Mullite-corundum-silicon carbide composite refractory raw material and in-situ synthesis method thereof under oxidizing atmosphere

Abstract

The application belongs to the field of inorganic nonmetallic refractory material, and particularly discloses a mullite-corundum-silicon carbide composite refractory raw material and an in-situ synthesis method thereof under oxidizing atmosphere. The mullite-corundum-silicon carbide composite refractory raw material is mainly prepared from low-aluminum coal gangue 60-70%, secondary aluminum ash 10-20% and carbon source 15-20% in terms of mass percentage. The raw materials are mixed, a binder is added and mixed to obtain a mixture; the mixture is pressed into a shape; and the shaped product is dried, calcined and cooled to obtain the mullite-corundum-silicon carbide composite refractory raw material. The product is mainly used as a raw material for shaped refractory products and unshaped refractory material. The application can generate silicon carbide in-situ under oxidizing atmosphere, and solves the technical problems that SiC cannot be stably synthesized under conventional oxidizing atmosphere in the prior art, and the utilization level of solid waste resources is low and the atmosphere self-regulation technology is lacking in the coordination of solid waste.

Description

Technical Field

[0001] This invention belongs to the field of inorganic non-metallic refractory materials technology, specifically relating to a mullite-corundum-silicon carbide multiphase refractory raw material and its in-situ synthesis method under an oxidizing atmosphere. Background Technology

[0002] The operating conditions in high-temperature industries such as steel, non-ferrous metals, building materials, and chemicals are becoming increasingly harsh. The high-temperature, high-pressure, and highly corrosive slag environments place significantly higher demands on the performance of refractory materials. Traditional single-phase refractory materials struggle to simultaneously achieve high-temperature stability, thermal shock resistance, wear resistance, and erosion resistance. This results in short kiln lining service life and frequent replacements, leading to production interruptions, increased energy consumption, and increased solid waste—a common problem in the industry.

[0003] Oxide-nonoxide multiphase refractories combine the oxidation resistance and high-temperature stability of oxides with the high hardness and high thermal conductivity of silicon carbide, making them a key focus of industry research and development. Existing powder mixing processes are prone to uneven phase distribution and poor interfacial bonding, resulting in large fluctuations in finished product performance and susceptibility to high-temperature cracking, hindering large-scale applications. Furthermore, single-phase materials such as corundum, mullite, and silicon carbide each have their own defects and cannot be used alone in complex high-temperature environments.

[0004] In-situ synthesis can generate multi-component composite crystalline phases within the billet, optimizing phase distribution and strengthening interfacial bonding to prepare mullite-silicon carbide and mullite-corundum-silicon carbide multiphase raw materials. The three phases work synergistically to achieve complementary properties, taking into account low thermal expansion, high wear resistance, and high thermal conductivity, improving the brittleness of corundum, and enhancing its resistance to thermal shock and corrosion, which can meet the high-temperature application requirements in metallurgy, electronics, aerospace and other fields.

[0005] Currently, there are also publicly reported patent documents regarding mullite-silicon carbide multiphase refractory raw materials. For example: 1) Existing patent CN103553583A discloses a porous mullite-silicon carbide composite ceramic material and its preparation process. This technical solution uses raw materials such as aluminum hydroxide, silicon powder, and carbon powder, which are calcined in stages in a reducing atmosphere after molding and drying, relying on carbothermic reduction to generate mullite-silicon carbide porous ceramics in situ. This process has obvious limitations: silicon carbide synthesis must rely on an oxygen-free reducing atmosphere. Under an oxidizing atmosphere, silicon and carbon raw materials are easily oxidized and burned off, and the SiC phase cannot be stably generated. 2) Patent CN113636849A uses various coal gangue and coal powder as raw materials to prepare mullite-silicon carbide multiphase materials by controlling the weak reducing atmosphere in a tunnel kiln, but it has many limitations. This atmosphere system is affected by multiple factors such as kiln pressure, air volume, and fuel, resulting in poor overall atmosphere stability and easy fluctuations in product quality; the carbon deposits generated by CO disproportionation will contaminate the matrix, damage the microstructure, and degrade the overall performance of the material. Meanwhile, weak reduction combustion results in low fuel utilization and high energy consumption. The reducing flue gas corrodes kiln equipment and also causes environmental problems such as waste gas and safety issues.

[0006] As can be seen from the above, firstly, the invention patent application CN103553583A requires the use of a dedicated reducing protective atmosphere for calcination throughout the process. In ordinary oxidation kilns, carbon and silicon raw materials are easily oxidized and burned off, making it impossible to generate silicon carbide. The technical solution disclosed in invention patent application CN113636849A relies on the airflow and fuel control of a tunnel kiln to create a weak reducing atmosphere. This atmosphere fluctuates greatly due to operational disturbances, resulting in unstable SiC generation and inconsistent product performance. Therefore, existing technologies must rely on closed / in-kiln weak reducing atmosphere furnaces, making it impossible to stably synthesize SiC under conventional oxidizing atmospheres. Secondly, the technical solution disclosed in invention patent application CN113636849A relies on fuel to create a weak reducing atmosphere, resulting in low fuel utilization and high calcination energy consumption. CO in the kiln easily undergoes disproportionation reactions, accumulating carbon and polluting the matrix, damaging the material's microstructure. Reducing flue gas corrodes the kiln body, leading to high waste gas treatment costs and safety hazards. Therefore, existing technologies suffer from drawbacks such as high energy consumption, environmental disadvantages, and significant equipment wear due to relying on overall kiln control of the reducing atmosphere. Finally, existing technologies simply use coal gangue as a basic raw material without exploring its solid waste functionality; therefore, existing technologies have low levels of solid waste resource utilization and lack the technical defects of achieving atmosphere self-regulation through solid waste synergy. Summary of the Invention

[0007] The technical problem this invention aims to solve is: addressing the shortcomings of existing technologies, such as reliance on closed / weakly reducing atmosphere kilns, inability to stably synthesize SiC under conventional oxidizing atmospheres, low levels of solid waste resource utilization, and lack of technology for co-regulating atmosphere with solid waste. This invention provides a method for in-situ synthesis of mullite-corundum-silicon carbide multiphase refractory materials under an oxidizing atmosphere. The technical solution of this invention relies on the oxygen-consuming and oxygen-reducing partial pressure effect of aluminum and aluminum nitride components in secondary alumina ash, enabling it to autonomously create an internal weakly reducing microenvironment within an open oxidizing atmosphere kiln, allowing for stable SiC synthesis without the need for external protective atmosphere introduction; simultaneously, it achieves high-end resource utilization of secondary alumina ash.

[0008] To solve the above problems, the present invention adopts the following technical solution:

[0009] On the one hand, the present invention provides a mullite-corundum-silicon carbide multiphase refractory raw material, expressed as a mass percentage, wherein the mullite-corundum-silicon carbide multiphase refractory raw material is mainly prepared from 60-70% low-alumina coal gangue, 10-20% secondary alumina ash and 15-20% carbon source.

[0010] According to the above-mentioned mullite-corundum-silicon carbide multiphase refractory raw material, the low-alumina coal gangue has a SiO2 mass percentage of 52-54%, an Al2O3 mass percentage of 43-46%, and a particle size of <74μm.

[0011] Based on the aforementioned mullite-corundum-silicon carbide multiphase refractory material, the secondary aluminum ash contains an alumina mass percentage of ≥78% and a particle size of <74µm.

[0012] According to the above-mentioned mullite-corundum-silicon carbide multiphase refractory material, the carbon source is at least one of petroleum coke, carbon black and flake graphite.

[0013] According to the above-mentioned mullite-corundum-silicon carbide multiphase refractory raw material, the petroleum coke has a carbon content ≥98%, ash content ≤0.5%, and particle size ≤100μm; the carbon black has a carbon content ≥99% and particle size ≤2μm; the flake graphite is natural flake graphite with a particle size of 1-5μm and a carbon content ≥99%.

[0014] On the other hand, the present invention provides a method for in-situ synthesis of mullite-corundum-silicon carbide multiphase refractory raw materials under an oxidizing atmosphere, the method comprising the following steps:

[0015] 1) Weigh out all raw materials according to the above proportions of mullite-corundum-silicon carbide multiphase refractory raw materials;

[0016] 2) Mix all the weighed raw materials evenly, then add the binder and mix well to obtain a mixture.

[0017] 3) Press the resulting mixture into shape;

[0018] 4) The pressed and shaped product is dried and calcined, and then cooled to obtain the product mullite-corundum-silicon carbide multiphase refractory raw material.

[0019] According to the above method for in-situ synthesis of mullite-corundum-silicon carbide multiphase refractory raw materials under an oxidizing atmosphere, the binder in step 2) is silica sol, and the amount of silica sol added is 10-15% of the total weight of various raw materials.

[0020] According to the above method for in-situ synthesis of mullite-corundum-silicon carbide multiphase refractory materials under an oxidizing atmosphere, the silica sol contains 30-40% silica, <0.3% sodium oxide, and has a pH of 8-10.

[0021] According to the above method for in-situ synthesis of mullite-corundum-silicon carbide multiphase refractory materials under an oxidizing atmosphere, the pressure is controlled at 120-150 MPa and the holding time is 30-60 s during the pressing process described in step 3).

[0022] The mold used in the pressing process is a cylindrical mold with a diameter of 50 mm and a thickness of 25 mm.

[0023] According to the above method for in-situ synthesis of mullite-corundum-silicon carbide multiphase refractory raw materials under an oxidizing atmosphere, the drying temperature in step 4) is 100-110℃ and the time is 8-12h; the heating rate during calcination is 5-10℃ / min, the calcination temperature is 1450-1550℃ and the time is 60-240min.

[0024] The technical solution of this invention is to synthesize mullite-corundum-silicon carbide multiphase refractory raw materials in situ under an oxidizing atmosphere. The prepared materials can be graded and processed into aggregates or fine powders, suitable for both shaped and unshaped refractory products. When added as raw materials, the product of this invention can be used to prepare shaped refractory components such as silicon-mullite-corundum bricks and precast parts, as well as unshaped refractory materials such as castables, ramming mixes, and sprayed mixes. It is widely used in the linings of high-temperature thermal equipment such as cement rotary kilns, metallurgical heating furnaces, non-ferrous smelting rotary kilns, glass regenerators, ceramic tunnel kilns, and circulating fluidized bed boilers. It is suitable for harsh conditions such as high-temperature erosion, alkali / slag corrosion, and frequent hot and cold cycles. It can also be used as a basic raw material for high-temperature firing components such as saggers and kiln furniture.

[0025] The positive and beneficial effects of this invention are as follows:

[0026] 1. The secondary aluminum ash used in the technical solution of the present invention contains aluminum and aluminum nitride mineral components. Relying on the oxygen consumption and oxygen reduction partial pressure effect of aluminum and aluminum nitride components in the secondary aluminum ash, as well as the effect of silica sol forming a dense silicon-aluminum anti-oxidation coating layer in situ, it can create an internal weak reduction microenvironment in an open oxidation atmosphere kiln and can stably synthesize SiC without the need for external protective atmosphere.

[0027] The technical solution of this invention relies on the self-consumption of oxygen by the internal components of the raw materials to create a micro-reducing environment, without the need to control the overall atmosphere of the kiln, thereby significantly reducing firing energy consumption and producing no reducing polluting flue gas, thus avoiding problems such as carbon buildup and kiln corrosion.

[0028] The technical solution of this invention uses secondary aluminum ash from industrial solid waste as the core functional raw material. By utilizing the consumption of oxygen within the system by the metallic aluminum and aluminum nitride mineral components, it simultaneously provides sufficient aluminum source to synthesize corundum and mullite, realizing high-end resource utilization of solid waste and possessing the dual advantages of energy saving and solid waste recycling.

[0029] Therefore, the technical solution of this invention can generate silicon carbide in situ under an oxidizing atmosphere. Through the in-situ generated antioxidant layer, a weakly reducing atmosphere is formed internally, eliminating the need for controlling the firing atmosphere. Furthermore, it follows normal batching, mixing, and pressing processes, without requiring additional complex procedures. This solves the problems of existing technologies, such as reliance on closed / kiln-based weakly reducing atmosphere furnaces, inability to stably synthesize SiC under conventional oxidizing atmospheres, low levels of solid waste resource utilization, and lack of technology for achieving atmosphere self-regulation through solid waste synergy.

[0030] 2. This invention uses silica sol as a molding binder, which can uniformly disperse the solid raw materials and improve the overall integrity of the green body. At the same time, the silica sol undergoes multi-stage continuous phase transformation reactions throughout the heating process: in the low-temperature stage, dehydration forms a complete and continuous gel film; in the medium-temperature stage, silanol undergoes condensation and cross-linking to construct a dense Si-O-Si inorganic network solidification isolation layer; in the high-temperature range, active silica and alumina undergo a solid-phase reaction to generate mullite, accompanied by trace amounts of liquid phase sintering to seal the micropores inside the green body. Finally, a dense and continuous silicon-alumina composite barrier layer is formed on the surface of the sample, which isolates the intrusion of external oxidizing atmosphere and provides a key weak reducing atmosphere for the in-situ stable generation of silicon carbide inside the green body.

[0031] 3. The technical solution of the present invention is to generate silicon carbide-containing multiphase materials in situ under an oxidizing atmosphere. By using a unique in-situ coating technology, a dense anti-oxidation layer is generated on the surface of the material during the heating process, which provides a weak reducing atmosphere for the in-situ generation of silicon carbide, and at the same time prevents the generated silicon carbide from being oxidized. Attached Figure Description

[0032] Figure 1 X-ray diffraction pattern of the product prepared in Example 2 of this invention.

[0033] Figure 2 X-ray diffraction pattern of the product prepared in Example 4 of this invention.

[0034] Figure 3 X-ray diffraction pattern of the product prepared in Example 6 of this invention.

[0035] Depend on Figure 1-3 It is known that the products prepared in Examples 2, 4 and 6 of the present invention are composed of mullite, corundum and silicon carbide (SiC). Detailed Implementation

[0036] The present invention will be further illustrated below with reference to the embodiments, but this does not limit the scope of protection of the technical solution of the present invention.

[0037] In the following embodiments, the content of relevant chemical components in the low-alumina coal gangue used in this invention is detailed in Table 1; the particle size of the low-alumina coal gangue is <74um.

[0038]

[0039] In the following embodiments, the content of relevant chemical components in the secondary aluminum ash used in this invention is detailed in Table 2; the particle size of the secondary aluminum ash is <74um.

[0040]

[0041] In the embodiments of the present invention, the petroleum coke used has a carbon content of ≥98%, an ash content of ≤0.5%, and a particle size of ≤100μm; the carbon black has a carbon content of ≥99% and a particle size of ≤2μm; and the flake graphite is natural flake graphite with a particle size of 1-5μm and a carbon content of ≥99%.

[0042] Example 1:

[0043] The mullite-corundum-silicon carbide multiphase refractory material of the present invention is prepared by means of 65% low-alumina coal gangue, 15% secondary alumina ash, 10% petroleum coke, 5% carbon black and 5% flake graphite, expressed as a mass percentage.

[0044] Example 2:

[0045] The detailed steps of the method for in-situ synthesis of the mullite-corundum-silicon carbide multiphase refractory material described in Example 1 under an oxidizing atmosphere of the present invention are as follows:

[0046] 1) Weigh out all raw materials according to the proportion of mullite-corundum-silicon carbide multiphase refractory material described in Example 1;

[0047] 2) Weigh out the raw materials low-alumina coal gangue, secondary aluminum ash, petroleum coke, carbon black and flake graphite and mix them evenly. Then add 10% of the total weight of the various raw materials as binder silica sol and mix evenly to obtain the mixture.

[0048] 3) Place the obtained mixture into a cylindrical mold with a diameter of 50 mm and a thickness of 25 mm, and press it at 120 MPa for 45 seconds.

[0049] 4) The green body obtained after pressing is dried at 110℃ for 12h; after drying, it is heated to 1450℃ at a heating rate of 5℃ / min and calcined for 3h; after calcination, it is cooled to obtain mullite-corundum-silicon carbide multiphase refractory raw material.

[0050] The relevant performance indicators of the mullite-corundum-silicon carbide multiphase refractory raw material prepared in this embodiment are as follows: bulk density is 1.8–1.95 g / cm³. 3 It has an apparent porosity of 15-17% and a compressive strength of 20-35 MPa.

[0051] The X-ray diffraction pattern of the product prepared in this embodiment is detailed in the appendix. Figure 1 .

[0052] Example 3:

[0053] The mullite-corundum-silicon carbide multiphase refractory raw material of the present invention is prepared from 65% low-alumina coal gangue, 20% secondary alumina ash, 10% petroleum coke and 5% carbon black, expressed as a mass percentage.

[0054] Example 4:

[0055] The detailed steps of the method for in-situ synthesis of the mullite-corundum-silicon carbide multiphase refractory material described in Example 3 under an oxidizing atmosphere of the present invention are as follows:

[0056] 1) Weigh out all raw materials according to the proportion of mullite-corundum-silicon carbide multiphase refractory material described in Example 3;

[0057] 2) Weigh out the raw materials low-alumina coal gangue, secondary aluminum ash, petroleum coke and carbon black and mix them evenly. Then add 12% of the binder silica sol, which accounts for the total weight of all raw materials, and mix them evenly to obtain a mixture.

[0058] 3) Place the obtained mixture into a cylindrical mold with a diameter of 50 mm and a thickness of 25 mm, and press it at 130 MPa for 35 seconds.

[0059] 4) The green body obtained after pressing is dried at 110℃ for 12h; after drying, it is heated to 1480℃ at a heating rate of 8℃ / min and calcined for 3h; after calcination, it is cooled to obtain mullite-corundum-silicon carbide multiphase refractory material.

[0060] The relevant performance indicators of the mullite-corundum-silicon carbide multiphase refractory raw material prepared in this embodiment are as follows: bulk density is 1.95–2.08 g / cm³. 3 The apparent porosity is 14-16%; the compressive strength is 35-40 MPa.

[0061] The X-ray diffraction pattern of the product prepared in this embodiment is detailed in the appendix. Figure 2 .

[0062] Example 5:

[0063] The mullite-corundum-silicon carbide multiphase refractory raw material of the present invention is prepared by means of 60% low-alumina coal gangue, 20% secondary alumina ash, 10% petroleum coke, 5% carbon black and 5% flake graphite, expressed as a mass percentage.

[0064] Example 6:

[0065] The detailed steps of the method for in-situ synthesis of the mullite-corundum-silicon carbide multiphase refractory material described in Example 5 under an oxidizing atmosphere of the present invention are as follows:

[0066] 1) Weigh out all raw materials according to the proportion of mullite-corundum-silicon carbide multiphase refractory material described in Example 5;

[0067] 2) Weigh out the raw materials low-alumina coal gangue, secondary aluminum ash, petroleum coke, carbon black and flake graphite and mix them evenly. Then add 15% of the binder silica sol, which accounts for the total weight of all raw materials, and mix them evenly to obtain a mixture.

[0068] 3) Place the obtained mixture into a cylindrical mold with a diameter of 50 mm and a thickness of 25 mm, and press it at 150 MPa for 30 seconds.

[0069] 4) The green body obtained after pressing is dried at 110℃ for 12h; after drying, it is heated to 1500℃ at a heating rate of 10℃ / min and calcined for 2h; after calcination, it is cooled to obtain mullite-corundum-silicon carbide multiphase refractory material.

[0070] The relevant performance indicators of the mullite-corundum-silicon carbide multiphase refractory raw material prepared in this embodiment are as follows: bulk density is 1.8–1.95 g / cm³. 3 It has an apparent porosity of 16-18% and a compressive strength of 20-30 MPa.

[0071] The X-ray diffraction pattern of the product prepared in this embodiment is detailed in the appendix. Figure 3 .

[0072] As can be seen from the relevant properties of the products prepared by the above embodiments of the present invention, the mullite-corundum-silicon carbide multiphase refractory raw material prepared by the present invention can be used as a raw material for both shaped refractory products and unshaped refractory materials.

Claims

1. A mullite-corundum-silicon carbide multiphase refractory material, characterized in that: Expressed as a percentage by mass, the mullite-corundum-silicon carbide multiphase refractory raw material is mainly prepared from 60-70% low-alumina coal gangue, 10-20% secondary alumina ash, and 15-20% carbon source.

2. The mullite-corundum-silicon carbide multiphase refractory material according to claim 1, characterized in that: The low-alumina coal gangue contains 52-54% SiO2 and 43-46% Al2O3 by mass, with a particle size of <74 μm.

3. The mullite-corundum-silicon carbide multiphase refractory material according to claim 1, characterized in that: The secondary aluminum ash contains ≥78% alumina by mass and has a particle size <74µm.

4. The mullite-corundum-silicon carbide multiphase refractory material according to claim 1, characterized in that: The carbon source is at least one of petroleum coke, carbon black, and flake graphite.

5. The mullite-corundum-silicon carbide multiphase refractory material according to claim 4, characterized in that: The petroleum coke has a carbon content ≥98%, ash content ≤0.5%, and particle size ≤100μm; the carbon black has a carbon content ≥99% and particle size ≤2μm; the flake graphite is natural flake graphite with a particle size of 1-5μm and a carbon content ≥99%.

6. A method for in-situ synthesis of the mullite-corundum-silicon carbide multiphase refractory material of claim 1 under an oxidizing atmosphere, characterized in that, The method includes the following steps: 1) Weigh out all raw materials according to the proportion of the mullite-corundum-silicon carbide multiphase refractory material as described in claim 1; 2) Mix all the weighed raw materials evenly, then add the binder and mix well to obtain a mixture. 3) Press the resulting mixture into shape; 4) The pressed and shaped product is dried and calcined, and then cooled to obtain the product mullite-corundum-silicon carbide multiphase refractory raw material.

7. The method for in-situ synthesis of mullite-corundum-silicon carbide multiphase refractory raw materials under an oxidizing atmosphere according to claim 6, characterized in that: The binder mentioned in step 2) is silica sol, and the amount of silica sol added is 10 to 15% of the total weight of all raw materials.

8. The method for in-situ synthesis of mullite-corundum-silicon carbide multiphase refractory raw materials under an oxidizing atmosphere according to claim 7, characterized in that: The silica sol contains 30-40% silica, <0.3% sodium oxide, and has a pH of 8-10.

9. The method for in-situ synthesis of mullite-corundum-silicon carbide multiphase refractory raw materials under an oxidizing atmosphere according to claim 6, characterized in that: In step 3), the pressure is controlled at 120-150 MPa and the holding time is 30-60 s during the pressing process.

10. The method for in-situ synthesis of mullite-corundum-silicon carbide multiphase refractory raw materials under an oxidizing atmosphere according to claim 6, characterized in that: In step 4), the drying temperature is 100-110℃ and the time is 8-12h; the heating rate during calcination is 5-10℃ / min, the calcination temperature is 1450-1550℃, and the time is 60-240min.

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