Wear-resistant thermal shock-resistant alumina honeycomb ceramic and method of making same

Abstract

The application discloses a kind of wear-resistant thermal shock resistance alumina honeycomb ceramic and its preparation method, the alumina honeycomb ceramic of the application includes: dense sintered alumina matrix;Electric melting corundum aggregate uniformly dispersed in matrix, and surface is pretreated to form weakly bonded interface;Spherical alumina aggregate uniformly dispersed in matrix, to form another weakly bonded interface with its inert surface;And uniformly dispersed spherical closed pores formed by pore-forming agent.Its dense matrix guarantees excellent wear resistance, and weakly bonded interface cooperates with spherical closed pores, by inducing controllable microcracks to release stress when thermal shock, thereby significantly improving thermal shock resistance.Its preparation method includes surface modification of electric melting corundum, mixing with spherical alumina, alumina powder and pore-forming agent, extrusion molding, drying, and high-temperature sintering at 1500-1680 DEG C.The honeycomb ceramic prepared by the application has excellent comprehensive performance, and service life is greatly improved.

Description

Technical Field

[0001] This invention relates to a honeycomb ceramic and its preparation method, specifically to an alumina honeycomb ceramic with excellent wear resistance and thermal shock resistance and its preparation method, belonging to the field of high-performance ceramic materials. Background Technology

[0002] Alumina (Al2O3), especially corundum-phase alumina, is widely used in the manufacture of honeycomb ceramic regenerators due to its advantages such as large heat storage capacity, excellent high-temperature resistance, good chemical stability, and high mechanical strength. These regenerators play a crucial role in high-temperature industrial equipment such as regenerative thermal oxidizers (RTOs) and hot blast stoves in the metallurgical industry.

[0003] However, in practical applications, traditional alumina honeycomb ceramics face a long-standing technical bottleneck: an irreconcilable contradiction between their wear resistance and thermal shock resistance. This is mainly reflected in the inherent defects of the following two technical approaches:

[0004] 1. To achieve high mechanical strength and excellent wear resistance, a common technical solution is to prepare dense alumina honeycomb ceramics. These ceramics have dense pore walls and extremely low porosity. While they can effectively resist the erosion and wear of high-temperature airflow, their high density also brings a fatal weakness: alumina itself has a large coefficient of thermal expansion. During the cycle of heat storage and release, the honeycomb ceramics must withstand drastic temperature gradient changes, i.e., thermal shock. The high coefficient of thermal expansion generates enormous thermal stress within the dense ceramic. When this stress exceeds the material's fracture toughness, it leads to the generation, propagation, and even macroscopic cracking of microcracks, ultimately causing structural damage to the ceramic body and significantly shortening its service life.

[0005] 2. To address the poor thermal shock resistance of dense ceramics, another technical approach has emerged: introducing numerous pores within the ceramic's pore walls to form a porous structure, particularly an open-pore structure. These pores, distributed throughout the matrix, can effectively hinder crack propagation or act as stress-relieving zones to absorb and release thermal stress, thus significantly improving the thermal shock resistance of alumina honeycomb ceramics. However, this approach comes at the cost of sacrificing the material's density. The presence of numerous open pores makes the ceramic's pore walls porous, significantly reducing mechanical strength and surface hardness. Under actual operating conditions such as incinerators, high-speed airflow and the hard dust particles it carries, coupled with high temperatures, continuously and severely scour and erode the porous honeycomb pore walls. This leads to the gradual peeling off of the pore wall material, pore enlargement, and even blockage, not only reducing heat storage efficiency but, more seriously, causing premature failure of the honeycomb ceramic due to excessive wear, thus failing to meet the requirements for long service life and high reliability.

[0006] In summary, existing technologies, whether employing densification or porosity approaches, can only partially meet the single performance requirement of wear resistance or thermal shock resistance, failing to achieve a balance between both. Therefore, developing a novel alumina honeycomb ceramic that can resist both high-temperature wear and severe thermal shock has become a pressing technical challenge in this field. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a wear-resistant and thermal shock-resistant alumina honeycomb ceramic and its preparation method. This ceramic, through a unique microstructure design, synergistically achieves a balance between high wear resistance and high thermal shock resistance, aiming to significantly extend its service life in high-temperature industrial environments.

[0008] To achieve the above objectives, the present invention provides a wear-resistant and thermal shock-resistant alumina honeycomb ceramic, characterized in that it comprises:

[0009] Dense sintered alumina matrix;

[0010] The fused alumina aggregate is uniformly dispersed in the matrix, and its surface is pretreated to form a first weak bonding interface with the matrix.

[0011] Spherical alumina aggregate, wherein the spherical alumina aggregate is uniformly dispersed in the matrix and forms a second weakly bonded interface with the matrix through its inert surface; and

[0012] Spherical air-sealing pores are uniformly dispersed in the matrix.

[0013] The fused alumina aggregate has a particle size of 45-180 μm and a content of 2-8% by weight. Its surface pretreatment involves coating the fused alumina powder with one or two of aluminum dihydrogen phosphate solution and acidic silica sol to form a weakly bonded surface layer.

[0014] The spherical alumina aggregate is a near-spherical alumina that is not fully dense and has an inert surface, formed by rapid melting; its particle size is 20-50 μm; and its content is 2-8% by weight.

[0015] The spherical closed pores are spherical pore remnants formed by the oxidative decomposition of organic microspheres during sintering, using organic microspheres as templates, and forming a closed structure due to the dense sintering of the alumina matrix. The organic microspheres are one or both of polystyrene (PS) microspheres and polymethyl methacrylate (PMMA) microspheres; the pore size of the spherical pores is 8-58 μm; and the porosity formed is 5-15%.

[0016] The dense sintered alumina matrix is ​​obtained by high-temperature sintering of highly active calcined alumina powder with a median particle size of less than 5 μm (preferably less than 3 μm) and SiO2-CaO sintering aids.

[0017] The present invention also provides a method for preparing the above-mentioned alumina honeycomb ceramic, including the following steps: raw material formulation, pretreatment of fused alumina raw material, pretreatment of matrix powder, mixing and kneading of raw materials, kneading and vacuum kneading, extrusion molding and drying, and firing.

[0018] The raw material formulation composition, by weight percentage, is as follows:

[0019] Fused alumina: 2-8%

[0020] Spherical alumina: 2-8%

[0021] Calcined alumina: 80-95%

[0022] Calcium carbonate: 0.2-0.5%

[0023] Quartz: 0.5-0.8%

[0024] Calcinated kaolin: 0-3%

[0025] Added pore-forming agent: 1-12%

[0026] Additional HPMC: 1-3%

[0027] External lubricant: 0.5-3%

[0028] The specific steps of the preparation method are as follows:

[0029] 1. Pretreatment of fused alumina raw materials: A 2%-15% aluminum dihydrogen phosphate solution is thoroughly mixed with 2%-10% acidic silica sol, and then mixed and stirred with fused alumina sand to achieve coating. The coated powder is calcined at 300-500℃ and then ball-milled to obtain modified fused alumina aggregate.

[0030] 2. Pretreatment of matrix powder: Calcined alumina powder, calcium carbonate, quartz, calcined kaolin and other matrix raw materials are ball-milled in a ball mill according to the specified ratio to ensure that the raw materials are fully mixed and that the particle size D50 of the raw materials is less than 3μm.

[0031] 3. Mixing and kneading of raw materials: The modified fused alumina aggregate, spherical alumina powder, pre-ground matrix powder, spherical pore-forming agent, hydroxypropyl methylcellulose, lubricant, etc. are thoroughly mixed in a high-speed mixer, and then water is added and kneaded in a kneader to form a plastic clay.

[0032] 4. Clay grinding and vacuum clay grinding: The plastic clay material is subjected to one coarse grinding and two vacuum clay grinding in a vacuum clay grinding machine to obtain uniform and dense clay segments.

[0033] 5. Extrusion molding and drying: The dense clay segments are extruded in an extruder to obtain honeycomb-shaped wet blanks, which are then quickly shaped in a microwave drying equipment and completely dried in a drying oven or continuous drying equipment.

[0034] 6. Firing: The dried green body is fired in a high-temperature kiln at 1500-1680℃ to obtain the wear-resistant and thermal shock resistant alumina honeycomb ceramic of the present invention.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. The alumina honeycomb ceramic of the present invention, through a composite microstructure, aims to simultaneously meet the performance requirements of wear resistance and thermal shock resistance. This structure consists of a dense sintered alumina matrix, a weakly bonded interface formed by two aggregates, and spherical closed pores. The dense matrix portion provides the material's wear resistance, while the weakly bonded interface and spherical closed pores enhance the material's thermal shock resistance.

[0037] 2. This invention forms a weak bonding interface between aggregate particles and the matrix by pretreating the surface of fused alumina and using spherical alumina with an inert surface. When the material is subjected to thermal shock, these weak bonding interfaces allow the formation of microcracks to absorb and release thermal stress, which is one of the technical approaches of this invention to improve thermal shock resistance.

[0038] 3. This invention forms spherical closed pores in a ceramic matrix by using an organic microsphere pore-forming agent. These closed pores can serve as stress relief points, helping to improve the thermal shock resistance of the material, while having a smaller negative impact on the mechanical properties of the material compared to open pores. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the microstructure of the alumina honeycomb ceramic of the present invention, used to illustrate its basic components and functional relationships;

[0040] Figure 2 This is a process flow diagram of the alumina honeycomb ceramic preparation method of the present invention, used to illustrate the complete process stages from raw materials to finished products;

[0041] Figure 3 This is a detailed flowchart of the pretreatment steps for fused alumina in this invention, used to illustrate the key process details of surface modification of fused alumina. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0043] This invention addresses the technical challenge of achieving both wear resistance and thermal shock resistance in traditional alumina honeycomb ceramics by constructing a composite microstructure that combines a dense sintered alumina matrix, a weak bonding interface, and spherical closed pores.

[0044] The dense sintered alumina matrix is ​​fundamental to ensuring the material's excellent wear resistance. In this invention, the matrix is ​​composed of highly active calcined alumina powder with a median particle size of less than 5 μm, preferably less than 3 μm. The fine powder has a higher specific surface area and sintering activity, enabling high densification at optimized firing temperatures. Simultaneously, the SiO2-CaO sintering aid (formed by the reaction of quartz and calcium carbonate) introduced into the formulation generates a low-melting-point liquid phase at high temperatures. This liquid phase wets the alumina particles, promoting particle rearrangement and densification through a liquid-phase sintering mechanism, ultimately forming a continuous, robust, and wear-resistant ceramic skeleton.

[0045] The weak bonding interface is a key technical means for improving the thermal shock resistance of this invention. This weak bonding interface is achieved through two approaches: First, surface pretreatment of the fused alumina aggregate. By coating its surface with an aluminum phosphate-nano silica coating, this coating acts as a physical or chemical isolation layer during high-temperature sintering, hindering strong chemical bonding and material diffusion between the aggregate and the matrix, thus forming a relatively weak bonding interface. Second, utilizing the physicochemical properties of the spherical alumina aggregate itself. This aggregate, prepared by a rapid melting process, has a smooth surface and is chemically inert, making it difficult to form a strong bond with the surrounding alumina matrix during sintering, naturally constituting another weak bonding interface. When the ceramic body is subjected to thermal shock, the enormous thermal stress preferentially concentrates on these pre-designed weak interfaces and is absorbed and dissipated in the form of numerous, diffusely distributed microcracks. This controllable microcrack propagation replaces catastrophic macrocrack propagation, thereby endowing the material with excellent resistance to drastic temperature changes. The selected aggregate particle size (45-180μm for fused alumina and 20-50μm for spherical alumina) has also been optimized to ensure that it can effectively inhibit crack propagation.

[0046] The spherical closed pores are another auxiliary means to improve thermal shock resistance. This invention incorporates organic microsphere pore-forming agents (such as polystyrene or polymethyl methacrylate microspheres). These microspheres completely decompose and volatilize during sintering, leaving a large number of uniformly distributed, regularly shaped spherical closed pores in the dense matrix. Unlike open pores, which severely weaken material strength and reduce wear resistance, these isolated, closed spherical pores act as stress release points, effectively mitigating thermal stress while maximizing the continuity and integrity of the matrix, resulting in minimal negative impact on the material's wear resistance. The selection of their pore size (8-58 μm) and porosity (5-15%) represents an optimized balance between thermal shock resistance and mechanical properties.

[0047] The present invention will now be described in detail through specific embodiments and comparative examples.

[0048] Example 1

[0049] This embodiment provides a method for preparing wear-resistant and thermal shock-resistant alumina honeycomb ceramic.

[0050] Raw material formulation (by weight percentage): 8% 120μm fused alumina, 6% 40μm spherical alumina, 82% calcined alumina, 0.4% calcium carbonate, 0.6% quartz, 3% calcined kaolin, 5% pore-forming agent (PMMA microspheres), 3% HPMC, and 3% lubricant.

[0051] Pretreatment of fused alumina: A 10% aluminum dihydrogen phosphate solution and a 10% acidic silica sol were mixed at a 1:1 volume ratio. This mixture was then stirred with 120μm fused alumina sand to uniformly coat the surface of the alumina sand. The amount of the mixture was 8% of the weight of the alumina sand. The coated alumina sand was dried and then calcined in a muffle furnace at 450℃ for 2 hours. After cooling, the calcined product was crushed using a ball mill to obtain modified fused alumina aggregate.

[0052] Pretreatment of matrix powder: Calcined alumina powder, calcium carbonate, quartz and calcined kaolin in the formula are placed in a ball mill, and ball stones and water are added for wet ball milling until the median particle size (D50) of the mixed powder is less than 3μm. Then the powder is dried to obtain pretreated matrix powder.

[0053] Mixing and Molding: The modified fused alumina aggregate, spherical alumina powder, pretreated matrix powder, PMMA microspheres, and HPMC were dry-mixed evenly in a high-speed mixer. Then, the mixture was transferred to a kneader, where lubricant and water were slowly added while stirring, kneading the mixture into a uniform, plastic clay. The clay was then placed in a vacuum ply mill for one coarse kneading and two vacuum kneading processes to remove gas and obtain dense clay segments. These segments were then placed in an extruder and extruded into honeycomb-shaped wet blanks.

[0054] Drying and firing: The wet blanks are cut into the required sizes and first rapidly dried and shaped in a microwave drying device, then transferred to a drying oven to be completely dried at 110°C. Finally, the dried blanks are placed in a high-temperature kiln and heated to 1600°C at a certain heating rate, held at that temperature for 3 hours, and then cooled in the kiln to obtain the finished product.

[0055] Example 2

[0056] Raw material formulation (weight percentage): 8% 180μm fused alumina, 6% 40μm spherical alumina, and the remaining components are in the same proportions as in Example 1, but the amount of pore-forming agent is adjusted to 10%. The preparation method is the same as in Example 1, but the firing temperature is increased to 1650℃ and held for 3 hours.

[0057] Example 3

[0058] Raw material formulation (weight percentage): 5% 60μm fused alumina, 10% 30μm spherical alumina, 2% calcined kaolin, with the remaining components in the same proportions as in Example 2. The preparation method is the same as in Example 1, but the firing temperature is 1580℃, and the holding time is 3 hours.

[0059] Comparative Example 1

[0060] To verify the role of the weak bonding interface in this invention, this comparative example was set up. Raw material formulation (weight percentage): 5% 60μm fused alumina, 92% calcined alumina, 2% calcined kaolin, with the remaining components in the same proportions as in Example 3. Compared to Example 3, this comparative example does not add spherical alumina, and the fused alumina used was not subjected to any surface pretreatment. The preparation method and firing conditions are the same as in Example 3.

[0061] Comparative Example 2

[0062] To verify the superiority of the formulation design of this invention, a comparative example was set up. Raw material formulation (weight percentage): 45% 60μm fused alumina, 52% calcined alumina, with the remaining components in the same proportions as in Comparative Example 1. This comparative example significantly increased the content of unmodified fused alumina and contained no spherical alumina. The preparation method and firing conditions were the same as in Example 2.

[0063] Performance Comparison and Analysis

[0064] The samples prepared in the above embodiments and comparative examples were subjected to performance tests, and the results are summarized in the table below.

[0065]

[0066] The performance test data listed in the table above allows for a thorough and detailed analysis of the technical effects of this invention:

[0067] 1. The decisive role of weak bonding interfaces in thermal shock resistance

[0068] The core of this analysis lies in the direct comparison between Example 3 and Comparative Example 1. The total amounts of aggregate and pore-forming agent in the raw material formulations of these two cases are similar, and their firing regimes are also identical. The most fundamental difference lies in the fact that the ceramic of Example 3 has a "weakly bonded interface" as described in this invention (achieved through surface-modified fused alumina and spherical alumina), while Comparative Example 1 does not contain these structures and represents the traditional dense ceramic technology route.

[0069] The data reveals a stark difference in performance between the two. Regarding thermal shock resistance, the sample in Example 3 withstood up to 46 cycles of rapid cooling from 1550°C to 500°C without cracking, while the sample in Comparative Example 1 suffered structural failure after only 3 cycles. This performance difference of over 15 times irrefutably demonstrates that the "weak bonding interface," as an effective thermal stress release mechanism, is the fundamental reason why this invention achieves superior thermal shock resistance. In the rigid structure of Comparative Example 1, thermal stress cannot be effectively dissipated and can only be released through catastrophic macroscopic crack propagation, leading to its rapid failure.

[0070] Regarding wear resistance, the mass loss rate of Comparative Example 1 (0.018%) was slightly lower than that of Example 3 (0.046%), which is due to its higher ceramic density (3.72 g / cm³). 3 This is due to the fact that, while thermal shock resistance is improved by more than 90%, the slight increase in wear resistance is meaningless in actual working conditions where frequent temperature changes are required. This precisely confirms the technical bottleneck mentioned in the background section, namely, that simply pursuing densification cannot meet the comprehensive performance requirements.

[0071] 2. The systematic nature and advanced nature of the technical solution of this invention

[0072] The core of this analysis lies in the comparison between Example 2 and Comparative Example 2. Comparative Example 2 adopted the traditional approach of significantly increasing the content of unmodified aggregate, attempting to improve performance through aggregate filling. However, experimental results show that this is an incorrect technical approach.

[0073] In terms of thermal shock resistance, the sample of Example 2 could withstand 58 cycles, while that of Comparative Example 2 could only withstand 12 cycles, a performance difference of nearly 5 times. In terms of wear resistance, the difference was even more significant, with the mass loss rate of Example 2 being only 0.055%, while that of Comparative Example 2 was as high as 1.257%, the latter being more than 20 times that of the former.

[0074] The reason for this is that in Comparative Example 2, a large amount of untreated fused alumina formed a strong but tough interface with the matrix, and the high internal stress caused by thermal mismatch resulted in poor thermal shock resistance. Simultaneously, the excessive coarse aggregate hindered the effective sintering of the matrix, leading to an apparent porosity as high as 14.7% (far higher than the 1.2% in Example 2), resulting in a loose and poorly wear-resistant structure. This fully demonstrates that the success of this invention does not stem from simple component stacking, but rather relies on precise proportional control of each component (especially the two aggregates with different mechanisms), and the advanced technical system constructed through surface modification of the key component (fused alumina), resulting in synergistic effects among the various parts.

[0075] 3. Stability and adjustability of the technical solution of this invention

[0076] By comparing the internal data of Examples 1, 2, and 3, the robustness of the technical solution of this invention can be observed. These three examples employed different aggregate particle sizes, aggregate ratios, pore-forming agent dosages, and firing temperatures, but all ultimately achieved comprehensive performance combining excellent thermal shock resistance (greater than 45 cycles) and high wear resistance (mass loss rate less than 0.06%). This indicates that the core technical concept of this invention is not an isolated technical point, but rather a technical platform with considerable flexibility. By adjusting the formulation and process parameters, the final performance of the product (such as the emphasis on density, porosity, thermal shock resistance, and wear resistance) can be fine-tuned within a relatively high performance range to adapt to more diverse specific application needs, demonstrating its promising prospects for industrial application.

[0077] In summary, through comparative analysis with comparative examples, it can be concluded that this invention, through its unique composite microstructure design of "dense matrix + weak bonding interface + spherical closed pores", solves the technical problem of simultaneously achieving wear resistance and thermal shock resistance in alumina honeycomb ceramics.

[0078] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A wear resistant, thermal shock resistant, alumina honeycomb ceramic characterized by, The ceramic is made of the following components: a dense sintered alumina matrix formed of 82% calcined alumina powder, 0.4% calcium carbonate, 0.6% quartz and 3% calcined kaolin by weight of the total raw materials; electro-fused corundum aggregates, 8% by weight of the total raw materials, uniformly dispersed in the matrix and having their surfaces pre-treated to form a first weakly bonded interface with the matrix; spherical alumina aggregates, 6% by weight of the total raw materials, uniformly dispersed in the matrix and having their inert surfaces form a second weakly bonded interface with the matrix; and spherical closed pores, 5-15% of the porosity of the ceramic, uniformly dispersed in the matrix. The particle size of the electro-fused corundum aggregates is 45-180 μm; and / or the pre-treatment is surface treatment of the electro-fused corundum aggregates with a liquid containing aluminum dihydrogen phosphate or acidic silica sol.

2. The alumina honeycomb ceramic of claim 1, wherein, The particle size of the spherical alumina aggregates is 20-50 μm.

3. The alumina honeycomb ceramic of claim 1, wherein, The spherical closed pores are formed by oxidation and decomposition of polystyrene microspheres or polymethyl methacrylate microspheres as pore-forming agents during the firing process, and have a pore size of 8-58 μm.

4. The alumina honeycomb ceramic of claim 1, wherein, The method comprises the following steps:

5. A method of making the alumina honeycomb ceramic of claim 4, wherein, a) surface modification: forming the electro-fused corundum aggregates for building the first weakly bonded interface through surface pre-treatment; b) mixing of ingredients: mixing the electro-fused corundum aggregates obtained in step a) with spherical alumina aggregates, calcined alumina powder, calcium carbonate, quartz, calcined kaolin and polystyrene microspheres or polymethyl methacrylate microspheres pore-forming agents to prepare a plasticizable paste; c) shaping and drying: extruding the plasticizable paste into a honeycomb-shaped wet body and drying; d) high-temperature firing: firing the dried body at 1500-1680 °C to obtain the alumina honeycomb ceramic. The surface pre-treatment in step a) comprises coating with a liquid containing aluminum dihydrogen phosphate or silica sol, followed by calcination at 300-500 °C.

6. The method of claim 5, wherein, Before step b), it further comprises mixing the calcined alumina powder with calcium carbonate, quartz, calcined kaolin and ball-milling to a median particle size of less than 3 μm.

7. The method of claim 5, wherein, ​

Images