A low thermal conductivity alkali-resistant alumina-based mullite synthetic material and preparation method thereof

Abstract

The present invention relates to a low-thermal-conductivity, alkali-resistant alumina-based mullite composite and a preparation method thereof, belonging to the technical field of refractory materials. The method comprises the following steps: step 1, wet-grinding 70-92 wt% of low-alumina pyrophyllite, 6-15 wt% of zirconia raw material, and 1-15 wt% of natural quartz according to mass percentage, adding a certain amount of organic binder and granulating, and calcining at 1420-1480°C for 1-2 hours to obtain modified SiO2 fine particles with a low melting point; step 2, uniformly mixing 70-85 wt% of low-grade bauxite fine powder, 10-25 wt% of modified SiO2 fine particles, and 4-8 wt% of alumina raw material according to mass percentage, forming a green body under a pressure of 80-120 MPa, calcining at 1550-1630°C for 3-10 hours, cooling, and crushing to obtain the low-thermal-conductivity, alkali-resistant alumina-based mullite composite. The invention uses low-grade high-alumina bauxite as the main raw material, modifies SiO2 at high temperature and diffuses it in situ to form pores, and the production process is pollution-free; the obtained alumina-based mullite synthetic material has the characteristics of low thermal conductivity, good high-temperature mechanical properties, and excellent alkali corrosion resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of refractory materials, and particularly relates to a low-thermal-conductivity, alkali-resistant alumina-based mullite synthetic material and a preparation method thereof. Background Art

[0002] At present, the thermal conductivity of the magnesia-alumina spinel and mullite-silicon carbide refractory materials used in the preheating zone and safety zone of the cement rotary kiln is relatively high, resulting in low thermal efficiency and high CO2 emissions. With the gradual deepening of my country's dual carbon policy, there is an urgent need to solve the pain point of excessive heat loss in the cement industry. About 60% of the heat in the cement rotary kiln is lost through the heat dissipation of refractory materials. The extensive use of low thermal conductivity refractory materials is an effective way to reduce heat loss in the cement industry. Although the porous refractory materials prepared by the traditional burning-out method have a low thermal conductivity, their high-temperature performance is poor and they are easily damaged by alkali corrosion. In severe cases, the kiln body will break, which will not only affect the normal operation of the cement kiln, but also bring great hidden dangers to production safety. It is necessary to develop refractory raw materials with low thermal conductivity, high strength and good alkali corrosion resistance to reduce heat loss and carbon emissions in the cement industry while meeting the service life of the furnace lining.

[0003] After high-temperature calcination, low-grade bauxite is mainly composed of mullite and high-silica glass phases. The thermal conductivity of these two phases is low and their alkali resistance is good, making them ideal high-temperature thermal insulation materials. Using low-grade bauxite as the main raw material to prepare refractory raw materials with low thermal conductivity, high strength and micro-closed pore structure is not only beneficial to energy conservation in high-temperature industries, but also plays a key role in upgrading the quality of low-grade bauxite and increasing the added value of products. Publication No. CN103979977A discloses a method using medium- and low-grade bauxite as the main raw material, introducing organic burnt materials to form pores, and sintering at 1250~1450℃ to obtain a volume density of ≤0.48g / cm 3 , mullite lightweight refractory material with compressive strength ≥1.2MPa. The mullite prepared by this method has low bulk density and high apparent porosity, and is suitable for thermal insulation layers at low temperatures. Publication No. CN106431434A discloses a closed-cell bauxite-based mullite material and its preparation method. Using bauxite raw ore powder and silicon dioxide as raw materials, a mullite with a bulk density of 1.3~2.3g / cm 3 , alumina-based mullite material containing closed pores. This method improves the high-temperature performance of porous mullite materials, but the diffusion activation energy required for the silica raw material is large, and it is difficult to achieve uniform distribution of structure and composition of the two raw materials used.

[0004] In recent years, with the development of co-processing technologies for solid waste in the cement industry, the content of alkaline oxides in cement rotary kilns has increased significantly, making the refractory lining more susceptible to alkali corrosion, forming nepheline minerals, which in turn causes alkali cracking, seriously shortening the service life of the refractory lining. Therefore, given the harsh service environment of cement kilns and the urgent need for energy conservation and carbon reduction in high-temperature industries, there is an urgent need to further modify and reshape low-thermal-conductivity mullite synthetic materials to improve their alkali corrosion resistance and high-temperature mechanical properties, thereby reducing heat loss in cement rotary kilns while improving the service performance of the refractory lining and meeting the requirements of modern cement industry applications. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a low thermal conductivity alkali-resistant alumina-based mullite synthetic material and a preparation method thereof. The prepared low thermal conductivity alkali-resistant alumina-based mullite synthetic material has the characteristics of low thermal conductivity, good high-temperature mechanical properties and excellent alkali corrosion resistance.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for preparing a low thermal conductivity alkali-resistant alumina-based mullite synthetic material comprises the following steps:

[0008] Step 1, grinding 70-92 wt% of low-aluminum pyrophyllite, 6-15 wt% of zirconia raw material, and 1-15 wt% of natural quartz into 800 mesh fine powder according to mass percentage, adding a certain amount of organic binder and granulating, and calcining at 1420-1480° C. for 1-2 hours to obtain modified SiO2 fine particles with a low melting point;

[0009] Step 2: 70-85 wt% of low-grade bauxite fine powder, 10-25 wt% of modified SiO2 fine particles, and 4-8 wt% of alumina raw materials are uniformly mixed according to mass percentage, formed into a green body under a pressure of 80-120 MPa, calcined at 1550-1630 ° C for 3-10 hours, cooled, and crushed to obtain a low thermal conductivity and alkali-resistant bauxite-based mullite synthetic material.

[0010] Furthermore, in step 1, the raw materials include 75-85 wt% of low-aluminum pyrophyllite, 7-10 wt% of zirconia raw material, and 7-15 wt% of natural quartz, and the calcination temperature is 1450-1480°C.

[0011] Furthermore, in step 2, the raw materials include 70-80 wt% of low-grade bauxite fine powder, 15-20 wt% of modified SiO2 fine particles, and 6-8 wt% of alumina raw materials by mass, and the calcination temperature is 1600-1630°C.

[0012] Furthermore, the Al2O3 content in the low-aluminum pyrophyllite described in step 1 is ≤18wt%, the SiO2 content is ≥80wt%, and the raw material particle size is ≤325 mesh.

[0013] Furthermore, the zirconia raw material described in step 1 is taken from one or two of zircon, post-used zirconia refractory material, post-used zirconia-corundum refractory material, and post-used zirconia-mullite refractory material, the ZrO2 content in the raw material is ≥45.5wt%, and the raw material particle size is ≤325 mesh.

[0014] Furthermore, the SiO2 content in the natural quartz described in step 1 is ≥99.0wt%, and the raw material particle size is ≤325 mesh.

[0015] Furthermore, the modified SiO2 fine particles prepared in step 1 have a particle size of 0.045~0.3mm and a melting temperature of ≤1530℃.

[0016] Furthermore, the organic binder in step 1 is one of yellow dextrin, pulp waste liquid powder, and polyvinyl alcohol solution.

[0017] Furthermore, the amount of the organic binder in step 1 is 2-5% of the total amount of the raw materials, preferably 4%.

[0018] Furthermore, the low-grade bauxite fine powder described in step 2 is taken from one or a combination of grade III and grade IV bauxite, and the Al2O3 content after ignition is 48~70wt%, the SiO2 content is 25~50wt%, the Fe2O3 content is ≤2.0wt%, and the raw material particle size is ≤200 mesh.

[0019] Furthermore, the alumina raw material described in step 2 is taken from one of γ-Al2O3, α-Al2O3, aluminum hydroxide, and gibbsite, and the Al2O3 content after ignition reduction is ≥97.5wt%, and the raw material particle size is ≤325 mesh.

[0020] A low thermal conductivity alkali-resistant alumina-based mullite synthetic material is prepared by the above preparation method. The prepared low thermal conductivity alkali-resistant alumina-based mullite synthetic material has a bulk density of 2.0-2.10 g / cm 3 The apparent porosity is 3~10%, the compressive strength at room temperature is 80~100MPa, the load softening temperature (0.2MPa) is 1500~1600℃, and the thermal conductivity at 1000℃ is 0.5~0.6W / (m·K).

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. In response to the problem that the thermal conductivity of current aluminum-silica refractory materials is relatively high and the alkali corrosion resistance is poor, the present invention designs the composition of modified SiO2 fine particles based on the low melting temperature region of the Al2O3-SiO2-ZrO2 ternary system. During the heating process, the modified SiO2 fine particles with a low melting temperature prepared in step 1 are converted into a silicon-rich liquid phase and diffuse to the surrounding to form a porous structure. The mullite crystals at the pore wall grow in a sufficient liquid phase environment, forming a cross-linked network structure, which optimizes the mechanical properties of the porous mullite synthetic material. The ZrO2 in the modified SiO2 fine particles is uniformly dispersed in the high silica glass phase of the synthetic material driven by liquid phase diffusion, thereby increasing the high-temperature liquid phase viscosity of the synthetic material and greatly improving the alkali corrosion resistance of the low thermal conductivity mullite synthetic material.

[0023] 2. This method uses abundant but difficult-to-process low-grade bauxite and low-alumina pyrophyllite as the primary raw materials to synthesize low-thermal-conductivity, alkali-resistant alumina-based mullite, thereby improving the comprehensive utilization rate of aluminosilicate refractory resources and the added value of the product. High-temperature liquid-phase diffusion in-situ pore-forming technology is used to produce the porous synthetic material, resulting in high-efficiency, large-scale production. The preparation process eliminates the need for organic burnt materials to create pores, thus preventing harmful gas emissions that could cause air pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a microstructure diagram of the low thermal conductivity and alkali-resistant alumina-based mullite synthetic material prepared in Example 1 at 100 times magnification.

[0025] Figure 2 The microstructure and element distribution photos of the low thermal conductivity alkali-resistant alumina-based mullite synthetic material prepared in Example 1.

[0026] Figure 3 This is the XRD diffraction pattern of the low thermal conductivity and alkali-resistant alumina-based mullite synthetic material prepared in Example 2. DETAILED DESCRIPTION

[0027] In order to better understand the present invention, the technical solutions and effects of the present invention are further described below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereto. Example 1

[0028] A method for preparing a low thermal conductivity alkali-resistant alumina-based mullite synthetic material comprises the following steps:

[0029] Step 1. Grind 85.0wt% of low-aluminum pyrophyllite, 8.0wt% of zirconia raw material, and 7wt% of natural quartz into 800-mesh fine powder according to mass percentage, add 4.0wt% of yellow dextrin binder as the sum of the above raw materials, and granulate. Calcined at 1450°C for 2h to obtain modified SiO2 fine particles with a low melting point; the prepared modified SiO2 fine particles have a particle size of 0.045~0.2mm and a melting point of 1515°C.

[0030] Step 2: 74.0wt% of low-grade bauxite fine powder, 20.0wt% of modified SiO2 fine particles, and 6wt% of γ-Al2O3 are mixed uniformly according to mass percentage, formed into a green body under a pressure of 120MPa, calcined at 1630℃ for 6h, and cooled to obtain a low thermal conductivity and alkali-resistant bauxite-based mullite synthetic material.

[0031] The low-grade bauxite fine powder described in this example is taken from grade III bauxite, and the Al2O3 content after ignition reduction is 60wt%, SiO2 content is 34.6wt%, Fe2O3 content is 1.2wt%, and the raw material particle size is ≤200 mesh.

[0032] The low-aluminum pyrophyllite described in step 1 of this example contains 15 wt% Al2O3 and 83.5 wt% SiO2. The zirconia raw material is derived from zircon, and the ZrO2 content in the raw material is 55.8 wt%; the SiO2 content in natural quartz is 99.8 wt%; and the particle sizes of the three raw materials are all ≤325 mesh.

[0033] The Al2O3 content in the γ-Al2O3 described in step 2 of this example is 98.5wt%, and the raw material particle size is ≤325 mesh.

[0034] The low thermal conductivity and alkali-resistant alumina-based mullite synthetic material prepared in this embodiment was tested and found to have a bulk density of 2.05 g / cm 3 , the apparent porosity is 5.6%, the compressive strength at room temperature is 89.5MPa, the refractoriness under load (0.2MPa) is 1540℃, and the thermal conductivity at 1000℃ is 0.56W / (m·K). Figure 1 and Figure 2 The microstructure and element distribution diagram of the low thermal conductivity alkali-resistant alumina-based mullite synthetic material show that the formed pores are isolated, the columnar mullite at the pore wall forms a cross-linked network structure, and ZrO2 is dispersed in the high silica glass phase. Example 2

[0035] A method for preparing a low thermal conductivity alkali-resistant alumina-based mullite synthetic material comprises the following steps:

[0036] Step 1. Grind 83.0wt% of low-aluminum pyrophyllite, 10.0wt% of zirconia raw material, and 7wt% of natural quartz into 800-mesh fine powder according to mass percentage, add 4.0wt% of yellow dextrin binder to the sum of the above raw materials, and granulate. Calcined at 1480°C for 2h to obtain modified SiO2 fine particles with a low melting temperature; the prepared modified SiO2 fine particles have a particle size of 0.045~0.25mm and a melting temperature of 1510°C.

[0037] Step 2: 78.0 wt% of low-grade bauxite fine powder, 15.0 wt% of modified SiO2 fine particles, and 7 wt% of α-Al2O3 are uniformly mixed according to mass percentage, formed into a green body under a pressure of 100 MPa, calcined at 1630 ° C for 8 h, and cooled to obtain a low thermal conductivity and alkali-resistant bauxite-based mullite synthetic material.

[0038] The low-grade bauxite fine powder described in this example is taken from grade III bauxite, and the Al2O3 content after ignition reduction is 70wt%, SiO2 content is 26.8wt%, Fe2O3 content is 1.4wt%, and the raw material particle size is ≤200 mesh.

[0039] The low-aluminum pyrophyllite described in step 1 of this example contains 16.0 wt% Al2O3 and 81.9 wt% SiO2. The zirconia raw material is derived from zircon, and the ZrO2 content in the raw material is 55.8 wt%; the SiO2 content in natural quartz is 99.8 wt%; and the particle size of the three raw materials is ≤325 mesh.

[0040] The Al2O3 content in the α-Al2O3 described in step 2 of this example is 98.5wt%, and the raw material particle size is ≤325 mesh.

[0041] The low thermal conductivity and alkali-resistant alumina-based mullite synthetic material prepared in this embodiment was tested and found to have a bulk density of 2.10 g / cm 3 , the apparent porosity is 4.8%, the compressive strength at room temperature is 96.8MPa, the refractoriness under load (0.2MPa) is 1565℃, and the thermal conductivity at 1000℃ is 0.59W / (m·K). Figure 3 The XRD diffraction pattern of the low thermal conductivity and alkali-resistant alumina-based mullite synthetic material shows that the main crystalline phase is mullite phase (73.37%), the secondary crystalline phase is m-ZrO2 phase (2.81%), and the amorphous phase (high silica glass phase) is 23.81%. Example 3

[0042] A method for preparing a low thermal conductivity alkali-resistant alumina-based mullite synthetic material comprises the following steps:

[0043] Step 1. Grind 78.0wt% of low-aluminum pyrophyllite, 7.0wt% of zirconia raw material, and 15wt% of natural quartz into 800 mesh fine powder according to mass percentage, add 4.0wt% of yellow dextrin binder as the sum of the above raw materials, and granulate. Calcined at 1470°C for 2h to obtain modified SiO2 fine particles with a low melting temperature; the prepared modified SiO2 fine particles have a particle size of 0.045~0.25mm and a melting temperature of 1503°C.

[0044] Step 2: 77.0 wt% of low-grade bauxite fine powder, 15.0 wt% of modified SiO2 fine particles, and 8 wt% of aluminum hydroxide are uniformly mixed according to mass percentage, formed into a green body under a pressure of 120 MPa, calcined at 1600 ° C for 6 hours, and cooled to obtain a low thermal conductivity and alkali-resistant bauxite-based mullite synthetic material.

[0045] The low-grade bauxite fine powder described in this example is taken from grade IV bauxite, and the Al2O3 content after ignition reduction is 55.6wt%, SiO2 content is 41.3wt%, Fe2O3 content is 1.5wt%, and the raw material particle size is ≤200 mesh.

[0046] The low-aluminum pyrophyllite described in step 1 of this example contains 13.5 wt% Al2O3 and 85.2 wt% SiO2. The zirconia raw material is obtained from used zirconia refractory materials, and the ZrO2 content in the raw material is 95.8 wt%; the SiO2 content in natural quartz is 99.8 wt%; and the particle size of the three raw materials is ≤325 mesh.

[0047] The Al2O3 content of the aluminum hydroxide after burning reduction described in step 2 of this example is 98.0wt%, and the particle size of the raw materials is ≤325 mesh.

[0048] The low thermal conductivity and alkali-resistant alumina-based mullite synthetic material prepared in this embodiment was tested and found to have a bulk density of 2.0 g / cm 3 The apparent porosity is 7.2%, the compressive strength at room temperature is 87.8MPa, the refractoriness under load (0.2MPa) is 1553℃, and the thermal conductivity at 1000℃ is 0.53W / (m·K).

[0049] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a low thermal conductivity alkali-resistant alumina-based mullite synthetic material for a cement rotary kiln, characterized in that: The preparation method comprises the following steps: Step 1, grinding 70-92 wt% of low-aluminum pyrophyllite, 6-15 wt% of zirconia raw material, and 1-15 wt% of natural quartz into 800 mesh fine powder according to mass percentage, adding a certain amount of organic binder and granulating, and calcining at 1420-1480° C. for 1-2 hours to obtain modified SiO2 fine particles with a low melting point; Step 2: 70-85 wt% of low-grade bauxite fine powder, 10-25 wt% of modified SiO2 fine particles, and 4-8 wt% of alumina raw material are uniformly mixed according to mass percentage, formed into a green body under a pressure of 80-120 MPa, calcined at 1550-1630° C. for 3-10 hours, cooled, and crushed to obtain a low thermal conductivity, alkali-resistant bauxite-based mullite synthetic material; The low-grade bauxite fine powder described in step 2 is taken from one or a combination of grade III and grade IV bauxite, and has an Al2O3 content of 48-70wt%, a SiO2 content of 25-50wt%, and a Fe2O3 content of ≤2.0wt% after ignition reduction, and a raw material particle size of ≤200 mesh; The Al2O3 content in the low-aluminum pyrophyllite described in step 1 is ≤18wt%, the SiO2 content is ≥80wt%, and the raw material particle size is ≤325 mesh.

2. The method for preparing the low thermal conductivity alkali-resistant alumina-based mullite synthetic material according to claim 1, characterized in that: In step 1, the raw materials are 75-85 wt% of low-aluminum pyrophyllite, 7-10 wt% of zirconia raw material, and 7-15 wt% of natural quartz, and the calcination temperature is 1450-1480°C.

3. The method for preparing the low thermal conductivity alkali-resistant alumina-based mullite synthetic material according to claim 1, characterized in that: The zirconia raw material described in step 1 is taken from one or two of zircon, post-used zirconia refractory material, post-used zirconia-corundum refractory material, and post-used zirconia-mullite refractory material. The ZrO2 content in the raw material is ≥45.5wt%, and the raw material particle size is ≤325 mesh.

4. The method for preparing the low thermal conductivity alkali-resistant alumina-based mullite synthetic material according to claim 1, characterized in that: The SiO2 content in the natural quartz described in step 1 is ≥99.0wt%, and the raw material particle size is ≤325 mesh.

5. The method for preparing the low thermal conductivity alkali-resistant alumina-based mullite synthetic material according to claim 1, characterized in that: The modified SiO2 fine particles described in step 1 have a particle size of 0.045-0.3 mm and a melting temperature of ≤1530°C.

6. The method for preparing the low thermal conductivity alkali-resistant alumina-based mullite synthetic material according to claim 1, characterized in that: The alumina raw material described in step 2 is taken from one of γ-Al2O3, α-Al2O3, and aluminum hydroxide, and the Al2O3 content after ignition reduction is ≥97.5wt%, and the raw material particle size is ≤325 mesh.

7. A low thermal conductivity alkali-resistant alumina-based mullite synthetic material, characterized in that: The low thermal conductivity alkali-resistant alumina-based mullite synthetic material prepared by the preparation method according to any one of claims 1 to 6 has a bulk density of 2.0-2.10 g / cm 3 The apparent porosity is 3~10%, the compressive strength at room temperature is 80~100MPa, the refractoriness under load is 1500~1600℃ under 0.2MPa conditions, and the thermal conductivity at 1000℃ is 0.5~0.6W / (m·K).

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