Crystallization and CO erosion resistant zero-expansion silica brick and preparation method thereof

Abstract

The invention relates to the technical field of metallurgical coking, and provides a devitrification and CO erosion resistant zero-expansion silica brick and a preparation method thereof.The devitrification and CO erosion resistant zero-expansion silica brick is prepared from, by weight, 3-10 parts of nanoscale alpha-Al2O3, 15-35 parts of andalusite, 30-40 parts of high-purity fused mullite, 10-20 parts of superfine silica powder, 2-5 parts of silica sol binding agent and 3-5 parts of composite mineralizer. Through the synergistic effect of the design of the composite mineralizer and the stepped heat treatment process, the technical problems that the existing zero-expansion silica brick is easy to devitrify and crystallize fused quartz, poor in CO erosion resistance and lack of crystallization degree during long-term use at high temperature are solved; the thermal shock cycle index and the high-temperature breaking strength of the material can be improved, the formation of alpha-cristobalite crystallization peak is effectively inhibited, and the mass loss is reduced in a reducing atmosphere, so that the structural stability of the material is enhanced, and the service life of the material is prolonged.

Description

Technical Field

[0001] This invention relates to the field of metallurgical coking technology, specifically to a zero-expansion silica brick resistant to crystallization and CO erosion, and its preparation method. Background Technology

[0002] In actual production, coke oven refractory materials are subjected to destructive effects such as high temperatures, mechanical impacts, and physicochemical reactions, leading to gradual aging and damage to the oven body. In particular, the walls of the coke oven carbonization chamber suffer from the long-term erosion caused by the lateral pressure and friction during coal charging and coke pushing, as well as high temperatures exceeding 1200℃ and harmful substances and corrosive gases produced during coal dry distillation. This results in defects such as gradual peeling of wall bricks, large-area deformation of the walls, cracks, even holes, depressions, and misalignments, and loosening or missing bottom bricks in the carbonization chamber, affecting the lifespan of the coke oven and normal production. Zero-expansion silica bricks are a special refractory material with a thermal expansion coefficient approaching zero. They overcome the shortcomings of ordinary silica bricks in terms of poor thermal stability and possess characteristics such as low linear expansion, structural stability, no dimensional changes allowing for repair without shutting down the oven, high thermal shock resistance, and high pressure resistance.

[0003] However, zero-expansion silica bricks are thermodynamically unstable high-energy glass materials, and their current use and preparation processes mainly have the following limitations:

[0004] (1) When used for a long time at temperatures above 1100 ℃ or when used in alternating hot and cold conditions (room temperature to 1100 ℃), molten silica (glassy SiO2) is prone to devitrification and crystallization into cristobalite with a high coefficient of thermal expansion. This causes liquid phase migration and structural reorganization of the material in a long-term high-temperature environment, resulting in pores and microcracks and reducing service life.

[0005] (2) Although the presence of Na2O, K2O, Al2O3 and other substances during the preparation process can promote the conversion of fused silica, excessive amounts will significantly reduce the material’s refractoriness and load softening temperature.

[0006] (3) Traditional preparation processes do not have precise temperature curve control, making it difficult to achieve controllable growth of crystal phase.

[0007] (4) The material has poor resistance to CO corrosion. Under a reducing CO atmosphere, SiO2 is easily reduced to gaseous SiO, which leads to powdering of the material surface and loose structure.

[0008] (5) Existing technologies lack synergistic solutions for simultaneously improving crystallinity or corrosion resistance. Summary of the Invention

[0009] The purpose of this invention is to provide a zero-expansion silica brick resistant to crystallization and CO corrosion, and its preparation method. By using a specific weight ratio of raw materials, including 3-10 parts of nano-sized α-Al₂O₃, 15-35 parts of andalusite, 30-40 parts of high-purity fused mullite, 10-20 parts of ultrafine silica powder, 2-5 parts of silica sol binder, and 3-5 parts of composite mineralizer, the composite mineralizer design and the step-type heat treatment process work synergistically to improve the thermal shock cycle count and high-temperature flexural strength of the material, effectively suppress the formation of α-cristobalite crystallization peaks, and reduce mass loss under a reducing atmosphere, thereby enhancing the structural stability and service life of the material and solving the problems mentioned in the background art.

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] A zero-expansion silica brick resistant to crystallization and CO erosion is made from the following raw materials in parts by weight: 3-10 parts of nano-sized α-Al2O3, 15-35 parts of andalusite, 30-40 parts of high-purity electrofused mullite, 10-20 parts of ultrafine silica powder, 2-5 parts of silica sol binder, and 3-5 parts of composite mineralizer.

[0012] Preferably, the composite mineralizer is composed of CaO, Fe2O3, Y2O3 and C3N4 in a molar ratio of 25:15:10:1.

[0013] Preferably, the andalusite contains ≥57% Al2O3 and the high-purity electrofused mullite contains ≥99.9% SiO2.

[0014] Preferably, the raw material is coarsely crushed and then subjected to magnetic separation to control the Fe2O3 content to below 0.05%, and then finely crushed.

[0015] A method for preparing a zero-expansion silica brick resistant to crystallization and CO corrosion, comprising the following steps:

[0016] Step 1: Raw material preparation: Weigh each raw material according to its weight proportions;

[0017] Step 2, Mixing and Molding: Mix the dry powder raw materials, add silica sol binder and water, perform ultrasonic dispersion and ball milling, age, press into shape, and let stand naturally;

[0018] Step 3, Step-by-Step Heat Treatment: This includes the drying and dehydration stage, the decomposition and pre-crystallization stage, the crystal nucleation stage, the crystal directional growth stage, and the cooling stage.

[0019] Preferably, in step two, the mixing step involves ultrasonic dispersion for 30 minutes, ball mill speed controlled at 200-300 rpm, and wet ball milling for 2 hours.

[0020] Preferably, for step three, the drying and dehydration stage is heated from room temperature to 300°C at a heating rate of 3-5°C / min and held for 3 hours; the decomposition and pre-crystallization stage is heated to 900°C and held for 4 hours; the crystal nucleation stage is heated to 1350°C and held for 5 hours; the crystal directional growth stage is heated to 1450°C and held for 4 hours; and the cooling stage is first cooled to 700°C in the furnace and then naturally cooled.

[0021] Preferably, in step two, the pressure in the pressing and molding step is 100 MPa, and the pressure is held for 10-20 seconds.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] 1. This invention, through the synergistic effect of composite mineralizer design and stepped heat treatment process, suppresses excessive crystallization of cristobalite. The composite mineralizer induces the formation of stable crystalline phases, while the precisely controlled heat treatment achieves uniform formation and directional growth of crystal nuclei, thereby reducing the generation of porosity and microcracks and improving the thermal stability of the material.

[0024] 2. This invention optimizes the raw material ratio, strictly controls the content of impurities such as Na2O and K2O, and fixes alkali metal impurities with a composite mineralizer to form a high-melting-point stable phase, avoiding a decrease in refractoriness and load softening temperature, and solving the problem of reduced refractoriness caused by excessive additives during the preparation process; the stepped heat treatment method controls the heating curve with an accuracy of ±1℃, ensuring controllable growth of the crystal phase and avoiding excessive crystallization; the problem of poor resistance to CO erosion is improved by forming a dense two-dimensional network structure, and under a reducing atmosphere, the reduction of SiO2 is suppressed, reducing surface pulverization. Attached Figure Description

[0025] Figure 1 Microstructure diagram of silica bricks prepared according to an embodiment of the present invention;

[0026] Figure 2 The image shows the microstructure of the silica bricks prepared as a comparative example of the present invention.

[0027] Figure 3 These are XRD diagrams of embodiments and comparative examples of the present invention;

[0028] Figure 4 This is a schematic diagram of thermogravimetric loss in the embodiments and comparative examples of the present invention;

[0029] Figure 5 This is a process flow diagram of the present invention. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] To address the technical problems of existing zero-expansion silica bricks, such as easy devitrification of molten quartz, poor resistance to CO2 corrosion, and lack of crystallinity during long-term high-temperature use, the following technical solutions are provided:

[0032] Please see Figure 5 The proposed method for preparing a zero-expansion silica brick resistant to crystallization and CO attack is as follows:

[0033] I. Raw Material Preparation

[0034] Ingredients are prepared by weight, and the core ingredients include:

[0035] 3-10 parts of nano-sized α-Al2O3 are used as additives to promote stable lattice formation and high-temperature sintering.

[0036] Andalusite 15-35 parts, of which Al2O3 content ≥57%, is used to enhance the material skeleton strength and thermal shock stability;

[0037] 30-40 parts of high-purity fused mullite with SiO2 purity ≥ 99.9% are used as the main crystalline phase raw material;

[0038] 10-20 parts of ultrafine silicon powder serve to fill the gaps between particles and promote sintering densification.

[0039] 2-5 parts of silica sol binder, with a solid content of 35%, are used to improve the strength of the green body.

[0040] The composite mineralizer, consisting of 3-5 parts, is a key component. It is made by mixing CaO, Fe2O3, Y2O3 and C3N4 in a molar ratio of 25:15:10:1. It is used to induce the precipitation of beneficial crystalline phases, fix alkali metal impurities to form a high-melting-point stable phase, and promote the formation of a two-dimensional network structure.

[0041] All raw materials are coarsely crushed and then subjected to magnetic separation to control the Fe2O3 content to below 0.05% in order to reduce the adverse effects of iron impurities on high-temperature performance. After that, they are finely crushed and fed into the granular silo.

[0042] II. Mixing and Molding

[0043] The mixing process employs a combination of ultrasonic dispersion and mechanical ball milling to ensure uniform distribution of the additives.

[0044] First, the measured dry powder raw materials (including main materials and compound mineralizers) are put into the silo for preliminary dry mixing.

[0045] Then, silica sol binder and an appropriate amount of water are added, and the ultrasonic dispersion device is started for 30 minutes to break up particle agglomeration using ultrasonic energy.

[0046] The particles were then wet-milled in a ball mill for 2 hours, with the mill speed controlled at 200-300 rpm. Zirconia balls were used as the grinding media to further refine the particles and achieve uniform mixing.

[0047] The mixed clay needs to be aged for a period of time, such as 12 hours, to increase its plasticity.

[0048] The molding process uses a hydraulic press with a set pressure of 100 MPa. In practice, the clay is filled into the mold, and the pressure is gradually increased in stages to the target pressure, which is then maintained for 10-20 seconds to ensure that the green body has uniform density and is free of delamination.

[0049] After molding, the brick blanks need to be left to stand naturally for 24 hours to allow the internal stress to be released and to reach a certain initial strength.

[0050] III. Stepped Heat Treatment

[0051] Heat treatment is the core process, employing a precisely controlled, stepped heating regime. The entire process takes place in a high-temperature kiln, with furnace temperature control accuracy required to reach ±1℃.

[0052] 1. Drying and Dehydration Stage: After the brick blanks are placed in the kiln, the temperature is slowly increased from room temperature to 300℃ at a rate of 3℃-5℃ / min, and then maintained at 300℃ for 3 hours. The purpose of this stage is to remove physically adsorbed water and some bound water from the brick blanks, and to avoid cracking caused by rapid heating.

[0053] 2. Decomposition and Precrystallization Stage: Continue heating to 900℃ and maintain this temperature for 4 hours. During this stage, carbonate decomposition and preliminary crystal transformation of quartz occur. Free water and low-melting-point substances in the mineral are burned off, preparing for subsequent high-temperature crystal phase growth.

[0054] 3. Crystal nucleus formation stage: Then, the temperature is raised to 1350℃ at the same rate and precisely held at this temperature for 5 hours. This is the key stage for the formation of cristobalite crystal nuclei, and precise temperature control ensures the uniform formation of crystal nuclei.

[0055] 4. Crystal-oriented growth stage: Further heat to 1450℃ and hold for 4 hours. This stage promotes the oriented growth of cristobalite crystals and the final sintering and densification of the material, forming a stable microstructure.

[0056] 5. Cooling Stage: After heat treatment, control the cooling rate. First, cool the furnace to 700℃, then open the kiln door for natural cooling to room temperature. This cooling method helps to lock in the high-temperature phase and reduce internal stress.

[0057] Finally, zero-expansion silica bricks resistant to crystallization and CO corrosion were obtained.

[0058] IV. Implementation Cases

[0059] An embodiment is provided here, which adopts the above preparation scheme. The ingredients are 5 parts of nano-sized α-Al2O3, 25 parts of andalusite, 45 parts of high-purity fused mullite, 15 parts of ultrafine silica powder, 4 parts of composite mineralizer, and 6 parts of silica sol. The heat treatment is carried out in sequence at 300℃×3h, 900℃×4h, 1350℃×5h, 1450℃×4h, and then cooled to 700℃ in the furnace.

[0060] The performance of the silica bricks prepared in this embodiment was tested. The results showed that the number of thermal shock cycles reached 40, the high temperature flexural strength was 14.8 MPa, and the crystallinity was significantly reduced when treated at 1300℃, and the resistance to CO erosion was enhanced.

[0061] A comparative example is also provided here, which uses a single mineralizer, CaO, according to the traditional process, and the sintering regime is 1500℃×2h.

[0062] The performance of the silica brick prepared in this comparative example was tested. The results showed that its thermal shock cycle count did not exceed 10 times, its high-temperature flexural strength was only 8.5 MPa, and its high-temperature crystallinity was relatively high, which was significantly poor.

[0063] Please see Figure 1 and Figure 2 This invention combines multiphase mineralizer design with staged heat treatment to significantly change the microstructure of the material, promote the formation of a dense two-dimensional network structure on the material surface, and form a high-melting-point stable phase.

[0064] Please see Figure 3 As can be seen from the comparison of XRD patterns, the method used in the example effectively suppressed the crystallization peak of α-cristobalite.

[0065] Please see Figure 4 The resistance to CO erosion was verified by thermogravimetric analysis. In an atmosphere of 92% N2, 8% CO, and 1100℃, the mass loss of the brick sample in the example was much lower than that in the comparative example, proving that its erosion resistance was improved.

[0066] Working principle: The composite mineralizer, composed of CaO, Fe2O3, Y2O3, and C3N4 in a specific molar ratio, promotes the uniform formation of cristobalite crystal nuclei during heat treatment and fixes alkali metal impurities to form a high-melting-point stable phase. The stepped heat treatment includes drying and dehydration, decomposition and pre-crystallization, crystal nucleation, directional crystal growth, and cooling stages. Precise temperature control enables controllable crystal growth, avoiding excessive crystallization. This process creates a dense two-dimensional network structure within the material, significantly enhancing thermal shock resistance and mechanical strength.

[0067] The anti-crystallization mechanism is manifested in the synergistic suppression of the crystallization peak of α-cristobalite by the mineralizer and heat treatment, reducing microcracks caused by the transformation of the glass phase to the crystalline phase at high temperatures. XRD pattern comparison shows that the crystallinity of the embodiment is significantly reduced, thereby maintaining the dimensional stability of the material during long-term use. Resistance to CO corrosion is achieved through the formation of a stable phase; under a reducing atmosphere, SiO2 on the material surface is not easily reduced to gaseous SiO. Thermogravimetric analysis verifies that the mass loss rate is far lower than that of traditional processes, ensuring structural integrity.

[0068] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0069] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A zero-expansion silica brick resistant to crystallization and CO attack, characterized in that, It is made from the following raw materials in parts by weight: 3-10 parts of nano-sized α-Al2O3, 15-35 parts of andalusite, 30-40 parts of high-purity electrofused mullite, 10-20 parts of ultrafine silica powder, 2-5 parts of silica sol binder, and 3-5 parts of composite mineralizer.

2. The zero-expansion silica brick resistant to crystallization and CO attack according to claim 1, characterized in that, The composite mineralizer is composed of CaO, Fe2O3, Y2O3 and C3N4 in a molar ratio of 25:15:10:

1.

3. The zero-expansion silica brick resistant to crystallization and CO corrosion according to claim 1, characterized in that, The andalusite contains ≥57% Al2O3, and the high-purity electrofused mullite contains ≥99.9% SiO2.

4. The zero-expansion silica brick resistant to crystallization and CO corrosion according to claim 1, characterized in that, The raw materials are coarsely crushed and then subjected to magnetic separation to control the Fe2O3 content to below 0.05%, and then finely crushed.

5. A method for preparing a zero-expansion silica brick resistant to crystallization and CO corrosion, used to achieve the zero-expansion silica brick resistant to crystallization and CO corrosion as described in any one of claims 1-4, characterized in that, Includes the following steps: Step 1: Raw material preparation: Weigh each raw material according to its weight proportions; Step 2, Mixing and Molding: Mix the dry powder raw materials, add silica sol binder and water, perform ultrasonic dispersion and ball milling, age, press and mold, and let stand naturally; Step 3, stepped heat treatment: including drying and dehydration stage, decomposition and pre-crystallization stage, crystal nucleation stage, crystal directional growth stage and cooling stage.

6. The method for preparing a zero-expansion silica brick resistant to crystallization and CO corrosion according to claim 5, characterized in that, For step two, in the mixing step, ultrasonic dispersion is performed for 30 minutes, the ball mill speed is controlled at 200-300 rpm, and wet ball milling is performed for 2 hours.

7. The method for preparing a zero-expansion silica brick resistant to crystallization and CO corrosion according to claim 5, characterized in that, For step three, the drying and dehydration stage is heated from room temperature to 300℃ at a rate of 3-5℃ / min and held for 3 hours; the decomposition and pre-crystallization stage is heated to 900℃ and held for 4 hours; the crystal nucleation stage is heated to 1350℃ and held for 5 hours; the crystal directional growth stage is heated to 1450℃ and held for 4 hours; and the cooling stage is first cooled to 700℃ in the furnace and then naturally cooled.

8. The method for preparing a zero-expansion silica brick resistant to crystallization and CO corrosion according to claim 5, characterized in that, For step two, in the pressing and molding step, the pressure is 100MPa and the pressure is held for 10-20 seconds.

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