High-performance alpha-Al2O3 refractory material and preparation method thereof

Abstract

This invention discloses a high-performance α-Al₂O₃ high-temperature resistant material and its preparation method. The high-performance α-Al₂O₃ high-temperature resistant material comprises 98% Al₂O₃, 1% Na₂O, and 1% ZrO₂. The preparation method employs a stepped heating and melting process, followed by rapid initial cooling and slow subsequent cooling, to obtain a stable 3%-5% volume expansion and shear strain. This generates reverse compressive stress to counteract crack propagation, thereby improving the fracture toughness, thermal shock resistance, and wear resistance of the high-performance α-Al₂O₃ high-temperature resistant material.

Description

Technical Field

[0001] This invention relates to the field of high-temperature resistant materials, and in particular to a high-performance α-Al2O3 high-temperature resistant material and its preparation method. Background Technology

[0002] High-temperature resistant materials (refractory bricks) are designed for extreme environments, capable of withstanding temperatures of 1580℃-1770℃, and are widely used in metallurgy, glass manufacturing, cement kilns, and other applications. Their core characteristics include high-temperature resistance, excellent thermal insulation, strong thermal shock resistance, and high chemical stability.

[0003] The main types include: Silicate-alumina refractory bricks: based on the Al2O3-SiO2 system, including silica bricks (containing over 93% SiO2, used in coke ovens and glass kilns) and clay bricks (Al2O3 content 30%-48%, refractoriness 1580℃-1750℃). High-alumina bricks: Al2O3 content 55%-85%, refractoriness exceeding 1770℃, apparent porosity 16%-22%, suitable for insulation layers in electric furnaces, heating furnaces, and other equipment. Lightweight insulating bricks: low thermal conductivity, high strength, bulk density 0.6-1.8 g / cm³, operating temperature 800℃-1600℃, can reduce the overall energy consumption of industrial furnaces and kilns by 15%-20%.

[0004] However, existing high-temperature resistant materials have problems such as poor stability, and are prone to cracking due to volume changes. Summary of the Invention

[0005] The problem to be solved by this invention is to propose an innovative solution to address the shortcomings of the prior art, and in particular, a solution that can effectively solve the problem of poor stability of existing high-temperature resistant materials.

[0006] To solve the above problems, the present invention adopts the following solution: a high-performance α-Al2O3 high-temperature resistant material, characterized in that the high-performance α-Al2O3 high-temperature resistant material contains 98% Al2O3, 1% Na2O, and 1% ZrO2.

[0007] A method for preparing a high-performance α-Al₂O₃ high-temperature resistant material, characterized by comprising the following steps: Raw material preparation and pretreatment: Prepare bauxite with an aluminum content ≥98% as the main raw material. Remove impurities such as iron and silicon through flotation or magnetic separation. Then add a foaming agent to the bauxite at a dosage of 0.5%-1.5%. Prepare pure sodium carbonate (Na2CO3) at a dosage of 1.2%-1.5% to compensate for volatilization losses during high-temperature sintering. Prepare zirconium oxide (ZrO2) powder and mix it evenly with the bauxite powder through ball milling to avoid local enrichment that could lead to performance fluctuations. Add 0.25%-0.5% boric acid (H3BO3) as a flux to lower the sintering temperature and increase the melt viscosity, thereby reducing crack defects.

[0008] High-pressure molding: Using a fully automatic hydraulic brick press with a pressure ≥200MPa, isostatic pressing is performed to ensure uniform body density and reduce porosity.

[0009] High-temperature sintering: High-temperature tunnel kiln sintering is adopted. During the heating stage, the temperature is increased in stages to 1650–1700℃ to avoid complete densification and retain grain boundary stress to trigger phase transformation. This process takes 2–3 hours to ensure complete transformation of the α-Al2O3 crystal phase and prevent excessive growth of ZrO2 grains. An air atmosphere is maintained throughout the sintering process to promote oxygen vacancy formation, lower the phase transformation energy barrier, and actively induce the t→m transformation. During the cooling stage, rapid cooling is adopted in the initial stage, followed by cooling to 800℃ at a rate of ≥100℃ / h after sintering to freeze the tetragonal metastable phase. Slow cooling is adopted in the later stage, with slow cooling at a rate of ≤50℃ / h below 800℃ to slowly release stress and achieve controllable phase transformation. Finally, high-performance α-Al2O3 high-temperature resistant materials are obtained.

[0010] Furthermore, the preparation method of the high-performance α-Al2O3 high-temperature resistant material is characterized in that the foaming agent is hydrogen peroxide (H2O2) or ammonium bicarbonate (NH4HCO3). Hydrogen peroxide (H2O2) or ammonium bicarbonate (NH4HCO3) serves as a foaming agent; they decompose at high temperatures to generate gases (such as O2 and CO2), forming uniform micropores.

[0011] Furthermore, the preparation method of the high-performance α-Al2O3 high-temperature resistant material is characterized in that 0.3% of the stabilizer yttrium oxide (Y2O3) is added to the raw materials to make some tetragonal phase metastable, preferentially transforming at cracks or stress concentration points, facilitating stress-induced phase transformation, and forming delayed burst toughening.

[0012] Furthermore, the preparation method of the high-performance α-Al2O3 high-temperature resistant material is characterized in that 1% mullite fiber (Al2O3 72%-75%) is added to the raw materials to improve the thermal shock resistance of the matrix.

[0013] The technical effects of this invention are as follows: During the cooling process, ZrO2 grains undergo a t→m phase transformation under thermal stress, accompanied by a 5% volume expansion. The 10%–12% porosity introduced by the foaming method provides a buffer space for expansion, avoiding macroscopic cracking.

[0014] Phase transformation toughening: The stress field at the crack tip induces the transformation of the tetragonal phase (t-ZrO2) to the monoclinic phase (m-ZrO2), accompanied by 3%-5% volume expansion and shear strain, generating reverse compressive stress to counteract the crack propagation dynamics.

[0015] Microcrack toughening: Phase transformation-induced microcracks alter the path of the main crack, dissipating fracture energy through crack branching. Residual stress toughening: The phase transformation gradient between the surface and the interior forms a residual compressive stress structure, which inhibits the initiation of surface cracks.

[0016] The high-performance α-Al₂O₃ high-temperature resistant material of this application improves fracture toughness, thermal shock resistance, and wear resistance: phase transformation absorbs energy, significantly improving the material's toughness; volume effect alleviates thermal stress, improving the material's resistance to temperature changes; and stabilized zirconia ceramics combine high toughness with high wear resistance. Detailed Implementation

[0017] The present invention will now be described in further detail.

[0018] Example: A high-performance α-Al2O3 high-temperature resistant material, comprising 98% Al2O3, 1% Na2O, and 1% ZrO2.

[0019] A method for preparing a high-performance α-Al₂O₃ high-temperature resistant material includes the following steps: Raw material preparation and pretreatment: Bauxite with an aluminum content ≥98% is prepared as the main raw material. Impurities such as iron and silicon are removed by flotation or magnetic separation. Then, 0.5% of hydrogen peroxide (H2O2) is added to the bauxite as a foaming agent. Pure sodium carbonate (Na2CO3) is prepared at a rate of 1.2% to compensate for volatilization losses during high-temperature sintering. Zirconia (ZrO2) powder is prepared and uniformly mixed with bauxite powder by ball milling to avoid local enrichment that could lead to performance fluctuations. 0.25% boric acid (H3BO3) is added as a flux to lower the sintering temperature and increase the melt viscosity, thereby reducing crack defects. 0.3% yttrium oxide (Y2O3) is added as a stabilizer to ensure the metastable existence of some tetragonal phases, which preferentially transform at cracks or stress concentration points, facilitating stress-induced phase transformation and forming delayed burst toughening. 1% mullite fiber (Al2O3 72%-75%) is added to improve the thermal shock resistance of the matrix.

[0020] High-pressure molding: Using a fully automatic hydraulic brick press with a pressure ≥200MPa, isostatic pressing is performed to ensure uniform body density and reduce porosity.

[0021] High-temperature sintering: High-temperature tunnel kiln sintering is adopted. During the heating stage, the temperature is increased in stages to 1650℃ to avoid complete densification and retain grain boundary stress to trigger phase transformation. The process lasts for 2 hours to ensure complete transformation of the α-Al2O3 crystal phase and prevent excessive growth of ZrO2 grains. An air atmosphere is maintained throughout the sintering process to promote the formation of oxygen vacancies, reduce the phase transformation energy barrier, and actively induce the t→m transformation. During the cooling stage, rapid cooling is adopted in the initial stage, and after sintering, the temperature is cooled to 800℃ at a rate of ≥100℃ / h to freeze the tetragonal metastable phase. Slow cooling is adopted in the later stage, and slow cooling is adopted below 800℃ at a rate of ≤50℃ / h to slowly release stress and achieve controllable phase transformation. Finally, high-performance α-Al2O3 high-temperature resistant material is obtained.

[0022] During cooling, ZrO2 grains undergo a t→m phase transformation under thermal stress, accompanied by a 5% volume expansion. The Y2O3 stabilizer ensures the metastable existence of some tetragonal phases, preferentially inducing phase transformation at cracks or stress concentration points, resulting in a "delayed-burst" toughening effect. The foaming method introduces 10%–12% porosity, providing a buffer for expansion and preventing macroscopic cracking. Mullite fiber reinforcement of the matrix prevents structural disintegration caused by the phase transformation.

[0023] Quality Inspection: Testing items method Detection structure Phase transition degree XRD (Rietveld Refinement) <![CDATA[t-ZrO2 residue rate ≤ 10%]]> Volume expansion rate Laser displacement meter + thermal expansion meter 4.8%–5.2%（1000–1200℃） Compressive strength Three-point bending test (ASTM C1421) ≥150 MPa Thermal shock stability 1100℃ → Water cooling circulation No cracks after ≥40 cycles Porosity Archimedes' method of drainage 10%–12% This invention involves an active phase transition mechanism that, through cooling system design, abandons traditional inert gas protection and utilizes thermal stress-induced ZrO2 phase transition to achieve a controllable 5% volume expansion. The high-performance α-Al2O3 high-temperature resistant material of this application achieves significantly improved performance. Combining foam-based pores with mullite fibers, it significantly enhances thermal shock resistance (≥40 cycles) and fracture toughness (≥40% improvement). This high-performance α-Al2O3 high-temperature resistant material has wide applications and is suitable for extreme working conditions in metallurgy, energy, aerospace, and other fields.

Claims

1. A high-performance α-Al₂O₃ high-temperature resistant material, characterized in that, The high-performance α-Al2O3 high-temperature resistant material contains 98% Al2O3, 1% Na2O, and 1% ZrO2.

2. The method for preparing the high-performance α-Al₂O₃ high-temperature resistant material according to claim 1, characterized in that, Includes the following steps: Raw material preparation and pretreatment: Prepare bauxite with an aluminum content ≥98% as the main raw material. Remove impurities such as iron and silicon through flotation or magnetic separation. Then, add a foaming agent to the bauxite at a dosage of 0.5%-1.5%. Prepare pure sodium carbonate (Na2CO3) at a dosage of 1.2%-1.5% to compensate for volatilization losses during high-temperature sintering. Prepare zirconium oxide (ZrO2) powder and mix it evenly with the bauxite powder through ball milling to avoid local enrichment that could lead to performance fluctuations. Add 0.25%-0.5% boric acid (H3BO3) as a flux to lower the sintering temperature and increase the melt viscosity, thereby reducing crack defects. High-pressure molding: Using a fully automatic hydraulic brick press with a pressure ≥200MPa, isostatic pressing is performed to ensure uniform body density and reduce porosity; High-temperature sintering: High-temperature tunnel kiln sintering is adopted. During the heating stage, the temperature is increased in stages to 1650–1700℃ to avoid complete densification and retain grain boundary stress to trigger phase transformation. This process takes 2–3 hours to ensure complete transformation of the α-Al2O3 crystal phase and prevent excessive growth of ZrO2 grains. The entire sintering process is carried out in an air atmosphere to promote the formation of oxygen vacancies, reduce the phase transformation energy barrier, and actively induce the t→m transformation. During the cooling stage, rapid cooling is adopted in the initial stage, followed by cooling to 800℃ at a rate of ≥100℃ / h after sintering to freeze the tetragonal metastable phase. Slow cooling is adopted in the later stage, with slow cooling at a rate of ≤50℃ / h below 800℃ to slowly release stress and achieve controllable phase transformation. Finally, high-performance α-Al2O3 high-temperature resistant materials are obtained.

3. The method for preparing the high-performance α-Al₂O₃ high-temperature resistant material according to claim 2, characterized in that, The foaming agent is hydrogen peroxide (H2O2) or ammonium bicarbonate (NH4HCO3).

4. The method for preparing the high-performance α-Al₂O₃ high-temperature resistant material according to claim 2, characterized in that, The raw materials also need to contain 0.3% of the stabilizer yttrium oxide (Y2O3) to ensure that some tetragonal phases are metastable and preferentially transform at cracks or stress concentration points, which facilitates stress-induced phase transformation and forms delayed burst toughening.

5. The method for preparing the high-performance α-Al₂O₃ high-temperature resistant material according to claim 2, characterized in that, The raw materials also need to contain 1% mullite fiber (Al2O3 72%-75%) to improve the thermal shock resistance of the matrix.