A core-shell lamellar cordierite raw material and a preparation method thereof

Abstract

The present invention discloses a core-shell lamellar cordierite raw material and a preparation method thereof. The specific steps of the preparation method are as follows: S1. Mix and stir a magnesium chloride solution, an aluminum chloride solution, and a sodium silicate solution to obtain a mixed solution; S2. Add a precipitating agent to the mixed solution for coprecipitation, and then filter to obtain a filter material; S3. Granulate and screen the filter material to obtain spherical granular materials; S4. Heat-treat the spherical granular materials and cool them to room temperature to obtain calcined materials; S5. Immerse the calcined materials in silica sol, take them out, and mix them with a premixed material to obtain coated materials; S6. Heat-treat the coated materials and cool them to room temperature to obtain the core-shell lamellar cordierite raw material; wherein, the premixed material includes amorphous Al<subgt;2< / subgt;O<subgt;3< / subgt> fine powder, rhodonite fine powder, mica powder, sillimanite fine powder, and boric acid. The synthesis temperature of this preparation method is low, and the prepared core-shell lamellar cordierite raw material has high purity, small specific gravity, low porosity, small thermal expansion coefficient, and a lamellar crystal morphology, improving the thermal conductivity and thermal expansion of the cordierite raw material.

Description

Technical Field

[0001] The present invention relates to the technical field of refractory materials, and particularly relates to a core-shell platelet cordierite raw material and a preparation method thereof. Background Art

[0002] Cordierite (2MgO·2Al2O3·5SiO2) has become a high-quality raw material widely used in the fields of refractory and ceramic materials due to its many advantages such as high temperature resistance, low bulk density, small thermal conductivity, and low thermal expansion coefficient (about 1.5×10 -6 / °C) (Zhang Wei. Research progress on the synthesis of cordierite [J]. Acta Petrologica et Mineralogica, 2014, 33(4): 747-762). There is almost no cordierite deposit in nature, so it is mainly prepared by artificial synthesis.

[0003] Different from other single-phase (such as corundum) or multi-phase materials (such as mullite, spinel, etc.), cordierite belongs to the MgO-Al2O3-SiO2 ternary system compound, and any two of the ternary systems can undergo chemical reactions at high temperatures to form new phases (see Figure 1 ), which undoubtedly further increases the synthesis difficulty of cordierite. In addition, cordierite is extremely easy to decompose and desolvate to form combined phases such as corundum, spinel, mullite or olivine at temperatures above the peritectic temperature (Xia Yi, Shi Kai. Phase and structure evolution during the synthesis of cordierite [J]. Bulletin of the Chinese Ceramic Society, 2018, 37(9): 2802-2805). Therefore, it is not possible to simply increase the conversion rate of cordierite by increasing the sintering temperature.

[0004] At present, the preparation of cordierite mainly adopts the high-temperature solid-phase process, that is, the magnesium source (or magnesium-silicon source), aluminum source (or aluminum-silicon source) and silicon source are proportioned according to the theoretical chemical composition of cordierite, and then the components are mixed evenly through processes such as co-grinding, mixed-grinding or wet-grinding and appropriate additives are introduced (Zhang Hui, Zhang Hong, Chai Qian, etc. Influence of lanthanum oxide on the synthesis and microstructure of cordierite phase [J]. Non-Metallic Mines, 2023, 46(5): 26-29), and then combined is formed by means of spraying, extrusion or pressing, and finally calcined at high temperature.

[0005] The patented technology "A cordierite and its preparation method (202211605138.5)" discloses using talc, kaolin, magnesium oxide powder and silicon dioxide powder as raw materials, pressing into a blank after mixing and granulating, and then preparing cordierite by means of staged heat preservation. This preparation method eliminates the impurity spinel phase through the optimization of the formula and firing process, and obtains cordierite with a low thermal expansion coefficient and high purity at a low cost. However, due to the failure to create a good liquid-phase medium environment in the raw material components, the diffusion mass transfer rate of cordierite formation is slow, and the sintering temperature is high (1420-1450 °C), which is extremely easy to cause the decomposition and desolvation of cordierite (seeFigure 1 )。

[0006] The patented technology "Cordierite Sintered Body and Its Manufacturing Method (202280014662.7)" discloses that after forming a mixed powder of cordierite powder (obtained by electrofusion method), mullite powder, and magnesium oxide powder and then heating, the obtained cordierite sintered body mainly solves its plasma resistance and thermal shock resistance. This preparation method belongs to the typical electrofusion-recombination process, which not only makes it difficult to ensure the content of cordierite phase, but also increases the preparation cost of cordierite materials.

[0007] The patented technology "A Cordierite Ceramic and Its Preparation Method (202211490871.7)" discloses that after wet mixing and granulating cordierite powder with different particle sizes, pre-sintering in stages, and then performing modification treatment such as placing it in a water-soluble binder such as rare earth element particles, and finally sintering again to obtain cordierite ceramics. This process mainly selects cordierite powder as the starting material to prepare corresponding cordierite ceramic products, and the key problem it focuses on solving is to introduce a small amount of components into cordierite ceramics evenly by using a simple and easy-to-operate preparation process, and then effectively regulate its structure and related properties.

[0008] In summary, it can be seen that the main problems faced in the field of synthesizing cordierite are as follows:

[0009] (1) Increasing the content of cordierite phase: Cordierite belongs to a ternary compound. Avoiding the formation of impurity phases (such as spinel, mullite and other phases) and ensuring the conversion rate of cordierite phase are the primary problems determining the properties of cordierite.

[0010] (2) Reducing the synthesis temperature of cordierite: The synthesis temperature of cordierite is too high, generally about 1400 °C, which is not conducive to the stable operation of high-temperature kilns, nor to energy conservation and environmental protection.

[0011] (3) Regulating the microstructure of cordierite: The structure of cordierite is variable, and the properties presented by different microstructures are significantly different. How to regulate the growth and crystal morphology of cordierite is the key to solving its service performance. Generally, the dendritic crystal structure has low stability and is difficult to be dense; in contrast, the lamellar crystal structure is more stable, has a high densification degree, and the thermal conductivity of the material is small, and the thermal expansion rate is further reduced.

[0012] (4) Reducing the preparation cost of cordierite: In addition to energy consumption (factors such as synthesis temperature), selecting reasonable industrial solid wastes or tailings as raw materials to synthesize cordierite can further reduce its preparation cost, but at the same time, it also causes a series of problems such as impurity components and impurity phases of cordierite, resulting in low purity of the synthesized cordierite. Summary of the Invention

[0013] The object of the present invention is, in view of the above deficiencies of the prior art, to provide a core-shell platelet cordierite raw material and a preparation method thereof. The preparation method has a low synthesis temperature, and the synthesized platelet cordierite raw material prepared has high purity, small specific gravity, low porosity, small thermal expansion coefficient, and a platelet-like crystal morphology, improving the thermal conductivity and thermal expansion of the cordierite raw material.

[0014] A preparation method of a core-shell platelet cordierite raw material of the present invention is as follows:

[0015] S1. Mix and stir a magnesium chloride solution, an aluminum chloride solution, and a sodium silicate solution to obtain a mixed solution;

[0016] S2. Add a precipitating agent to the mixed solution for coprecipitation, and then filter by suction to obtain a filter material;

[0017] S3. Granulate and screen the filter material to obtain spherical granular material; the specific process can be:

[0018] S4. Heat-treat the spherical granular material and cool it to room temperature to obtain a calcined material;

[0019] S5. Immerse the calcined material in silica sol, take it out, and mix it with a premix. The premix is coated on the surface of the calcined material to obtain a coated material;

[0020] S6. Heat-treat the coated material and cool it to room temperature to obtain the core-shell platelet cordierite raw material;

[0021] Wherein, the premix includes amorphous Al2O3 fine powder, rhodonite fine powder, mica powder, sillimanite fine powder, and boric acid.

[0022] Further, in step S1, the concentration of the magnesium chloride solution is 2.0 - 2.2 mol / L; the concentration of the aluminum chloride solution is 1.8 - 2.2 mol / L; the concentration of the sodium silicate solution is 2.2 - 2.5 mol / L; the volume ratio of the magnesium chloride solution: aluminum chloride solution: sodium silicate solution is 1:(1.2 - 1.4):(1.3 - 1.6); stir at 45 - 55 °C for 10 - 12 minutes to obtain a mixed solution; and / or,

[0023] In step S2, the precipitating agent is urea, and the mass ratio of the mixed solution to urea is 100:(8 - 15);

[0024] And / or, in step S3, after granulation, screen through a 100-mesh sieve.

[0025] According to the mass ratio of the mixed solution: urea of 100:(8 - 15), add it to a container, stir at 55 - 65 °C for 25 - 30 minutes, and then let it stand for 15 - 20 minutes to obtain a mixed precursor. Add the mixed precursor to a vacuum suction filter, and filter by suction 3 - 5 times to obtain a filter material.

[0026] Further, in step S4, it is heated to 1300 - 1360°C at a heating rate of 40 - 60°C / min, held for 1 - 2 hours, and then cooled to room temperature at a cooling rate of 3 - 5°C / min to obtain a calcined material.

[0027] Further, it is proportioned according to the mass ratio of amorphous Al2O3 fine powder : rhodonite fine powder : mica powder : sillimanite fine powder : boric acid of 100 : (55 - 60) : (10 - 15) : (20 - 25) : (2.2 - 2.5), added to a vibration ball mill and mixed and ground until the particle size ≤ 45μm to obtain a premixed material.

[0028] Further, in step S5, the calcined material and the premixed material are mixed and coated according to a mass ratio of (7 - 9) : 1. The calcined material can be immersed in silica sol for 15 - 20 minutes and then taken out, and added to a roller mixer together with the premixed material according to a mass ratio of (7 - 9) : 1 for coating, and mixed for 15 - 20 minutes to obtain a coated material.

[0029] Further, in step S5, the solid content of the silica sol is 35 - 40wt%, and the pH of the silica sol is 7 - 8.

[0030] Further, in step S4, the spherical pellet material is heat - treated in an induction sintering furnace; and / or,

[0031] In step S6, the coated material is heat - treated in a rotary sintering furnace.

[0032] Further, in step S6, it is heated to 1275 - 1285°C at a heating rate of 3 - 5°C / min, held for 4 - 6 hours, and then cooled to room temperature at a cooling rate of 2 - 3°C / min to obtain the core - shell lamellar cordierite raw material.

[0033] Further, the amorphous Al2O3 fine powder is amorphous; the Al2O3 content of the amorphous Al2O3 fine powder ≥ 99wt%; and / or,

[0034] The mass ratio of MgO, CaO and SiO2 in the rhodonite fine powder is (25 - 28) : (40 - 42) : (28 - 30), and the sum of the contents of MgO, CaO and SiO2 is 98wt% - 99.9wt%; and / or,

[0035] The mica powder, sillimanite fine powder and boric acid are of industrial purity; and / or,

[0036] The urea is of industrial purity.

[0037] A core - shell lamellar cordierite raw material prepared by the above - mentioned preparation method.

[0038] The beneficial effects of the present invention are:

[0039] (1) The present invention utilizes the amorphous (disordered) structure of amorphous alumina to reduce the activation energy of the chemical reaction with boric acid, thereby reducing the sintering temperature of the material system. At the same time, combined with the relatively large lattice voids of rhodonite, it accelerates the dissolution and diffusion mass transfer of aluminum and silicon components at high temperatures, which is beneficial to improving the conversion rate of cordierite.

[0040] (2) The present invention improves the uniformity of magnesium-aluminum-silicon components through the ionic electrostatic adsorption of each component in the solution system, and uses the coprecipitation of urea to form a stable combination, improving the sintering thermodynamic activity of the material system, thereby improving the density of the synthesized cordierite and reducing the water absorption rate and porosity of cordierite.

[0041] (3) The present invention uses induction sintering to achieve rapid heating, promotes the formation of a large number of cordierite crystal nuclei and inhibits the development and abnormal growth of crystal nuclei, forming a large number of microcrystalline structures. During the slow cooling stage, it induces the growth of cordierite microcrystals along the c-axis direction, which is beneficial to the formation of platelets. Furthermore, it reduces the thermal conductivity and thermal expansion coefficient of the material, and the large number of microcrystalline structures also reduces the specific gravity of cordierite, realizing the lightweight of cordierite.

[0042] (4) The present invention forms a network structure through the infiltration of silica sol, which is fully wrapped with the premix to form a good "core-shell" structure. Utilizing the high sintering activity of silica sol particles, it promotes the rapid sintering on the surface of the "core-shell" structure. In addition, since the microcrystalline cordierite formed by pre-sintering is introduced as crystal seeds, it significantly reduces the synthesis temperature of platelet cordierite, saving energy and environmental protection while reducing the preparation cost of cordierite.

[0043] (5) The present invention uses rotary sintering and slow heating and cooling methods to achieve the dynamic sintering and uniform heating of the material, avoiding the incomplete development of the two-dimensional structure of platelet cordierite, eliminating the false crystal structure of the mother salt generated by in-situ formation of cordierite under the static heating method, and further improving the conversion rate of cordierite.

[0044] The raw materials of the core-shell platelet cordierite prepared by the present invention are detected as follows:

[0045] The conversion rate of cordierite ≥ 99%; the particle density is 1.58 - 1.66 g / cm 3 ; the porosity is 6.7 - 7.3%; the thermal expansion rate is 0.34 - 0.58% (1000 °C); the thermal conductivity is 0.65 - 0.84 W / (m·K); the water absorption rate is 5.3 - 6.2%. Description of the Drawings

[0046] Figure 1 is the MgO-Al2O3-SiO2 ternary phase diagram;

[0047] Figure 2SEM image of the core-shell lamellar cordierite raw material prepared in Example 1;

[0048] Figure 3 Diffraction peak crystal plane and diffraction angle diagram of cordierite prepared in Example 1. Detailed implementation manners

[0049] The following are specific embodiments of the present invention and in combination with the accompanying drawings, the technical solutions of the present invention are further described, but the present invention is not limited to these embodiments.

[0050] Example 1

[0051] A preparation method of a core-shell lamellar cordierite raw material, the specific steps are as follows:

[0052] 1) Weigh amorphous Al2O3 fine powder, rhodonite fine powder, mica powder, sillimanite fine powder, and boric acid according to the mass ratio of 100:55:15:20:2.3, add them to a vibration ball mill and mix and grind until the particle size is ≤ 45 μm to obtain a premix;

[0053] 2) Mix magnesium chloride solution, aluminum chloride solution, and sodium silicate solution according to the volume ratio of 1:1.2:1.5, add them to a container and stir at 45 - 55 °C for 10 - 12 minutes to obtain a mixed solution;

[0054] 3) Mix the mixed solution and urea according to the mass ratio of 100:15, add them to a container and stir at 55 - 65 °C for 25 - 30 minutes, then let it stand for 15 - 20 minutes to obtain a mixed precursor;

[0055] 4) Add the mixed precursor to a vacuum filter and filter it cyclically 3 - 5 times to obtain a filter material;

[0056] 5) Add the filter material to a disk granulator for granulation and forming, pass through a 100-mesh round-hole sieve, and take the undersize to obtain spherical granular material;

[0057] 6) Place the spherical granular material in an induction sintering furnace, heat it to 1300 °C at a heating rate of 60 °C / min, hold for 2 hours, and then cool it to room temperature at a cooling rate of 5 °C / min to obtain a calcined material;

[0058] 7) Immerse the calcined material in silica sol for 15 - 20 minutes, then take it out, and add it to a roller mixer with the premix according to the mass ratio of 7:1 for coating, and mix for 15 - 20 minutes. The premix is coated on the surface of the calcined material to obtain a coated material;

[0059] 8) Place the coated material in a rotary sintering furnace, heat it to 1278 °C at a heating rate of 5 °C / min, hold for 6 hours, and then cool it to room temperature at a cooling rate of 2 °C / min to obtain the core-shell lamellar cordierite raw material.

[0060] The amorphous Al2O3 fine powder is amorphous; the Al2O3 content of the amorphous Al2O3 fine powder is ≥ 99 wt%.

[0061] The mass ratio of MgO, CaO and SiO2 in the rhodonite fine powder is (25 - 28) : (40 - 42) : (28 - 30), and the sum of the contents of MgO, CaO and SiO2 is 98 wt% - 99.9 wt%.

[0062] The mica powder, sillimanite fine powder and boric acid are of industrial purity.

[0063] The concentration of the magnesium chloride solution is 2.0 mol / L.

[0064] The concentration of the aluminum chloride solution is 1.8 mol / L.

[0065] The concentration of the sodium silicate solution is 2.2 mol / L.

[0066] The urea is of industrial purity.

[0067] The solid content of the silica sol is 35 - 40 wt%, and the pH of the silica sol is 7 - 8.

[0068] Figure 2 SEM image of the core-shell platelet cordierite raw material prepared in Example 1. From Figure 2 it can be seen that the core-shell platelet cordierite raw material prepared in this example has an obvious platelet structure, and the platelets interpenetrate and interleave with each other, which is beneficial to maintaining the stability of the cordierite structure and properties.

[0069] Figure 3 XRD pattern of the core-shell platelet cordierite raw material prepared in Example 1. From Figure 3 it can be seen that there are no other mullite, olivine or spinel and other impurity phase peaks in the core-shell platelet cordierite raw material prepared in this example, indicating a high phase content and conversion rate of cordierite.

[0070] The core-shell platelet cordierite raw material prepared in this example was tested:

[0071] The cordierite conversion rate is 99.2%; the particle density: 1.58 g / cm 3 ; the porosity: 7.3%; the thermal expansion rate: 0.34% (1000 °C); the thermal conductivity: 0.65 W / (m·K); the water absorption rate: 6.1%.

[0072] Example 2

[0073] A preparation method of a core-shell platelet cordierite raw material, the specific steps are as follows:

[0074] 1) Weigh the raw materials according to the mass ratio of amorphous Al2O3 fine powder : rhodonite fine powder : mica powder : sillimanite fine powder : boric acid as 100 : 60 : 10 : 25 : 2.2, add them into a vibration ball mill and mix and grind until the particle size is ≤ 45 μm to obtain a premixed material;

[0075] 2) Mix according to the volume ratio of magnesium chloride solution : aluminum chloride solution : sodium silicate solution as 1 : 1.4 : 1.3, add them into a container and stir at 45 - 55 °C for 10 - 12 minutes to obtain a mixed solution;

[0076] 3) Mix according to the mass ratio of the mixed solution : urea as 100 : 8, add them into a container and stir at 55 - 65 °C for 25 - 30 minutes, then let it stand for 15 - 20 minutes to obtain a mixed precursor;

[0077] 4) Add the mixed precursor into a vacuum filter, and filter it cyclically for 3 - 5 times to obtain a filter material;

[0078] 5) Add the filter material into a disk granulator for granulation and forming, pass through a 100 - mesh round hole sieve, and take the undersize to obtain spherical granular materials;

[0079] 6) Place the spherical granular materials in an induction sintering furnace, heat them to 1360 °C at a heating rate of 40 °C / min, hold for 1 hour, and then cool to room temperature at a cooling rate of 3 °C / min to obtain a calcined material;

[0080] 7) Immerse the calcined material in silica sol for 15 - 20 minutes and then take it out, add it into a roller mixer with the premixed material according to the mass ratio of 9 : 1 for coating, and mix for 15 - 20 minutes so that the premixed material is coated on the surface of the calcined material to obtain a coated material;

[0081] 8) Place the coated material in a rotary sintering furnace, heat it to 1275 °C at a heating rate of 3 °C / min, hold for 4 hours, and then cool to room temperature at a cooling rate of 3 °C / min to obtain the core - shell laminated cordierite raw material.

[0082] The parameters of other raw materials are the same as those in Example 1.

[0083] The core - shell laminated cordierite raw material prepared in this example is detected:

[0084] The conversion rate of cordierite is 99%; the particle density: 1.66 g / cm 3 ; the porosity: 6.7%; the thermal expansion rate: 0.47% (at 1000 °C); the thermal conductivity: 0.77 W / (m·K); the water absorption rate: 5.3%.

[0085] Example 3

[0086] A preparation method of core - shell laminated cordierite raw material, the specific steps are as follows:

[0087] 1) Weigh the amorphous Al2O3 fine powder, rhodonite fine powder, mica powder, sillimanite fine powder, and boric acid according to the mass ratio of 100:56:14:22:2.5, add them to a vibration ball mill for mixing and grinding until the particle size is ≤45 μm to obtain a premix;

[0088] 2) Mix magnesium chloride solution, aluminum chloride solution, and sodium silicate solution according to the volume ratio of 1:1.3:1.6, add them to a container and stir at 45 - 55 °C for 10 - 12 minutes to obtain a mixed solution;

[0089] 3) Mix the mixed solution and urea according to the mass ratio of 100:11, add them to a container and stir at 55 - 65 °C for 25 - 30 minutes, then let it stand for 15 - 20 minutes to obtain a mixed precursor;

[0090] 4) Add the mixed precursor to a vacuum filter and filter it cyclically 3 - 5 times to obtain a filter material;

[0091] 5) Add the filter material to a disk granulator for granulation and forming, pass through a 100 - mesh round hole sieve, and take the material under the sieve to obtain spherical granular materials;

[0092] 6) Place the spherical granular materials in an induction sintering furnace and heat them to 1320 °C at a heating rate of 55 °C / min, hold for 2 hours, and then cool to room temperature at a cooling rate of 4 °C / min to obtain a calcined material;

[0093] 7) Immerse the calcined material in silica sol for 15 - 20 minutes, then take it out and add it to a roller mixer according to the mass ratio of 8:1 with the premix for coating, mix for 15 - 20 minutes, and coat the premix on the surface of the calcined material to obtain a coated material;

[0094] 8) Place the coated material in a rotary sintering furnace and heat it to 1285 °C at a heating rate of 5 °C / min, hold for 5 hours, and then cool to room temperature at a cooling rate of 3 °C / min to obtain the core - shell platelet cordierite raw material.

[0095] The other raw material parameters are the same as those in Example 1.

[0096] The core - shell platelet cordierite raw material prepared in this example was tested:

[0097] The cordierite conversion rate is 99.4%; the particle density is 1.65 g / cm 3 ; the porosity is 7.0%; the thermal expansion rate is 0.58% (at 1000 °C); the thermal conductivity is 0.84 W / (m·K); the water absorption rate is 6.2%.

[0098] Comparative Example 1

[0099] A method for preparing cordierite raw material, the specific steps are as follows:

[0100] 1) Weigh the amorphous Al2O3 fine powder, forsterite fine powder, mica powder, sillimanite fine powder, and boric acid according to the mass ratio of 100:56:14:22:2.5, add them to a vibration ball mill for mixing and grinding until the particle size is ≤45μm to obtain a premix;

[0101] 2) Mix magnesium chloride solution, aluminum chloride solution, and sodium silicate solution according to the volume ratio of 1:1.3:1.6, add them to a container, and stir at 45 - 55°C for 10 - 12 minutes to obtain a mixed solution;

[0102] 3) Mix the mixed solution and urea according to the mass ratio of 100:11, add them to a container, stir at 55 - 65°C for 25 - 30 minutes, and then let it stand for 15 - 20 minutes to obtain a mixed precursor;

[0103] 4) Add the mixed precursor to a vacuum filter, and perform cyclic suction filtration 3 - 5 times to obtain a filter material;

[0104] 5) Add the filter material to a disk granulator for granulation and forming, pass through a 100 - mesh round hole sieve, and take the undersize material to obtain spherical granular material;

[0105] 6) Place the spherical granular material in an induction sintering furnace, heat it to 1320°C at a heating rate of 55°C / min, hold for 2 hours, and then cool it to room temperature at a cooling rate of 4°C / min to obtain a calcined material;

[0106] 7) Immerse the calcined material in silica sol for 15 - 20 minutes, then take it out, and add it to a roller mixer with the premix according to the mass ratio of 8:1 for coating. Mix for 15 - 20 minutes so that the premix is coated on the surface of the calcined material to obtain a coated material;

[0107] 8) Place the coated material in a rotary sintering furnace, heat it to 1285°C at a heating rate of 5°C / min, hold for 5 hours, and then cool it to room temperature at a cooling rate of 3°C / min to obtain the core - shell platelet cordierite raw material.

[0108] The parameters of other raw materials are the same as those in Example 1.

[0109] The cordierite raw material prepared in this comparative example was tested:

[0110] The cordierite conversion rate is 85.5%; the particle density is 1.92 g / cm 3 ; the porosity is 10.3%; the thermal expansion rate is 1.22% (at 1000°C); the thermal conductivity is 1.15 W / (m·K); the water absorption rate is 8.4%.

[0111] In Comparative Example 1, except that in step 1), the powdery rhodonite in the premix was replaced with powdery forsterite, and other process parameters were the same as those in Example 3. It can be seen that when forsterite was used as the magnesium-silicon source, due to the change in the voids of the forsterite crystal structure, the diffusion of aluminum-silicon components was inhibited, and the conversion of cordierite was reduced. Due to the derivation of impurity phases, the particle density and porosity of the cordierite raw material were increased, and thus the thermal expansion coefficient and thermal conductivity of the cordierite raw material were also increased.

[0112] Comparative Example 2

[0113] A method for preparing a cordierite raw material, comprising the following specific steps:

[0114] 1) Weigh amorphous Al2O3 fine powder, powdery rhodonite, mica powder, sillimanite fine powder, and boric acid according to the mass ratio of 100:60:10:25:2.2, add them to a vibration ball mill and mix and grind until the particle size ≤ 45 μm to obtain a premix;

[0115] 2) Mix magnesium chloride solution, aluminum chloride solution, and sodium silicate solution according to the volume ratio of 1:1.4:1.3, add them to a container and stir at 45 - 55 °C for 10 - 12 minutes to obtain a mixed solution;

[0116] 3) Mix the mixed solution and urea according to the mass ratio of 100:8, add them to a container and stir at 55 - 65 °C for 25 - 30 minutes, then let it stand for 15 - 20 minutes to obtain a mixed precursor;

[0117] 4) Add the mixed precursor to a vacuum filter and filter it 3 - 5 times cyclically to obtain a filter material;

[0118] 5) Add the filter material to a disk granulator for granulation and forming, pass through a 100-mesh round-hole sieve, and take the undersize to obtain spherical granular materials;

[0119] 6) Place the spherical granular materials in an induction sintering furnace, heat them to 1360 °C at a heating rate of 5 °C / min, hold for 1 hour, and then cool to room temperature at a cooling rate of 3 °C / min to obtain a calcined material;

[0120] 7) Immerse the calcined material in silica sol for 15 - 20 minutes, then take it out, add it to a roller mixer according to the mass ratio of 9:1 with the premix for coating, and mix for 15 - 20 minutes so that the premix is coated on the surface of the calcined material to obtain a coated material;

[0121] 8) Place the coated material in a rotary sintering furnace, heat it to 1275 °C at a heating rate of 3 °C / min, hold for 4 hours, and then cool to room temperature at a cooling rate of 3 °C / min to obtain the core-shell platelet cordierite raw material.

[0122] Other raw material parameters are the same as those in Example 1.

[0123] The cordierite raw materials prepared in this comparative example were tested as follows:

[0124] The cordierite conversion rate was 78.5%; the particle density was 1.89 g / cm 3 ; the porosity was 11.2%; the thermal expansion rate was 0.85% (at 1000 °C); the thermal conductivity was 1.24 W / (m·K); the water absorption rate was 8.0%.

[0125] In Comparative Example 2, except that the heating rate in Step 6) was different from that in Example 2, other process parameters were the same as those in Example 2. It can be seen that heating the spherical granular material in a low-rate heating manner in Step 6) led to inability to crystallize quickly, reduced the nucleation rate of cordierite crystal nuclei, and thus caused a decrease in the cordierite conversion rate, weakening the sintering of the cordierite raw materials and increasing the porosity and water absorption rate of the material and other properties.

[0126] Where not otherwise involved above, it shall apply to the prior art.

[0127] Although some specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are only for illustration and not for limiting the scope of the present invention. Those skilled in the technical field to which the present invention pertains can make various modifications or supplements to the described specific embodiments or use similar ways to substitute, but will not deviate from the direction of the present invention or exceed the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc. made to the above embodiments based on the technical essence of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a core-shell lamellar cordierite raw material, characterized in that, The specific steps are as follows: S1. Mix and stir a magnesium chloride solution, an aluminum chloride solution, and a sodium silicate solution to obtain a mixed solution; S2. Add a precipitant to the mixed solution for coprecipitation, and then perform suction filtration to obtain a filter material; S3. Granulate the filter material and sieve it to obtain spherical granular materials; S4. After heat-treating the spherical granular materials, cool them to room temperature to obtain calcined materials; S5. Immerse the calcined materials in silica sol, take them out, and mix them with a premix. The premix is coated on the surface of the calcined materials to obtain coated materials; S6. After heat-treating the coated materials, cool them to room temperature to obtain core-shell platelet cordierite raw materials; Wherein, the premix includes amorphous Al2O3 fine powder, rhodonite fine powder, mica powder, sillimanite fine powder, and boric acid.

2. The preparation method of a core-shell lamellar cordierite raw material according to claim 1, characterized in that, In step S1, the concentration of the magnesium chloride solution is 2.0 - 2.2 mol / L; the concentration of the aluminum chloride solution is 1.8 - 2.2 mol / L; the concentration of the sodium silicate solution is 2.2 - 2.5 mol / L; the volume ratio of the magnesium chloride solution : aluminum chloride solution : sodium silicate solution is 1 : (1.2 - 1.4) : (1.3 - 1.6); and / or, In step S2, the precipitant is urea, and the mass ratio of the mixed solution to urea is 100 : (8 - 15); and / or, in step S3, after granulation, sieve through a 100-mesh sieve.

3. The preparation method of a core-shell lamellar cordierite raw material according to claim 1, characterized in that, In step S4, heat to 1300 - 1360 °C at a heating rate of 40 - 60 °C / min, hold for 1 - 2 hours, and then cool to room temperature at a cooling rate of 3 - 5 °C / min to obtain calcined materials.

4. The preparation method of a core-shell lamellar cordierite raw material according to claim 1, wherein, Charge according to the mass ratio of amorphous Al2O3 fine powder : rhodonite fine powder : mica powder : sillimanite fine powder : boric acid of 100 : (55 - 60) : (10 - 15) : (20 - 25) : (2.2 - 2.5), add to a vibration ball mill for mixing and grinding until the particle size ≤ 45 μm to obtain a premix.

5. The preparation method of a core-shell lamellar cordierite raw material according to claim 1, characterized in that, In step S5, the calcined materials and the premix are mixed and coated in a mass ratio of (7 - 9) :

1.

6. The preparation method of a core-shell platelet cordierite raw material as described in claim 1, characterized in that, In step S5, the solid content of the silica sol is 35-40 wt%, and the pH is 7-8.

7. The preparation method of a core-shell lamellar cordierite raw material according to claim 1, characterized in that, In step S4, the spherical granular materials are heat-treated in an induction sintering furnace; and / or, In step S6, the coated materials are heat-treated in a rotary sintering furnace.

8. The preparation method of a core-shell lamellar cordierite raw material according to claim 1, wherein, In step S6, heat to 1275 - 1285 °C at a heating rate of 3 - 5 °C / min, hold for 4 - 6 hours, and then cool to room temperature at a cooling rate of 2 - 3 °C / min to obtain core-shell platelet cordierite raw materials.

9. The preparation method of a core-shell lamellar cordierite raw material according to claim 2, characterized in that, The amorphous Al2O3 fine powder is amorphous; the Al2O3 content of the amorphous Al2O3 fine powder ≥ 99 wt%; and / or, The mass ratio of MgO, CaO, and SiO2 in the rhodonite fine powder is (25 - 28) : (40 - 42) : (28 - 30), and the sum of the contents of MgO, CaO, and SiO2 is 98 wt% - 99.9 wt%; and / or, The mica powder, sillimanite fine powder, and boric acid are of industrial purity; and / or, The urea is of industrial purity.

10. A core-shell platelet cordierite raw material prepared by the preparation method according to any one of claims 1 - 9.

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