Modified hollow silicate as well as preparation method and application thereof

Abstract

The invention discloses modified hollow silicate as well as a preparation method and application thereof, the modified hollow silicate provided by the invention is obtained by taking octa (phenyldimethoxysiloxy) polyhedral oligomeric silsesquioxane as a modifier and carrying out surface modification on hollow silicate by adopting the modifier. Compared with an unmodified silicate filler, the modified hollow silicate has good compatibility and reactivity in a silicone rubber thermal insulation material, and when the modified hollow silicate is used in a silicone rubber thermal protection material, the problem that high mechanics, low density and excellent ablation resistance of the existing silicone rubber thermal protection material are difficult to balance can be effectively solved; on the premise of ensuring the mechanical property and the ablation resistance, the total proportion of the formula filler is reduced, so that the viscosity of the silicone rubber-based thermal insulation material is reduced, and the silicone rubber-based thermal insulation material has good spraying process performance.

Description

Technical Field

[0001] The present invention relates to the technical field of powder modification and surface thermal protection materials, and in particular to a modified hollow silicate and a preparation method and application thereof. Background Art

[0002] Thermal protection materials are essential for ensuring the safe and stable operation of aerospace vehicles in extreme environments. With the continued development of manned spaceflight, deep space exploration, and new aircraft, lightweight, high-strength, and highly effective ablation-resistant thermal protection systems are in urgent demand. Excessively heavy thermal protection materials increase the vehicle's kinetic energy consumption, leading to lower thrust-to-weight ratios and reduced payload weight as key development priorities.

[0003] Silicone rubber is a linear polymer composed of alternating silicon and oxygen. Its side chains can be connected to heat-resistant functional groups such as vinyl and phenyl. It has excellent thermal stability and ablation resistance, making it an ideal material for thermal protection in rocket engines, spacecraft return capsules, and other fields. However, its strength after cross-linking is less than 0.5 MPa, and its density is about 1.0 g / cm 3 , lacking any practical value, requiring the use of reinforcing fillers, anti-ablation fillers, and density-reducing fillers to adjust various technical specifications. However, the addition of functional fillers inevitably increases the material's density and reduces its mechanical properties. Balancing the insulation's mechanical, density, and ablation properties is a key issue that urgently needs to be addressed with silicone rubber insulation.

[0004] Furthermore, the rubber-based thermal insulation layer for solid rocket engines currently relies on a process that uses artificial raw rubber sheets for fabrication, resulting in insufficient safety and reliability, as well as low production efficiency. To reduce the manufacturing complexity of solid rocket engines and enhance the performance stability of the thermal insulation layer, the thermal insulation layer fabrication process is evolving from traditional manual application to automated spraying, which in turn places extremely high demands on the viscosity of the insulation material. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above-mentioned deficiencies of the prior art and to provide a modified hollow silicate and a preparation method and application thereof.

[0006] The present invention solves the technical problem by adopting the following technical solutions.

[0007] The present invention provides a modified hollow silicate. The modified hollow silicate is obtained by using octa(phenyldimethoxysiloxy) cage-shaped silsesquioxane as a modifier and performing surface modification on the hollow silicate using the modifier.

[0008] The present invention also provides a method for preparing a modified hollow silicate, which comprises: using octa(phenyldimethoxysilyloxy) cage-shaped silsesquioxane and hollow silicate as raw materials, and adopting a hydrothermal method to prepare the modified hollow silicate.

[0009] The present invention also provides a use of the modified hollow silicate in preparing a sprayable silicone rubber thermal insulation material.

[0010] The present invention has the following beneficial effects: The present invention provides a modified hollow silicate, a preparation method, and an application thereof. The modified hollow silicate provided by the present invention is obtained by modifying the hollow silicate with octa(phenyldimethoxysiloxy) cage-shaped silsesquioxane as a modifier. The hollow silicate modified with the modifier has good compatibility and reactivity in silicone rubber thermal insulation materials. The modified hollow silicate is used to replace conventional hollow glass microspheres as a density-reducing filler. The prepared silicone rubber thermal protection material has excellent ablation resistance, dispersibility, and a low expansion coefficient, allowing the silicone rubber thermal protection material to be spray-applied and having excellent ablation resistance. In addition, the modified silicate can further react with the silicone rubber base glue / crosslinker system after modification, so that the mechanical properties of the thermal insulation material are not reduced, thereby achieving the purpose of balancing mechanical-density-ablation properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0012] Figure 1 is a TEM image of the hollow tubular magnesium silicate prepared in Example 1; Figure 2 This is a SEM image of the hollow spherical calcium silicate prepared in Example 4. DETAILED DESCRIPTION

[0013] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0014] The following is a detailed description of a modified hollow silicate provided in an embodiment of the present invention, and its preparation method and application.

[0015] In a first aspect, an embodiment of the present invention provides a modified hollow silicate, wherein the modified hollow silicate is obtained by surface-modifying the hollow silicate using octa(phenyldimethoxysiloxy) cage-shaped silsesquioxane as a modifier.

[0016] The present invention provides a modified hollow silicate. This modified hollow silicate is surface-modified using octa(phenyldimethoxysiloxy) cage-shaped silsesquioxane as a modifier. The hollow silicate's hollow structure can reduce the density of silicone rubber systems. The modified hollow silicate exhibits excellent compatibility, reactivity, and dispersibility within the silicone rubber system, effectively balancing the density, mechanical properties, and ablation resistance of silicone rubber insulation materials. This reduces the overall proportion of functional fillers while maintaining sprayability. All technical specifications meet application requirements.

[0017] In some optional embodiments, the structural formula of octa(phenyldimethylsilyloxy) cage-shaped silsesquioxane is shown below: The above modifier was prepared using the method provided in 202411996617.3.

[0018] In some optional embodiments, the silicate material is one or more of iron silicate, calcium silicate, magnesium silicate, titanium silicate, and zirconium silicate having a hollow spherical or tubular structure.

[0019] In some optional embodiments, the mass ratio of the hollow silicate to the octa(phenyldimethoxysiloxy) cage-type silsesquioxane is 100:1 to 5. Extensive experiments have demonstrated that a mass ratio of the hollow silicate to the octa(phenyldimethoxysiloxy) cage-type silsesquioxane of 100:1 to 5 is appropriate. If the ratio is too low, the modification of the hollow silicate has no significant effect. If the amount of modifier is too high, the active sites increase excessively, resulting in an excessively high crosslink density of the thermal insulation material, which negatively affects the mechanical properties.

[0020] In a second aspect, an embodiment of the present invention further provides a method for preparing the modified hollow silicate, comprising: using octa(phenyldimethoxysilyloxy) cage-shaped silsesquioxane and hollow silicate as raw materials, and preparing the modified hollow silicate by a hydrothermal method.

[0021] An embodiment of the present invention provides a method for preparing a modified hollow silicate, comprising: surface-modifying a hollow silicate anti-ablation filler using octa(phenyldimethoxysiloxy) cage-shaped silsesquioxane to produce the modified hollow silicate. This modified hollow silicate exhibits excellent compatibility and reactivity in silicone rubber thermal insulation materials. Compared to unmodified silicate fillers, its use in silicone rubber thermal protection materials can effectively address the current challenge of balancing high mechanical properties, low density, and excellent anti-ablation performance in thermal protection materials. While ensuring both mechanical and anti-ablation performance, the total filler content in the formulation can be reduced, thereby lowering the viscosity of the silicone rubber-based thermal insulation material and improving spraying performance.

[0022] In some optional embodiments, the hydrothermal reaction temperature is 50°C to 200°C, and the reaction time is 0.5h to 10h. During the preparation of the modified hollow silicate, both the temperature and time of the hydrothermal reaction can affect the modification effect of the hollow silicate. For example, if the reaction temperature is too low, the yield is too low, resulting in poor modification effect. If the temperature is too high, the morphology of the hollow silicate may be changed. Therefore, it is more appropriate to control the hydrothermal reaction temperature to 50°C to 200°C and the reaction time to 0.5h to 10h.

[0023] In some optional embodiments, an auxiliary agent is further added during the hydrothermal reaction, and the auxiliary agent is one or more of methanol, ethanol, isopropanol, toluene, acetone, cyclohexane, and n-heptane.

[0024] In some optional embodiments, the method for preparing the modified hollow silicate comprises the following steps: 100 parts of silicate material, 1-5 parts of octa(phenyldimethoxysiloxy) cage-shaped silsesquioxane, 30-50 parts of auxiliary agent, and 50-100 parts of water are placed in a reaction kettle, sealed and tightly sealed, and reacted at a temperature of 50°C to 200°C for 0.5h to 10h. After cooling, the reaction is filtered, washed, and dried to obtain a modified hollow silicate.

[0025] In a third aspect, an embodiment of the present invention provides a use of the above-mentioned modified hollow silicate in the preparation of a sprayable silicone rubber insulation material.

[0026] The present invention will be further described below through specific examples.

[0027] Example 1 A hydrothermal autoclave was charged with 5g of octa(phenyldimethoxysiloxy) cage-shaped silsesquioxane, 100g of hollow tubular magnesium silicate material, 50g of ethanol as an auxiliary agent, and 100g of water. After being tightly sealed, the autoclave was placed in an oven and heated at 120°C for 3 hours. After cooling, the modified hollow magnesium silicate was obtained by filtration, washing, and drying.

[0028] Example 2 A hydrothermal autoclave was charged with 3g of octa(phenyldimethoxysiloxy) cage-shaped silsesquioxane, 100g of hollow spherical zirconium silicate (particle size 3-5 μm), 30g of isopropyl alcohol, and 50g of water. The autoclave was sealed and heated in an oven at 80°C for 8 hours. After cooling, the modified hollow zirconium silicate was obtained by filtration, washing, and drying.

[0029] Example 3 A hydrothermal autoclave was charged with 1g of octa(phenyldimethoxysiloxy) cage-shaped silsesquioxane, 100g of hollow spherical iron silicate material (1-2 μm particle size), 35g of toluene additive, and 50g of water. The autoclave was sealed tightly and heated in an oven at 150°C for 10 hours. After cooling, the product was filtered, washed, and dried to obtain the modified hollow iron silicate.

[0030] Example 4 A hydrothermal autoclave was charged with 2 g of octa(phenyldimethoxysiloxy) cage-shaped silsesquioxane, 100 g of hollow spherical calcium silicate material (particle size 0.5-1 μm), 35 g of isopropyl alcohol as a catalyst, and 70 g of water. The autoclave was sealed tightly and heated in an oven at 100°C for 12 hours. After cooling, the modified hollow calcium silicate was filtered, washed, and dried.

[0031] The modified hollow silicate filler is used to prepare silicone rubber thermal protection material: 100 g of terminal hydroxy vinyl polysiloxane, 15 g of modified silicate, 20 g of fumed silica, 15 g of basalt fiber, and 15 g of aluminum hydroxide were mixed evenly. The above materials were mixed evenly using a dynamic mixer and vacuumed at 120°C for 30 min under a negative pressure of -0.09 MPa. Then, 15 g of tetrapropoxysilane and 1 g of dibutyltin dilaurate were added after depressurization, and the mixture was rapidly stirred for 15 min to obtain a silicone rubber insulation material.

[0032] A 3 mm thick silicone rubber thermal protection material film was prepared by spray molding method and used to test the mechanical properties and ablation properties.

[0033] Comparative Example 1 100 g of hydroxyl-terminated vinyl polysiloxane, 15 g of hollow glass microspheres, 20 g of fumed silica, 15 g of basalt fiber, and 15 g of aluminum hydroxide were mixed evenly. The above materials were mixed evenly using a dynamic mixer and vacuumed at 120°C for 30 min under a negative pressure of -0.09 MPa. Then, 15 g of tetrapropoxysilane and 1 g of dibutyltin dilaurate were added after depressurization, and the mixture was rapidly stirred for 15 min to obtain a silicone rubber insulation material.

[0034] Comparative Example 2 100 g of terminal hydroxy vinyl polysiloxane, 15 g of hollow magnesium silicate (unmodified), 20 g of fumed silica, 15 g of basalt fiber, and 15 g of aluminum hydroxide were mixed evenly. The above materials were mixed evenly using a dynamic mixer, and vacuumed at 120°C for 30 min under a negative pressure environment of -0.09 MPa. Then, 15 g of tetrapropoxysilane and 1 g of dibutyltin dilaurate were added after depressurization, and the mixture was rapidly stirred for 15 min to obtain a silicone rubber insulation material.

[0035] A 3 mm thick silicone rubber thermal protection material film was prepared by spray molding method and used to test the mechanical properties and ablation properties.

[0036] Examples 1-4 and Comparative Examples 1-2 were subjected to relevant performance tests, and their performance data are shown in Table 1. The test standards for tensile strength and elongation at break are GB / T 528-2009, the test standard for linear ablation rate is GJB 323B-2018, and the test standard for density is GB / T 4472-2011.

[0037] Table 1 Summary of silicone rubber thermal protection material properties

[0038] Table 1 above shows the performance indicators of silicone rubber insulation materials prepared by using modified magnesium silicate, zirconium silicate, iron silicate, calcium silicate and conventional density-reducing filler hollow glass microspheres. Comparing Examples 1-4 with Comparative Examples 1-2, it can be found that the modified hollow silicates have good mechanical properties in the silicone rubber insulation material system, with tensile strengths above 3.0 MPa, elongation at break having a minimum value of 140% and a maximum value of 240%, which are significantly improved compared to the tensile strength of 2.1 MPa and elongation at break of 120% of the comparative example. At the same time, from the density data, the density reduction effect of adding the modified tubular hollow magnesium silicate is particularly significant, down to 1.15 g / cm 3 , which is nearly 10% higher than the density reduction effect of hollow glass microspheres. This may be because the modified tubular magnesium silicate forms tiny cavities when it acts in the silicone rubber insulation material, causing a further decrease in density.

[0039] By comparing the mechanical properties and density of silicone rubber insulation materials with modified hollow magnesium silicate and unmodified hollow magnesium silicate added in Example 1 and Comparative Example 2, it was found that the tensile strength of the modified hollow magnesium silicate group was lower than that of the unmodified group, but the elongation at break was higher than that of the unmodified group. This is because there are a large number of hydroxyl groups on the surface of the unmodified hollow magnesium silicate, which act quickly during the mixing and cross-linking curing process of the silicone rubber insulation material, significantly improving the strength of the material. However, the cross-linking is too fast and dense, resulting in difficulty in the movement between silicone rubber molecules, thereby reducing the elongation at break. After the surface hydroxyl groups of the modified hollow magnesium silicate react with the modifier, a large number of alkoxy active sites are also introduced. However, the active sites are branched and have steric hindrance. The reaction speed is slower than that of the hydroxyl groups, and no thickening phenomenon occurs during the mixing process of the silicone rubber. The participation of multiple active sites in cross-linking during the cross-linking curing process can also further improve the mechanical properties. In addition, there are obvious differences in the density indicators of the two groups. This is because the polarity of the hollow magnesium silicate changes after modification, and there is minimal repulsion at the interface between the hollow cavity and the silicone rubber base glue. The silicone rubber base glue cannot fill the cavity, retaining the cavity, thereby achieving a density reduction effect; while the cavity of the unmodified hollow magnesium silicate is filled when preparing silicone rubber insulation materials, and there is no hollow advantage, so the density reduction advantage is not retained.

[0040] On the other hand, the distribution of linear ablation rate data is consistent with expectations. Compared with Comparative Examples 1 and 2, Example 1 shows a linear ablation rate of 0.09 mm / s after adding the modified hollow magnesium silicate, and the anti-ablation effect is very significant. Compared with Comparative Example 1, Example 2 shows a group tensile strength of 4.0 MPa after adding the modified hollow zirconium silicate, while the ablation performance and density distribution are relatively similar. In summary, it can be seen that modified silicate fillers have better application performance in silicone rubber insulation materials than hollow glass microspheres, and can effectively balance the mechanical-ablation-density performance distribution.

[0041] In addition, the modified hollow silicate filler also has good processability in silicone rubber insulation materials, which helps the implementation of the spraying process of silicone rubber insulation materials and can effectively improve its processing efficiency and product processing reliability.

[0042] The viscosity of the spray construction materials prepared in Examples 1-4 and Comparative Examples 1-2 was tested in accordance with GB / T 10247-2008 "Viscosity Measurement Methods". The viscosity test results are shown in Table 2.

[0043] Table 2 Viscosity data of silicone rubber thermal protection material spray coating

[0044] As can be seen from the data in Table 2 above, the viscosity of the spray coating of the silicone rubber insulation material group containing the modified hollow silicate filler is significantly lower than that of Comparative Example 1, which contains hollow glass microspheres. This reduction in spray coating viscosity facilitates the implementation of the spraying process. Table 2 also shows that the viscosity of the silicone rubber insulation material in Comparative Example 2, containing the hollow magnesium silicate filler, is significantly higher than that of the silicone rubber insulation material containing the modified hollow magnesium silicate, and is even nearly double that of the group containing the hollow glass microspheres. This is because the surface of unmodified hollow magnesium silicate contains a large number of hydroxyl groups, which have a thickening effect when used in the preparation of silicone rubber insulation, causing a sharp increase in the viscosity of the system. This further demonstrates that the hollow silicate filler has a viscosity-reducing application effect only after modification.

[0045] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A modified hollow silicate, characterized in that: The modified hollow silicate is obtained by using octa(phenyldimethoxysilyloxy) cage-shaped silsesquioxane as a modifier and performing surface modification on the hollow silicate using the modifier.

2. The modified hollow silicate according to claim 1, characterized in that: The structural formula of the octa(phenyldimethylsilyloxy) cage-shaped silsesquioxane is shown below: 。 3. The modified hollow silicate according to claim 1, characterized in that: The hollow silicate is one or more of iron silicate, calcium silicate, magnesium silicate, titanium silicate and zirconium silicate with a hollow spherical or tubular structure.

4. The modified hollow silicate according to claim 1, characterized in that: The mass ratio of the hollow silicate to the octa(phenyldimethoxysilyloxy) cage-shaped silsesquioxane is 100:1-5.

5. A method for preparing the modified hollow silicate according to any one of claims 1 to 4, characterized in that: It includes: Modified hollow silicate was prepared by hydrothermal method with octa(phenyldimethoxysilyl) cage-shaped silsesquioxane and hollow silicate as raw materials.

6. The preparation method according to claim 5, characterized in that: The temperature of the hydrothermal reaction is 50°C to 200°C.

7. The preparation method according to claim 5, characterized in that: The hydrothermal reaction time is 0.5h~10h.

8. The preparation method according to claim 5, characterized in that: An auxiliary agent is also added during the hydrothermal reaction, and the auxiliary agent is one or more of methanol, ethanol, isopropanol, toluene, acetone, cyclohexane, and n-heptane.

9. The preparation method according to any one of claims 5 to 8, characterized in that: The following steps are involved: 100 parts of silicate material, 1-5 parts of octa(phenyldimethoxysiloxy) cage-shaped silsesquioxane, 30-50 parts of auxiliary agent, and 50-100 parts of water are placed in a reaction kettle, sealed and tightly sealed, and reacted at a temperature of 50°C to 200°C for 0.5h to 10h. After cooling, the reaction is filtered, washed, and dried to obtain a modified hollow silicate.

10. Use of the modified hollow silicate according to any one of claims 1 to 4 or the modified hollow silicate prepared by the preparation method according to any one of claims 5 to 9 in preparing a sprayable silicone rubber thermal insulation material.

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