High-alkali-resistant and erosion-resistant corundum-spinel castable for alkali kiln and construction method thereof

Abstract

This invention discloses a corundum spinel castable resistant to high alkali corrosion and erosion in alkaline kilns, along with its construction method, belonging to the field of refractory materials. The castable uses high-purity fused alumina as aggregate, with the core components being aluminum-rich spinel micro-powder (Al2O3 ≥ 80%), active α-Al2O3 micro-powder, and fine fused alumina powder, solving the problem of insufficient corrosion resistance of traditional magnesium-aluminum spinel in alkaline kiln environments. Through the matching of thermal expansion between the active α-Al2O3 micro-powder, toughening fibers, and the matrix, an "in-situ toughening structure" is constructed within the material, achieving a balance between high strength and high thermal shock resistance. The product exhibits excellent performance: apparent porosity ≤ 18%, and compressive strength at room temperature and 1300℃ ≥ 80 MPa and ≥ 75 MPa, respectively. During construction, the raw materials are mixed, water is added, and the mixture is poured and cured. Then, it is baked at a rate of ≤ 25℃ / h to above 300℃. This invention is suitable for the preheating, transition, and firing zones of alkaline kilns, significantly extending the lining life.

Description

Technical Field

[0001] This invention relates to a castable, and more particularly to an alkaline corundum spinel castable for kilns that is resistant to high alkali erosion and scouring, and its construction method. It belongs to the technical field of refractory castables. Background Technology

[0002] The linings of the preheating section, transition zone, and firing zone of alkaline kilns are subjected to long-term high temperatures of 1100~1400℃, erosion by high-concentration CaO media, material scouring, and thermal shock cycles. Traditional high-alumina or corundum refractories have short service lives under these conditions because they are difficult to resist high-alkali erosion while maintaining excellent thermal shock resistance.

[0003] To improve alkali resistance, existing technologies typically introduce spinel phases. For example, patent CN118084516B discloses an alkali-resistant castable for a lime rotary kiln working lining, its preparation method, and its application, explicitly using magnesium aluminum spinel as a key corrosion-resistant component. However, in this approach, the high MgO content in the spinel may become a weakness in the high-calcium, low-silica environment unique to alkaline kilns. This is because MgO readily reacts with the corrosive medium CaO to form low-melting-point phases such as calcium magnesium olivine (CMS), which not only weakens the stability of the spinel phase itself but also reduces the overall high-temperature chemical resistance of the material. In other words, the magnesium aluminum spinel component relied upon in this technology does not exhibit optimal intrinsic chemical stability in the specific high-calcium environment of an alkaline kiln, resulting in inherent defects in its long-term corrosion resistance.

[0004] Meanwhile, existing improvement schemes often compromise on one aspect while addressing the common problem of insufficient thermal shock resistance in such high-strength castables. For example, another existing technology (CN103044053A) points out that lightweight aggregates or pore-forming agents are often introduced to buffer thermal stress in order to improve thermal shock resistance. However, this method inevitably and significantly reduces the bulk density, room temperature and high temperature strength of the material, impairing its erosion and impermeability, and failing to meet the high mechanical strength requirements of alkaline kiln linings. This reveals a deep contradiction: traditional technical approaches are inherently disconnected between the two dimensions of "alkali resistance" and "thermal shock resistance," lacking a material design strategy that can unify and strengthen both. If a material focuses on alkali resistance (such as using specific spinels), it is often difficult to maintain toughness; if it focuses on thermal shock resistance (such as introducing pores), it will inevitably compromise its density and strength.

[0005] Therefore, a long-standing core technical problem in this field is how to break the mutual constraints between "alkali-resistant components" and "toughening methods" in existing technologies and develop a completely new material system. This system must not only overcome the stability bottleneck of traditional magnesium aluminum spinel in high-calcium environments from a chemical perspective, but also generate an effective toughening mechanism from a physical structure perspective without sacrificing material strength and density, thereby truly achieving a high level of synergy between alkali resistance, thermal shock resistance, and high-temperature strength. Summary of the Invention

[0006] To solve the above-mentioned problems, the present invention provides, in a first aspect, an alkaline corundum spinel castable for kilns that is resistant to high alkali erosion and scouring.

[0007] The technical solution of the present invention to solve the above problems is as follows: A highly alkali-resistant and erosion-resistant alkaline kiln corundum spinel castable, by weight, comprises the following raw material components: Refractory aggregate: 50-70 parts, wherein the refractory aggregate is fused alumina with a gradation of 0-8mm; Refractory powder: 20-40 parts, wherein the refractory powder includes fused alumina fine powder, active α-Al2O3 micro powder and aluminum-rich spinel micro powder; Binder: 4-8 parts, pure calcium aluminate cement; Additives: 0.1 to 2 parts, wherein the additives include water-reducing agents and toughening fibers; After molding and heat treatment, the castable refractory forms an in-situ toughening structure inside, which is used to dissipate heat stress and improve resistance to thermal shock damage.

[0008] This invention provides a high-performance corundum spinel castable designed for extreme and harsh conditions in alkaline kilns, including high temperature, high alkali content, strong erosion, and thermal shock cycles. Through key component innovation and multi-level structural design, a composite system with an intrinsic alkali-resistant chemical barrier, a high-strength dense matrix, and an embedded in-situ toughening structure is constructed, thus systematically resolving the inherent contradiction between high alkali resistance, high thermal shock resistance, and high strength.

[0009] First, the construction of an "aluminum-rich spinel" chemical barrier aims to fundamentally revolutionize the material basis for alkali corrosion resistance. The technical logic is to abandon the magnesium aluminum spinel commonly used in traditional alkaline kiln alkali-resistant materials, which has inherent defects in chemical stability in high-calcium environments, and instead use aluminum-rich spinel micropowder with an Al2O3 content ≥80% as the core anti-corrosion component. The mechanism is as follows: in the high-calcium (CaO) environment of an alkaline kiln, aluminum-rich spinel (Al2O3·MgO), with its extremely high Al2O3 content, can preferentially and stably react with the invading CaO, generating in situ high-melting-point calcium hexaaluminate (CaO·6Al2O3, melting point ~1850℃) and other phases, thereby constructing a dense, highly chemically stable reaction barrier layer on the working surface of the material. Its technical effect is that it breaks through the limitations of traditional magnesium aluminum spinel from the essence of materials chemistry, realizes active and long-term resistance to the erosion of alkaline media in alkaline kilns, and solves the core problem pointed out in the background technology that the "intrinsic chemical stability of existing alkali-resistant components is not optimal".

[0010] Second, the construction of a high-strength, dense matrix and an "in-situ toughening structure" aims to synergistically achieve high strength and high toughness. The technical logic is to obtain intrinsic alkali resistance while optimizing particle size distribution to achieve a highly dense, high-strength corundum matrix, and to actively design an endogenous toughening mechanism within this matrix. Specifically: 1) High-strength matrix: Using high-purity fused alumina as the framework, continuous gradation and micro-powder filling achieve the densest packing, ensuring the material possesses high bulk density, low apparent porosity (≤18%), and high ambient / high temperature strength (≥80 / 75 MPa), providing a physical basis for resisting mechanical erosion and slag penetration. 2) Endogenous toughening: Introducing active α-Al2O3 micro-powder, and utilizing the appropriate thermal expansion mismatch between it, aluminum-rich spinel micro-powder, and the bonding phase, induces the formation of a uniformly dispersed "in-situ toughening structure" (composed of numerous micron-scale interfacial microstructures) within the material. This structure is not a defect, but rather a pre-designed energy dissipation system: when thermal shock stress occurs, it efficiently dissipates energy by causing frequent crack deflection, branching, and bridging, thus preventing unstable crack propagation. Its technical effect is that, without sacrificing the material's high strength and density, it simultaneously endows the material with excellent fracture toughness and resistance to thermal shock damage, thereby resolving the inherent contradiction in the background technology that "introducing porosity for toughening will damage strength," and achieving a unity of "high strength" and "high thermal shock resistance."

[0011] Third, the integral casting and process adaptation aim to ensure structural integrity and performance reproducibility. The use of a pure calcium aluminate cement bonding system and an optimized baking regime ensures excellent workability, curing strength, and safe dehydration of the materials. Finally, through integral casting, a seamless monolithic lining is obtained, fundamentally eliminating weak points in brick masonry structures caused by slag penetration and spalling in mortar joints.

[0012] As a preferred embodiment of the above technical solution, the chemical composition of the aluminum-rich spinel micro powder, by mass percentage, is: Al2O3: 80~90%, MgO: 10~20%, particle size D90≤15μm, and its dosage accounts for 8~20% of the total mass of the castable.

[0013] This range ensures that the aluminum-rich spinel micropowder can be fully and uniformly dispersed in the matrix, which is sufficient to form a continuous and effective surface chemical barrier, and also participates in the construction of in-situ toughening structure as one of the key phases. It is the optimal window for balancing alkali resistance, high temperature strength and toughening effect.

[0014] As a preferred embodiment of the above technical solution, the particle size D50 of the active α-Al2O3 micro powder is ≤5μm.

[0015] Ultrafine active micro powders have high surface energy, which not only can fill the pores to the extreme and promote sintering densification, but are also a key factor in inducing and regulating the formation of in-situ toughening structures, which is crucial for achieving high toughness of materials.

[0016] As a preferred embodiment of the above technical solution, the physical properties of the castable meet the following indicators: Al2O3 content ≥65%, apparent porosity ≤18%, and room temperature compressive strength ≥80MPa after molding and drying at 110℃.

[0017] These quantitative indicators directly reflect the high chemical purity, high structural density, and high mechanical strength of materials, and are the physical basis for resisting complex working conditions.

[0018] As a preferred embodiment of the above technical solution, the castable refractory, after being heat-treated at 1300℃ for 3 hours, has a compressive strength ≥75MPa.

[0019] This indicator directly verifies the strength retention rate of the material at temperatures close to the upper limit of the alkaline kiln firing zone, demonstrating its excellent high-temperature structural stability and volume stability, which is an important guarantee for its long service life.

[0020] As a preferred embodiment of the above technical solution, after the castable is used in an alkaline kiln at ≥1200℃, a dense reaction layer with a thickness of 20~100μm is formed on its working surface.

[0021] Secondly, the present invention provides a method for constructing refractory castables.

[0022] The technical solution is as follows: The construction method of the refractory castable includes the following steps: S1. After the raw materials are dry-mixed evenly, add water accounting for 4.5~6.5% of the total dry material mass, and stir to obtain the casting slurry; S2. Pour the slurry into the mold and vibrate it to compact it; S3. Curing in an environment of 20~30℃ and humidity ≥90% for 24~48 hours; S4. Bake at a rate of ≤25℃ / h to above 300℃.

[0023] As a preferred embodiment of the above technical solution, the final baking temperature is 300~600℃, and the temperature is maintained at the final temperature for 4~12 hours.

[0024] This gentle baking process ensures the safe and complete removal of bound water, preventing the lining from cracking during subsequent rapid heating, while giving the material sufficient initial strength for safe use and achieving final performance optimization at the actual high temperatures inside the kiln.

[0025] In summary, the present invention has the following beneficial effects: 1. Fundamental improvement in alkali resistance: By using aluminum-rich spinel instead of traditional magnesium aluminum spinel as the alkali-resistant core, the intrinsic stability problem in high-calcium environments is solved from the perspective of material chemistry, achieving a breakthrough in alkali resistance. 2. Synergistic unity of high strength and high thermal shock resistance: Through the composite design of "high-purity corundum dense matrix" and "in-situ toughening structure", an efficient toughening mechanism is generated without sacrificing the high strength and high density of the material, successfully solving the traditional contradiction of "high strength is brittle and toughening is weak". 3. Systematic optimization and long-term performance: The synergistic effect of chemical barrier, physical densification and structural toughening enables the material to systematically cope with the erosion, scouring and thermal shock of alkaline kilns; the integral casting structure further eliminates the risk of penetration and spalling, ensuring the long-term overall stability of the lining. 4. In summary, this invention constructs a three-in-one material system of "inherent alkali resistance - high-strength matrix - endogenous toughening". Among them, the aluminum-rich spinel constitutes an active defense "chemical armor", the high-density corundum matrix constitutes a "rigid fortress" against erosion and penetration, and the in-situ toughening structure constitutes a "buffer network" that absorbs stress and prevents damage. This multi-level synergistic design achieves a synergistic leap in the key properties of alkaline kiln lining materials, such as alkali resistance, thermal shock resistance, and erosion resistance. Detailed Implementation

[0026] This specific embodiment is merely an explanation of the present invention and is not intended to limit the present invention. Any changes made by those skilled in the art after reading the specification of the present invention, as long as they are within the scope of the claims, will be protected by patent law. Example 1

[0027] This embodiment provides a preferred formulation for the lining of the firing zone in a lime rotary kiln.

[0028] 1. Formula (by weight parts) Refractory aggregate (65 parts): fused alumina aggregate with a continuous gradation of 0~8mm particle size (Al2O3≥99%).

[0029] Refractory powder (32 parts): Fused corundum fine powder (≤0.088mm): 10 parts; Activated α-Al₂O₃ micro powder (D50=2μm): 7 parts; Aluminum-rich spinel micro powder (Al2O3: 85%, MgO: 15%, D90=10μm): 15 parts; Binder (4.5 parts): Pure calcium aluminate cement (Al2O3≥70%); Additives (0.5 parts): 0.3 parts polycarboxylate-based water-reducing agent, 0.2 parts polypropylene toughening fiber.

[0030] 2. Preparation and Construction Mixing: Weigh all dry materials according to the formula and dry mix them in a forced mixer for 5 minutes until uniform.

[0031] Add water and stir: Add 5.2% clean water by weight of the dry material and wet mix for 8 minutes to obtain a castable slurry with good fluidity.

[0032] Casting and molding: The slurry is poured into a standard test mold (e.g., 40mm×40mm×160mm) or a precast mold and compacted by vibration table.

[0033] Maintenance: Allow to cure naturally for 48 hours in an environment with a temperature of (25±2)℃ and a humidity of ≥95%.

[0034] Demolding and baking: After demolding, dry at 110℃ for 24 hours. Then bake at a heating rate of ≤20℃ / h to 500℃ and hold for 6 hours to obtain the sample. Example 2

[0035] The method is basically the same as in Example 1, except that the amount of aluminum-rich spinel powder is adjusted to 10 parts, and the amount of fused alumina fine powder is adjusted to 15 parts. Example 3

[0036] The method is basically the same as in Example 1, except that the amount of aluminum-rich spinel powder is adjusted to 20 parts, and the amount of fused alumina fine powder is adjusted to 8 parts. Example 4

[0037] It is basically the same as Example 1, except that active α-Al2O3 micro powder is not used, and its amount is replaced by an equal amount of fused alumina fine powder. Example 5

[0038] The method is basically the same as in Example 1, except that aluminum-rich spinel powder is not used, and its amount is replaced by an equal amount of fused alumina fine powder.

[0039] Comparative Example 1 Referring to the existing solution mentioned in the background art (CN118084516B), 15 parts of magnesium aluminum spinel (Al2O3: 72%, MgO: 28%) micro powder were used to replace the aluminum-rich spinel micro powder in this invention. The binder was pure calcium aluminate cement of the same mass, and the types and amounts of other raw materials were the same as in Example 1.

[0040] Comparative Example 2 A commercially available high-alumina castable with an Al2O3 content of approximately 75% was selected as a comparison to represent traditional technology.

[0041] Testing and Characterization Methods To systematically evaluate and verify the performance claimed in the claims, the following standard methods were used for testing: Chemical composition and physical properties: Al2O3 content was determined according to GB / T 21114-2019; apparent porosity was determined according to GB / T 2997-2015.

[0042] Mechanical properties: Compressive strength at room temperature: After drying at 110℃, the sample is tested according to GB / T 3001-2017.

[0043] High temperature compressive strength: The sample was heat-treated at 1300℃ for 3 hours and then tested according to GB / T 3001-2017.

[0044] Alkali corrosion resistance: Referring to GB / T 8931-2007 static crucible method, using analytical grade CaO as the corrosion medium, the crucible was kept at 1400℃ for 3 hours, cooled, and then cut along the axis to measure the maximum corrosion penetration depth (mm).

[0045] Thermal shock resistance: Referring to the water quenching method of GB / T 30873-2014, the sample was kept at 1100℃ for 20 minutes and then quickly immersed in flowing water at 25℃ for 3 minutes. The number of cycles (N) was recorded when the damaged area of ​​the heated end face of the sample reached 50%.

[0046] Abrasion resistance at room temperature: Tested according to GB / T 18301-2012, measuring wear volume (cm²). 3 ).

[0047] Results and Analysis The test results are shown in Table 1.

[0048] Table 1. Data for the Examples and Comparative Examples

[0049] As shown in Table 1, the apparent porosity (16.0~17.2%) of Examples 1-3 is ≤ 18%, the compressive strength at 110℃ (90~98 MPa) is ≥ 80 MPa, and the compressive strength at 1300℃×3h (82~88 MPa) is ≥ 75 MPa, fully meeting the required indicators. The alkali erosion resistance depth (7.5 mm) of Example 5 (without aluminum-rich spinel) is significantly worse than that of Example 1 (1.8 mm), proving that aluminum-rich spinel micropowder is the decisive component for achieving "high alkali erosion resistance". The alkali resistance (4.2 mm) of Comparative Example 1 (with magnesium-aluminum spinel) is also significantly worse than that of Example 1, proving that the aluminum-rich design is superior to traditional magnesium-aluminum spinel. The thermal shock resistance (8 cycles) of Example 4 (without active micropowder) decreases sharply compared to Example 1 (18 cycles), while other components are the same, directly proving that active α-Al2O3 micropowder is the key to inducing the formation of "in-situ toughening structure" and thus obtaining excellent thermal shock resistance. Comparative Example 2 (traditional high-alumina material) is inferior in all aspects of performance, which demonstrates the comprehensive advantages of this invention in terms of strength, density, thermal shock resistance and alkali resistance.

Claims

1. A type of alkaline corundum spinel castable for kilns, resistant to high alkali erosion and scouring, characterized in that, The raw material composition, by mass parts, includes: Refractory aggregate: 50~70, wherein the refractory aggregate is fused alumina with a gradation of 0~8mm; Refractory powder: 20~40, wherein the refractory powder includes fused alumina fine powder, active α-Al2O3 micro powder and aluminum-rich spinel micro powder; Binder: 4~8, which is pure calcium aluminate cement; Additives: 0.1~2, wherein the additives include water-reducing agents and toughening fibers; After molding and heat treatment, the castable refractory forms an in-situ toughening structure inside, which is used to dissipate heat stress and improve resistance to thermal shock damage.

2. The castable refractory according to claim 1, characterized in that, The chemical composition of the aluminum-rich spinel micro powder, by mass percentage, is: Al2O3: 80~90%, MgO: 10~20%, particle size D90≤15μm, and its usage accounts for 8~20% of the total mass of the castable.

3. The castable refractory according to claim 1, characterized in that, The particle size D50 of the active α-Al2O3 micro powder is ≤5μm.

4. The castable refractory according to claim 1, characterized in that, The refractory aggregate has a continuous particle size distribution of 0~8mm.

5. The castable refractory according to claim 1, characterized in that, The physical properties of the castable meet the following indicators: Al2O3 content ≥65%, apparent porosity ≤18%, and room temperature compressive strength ≥80MPa after molding and drying at 110℃.

6. The castable refractory according to claim 5, characterized in that, After being heat-treated at 1300℃ for 3 hours, the compressive strength of the castable is ≥75MPa.

7. The castable refractory according to claim 1, characterized in that, The water-reducing agent is a polycarboxylate-based water-reducing agent, and the toughening fiber is a polymer fiber with a thermal decomposition temperature between 150 and 400°C.

8. The castable refractory according to claim 1, characterized in that, When the castable is used in an alkaline kiln at ≥1200℃, a dense reactive layer with a thickness of 20~100μm is formed on its working surface.

9. A construction method for the castable refractory as described in any one of claims 1 to 8, characterized in that, Includes the following steps: S1. After the raw materials are dry-mixed evenly, add water accounting for 4.5~6.5% of the total dry material mass, and stir to obtain the casting slurry; S2. Pour the slurry into the mold and vibrate it to compact it; S3. Curing in an environment of 20~30℃ and humidity ≥90% for 24~48 hours; S4. Bake at a rate of ≤25℃ / h to above 300℃.

10. The construction method according to claim 9, characterized in that, In step S4, the final baking temperature is 300~600℃, and the temperature is maintained at the final temperature for 4~12 hours.

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