Sodium caseinate modified silica sol bonded silicon carbide castable and method of making

Abstract

The application discloses a kind of sodium caseinate modified silica sol combined with silicon carbide castable and preparation method thereof, its composition is by mass percentage: silicon carbide particle 56~68%, silicon carbide powder 18‑25%, silicon micro powder 2~5%, active alumina powder 7‑14%, composite additive 1~2%, water reducing agent 0.05‑0.1%, on this basis, additional sodium caseinate modified silica sol 7.2~8.5wt%;Wherein, the sodium caseinate modified silica sol is formed by mixing sodium caseinate and silica sol, wherein the amount of sodium caseinate is 0.5‑2% of the mass of silica sol;The low temperature strength of the silicon carbide castable combined with sodium caseinate modified silica sol added in the application is significantly improved, and the stability and system uniformity of the silicon carbide castable are also improved, which provides an effective solution to the problems of low low temperature strength and easy precipitation and stratification of the silica sol combined with silicon carbide castable, and promotes the large-scale popularization and application of the silica sol combined with silicon carbide castable.

Description

Technical Field

[0001] This invention belongs to the technical field of unshaped refractory materials, specifically relating to a silicon carbide castable and its preparation method. Background Technology

[0002] The safe, stable operation and extended service life of blast furnaces are core prerequisites for ensuring continuous production and improving economic efficiency in steel enterprises. Therefore, the extreme operating conditions of blast furnaces, characterized by high temperature, high pressure, and dust erosion, place even more stringent demands on the comprehensive performance of refractory materials, including their high-temperature resistance, erosion resistance, corrosion resistance, and structural stability. Currently, the refractory materials used in blast furnace systems are highly susceptible to severe damage under the intense erosion of high-temperature molten slag and the long-term effects of various corrosive impurities, leading to structural defects such as cracking and pitting. In extreme cases, this can even cause material collapse and spalling, posing a significant threat to production safety and the safety of personnel and property.

[0003] Silicon carbide castables possess excellent properties such as good structure and organization, high purity, low creep rate, low thermal expansion, good thermal shock resistance, and strong resistance to chemical attack. They are mainly used for linings of blast furnaces, hot blast stoves, and other furnaces. Aluminate cement is widely used as a binder for silicon carbide castables due to its good rheological properties and high early strength; however, its low strength at medium and high temperatures, poor durability, and long construction period limit its large-scale use. With the continuous research and application of nanotechnology in the refractory materials industry, silica sol as a binder for refractory castables has become a research hotspot both domestically and internationally. Compared to aluminate cement, silica sol binding systems can avoid the introduction of Ca2+. 2+ Therefore, the castable does not form low-melting-point substances such as calcium feldspar, calcium aluminum feldspar, and tricalcium aluminate at high temperatures, significantly enhancing its erosion resistance and medium-to-high temperature strength. At the same time, the silica sol-bonded system does not produce hydration products and has extremely low crystal water content, enabling rapid construction and baking of the castable, greatly shortening the overall construction cycle.

[0004] However, silica sol-bonded silicon carbide castables face critical technical bottlenecks that urgently need to be addressed: insufficient low-temperature strength and a tendency to precipitate and delaminate. These defects severely restrict the large-scale application of silica sol-bonded silicon carbide castables. The reason for this is that the low-temperature strength of the castable mainly depends on the condensation reaction of siloxane groups (-Si-OH) within the system. However, at low temperatures, the spontaneous condensation degree of siloxane groups is extremely low, resulting in a sparse siloxane bond (Si-O-Si) cross-linked network that is difficult to form a three-dimensional network structure in a short time. The interfacial bonding between particles is weak, making it difficult to support the green body with the mechanical properties required for transport and transfer. Summary of the Invention

[0005] To address the technical shortcomings of silica sol-bonded silicon carbide castables, such as insufficient low-temperature strength and susceptibility to precipitation and stratification, this invention provides a sodium caseinate-modified silica sol-bonded silicon carbide castable. The addition of sodium caseinate significantly improves the low-temperature strength of the silica sol-bonded silicon carbide castable, while also enhancing its stability and system homogeneity. This provides an effective solution to the problems of low low-temperature strength and susceptibility to precipitation and stratification in silica sol-bonded silicon carbide castables, thus promoting the large-scale application of silica sol-bonded silicon carbide castables.

[0006] To achieve the above objectives, the following technical solution is adopted: A sodium caseinate-modified silica sol-bonded silicon carbide castable, comprising, by mass percentage: 56-68% silicon carbide particles, 18-25% silicon carbide powder, 2-5% silica micropowder, 7-14% activated alumina powder, 1-2% composite additives, 0.05-0.1% water-reducing agent, and 7.2-8.5 wt% sodium caseinate-modified silica sol; wherein the sodium caseinate-modified silica sol is prepared by mixing sodium caseinate with silica sol, and the amount of sodium caseinate is 0.5-2% of the mass of silica sol.

[0007] According to the above scheme, the preparation method of the sodium caseinate modified silica sol includes the following steps: Sodium caseinate is prepared by adding it to silica sol, stirring for 10-15 min, and then ultrasonically mixing for 20-30 min to ensure complete dissolution.

[0008] According to the above scheme, the sodium caseinate has a protein content of 70wt%~85wt% and a particle size of ≤0.074mm.

[0009] According to the above scheme, the particle size of the silica sol is 10-30 nm; and the mass fraction of SiO2 is 25wt%-35wt%.

[0010] According to the above scheme, the silicon carbide particles are composed of three types of silicon carbide particles with particle sizes of 5~3 mm, 3~1 mm, and 1~0 mm, mixed in a mass ratio of 1:(2.8-3.2):(2.0~2.3); wherein the SiC content is ≥96wt%.

[0011] According to the above scheme, the particle size of the silicon carbide powder is ≤0.074mm; and the SiC content is ≥96wt%.

[0012] According to the above scheme, the particle size of the silicon micro powder is ≤5μm; and the SiO2 content is ≥96wt%.

[0013] According to the above scheme, the particle size of the activated alumina powder is ≤5μm; and the Al2O3 content is ≥98wt%.

[0014] According to the above scheme, the composite additive is a mixture of magnesium oxide particles and boron carbide particles in a mass ratio of 1:(1.5-2.5); the particle size of the composite additive is ≤0.088mm.

[0015] According to the above scheme, the water-reducing agent is one or more of sodium hexametaphosphate, sodium pyrophosphate, and sodium tripolyphosphate; the particle size of the water-reducing agent is ≤0.074mm.

[0016] This invention also provides a method for preparing the above-mentioned sodium caseinate modified silica sol-bonded silicon carbide castable, comprising the following steps: Silicon carbide particles, silicon carbide powder, silicon micro powder, activated alumina powder, composite additives, and water-reducing agents are mechanically mixed into a dry, uniform aggregate. Then, sodium caseinate-modified silica sol is added, and the mixture is thoroughly mixed and stirred until homogeneous to obtain sodium caseinate-modified silica sol-bonded silicon carbide castable.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. In existing technologies, the degree of spontaneous condensation reaction (-Si-OH + HO-Si- = -Si-O-Si-) in unmodified silica sol-bonded silicon carbide castables is extremely low, resulting in weak interparticle bonding. Consequently, the low-temperature strength of silicon carbide castables limits their large-scale industrial application. This invention solves this problem by significantly improving the low-temperature strength of sodium caseinate-modified silica sol-bonded silicon carbide castables. Firstly, this is because sodium caseinate molecules themselves can form a certain bonding force through hydrogen bonds, etc. Secondly, sodium caseinate undergoes hydrolysis in silica sol, and its carboxyl groups (-COOH) and amino groups (-NH2) can simultaneously react with the -Si-OH groups of the silica sol. When the carboxyl groups (-COOH) of sodium caseinate undergo esterification with the silanol groups (-Si-OH) on the surface of silica particles in the silica sol, some water is removed, forming -COO-Si- covalent bonds, thereby promoting the dehydration condensation reaction of the silica sol and forming a stable chemical bond. Meanwhile, because the amino group (-NH2) of sodium caseinate contains lone pair electrons, and the silicon atoms in silica sol have empty orbitals due to the difference in electronegativity, the two can form Si-N coordination bonds, which strengthens the connection between organic molecules and inorganic particles, and finally constructs a cross-linked structure of "organic polymer-inorganic particles", enhancing the low-temperature strength of silicon carbide castable.

[0018] 2. In existing technologies, due to the extremely low rate of spontaneous reaction in silica sol, nano-SiO2 particles in the silica sol are prone to agglomeration and sedimentation due to Brownian motion and gravity, making it difficult to form a three-dimensional network structure in a short time. Therefore, silicon carbide particles are prone to precipitation and stratification under gravity, leading to pipeline blockage during construction and causing inconvenience. When silica sol is modified with sodium caseinate, the formation of an "organic polymer-inorganic particle" cross-linked structure is accelerated. The long molecular chains of sodium caseinate act as "bridges" connecting the dispersed silica sol particles, forming a spatial network structure. On the one hand, this structure can prevent silica sol particles from approaching each other and agglomerating and precipitating through steric hindrance; on the other hand, this structure can improve the suspension and system homogeneity of silicon carbide castables, ensuring that the castables remain in a stable suspension state during construction and reducing stratification or precipitation.

[0019] 3. Prolonged exposure to high temperatures can lead to a decrease in the high-temperature strength of silicon carbide castables, resulting in large-scale spalling and collapse. However, this invention utilizes sodium caseinate-modified silica sol to significantly improve the high-temperature resistance of the silicon carbide castable. The addition of sodium caseinate significantly enhances the low-temperature strength of the castable, strengthens the bonding between particles, reduces porosity, and makes the material more dense. Therefore, the degree of sintering between castable particles is significantly improved in high-temperature environments. Simultaneously, sodium caseinate contains very little sodium (Na). + The formed liquid phase encourages the particles to fill the voids, which promotes sintering between particles and helps to improve the density of the castable, resulting in a significant increase in the high-temperature strength of the castable.

[0020] 4. In existing technologies, expensive additives or complex processes are typically used to improve the low-temperature strength of silica sol-bonded silicon carbide castables, resulting in highly unstable product performance and significantly increased production costs. The sodium caseinate added to the silicon carbide castable of this invention is inexpensive, readily available, safe, non-toxic, and has stable performance. It can significantly improve the low-temperature strength and high-temperature performance of silica sol-bonded castables, reducing production costs. Furthermore, the silicon carbide castable of this invention has a simple preparation process, produces high-quality products, requires no vibration equipment, and can uniformly fill narrow gaps and complex-shaped construction areas solely through its own fluidity, enabling large-scale production. Detailed Implementation

[0021] The following embodiments further illustrate the technical solution of the present invention, but are not intended to limit the scope of protection of the present invention.

[0022] The specific implementation method uses the following raw materials: a sodium caseinate modified silica sol combined with silicon carbide castable, the composition of which, by mass percentage, is: 56-68% silicon carbide particles, 18-25% silicon carbide powder, 2-5% silica micro powder, 7-14% activated alumina powder, 1-2% composite additives, 0.05-0.1% water-reducing agent, and 7.2-8.5 wt% sodium caseinate modified silica sol is added on this basis; wherein, the sodium caseinate modified silica sol is formed by mixing sodium caseinate and silica sol, and the amount of sodium caseinate is 0.5-2% of the mass of silica sol.

[0023] Specifically, the preparation method of the sodium caseinate modified silica sol includes the following steps: adding sodium caseinate to silica sol, stirring for 10-15 min, and then ultrasonically mixing for 20-30 min to fully dissolve it.

[0024] Specifically, the sodium caseinate has a protein content of 80 wt% and a particle size ≤0.074 mm. The silica sol has a particle size of 15 nm and a SiO2 mass fraction of 30 wt%. The silicon carbide particles are a mixture of three types of silicon carbide particles with particle sizes of 5-3 mm, 3-1 mm, and 1-0 mm in a mass ratio of 1:3:2.2, with a SiC content ≥96 wt%. The silicon carbide powder has a particle size ≤0.074 mm and a SiC content ≥96 wt%. The silica micropowder has a particle size ≤5 μm and a SiO2 content ≥96 wt%. The activated alumina powder has a particle size ≤5 μm and an Al2O3 content ≥98 wt%. The composite additive is a mixture of magnesium oxide particles and boron carbide particles in a mass ratio of 1:(1.5-2.5); the composite additive particle size is ≤0.088 mm. The water-reducing agent is sodium pyrophosphate with a particle size ≤0.074 mm. Unless otherwise specified, all raw materials used in the specific embodiments are commercially available.

[0025] Example 1 A sodium caseinate-modified silica sol-bonded silicon carbide castable is provided. The components and their mass percentages are as follows: 65% silicon carbide particles, 19% silicon carbide powder, 4% silica micropowder, 10% activated alumina powder, 1.93% composite additives, and 0.07% sodium pyrophosphate; 10.8 wt% sodium caseinate-modified silica sol is added externally. The sodium caseinate-modified silica sol is prepared by adding 0.8 wt% sodium caseinate to the silica sol, mechanically stirring for 10 min, and then ultrasonically mixing for 25 min until fully dissolved. The mass fraction of SiO2 in the silica sol used is 30%.

[0026] According to the above formula, silicon carbide particles, silicon carbide powder, silica powder, activated alumina powder, composite additives, and water-reducing agents are mechanically mixed into a dry, uniform aggregate, packaged, and transported to the construction site. Then, silica sol modified with sodium caseinate is added and stirred until uniformly mixed to obtain silicon carbide castable, which can be applied to the lining construction of blast furnaces and hot blast stoves. The performance test results of the silicon carbide castable obtained in this embodiment are shown in Table 1.

[0027] Comparative Example 1 A silica sol-bonded silicon carbide castable is provided, with the same raw materials and proportions as in Example 1, except that the silica sol is not modified. The performance test results of the silicon carbide castable obtained in this comparative example are shown in Table 1.

[0028] Example 2 A silicon carbide castable with sodium caseinate-modified silica sol is provided. The components and their mass percentages are as follows: 60% silicon carbide particles, 25% silicon carbide powder, 3% silica micropowder, 10% activated alumina powder, 1.91% composite additives, 0.09% sodium pyrophosphate, and 10.5% sodium caseinate-modified silica sol. The silica sol contains 30% SiO2 by mass. The sodium caseinate-modified silica sol is prepared by adding 0.5% (by mass) of sodium caseinate to the silica sol, mechanically stirring for 15 min, and then ultrasonically mixing for 20 min to ensure complete dissolution. The performance test results of the silicon carbide castable obtained in this embodiment are shown in Table 1.

[0029] Comparative Example 2 A silica sol-bonded silicon carbide castable is provided, with the same raw materials and proportions as in Example 2, except that the silica sol is not modified. The performance test results of the silicon carbide castable obtained in this comparative example are shown in Table 1.

[0030] Example 3 A sodium caseinate-modified silica sol-bonded silicon carbide castable is provided. The components and their mass percentages are as follows: silicon carbide particles 61%, silicon carbide powder 23%, silica micropowder 4%, activated alumina powder 10%, composite additives 1.9%, sodium pyrophosphate 0.1%, and added modified silica sol 11.5%. The mass fraction of SiO2 in the silica sol used is 30%. The sodium caseinate-modified silica sol is prepared by adding 2% (by mass) of sodium caseinate to the silica sol, mechanically stirring for 15 min, and then ultrasonically mixing for 20 min to ensure complete dissolution. The performance test results of the silicon carbide castable obtained in this embodiment are shown in Table 1.

[0031] Comparative Example 3 A silica sol-bonded silicon carbide castable is provided, with the same raw materials and proportions as in Example 3, except that the silica sol is not modified. The performance test results of the silicon carbide castable obtained in this comparative example are shown in Table 1.

[0032] Comparative Example 4 A silica sol-bonded silicon carbide castable is provided, with the following components and their mass percentages: 61% silicon carbide particles, 23% silicon carbide powder, 4% silica micropowder, 10% activated alumina powder, 1.9% composite additives, 0.1% sodium pyrophosphate, and 11.5% modified silica sol. The mass fraction of SiO2 in the silica sol is 30%. Specifically, 0.2% (by mass) of sodium caseinate is added to the silica sol, mechanically stirred for 15 min, and then ultrasonically mixed for 20 min to ensure complete dissolution, thus obtaining the modified silica sol for later use. The performance test results of the silicon carbide castable obtained in this comparative example are shown in Table 1.

[0033] Comparative Example 5 The sodium caseinate-modified silica sol-bonded silicon carbide castable has the following components and their mass percentages: silicon carbide particles 61%, silicon carbide powder 23%, silica micropowder 4%, activated alumina powder 10%, composite additives 1.9%, sodium pyrophosphate 0.1%, and added modified silica sol 11.5%. The mass fraction of SiO2 in the silica sol used is 30%. Specifically, 2.5% (by mass) of sodium caseinate was added to the silica sol, mechanically stirred for 15 min, and then ultrasonically mixed for 20 min to ensure complete dissolution, thus obtaining the modified silica sol for later use. The performance test results of the silicon carbide castable obtained in this comparative example are shown in Table 1.

[0034] Table 1 Performance Test Results

[0035] As can be seen from the data in Table 1, by modifying silica sol with sodium caseinate and using the modified silica sol as a binder for silicon carbide castables, the flexural and compressive strengths of the castables at low, medium, and high temperatures are significantly higher than those of unmodified silica sol-bound silicon carbide castables. In particular, after curing at 110℃ for 24 hours, the flexural and compressive strengths of the unmodified silica sol-bound silicon carbide castables are only about 4.5 MPa and 24 MPa, respectively. After curing at 110℃ for 24 hours, the flexural and compressive strengths reach over 8.0 MPa and 30 MPa, respectively. Because the degree of spontaneous condensation reaction (-Si-OH+HO-Si-=-Si-O-Si-) in the silica sol-bound castables is extremely low, the bonding force between particles is weak, thus resulting in lower low-temperature strength. This technical solution modifies silica sol. When an appropriate amount of sodium caseinate is added to the silica sol, on the one hand, the sodium caseinate molecules themselves can form a certain binding force through hydrogen bonds, etc. On the other hand, sodium caseinate undergoes hydrolysis in the silica sol, and its carboxyl groups (-COOH) and amino groups (-NH2) can simultaneously react with the -Si-OH groups of the silica sol. When the carboxyl groups (-COOH) of sodium caseinate undergo an esterification reaction with the silanol groups (-Si-OH) on the surface of silica particles in the silica sol, some water is removed, forming -COO-Si- covalent bonds, thereby promoting the dehydration condensation reaction of the silica sol and forming a stable chemical bond. At the same time, since the amino group (-NH2) of sodium caseinate contains lone pair electrons, and the silicon atoms in the silica sol have empty orbitals due to the difference in electronegativity, the two can form Si-N coordination bonds, which strengthens the connection between organic molecules and inorganic particles, ultimately constructing a cross-linked structure of "organic polymer-inorganic particles" and enhancing the low-temperature strength of silicon carbide castables. When the bonding force between particles is strong, the porosity of the castable is significantly reduced (see Table 1), making the material more compact. Therefore, the degree of sintering between castable particles is significantly improved in high-temperature environments. Meanwhile, sodium caseinate contains very little sodium. + The formed liquid phase encourages particles to fill the voids, which also promotes sintering between particles, increases the packing density of the castable, and effectively reduces the post-firing linear shrinkage rate (see Table 1), significantly improving the high-temperature strength of the castable. Furthermore, the long molecular chains of sodium caseinate act as "bridges" connecting dispersed silica sol particles, forming a spatial network structure. On one hand, this structure can prevent silica sol particles from agglomerating and precipitating due to steric hindrance; on the other hand, it can improve the suspension and system homogeneity of the silicon carbide castable, ensuring the castable remains in a stable suspension state during construction and reducing stratification or sedimentation. Therefore, as shown in Table 1, when the flow values ​​are similar, the suspension time of the castable modified with sodium caseinate silica sol is significantly prolonged.

[0036] However, comparing the results of Example 3 and Comparative Example 4, it can be seen that when the amount of sodium caseinate added is insufficient, the suspension time is significantly shortened. Although the addition of a small amount of sodium caseinate has a certain effect on improving the strength and suspension of silicon carbide castables, the improvement effect is limited. Comparative Example 5 added excessive sodium caseinate, which led to an increase in the viscosity of the silica sol system, a significant increase in apparent porosity, and a significant decrease in the flow value of the silicon carbide castable. The results indicate that the strength and suspension time of the castable prepared in Comparative Example 5 are lower than those in Example 3.

[0037] In summary, this invention modifies silica sol using sodium caseinate and uses the modified silica sol as a binder for silicon carbide castables. Compared to unmodified silica sol-bound castables, the low-temperature and high-temperature strength of the silicon carbide castables are significantly improved, while suspension properties are enhanced and construction time is extended. This provides an effective solution to the problems of low demolding strength and easy sedimentation in silica sol-bound silicon carbide castables at low temperatures, and further promotes the widespread application of silica sol-bound silicon carbide castables. Furthermore, the modified silica sol, sodium caseinate, is environmentally friendly, non-toxic, inexpensive, readily available, and has stable performance, significantly reducing production costs. In addition, the silicon carbide castable preparation process of this invention is simple and effective, requires low equipment requirements, and can be mass-produced industrially, offering good economic benefits and broad development prospects.

Claims

1. A sodium caseinate modified silica sol-bonded silicon carbide castable, characterized in that... The composition, by mass percentage, is as follows: 56-68% silicon carbide particles, 18-25% silicon carbide powder, 2-5% silica micropowder, 7-14% activated alumina powder, 1-2% composite additives, 0.05-0.1% water-reducing agent, and 7.2-8.5 wt% sodium caseinate modified silica sol is added on top of this. The sodium caseinate modified silica sol is formed by mixing sodium caseinate with silica sol, wherein the amount of sodium caseinate is 0.5-2% of the mass of silica sol.

2. The sodium caseinate modified silica sol-bonded silicon carbide castable as described in claim 1, characterized in that... The preparation method of the sodium caseinate modified silica sol includes the following steps: Sodium caseinate is prepared by adding it to silica sol, stirring for 10-15 min, and then ultrasonically mixing for 20-30 min to ensure complete dissolution.

3. The sodium caseinate modified silica sol-bonded silicon carbide castable as described in claim 2, characterized in that... The sodium caseinate has a protein content of 70wt%~85wt% and a particle size of ≤0.074mm.

4. The sodium caseinate modified silica sol-bonded silicon carbide castable as described in claim 2, characterized in that... The particle size of the silica sol is 10-30 nm; the mass fraction of SiO2 is 25 wt%-35 wt%.

5. The sodium caseinate modified silica sol-bonded silicon carbide castable as described in claim 1, characterized in that... The silicon carbide particles are composed of three types of silicon carbide particles with particle sizes of 5~3 mm, 3~1 mm, and 1~0 mm, mixed in a mass ratio of 1:(2.8-3.2):(2.0~2.3); wherein the SiC content is ≥96wt%.

6. The sodium caseinate modified silica sol-bonded silicon carbide castable as described in claim 1, characterized in that... The silicon carbide powder has a particle size ≤0.074mm and a SiC content ≥96wt%.

7. The sodium caseinate modified silica sol-bonded silicon carbide castable as described in claim 1, characterized in that... The silicon micropowder has a particle size of ≤5μm and a SiO2 content of ≥96wt%.

8. The sodium caseinate modified silica sol-bonded silicon carbide castable as described in claim 1, characterized in that... The activated alumina powder has a particle size ≤ 5 μm and an Al2O3 content ≥ 98 wt%.

9. The sodium caseinate modified silica sol-bonded silicon carbide castable as described in claim 1, characterized in that... The composite additive is a mixture of magnesium oxide particles and boron carbide particles in a mass ratio of 1:(1.5-2.5); the particle size of the composite additive is ≤0.088mm; the water-reducing agent is one or more of sodium hexametaphosphate, sodium pyrophosphate, and sodium tripolyphosphate; the particle size of the water-reducing agent is ≤0.074mm.

10. The preparation method of the sodium caseinate modified silica sol-bonded silicon carbide castable according to claim 1, characterized in that... Includes the following steps: Silicon carbide particles, silicon carbide powder, silicon micro powder, activated alumina powder, composite additives, and water-reducing agents are mechanically mixed into a dry, uniform aggregate. Then, sodium caseinate-modified silica sol is added, and the mixture is thoroughly mixed and stirred until homogeneous to obtain sodium caseinate-modified silica sol-bonded silicon carbide castable.

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