Method for modifying calcined kaolin, use

Abstract

The application discloses a modified method and application of calcined kaolin, and belongs to the technical field of building materials. By introducing a thermal expansion coefficient regulator with the function of adjusting the thermal expansion coefficient into the calcined kaolin, the thermal expansion coefficient of the calcined kaolin can be adjusted, the compatibility of the calcined kaolin with a ceramic body is better, the firing defects of ceramic products are effectively reduced, and the problem of product defects caused by the mismatch of the thermal expansion coefficient in ceramic application is effectively solved. In addition, the surface of the calcined kaolin is treated, the particle fineness is effectively controlled, and the problem of easy agglomeration of the calcined kaolin is reduced, so that excellent thermal expansion coefficient adjusting effect can be achieved, the dispersibility of the modified calcined kaolin can be ensured, a more stable slurry system can be formed in the application process, the combination with the ceramic matrix is fully dispersed and enhanced, and the modified calcined kaolin is suitable for the preparation of the ceramic body.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and more specifically, to a method for modifying calcined kaolin and its application. Background Technology

[0002] The coefficient of thermal expansion of kaolin is primarily influenced by its crystal structure. Kaolin is mainly composed of silicate minerals, with kaolinite as its main component. The hydrogen bonds within the kaolinite crystal structure result in a layered structure. During heating, the internal structure of the kaolinite mineral changes, leading to variations in its thermal expansion properties. Secondly, the thermal expansion properties of kaolin are also affected by its chemical composition and mineral composition. Kaolin contains a high proportion of alumina (Al₂O₃) and a low proportion of aluminum silicate (SiO₂), which contributes to its relatively high coefficient of thermal expansion. Furthermore, kaolin contains a certain proportion of impurity elements, such as potassium and sodium, which also affect its thermal expansion properties. In addition, crystal defects in kaolin also influence its thermal expansion properties. For example, crystal defects increase lattice instability, leading to enhanced thermal expansion.

[0003] Existing technologies improve the properties of kaolin by calcining it. After calcination, kaolin (Al2O3·2SiO2) loses its structural water, transforming into highly stable mullite and amorphous SiO2. This process alters its coefficient of thermal expansion. Calcined kaolin is then applied in ceramic manufacturing, such as in ceramic green bodies. Ceramic green bodies are complex systems composed of various raw materials (such as quartz, feldspar, and clay), each with its specific thermal expansion behavior. If the coefficient of expansion of calcined kaolin does not match that of other components in the green body system, significant internal stress will be generated during the cooling process after firing, leading to defects such as warping, cracking, and microcracks in the product, severely affecting the yield and strength of the ceramic product. Furthermore, in the preparation of ceramic green bodies, calcined kaolin can increase the Al2O3 content, promote mullite formation, and improve the stability and strength of the ceramic product. However, in ceramic processing, there are high requirements for the fineness and crystallinity of calcined kaolin. During the modification process of calcined kaolin, the balance between calcined kaolin and the coefficient of thermal expansion was not achieved. That is, during the adjustment of the coefficient of thermal expansion, the calcined kaolin agglomerated, resulting in poor modification effect. Therefore, further modification of calcined kaolin is still needed to improve its quality and enhance its applicability in the ceramic field. Summary of the Invention

[0004] Based on this, in order to solve one of the above-mentioned technical problems, the present invention provides a method for modifying calcined kaolin and its application, the specific technical solution of which is as follows:

[0005] A method for modifying calcined kaolin includes the following steps:

[0006] S1. Pre-treat the calcined kaolin raw material;

[0007] S2. The pretreated calcined kaolin is mixed with a thermal expansion coefficient regulator and ball-milled to obtain a mixture;

[0008] S3. Add the mixture to treatment agent A, stir under certain conditions, then add treatment agent B, and continue stirring to obtain modified slurry;

[0009] S4. After heat treatment and spray drying of the modified slurry, modified calcined kaolin is obtained.

[0010] Preferably, in step S1, the pretreatment includes: adding water to calcined kaolin raw material to prepare a slurry, then adding sodium carboxymethyl cellulose and silane coupling agent, stirring at 100r / min to 500r / min for 1h to 2h, and then concentrating to a mass concentration of 30% to 50%.

[0011] Preferably, in step S2, the weight ratio of the calcined kaolin to the thermal expansion regulator is 100:(1~15).

[0012] Preferably, in step S2, the coefficient of thermal expansion regulator includes at least one of silicon dioxide, aluminum titanate, magnesium oxide, zirconium oxide, and calcium oxide.

[0013] Preferably, in step S2, the ball milling speed is 100 r / min to 500 r / min, and the ball milling time is 1 h to 3 h.

[0014] Preferably, in step S3, the treatment agent A is an aqueous dispersion of tetraisopropyl titanate, and the mass percentage content of tetraisopropyl titanate is 12%~20%.

[0015] Preferably, in step S3, the treatment agent B is a cellulose ether.

[0016] Preferably, in step S3, the weight ratio of the mixture, treatment agent A, and treatment agent B is (20~25):(35~50):(25~45).

[0017] Preferably, in step S4, the heat treatment is: heating to 120°C to 150°C at a heating rate of 3°C / min to 8°C / min, and holding at that temperature for 20 min to 60 min.

[0018] In addition, the present invention also provides an application of modified calcined kaolin, wherein the modified calcined kaolin obtained by the modification method is used in the preparation of ceramic bodies and / or ceramic glazes.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. This invention introduces a thermal expansion coefficient regulator into the interior of calcined kaolin, which enables the thermal expansion coefficient of calcined kaolin to be adjustable and has better compatibility with ceramic bodies, effectively reducing firing defects in ceramic products and effectively solving the problem of product defects caused by mismatch in thermal expansion coefficients in ceramic applications.

[0021] 2. This invention uses tetraisopropyl titanate and cellulose ether to further surface treat calcined kaolin, effectively controlling particle fineness and reducing the problem of easy agglomeration of calcined kaolin. It not only achieves excellent adjustment effect of thermal expansion coefficient, but also ensures the dispersibility of modified calcined kaolin, so that it forms a more stable slurry system during application, which can fully disperse and enhance its bonding force with the ceramic matrix, and is suitable for the preparation of ceramic green bodies. Detailed Implementation

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. In the embodiments, all original reagent materials are commercially available, and experimental methods not specifically described are conventional methods and conditions well known in the art, or as recommended by the instrument manufacturer.

[0023] A method for modifying calcined kaolin according to one embodiment of the present invention includes the following steps:

[0024] S1. Pre-treat the calcined kaolin raw material;

[0025] S2. The pretreated calcined kaolin is mixed with a thermal expansion coefficient regulator and ball-milled to obtain a mixture;

[0026] S3. Add the mixture to treatment agent A, stir under certain conditions, then add treatment agent B, and continue stirring to obtain modified slurry;

[0027] S4. After heat treatment and spray drying of the modified slurry, modified calcined kaolin is obtained.

[0028] In one embodiment, step S1 includes the following pretreatment process: calcined kaolin raw material is mixed with water to prepare a slurry, then sodium carboxymethyl cellulose and silane coupling agent are added, the mixture is stirred at 100 r / min to 500 r / min for 1 h to 2 h, and then concentrated to a mass concentration of 30% to 50%.

[0029] In one embodiment, the ratio of calcined kaolin, sodium carboxymethyl cellulose and silane coupling agent by weight is 100:(1~9):(7~15).

[0030] In one embodiment, the silane coupling agent is at least one of vinyltrimethoxysilane, divinyldimethylsilane, and dimethylphenylvinylsilane.

[0031] In one embodiment, in step S2, the weight ratio of the calcined kaolin to the thermal expansion regulator is 100:(1~15).

[0032] In one embodiment, in step S2, the coefficient of thermal expansion adjuster includes at least one of silicon dioxide, aluminum titanate, magnesium oxide, zirconium oxide, and calcium oxide.

[0033] In one embodiment, in step S2, the ball milling speed is 100 r / min to 500 r / min, and the ball milling time is 1 h to 3 h.

[0034] In one embodiment, in step S3, the treatment agent A is an aqueous dispersion of tetraisopropyl titanate, and the mass percentage content of tetraisopropyl titanate is 12%~20%.

[0035] In one embodiment, in step S3, the treatment agent B is a cellulose ether.

[0036] In one embodiment, in step S3, the weight ratio of the mixture, treatment agent A and treatment agent B is (20~25):(35~50):(25~45).

[0037] In one embodiment, in step S3, the mixed powder is added to treatment agent A and stirred for 10 to 30 minutes at a rotation speed of 50 to 100 r / min and a temperature of 45 to 65°C. Then treatment agent B is added and stirring is continued for 1 to 3 hours to obtain the modified slurry.

[0038] In one embodiment, in step S4, the heat treatment is: heating to 120°C to 150°C at a heating rate of 3°C / min to 8°C / min, and holding at that temperature for 20 min to 60 min.

[0039] In one embodiment, the calcined kaolin contains not less than 95% kaolinite and not more than 0.5% quartz.

[0040] In addition, the present invention also provides an application of modified calcined kaolin, wherein the modified calcined kaolin obtained by the modification method is used in the preparation of ceramic bodies and / or ceramic glazes.

[0041] The above-mentioned process is simple, allows for adjustable thermal expansion coefficients of calcined kaolin, and provides better compatibility with ceramic bodies. This effectively reduces firing defects in ceramic products and solves the problem of product defects caused by mismatched thermal expansion coefficients in ceramic applications.

[0042] The implementation schemes of the present invention will now be described in detail with reference to specific embodiments. Example 1:

[0043] A method for modifying calcined kaolin includes the following steps:

[0044] S1. Prepare a slurry by adding 100 parts by weight of calcined kaolin raw material to 150 parts by weight. Then add 8 parts by weight of sodium carboxymethyl cellulose and 12 parts by weight of vinyltrimethoxysilane. Stir at 100 rpm for 2 hours, and then concentrate to a mass concentration of 30%.

[0045] S2. According to the weight ratio, 100 parts of pretreated calcined kaolin and 12 parts of zirconium oxide are mixed and ball-milled at 100 r / min for 2 h to obtain a mixture;

[0046] S3. According to the weight ratio, 25 parts of the mixture were added to 50 parts of an aqueous dispersion of 18% tetraisopropyl titanate. The mixture was stirred for 20 minutes at a speed of 50 r / min and a temperature of 60°C. Then, 28 parts of cellulose ether were added and the mixture was stirred for another 2 hours to obtain the modified slurry.

[0047] S4. The modified slurry is heated to 125°C at a heating rate of 5°C / min and kept at that temperature for 20 min. After spray drying, modified calcined kaolin is obtained. Example 2:

[0048] A method for modifying calcined kaolin includes the following steps:

[0049] S1. According to the weight ratio, 100 parts of calcined kaolin raw material are added to 150 parts of water to prepare a slurry. Then, 9 parts of sodium carboxymethyl cellulose and 12 parts of vinyltrimethoxysilane are added. The mixture is stirred at 100 r / min for 2 h and then concentrated to a mass concentration of 30%.

[0050] S2. According to the weight ratio, 100 parts of pretreated calcined kaolin and 12 parts of zirconium oxide are mixed and ball-milled at a speed of 100 r / min for 2 h to obtain a mixture;

[0051] S3. According to the weight ratio, 25 parts of the mixture were added to 50 parts of an aqueous dispersion of tetraisopropyl titanate with a mass percentage of 16%, and stirred for 20 minutes at a speed of 50 r / min and a temperature of 65°C. Then, 30 parts of cellulose ether were added, and stirring was continued for 2 hours to obtain the modified slurry.

[0052] S4. The modified slurry is heated to 125°C at a heating rate of 5°C / min and kept at that temperature for 20 min. After spray drying, modified calcined kaolin is obtained. Example 3:

[0053] A method for modifying calcined kaolin includes the following steps:

[0054] S1. According to the weight ratio, 100 parts of calcined kaolin raw material are added to 150 parts of water to prepare a slurry, then 9 parts of sodium carboxymethyl cellulose and 15 parts of vinyltrimethoxysilane are added, and the mixture is stirred at 100 r / min for 2 h, and then concentrated to a mass concentration of 30%;

[0055] S2. According to the weight ratio, 100 parts of pretreated calcined kaolin and 12 parts of zirconium oxide are mixed and ball-milled at a speed of 100 r / min for 2 h to obtain a mixture;

[0056] S3. According to the weight ratio, 25 parts of the mixture were added to 50 parts of an aqueous dispersion of tetraisopropyl titanate with a mass percentage of 18%, and stirred for 20 minutes at a speed of 50 r / min and a temperature of 65°C. Then, 28 parts of cellulose ether were added, and stirring was continued for 2 hours to obtain the modified slurry.

[0057] S4. The modified slurry is heated to 125°C at a heating rate of 6°C / min and kept at that temperature for 20 min. After spray drying, modified calcined kaolin is obtained.

[0058] Comparative Example 1:

[0059] The difference between Comparative Example 1 and Example 3 is that vinyltrimethoxysilane (silane coupling agent) was not added in step S1 of Comparative Example 1, while the rest is the same as Example 3.

[0060] Comparative Example 2:

[0061] The difference between Comparative Example 2 and Example 3 is that zirconium oxide (a coefficient of thermal expansion regulator) was not added in step S2 of Comparative Example 2, while the rest was the same as Example 3.

[0062] Comparative Example 3:

[0063] The difference between Comparative Example 3 and Example 3 is that cellulose ether was not added in step S3 of Comparative Example 3, while the rest is the same as Example 3.

[0064] The modified calcined kaolin samples prepared in Examples 1-3 and the modified calcined kaolin samples prepared in Comparative Examples 1-3 were subjected to performance tests, and the results are shown in Table 1.

[0065] The thermal expansion properties of modified calcined kaolin can be measured using thermal analysis instruments such as a thermal dilatometer. The particle size distribution method is employed for testing, and the D50 and D90 data are recorded.

[0066] Group <![CDATA[Coefficient of thermal expansion (×10 -6 / °C) (20 - 800°C)]]> Particle size distribution D50 (μm) Particle size distribution D90 (μm) Example 1 5.9 2.9 8.4 Example 2 6.1 2.8 7.9 Example 3 5.8 2.9 8.2 Comparative Example 1 7.2 20.3 80.6 Comparative Example 2 7.8 3.2 10.5 Comparative Example 3 6.9 15.3 70.9

[0067] Analysis of the data in Table 1 shows that the modification method of this invention can effectively adjust the thermal expansion coefficient of modified calcined kaolin, stabilizing it within the ideal range, achieving controllable thermal expansion coefficient, and adapting it to the thermal expansion coefficient of common ceramic bodies of 5-7×10⁻⁶. -6 At / ℃, due to the good matching between the coefficient of thermal expansion and the coefficient of thermal expansion of the ceramic body, the stress influence during sintering can be reduced, and defects can be decreased. In addition, the obtained modified calcined kaolin has better dispersibility. Compared with Example 3, Comparative Example 1 did not add vinyltrimethoxysilane (silane coupling agent), which affected the surface activity of the calcined kaolin. Since its dispersibility and surface activity were worse than those of Example 3, the modification effect was not as good as that of Example 3 when the coefficient of thermal expansion regulator was added, and the ideal coefficient of thermal expansion adjustment effect was not achieved. Comparative Example 2 did not add zirconium oxide (coefficient of thermal expansion regulator), and had a higher coefficient of thermal expansion. Comparative Example 3 did not add cellulose ether, and its dispersibility was poor, which affected the coefficient of thermal expansion adjustment effect. In summary, the treatment steps of adding silane coupling agent and cellulose ether in this application can help to obtain a stable coefficient of thermal expansion adjustment effect, and the modified calcined kaolin has excellent dispersibility. That is, it can achieve both coefficient of thermal expansion adjustment and obtain modified calcined kaolin with significant dispersibility, which has better application performance.

[0068] Application example:

[0069] The modified calcined kaolin prepared in Example 3 was used in the preparation of ceramic green bodies. The ceramic green bodies in the application example were prepared using the following methods:

[0070] By weight, 30 parts of ball clay, 15 parts of bentonite, 25 parts of quartz, 15 parts of wollastonite, 8 parts of sodium feldspar, 10 parts of potassium feldspar, and 20 parts of calcined kaolin prepared in Example 3 were mixed, wet ball milled to make slurry, prepared, poured into molds, demolded, dried, and fired to obtain ceramic green bodies.

[0071] Performance tests were conducted on the ceramic green body corresponding to the application example. The results showed that the coefficient of thermal expansion of the ceramic green body in the application example at 200℃ was 6.1×10⁻⁶. -6 The hygroscopic expansion rate was 0.09% at ℃, the absorption rate was 8.1%, the flexural strength after firing was 72.6 MPa, and the crack resistance was excellent with no stress cracks observed. This indicates that the modified calcined kaolin of this application has high compatibility in the preparation of ceramic green bodies and can produce ceramic green bodies with excellent performance.

[0072] The above embodiments are only used to illustrate the implementation process and features of the present invention, and are not intended to limit the technical methods of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention without departing from the spirit and scope of the present invention. Any modifications or partial substitutions should be covered within the protection scope of the present invention.

Claims

1. A method for modifying calcined kaolin, characterized in that, Includes the following steps: S1. The calcined kaolin raw material is pretreated as follows: the calcined kaolin raw material is mixed with water to prepare a slurry, then sodium carboxymethyl cellulose and silane coupling agent are added, and the mixture is stirred at 100 r / min to 500 r / min for 1 h to 2 h, and then concentrated to a mass concentration of 30% to 50%; S2. The pretreated calcined kaolin is mixed with a thermal expansion coefficient regulator and ball-milled to obtain a mixture; The thermal expansion coefficient regulator includes at least one of silicon dioxide, aluminum titanate, magnesium oxide, zirconium oxide, and calcium oxide. S3. Add the mixture to treatment agent A, stir under certain conditions, then add treatment agent B, and continue stirring to obtain modified slurry; Wherein, the treatment agent A is an aqueous dispersion of tetraisopropyl titanate, and the mass percentage content of tetraisopropyl titanate is 12%~20%; the treatment agent B is cellulose ether. S4. After heat treatment and spray drying of the modified slurry, modified calcined kaolin is obtained.

2. The modification method according to claim 1, characterized in that, In step S2, the weight ratio of calcined kaolin to thermal expansion coefficient regulator is 100:(1~15).

3. The modification method according to claim 1, characterized in that, In step S2, the ball milling speed is 100 r / min to 500 r / min, and the ball milling time is 1 h to 3 h.

4. The modification method according to claim 1, characterized in that, In step S3, the weight ratio of the mixture, treatment agent A and treatment agent B is (20~25):(35~50):(25~45).

5. The modification method according to claim 1, characterized in that, In step S4, the heat treatment is as follows: the temperature is increased to 120℃~150℃ at a heating rate of 3℃ / min~8℃ / min, and then held at that temperature for 20min~60min.

6. An application of modified calcined kaolin, characterized in that, The application refers to the use of modified calcined kaolin obtained by the modification method according to any one of claims 1 to 5 in the preparation of ceramic bodies and / or ceramic glazes.