Preparation method of silicon nitride multiphase refractory material

Abstract

The invention relates to the field of refractory materials, in particular to a preparation method of a silicon nitride multiphase refractory material. The invention relates to a preparation method of a silicon nitride multiphase refractory material. The preparation method comprises the following steps: magnetizing investment casting waste sand; preparing a refractory premix; performing nitrogen sintering on the refractory premix; and directionally pressing and sintering the magnetized refractory blank. Nanometer barium ferrite magnetic particles are added into investment casting waste sand, then nitrogen sintering is conducted on a refractory premix, the nanometer barium ferrite magnetic particles are evenly dispersed in silicon nitride crystals, and then magnetizing and magnetic field directional pressing are conducted on the obtained refractory blank. The silicon nitride crystals combined with the nano barium ferrite magnetic particles are directionally arranged, the internal stress of the silicon nitride complex-phase refractory material during thermal expansion is reduced, the thermal expansion coefficient of the silicon nitride complex-phase refractory material is reduced, meanwhile, the thermal conductivity of the silicon nitride complex-phase refractory material can be effectively improved, and the fire resistance of the silicon nitride complex-phase refractory material is improved.

Description

Technical Field

[0001] The 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 also 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 which has low cost, simple preparation method and can make the material have excellent refractory properties.

[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 rolled for dry mixing, and then an aqueous polyurethane resin is added for mixing and rolling to obtain aqueous polyurethane resin coated waste sand, the aqueous polyurethane resin coated waste sand and nano barium ferrite magnetic particles are placed in a drum mixer for dry mixing, and then placed in a mixer and rolled for further mixing, and then placed in a molding press for compression molding to obtain a waste sand blank, and the waste sand blank is subjected to heat treatment and then naturally cooled to room temperature to obtain a magnetic waste sand casting;

[0008] S2: Preparation of refractory premix

[0009] The magnetic waste sand casting is crushed to obtain casting particles, the casting particles, silicon powder and zirconium oxide balls are put into a ball mill, deionized water is added and ball milled to obtain ball milling slurry, and the ball milling slurry is spray-dried 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 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 uniformly pressurized 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: 8-10 parts by weight of investment casting waste sand is added to a mixer, and dry mixed at a mixing speed of 100-120 rpm for 15-20 minutes, and then 1.5-2 parts by weight of a waterborne polyurethane resin with a concentration of 65-75% is added to the mixer, and the mixing is continued at a speed of 100-120 rpm for 15-20 minutes to obtain waterborne polyurethane resin coated waste sand;

[0016] S1.2: The waterborne polyurethane resin-coated waste sand obtained in step S1.1 and 1-2 parts by weight of nano-barium ferrite magnetic particles are placed in a drum mixer and dry-mixed at a speed of 120-150 rpm for 20-25 minutes, then added to a mixer and continued to be mixed and milled for 15-20 minutes, and then placed in a molding machine and pressed 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, keep it warm for 30-40 minutes, then heat it to 350-400°C at a heating rate of 2-3°C / min, keep it warm for 55-60 minutes, 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 placed in a crusher and crushed to a particle size of 20-30 mm to obtain casting particles, and the casting particles, silicon powder and zirconium oxide balls are mixed in a mass ratio of 1: (2-3): (3-3.5) and put into a ball mill, and after adding deionized water, the ball mill is started, and the speed of the ball mill is adjusted to 250-300 rpm, and the ball mill is ball milled for 1-1.5 hours to obtain a ball mill slurry;

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

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

[0022] S3.1: placing the refractory premix prepared in step S2.2 in a reactor, sealing the reactor, and then evacuating the reactor to a vacuum, introducing nitrogen to make the pressure in the reactor reach 1.5-2.5 MPa, and then heating the refractory premix at a temperature of 1250-1300° C. and keeping the temperature for 2-3 hours to obtain a refractory blank;

[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, and obtaining a magnetized refractory blank.

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

[0025] S4.1: Fill the magnetized refractory blank into the 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 pressurization speed of 18-20MPa / min, and 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, 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 warm 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 meshes, and the composition is 50-55wt% SiO 2 , 35-40wt% Al 2 O 3 , 6-8wt% ZrO 2 , 1.5-2wt% Fe 2 O 3 The rest is a small amount of CaO, MgO, K 2 O and Na 2 O metal oxides.

[0028] Furthermore, the particle size of the zirconium oxide 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 arranging 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, and 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 reducing 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 the waste sand of investment casting, and then mixes and grinds and heat treats the waste sand to make SiO 2 The nano-barium ferrite magnetic particles are adsorbed, and 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, avoiding uneven distribution of structural components of the silicon nitride composite refractory material in 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 waste sand coated with the aqueous polyurethane resin 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 investment casting waste sand on the barium ferrite magnetic particles during the subsequent heat treatment process, and introducing C and N elements into the magnetic waste sand casting, which form a ceramic-bonded carbon network with silicon nitride during the subsequent nitrogen sintering process of the refractory premix, thereby improving the refractory performance of the silicon nitride composite refractory material.

[0035] 4. The present invention uses silicon powder and investment casting waste sand as main materials to prepare silicon nitride composite refractory materials, wherein the main component of the investment casting waste sand is SiO 2 and Al 2 O 3After mixing with silicon powder and sintering in a nitrogen atmosphere, a silicon nitride composite refractory material with silicon nitride phase, silicon oxynitride phase and Sialon phase as main components is obtained. 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 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 1 The present invention 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 be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] Example 1

[0040] A method for preparing a silicon nitride composite refractory material, 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 is added into a mixer, wherein the mesh size of the investment casting waste sand is 80 mesh and the composition is 50wt% SiO 2 , 40wt%Al 2 O 3 , 6wt% ZrO 2 , 2wt%Fe 2 O 3 The rest is a small amount of CaO, MgO, K 2 O and Na 2 O metal oxide, dry-mixing at a mixing speed of 100 rpm for 15 minutes, then adding 1.5 parts by weight of a 65% aqueous polyurethane resin into the mixer, and continuing to mix at a 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 obtained in step S1.1 and 1 part by weight of nano-barium ferrite magnetic particles are placed in a drum mixer and dry-mixed at a speed of 120 rpm for 20 minutes, then added to a mixer and continuously mixed for 15 minutes, and then placed in a molding machine and pressed at a pressure of 80 MPa to obtain a waste sand blank;

[0044] S1.3: Place the waste sand blank in a box furnace, heat it from room temperature to 250°C at a heating rate of 4°C / min, keep it warm for 30 minutes, then heat it to 350°C at a heating rate of 2°C / min, keep it warm for 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 placed in a crusher and crushed to a particle size of 20 mm to obtain casting particles, and 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 put into a ball mill, and deionized water is added to make the solid content of the slurry 60%, and then the ball mill is started, and the speed of the ball mill is adjusted to 250 rpm, and ball milling is performed for 1 hour to obtain ball milled slurry;

[0047] S2.2: The ball mill slurry is placed in a spray dryer, and the feed temperature is adjusted to 250°C, the nozzle angle is 40°, and the discharge temperature is 80°C. The ball mill slurry is spray dried to obtain a refractory premix with a particle size of 10 μm.

[0048] S3: Nitrogen sintering of refractory premix

[0049] S3.1: placing the refractory premix prepared in step S2.2 in a reactor, sealing the reactor, and then evacuating the reactor to a vacuum, introducing nitrogen to make the pressure in the reactor reach 1.5 MPa, and then heating the refractory premix at a temperature of 1250° C. and keeping the temperature for 2 hours to obtain a refractory blank;

[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: The magnetized refractory blank is filled into a strip mold of 40 mm × 40 mm × 160 mm, and then the mold is placed in a molding press, and a 2T magnetic field is set around the mold, and the pressure of the molding press is adjusted to increase the pressure to 100 MPa at a pressurization speed of 18 MPa / min, and the pressing is continued for 1 minute to obtain a blank;

[0053] S4.2: The green body is placed in a flowing atmosphere sintering furnace, nitrogen is continuously introduced, and the temperature is increased to 1000°C at a heating rate of 5°C / min in a nitrogen atmosphere, and then the temperature is increased to 1250°C at a heating rate of 2°C / min, and the temperature is kept for 2 hours, and the green body is naturally cooled to room temperature to obtain a silicon nitride composite refractory material. The silicon nitride composite refractory material is observed 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, 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 investment casting waste sand is added into a mixer, wherein the mesh size of the investment casting waste sand is 80 mesh and the composition is 55wt% SiO 2 , 35wt%Al 2 O 3 , 8wt% ZrO 2 , 1.5wt%Fe 2 O 3 The rest is a small amount of CaO, MgO, K 2 O and Na 2 O metal oxide, dry-mix at a mixing speed of 100 rpm for 15 minutes, then add 2 parts by weight of a 65% aqueous polyurethane resin into the mixer, and continue mixing at a speed of 100 rpm for 15 minutes to obtain aqueous polyurethane resin-coated waste sand;

[0058] S1.2: The waterborne polyurethane resin-coated waste sand obtained in step S1.1 and 2 parts by weight of nano-barium ferrite magnetic particles are placed in a drum mixer and dry-mixed at a speed of 120 rpm for 20 minutes, then added to a mixer and continuously mixed for 15 minutes, and then placed in a molding machine and pressed at a pressure of 80 MPa to obtain a waste sand blank;

[0059] S1.3: Place the waste sand blank in a box furnace, heat it from room temperature to 250°C at a heating rate of 4°C / min, keep it warm for 30 minutes, then heat it to 350°C at a heating rate of 2°C / min, keep it warm for 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 placed in a crusher and crushed to a particle size of 20 mm to obtain casting particles, and 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 put into a ball mill, and deionized water is added to make the slurry solid content 65%, and then the ball mill is started, and the speed of the ball mill is adjusted to 250 rpm, and ball milling is performed for 1 hour to obtain ball milled slurry;

[0062] S2.2: The ball mill slurry is placed in a spray dryer, and the feed temperature is adjusted to 250°C, the nozzle angle is 40°, and the discharge temperature is 80°C. The ball mill slurry is spray dried to obtain a refractory premix with a particle size of 10 μm.

[0063] S3: Nitrogen sintering of refractory premix

[0064] S3.1: placing the refractory premix prepared in step S2.2 in a reactor, sealing the reactor, and then evacuating the reactor to a vacuum, introducing nitrogen to make the pressure in the reactor reach 1.5 MPa, and then heating the refractory premix at a temperature of 1250° C. and keeping the temperature for 2 hours to obtain a refractory blank;

[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: The magnetized refractory blank is filled into a strip mold of 40 mm × 40 mm × 160 mm, and then the mold is placed in a molding press, and a 2T magnetic field is set around the mold, and the pressure of the molding press is adjusted to increase the pressure to 100 MPa at a pressurization speed of 18 MPa / min, and the pressing is continued for 1 minute to obtain a blank;

[0068] S4.2: The green body is placed in a flowing atmosphere sintering furnace, nitrogen is continuously introduced, and the temperature is increased to 1000°C at a heating rate of 5°C / min in a nitrogen atmosphere, and then the temperature is increased to 1250°C at a heating rate of 2°C / min, and the temperature is kept for 2 hours, and the green body is naturally cooled to room temperature to obtain a silicon nitride composite refractory material. The silicon nitride composite refractory material is observed 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, 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 investment casting waste sand is added into a mixer, wherein the mesh size of the investment casting waste sand is 120 mesh and the composition is 50wt% SiO 2 , 40wt%Al 2 O 3 , 6wt% ZrO 2 , 2wt%Fe 2 O 3 The rest is a small amount of CaO, MgO, K 2 O and Na 2 O metal oxide, dry-mix at a mixing speed of 120 rpm for 20 minutes, then add 1.5 parts by weight of a 75% aqueous polyurethane resin into the mixer, and continue mixing at a speed of 120 rpm for 20 minutes to obtain aqueous polyurethane resin coated waste sand;

[0073] S1.2: The waterborne polyurethane resin-coated waste sand obtained in step S1.1 and 1 part by weight of nano-barium ferrite magnetic particles are placed in a drum mixer and dry-mixed at a speed of 150 rpm for 25 minutes, then added to a mixer and continuously mixed for 20 minutes, and then placed in a molding machine and pressed at a pressure of 100 MPa to obtain a waste sand blank;

[0074] S1.3: Place the waste sand blank in a box furnace, heat it from room temperature to 3000°C at a heating rate of 5°C / min, keep it warm for 40 minutes, then heat it to 400°C at a heating rate of 3°C / min, keep it warm for 60 minutes, and then naturally cool it 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 placed in a crusher and crushed to a particle size of 30 mm to obtain casting particles, and 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 put into a ball mill, and deionized water is added to make the solid content of the slurry 60%, and then the ball mill is started, and the speed of the ball mill is adjusted to 300 rpm, and ball milling is performed for 1.5 hours to obtain ball milled slurry;

[0077] S2.2: The ball mill slurry is placed in a spray dryer, the feed temperature is adjusted to 300°C, the nozzle angle is 60°, and the discharge temperature is 90°C, and the ball mill slurry is spray dried to obtain a refractory premix with a particle size of 100 μm.

[0078] S3: Nitrogen sintering of refractory premix

[0079] S3.1: placing the refractory premix prepared in step S2.2 in a reactor, sealing the reactor, and then evacuating the reactor to a vacuum, introducing nitrogen to make the pressure in the reactor reach 2.5 MPa, and then heating the refractory premix at a temperature of 1300° C. and keeping the temperature for 3 hours to obtain a refractory blank;

[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, and obtaining a magnetized refractory blank.

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

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

[0083] S4.2: The green body is placed in a flowing atmosphere sintering furnace, nitrogen is continuously introduced, and the temperature is increased to 1050°C at a heating rate of 6°C / min in a nitrogen atmosphere, and then the temperature is increased to 1300°C at a heating rate of 3°C / min, and the temperature is kept for 3 hours, and the green body is naturally cooled to room temperature to obtain a silicon nitride composite refractory material. The silicon nitride composite refractory material is observed 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.

[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, and step S3.2 is removed. In step S4.1, a 2T magnetic field is not set around the mold, 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 prepared 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 a ball mill with the casting particles, silicon powder and zirconium oxide balls, and the remaining steps are the same as those in Example 1. The prepared 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 a mixer and dry-mixed, and then directly placed in a drum mixer with nano-barium ferrite magnetic particles for dry mixing, and the remaining steps are the same as those of Example 1. The obtained silicon nitride composite refractory material is recorded as Comparative Example 3.

[0090] The silicon nitride composite refractory material prepared in the embodiment, comparative example 1, comparative example 2 and comparative example 3 were respectively taken, and three test cones with each side of the upper bottom being 2 mm long, each side of the lower bottom being 8 mm long and the height being 30 mm were sawed out respectively. Referring to "GBT7322-2007 Test Method for Refractoriness of Refractory Materials", the test cones were placed in a refractory furnace and heated at a heating rate of 5°C / min. The furnace was kept in an oxidizing atmosphere with an oxygen concentration of 21%. When any test cone was bent to the point where its tip contacted the cone, the temperature tested by the temperature measuring thermocouple was recorded. When all the test cones or the standard temperature measuring cones were bent to the point where their tips contacted the cone, the data were recorded and tabulated. As shown in Table 1, it can be seen that the silicon nitride composite refractory material prepared in the embodiment 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, which can prove that adding 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 directional pressing in the magnetic field. It can also be proved that coating the investment casting waste sand with water-based polyurethane resin and then mixing and grinding it with nano barium ferrite magnetic particles 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 familiar with 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 a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still 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 rolled for dry mixing, and then an aqueous polyurethane resin is added for mixing and rolling to obtain aqueous polyurethane resin coated waste sand, the aqueous polyurethane resin coated waste sand and nano barium ferrite magnetic particles are placed in a drum mixer for dry mixing, and then placed in a mixer and rolled for further mixing, and then placed in a molding press for compression molding to obtain a waste sand blank, and the waste sand blank is subjected to heat treatment and then naturally cooled to room temperature to obtain a magnetic waste sand casting; S2: Preparation of refractory premix The magnetic waste sand casting is crushed to obtain casting particles, the casting particles, silicon powder and zirconium oxide balls are put into a ball mill, deionized water is added and ball milled to obtain ball milling slurry, and the ball milling slurry is spray-dried 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 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 uniformly pressurized 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, characterized in that: Step S1: magnetizing waste sand from investment casting, comprising the following steps: S1.1: 8-10 parts by weight of investment casting waste sand is added to a mixer, and dry mixed at a mixing speed of 100-120 rpm for 15-20 minutes, and then 1.5-2 parts by weight of a waterborne polyurethane resin with a concentration of 65-75% is added to the mixer, and the mixing is continued at a speed of 100-120 rpm for 15-20 minutes to obtain waterborne polyurethane resin coated waste sand; S1.2: The waterborne polyurethane resin-coated waste sand obtained in step S1.1 and 1-2 parts by weight of nano-barium ferrite magnetic particles are placed in a drum mixer and dry-mixed at a speed of 120-150 rpm for 20-25 minutes, then added to a mixer and continued to be mixed and milled for 15-20 minutes, and then placed in a molding machine and pressed 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, keep it warm for 30-40 minutes, then heat it to 350-400°C at a heating rate of 2-3°C / min, keep it warm for 55-60 minutes, 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 1, characterized in that: Step S2: Preparation of refractory premix, comprising the following steps: S2.1: The magnetic waste sand casting obtained in step S1.3 is placed in a crusher and crushed to a particle size of 20-30 mm to obtain casting particles, and the casting particles, silicon powder and zirconium oxide balls are mixed in a mass ratio of 1: (2-3): (3-3.5) and put into a ball mill, and after adding deionized water, the ball mill is started, and the speed of the ball mill is adjusted to 250-300 rpm, and the ball mill is ball milled for 1-1.5 hours to obtain a ball mill slurry; S2.2: The ball mill slurry is placed in a spray dryer, the feed temperature is adjusted to 250-300°C, the nozzle angle is 40-60°, the discharge temperature is 80-90°C, and the ball mill slurry is spray dried 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 1, characterized in that: Step S3: Nitrogen sintering of the refractory premix, comprising the following steps: S3.1: placing the refractory premix prepared in step S2.2 in a reactor, sealing the reactor, and then evacuating the reactor to a vacuum, introducing nitrogen to make the pressure in the reactor reach 1.5-2.5 MPa, and then heating the refractory premix at a temperature of 1250-1300° C. and keeping the temperature for 2-3 hours to obtain a refractory blank; 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, and obtaining a magnetized refractory blank.

5. The method for preparing a silicon nitride composite refractory material according to claim 1, characterized in that: Step S4: Directional pressing and sintering of the magnetized refractory blank, comprising the following steps: S4.1: Fill the magnetized refractory blank into the 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 pressurization speed of 18-20MPa / min, and 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, 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 warm 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 meshes, 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 zirconium oxide 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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