Wear-resistant thermal shock-resistant alumina honeycomb ceramic and preparation method thereof

Abstract

The invention discloses a wear-resistant thermal shock-resistant aluminum oxide honeycomb ceramic and a preparation method thereof. The aluminum oxide honeycomb ceramic comprises a compactly sintered aluminum oxide matrix; the fused corundum aggregate is uniformly dispersed in the matrix, and the surface of the fused corundum aggregate is pretreated to form a weak bonding interface; the spherical aluminum oxide aggregate is uniformly dispersed in the matrix, and the inert surface of the spherical aluminum oxide aggregate forms another weak bonding interface; and uniformly dispersed spherical closed pores formed by a pore forming agent. The compact matrix ensures excellent wear resistance, the weak bonding interface and the spherical closed pores have a synergistic effect, and controllable microcracks are triggered during thermal shock to release stress, so that the thermal shock resistance is remarkably improved. The preparation method comprises the following steps: carrying out surface modification on the fused alumina, mixing with the spherical alumina, the alumina powder, the pore-forming agent and the like, carrying out extrusion molding, drying, and sintering at a high temperature of 1500-1680 DEG C. The prepared honeycomb ceramic is excellent in comprehensive performance, and the service life is greatly prolonged.

Description

TECHNICAL FIELD

[0001] The present application relates to a honeycomb ceramic and a preparation method thereof, in particular, to an alumina honeycomb ceramic with excellent wear resistance and thermal shock resistance and a preparation method thereof, and belongs to the field of high-performance ceramic materials. BACKGROUND

[0002] Alumina (Al2O3), especially alumina with corundum phase, is widely used in the manufacture of honeycomb ceramic regenerators due to its large heat storage capacity, excellent high-temperature resistance, good chemical stability, and high mechanical strength, etc. This type of regenerator plays a crucial role in high-temperature industrial equipment such as regenerative high-temperature incinerators (RTO) and hot blast furnaces in the metallurgical industry.

[0003] However, in practical applications, traditional alumina honeycomb ceramics face a long-standing technical bottleneck that has not been effectively addressed, which is the inherent contradiction between their wear resistance and thermal shock resistance. This mainly reflects in the inherent defects of the following two technical routes: 1. In order to pursue high mechanical strength and excellent wear resistance, a common technical solution is to prepare a dense alumina honeycomb ceramic. The pore walls of this ceramic are dense, with very low porosity. Although it can effectively resist the erosion and wear of high-temperature gas flow, its high density also brings a fatal weakness: alumina material itself has a large thermal expansion coefficient. In the cycle of heat storage and heat release, the honeycomb ceramic needs to withstand severe temperature gradient changes, i.e. thermal shock. The high thermal expansion coefficient causes a large thermal stress in the dense ceramic, which can lead to the generation, propagation, and even macroscopic cracking of microcracks, ultimately causing structural damage to the ceramic body, greatly shortening its service life.

[0004] 2. In order to solve the problem of poor thermal shock resistance of dense ceramics, another technical route has emerged, which is to introduce a large number of pores into the pore walls of the ceramic, forming a porous structure, especially an open pore structure. These pores distributed in the matrix can effectively hinder the propagation of cracks, or act as stress relaxation zones to absorb and release thermal stress, thereby significantly improving the thermal shock resistance of alumina honeycomb ceramics. However, this solution is at the expense of the density of the material. The presence of a large number of open pores makes the pore walls of the ceramic loose, and the mechanical strength and surface hardness decrease significantly. In actual working conditions such as incinerators, high-speed gas flow and hard dust particles carried by it will cause continuous and severe erosion and abrasion of the loose honeycomb pore walls under high-temperature coupling. This will cause the pore wall material to gradually peel off, the pore channel to expand or even block, not only reducing the heat storage efficiency, but also more seriously, causing the honeycomb ceramic to fail prematurely due to excessive wear, which also cannot meet the requirements of long service life and high reliability.

[0005] In summary, the existing technology, whether it is to adopt the densification route or the porous route, can only one-sidedly meet the single performance requirement of wear resistance or thermal shock resistance, and cannot achieve the compromise of both. Therefore, developing a new type of alumina honeycomb ceramic that can resist high-temperature wear and withstand severe thermal shock has become a technical problem that urgently needs to be solved in the field. SUMMARY

[0006] The purpose of the present application is to overcome the shortcomings of the prior art and provide a wear-resistant and thermal shock-resistant alumina honeycomb ceramic and a preparation method thereof. The ceramic, through unique microstructure design, cooperatively realizes the unity of high wear resistance and high thermal shock resistance, aiming to significantly prolong its service life in high-temperature industrial environments.

[0007] To achieve the above-mentioned purpose, the present application provides a wear-resistant and thermal shock-resistant alumina honeycomb ceramic, characterized in that it comprises: a dense sintered alumina matrix; electro-fused corundum aggregates uniformly dispersed in the matrix, and the surface of which is pretreated to form a first weakly bonded interface with the matrix; spherical alumina aggregates uniformly dispersed in the matrix and forming a second weakly bonded interface with the matrix with their inert surfaces; and spherical closed pores uniformly dispersed in the matrix.

[0008] The particle size of the electro-fused corundum aggregate is 45-180 μm; its content is 2-8% by weight; and the surface pretreatment is surface coating of electro-fused corundum powder with one or both of aluminum dihydrogen phosphate solution and acidic silica sol to form a weakly bonded surface layer.

[0009] The spherical alumina aggregate is a near-spherical alumina formed by rapid melting, which is not completely dense and has an inert surface; its particle size is 20-50 μm; and its content is 2-8% by weight.

[0010] The spherical closed pores are spherical pore residues formed by oxidative decomposition of organic microspheres as templates during sintering, and form 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 spherical pore diameter is 8-58 μm; and the porosity formed is 5-15%.

[0011] The dense sintered alumina matrix is obtained by high-temperature sintering of high-activity calcined alumina powder with a median particle size of less than 5 μm (preferably less than 3 μm) and SiO2-CaO system sintering aids.

[0012] The application also provides a preparation method of the above alumina honeycomb ceramic, which comprises the following steps: raw material formula composition, pretreatment of the raw material of electrically fused corundum, pretreatment of the matrix powder, mixing and kneading of the raw material, mud refining and vacuum mud refining, extrusion molding and drying, and firing.

[0013] The raw material formula composition is as follows in terms of percentage by weight: Electrically fused corundum: 2-8% Spherical alumina: 2-8% Calcined alumina: 80-95% Calcium carbonate: 0.2-0.5% Quartz: 0.5-0.8% Calcined kaolin: 0-3% External pore-forming agent: 1-12% External HPMC: 1-3% External lubricant: 0.5-3% The specific steps of the preparation method are as follows: 1. Pretreatment of the raw material of electrically fused corundum: fully mix aluminum dihydrogen phosphate solution with a concentration of 2%-15% and acidic silica sol with a concentration of 2%-10%, then mix and stir with the electrically fused corundum sand to realize coating, calcine the coated powder at 300-500 DEG C, then break it by ball milling to obtain modified electrically fused corundum aggregate.

[0014] 2. Pretreatment of the matrix powder: ball mill the matrix raw materials such as calcined alumina powder, calcium carbonate, quartz, calcined kaolin and the like according to the proportion in a ball mill to fully mix the raw materials and make the particle size D50 of the raw materials less than 3 microns.

[0015] 3. Mixing and kneading of the raw material: fully mix the modified electrically fused corundum aggregate, spherical alumina powder, pre-milled matrix powder, spherical pore-forming agent, hydroxypropyl methyl cellulose and lubricant in a high-speed stirrer, then add water to knead in a kneader to form plastic mud.

[0016] 4. Mud refining and vacuum mud refining: coarsely refine the plastic mud once and vacuum refine it twice in a vacuum mud refiner to obtain uniform and dense mud sections.

[0017] 5. Extrusion molding and drying: extrude the dense mud sections in an extruder to obtain honeycomb-shaped wet blanks, then quickly shape them in a microwave drying device, and then completely dry them in an oven or a continuous drying device.

[0018] 6. Firing: fire the dried blanks in a high-temperature kiln at 1500-1680 DEG C to obtain the wear-resistant and thermal shock-resistant alumina honeycomb ceramic of the application.

[0019] Compared with the prior art, the application has the following beneficial effects: 1. The alumina honeycomb ceramic of the present invention meets the performance requirements of both wear resistance and thermal shock resistance by means of a composite microstructure. The structure is composed of a dense sintered alumina matrix, weakly bonded interfaces formed by two kinds of aggregates, and spherical closed pores. Among them, the dense matrix part is used to provide the wear resistance of the material, while the weakly bonded interfaces and spherical closed pores are used to improve the thermal shock resistance of the material.

[0020] 2. The present invention forms weakly bonded interfaces between aggregate particles and the matrix by surface pretreatment of the electrofused corundum and the use of spherical alumina with an inert surface. When the material is subjected to thermal shock, these weakly bonded interfaces allow the formation of microcracks to absorb and release thermal stress, which is one of the technical approaches of the present invention to improve the thermal shock resistance.

[0021] 3. The present invention forms spherical closed pores in the ceramic matrix by using organic microspheres as pore-forming agents. These closed pores can act as stress release points, helping to improve the thermal shock resistance of the material, while their negative impact on the mechanical properties of the material is smaller compared to open pores. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a schematic diagram of the microstructure of the alumina honeycomb ceramic of the present invention, used to show the basic component parts and functional relationships thereof; Figure 2 is a process flow chart of the preparation method of the alumina honeycomb ceramic of the present invention, used to show the complete process stages from raw materials to finished products; Figure 3 is a detailed flow chart of the pretreatment step of electrofused corundum in the present invention, used to show the key process details of surface modification of electrofused corundum. DETAILED DESCRIPTION

[0023] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be described clearly and completely below. Obviously, the described embodiments are only some of the embodiments of the present invention, not all. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present invention.

[0024] The present invention solves the technical problem that traditional alumina honeycomb ceramics cannot simultaneously meet the requirements of wear resistance and thermal shock resistance by constructing a composite microstructure composed of a dense sintered alumina matrix, weakly bonded interfaces, and spherical closed pores.

[0025] The dense sintered alumina matrix is the foundation of the excellent wear resistance of the material. In the present invention, the matrix is composed of high-activity calcined alumina powder with a median particle size less than 5 μm, preferably less than 3 μm. The fine powder has a higher specific surface area and sintering activity, and can achieve high densification at an optimized sintering temperature. At the same time, the SiO2-CaO system sintering aid (formed by the reaction of quartz and calcium carbonate) introduced in the formulation will generate a low-melting liquid phase at high temperature, which can wet the alumina particles and promote the rearrangement and densification process of the particles through the liquid phase sintering mechanism, ultimately forming a continuous, strong and wear-resistant ceramic skeleton.

[0026] The weakly bonded interface is the key technical means of the present invention to improve the thermal shock resistance. This weakly bonded interface is achieved through two ways: one is the surface pretreatment of the fused corundum aggregate. By coating a layer of aluminum phosphate-nano silicon oxide coating on its surface, this coating acts as a physical or chemical isolation layer during high-temperature sintering, hindering the strong chemical bonding and material diffusion between the aggregate and the matrix, thereby forming a relatively weakly bonded interface between the two. The second is to use the physical and chemical properties of the spherical alumina aggregate itself. The aggregate is prepared by a rapid melting process, has a smooth surface and inert chemical properties, and is difficult to form a strong bond with the surrounding alumina matrix during sintering, naturally forming another weakly bonded interface. When the ceramic body is subjected to thermal shock, the huge thermal stress will first concentrate on these pre-set weak interfaces and be absorbed and dissipated in the form of a large number of, dispersedly distributed micro-cracks. This controllable micro-crack propagation replaces the catastrophic macro-crack propagation, thereby endowing the material with excellent ability to withstand temperature changes. The particle size of the selected aggregate (fused corundum 45-180 μm, spherical alumina 20-50 μm) is also optimized to ensure that it can effectively hinder crack propagation.

[0027] The spherical closed pores are another auxiliary means to improve the thermal shock resistance. The present invention adds organic microsphere pore-forming agents (such as polystyrene or polymethyl methacrylate microspheres), which completely decompose and volatilize during sintering, leaving a large number of uniformly distributed, regular spherical closed pores in the dense matrix. Unlike open pores, which severely weaken the material strength and reduce wear resistance, these isolated, closed spherical pores act as stress release points and effectively moderate thermal stress while maximizing the continuity and integrity of the matrix, having minimal negative impact on the material's wear resistance. The selection of the pore size (8-58 μm) and porosity (5-15%) is an optimized result of balancing the thermal shock resistance and mechanical properties.

[0028] The present invention will be described in detail below through specific examples and comparative examples.

[0029] Example 1 The present embodiment provides a preparation method of a wear-resistant and thermal shock-resistant alumina honeycomb ceramic.

[0030] Raw material formula (by weight percentage): 120 μm fused corundum 8%, 40 μm spherical alumina 6%, calcined alumina 82%, calcium carbonate 0.4%, quartz 0.6%, calcined kaolin 3%, additional pore-forming agent (PMMA microspheres) 5%, additional HPMC 3%, additional lubricant 3%.

[0031] Fused corundum pretreatment: 10% aluminum dihydrogen phosphate solution and 10% acidic silica sol are mixed in a volume ratio of 1:1, and the mixture is stirred and mixed with 120 μm fused corundum sand to evenly coat the surface of the corundum sand. The amount of the mixture is 8% of the weight of the corundum sand. The coated corundum sand is dried, and then calcined at 450°C in a muffle furnace for 2 hours. After cooling, the calcined product is broken by a ball mill to obtain modified fused corundum aggregate.

[0032] Matrix powder pretreatment: The 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 3 μm, and then dried to obtain pretreated matrix powder.

[0033] Mixing and molding: The modified fused corundum aggregate, spherical alumina powder, pretreated matrix powder, PMMA microspheres, and HPMC are dry mixed uniformly in a high-speed mixer. Then, they are transferred to a kneader, and the lubricant and water are slowly added while stirring to knead into a uniform and plastic mud. The mud is placed in a vacuum mud mill for 1 time of rough milling and 2 times of vacuum milling to remove the gas in the mud, and a dense mud segment is obtained. The mud segment is placed in an extruder and extruded into a honeycomb-shaped wet blank.

[0034] Drying and firing: The wet blank is cut to the required size, and then dried and shaped in a microwave drying device, and then completely dried at 110°C in an oven. Finally, the dried blank is placed in a high-temperature kiln, and the temperature is increased to 1600°C at a certain rate, and then kept for 3 hours, and then cooled with the furnace to obtain the finished product.

[0035] Example 2 Raw material formula (by weight percentage): 120 μm fused corundum 8%, 40 μm spherical alumina 6%, the rest of the components are the same as in Example 1, but the amount of the additional 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°C, and the holding time is 3 hours.

[0036] Example 3 Raw material formulation (wt%): 5% 60 μm fused alumina, 10% 30 μm spherical alumina, 2% calcined kaolin, and the rest of the 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°C, and the holding time is 3 hours.

[0037] Comparative Example 1 To verify the effect of the weakly bonded interface in the present application, this comparative example was set up. Raw material formulation (wt%): 5% 60 μm fused alumina, 92% calcined alumina, 2% calcined kaolin, and the rest of the components in the same proportions as in Example 3. Compared with Example 3, this comparative example does not add spherical alumina, and the fused alumina used is not surface-treated. The preparation method and firing conditions are the same as in Example 3.

[0038] Comparative Example 2 To verify the superiority of the formulation design in the present application, this comparative example was set up. Raw material formulation (wt%): 45% 60 μm fused alumina, 52% calcined alumina, and the rest of the components in the same proportions as in Comparative Example 1. This comparative example greatly increases the content of unmodified fused alumina and does not contain spherical alumina. The preparation method and firing conditions are the same as in Example 2.

[0039] Performance comparison and analysis The samples prepared in the above examples and comparative examples were tested for performance, and the results are shown in the following table.

[0040]

[0041] From the performance test data listed in the above table, the technical effects of the present application can be analyzed in depth and detail: 1. The decisive role of the weakly bonded interface in thermal shock resistance The core of this analysis is the direct comparison between Example 3 and Comparative Example 1. The total amount of aggregates and pore-forming agents in the raw material formulations of these two cases is similar, and the firing schedule is also completely the same. The most essential difference lies in the fact that Example 3 has a "weakly bonded interface" (achieved by surface-modified fused alumina and spherical alumina) inside the ceramic, while Comparative Example 1 does not contain such a structure, representing the traditional dense ceramic technology route.

[0042] From the data, the performance of the two is very different. In terms of thermal shock resistance, the sample of Example 3 can withstand up to 46 times of 1550℃-500℃ quenching cycles without cracking, while the sample of Comparative Example 1 has structural damage after only 3 cycles. This more than 15 times performance gap, irrefutably proves that "weakly bonded interface" as an effective thermal stress release mechanism is the fundamental reason for the excellent thermal shock resistance of the present application. In the rigid structure of Comparative Example 1, thermal stress cannot be effectively dissipated, but only released through catastrophic macroscopic crack propagation, leading to its rapid failure.

[0043] Looking at the wear resistance, the mass loss rate of Comparative Example 1 (0.018%) is slightly lower than that of Example 3 (0.046%), which is due to its higher density of porcelain parts (3.72 g / cm 3 ). However, this slight wear resistance improvement at the expense of more than 90% of thermal shock resistance is meaningless in actual working conditions that require frequent temperature changes. This exactly confirms the technical bottleneck described in the background art, that is, simply pursuing densification cannot meet the comprehensive performance requirements.

[0044] 2、The systematicness and advancement of the technical solution of the present application The core of this analysis is the comparison between Example 2 and Comparative Example 2. Comparative Example 2 adopts the traditional approach of significantly increasing the content of unmodified aggregate, trying to improve performance through aggregate filling. However, the experimental results show that this is a wrong technical route.

[0045] In terms of thermal shock resistance, the sample of Example 2 can withstand 58 cycles, while the sample of Comparative Example 2 can only withstand 12 cycles, with a performance gap of nearly 5 times. In terms of wear resistance, the gap is even more disproportionate, with the mass loss rate of Example 2 being only 0.055%, while that of Comparative Example 2 being as high as 1.257%, which is more than 20 times that of Example 2.

[0046] The reason is that in Comparative Example 2, a large amount of unmodified electrically fused corundum forms a strong bonding interface with the matrix, which has high strength but poor toughness. The high internal stress caused by thermal mismatch makes it poor in thermal shock resistance. At the same time, the excessive coarse aggregate hinders the effective sintering of the matrix, resulting in a high apparent porosity of 14.7% (much higher than the 1.2% of Example 2), forming a loose and not wear-resistant structure. This fully proves that the success of the present application does not come from simple component stacking, but relies on the precise proportion control of each component (especially the two different mechanism aggregates), as well as the surface modification of the key component (electrically fused corundum) to build an advanced technical system in which each part works synergistically.

[0047] 3、The stability and adjustability of the technical solution of the present application By comparing the internal data of Examples 1, 2 and 3, it can be seen that the robustness of the technical scheme of the present application. The three examples respectively use different aggregate particle size, aggregate ratio, pore-forming agent amount and sintering temperature, but finally all obtain the comprehensive performance of excellent thermal shock resistance (all greater than 45 times) and high wear resistance (mass loss rate is less than 0.06%). This shows that the core technical idea of the present application is not a isolated technical point, but a technical platform with considerable tolerance. By adjusting the formula and process parameters, the final performance of the product (such as density, porosity, thermal shock resistance and wear resistance) can be fine-tuned within a relatively high performance range to meet more diversified specific application requirements, showing its good industrial application prospect.

[0048] In summary, through comparative analysis with the comparative examples, it can be concluded that: through the unique "dense matrix + weakly bonded interface + spherical closed pores" composite microstructure design, the technical problem that the wear resistance and thermal shock resistance of alumina honeycomb ceramics are difficult to be considered together is solved.

[0049] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto. Any changes or replacements within the technical range disclosed by the present application can be easily thought of by those skilled in the art, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A wear-resistant and thermal shock-resistant alumina honeycomb ceramic, characterized in that, The ceramic is made of the following components: The dense sintered alumina matrix is ​​formed from calcined alumina powder, which accounts for 80-95% of the total weight of the raw materials. Fused corundum aggregate, accounting for 2-8% of the total weight of raw materials, is uniformly dispersed in the matrix, and its surface is pretreated to form a first weak bonding interface with the matrix. Spherical alumina aggregate, accounting for 2-8% of the total weight of the raw materials, is uniformly dispersed in the matrix and forms a second weak bonding interface with the matrix with its inert surface; as well as The spherical closed pores have a porosity of 5-15% in the ceramic and are uniformly dispersed in the matrix.

2. The alumina honeycomb ceramic according to claim 1, characterized in that, The particle size of the fused alumina aggregate is 45-180 μm; and / or the pretreatment is obtained by surface treatment of the fused alumina raw material with a coating containing aluminum dihydrogen phosphate or acidic silica sol.

3. The alumina honeycomb ceramic according to claim 1, characterized in that, The spherical alumina aggregate has a particle size of 20-50 μm.

4. The alumina honeycomb ceramic according to claim 1, characterized in that, The spherical closed pores are formed by the oxidative decomposition of polystyrene microspheres or polymethyl methacrylate microspheres as pore-forming agents during the firing process, and their pore size is 8-58 μm.

5. A method for preparing alumina honeycomb ceramics as described in any one of claims 1-4, characterized in that, Includes the following steps: a) Surface modification: The fused alumina raw material is surface pretreated to form modified fused alumina aggregate for constructing the first weak bonding interface; b) Ingredient mixing: The modified fused alumina aggregate, spherical alumina aggregate, alumina powder constituting the matrix, and organic microsphere pore-forming agent obtained in step a) are mixed to prepare a plastic clay. c) Molding and drying: The plastic clay is extruded into a honeycomb-shaped wet blank and then dried; d) High-temperature firing: The dried green body is fired at 1500-1680℃ to obtain the alumina honeycomb ceramic.

6. The method according to claim 5, characterized in that, The surface pretreatment described in step a) includes: coating the fused alumina raw material with a mixture containing aluminum dihydrogen phosphate or silica sol, and then calcining it at 300-500°C.

7. The method according to claim 5, characterized in that, Before step b), the process further includes a pretreatment step of the alumina powder constituting the matrix, which is mixed with a sintering aid and ball-milled until the median particle size is less than 3 μm.

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