Silica sol and aluminum titanate based castable, preparation method and application thereof

Abstract

The application discloses a functional adjustment type heat shock resistant alkali resistant castable based on silica sol and aluminum titanate and a preparation method and application thereof. The castable comprises 50-60% mullite, 10-13% silicon carbide, 8-10% micro powder of microcline, 0.5-1.5% boron nitride nanosheet, 1-3% rare earth oxide, 10-14% silica sol (dry base), 8-12% functional regulator (containing metakaolin and aluminum titanate) and 0.1-0.3% dispersant. The application breaks through the technical prejudice of "thermal instability" of aluminum titanate, realizes multiphase synergistic reinforcement, and is suitable for high damage areas such as a cement rotary kiln mouth and a coal injection pipe.

Description

Technical Field

[0001] This invention belongs to the field of refractory materials technology, specifically relating to a high-performance cement-free castable, and more particularly to a castable based on silica sol synergistic aluminum titanate, its preparation method, and its application. Background Technology

[0002] The rotary kiln is the core equipment for cement clinker calcination. Its kiln mouth, pulverized coal injection pipe, cooling zone, and other areas are subjected to complex conditions such as high temperature (1100–1450℃), severe thermal shock, alkali vapor erosion, molten clinker scouring, and mechanical wear. Traditional high-alumina castables or low-cement castables, due to their high CaO content, rapid decline in high-temperature performance, and poor thermal shock resistance, can no longer meet the requirements of modern cement kilns for high efficiency, long service life, and energy saving.

[0003] In recent years, silica sol-bonded castables have attracted widespread attention due to their advantages such as being cement-free, low in impurities, and capable of high-temperature self-sintering. After dehydration, silica sol forms a Si–O–Si network, providing good low-temperature strength, and reacts with Al2O3 at high temperatures to form mullite, further enhancing the bonding strength. However, existing silica sol systems still have some problems, such as weak interfacial bonding between pure silica sol and inert aggregates (such as mullite), resulting in limited improvement in high-temperature strength.

[0004] Thermal shock resistance mainly relies on microcracks, which are difficult to cope with the accumulation of thermal stress caused by frequent start-stop cycles; alkali metals (K2O, Na2O) in the environment are prone to react with SiO2 to form low-melting-point alkali silicates, leading to loose structure and spalling.

[0005] To improve performance, existing technologies often incorporate nano-SiO2, alumina micropowder, or zircon. For example, CN117567140A discloses a mullite composite castable for enhancing seismic resistance, comprising, by mass ratio: 18–20% andalusite aggregate, 35–50% corundum aggregate, 4–5% micropowder, 7.5–8.5% silica sol, 0.5–1.2% antifreeze agent, 0.8–1.0% steel fiber, 0.4–0.6% silicon carbide nanoparticles, 0.2–0.3% sound-absorbing fiber sponge powder, and the balance being porous mullite; the micropowder is composed of alumina and silicon dioxide in a mass ratio of 2.5–3.2:1. The use of andalusite aggregate in this castable strengthens the bond between the aggregate and the matrix, which not only improves thermal shock resistance but also increases the high-temperature rupture modulus of the castable after firing. The addition of alumina and silica works together to significantly improve the strength and other properties of the castable. The addition of steel fibers can improve the fracture toughness and crack propagation resistance of the castable.

[0006] However, at locations such as the rear kiln inlet and pulverized coal injection pipe in cement rotary kilns, the heat load increases, requiring refractory materials to withstand higher temperatures and mechanical stresses. Increased kiln speed exacerbates the wear and thermal shock damage to refractory materials caused by clinker. This results in a relatively short service life for existing castables in these locations, making them prone to localized cracking and spalling. Summary of the Invention

[0007] This invention aims to solve the problems of insufficient high-temperature strength, poor thermal shock resistance, weak alkali corrosion resistance, and difficulty in sintering densification of existing silica sol-bonded castables. It provides a composite castable based on silica sol synergistic aluminum titanate, its preparation method, and its application, which has high thermal shock resistance, high alkali corrosion resistance, and high high-temperature strength.

[0008] To achieve the above objectives, the present invention provides a castable based on silica sol and aluminum titanate, comprising the following components:

[0009] 50–60% mullite, 10–13% silicon carbide, 8–10% andalusite micropowder, 0.5–1.5% boron nitride nanosheets, 1–3% rare earth oxides, 10–14% silica sol, 8–12% functional modifiers, and 0.1–0.3% dispersant, wherein the functional modifiers include metakaolin and aluminum titanate.

[0010] In the above-described solution of the present invention, a pure calcium aluminate-free cement system is used, with silica sol replacing the adhesive function of cement. Simultaneously, to overcome the defects of the silica sol system as described in the background art, the composition of the castable is optimized, particularly by adding functional modifiers including metakaolin and aluminum titanate.

[0011] Aluminum titanate (Al2TiO5) has long been considered an "unstable phase" and is rarely used in structural refractory materials because it easily decomposes into Al2O3 and TiO2 at temperatures above 1280°C and has large anisotropy in thermal expansion, making it prone to microcracks.

[0012] However, the inventors discovered that in the highly active and highly dispersed SiO2 environment provided by silica sol, aluminum titanate can not only be stabilized but also react with SiO2 to form an aluminum titanate solid solution, creating a high-strength interfacial phase. This achieves in-situ strengthening of the matrix interface, while simultaneously utilizing its negative thermal expansion characteristics to regulate overall thermal stress. This discovery breaks through traditional technological biases and realizes a technological leap of "turning defects into functions."

[0013] Silica sol is a highly dispersed SiO2 colloidal solution with inherent good stability and film-forming properties. When combined with aluminum titanate, silica sol can form a protective film on the material surface, enhancing the material's chemical stability and mechanical strength. It can also effectively prevent the intrusion of external corrosive substances, thereby improving the material's corrosion resistance.

[0014] Furthermore, the metakaolinite and silica sol undergo a sol-gel synergistic reaction at 800–1200℃ to generate needle-like mullite in situ, forming a network-reinforced structure.

[0015] Preferably, the mass ratio of metakaolin to aluminum titanate in the functional regulator is (1.5–4):1, more preferably (2–3):1. This ensures a balance between the reaction driving force and structural stability; too much metakaolin can easily lead to shrinkage, while too little aluminum titanate results in insufficient thermal expansion regulation.

[0016] Preferably, the aluminum titanate has a particle size of 1–5 μm, which is used to utilize its negative thermal expansion characteristics along the c-axis (-8 to -10 × 10⁻⁶) during thermal cycling. -6 / K) compensates for the positive thermal expansion of mullite and silicon carbide, inhibiting the propagation of microcracks.

[0017] Preferably, the silica sol has a SiO2 content of 28–32 wt% and a pH of 8–10.

[0018] Preferably, the rare earth oxide includes at least one of CeO2 and La2O3, and reacts with alkali metal ions (Na+). + K + It forms a stable composite oxide, which inhibits the alkaline cracking reaction.

[0019] Preferably, the mullite comprises fused mullite and / or sintered mullite with a particle size distribution of 0.074–5 mm, forming a rigid skeleton structure.

[0020] Preferably, the castable has no through cracks after undergoing ≥50 cycles of water cooling thermal shock at 1100℃, and the erosion depth is less than 2.0 mm after 24 hours of alkali vapor erosion at 1350℃.

[0021] The present invention also provides a method for preparing the above-mentioned silica sol-based aluminum titanate casting material, comprising the following steps:

[0022] (1) Mullite, silicon carbide, andalusite powder, functional regulator, boron nitride nanosheets, rare earth oxides and dispersant are mixed to obtain dry-based material;

[0023] (2) Add silica sol and water, and stir until the flow value is ≥180 mm;

[0024] (3) Vibration molding, curing at 25–35℃ for 12–24 hours, then demolding;

[0025] (4) Dry at 110–150℃ for 8–24 hours;

[0026] (5) Heat treatment at 1100–1350℃ for 2–4 hours to promote the synergistic reaction between the functional regulator and the silica sol to obtain the casting material.

[0027] Preferably, the heat treatment temperature in step (5) is 1200–1300℃, and the holding time is 3 hours.

[0028] The present invention also provides the application of the above-mentioned castable in cement rotary kilns, especially for the lining of kiln mouth, pulverized coal injection pipe, cooling zone or transition zone, with an operating temperature of 1100–1450℃.

[0029] By implementing the above technical solution, compared with the prior art, the present invention has the following beneficial effects:

[0030] This invention, in a silica sol system, utilizes functional modifiers including metakaolin and aluminum titanate to solve the problem of weak interfacial bonding between silica sol and inert aggregates (such as mullite), and particularly overcomes the technical prejudice that aluminum titanate cannot be used in high-performance castables due to its thermal instability, achieving simultaneous improvement in thermal shock resistance, alkali resistance, and high-temperature strength. Specifically:

[0031] The aluminum titanate in the castable reacts with the active SiO2 provided by the silica sol at 1000–1350°C to form an aluminum titanate solid solution (Al2Ti). X Si 1-X O5) forms a high-strength chemical bonding interface, enhancing corrosion resistance; it can also use its negative thermal expansion along the c-axis to counteract the positive expansion of mullite and silicon carbide during thermal cycling, reducing the accumulation of thermal stress.

[0032] Metakaolin in the castable undergoes a sol-gel synergistic reaction with silica sol at 800–1200℃, generating needle-like mullite in situ and forming a network-reinforced structure.

[0033] Rare earth oxides and alkali metal ions (Na) in castables + K + It forms a stable composite oxide, which inhibits the alkaline cracking reaction. Detailed Implementation

[0034] The present invention will be further described in detail below through specific embodiments.

[0035] It should be noted that the following embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

[0036] Example 1

[0037] This embodiment provides a castable based on a silica sol system, particularly utilizing silica sol in synergy with aluminum titanate to improve the performance of the castable. The castable includes...

[0038] Fused mullite (3–5 mm particle size): 35%;

[0039] Sintered mullite (particle size 1–3 mm): 20%;

[0040] Silicon carbide (particle size ≤ 0.074 μm): 12%;

[0041] andalusite micro powder (particle size ≤ 0.045 μm): 9%;

[0042] Metakaolin (Al₂O₃ 43%, SiO₂ 53%, specific surface area 20 m²) 2 / g, D50=3 μm): 6.7%;

[0043] Aluminum titanate micron powder (Al2TiO5, particle size 1–5 μm): 3.3%;

[0044] Boron nitride nanosheets (BNNS, thickness <5 nm): 1%;

[0045] Rare earth oxide composite (CeO2 to La2O3 mass ratio of 3:1): 2%;

[0046] Silica sol (SiO2 content 30 wt%): 12%, on a dry basis;

[0047] Dispersant: Citric acid: 0.2%.

[0048] Example 2

[0049] This embodiment provides a castable based on a silica sol system, particularly utilizing silica sol in synergy with aluminum titanate to improve the performance of the castable. The castable includes...

[0050] Fused mullite (3–5 mm particle size): 40%;

[0051] Sintered mullite (particle size 1–3 mm): 20%;

[0052] Silicon carbide (particle size ≤ 0.074 μm): 10%;

[0053] andalusite micro powder (particle size ≤ 0.045 μm): 8%;

[0054] Metakaolin (Al₂O₃ 43%, SiO₂ 53%, specific surface area 20 m²) 2 / g, D50=3 μm): 8%;

[0055] Aluminum titanate micron powder (Al2TiO5, particle size 1–5 μm): 4%;

[0056] Boron nitride nanosheets (BNNS, thickness <5 nm): 1.5%;

[0057] Rare earth oxide composite (CeO2 to La2O3 mass ratio of 3:1): 2%;

[0058] Silica sol (SiO2 content 30wt%): 14%, on a dry basis;

[0059] Dispersant: Citric acid: 0.2%.

[0060] Example 3

[0061] This embodiment provides a castable based on a silica sol system, particularly utilizing silica sol in synergy with aluminum titanate to improve the performance of the castable. The castable includes...

[0062] Fused mullite (3–5 mm particle size): 38%;

[0063] Sintered mullite (particle size 1–3 mm): 18%;

[0064] Silicon carbide (particle size ≤ 0.074 μm): 12%;

[0065] andalusite micro powder (particle size ≤ 0.045 μm): 10%;

[0066] Metakaolin (Al₂O₃ 43%, SiO₂ 53%, specific surface area 20 m²) 2 / g, D50=3 μm): 7%;

[0067] Aluminum titanate micron powder (Al2TiO5, particle size 1–5 μm): 3%;

[0068] Boron nitride nanosheets (BNNS, thickness <5 nm): 1%;

[0069] Rare earth oxide composite (CeO2 to La2O3 mass ratio of 3:1): 2%;

[0070] Silica sol (SiO2 content 30 wt%): 12%, on a dry basis;

[0071] Dispersant: Citric acid: 0.2%.

[0072] Example 4

[0073] This embodiment provides a castable based on a silica sol system, particularly utilizing silica sol in synergy with aluminum titanate to improve the performance of the castable. The castable includes...

[0074] Fused mullite (3–5 mm particle size): 35%;

[0075] Sintered mullite (particle size 1–3 mm): 20%;

[0076] Silicon carbide (particle size ≤ 0.074 μm): 12%;

[0077] andalusite micro powder (particle size ≤ 0.045 μm): 9%;

[0078] Metakaolin (Al₂O₃ 43%, SiO₂ 53%, specific surface area 20 m²) 2 / g, D50=3 μm): 7%;

[0079] Aluminum titanate micron powder (Al2TiO5, particle size 1–5 μm): 1%;

[0080] Boron nitride nanosheets (BNNS, thickness <5 nm): 1%;

[0081] Rare earth oxide composite (CeO2 to La2O3 mass ratio of 3:1): 2%;

[0082] Silica sol (SiO2 content 30 wt%): 12%, on a dry basis;

[0083] Dispersant: Citric acid: 0.2%.

[0084] Example 5

[0085] This embodiment provides a castable based on a silica sol system, particularly utilizing silica sol in synergy with aluminum titanate to improve the performance of the castable. The castable includes...

[0086] Fused mullite (3–5 mm particle size): 35%;

[0087] Sintered mullite (particle size 1–3 mm): 20%;

[0088] Silicon carbide (particle size ≤ 0.074 μm): 12%;

[0089] andalusite micro powder (particle size ≤ 0.045 μm): 9%;

[0090] Metakaolin (Al₂O₃ 43%, SiO₂ 53%, specific surface area 20 m²) 2 / g, D50=3 μm): 5%;

[0091] Aluminum titanate micro powder (Al2TiO5 particle size 1–5 μm): 5%;

[0092] Boron nitride nanosheets (BNNS, thickness <5 nm): 1%;

[0093] Rare earth oxide composite (CeO2 to La2O3 mass ratio of 3:1): 2%;

[0094] Silica sol (SiO2 content 30wt%): 12%, on a dry basis;

[0095] Dispersant: Citric acid: 0.2%.

[0096] Comparative Example 1:

[0097] This comparative example provides a castable that differs from Example 1 in that the functional modifier does not contain aluminum titanate, but only metakaolin: 10%.

[0098] Comparative Example 2:

[0099] This comparative example provides a castable refractories, which differs from Example 1 in that the functional modifier is:

[0100] Metakaolin: 6.7%;

[0101] Nano SiO2: 3.3%.

[0102] Comparative Example 3:

[0103] This comparative example provides a castable that differs from Example 1 in that the functional modifier does not contain metakaolin, but only aluminum titanate: 10%.

[0104] The castables of each embodiment and comparative example can be prepared according to the following preparation method:

[0105] (1) Mix fused mullite, sintered mullite, silicon carbide, andalusite, metakaolinite, aluminum titanate micro powder, nano-zirconia, boron nitride nanosheets, rare earth oxide composite, β-alumina micro powder and dispersant to obtain dry-based material;

[0106] (2) Add silica sol and water (the amount of water added should be adjusted to a slurry flow value of about 200 mm (determined according to GB / T22459.3-2008)), stir until good fluidity, and then vibrate to form the slurry;

[0107] (3) Vibration molding, curing at 25–35℃ for 12–24 hours, then demolding;

[0108] (4) Dry at 110–150℃ for 8–24 hours;

[0109] (5) Heat treatment at 1100–1350℃ for 2–4 hours to promote the synergistic reaction between the functional regulator and the silica sol to obtain the casting material.

[0110] To fully verify the technical effects of the present invention, the following system performance tests were conducted on the samples of each embodiment and comparative example. All samples were prepared according to the aforementioned method, and after demolding, they were dried at 110°C for 24 hours, then heat-treated at 1250°C for 3 hours, and their performance was tested after cooling.

[0111] I. Testing Items and Methods

[0112] Table 1. Test Items and Methods

[0113] Testing items Testing standards / methods illustrate High temperature flexural strength GB / T 3002-2017 Flexural strength was determined at 1400℃. thermal shock resistance GB / T 30873-2014 Heating at 1100℃ for 15 minutes, followed by rapid cooling with compressed air at 0.1MPa (at room temperature) as the cooling medium, is performed to check for cracks. This process is repeated until a through crack appears, and the number of cycles is recorded. Alkali erosion resistance YB / T 5200-1993 <![CDATA[Alkali vapor erosion at 1350°C for 24 h (in K2CO3 atmosphere), slice observation of erosion depth]]>

[0114] II. Test Results

[0115] Table 2 Test Results

[0116] sample Flexural strength (MPa) at 1400℃ Thermal shock cycles (times) Alkali erosion depth (mm) Example 1 11.8 48 1.5 Example 2 10.5 40 1.8 Example 3 11.0 45 1.7 Example 4 9.8 35 2.3 Example 5 10.2 38 2.0 Comparative Example 1 8.0 22 5.3 Comparative Example 2 9.6 31 3.8 Comparative Example 3 8.2 26 4.5

[0117] According to the test results in Table 2, the castables obtained using the technical solution of this invention in Examples 1–5 are superior to the comparative examples in terms of high-temperature flexural strength, thermal shock cycling, and alkali corrosion resistance. Specifically, Example 1 achieved a flexural strength of 11.8 MPa at 1400℃, a 47.5% increase compared to Comparative Example 1 (8.0 MPa). After 48 thermal shock cycles, no through-cracks were observed, far exceeding Comparative Example 1 (22 cycles). The alkali corrosion depth was only 1.5 mm, significantly lower than Comparative Example 1 (4.5 mm). This demonstrates that aluminum titanate plays a crucial role in the silica sol system of the castable; without the addition of aluminum titanate, the various properties of the castable significantly decreased to varying degrees.

[0118] Although the performance of Comparative Example 2 decreased less than that of Comparative Example 1, it still showed a significant difference from Example 1. This indicates that aluminum titanate in the castable of the present invention is the key to improving high-temperature performance and alkali resistance, and nano-SiO2 cannot completely replace aluminum titanate to achieve the dual functions of negative expansion and interface reconstruction.

[0119] Compared to Example 1, Comparative Example 3, which did not contain metakaolin, also showed a decline in performance, indicating that metakaolin and aluminum titanate have a certain synergistic effect, jointly improving the overall performance of the castable.

[0120] Comparing Examples 4 and 5 with Example 1, the ratio of metakaolin to aluminum titanate in the functional modifier was adjusted. In Example 4, metakaolin was dominant in the functional modifier, while the aluminum titanate content was too low, failing to fully realize the synergistic effect. In Example 5, the insufficient metakaolin resulted in insufficient driving force for the sol-gel reaction, weakened network reinforcement, and a decline in the performance of the castable.

Claims

1. A castable based on a silica sol in synergy with aluminum titanate, characterized in that, It comprises the following components: 50–60% mullite, 10–13% silicon carbide, 8–10% andalusite micro powder, 0.5–1.5% boron nitride nanosheets, 1–3% rare earth oxides, 10–14% silica sol, 8–12% functional modifier, and 0.1–0.3% dispersant, wherein the functional modifier includes metakaolin and aluminum titanate; the mass ratio of metakaolin to aluminum titanate in the functional modifier is (1.5–4):1; and the particle size of the aluminum titanate is 1–5 μm.

2. A silicon sol based castable according to claim 1, wherein In the functional regulator, the mass ratio of metakaolin to aluminum titanate is (2–3):

1.

3. A silicon sol based castable according to claim 1, wherein The SiO2 content of the silica sol is 28–32 wt%.

4. A silicon sol based castable according to claim 1, wherein The rare earth oxides include at least one of CeO2 and La2O3.

5. A method for preparing a castable based on silica sol and aluminum titanate as described in any one of claims 1-4, characterized in that, Includes the following steps: (1) Mullite, silicon carbide, andalusite powder, functional regulator, boron nitride nanosheets, rare earth oxides and dispersant are mixed to obtain dry-based material; (2) Add silica sol and water to the dry base material and stir until the flow value is ≥180 mm to obtain a slurry; (3) Vibrate the slurry to form a mold, cure it at 25–35℃ for 12–24 hours, and then demold to obtain the demolded product; (4) Dry the demolded product at 110–150°C for 8–24 hours to obtain the dried product; (5) The dried product is heat-treated at 1100–1350°C for 2–4 hours to promote the synergistic reaction between the functional regulator and the silica sol to obtain the casting material.

6. The preparation method according to claim 5, characterized in that, The heat treatment temperature in step (5) is 1200–1300℃, and the holding time is 3 hours.

7. The application of a silica sol-based castable synergistic with aluminum titanate as described in any one of claims 1-4, characterized in that, Used in cement rotary kilns.

8. The application according to claim 7, characterized in that, Kiln inlet and pulverized coal injection pipe used in cement rotary kilns.