A freeze-resistant thermal protective coating for rocket launch pads and its application

Abstract

This invention discloses a formulation and application of an antifreeze thermal protective coating for rocket launch pads. The antifreeze thermal protective coating of this invention consists of solid and liquid components. This coating can solve the problems of difficulty in applying thermal protective coatings to rocket launch pads at ambient temperatures as low as -30°C and the failure of the coating strength to meet design specifications due to low temperatures.

Description

Technical Field

[0001] This invention relates to a thermal protective coating for rocket launch pads, specifically an antifreeze thermal protective coating for rocket launch pads, belonging to the field of high-temperature insulation and protection. Background Technology

[0002] With the development of aerospace and astronautics, in addition to thermal protection for the spacecraft themselves, thermal protection measures have also been added to ground facilities such as rocket launch pads. Domestic rocket launch pads use inorganic refractory materials coated on the surface of the base material to protect the launch pad from thermal erosion and thermal shock from high-temperature exhaust gases. However, in some regions of my country, the ambient temperature at launch pads can drop as low as -30°C every winter. Low temperatures have varying degrees of impact on the application and protective performance of inorganic thermal protective coatings. To reduce the impact of low temperatures on the application and performance of inorganic thermal protective materials, a freeze-resistant thermal protective coating for rocket launch pads has been developed.

[0003] This invention consists of a solid component with particle size distribution and a special liquid component. It can be applied to the thermal protective coating at ambient temperatures as low as -30°C, ensuring that the thermal protective coating can be applied normally under low temperature conditions. Moreover, the coating performance after application can withstand the ablation of rocket exhaust flames, providing effective protection for the launch pad. Summary of the Invention

[0004] To address the challenges of applying inorganic thermal protective coatings at ambient temperatures as low as -30°C, and the issue of incomplete curing resulting in coatings failing to meet design specifications and thus providing ineffective protection for the launch pad, the technical solution of this invention is as follows:

[0005] The antifreeze thermal protective coating for rocket launch pads consists of solid and liquid components.

[0006] The solid component is prepared from raw materials in the following weight ratio, totaling 100%:

[0007]

[0008]

[0009] The preferred weight ratio of the solid components is:

[0010] High alumina bauxite 47％～72％ silicon carbide 6％～18％ <![CDATA[Al2O3 powder]]> 1.5％～4.8％ High-alumina cement 11％～22％ Silica powder 9％～18％ Sodium tripolyphosphate 0.01％～0.4％ Sodium hexametaphosphate 0.01％～0.3％

[0011] The optimal weight ratio of the solid components is as follows:

[0012] High alumina bauxite 50％～70％ silicon carbide 6.3％～12％ <![CDATA[Al2O3 powder]]> 1.7％～4.7％ High-alumina cement 12％～30％ Silica powder 9.5％～17.8％ Sodium tripolyphosphate 0.01％～0.30％ Sodium hexametaphosphate 0.01％～0.23％

[0013] The high-alumina bauxite contains ≥85% Al2O3 by mass; the high-alumina bauxite has a bulk density ≥2.85 g / cm³. 3 The high-alumina bauxite has a water absorption rate of ≤5%; the high-alumina bauxite is preferably a homogenized material. The high-alumina bauxite is a mixture of particles with particle sizes of 6-4mm, 4-2mm, 2-0mm, 0-0.15mm (100 mesh), and 0-0.028mm (325 mesh), with a mass ratio of 1:(1.8-2.4):(1.2-1.8):(1.2-1.8):(0.1-0.8).

[0014] The silicon carbide is SiC with a particle size of 0-0.075 mm (200 mesh), and the mass percentage of SiC in the silicon carbide is ≥90%.

[0015] The Al2O3 has an average particle size of submicron, with a diameter of 100 nm to 1.0 μm, a purity of 99.9%, and a spherical morphology.

[0016] The silicon micropowder is silica fume, preferably of type 970;

[0017] The high-alumina cement is aluminate cement, preferably Secar71 cement;

[0018] The sodium tripolyphosphate contained in Na5P3O 10 The content is ≥80%, preferably sodium tripolyphosphate containing Na5P3O. 10 Percentage content ≥90%;

[0019] The solid component is prepared from raw materials in the following weight ratio, totaling 100%:

[0020] Sodium chloride (NaCl) 18％～25％ <![CDATA[Sodium nitrate (NaNO3)]]> 0.5～2％ <![CDATA[Calcium chloride (CaCl2)]]> 0.5％～3.5％ Triethanolamine (TEOA) 0.01％～0.1％ water -

[0021] Sodium chloride (NaCl), sodium nitrate (NaNO3), calcium chloride (CaCl2), and triethanolamine (TEOA) were all of analytical grade.

[0022] Its characteristic is that it is prepared from the following raw materials in the indicated weight ratios, totaling 100%: an aqueous solution of sodium chloride (NaCl) 18%–25%, sodium nitrate (NaNO3) 0.5%–2%, calcium chloride (CaCl2) 0.5%–3.5%, and triethanolamine (TEOA) 0.01%–0.1%.

[0023] The preparation method of the antifreeze thermal protective coating for rocket launch pads is as follows:

[0024] (1) Preparation of solid components

[0025] The gradation of solid components in an antifreeze thermal protective coating is characterized by the following method for preparing the gradation powder of the thermal protective coating repair material: First, the aggregates are mixed by weighing 6-4mm, 4-2mm, and 2-0mm high-alumina bauxite according to the weight ratio and adding them to a planetary mixer for 30 minutes; second, the powders are mixed by weighing 0-0.15mm (100 mesh) and 0-0.028mm (325 mesh) high-alumina bauxite, 0-0.075mm (200 mesh) SiC, Al2O3 powder, silica fume, high-alumina cement, sodium tripolyphosphate, and sodium hexametaphosphate according to the weight ratio and adding them to a planetary mixer for 30 minutes; finally, the aggregates and powders are added together to the mixer and mixed for 30 minutes to ensure that all raw materials are mixed evenly.

[0026] (2) Preparation of liquid components

[0027] The preparation of the liquid components of the antifreeze thermal protective coating is characterized by: weighing sodium chloride (NaCl), sodium nitrate (NaNO3), calcium chloride (CaCl2), and triethanolamine (TEOA) (the remaining components are water) according to the weight ratio to prepare an aqueous solution. (3) Application of the antifreeze thermal protective coating

[0028] The solid and liquid components of the antifreeze thermal protective coating are mixed and stirred in a ratio of 1:(0.07~0.16) before being applied.

[0029] This antifreeze thermal protective coating solves the problems of difficulty in applying thermal protective coatings to rocket launch pads at ambient temperatures as low as -30°C and the failure of the coating strength to meet design specifications due to low temperatures. This antifreeze thermal protective coating has the following advantages: 1. It consists of solid and liquid components, which are pre-mixed in the factory and simply stirred upon delivery to the construction site before application. It can be applied normally even at ambient temperatures as low as -30°C; 2. The strength of this antifreeze thermal protective coating is not affected by low ambient temperatures during later strength development; 3. It sets quickly after application, with a short strength formation period; 4. It is suitable for use in ambient temperatures as low as -30°C; 5. The antifreeze thermal protective coating exhibits normal ablation and thinning phenomena in scaled-down engine ablation tests, without coating penetration or delamination; 6. After curing, the antifreeze thermal protective coating can withstand the ablation of rocket engine exhaust flames, providing protection for the rocket launch pad.

[0030] The advantages and beneficial effects of this invention are:

[0031] This invention addresses the low-temperature construction performance and low-temperature protection performance of the material from three aspects:

[0032] (1) Water reduction: ① Selection of raw materials: High-alumina bauxite with high density and low porosity is used; ② Four-level particle size distribution is used, and micro-powder and sub-micro-powder are used to fill the pores, ultimately reducing the overall porosity of the coating; ③ Sodium tripolyphosphate and sodium hexametaphosphate are added to reduce the amount of water added.

[0033] (2) Antifreeze: The addition of antifreeze agents sodium chloride (NaCl) and sodium nitrate (NaNO3) lowers the freezing point of water and enhances the coating’s performance under low temperature conditions.

[0034] (3) Early strength: The addition of early strength agents calcium chloride (CaCl2) and triethanolamine (TEOA) accelerates the solidification time and strength development of the coating and reduces the impact of low temperature on the coating performance.

[0035] By reducing water content, preventing freezing, and accelerating early strength, the coating can be cured at low temperatures, ensuring that it meets the requirements for low-temperature construction and possesses the corresponding mechanical and ablation resistance properties, thus providing effective protection for the launch pad. Attached Figure Description

[0036] Figure 1 Image after ablation. Detailed Implementation

[0037] The present invention will be further described below with reference to specific embodiments and appendices, and the advantages and features of the present invention will become clearer as the description proceeds.

[0038] Example 1

[0039] 1. Preparation of antifreeze thermal protective coatings

[0040] (1) Preparation of solid components

[0041] The preparation method of the graded powder of thermal protective coating repair material is as follows: First, the aggregate is mixed by weighing 6-4mm, 4-2mm, and 2-0mm high-alumina bauxite at a weight ratio of 10%, 18.98%, and 16%, and adding it to a planetary mixer and mixing for 30 minutes. Second, the powder is mixed by weighing 0-0.15mm (100 mesh) and 0-0.028mm (325 mesh) high-alumina bauxite at a weight ratio of 15% and 5%, 0-0.075mm (200 mesh) SiC at a mass ratio of 7%, 2% Al2O3 powder (particle diameter of 0.3μm), 11% silica fume, 15% high-alumina cement, 0.01% sodium tripolyphosphate, and 0.01% sodium hexametaphosphate, and adding them to a planetary mixer and mixing for 30 minutes. Finally, the aggregate and powder are added together to the mixer and mixed for 30 minutes to ensure that all raw materials are mixed evenly.

[0042] (2) Preparation of liquid components

[0043] The liquid components of the antifreeze thermal protective coating are characterized by: weighing sodium chloride (NaCl), sodium nitrate (NaNO3), calcium chloride (CaCl2), and triethanolamine (TEOA) (the remaining components are water) in weight ratios of 20%, 1%, 2%, and 0.01% to prepare an aqueous solution.

[0044] (3) Application of antifreeze thermal protective coatings

[0045] The solid and liquid components of the antifreeze thermal protective coating are mixed and stirred at a mass ratio of 1:0.08 before being applied.

[0046] 2. Testing of the low-temperature physical properties of antifreeze thermal protective coatings

[0047] The antifreeze thermal protective coating from Example 1 was applied to a 40mm×40mm×160mm triple mold at an ambient temperature of -30℃ to prepare a sample block with dimensions of 40mm×40mm×160mm. The sample block was then cured at an ambient temperature of -30℃. The compressive and flexural strength of the sample block were tested at 24h, 48h, 72h, 96h, and 7×24h under the low temperature curing conditions.

[0048] Table 1 Compressive and flexural strength data

[0049] Compressive strength 20.1MPa 24.4MPa 33.1a 33.2MPa 33.4MPa Flexural strength 6.1MPa 7.1MPa 7.12MPa 7.18MPa 7.18MPa

[0050] As shown in Table 1, the antifreeze thermal protective coating still completed the sample preparation when the ambient temperature was as low as -30℃. It formed strength after 24 hours of low-temperature curing and reached its maximum strength at 96 hours. After curing for 7×24 hours at an ambient temperature as low as -30℃, the strength did not decrease with the low temperature. Therefore, the antifreeze thermal protective coating can be applied at an ambient temperature of -30℃ and can achieve the designed strength, and the strength will not decrease with the low temperature.

[0051] 3. Ablation Results

[0052] The antifreeze thermal protective coating from Example 1 was applied to a 190×120×30mm steel plate at an ambient temperature of -30℃. The coating was applied to an ablation sample with a thickness of 30mm and then cured at -30℃. After 96 hours of curing under low-temperature conditions, an ablation resistance test was conducted.

[0053] The back surface temperature of the prepared sample was tested using a YA6804 oxygen-kerosene engine. Test conditions: Engine combustion chamber pressure: Pc = 1.4 ± 0.05 MPa; Engine residual oxygen coefficient: α = 0.7 ± 0.03; Engine nozzle diameter: 65 mm; Nozzle outlet gas temperature: 2210 K; Nozzle outlet gas velocity: 2390 m / s; Combustion chamber temperature: 3470 K; Ablation test time: 5 s / sample; Heat flux density: 13.1 Mw / m³ 2 Ablation results: such as Figure 1 As shown, the surface of the antifreeze thermal protective coating exhibited normal ablation after ablation, without any abnormal phenomena such as burn-through or delamination.

[0054] Example 2

[0055] 1. Preparation of antifreeze thermal protective coatings

[0056] (1) Preparation of solid components

[0057] The preparation method of graded powder for thermal protective coating repair is as follows: First, the aggregate is mixed by weighing high-alumina bauxite of 6-4mm, 4-2mm, and 2-0mm according to the weight ratio of 11%, 20%, and 17%, and adding it to a planetary mixer for 30 minutes; second, the powder is mixed by weighing high-alumina bauxite of 0-0.15mm (100 mesh) and 0-0.028mm (325 mesh) according to the weight ratio of 16% and 6%. The following ingredients were added to a planetary mixer and mixed for 30 minutes: 6.3% SiC (0-0.075mm, 200 mesh), 1.7% Al2O3 powder (0.3μm particle diameter), 8.5% silica fume, 13.47% high-alumina cement, 0.02% sodium tripolyphosphate, and 0.01% sodium hexametaphosphate. Finally, the aggregate and powder were added to the mixer and mixed for 30 minutes to ensure that all raw materials were mixed evenly.

[0058] (2) Preparation of liquid components

[0059] The preparation method (process and conditions) of the liquid component is the same as that of the liquid component in Example 1.

[0060] (3) Application of antifreeze thermal protective coatings

[0061] The solid and liquid components of the antifreeze thermal protective coating are mixed and stirred at a mass ratio of 1:0.09 before being applied.

[0062] 2. Testing of the low-temperature physical properties of antifreeze thermal protective coatings

[0063] The antifreeze thermal protective coating from Example 2 was applied to a 40mm×40mm×160mm triple mold at an ambient temperature of -30℃ to prepare a sample with dimensions of 40mm×40mm×160mm. The sample was then cured at an ambient temperature of -30℃. Under these low-temperature curing conditions, pressure resistance and flexural strength tests were conducted at 24h, 48h, 72h, 96h, and 7×24h.

[0064] Table 2 Compressive and flexural strength data

[0065] Compressive strength 18.80MPa 19.0MPa 19.80MPa 20.10MPa 20.11MPa Flexural strength 5.20MPa 5.50MPa 5.52MPa 5.80MPa 5.81MPa

[0066] As can be seen from Table 2, when the ambient temperature is as low as -30℃, the antifreeze thermal protective coating in Example 2 can complete the preparation of the sample, but the strength is lower than that of the antifreeze thermal protective coating in Example 1.

[0067] 3. Ablation Results

[0068] The thermal protective coating in Example 2 was ablated according to the ablation method and test steps (process and conditions) in Example 1. After ablation, the surface of the antifreeze thermal protective coating also showed normal ablation phenomenon, and no abnormal phenomena such as burn-through and delamination occurred.

[0069] Example 3

[0070] 1. Preparation of antifreeze thermal protective coatings

[0071] (1) Preparation of solid components

[0072] The preparation method of the graded powder of thermal protective coating repair material is as follows: First, the aggregate is mixed by weighing 6-4mm, 4-2mm, and 2-0mm high-alumina bauxite according to the weight ratio of 7%, 17%, and 12%, and adding it to a planetary mixer and mixing for 30 minutes; second, the powder is mixed by weighing 0-0.15mm (100 mesh) and 0-0.028mm (325 mesh) high-alumina bauxite according to the weight ratio of 13% and 3%, 0.075mm (200 mesh) SiC, 4.7% Al2O3 powder (particle diameter of 0.3μm), 9.0% silica fume, 22% high-alumina cement, 0.16% sodium tripolyphosphate, and 0.14% sodium hexametaphosphate according to the mass ratio, and adding them to a planetary mixer and mixing for 30 minutes; finally, the aggregate and powder are added together to the mixer and mixed for 30 minutes to ensure that all raw materials are mixed evenly.

[0073] (2) Preparation of liquid components

[0074] The preparation method (process and conditions) of the liquid component is the same as that of the liquid component in Example 1.

[0075] (3) Application of antifreeze thermal protective coatings

[0076] The solid and liquid components of the antifreeze thermal protective coating are mixed and stirred at a weight ratio of 1:0.06 before being applied.

[0077] 2. Testing of the low-temperature physical properties of antifreeze thermal protective coatings

[0078] The antifreeze thermal protective coating from Example 3 was applied to a 40mm×40mm×160mm triple mold at an ambient temperature of -30℃ to prepare a sample with dimensions of 40mm×40mm×160mm. The sample was then cured at an ambient temperature of -30℃. Under these low-temperature curing conditions, pressure resistance and flexural strength tests were conducted at 24h, 48h, 72h, 96h, and 7×24h.

[0079] Table 3 Compressive and flexural strength data

[0080] Compressive strength 17.80MPa 17.90MPa 19.20MPa 19.60MPa 19.62MPa Flexural strength 4.90MPa 4.950MPa 5.10MPa 5.25MPa 5.25MPa

[0081] As can be seen from Table 3, when the ambient temperature is as low as -30℃, the antifreeze thermal protective coating in Example 3 can complete the preparation of the sample, but the strength is lower than that of the antifreeze thermal protective coating formulations in Example 1 and Example 2.

[0082] 3. Ablation Results

[0083] The thermal protective coating in Example 3 was ablated according to the ablation method and test steps (process and conditions) in Example 1. After ablation, the surface of the antifreeze thermal protective coating also showed normal ablation phenomenon, and no abnormal phenomena such as burn-through and delamination occurred.

[0084] Comparative Example 1

[0085] The solid component powder was the same as the solid component in Example 1 (process and conditions). Water was used as the liquid component. The solid component and liquid component were mixed and stirred at a mass ratio of 1:0.08. It was found that the coating solidified and could not be used to prepare sample blocks.

[0086] Comparative Example 2

[0087] 1. Coating preparation and sample preparation

[0088] The solid component powder is the same as the solid component in Example 1 (process and conditions). The liquid component is prepared by weighing 20% ​​sodium chloride (NaCl) and (the remainder is water) to make an aqueous solution. The solid and liquid components of the coating are mixed and stirred at a ratio of 1:0.14 before being applied.

[0089] 2. Testing of the low-temperature physical properties of antifreeze thermal protective coatings

[0090] The antifreeze thermal protective coating from Comparative Example 2 was applied to a 40mm×40mm×160mm triple mold at an ambient temperature of -30℃ to prepare a sample with dimensions of 40mm×40mm×160mm. The sample was then cured at an ambient temperature of -30℃. Under these low-temperature curing conditions, compressive strength and flexural strength tests were conducted at 24h, 48h, 72h, 96h, and 7×24h.

[0091] Table 4 Compressive and flexural strength data

[0092] Compressive strength 8.2MPa 9.2MPa 9.6MPa 9.8MPa 9.2MPa Flexural strength 1.9MPa 2.12MPa 2.20MPa 2.35MPa 2.23MPa

[0093] As shown in Table 4, although the coating was successfully applied at an ambient temperature as low as -30°C without sodium nitrate (NaNO3), calcium chloride (CaCl2), and triethanolamine (TEOA), its strength was lower than that of Example 1.2.3, and the strength decreased as the low temperature time increased.

Claims

1. Use of a non-freezing thermal protection paint on a launch pad for a rocket, characterized in that, The application is as follows: the antifreeze thermal protective coating is applied to the surface of the rocket launch pad at an ambient temperature of -30°C to form a thermal protective coating that resists the ablation of the rocket engine exhaust flame. The formulation of the antifreeze thermal protective coating includes solid components and liquid components; The weight ratio of solid components to liquid components is 1:(0.07~0.16); The solid components, by weight percentage, totaling 100%, consist of 45%–75% high-alumina bauxite, 5%–21% silicon carbide, 1%–5% Al2O3 powder, 10%–35% high-alumina cement, 8%–20% silica fume, 0.01%–0.5% sodium tripolyphosphate, and 0.01%–0.4% sodium hexametaphosphate. The liquid component is composed of the following raw materials in the indicated weight ratios, totaling 100%: sodium chloride 18%–25%, sodium nitrate 0.5%–2%, calcium chloride 0.5%–3.5%, triethanolamine 0.01%–0.1%, with the remainder being water; The mass percentage of Al2O3 in the bauxite is ≥ 85%; the volume density of the bauxite is ≥ 2.85 g / cm 3 ; the water absorption of the bauxite is ≤ 5%; and the bauxite is a homogenized material. The high-alumina bauxite is formed by fully mixing three-stage continuous particle size distribution and two-stage powder filling, with particle sizes of 6-4mm, 4-2mm, 2-0mm, 0-0.15mm, and 0-0.028mm, and a weight ratio of 1:(1.8-2.5):(1.2-1.8):(1.2-1.9):(0.1-0.8).

2. Use according to claim 1, characterized in that: The solid components, by weight percentage, total 100%, and consist of 47%–72% high-alumina bauxite, 6%–18% silicon carbide, 1.5%–4.8% nano-Al2O3 powder, 11%–32% high-alumina cement, 9%–18% silica fume, 0.01%–0.4% sodium tripolyphosphate, and 0.01%–0.3% sodium hexametaphosphate.

3. Use according to claim 1, characterized in that: The solid components, by weight percentage, total 100%, and consist of 50%–70% high-alumina bauxite, 6.3%–17% silicon carbide, 1.7%–4.7% Al2O3 powder, 12%–30% high-alumina cement, 9.5%–17.8% silica fume, 0.01%–0.30% sodium tripolyphosphate, and 0.01%–0.23% sodium hexametaphosphate.

4. Use according to claim 1, characterized in that: The weight ratio of the solid component to the liquid component is 1:(0.08~0.14); The liquid component is composed of the following raw materials in the indicated weight ratios, totaling 100%: sodium chloride 19%–24%, sodium nitrate 0.6%–1.9%, calcium chloride 0.6%–3.4%, triethanolamine 0.02%–0.09%, with the remainder being water; The high-alumina bauxite is formed by fully mixing three-stage continuous particle size distribution and two-stage powder filling, with particle sizes of 6-4mm, 4-2mm, 2-0mm, 0-0.15mm, and 0-0.028mm = 1:(1.8-2.3):(1.2-1.7):(1.2-1.7):(0.1-0.7).

5. The use according to claim 1, characterized in that: The weight ratio of the solid component to the liquid component is 1:(0.08~0.13); The liquid component is composed of the following raw materials in the indicated weight ratios, totaling 100%: sodium chloride 19%–23.5%, sodium nitrate 0.7%–1.8%, calcium chloride 0.7%–3.2%, triethanolamine 0.02%–0.08%, with the remainder being water; The high-alumina bauxite is formed by fully mixing three-stage continuous particle size distribution and two-stage powder filling, with particle sizes of 6-4mm, 4-2mm, 2-0mm, 0-0.15mm, and 0-0.028mm = 1:(1.9-2.3):(1.2-1.7):(1.3-1.7):(0.2-0.7).

6. The application according to claim 1, characterized in that: The silicon carbide powder has a particle size of 0-0.075 mm and a SiC mass percentage content of ≥90% in the silicon carbide. The Al2O3 has an average particle size of submicron, with a diameter of 100 nm to 1.0 μm, a purity of ≥99.9%, and a spherical morphology. The silicon micropowder mentioned is silica ash; The high-alumina cement mentioned above is aluminate cement; The sodium tripolyphosphate has a percentage of ≥ 90% of Na5P3O 10 10. The sodium hexametaphosphate contained in the form of P2O5, with a percentage content of ≥68%.

7. The use according to claim 1, characterized in that: The solid and liquid components are mixed and stirred at a weight ratio of 1:(0.07~0.16) and then coated on the rocket launch pad.

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