED DESCRIPTION

[0038] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments 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.

[0039] Example 1

[0040] A method for preparing a silicon nitride composite refractory material, such as Figure 1 As shown, the following steps are included:

[0041] S1: Magnetic treatment of investment casting waste sand

[0042] S1.1: 8 parts by weight of investment casting waste sand having a mesh size of 80 mesh and a composition of 50 wt% SiO2, 40 wt% Al2O3, 6 wt% ZrO2, 2 wt% Fe2O3, and the remainder being small amounts of CaO, MgO, K2O, and Na2O metal oxides are added to a mixer and dry-mixed at a mixing speed of 100 rpm for 15 minutes. Then, 1.5 parts by weight of a 65% aqueous polyurethane resin is added to the mixer and mixing is continued at a mixing speed of 100 rpm for 15 minutes to obtain aqueous polyurethane resin-coated waste sand.

[0043] S1.2: The waterborne polyurethane resin-coated waste sand prepared in step S1.1 and 1 part by weight of nano-barium ferrite magnetic particles were dry-mixed in a drum mixer at 120 rpm for 20 minutes. The mixture was then added to a mixer and milled for a further 15 minutes. The mixture was then pressed in a molding press at a pressure of 80 MPa to obtain a waste sand blank.

[0044] S1.3: Place the waste sand blank in a box furnace and heat it from room temperature to 250°C at a heating rate of 4°C / min. Hold the temperature for 30 minutes, then heat it to 350°C at a heating rate of 2°C / min. Hold the temperature for another 55 minutes, and then cool it naturally to room temperature to obtain a magnetic waste sand casting.

[0045] S2: Preparation of refractory premix

[0046] S2.1: The magnetic waste sand casting obtained in step S1.3 is crushed in a crusher to a particle size of 20 mm to obtain casting particles. The casting particles, silicon powder, and zirconia balls with a particle size of 1 mm are mixed in a mass ratio of 1:2:3 and placed in a ball mill. Deionized water is added to adjust the solid content of the slurry to 60%. The ball mill is then started and the speed is adjusted to 250 rpm. Ball milling is performed for 1 hour to obtain a ball-milled slurry.

[0047] S2.2: Place the ball-milled slurry in a spray dryer, adjust the feed temperature to 250°C, the nozzle angle to 40°, and the discharge temperature to 80°C, and spray dry the ball-milled slurry to obtain a refractory premix with a particle size of 10 μm.

[0048] S3: Nitrogen sintering of refractory premix

[0049] S3.1: The refractory premix prepared in step S2.2 is placed in a reactor, which is sealed. The reactor is then evacuated to a vacuum, and nitrogen is introduced to bring the pressure in the reactor to 1.5 MPa. The refractory premix is then heated at 1250°C for 2 hours to obtain a refractory billet.

[0050] S3.2: placing the refractory blank in a pulse magnetic field magnetizer, adjusting the magnetic field of the pulse magnetic field magnetizer to 1T to magnetize the refractory blank, and obtaining a magnetized refractory blank.

[0051] S4: Directional pressing and sintering of magnetized refractory blanks

[0052] S4.1: Fill the magnetized refractory blank into a 40 mm × 40 mm × 160 mm strip mold. Then, place the mold in a molding press. Set a 2 T magnetic field around the mold. Adjust the pressure of the molding press to 100 MPa at a rate of 18 MPa / min. Continue pressing for 1 minute to obtain a blank.

[0053] S4.2: Place the green body in a flowing atmosphere sintering furnace, continuously introduce nitrogen, and heat it to 1000°C at a heating rate of 5°C / min in a nitrogen atmosphere, then heat it to 1250°C at a heating rate of 2°C / min, keep it at that temperature for 2 hours, and naturally cool it to room temperature to obtain a silicon nitride composite refractory material. Observe the silicon nitride composite refractory material under a microscope to obtain a microstructure diagram, as shown in FIG. Figure 2 As shown, the columnar phase is silicon oxynitride phase and sialon phase, and the enriched granular phase is silicon nitride phase.

[0054] Example 2

[0055] A method for preparing a silicon nitride composite refractory material, such as Figure 1 As shown, the following steps are included:

[0056] S1: Magnetic treatment of investment casting waste sand

[0057] S1.1: 10 parts by weight of 80-mesh investment casting waste sand is added to a mixer, wherein the sand comprises 55 wt% SiO2, 35 wt% Al2O3, 8 wt% ZrO2, 1.5 wt% Fe2O3, and the remainder is a small amount of CaO, MgO, K2O, and Na2O metal oxides. The mixture is dry-mixed at a mixing speed of 100 rpm for 15 minutes. Then, 2 parts by weight of a 65% aqueous polyurethane resin is added to the mixer, and mixing is continued at 100 rpm for 15 minutes to obtain aqueous polyurethane resin-coated waste sand.

[0058] S1.2: The waterborne polyurethane resin-coated waste sand prepared in step S1.1 and 2 parts by weight of nano-barium ferrite magnetic particles were dry-mixed in a drum mixer at 120 rpm for 20 minutes. The mixture was then added to a mixer and milled for a further 15 minutes. The mixture was then pressed in a molding press at a pressure of 80 MPa to obtain a waste sand blank.

[0059] S1.3: Place the waste sand blank in a box furnace and heat it from room temperature to 250°C at a heating rate of 4°C / min. Hold the temperature for 30 minutes, then heat it to 350°C at a heating rate of 2°C / min. Hold the temperature for another 55 minutes, and then cool it naturally to room temperature to obtain a magnetic waste sand casting.

[0060] S2: Preparation of refractory premix

[0061] S2.1: The magnetic waste sand casting obtained in step S1.3 is crushed in a crusher to a particle size of 20 mm to obtain casting particles. The casting particles, silicon powder, and zirconia balls with a particle size of 1 mm are mixed in a mass ratio of 1:3:3.5 and placed in a ball mill. Deionized water is added to adjust the solid content of the slurry to 65%. The ball mill is then started and the speed is adjusted to 250 rpm. The mixture is ball-milled for 1 hour to obtain a ball-milled slurry.

[0062] S2.2: Place the ball-milled slurry in a spray dryer, adjust the feed temperature to 250°C, the nozzle angle to 40°, and the discharge temperature to 80°C, and spray dry the ball-milled slurry to obtain a refractory premix with a particle size of 10 μm.

[0063] S3: Nitrogen sintering of refractory premix

[0064] S3.1: The refractory premix prepared in step S2.2 is placed in a reactor, which is sealed. The reactor is then evacuated to a vacuum, and nitrogen is introduced to bring the pressure in the reactor to 1.5 MPa. The refractory premix is then heated at 1250°C for 2 hours to obtain a refractory billet.

[0065] S3.2: placing the refractory blank in a pulse magnetic field magnetizer, adjusting the magnetic field of the pulse magnetic field magnetizer to 1T to magnetize the refractory blank, and obtaining a magnetized refractory blank.

[0066] S4: Directional pressing and sintering of magnetized refractory blanks

[0067] S4.1: Fill the magnetized refractory blank into a 40 mm × 40 mm × 160 mm strip mold. Then, place the mold in a molding press. Set a 2 T magnetic field around the mold. Adjust the pressure of the molding press to 100 MPa at a rate of 18 MPa / min. Continue pressing for 1 minute to obtain a blank.

[0068] S4.2: Place the green body in a flowing atmosphere sintering furnace, continuously introduce nitrogen, and heat it to 1000°C at a heating rate of 5°C / min in a nitrogen atmosphere, then heat it to 1250°C at a heating rate of 2°C / min, keep it at that temperature for 2 hours, and naturally cool it to room temperature to obtain a silicon nitride composite refractory material. Observe the silicon nitride composite refractory material under a microscope to obtain a microstructure diagram, as shown in FIG. Figure 2 As shown, the columnar phase is silicon oxynitride phase and sialon phase, and the enriched granular phase is silicon nitride phase.

[0069] Example 3

[0070] A method for preparing a silicon nitride composite refractory material, such as Figure 1 As shown, the following steps are included:

[0071] S1: Magnetic treatment of investment casting waste sand

[0072] S1.1: 8 parts by weight of 120-mesh investment casting waste sand is added to a mixer, wherein the sand comprises 50 wt% SiO2, 40 wt% Al2O3, 6 wt% ZrO2, 2 wt% Fe2O3, and the remainder is a small amount of CaO, MgO, K2O, and Na2O metal oxides. The mixture is dry-mixed at a mixing speed of 120 rpm for 20 minutes. Then, 1.5 parts by weight of a 75% aqueous polyurethane resin is added to the mixer, and mixing is continued at 120 rpm for 20 minutes to obtain aqueous polyurethane resin-coated waste sand.

[0073] S1.2: The waterborne polyurethane resin-coated waste sand prepared in step S1.1 and 1 part by weight of nano-barium ferrite magnetic particles were dry-mixed in a drum mixer at 150 rpm for 25 minutes. The mixture was then added to a mixer and milled for a further 20 minutes. The mixture was then pressed in a molding press at a pressure of 100 MPa to obtain a waste sand blank.

[0074] S1.3: Place the waste sand blank in a box furnace and heat it from room temperature to 3000°C at a heating rate of 5°C / min. Hold the temperature for 40 minutes, then heat it to 400°C at a heating rate of 3°C / min. Hold the temperature for another 60 minutes, and then cool it naturally to room temperature to obtain a magnetic waste sand casting.

[0075] S2: Preparation of refractory premix

[0076] S2.1: The magnetic waste sand casting obtained in step S1.3 is crushed in a crusher to a particle size of 30 mm to obtain casting particles. The casting particles, silicon powder, and zirconia balls with a particle size of 1 mm are mixed in a mass ratio of 1:2:3 and placed in a ball mill. Deionized water is added to adjust the solid content of the slurry to 60%. The ball mill is then started and the speed is adjusted to 300 rpm. Ball milling is performed for 1.5 hours to obtain a ball-milled slurry.

[0077] S2.2: Place the ball-milled slurry in a spray dryer, adjust the feed temperature to 300°C, the nozzle angle to 60°, and the discharge temperature to 90°C, and spray dry the ball-milled slurry to obtain a refractory premix with a particle size of 100 μm.

[0078] S3: Nitrogen sintering of refractory premix

[0079] S3.1: Place the refractory premix prepared in step S2.2 into a reactor, seal the reactor, and then evacuate the reactor to a vacuum. Then, introduce nitrogen to raise the pressure in the reactor to 2.5 MPa. Then, heat the refractory premix at 1300°C and hold the temperature for 3 hours to obtain a refractory billet.

[0080] S3.2: placing the refractory blank in a pulse magnetic field magnetizer, adjusting the magnetic field of the pulse magnetic field magnetizer to 1.5 T to magnetize the refractory blank, thereby obtaining a magnetized refractory blank.

[0081] S4: Directional pressing and sintering of magnetized refractory blanks

[0082] S4.1: The magnetized refractory blank was placed into a 40 mm × 40 mm × 160 mm strip mold. The mold was then placed in a molding press. A 2.5 T magnetic field was set around the mold. The pressure of the molding press was adjusted to 120 MPa at a rate of 20 MPa / min. The pressing was continued for 2 minutes to obtain a blank.

[0083] S4.2: Place the green body in a flowing atmosphere sintering furnace, continuously introduce nitrogen, and heat it to 1050°C at a heating rate of 6°C / min in a nitrogen atmosphere, then heat it to 1300°C at a heating rate of 3°C / min, keep it at that temperature for 3 hours, and naturally cool it to room temperature to obtain a silicon nitride composite refractory material. Observe the silicon nitride composite refractory material under a microscope to obtain a microstructure diagram, as shown in FIG. Figure 2As shown, the columnar phase is silicon oxynitride phase and sialon phase, and the enriched granular phase is silicon nitride phase.

[0084] Comparative Example 1

[0085] Compared with Example 1, the difference of Comparative Example 1 is that, in step S1.2, no nano-barium ferrite magnetic particles are added to Comparative Example 1, step S3.2 is removed, a 2T magnetic field is not set around the mold in step S4.1, the magnetic waste sand casting is replaced by waste sand casting, and the magnetized refractory blank is replaced by refractory blank. The remaining steps are the same as in Example 1. The obtained silicon nitride composite refractory material is recorded as Comparative Example 1.

[0086] Comparative Example 2

[0087] Compared with Example 1, the difference of Comparative Example 2 is that, in step S1.2, no nano-barium ferrite magnetic particles are added to Comparative Example 2. Instead, in step S2.1, the nano-barium ferrite magnetic particles are directly put into the ball mill together with the casting particles, silicon powder and zirconia balls. The remaining steps are the same as in Example 1. The obtained silicon nitride composite refractory material is recorded as Comparative Example 2.

[0088] Comparative Example 3

[0089] Compared with Example 1, the difference of Comparative Example 3 is that no water-based polyurethane resin is added in step S1.1 of Comparative Example 3, and the waste sand from investment casting is added to the mixer and dry-mixed, and then directly placed in a drum mixer with nano-barium ferrite magnetic particles for dry mixing. The remaining steps are the same as those in Example 1, and the obtained silicon nitride composite refractory material is recorded as Comparative Example 3.

[0090] Take the silicon nitride composite refractory material prepared in Example 1, Comparative Example 2 and Comparative Example 3 respectively, and saw out three test cones with an upper bottom of 2 mm on each side, a lower bottom of 8 mm on each side and a height of 30 mm. Referring to "GBT7322-2007 Test Method for Refractoriness of Refractory Materials", the test cone is placed in a refractory furnace and heated at a heating rate of 5 ° C / min. The furnace is maintained at an oxidizing atmosphere with an oxygen concentration of 21%. When any test cone is bent to the point where its tip contacts the cone, the temperature of the temperature measuring thermocouple test is recorded. When all test cones or standard temperature measuring cones are bent to the point where their tips contact the cone, the data is recorded and tabulated. As shown in Table 1, it can be seen that the silicon nitride composite refractory material prepared in Example 1 has a good thermal conductivity. The refractoriness of the comparative example 2 is greater than that of the comparative example 3 and greater than that of the comparative example 1. This proves that the addition of nano-barium ferrite magnetic particles to the investment casting waste sand ensures that the structural components of the silicon nitride composite refractory material are evenly distributed during the sintering process, thereby improving the refractory performance of the refractory material. At the same time, it can be proved that after the nano-barium ferrite magnetic particles and silicon nitride are combined, the refractory performance of the silicon nitride composite refractory material can be effectively improved by magnetizing the refractory blank and performing magnetic field-oriented pressing. It can also be proved that the investment casting waste sand is coated with water-based polyurethane resin and then mixed with nano-barium ferrite magnetic particles, which can also improve the refractory performance of the silicon nitride composite refractory material.

[0091] Table 1: Refractoriness of refractory materials

[0092] Refractoriness / ℃ The first Second copy The third Example 1 ＞1800 ＞1800 ＞1800 Example 2 ＞1800 ＞1800 ＞1800 Example 3 ＞1800 ＞1800 ＞1800 Comparative Example 1 1523 1521 1520 Comparative Example 2 1726 1728 1725 Comparative Example 3 1712 1716 1714

[0093] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A method for preparing a silicon nitride composite refractory material, characterized in that: The following steps are involved: S1: Magnetic treatment of investment casting waste sand The investment casting waste sand is added into a mixer and dry-mixed, and then a water-based polyurethane resin is added and mixed and rolled to obtain water-based polyurethane resin-coated waste sand. The water-based polyurethane resin-coated waste sand and nano-barium ferrite magnetic particles are placed in a drum mixer and dry-mixed, and then placed in a mixer and continued to be mixed and rolled, and then placed in a molding machine for compression molding to obtain a waste sand blank. The waste sand blank is heat-treated and then naturally cooled to room temperature to obtain a magnetic waste sand casting. S2: Preparation of refractory premix Crushing the magnetic waste sand casting to obtain casting particles, placing the casting particles, silicon powder and zirconia balls into a ball mill, adding deionized water and ball milling to obtain ball milling slurry, spray drying the ball milling slurry to obtain a refractory premix; S3: Nitrogen sintering of refractory premix The refractory premix is placed in a reactor, the reactor is evacuated and nitrogen is introduced, and then the refractory premix is heated at a high temperature to obtain a refractory blank, and the refractory blank is placed in a pulse magnetic field magnetizer for magnetization to obtain a magnetized refractory blank; S4: Directional pressing and sintering of magnetized refractory blanks The magnetized refractory blank is filled into a mold, and then the mold is placed in a molding machine, and uniform speed pressurization is performed in a magnetic field to obtain a blank. The blank is placed in a flowing atmosphere sintering furnace, and nitrogen is continuously introduced and sintered. After natural cooling, a silicon nitride composite refractory material is obtained.

2. The method for preparing a silicon nitride composite refractory material according to claim 1, wherein: Step S1: magnetizing investment casting waste sand, comprising the following steps: S1.1: Add 8-10 parts by weight of investment casting waste sand to a mixer and dry mix at a mixing speed of 100-120 rpm for 15-20 minutes. Then, add 1.5-2 parts by weight of a 65-75% aqueous polyurethane resin to the mixer and continue mixing at a speed of 100-120 rpm for 15-20 minutes to obtain aqueous polyurethane resin-coated waste sand. S1.2: The waterborne polyurethane resin-coated waste sand prepared in step S1.1 and 1-2 parts by weight of nano-barium ferrite magnetic particles are dry-mixed in a drum mixer at a speed of 120-150 rpm for 20-25 minutes, then added to a mixer and continuously mixed for 15-20 minutes. The mixture is then pressed in a molding press at a pressure of 80-100 MPa to obtain a waste sand blank. S1.3: Place the waste sand blank in a box furnace, heat it from room temperature to 250-300°C at a heating rate of 4-5°C / min, hold it for 30-40 minutes, then heat it to 350-400°C at a heating rate of 2-3°C / min, hold it for 55-60 minutes, and then cool it naturally to room temperature to obtain a magnetic waste sand casting.

3. The method for preparing a silicon nitride composite refractory material according to claim 2, wherein: Step S2: Preparation of refractory premix, comprising the following steps: S2.1: The magnetic waste sand casting obtained in step S1.3 is crushed in a crusher to a particle size of 20-30 mm to obtain casting particles. The casting particles, silicon powder, and zirconium oxide balls are mixed in a mass ratio of 1:2-3:3-3.5 and added to a ball mill. After adding deionized water, the ball mill is started and the speed of the ball mill is adjusted to 250-300 rpm. The ball mill is milled for 1-1.5 hours to obtain a ball-milled slurry. S2.2: Place the ball-milled slurry in a spray dryer, adjust the feed temperature to 250-300°C, the nozzle angle to 40-60°, and the discharge temperature to 80-90°C, and spray dry the ball-milled slurry to obtain a refractory premix with a particle size of 10-100 μm.

4. The method for preparing a silicon nitride composite refractory material according to claim 3, wherein: Step S3, nitrogen sintering of the refractory premix, comprises the following steps: S3.1: Place the refractory premix prepared in step S2.2 into a reactor, seal the reactor, and then evacuate the reactor to a vacuum. Then, introduce nitrogen to bring the pressure in the reactor to 1.5-2.5 MPa. Then, heat the refractory premix at 1250-1300°C for 2-3 hours to obtain a refractory billet. S3.2: placing the refractory blank in a pulse magnetic field magnetizer, adjusting the magnetic field of the pulse magnetic field magnetizer to 1-1.5 T to magnetize the refractory blank to obtain a magnetized refractory blank.

5. The method for preparing a silicon nitride composite refractory material according to claim 1, wherein: Step S4, directional pressing and sintering of the magnetized refractory blank, comprises the following steps: S4.1: Place the magnetized refractory blank into a mold, then place the mold in a molding press. Set a 2-2.5T magnetic field around the mold. Adjust the pressure of the molding press to 100-120MPa at a rate of 18-20MPa / min. Continue pressing for 1-2 minutes to obtain a blank. S4.2: Place the green body in a flowing atmosphere sintering furnace, continuously introduce nitrogen, and heat it to 1000-1050°C at a heating rate of 5-6°C / min in a nitrogen atmosphere, then heat it to 1250-1300°C at a heating rate of 2-3°C / min, keep it at that temperature for 2-3 hours, and naturally cool it to room temperature to obtain a silicon nitride composite refractory material.

6. The method for preparing a silicon nitride composite refractory material according to claim 2, characterized in that: The mesh size of the investment casting waste sand in step S1.1 is 80-120 mesh, and the composition is 50-55wt% SiO2, 35-40wt% Al2O3, 6-8wt% ZrO2, 1.5-2wt% Fe2O3, and the rest is a small amount of CaO, MgO, K2O and Na2O metal oxides.

7. The method for preparing a silicon nitride composite refractory material according to claim 3, characterized in that: The particle size of the zirconia balls in step S2.1 is 1-2 mm.

8. The method for preparing a silicon nitride composite refractory material according to claim 3, characterized in that: After adding deionized water in step S2.1, the solid content of the slurry in the ball mill is 60-65%.

9. The method for preparing a silicon nitride composite refractory material according to claim 5, characterized in that: The mold in step S4.1 is a strip mold of 40 mm×40 mm×160 mm.

10. The method for preparing a silicon nitride composite refractory material according to claim 5, characterized in that: The magnetic field in step S4.1 is generated by placing electromagnets around the mold and energizing the electromagnets.

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