High-strength β-alumina corundum bricks for the upper structure of glass furnaces and their preparation method

Abstract

This invention relates to the field of alumina corundum brick production technology, specifically to high-strength β-alumina corundum bricks for the upper structure of glass furnaces and their preparation method. The high-strength β-alumina corundum bricks for the upper structure of glass furnaces are composed of the following chemical components by mass percentage: Na₂O: 4.8-6.3%; B₂O₃: 0.1-0.5%; SiO₂+CaO+Fe₂O₃+TiO₂+MgO+K₂O≤1.2%; the remainder is Al₂O₃. The β-alumina corundum bricks prepared by this invention have high room temperature compressive strength, ≥80MPa; this is more than 30% higher than the room temperature compressive strength of existing β-alumina corundum bricks.

Description

Technical Field

[0001] This invention relates to the field of alumina corundum brick production technology, specifically to high-strength β-alumina corundum bricks for the upper structure of glass kilns and their preparation method. Background Technology

[0002] Due to its unique crystal structure and chemical properties, β-alumina bricks have become a core refractory material for the upper structure of furnaces used in high-end float glass, ultra-clear glass, electronic glass, and specialty glass production. Its structure is predominantly composed of the β-corundum phase, exhibiting excellent resistance to high-temperature alkaline vapors within the furnace. Furthermore, because it contains virtually no glass phase, it effectively prevents contamination of the molten glass, meeting the stringent requirements of high-end glass production for refractory materials and finding wide application in related fields.

[0003] Currently, the physicochemical properties of β-alumina corundum bricks comply with the JC / T493-2013 standard. This standard stipulates that the total content of sodium oxide and potassium oxide in the product must be controlled between 5.5% and 7.5%, the aluminum oxide content must be 92% to 94%, and the room temperature compressive strength must not be less than 30 MPa. However, the room temperature compressive strength of β-alumina corundum bricks in actual production is usually only maintained at 30-60 MPa. During subsequent processing (such as cutting and grinding), defects such as missing corners and edges are easily caused due to insufficient strength, resulting in a reduced product qualification rate. Similarly, during the construction of glass kilns, missing corners and edges due to their low strength can lead to abnormal erosion at the missing corners and edges during use, affecting the product's performance and posing a risk to its use.

[0004] More importantly, during long-term indoor storage, the alkali metal oxides (such as Na₂O and K₂O) contained in β-alumina corundum bricks are prone to chemical reactions with moisture and carbon dioxide in the air, triggering tissue decomposition and ultimately leading to complete product pulverization—a phenomenon commonly known in the industry as "hydration." This phenomenon means that β-alumina corundum bricks cannot be stored for extended periods, especially in humid environments, causing significant economic losses to both manufacturers and users.

[0005] Chinese patent application CN1138724C, published on February 18, 2004, discloses a refractory material composed of β-alumina, with a chemical composition of Na2O: 7.25-10%, SiO2: 0-1.85%, Al2O3: 87.95-92.75%, and at most 0.2% impurities. Although it mentions that the material can be used in the upper structure of glass kilns and that the effect of hydration can be judged by the change of elastic modulus, it does not involve the specific value of the compressive strength at room temperature, nor does it study the influence of hydration on the compressive strength. Therefore, it cannot provide a reference for the actual performance and storage period of β-alumina corundum bricks.

[0006] Chinese patent application CN116368108A, published on September 17, 2024, discloses a sintered bauxite product with a β-alumina content of 5%-37%, and its chemical composition is Na2O: 0.26-4%, SiO2: ≤2%, and oxides other than Al2O3 and Na2O ≤6% (Al2O3 as the balance). This product is a bauxite product prepared by sintering, which is fundamentally different from the casting production process of β-alumina corundum bricks. Its technical solution cannot be simply replicated or applied to casting β-alumina corundum bricks through limited experiments, and has no practical reference value for solving the strength and hydration problems of the latter.

[0007] Chinese patent application CN116873761A, published on July 12, 2024, discloses a hoisting device for grinding electrofused β-alumina bricks. It only improves the hoisting stability during the β-alumina brick processing and does not involve the improvement of the material's strength or the optimization of its hydration resistance. It is not related to the technical problem solved by this invention.

[0008] Chinese patent application CN115448341A, published on June 11, 2024, discloses a method for preparing sheet-like β-alumina. Using graphene oxide as a template, high-conductivity sheet-like β-alumina powder is prepared through a wet chemical reaction. Its application field is energy storage, and the product form, preparation process and performance requirements are completely different from β-alumina corundum bricks used in glass furnaces. It does not involve the content related to material strength and hydration resistance.

[0009] Chinese patent application CN1331815C, published on August 15, 2007, discloses a method for manufacturing zirconia-alumina refractory bricks. The method uses high-temperature alumina powder, zircon sand, desilicationized zircon, borax, and secondary casting material as raw materials. The aim is to reduce production costs by optimizing the raw material ratio. The purpose of adding borax is to promote the melting of raw materials. However, no technical ideas related to improving the strength of β-alumina corundum bricks are mentioned, and it cannot provide any reference for solving the strength problem of β-alumina corundum bricks.

[0010] Chinese patent application CN102603341A, published on June 5, 2013, discloses a cast corundum-spinel brick for the sidewall of an aluminum electrolysis cell. Its crystal phase composition is mainly α-corundum and spinel, and it is suitable for the aluminum electrolysis industry. However, its application scenario, crystal phase structure and performance requirements are significantly different from those of β-alumina corundum bricks used in glass furnaces. The two technical solutions are unrelated and have no reference value for this invention.

[0011] In summary, existing technologies lack effective solutions that can simultaneously address the issues of low room temperature compressive strength and easy hydration during long-term storage of β-alumina corundum bricks. There is an urgent need to develop a β-alumina corundum brick with high room temperature compressive strength and excellent hydration resistance to meet the pressing needs of the glass kiln industry for high-performance refractory materials and to make up for the shortcomings of existing technologies. Summary of the Invention

[0012] In view of the shortcomings of the prior art, the purpose of this invention is to provide a high-strength β-alumina corundum brick for the upper structure of a glass kiln, which has high room temperature compressive strength and is not prone to hydration reaction after long-term storage.

[0013] Another objective of this invention is to provide a method for preparing high-strength β-alumina corundum bricks for the upper structure of glass furnaces. The resulting β-alumina corundum bricks have high room temperature compressive strength, ≥80MPa, which is more than 30% higher than that of existing β-alumina corundum bricks.

[0014] This invention is achieved using the following technical solution:

[0015] The upper structure of the glass furnace is made of high-strength β-alumina corundum bricks, which, by mass percentage, consist of the following chemical components:

[0016] Na2O: 4.8-6.3%;

[0017] B2O3: 0.1-0.5%;

[0018] SiO2+CaO+Fe2O3+TiO2+MgO+K2O≤1.2%;

[0019] The remaining components are Al2O3.

[0020] The content of Al2O3 is preferably 92-94%, more preferably 92.5-93.5%; the content of Na2O is preferably 5.0-6.0%, more preferably 5.2-5.8%.

[0021] The B2O3 is introduced by anhydrous borax or boron oxide powder, preferably boron oxide powder, and the purity of the boron oxide powder is not less than 99%.

[0022] The room temperature compressive strength of β-alumina corundum bricks is ≥80MPa; after 8 hours at a temperature of 166℃ and a water vapor pressure of 5atm, no crystals fall off at the corners of the β-alumina corundum bricks, demonstrating excellent water resistance.

[0023] The room temperature compressive strength of β-alumina corundum bricks is ≥100MPa.

[0024] The method for preparing high-strength β-alumina corundum bricks for the upper structure of the glass furnace includes the following steps:

[0025] (1) Melting: Mix alumina raw materials and alkali powder, and perform open arc melting in an electric arc furnace at a current of 3000-4500A for 50-70 minutes, while continuously blowing in oxygen during the melting process;

[0026] (2) Conditioning: After the melting is basically completed, add boron-containing raw materials, then adjust the electrode to be close to the liquid surface, and continue melting for 5-10 minutes under a current of 2500-3000A;

[0027] (3) Clarification: Adjust the current to 2000-2500A and clarify for 3-5 minutes;

[0028] (4) Casting: Casting shall be carried out at a casting temperature of 1950-2100℃ and a casting speed of not less than 25kg / s.

[0029] In step (1), the alumina raw material is calcined alumina with an α-phase conversion rate ≥92%.

[0030] In step (1), the alkali powder is heavy alkali powder with a Na2CO3 content ≥98.5%.

[0031] At high temperatures, B2O3 acts as a binder, promoting the nucleation of α-Al2O3 crystals and reducing the proportion of β-Al2O3, thereby improving the microstructure and density of the product. The reduced β-Al2O3 content decreases the product's water absorption and enhances its resistance to hydration.

[0032] Compared with the prior art, the beneficial effects of the present invention are:

[0033] (1) The β-alumina corundum brick prepared by the present invention has high room temperature compressive strength, which is more than 30% higher than that of existing β-alumina corundum bricks.

[0034] (2) The β-alumina corundum brick prepared by the present invention has strong resistance to hydration and no crystals fall off at the corners under high temperature and high humidity conditions.

[0035] (3) It was unexpectedly discovered that the β-alumina corundum brick prepared by the present invention has strong resistance to high temperature spalling, and the surface spalling performance in a high concentration of alkaline vapor environment is reduced by 40% compared with ordinary products. Detailed Implementation

[0036] To make the objectives and technical solutions of this invention clearer, the invention will be further described in detail below.

[0037] Unless otherwise specified, all raw materials used in the examples were commercially available.

[0038] The alumina raw material is alumina from Sumitomo Chemical Co., Ltd. of Japan, with the grade A. 210 calcined alumina; heavy alkali powder from Shandong Haitian Biochemical Co., Ltd.; boron trioxide from Henan Hongjin Chemical Products Co., Ltd.

[0039] The α of the alumina raw material Phase conversion rate ≥92%, Al2O3 ≥99.0%.

[0040] The purity of the boron trioxide (boron oxide powder) is ≥99%.

[0041] The purity of Na2CO3 in the heavy alkali powder is ≥98.5%.

[0042] Example 1

[0043] A method for preparing high-strength β-alumina corundum bricks for the upper structure of a glass furnace includes the following steps:

[0044] (1) Mix the alumina powder and alkali powder raw materials in proportion and then put them into the three-phase electric arc furnace;

[0045] (2) After melting begins, keep the current at 3000A and melt in an open arc for 50 minutes. Keep blowing oxygen during the melting process. When melting is basically complete, add boron oxide powder and adjust the electrode to be close to the liquid surface for 5 minutes. Control the current at 2700A.

[0046] (3) After melting, clarify for 3 minutes with a current of 2000A.

[0047] (4) Maintain the casting temperature at 1950℃ and the casting speed at 25kg / s during casting.

[0048] (5) After that, cover with insulation material and perform natural annealing and heat preservation until the surface temperature is below 80°C. Then take it out and grind the surface to obtain high-strength β-alumina corundum bricks for the upper structure of the glass furnace.

[0049] Example 2

[0050] A method for preparing high-strength β-alumina corundum bricks for the upper structure of a glass furnace includes the following steps:

[0051] (1) Mix the alumina powder and alkali powder raw materials in proportion and then put them into the three-phase electric arc furnace;

[0052] (2) After melting begins, keep the current at 3500A and melt in an open arc for 55 minutes. Keep blowing oxygen during the melting process. When melting is basically complete, add boron oxide powder and adjust the electrode to be close to the liquid surface for 8 minutes. Control the current at 2800A.

[0053] (3) After melting, clarify for 3 minutes with a current of 2000A.

[0054] (4) Maintain the casting temperature at 1970℃ and the casting speed at 27kg / s during casting.

[0055] (5) After that, cover with insulation material and perform natural annealing and heat preservation until the surface temperature is below 80°C. Then take it out and grind the surface to obtain high-strength β-alumina corundum bricks for the upper structure of the glass furnace.

[0056] Example 3

[0057] A method for preparing high-strength β-alumina corundum bricks for the upper structure of a glass furnace includes the following steps:

[0058] (1) After mixing the alumina powder and alkali powder, put them into the three-phase electric arc furnace.

[0059] (2) After melting begins, keep the current at 4500A and melt in an open arc for 70 minutes. Keep blowing oxygen during the melting process. When melting is basically complete, add boron oxide powder and adjust the electrode to be close to the liquid surface for 5 minutes. Control the current at 2500A.

[0060] (3) After melting, clarify for 5 minutes with a current of 2500A.

[0061] (4) Maintain the casting temperature at 2100℃ and the casting speed at 31kg / s during casting.

[0062] (5) After that, cover with insulation material and perform natural annealing and heat preservation until the surface temperature is below 80°C. Then take it out and grind the surface to obtain high-strength β-alumina corundum bricks for the upper structure of the glass furnace.

[0063] Example 4

[0064] A method for preparing high-strength β-alumina corundum bricks for the upper structure of a glass furnace includes the following steps:

[0065] (1) After mixing the alumina powder and alkali powder, put them into the three-phase electric arc furnace;

[0066] (2) After melting begins, keep the current at 4300A and melt in an open arc for 70 minutes. Keep blowing oxygen during the melting process. When melting is basically complete, add boron oxide powder and adjust the electrode to be close to the liquid surface for 5 minutes. Control the current at 2600A.

[0067] (3) After melting, clarify for 5 minutes with a current of 2300A.

[0068] (4) Maintain the casting temperature at 2000℃ and the casting speed at 32kg / s during casting.

[0069] (5) After that, cover with insulation material and perform natural annealing and heat preservation until the surface temperature is below 80°C. Then take it out and grind the surface to obtain high-strength β-alumina corundum bricks for the upper structure of the glass furnace.

[0070] Example 5

[0071] A method for preparing high-strength β-alumina corundum bricks for the upper structure of a glass furnace includes the following steps:

[0072] (1) After mixing the alumina powder and alkali powder, put them into the three-phase electric arc furnace;

[0073] (2) After melting begins, keep the current at 4400A and melt in an open arc for 60 minutes. Keep blowing oxygen during the melting process. When melting is basically complete, add boron oxide powder and adjust the electrode to be close to the liquid surface for 5 minutes. Control the current at 3000A.

[0074] (3) After melting, clarify for 5 minutes with a current of 2000A.

[0075] (4) Maintain the casting temperature at 1990℃ and the casting speed at 27kg / s during casting.

[0076] (5) After that, cover with insulation material and perform natural annealing and heat preservation until the surface temperature is below 80°C. Then take it out and grind the surface to obtain high-strength β-alumina corundum bricks for the upper structure of the glass furnace.

[0077] Example 6

[0078] A method for preparing high-strength β-alumina corundum bricks for the upper structure of a glass furnace includes the following steps:

[0079] (1) Mix alumina powder and alkali powder in proportion and then put them into a three-phase electric arc furnace;

[0080] (2) After melting begins, keep the current at 4000A and melt in an open arc for 70 minutes. Keep blowing oxygen during the melting process. When melting is basically complete, add boron oxide powder and adjust the electrode to be close to the liquid surface for 5 minutes. Control the current at 2800A.

[0081] (3) After melting, clarify for 5 minutes with a current of 2300A.

[0082] (4) Maintain the casting temperature at 2080℃ and the casting speed at 32kg / s during casting.

[0083] (5) After that, cover with insulation material and perform natural annealing and heat preservation until the surface temperature is below 80°C. Then take it out and grind the surface to obtain high-strength β-alumina corundum bricks for the upper structure of the glass furnace.

[0084] Comparative Example 1

[0085] The difference from Example 1 is that boron oxide powder is not added to the raw materials.

[0086] According to JC / T494 standard, cast samples measuring 200mm (width) * 300mm (length) * 300mm (height). From the bottom of the cast sample, take a 150mm * 100mm * 120mm specimen, then a 120mm * 100mm * 120mm specimen for spalling resistance, and finally a 40mm * 40mm hydration test specimen from the remaining bottom surface. Determine the chemical composition, bulk density, and room temperature compressive strength of the samples according to the JC / T494 standard method. Chemical composition determination is performed according to GB / T2114 standard, bulk density according to GB / T2997 standard, and room temperature compressive strength according to GB / T5072 standard.

[0087] Table 1 shows the results of chemical composition, bulk density, and room temperature compressive strength analysis of the 150mm*100mm*120mm sample:

[0088] Table 1. Chemical composition, bulk density, and room temperature compressive strength of β-alumina corundum bricks prepared in Examples 1-6 and Comparative Example 1

[0089]

[0090] The results show that the bulk density and compressive strength of Examples 1-6 are all higher than those of Comparative Example 1, with the bulk density increasing by 6-11% and the compressive strength increasing by more than double.

[0091] A cylindrical sample with a diameter of 40mm x 40mm was subjected to a hydration test. The sample was placed in a container at 166℃ and a pressure of 5 atm for 8 hours. The change in strength before and after the test was confirmed, and any corners were observed to show any signs of chipping. The results are shown in Table 2.

[0092] Table 2. Hydration test results of β-alumina corundum bricks prepared in Examples 1-6 and Comparative Example 1.

[0093]

[0094] As can be seen from Table 2, the strength of Comparative Example 1 decreased by more than 50% after the hydration test, while that of the Example was basically around 20%, showing a significant improvement in performance.

[0095] In addition, to confirm the differences after long-term storage, the 200mm*300mm*300mm samples cast by Comparative Example 1 and Examples 1-6 were cut in the middle and placed on the factory site for comparison. After 2 years, it was found that the internal structure of Comparative Example 1 was completely broken and the overall strength was lost, while the Examples did not show any internal structure breakage.

[0096] For the alkali erosion resistance test samples, they were placed in the glass furnace at the observation hole position. After 2 years, they were taken out and the thickness of the surface metamorphic layer was measured. The results are shown in Table 3:

[0097] Table 3. Alkali erosion resistance test results of β-alumina corundum bricks prepared in Examples 1-6 and Comparative Example 1

[0098]

[0099] The test results show that the thickness of the modified layer in the example is reduced by 40% compared to that in Comparative Example 1, and the resistance to alkali corrosion is significantly improved. These beneficial effects are essentially due to the finer crystallization of the surface layer after the sodium oxide content is reduced, resulting in an increased proportion of α-corundum phase within the top 20mm of the product.

Claims

1. A high-strength β-alumina corundum brick for the upper structure of a glass kiln, characterized in that, It consists of the following chemical components by mass percentage: Na2O: 4.8-5.8%; B2O3: 0.1-0.5%; SiO2+CaO+Fe2O3+TiO2+MgO+K2O≤1.2%; The remaining components are Al2O3; The room temperature compressive strength of β-alumina corundum bricks is ≥80MPa; after 8 hours at a temperature of 166℃ and a water vapor pressure of 5atm, no crystals fall off at the corners of the β-alumina corundum bricks. The method for preparing high-strength β-alumina corundum bricks for the upper structure of the glass furnace includes the following steps: (1) Melting: Mix alumina raw materials and alkali powder, and perform open arc melting in an electric arc furnace at a current of 3000-4500A for 50-70 minutes, while continuously blowing in oxygen during the melting process; (2) Conditioning: After the melting is basically completed, add boron-containing raw materials, then adjust the electrode to be close to the liquid surface, and continue melting for 5-10 minutes under a current of 2500-3000A; (3) Clarification: Adjust the current to 2000-2500A and clarify for 3-5 minutes; (4) Casting: Casting shall be carried out at a casting temperature of 1950-2100℃ and a casting speed of not less than 25kg / s; The B2O3 is introduced by boron oxide powder, and the purity of the boron oxide powder is not less than 99%. In step (1), the alumina raw material is calcined alumina with an α-phase conversion rate ≥92%; In step (1), the alkali powder is heavy alkali powder with a Na2CO3 content ≥98.5%.

2. The high-strength β-alumina corundum brick for the upper structure of the glass furnace according to claim 1, characterized in that, The room temperature compressive strength of β-alumina corundum bricks is ≥100MPa.

Images