论文总字数：30935字

摘 要

在当今这个高科技时代，航天技术已经相对成熟并且还在飞速进步和发展中，对于航天飞行器，其飞行时间和飞行速度都在不断地提升，当运载火箭长时间或反复地进入或离开大气层时，导致外表面产生强烈的空气动力学热负荷，这将破坏运载火箭及其内部结构。其外表面层与大气间存着在极大的相对运动摩擦从而导致周围气动环境对飞行器本磨损相当严重，一方面导致飞行器处于相当恶劣的工作环境当中，另一方面很大部分的热量会通过其表面传到系统的内部，从而可能导致系统内部一直处于高温状态甚至持续升温，这样恶劣的工作环境对飞行器会降低飞行器的使用寿命也是对其防护系统有更高的性能要求。因此必须通过可重复使用的、轻便的、低浇铸的热保护系统来保护其外部，该系统由表面的高发射率涂层和内部的低导热率绝缘涂层组成。本文针对飞行器防护系统的以上需求开展对原位生长SiC纳米线增强硅化物涂层制备与性能的研究。

SiC是一种具有高模量、高硬度、低比重、耐高温等优良性能的材料，其低维化和纳米化的SiC纳米线比块状的具有更高的模量和硬度，而高发射率抗氧化的硅化物涂层能以辐射传热的方式散出与大气摩擦产生大量热量，但抗氧化涂层在高温高压环境中易开裂破损，尤其在飞行器的恶劣的工作环境中更需要提高性能以延长使用寿命，所以采用SiC纳米线作为界面相引入涂层界面相中，增强硅化物涂层的韧度和硬度等性能，对于长期在高温高压环境中工作的飞行器，既做到抗氧化保护同时又能提高飞行器使用性能以延长使用寿命，因此SiC纳米线增强的高发射率抗氧化涂层的研究和发展对于航空航天事业都相当的重要。

本课题旨在通过纤维增强C/SiO₂复合气凝胶表面制备SiC纳米线增强硅化物涂层，然后研究其热导率、抗裂纹性能和抗氧化性能等，优化确定SiC纳米线增强涂层的最佳组成和结构。首先，对湿凝胶进行超临界干燥，并经过800 ℃ 和1300 ℃ 两步热处理制得碳纤维增强C/SiO₂气凝胶基体材料，然后采用热解先驱体法原位引入SiC纳米线，将基体材料浸渍于前驱体溶液中在1400 ℃ 下裂解，同时制得SiC基体及SiC纳米线增强相，采用原位生长法在基体材料表面原位引入的SiC纳米线分散更均匀，且与基体纤维的结合强度更高。第二步，以乙醇为溶剂，以羧甲基纤维素钠为分散剂，以硼硅酸盐玻璃粉末为粘结剂，以MoSi₂为辐射剂，以SiB₆为烧结助剂，通过球磨混合后用刷涂的方法涂覆在基体材料表面然后干燥处理，在其表面制备MoSi₂含量为10%的过渡涂层，再以同样方式制得MoSi₂含量分别为30%、40%、50%的外涂层浆料，分别涂覆在涂有预涂层的基体表面，然后通过石墨粉固相包埋快速热处理，在基体材料表面制备了耐高温、高发射率、抗氧化的硅化物涂层。最后，对碳纤维增强C/SiO₂气凝胶和抗氧化硅化物涂层进行表征，采用X射线衍射、红外光谱研究涂层氧化前后的组成变化，采用SEM表征基体气凝胶、SiC纳米线和涂层的形貌结构，并对组分含量不同的涂层进行发射率测试和抗氧化测试，探究不同工艺参数情况下，对SiC纳米线增强硅化物涂层的结构组成、热导率、抗裂/氧化性能的变化规律。

关键词： 碳基气凝胶 SiC纳米线 原位生长 硅化物 涂层

Preparation and properties of in-situ grown SiC nanowire reinforced silicide coating

Abstract

In today's high-tech era, aerospace technology is relatively mature and is still progressing and developing rapidly. For aerospace vehicles, the flight time and flight speed are constantly increasing. When the launch vehicle enters or leaves the atmosphere for a long time or repeatedly , Resulting in a strong aerodynamic heat load on the outer surface, which will destroy the launch vehicle and its internal structure. There is great relative motion friction between the outer surface layer and the atmosphere, which causes the surrounding aerodynamic environment to wear the aircraft very seriously. On the other hand, a large part of the heat will pass through the surface to the interior of the system, which may cause the system to remain in a high temperature state or even continue to heat up. Such a harsh working environment will reduce the service life of the aircraft and have higher performance requirements for its protection system. The exterior must therefore be protected by a reusable, lightweight, low-cast thermal protection system consisting of a high emissivity coating on the surface and a low thermal conductivity insulating coating on the inside. In this paper, the preparation and properties of SiC nanowire reinforced silicide coatings grown in situ were studied in accordance with the requirements of aircraft protection system.

SiC is a wide bandgap semiconductor material with high modulus, high hardness, low specific gravity, and high temperature resistance. Its low-dimensional and nano-sized SiC nanowires have higher modulus and hardness than the bulk, while high emission The anti-oxidation silicide coating can radiate heat and generate a lot of heat with atmospheric friction, but the anti-oxidation coating is easy to crack and break in high temperature and high pressure environments, especially in the harsh working environment of the aircraft. The performance is to prolong the service life, so SiC nanowires are used as the interface phase to introduce into the coating interface phase to enhance the toughness and hardness of the silicide coating. At the same time, the protection can also improve the performance of the aircraft to extend the service life, so the research and development of the high emissivity anti-oxidation coating enhanced by SiC nanowires is very important for the aerospace industry.

This subject aims to prepare SiC nanowire reinforced silicide coating on the surface of fiber-reinforced C / SiO₂ composite aerogel, and then study its thermal conductivity, crack resistance and oxidation resistance, etc., to optimize the determination of SiC nanowire reinforced coating The best composition and structure. First, the wet gel was supercritically dried and subjected to two-step heat treatment at 800 ℃ and 1300 ℃ to obtain carbon fiber-reinforced C / SiO₂ aerogel matrix materials. The material is immersed in the precursor solution and cracked at 1400 ℃. At the same time, the SiC matrix and the SiC nanowire reinforcement phase are prepared. The bonding strength is higher. The second step is to use ethanol as a solvent, sodium carboxymethyl cellulose as a dispersant, borosilicate glass powder as a binder, MoSi₂ as a radiation agent, and SiB₆ as a sintering aid, mixed by ball milling The method of brush coating is applied on the surface of the base material and then dried, and a transition coating with a MoSi₂ content of 10% is prepared on the surface, and then an outer coating with a MoSi₂ content of 30%, 40%, and 50% is prepared in the same manner The slurry was separately coated on the surface of the substrate coated with pre-coating, and then subjected to rapid heat treatment by graphite powder solid phase embedding, and a silicide coating with high temperature resistance, high emissivity and oxidation resistance was prepared on the surface of the substrate material. Finally, the carbon fiber-reinforced C / SiO₂ aerogel and anti-oxidation silicide coating were characterized. The composition changes of the coating before and after oxidation were studied by X-ray diffraction and infrared spectroscopy. The matrix aerogel, SiC nanowires and coating were characterized by SEM. The morphology and structure of the layer, and the emissivity test and anti-oxidation test of the coatings with different component contents, to explore the structural composition, thermal conductivity, and crack resistance of the SiC nanowire enhanced silicide coating under different process parameters The change of oxidation performance.

Key Words: Carbon-based aerogel; SiC nanowires; In-situ growth；Silicide; Coating

目 录

摘 要 I

Abstract III

第一章 文献综述 1

1.1 引言 1

1.2 耐高温低热导率的气凝胶材料 2

1.2.1 气凝胶材料 2

1.2.2 气凝胶材料的复合 3

1.3 原位生长SiC纳米线 4

1.3.1 原位生长SiC纳米线的增韧性能 4

1.3.2 原位生长SiC纳米线的制备方法 6

1.4 硅化物涂层 8

1.4.1高发射率涂层 8

1.4.2 难熔金属硅化物涂层 8

1.5 研究目的 9

第二章 实验研究方案 10

2.1 实验所用的原料及设备 10

2.1.1 原料 10

2.1.2 设备 10

2.2 实验方法 11

2.2.1 纤维增强C/SiO₂复合气凝胶基体的制备 11

2.2.2 原位生长SiC纳米线增强相的制备 12

2.2.3 硼硅酸盐玻璃粉末的制备 12

2.2.4 硅化物涂层的制备 13

2.3 测试表征方法 14

第三章 原位生长SiC纳米线增强硅化物涂层的研究 16

3.1 气凝胶基体材料的表征 16

3.1.1 气凝胶基体的红外光谱检测 16

3.1.2 气凝胶基体的X衍射检测 17

3.1.3 气凝胶基体的热重-差热检测 18

3.1.4 气凝胶基体的微观形貌检测 19

3.2 硼硅酸盐玻璃粉末的表征 21

3.2.1 粘结剂的红外光谱检测 21

3.2.2 粘结剂的热重-差热检测 22

3.3 硅化物涂层材料的表征 23

3.3.1 硅化物涂层微观形貌检测 24

3.3.1 硅化物涂层微观形貌检测 25

3.3.2硅化物涂层的发射率测试 25

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