Si3n4 / sic composite powder, low-carbon magnesium-carbon refractory and preparation method thereof

Abstract

Si3N4 / SiC composite powder, low-carbon magnesia-carbon refractory material and preparation method thereof, relate to the technical field of low-carbon magnesia-carbon refractory material. The Si3N4 / SiC composite powder contains 70-80 wt% of Si3N4 and 20-25 wt% of SiC, and both Si3N4 and SiC are in a whisker structure and interweave to form a network structure. The Si3N4 / SiC composite powder has the advantages of high crystallinity, few defects, high purity and few micropores, and its preparation process is simple and low in cost, solves the problem of deterioration of the performance of carbon-containing refractory material caused by non-crystalline SiO2, micropores and crystal defects in the synthesis of Si3N4 / SiC composite powder from rice husk, makes the agricultural waste rice husk get high-value utilization, and plays a positive role in environmental protection, and the low-carbon magnesia-carbon refractory material added with the Si3N4 / SiC composite powder has excellent thermal shock resistance and corrosion resistance.

Description

Technical Field

[0001] This invention relates to the field of low-carbon magnesium-carbon refractory materials technology, and in particular to a Si3N4 / SiC composite powder, a low-carbon magnesium-carbon refractory material with added Si3N4 / SiC composite powder, and its preparation method. Background Technology

[0002] Currently, the reduction of carbon content in magnesia-carbon refractories has become a development trend, but the reduction of graphite content will inevitably reduce the material's thermal shock resistance and erosion resistance.

[0003] Some researchers have found that introducing Al4O4C powder into magnesia-carbon refractories allows Al4O4C to oxidize into Al2O3 and carbon, compensating for carbon loss and forming a MgAl2O4 protective layer on the refractory surface, thus improving the refractories' oxidation resistance. Other researchers have found that partially replacing flake graphite in magnesia-carbon refractories with MAX phase Ti3AlC2 powder, along with the composite addition of Ti3AlC2 and Si powder, can slow down the oxidation rate of Ti3AlC2 and reduce excessive expansion of the material, thereby improving its thermomechanical strength. Furthermore, the oxidation products of Ti3AlC2 can effectively prevent slag erosion. While these additives possess excellent high-temperature oxidation resistance, high thermal conductivity, and high fracture toughness, and their introduction into carbon-containing refractories can improve oxidation resistance while maintaining or even enhancing thermal shock resistance and erosion resistance, the high cost of these additives limits their large-scale application in the refractory market.

[0004] Si3N4 whiskers and SiC whiskers possess excellent physicochemical properties, making them excellent additives for carbon-containing refractories. Rice husks, agricultural waste, are rich in Si and C elements, and can be used to prepare high-purity, high-value-added ceramic materials. If abundant and inexpensive rice husks could be converted into Si3N4 and SiC and applied to carbon-containing refractories, it would help improve material properties, comprehensively utilize rice husks, avoid resource waste, and reduce environmental pollution. However, current rice husk-based Si3N4 and SiC products contain high levels of amorphous SiO2, exhibiting numerous micropores and crystal defects, limiting their application in carbon-containing refractories. To date, there are no reports on the application of Si3N4 / SiC composite powder synthesized from rice husks in low-carbon magnesia-carbon refractories. Summary of the Invention

[0005] One of the objectives of this invention is to provide a Si3N4 / SiC composite powder with high crystallinity, few defects, high purity, and few micropores.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: Si3N4 / SiC composite powder, comprising 70~80wt% Si3N4 and 20~25wt% SiC, wherein both Si3N4 and SiC are whisker structures and intertwine to form a network structure.

[0007] The above-mentioned Si3N4 / SiC composite powder can be prepared by the following steps:

[0008] Step 1: Mix the catalyst and rice husk powder evenly under water bath conditions, and dry them to obtain the raw material with the catalyst supported.

[0009] Step 2: Under a nitrogen atmosphere and at 1350~1450℃, keep warm for 3~5 hours to obtain the nitrided product;

[0010] Step 3: Wet-mix the nitrided product and dry it to obtain Si3N4 / SiC composite powder.

[0011] The mass ratio of the catalyst to rice husk powder is 1:(40-50).

[0012] The catalyst is one of ferric nitrate nonahydrate, nickel nitrate hexahydrate, and cobalt nitrate hexahydrate.

[0013] In step 1, the water bath temperature is 25-40℃, the drying temperature is 90-110℃, and the drying time is 24-30h.

[0014] In step 2, the supported catalyst raw material is heated to 1350-1450℃ at a rate of 4-5℃ / min.

[0015] In step 3, the nitrided product is wet-mixed with anhydrous ethanol as a solvent for 3-4 hours and dried at 90-110°C.

[0016] Another object of the present invention is to provide a low-carbon magnesia-carbon refractory material with added Si3N4 / SiC composite powder, comprising the following components: 60-70 wt% fused magnesia aggregate, 20-30 wt% fused magnesia fine powder, 1-4 wt% alumina powder, 3-5 wt% silicon powder, 2-4 wt% flake graphite, 1-3 wt% Si3N4 / SiC composite powder, and a binder comprising 3-5 wt% of the total amount of the aforementioned components.

[0017] The fused magnesia aggregate is composed of fused magnesia with particle sizes of 1-3 mm and 0-1 mm, and has a purity of ≥97 wt%.

[0018] The fused magnesia fine powder has a particle size ≤100μm and a purity ≥97wt%; the alumina powder has a particle size ≤100μm and a purity ≥98wt%; the silicon powder has a particle size ≤100μm and a purity ≥99wt%; and the flake graphite has a particle size ≤150μm and a purity ≥97wt%.

[0019] The binder is a liquid thermosetting phenolic resin with a residual carbon content of 45-48 wt%.

[0020] In addition, the present invention also provides a method for preparing a low-carbon magnesium-carbon refractory material with added Si3N4 / SiC composite powder, which includes the following steps:

[0021] The raw materials of each component are stirred evenly, pressed into shape under 150-200 MPa, and cured at 110-150℃ for 12-16 hours; then, in a nitrogen atmosphere, the temperature is raised to 1300-1500℃ at 5-10℃ / min, held for 3-5 hours, and naturally cooled to obtain a low-carbon magnesium-carbon refractory material with added Si3N4 / SiC composite powder.

[0022] The Si3N4 / SiC composite powder of this invention has the advantages of high crystallinity, few defects, high purity, and few micropores. Moreover, its preparation process is simple and low-cost. It solves the problem that the presence of amorphous SiO2, micropores, and crystal defects in the synthesis of Si3N4 / SiC composite powder using rice husks degrades the performance of carbon-containing refractory materials. This enables the high-value utilization of agricultural waste rice husks and plays a positive role in environmental protection. Furthermore, the low-carbon magnesium-carbon refractory material prepared with Si3N4 / SiC composite powder has excellent thermal shock resistance and erosion resistance. Attached Figure Description

[0023] Figure 1 The XRD pattern of the Si3N4 / SiC composite powder prepared in this invention;

[0024] Figure 2 SEM image 1 of the low-carbon magnesium-carbon refractory material with added Si3N4 / SiC composite powder prepared for this invention;

[0025] Figure 3 SEM image 2 of the low-carbon magnesium-carbon refractory material with added Si3N4 / SiC composite powder prepared according to the present invention. Detailed Implementation

[0026] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments and accompanying drawings. The content mentioned in the embodiments is not intended to limit the present invention. It should be noted in advance that the following embodiments were completed in a laboratory setting. Those skilled in the art should understand that the amounts of each component given in the embodiments only represent the ratio between the components, and are not specific limitations.

[0027] Most existing low-carbon magnesia-carbon refractory materials are made from fused magnesia aggregate and flake graphite as the main raw materials, phenolic resin as the binder, and a small amount of silica powder, alumina and other additives. They are prepared by mixing, molding, curing and heat treatment.

[0028] From the perspective of raw materials: existing low-carbon magnesia-carbon refractories have not successfully applied rice husk-based Si3N4 / SiC composite powder to low-carbon carbon-containing refractories. This invention uses rice husks as a raw material to synthesize Si3N4 / SiC composite powder and successfully applies it to low-carbon magnesia-carbon refractories. This realizes the transformation of agricultural waste rice husks into a valuable resource, achieving high-value utilization and promoting environmental protection, thus possessing significant economic and social value.

[0029] From a technological perspective: 1) Existing rice husk-based SiC and Si3N4 products contain high levels of amorphous SiO2, exhibiting numerous micropores and crystal defects. Applying these to carbon-containing refractory materials degrades their high-temperature performance. This invention employs a catalytic nitridation method to synthesize a Si3N4 / SiC composite powder with high crystallinity, few defects, and high purity. A wet mixing process is used on the rice husk-based product to effectively reduce micropores in the Si3N4 / SiC composite powder, solving the problem of amorphous SiO2, micropores, and crystal defects in existing rice husk-based Si3N4 / SiC composite powders degrading the performance of magnesia-carbon refractory materials. 2) Existing magnesia-carbon refractory materials primarily rely on additives or in-situ ceramic phases to improve material properties. This invention utilizes the additive Si3N4 / SiC composite powder and the in-situ ceramic phase to synergistically enhance low-carbon magnesia-carbon refractory materials, achieving a synergistic effect greater than the sum of its parts.

[0030] Based on the above-mentioned inventive concept, the present invention provides a method for preparing a low-carbon magnesium-carbon refractory material with added Si3N4 / SiC composite powder, as detailed below:

[0031] Using 60–70 wt% fused magnesia aggregate, 20–30 wt% fused magnesia fine powder, 1–4 wt% alumina powder, 3–5 wt% silicon powder, 2–4 wt% flake graphite, and 1–3 wt% Si3N4 / SiC composite powder as raw materials, and adding 3–5 wt% binder to the raw materials, the mixture is stirred evenly, pressed into shape under 150–200 MPa, and cured at 110–150 °C for 12–16 h; then, under a nitrogen atmosphere, the temperature is raised to 1300–1500 °C at 5–10 °C / min, held for 3–6 h, and naturally cooled to obtain a low-carbon magnesia-carbon refractory material with added Si3N4 / SiC composite powder.

[0032] The fused magnesia aggregate is composed of a mixture of fused magnesia with particle sizes of 3-1 mm and 1-0 mm, with a purity ≥97 wt%. The fine fused magnesia powder has a particle size ≤100 μm and a purity ≥97 wt%. The alumina powder has a particle size ≤100 μm and a purity ≥98 wt%. The silica powder has a particle size ≤100 μm and a purity ≥99 wt%. The flake graphite has a particle size ≤150 μm and a purity ≥97 wt%. The binder is liquid thermosetting phenolic resin with a residual carbon content of 45-48 wt%. The nitrogen gas has a purity ≥99.9 vol.

[0033] The preparation method of the Si3N4 / SiC composite powder in the above raw materials is as follows:

[0034] Step 1: Mix the catalyst and rice husk powder evenly in a water bath at 25-40℃ according to the mass ratio of catalyst to rice husk powder of 1:(40-50), and then dry them at 90-110℃ for 24-30h to obtain the raw material with catalyst support.

[0035] Step 2: Under a nitrogen atmosphere, the raw material with the supported catalyst is heated to 1350-1450℃ at a rate of 4-5℃ / min, held at that temperature for 3-5 hours, and then naturally cooled to obtain the nitrided product.

[0036] Step 3: Using anhydrous ethanol as a solvent, wet mix the nitrided product at a speed of 200~250 r / min for 3~4 h, and dry it at 90~110℃ to obtain Si3N4 / SiC composite powder.

[0037] The Si3N4 / SiC composite powder prepared by the above method has a network structure in which Si3N4 whiskers and SiC whiskers are interwoven, with the content of Si3N4 being 70~80wt% and the content of SiC being 20~25wt%.

[0038] The catalyst is one of ferric nitrate nonahydrate, nickel nitrate hexahydrate, and cobalt nitrate hexahydrate; the purity of ferric nitrate nonahydrate is ≥98.5wt%, the purity of nickel nitrate hexahydrate is ≥98.0wt%, and the purity of cobalt nitrate hexahydrate is ≥98.5wt%; the particle size of rice husk powder is ≤60μm.

[0039] The following detailed explanation uses specific examples. Example 1

[0040] This embodiment prepares a low-carbon magnesium-carbon refractory material with added Si3N4 / SiC composite powder according to the following method:

[0041] Using 64 wt% fused magnesia aggregate, 25 wt% fused magnesia fine powder, 1 wt% alumina powder, 4 wt% silicon powder, 4 wt% flake graphite, and 2 wt% Si3N4 / SiC composite powder as raw materials, and adding 4 wt% of the raw materials as binder (liquid thermosetting phenolic resin was used in this embodiment), the mixture was stirred evenly, pressed into shape under 160 MPa, and cured at 120°C for 14 h; then, in a nitrogen atmosphere, the temperature was raised to 1350°C at 5°C / min, held for 4 h, and naturally cooled to obtain a low-carbon magnesia-carbon refractory material with added Si3N4 / SiC composite powder.

[0042] In this embodiment, the Si3N4 / SiC composite powder in the raw material is prepared according to the following method:

[0043] Step 1: Mix the catalyst (ferric nitrate nonahydrate is used in this example) and rice husk powder at a mass ratio of 1:50 in a water bath at 25°C until homogeneous. Then dry the mixture at 110°C for 24 hours to obtain the raw material with the catalyst supported.

[0044] Step 2: Under a nitrogen atmosphere, the supported catalyst raw material is heated to 1350°C at a rate of 5°C / min, held at that temperature for 4 hours, and then naturally cooled to obtain the nitrided product.

[0045] Step 3: Using anhydrous ethanol as a solvent, the nitrided product is wet-mixed at 200 r / min for 3 h, and then dried at 110 °C to obtain Si3N4 / SiC composite powder.

[0046] The low-carbon magnesium-carbon refractory material with added Si3N4 / SiC composite powder prepared in this embodiment has the following properties after testing: room temperature flexural strength is 16.3 MPa; room temperature compressive strength is 81.0 MPa; high temperature flexural strength is 10.0 MPa (held at 1400℃ for 30 min); residual flexural strength retention rate is 77% (quenched in water at 1100℃ 4 times); residual compressive strength retention rate is 80% (quenched in water at 1100℃ 4 times); and erosion depth is 784 μm (eroded at 1400℃ for 4 h). Example 2

[0047] This embodiment prepares a low-carbon magnesium-carbon refractory material with added Si3N4 / SiC composite powder according to the following method:

[0048] Using 66 wt% fused magnesia aggregate, 20 wt% fused magnesia fine powder, 2 wt% alumina powder, 5 wt% silicon powder, 4 wt% flake graphite, and 3 wt% Si3N4 / SiC composite powder as raw materials, and adding 5 wt% of the raw materials as binder (liquid thermosetting phenolic resin was used in this embodiment), the mixture was stirred evenly, pressed into shape under 150 MPa, and cured at 120°C for 12 h; then, under a nitrogen atmosphere, the temperature was raised to 1400°C at 6°C / min, held for 3.5 h, and naturally cooled to obtain a low-carbon magnesia-carbon refractory material with added Si3N4 / SiC composite powder.

[0049] In this embodiment, the Si3N4 / SiC composite powder in the raw material is prepared according to the following method:

[0050] Step 1: Mix the catalyst (cobalt nitrate hexahydrate is used in this embodiment) and rice husk powder at a mass ratio of 1:40 in a water bath at 25°C until homogeneous. Then dry the mixture at 100°C for 24 hours to obtain the raw material with the catalyst supported.

[0051] Step 2: Under a nitrogen atmosphere, the supported catalyst raw material is heated to 1400℃ at a rate of 4℃ / min, held at that temperature for 3.5h, and then naturally cooled to obtain the nitrided product.

[0052] Step 3: Using anhydrous ethanol as a solvent, the nitrided product is wet-mixed at 220 r / min for 3.5 h and then dried at 90 °C to obtain Si3N4 / SiC composite powder.

[0053] The low-carbon magnesium-carbon refractory material with added Si3N4 / SiC composite powder prepared in this embodiment has the following properties after testing: room temperature flexural strength is 17.3 MPa; room temperature compressive strength is 93.0 MPa; high temperature flexural strength is 12.5 MPa (held at 1400℃ for 30 min); residual flexural strength retention rate is 81% (quenched in water at 1100℃ 4 times); residual compressive strength retention rate is 90% (quenched in water at 1100℃ 4 times); and erosion depth is 724 μm (eroded at 1400℃ for 4 h). Example 3

[0054] This embodiment prepares a low-carbon magnesium-carbon refractory material with added Si3N4 / SiC composite powder according to the following method:

[0055] Using 65wt% fused magnesia aggregate, 23wt% fused magnesia fine powder, 4wt% alumina powder, 3wt% silicon powder, 2wt% flake graphite, and 3wt% Si3N4 / SiC composite powder as raw materials, and adding 5wt% of the raw materials as binder (liquid thermosetting phenolic resin was used in this embodiment), the mixture was stirred evenly, pressed into shape under 200MPa, and cured at 140℃ for 15h; then, in a nitrogen atmosphere, the temperature was raised to 1500℃ at 6℃ / min, held for 5h, and naturally cooled to obtain a low-carbon magnesia-carbon refractory material with added Si3N4 / SiC composite powder.

[0056] In this embodiment, the Si3N4 / SiC composite powder in the raw material is prepared according to the following method:

[0057] Step 1: Mix the catalyst (nickel nitrate hexahydrate is used in this embodiment) and rice husk powder at a mass ratio of 1:45 in a water bath at 40°C until homogeneous. Then dry the mixture at 110°C for 28 hours to obtain the raw material with the catalyst supported.

[0058] Step 2: Under a nitrogen atmosphere, the supported catalyst raw material is heated to 1400℃ at a rate of 4.5℃ / min, held at that temperature for 4 hours, and then naturally cooled to obtain the nitrided product.

[0059] Step 3: Using anhydrous ethanol as a solvent, the nitrided product is wet-mixed at 250 r / min for 3 h, and then dried at 100 °C to obtain Si3N4 / SiC composite powder.

[0060] The low-carbon magnesium-carbon refractory material with added Si3N4 / SiC composite powder prepared in this embodiment has the following properties after testing: room temperature flexural strength is 15.0 MPa; room temperature compressive strength is 86.6 MPa; high temperature flexural strength is 11.3 MPa (held at 1400℃ for 30 min); residual flexural strength retention rate is 75% (quenched in water at 1100℃ 4 times); residual compressive strength retention rate is 91% (quenched in water at 1100℃ 4 times); and erosion depth is 846 μm (eroded at 1400℃ for 4 h). Example 4

[0061] This embodiment prepares a low-carbon magnesium-carbon refractory material with added Si3N4 / SiC composite powder according to the following method:

[0062] Using 60wt% fused magnesia aggregate, 30wt% fused magnesia fine powder, 3wt% alumina powder, 3wt% silicon powder, 3wt% flake graphite, and 1wt% Si3N4 / SiC composite powder as raw materials, and adding 3wt% of the raw materials as binder (liquid thermosetting phenolic resin is used in this embodiment), the mixture is stirred evenly, pressed into shape under 150MPa, and cured at 150℃ for 16h; then, in a nitrogen atmosphere, the temperature is raised to 1450℃ at 8℃ / min, held for 4h, and naturally cooled to obtain a low-carbon magnesia-carbon refractory material with added Si3N4 / SiC composite powder.

[0063] In this embodiment, the Si3N4 / SiC composite powder in the raw material is prepared according to the following method:

[0064] Step 1: Mix the catalyst (ferric nitrate nonahydrate used in this embodiment) and rice husk powder at a mass ratio of 1:45 in a water bath at 25°C until homogeneous, and then dry at 110°C for 24 hours to obtain the raw material with the catalyst supported.

[0065] Step 2: Under a nitrogen atmosphere, the supported catalyst raw material is heated to 1350°C at a rate of 5°C / min, held at that temperature for 5 hours, and then naturally cooled to obtain the nitrided product.

[0066] Step 3: Using anhydrous ethanol as a solvent, the nitrided product is wet-mixed at 220 r / min for 4 h, and then dried at 90 °C to obtain Si3N4 / SiC composite powder.

[0067] The low-carbon magnesium-carbon refractory material with Si3N4 / SiC composite powder prepared in this embodiment has the following properties after testing: room temperature flexural strength is 16.8 MPa; room temperature compressive strength is 89.2 MPa; high temperature flexural strength is 11.7 MPa (held at 1400℃ for 30 min); residual flexural strength retention rate is 88% (quenched in water at 1100℃ 4 times); residual compressive strength retention rate is 93% (quenched in water at 1100℃ 4 times); and erosion depth is 813 μm (eroded at 1400℃ for 4 h). Example 5

[0068] This embodiment prepares a low-carbon magnesium-carbon refractory material with added Si3N4 / SiC composite powder according to the following method:

[0069] Using 70wt% fused magnesia aggregate, 21wt% fused magnesia fine powder, 2wt% alumina powder, 3wt% silicon powder, 2wt% flake graphite, and 2wt% Si3N4 / SiC composite powder as raw materials, and adding 5wt% of the raw materials as binder (liquid thermosetting phenolic resin is used in this embodiment), the mixture is stirred evenly, pressed into shape under 200MPa, and cured at 150℃ for 12h; then, in a nitrogen atmosphere, the temperature is raised to 1400℃ at 5℃ / min, held for 4h, and naturally cooled to obtain a low-carbon magnesia-carbon refractory material with added Si3N4 / SiC composite powder.

[0070] In this embodiment, the Si3N4 / SiC composite powder in the raw material is prepared according to the following method:

[0071] Step 1: Mix the catalyst (nickel nitrate hexahydrate is used in this embodiment) and rice husk powder at a mass ratio of 1:50 in a water bath at 40°C until homogeneous. Then dry the mixture at 100°C for 30 hours to obtain the raw material with the catalyst supported.

[0072] Step 2: Under a nitrogen atmosphere, the supported catalyst raw material is heated to 1450°C at a rate of 5°C / min, held at that temperature for 3 hours, and then naturally cooled to obtain the nitrided product.

[0073] Step 3: Using anhydrous ethanol as a solvent, the nitrided product is wet-mixed at 250 r / min for 3.5 h and then dried at 100 °C to obtain Si3N4 / SiC composite powder.

[0074] The low-carbon magnesium-carbon refractory material with added Si3N4 / SiC composite powder prepared in this embodiment has the following properties after testing: room temperature flexural strength is 18.0 MPa; room temperature compressive strength is 91.3 MPa; high temperature flexural strength is 13.0 MPa (held at 1400℃ for 30 min); residual flexural strength retention rate is 77% (quenched in water at 1100℃ 4 times); residual compressive strength retention rate is 84% ​​(quenched in water at 1100℃ 4 times); and erosion depth is 985 μm (eroded at 1400℃ for 4 h).

[0075] Compared with the prior art, the present invention has the following characteristics:

[0076] The preparation method used in this invention mainly involves mixing fused magnesia aggregate, fused magnesia fine powder, alumina powder, silicon powder, flake graphite, Si3N4 / SiC composite powder and phenolic resin, pressing them into shape, curing them, and then firing them in a nitrogen atmosphere furnace. The whole process is very simple and suitable for large-scale production. Moreover, all the main raw materials used are commercially available, inexpensive, and have low production costs.

[0077] This invention uses rice husks as raw material to synthesize Si3N4 / SiC composite powder and successfully applies it to low-carbon magnesium-carbon refractory materials. This realizes the transformation of agricultural waste rice husks into valuable resources and high-value utilization, and promotes environmental protection, thus having significant economic and social value.

[0078] This invention uses inexpensive, renewable rice husks as raw material and employs a catalytic nitridation method to synthesize a highly crystalline, defect-free, and high-purity Si3N4 / SiC composite powder (see...). Figure 1 The method involves wet mixing of the rice husk-synthesized product, effectively reducing micropores in the Si3N4 / SiC composite powder. This solves the problem of amorphous SiO2, micropores, and crystal defects in existing rice husk-synthesized Si3N4 / SiC composite powders degrading the performance of magnesia-carbon refractories. Furthermore, the added Si3N4 / SiC composite powder contains whisker-like structures for both Si3N4 and SiC, exhibiting high fracture toughness, high thermal conductivity, and a low coefficient of thermal expansion, thus enhancing the toughening properties of the material. Therefore, the low-carbon magnesia-carbon refractories prepared by this invention possess excellent thermal shock resistance.

[0079] The silicon powder and alumina powder used in this invention react with magnesia and nitrogen during the high-temperature nitriding process to generate in-situ columnar Si3N4, conical MgSiN2, plate-like Mg2SiO4, and MgAl2O4 reinforcing phases anchored to the aggregate and matrix (see...). Figure 2 , Figure 3 This process generates volume expansion and intergranular phase reinforcement effects. At the same time, the generated MgAl2O4 and Mg2SiO4 can absorb and dissolve elements such as Mg, Al and Fe in the slag to form spinel and high-temperature solid solutions, further improving the strength, thermal shock resistance and erosion resistance of the material.

[0080] After testing, the low-carbon magnesium-carbon refractory material prepared by this invention with added Si3N4 / SiC composite powder has excellent properties: room temperature flexural strength is 15-18 MPa; room temperature compressive strength is 81-93 MPa; high temperature flexural strength is 10-13 MPa (held at 1400℃ for 30 min); residual flexural strength retention rate is 75-88% (water quenched at 1100℃ 4 times); residual compressive strength retention rate is 80-93% (water quenched at 1100℃ 4 times); erosion depth is 724-985 μm (eroded at 1400℃ for 4 h).

[0081] In summary, this invention features low cost and simple process; it also solves the problem that the presence of amorphous SiO2, micropores and crystal defects in rice husks degrades the performance of carbon-containing refractory materials, enabling the high-value utilization of agricultural waste rice husks and playing a positive role in environmental protection; furthermore, the low-carbon magnesium-carbon refractory material prepared by this invention exhibits excellent thermal shock resistance and erosion resistance.

[0082] The above embodiments are preferred implementations of the present invention. In addition, the present invention can be implemented in other ways. Any obvious substitutions without departing from the concept of the present technical solution are within the protection scope of the present invention.

[0083] Finally, it should be emphasized that, in order to make it easier for those skilled in the art to understand the improvements of the present invention compared with the prior art, some descriptions of the present invention have been simplified, and for clarity, some other elements have been omitted from this application. Those skilled in the art should realize that these omitted elements can also constitute the content of the present invention.

Claims

1. A low-carbon magnesia-carbon refractory material to which Si3N4 / SiC composite powder is added, characterized in that, The low-carbon magnesia-carbon refractory material comprises the following components: 60-70 wt% of fused magnesia aggregate, 20-30 wt% of fused magnesia fine powder, 1-4 wt% of alumina powder, 3-5 wt% of silicon powder, 2-4 wt% of flake graphite, 1-3 wt% of Si3N4 / SiC composite powder, and 3-5 wt% of binder based on the total amount of the aforementioned components. The Si3N4 / SiC composite powder is prepared by the following steps: Step 1, uniformly mixing the catalyst and rice husk powder under water bath conditions, drying to obtain the catalyst-loaded raw material; Step 2, under the conditions of nitrogen atmosphere and 1350-1450℃, heat preservation for 3-5h to obtain the nitrided product; Step 3, wet mixing the nitrided product, drying to obtain the Si3N4 / SiC composite powder; The Si3N4 / SiC composite powder comprises 70-80 wt% of Si3N4 and 20-25 wt% of SiC, and the Si3N4 and SiC are both in the form of whiskers and interweave to form a network structure; The low-carbon magnesia-carbon refractory material is prepared by the following steps: uniformly stirring the raw materials, pressing and forming, curing at 110-150℃ for 12-16h, then heat preservation at 1300-1500℃ for 3-5h under nitrogen atmosphere, and cooling to obtain the low-carbon magnesia-carbon refractory material added with Si3N4 / SiC composite powder; The silicon powder and alumina powder react with magnesia and nitrogen during high-temperature nitriding to in-situ generate columnar Si3N4, conical MgSiN2, plate-like Mg2SiO4 and MgAl2O4 reinforcing phases.

2. The low-carbon magnesia-carbon refractory added with Si3N4 / SiC composite powder according to claim 1, characterized in that: The mass ratio of the catalyst to the rice husk powder is 1: (40-50).

3. The low-carbon magnesia-carbon refractory material added with Si3N4 / SiC composite powder according to claim 1, characterized in that: The catalyst is one of ferric nitrate nonahydrate, nickel nitrate hexahydrate and cobalt nitrate hexahydrate.

4. The low-carbon magnesia-carbon refractory material added with Si3N4 / SiC composite powder according to claim 1, characterized in that: In step 1, the water bath temperature is 25-40℃, the drying temperature is 90-110℃, and the drying time is 24-30h.

5. The low-carbon magnesia-carbon refractory material added with Si3N4 / SiC composite powder according to claim 1, characterized in that: In step 2, the catalyst-loaded raw material is heated to 1350-1450℃ at a rate of 4-5℃ / min.

6. The low-carbon magnesia-carbon refractory material added with Si3N4 / SiC composite powder according to claim 1, characterized in that: In step 3, the nitrided product is wet mixed with anhydrous ethanol as the solvent, the wet mixing time is 3-4h, and the drying temperature is 90-110℃.

7. The low-carbon magnesia-carbon refractory material added with Si3N4 / SiC composite powder according to claim 1, characterized in that: The fused magnesia aggregate is a mixture of fused magnesia with particle sizes of 1-3mm and 0-1mm; the particle size of the fused magnesia fine powder is ≤100μm; the particle size of the alumina powder is ≤100μm; the particle size of the silicon powder is ≤100μm; the particle size of the flake graphite is ≤150μm; and the binder is liquid thermosetting phenolic resin with a carbon residue of 45-48wt%.

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