An unburned Al-SiC refractory material for blast furnaces and its preparation method

Abstract

The present invention belongs to the field of refractory materials, and in particular, relates to an unburned Al-SiC refractory material for blast furnaces and a preparation method thereof. The Al-SiC refractory material comprises the following raw materials: 60-97wt% of silicon carbide, 2-25wt% of metal aluminum powder, 1-15wt% of carbon black, and 3-5wt% of phenolic resin as a binder. After the above raw materials and the binder are batched and evenly mixed, they are pressed into shape by a machine and dried at 220°C to 300°C for 12h to 48h to obtain an unburned Al-SiC refractory material. The present invention is directed to the prior art Si for blast furnaces. 3 N 4 ‑Si in SiC refractory 3 N 4 As the problem of failure of the binding phase during long-term service and the complication of the preparation process of SiC-based refractory materials is solved, Al is innovatively introduced into the SiC matrix. By utilizing the high-temperature activity of Al, it can react with the main atmosphere (N) in the blast furnace during its service. 2 The (g)+CO(g)) reaction is further in-situ converted into high-performance AlN and dissolved into the SiC matrix, making it stably combined with SiC to solve the problems of green refractory preparation and long life of SiC-based refractory materials for blast furnaces.

Description

Technical Field

[0001] The present invention belongs to the field of refractories, and particularly relates to an unburned Al-SiC refractory for blast furnaces and a preparation method thereof. Background Art

[0002] With the annual increase in the world's steel demand, China has become a major steel manufacturing country and has ranked first in the world for many years. With resource shortages and environmental deterioration, low-carbon environmental protection and sustainable development have become the primary tasks of the steel industry. Blast furnace ironmaking is the main method of ironmaking, and refractories are the basic materials for building blast furnaces. Their performance will directly determine the cycle life of blast furnaces. Therefore, developing and adapting refractories for blast furnace long life and simultaneously realizing the greening of their preparation processes are urgent problems to be solved.

[0003] Non-oxide composite refractories not only have the high melting points, excellent high-temperature mechanical and thermal properties of traditional oxide refractories, but also have the excellent erosion resistance and thermal shock resistance of carbon-containing refractories. At the same time, they will not cause problems such as carbon increase in molten steel during service, and have become a research hotspot for composite refractories at the present stage. Among them, SiC-based composite refractories are typical representatives of non-oxide refractories. They are widely used in high-temperature industries such as iron and steel metallurgy due to their high high-temperature strength, large thermal conductivity, good thermal shock resistance, low thermal expansion coefficient, good erosion resistance, and non-wetting by non-ferrous metals. They are the core raw materials of a new generation of refractories. Among them, Si 3 N 4 -SiC refractories have been successfully applied to the blast furnace system. However, with the extension of the blast furnace service life, problems in the service process of Si 3 N 4 -SiC refractories have been continuously exposed. The action of alkali metal erosion and cyclic thermal shock in the blast furnace system will seriously endanger the service life of Si 3 N 4 -SiC refractories, resulting in the formation of a cyclic damage mechanism inside the brick body, that is: oxidation of the brick body matrix → alkali metal erosion → slag shell spalling → matrix exposure and re-oxidation. In addition, the main gas components in the blast furnace system are N 2 (g)+CO(g), and Fe easily erodes Si 3 N 4 to form Fe-Si alloy. Under the synergistic action of Fe-Si alloy and CO(g), Si 3 N 4 is converted to SiC, and finally the bonding phase Si 3 N 4 gradually disappears and loses its bonding strength.

[0004] In addition, Si 3 N 4Both belong to covalent compounds with SiC and still have relatively high bonding strength at high temperatures. It is difficult to densify and sinter them under low temperature and normal pressure. High pressure or special sintering processes are often required, which limits their large-scale industrial production. Therefore, for current Si 3 N 4 -SiC refractory preparation processes, generally Si powder is incorporated into SiC raw materials, and after die pressing, the green body is fired at about 1400 °C in a high-purity nitrogen atmosphere. However, during the nitridation process of the material, the Si powder inside the green body needs to be completely nitrided (free Si ≤ 1 wt%), so special nitridation processes need to be developed or high-purity nitrogen is used, which will undoubtedly increase the industrial preparation cost. Therefore, developing a SiC-based refractory with more stable high-temperature performance for service in the blast furnace system and making its preparation process green and energy-saving are urgent problems to be solved in the present invention. Summary of the Invention

[0005] To improve the problem of bonding phase failure that occurs when SiC-based refractories are applied in the blast furnace system and to make the material green and energy-saving during the preparation process, the present invention innovatively develops a non-fired Al-SiC refractory for blast furnaces without high-temperature pre-sintering. Utilizing the high activity of metallic Al, it reacts with the main atmosphere (N 2 (g)) in the blast furnace during service to be further in-situ transformed into high-performance AlN and achieve unlimited solid solution with SiC. As the service cycle extends, it is finally completely transformed into an AlN-SiC solid solution refractory, ultimately achieving the purpose of stable operation and long-term safety of the blast furnace.

[0006] The technical solution adopted by the present invention is as follows: Using silicon carbide, metallic aluminum powder, and carbon black as raw materials, the raw material composition is calculated according to the following weight percentages: silicon carbide 60 - 97 wt%, metallic aluminum powder 2 - 25 wt%, carbon black 1 - 15 wt%, and at the same time, 3 - 5 wt% of a binder is added externally.

[0007] Preferably, the binder is selected as thermosetting phenolic resin.

[0008] Preferably, the silicon carbide includes particulate materials with particle sizes of 3 - 1 mm and 1 - 0 mm, and silicon carbide fine powder with a particle size of ≤ 0.088 mm, where the mass ratio of the silicon carbide particulate materials is 55% - 85%, and the mass ratio of the silicon carbide fine powder is 5% - 12%.

[0009] The preparation method of the non-fired Al-SiC refractory as described above includes the following steps:

[0010] (1) Weigh accurately the silicon carbide particulate materials, silicon carbide fine powder, metallic aluminum powder, carbon black, and phenolic resin according to the ratio, and then stir for 40 min - 60 min to make them evenly mixed;

[0011] (2) Use a press to press the mixture in step (1) into green bricks, and then place the green bricks in a drying kiln at 220°C to 300°C for 12h to 48h to obtain unburned Al-SiC refractory materials.

[0012] In this technical solution, metallic Al is a commonly used raw material in refractory materials. After drying at 220°C to 300°C, phenolic resin can tightly wrap the granular materials and fine powders together. At low temperatures, plastic forming is achieved by the plastic deformation of metallic Al, improving the density of the green body to enhance the strength. When the unburned Al-SiC refractory material is applied to the blast furnace system, Al can be in-situ transformed into AlN under its service environment. As the service cycle extends, Al can be completely transformed into AlN and achieve unlimited solid solution with SiC, ultimately forming an AlN-SiC solid solution refractory material with more stable properties. Due to its high thermal conductivity, low thermal expansion performance, low dielectric constant, and high thermal shock stability, etc., AlN has been widely used in fields such as metal smelting and electronic devices. However, under natural conditions, AlN is extremely prone to hydration, which limits its application to a certain extent. SiC has multiple crystal phases, while AlN has only a unique 2H phase (wurtzite type). SiC and AlN can form a solid solution under certain conditions. Due to the highly covalent bond binding characteristics between SiC and AlN, it is difficult to combine below 2000°C, often requiring high temperature and high pressure or special sintering processes. α-SiC has a similar structure to AlN and a very small difference in lattice constants. It can combine more densely with 2H-AlN to form a solid solution better than β-SiC, endowing the material with the excellent molten iron erosion resistance of nitrides and the thermal shock stability of carbides, thus solving the problems of easy oxidation of single SiC materials and easy hydration of single AlN materials.

[0013] When the temperature in the blast furnace reaches above 660°C, metallic Al melts to form a liquid phase, thereby accelerating the migration rate of Al atoms. Al(l) can react with N in the environment 2(g) AlN is formed through a liquid-gas reaction. Since the newly formed AlN has high activity, it can significantly reduce the activation energy of the AlN-SiC solid solution and enable its formation at low temperatures. At the same time, some Al(l) inclusions flow along the internal pore channels of the material with the highly active nano-sized residual C generated by the pyrolysis of phenolic resin at high temperatures. When it flows to the surface of SiC particles, the residual C with a high specific surface area can increase the wettability of Al to SiC. Subsequently, Al(l) and N deposit on the SiC surface in atomic form and gradually diffuse into the SiC interior, finally forming a solid solution layer on the SiC particle surface. This process can hinder the excessive growth of SiC grains, thereby promoting the densification sintering of the material. With the in-situ formation of AlN, the grain size of the AlN-SiC solid solution is significantly refined, showing a multi-level effect. Both the primary grain refinement caused by the formation of the solid solution and the secondary grain refinement caused by the sub-grain boundaries within the grains are beneficial to the improvement of the comprehensive service performance of the material. At the same time, due to the existence of multiple paths for the formation of the AlN-SiC solid solution, its morphology and position may vary, playing a role in toughening with multi-morphology and multi-point synergism.

[0014] In this technical solution, metallic Al, as a plastic intermediate phase, can be in-situ transformed into AlN during the operation of the blast furnace and infinitely solidify with the SiC matrix. The in-situ synthesized AlN-SiC solid solution material has stable thermodynamic properties, pollution-free interfacial bonding, and high bonding strength, solving problems such as the failure of the bonding phase at high temperatures and the cumbersome preparation process of SiC-based refractory materials, and truly realizing the greening and energy-saving of the material preparation process. In addition, as the operation cycle of the blast furnace extends, the unreacted Al in the brick body can be continuously transformed into AlN under the continuous catalytic action of N 2 (g) and then solidify into the SiC matrix, endowing the material with the characteristics of self-formation and gradient transformation, and prolonging the service life of the material.

[0015] Beneficial effects:

[0016] The present invention aims at the current situation that Si 3 N 4 -SiC refractory materials in blast furnaces fail during service and cannot meet the requirements of stable and long-life blast furnaces. At the same time, considering the current preparation of Si 3 N 4 which fails during service and thus cannot meet the requirements of stable and long-life blast furnaces for blast furnaces, and at the same time considering the current preparation of Si 3 N 4- The complex nitriding process and high cost of SiC refractories. The present invention innovatively introduces metallic Al as a raw material into the SiC matrix to prepare unburned Al-SiC refractories. By utilizing the high activity of Al, AlN is formed in-situ during the service process inside the blast furnace and infinitely dissolved into the SiC matrix. As the service cycle extends, it is finally completely transformed into an AlN-SiC solid solution refractory, effectively solving the problem of the bonding phase failure of SiC-based refractories. At the same time, the sintering process of traditional refractories is omitted, making its preparation process tend to be green and energy-saving. Specifically as follows:

[0017] (1) Comparing with the current preparation process of Si 3 N 4 -SiC refractories, by introducing Si powder into the SiC matrix and pressing it into a green body, and then through complex nitriding processes such as stepwise heating in a high-temperature nitrogen atmosphere, the Si powder can be completely nitrided. There are problems such as high cost, high energy consumption, and high pollution. This technology utilizes the high-temperature activity of Al in the brick blank, which can be in-situ transformed into AlN during service and infinitely dissolved with the SiC matrix. As the operation cycle of the blast furnace extends, it will finally spontaneously transform into an AlN-SiC solid solution refractory. The preparation process of the material can be simplified to achieve the purpose of green and energy-saving.

[0018] (2) Comparing with the current preparation process of AlN-SiC solid solution materials, in this technology, the metallic Al in the brick blank is in-situ transformed into an AlN bonding phase during the service process in the blast furnace environment, omitting the secondary synthesis process of pre-synthesizing and then introducing AlN in the traditional process. At the same time, it solves the disadvantages of the AlN bonding phase introduced in the traditional process, such as large particle size, resulting in low interfacial bonding strength with SiC. The AlN bonding phase obtained by in-situ synthesis has stable thermodynamic properties, particle size matching with the SiC phase, and can achieve advantages such as pollution-free interfacial bonding with SiC particles and high bonding strength.

[0019] (3) The melting point of AlN is as high as 2517 °C, much higher than the melting point of the bonding phase Si 3 N 4 (1870 °C) of the current SiC-based refractories used in blast furnaces. Therefore, the performance of AlN-SiC solid solution refractories at high temperatures is more stable and can meet the requirements of higher smelting temperatures in future blast furnace systems.

[0020] (4) The formation of AlN-SiC solid solution enables the material to possess both the excellent molten iron erosion resistance of nitrides and the thermal shock stability of carbides, solving the problems of easy oxidation of single SiC materials and easy hydration of single AlN materials, and can well meet the urgent needs of high-performance and long-life refractories for blast furnaces.

[0021] (5) Due to the existence of multiple paths for the formation of the AlN-SiC solid solution within the material, there are differences in its formation position and morphology. Therefore, the AlN-SiC solid solution can play a role in toughening through multi-site and multi-morphology synergy, which helps to improve the comprehensive performance of the material. Detailed implementation method

[0022] Example 1

[0023] Pre-mix 80 wt% of silicon carbide granular material, 5 wt% of silicon carbide fine powder, 10 wt% of metallic aluminum powder, and 5 wt% of carbon black for 25 min. Subsequently, add 4 wt% of phenolic resin as a binder and continue mixing for 25 min. After mixing evenly, press it into a brick blank, and then place the brick blank in a drying kiln at 240 °C for 24 h to obtain an unburned Al-SiC refractory material.

[0024] Example 2

[0025] Pre-mix 85 wt% of silicon carbide granular material, 12 wt% of silicon carbide fine powder, 2 wt% of metallic aluminum powder, and 1 wt% of carbon black for 20 min. Subsequently, add 3 wt% of phenolic resin as a binder and continue mixing for 20 min. After mixing evenly, press it into a brick blank, and then place the brick blank in a drying kiln at 220 °C for 12 h to obtain an unburned Al-SiC refractory material.

[0026] Example 3

[0027] Pre-mix 55 wt% of silicon carbide granular material, 5 wt% of silicon carbide fine powder, 25 wt% of metallic aluminum powder, and 15 wt% of carbon black for 30 min. Subsequently, add 5 wt% of phenolic resin as a binder and continue mixing for 30 min. After mixing evenly, press it into a brick blank, and then place the brick blank in a drying kiln at 300 °C for 48 h to obtain an unburned Al-SiC refractory material.

[0028] Example 4

[0029] Pre-mix 65 wt% of silicon carbide granular material, 15 wt% of silicon carbide fine powder, 15 wt% of metallic aluminum powder, and 5 wt% of carbon black for 30 min. Subsequently, add 5 wt% of phenolic resin as a binder and continue mixing for 30 min. After mixing evenly, press it into a brick blank, and then place the brick blank in a drying kiln at 300 °C for 48 h to obtain an unburned Al-SiC refractory material.

[0030] Example 5

[0031] 70 wt% of silicon carbide granular material, 24 wt% of silicon carbide fine powder, 5 wt% of metallic aluminum powder and 1 wt% of carbon black were premixed for 30 min, and then 4 wt% of phenolic resin was added as a binder and mixing continued for 30 min. After being uniformly mixed, the mixture was pressed into green bricks, and then the green bricks were placed in a drying kiln at 240 °C for 24 h to obtain the unburned Al-SiC refractory material.

Claims

1. An unburned Al-SiC refractory material for blast furnaces, characterized in that, the material is composed of raw materials with the following mass fractions: 60-97wt% of silicon carbide, 2-25wt% of metallic aluminum powder, 1-15wt% of carbon black, and additionally 3-5wt% of a binder; the silicon carbide includes granular materials with particle sizes of 3-1mm and 1-0mm, and silicon carbide fine powder; among them, the silicon carbide granular materials with particle sizes of 3-1mm and 1-0mm account for 55%-85%, and the mass of the silicon carbide fine powder accounts for 5%-12%; the preparation method of the unburned Al-SiC refractory material includes the following steps: (1) Weigh accurately the silicon carbide granular materials, silicon carbide fine powder, metallic aluminum powder, carbon black and binder according to the ratio, and then stir for 40-60 min to make them evenly mixed; (2) Use a press to press the mixture in step (1) into a brick blank, and then place the brick blank in a drying kiln at 220°C - 300°C for 12h - 48h to obtain the unburned Al-SiC refractory material; The unburned Al-SiC refractory material for blast furnaces utilizes the high-temperature activity of Al in the brick blank, which can be in-situ converted into AlN during service and is infinitely solid-soluble with the SiC matrix. As the operation cycle of the blast furnace extends, it will ultimately spontaneously transform into an AlN-SiC solid solution refractory material.

2. The unburned Al-SiC refractory material according to claim 1, characterized in that: the binder is selected as a thermosetting phenolic resin.

3. The preparation method of the unburned Al-SiC refractory material according to claim 1 or 2, characterized in that, it includes the following steps: (1) Weigh accurately the silicon carbide granular materials, silicon carbide fine powder, metallic aluminum powder, carbon black and binder according to the ratio, and then stir for 40-60 min to make them evenly mixed; (2) Use a press to press the mixture in step (1) into a brick blank, and then place the brick blank in a drying kiln at 220°C - 300°C for 12h - 48h to obtain the unburned Al-SiC refractory material.

4. The preparation method of the unburned Al-SiC refractory material according to claim 3, characterized in that: in step (1), first pre-mix the silicon carbide granular materials, silicon carbide fine powder, carbon black and aluminum powder for 20-30 min, and then add the phenolic resin binder and continue to mix for 20-30 min until evenly mixed.