Physicochemical Study on Preparation of Oxidation-Resistant Films on High Temperature Materials and Their Oxidation Rate.

能源效率的提高需要在氧化气氛中高温使用的材料。在材料上涂覆抗氧化膜是最有利的方法之一，而不会降低其机械性能。氧化硅和氧化铝是在氧化条件下在高于1000 ℃的温度下抗氧化膜的潜在材料。本文研究了高温材料表面氧化硅和氧化铝的制备和形成过程中的物理化学过程，以及氧化硅和氧化铝的抗氧化性能。(1)硅衬底上二氧化硅薄膜的物理化学研究（a）硅的热氧化机理采用热氧化、化学气相沉积和旋涂玻璃技术在硅衬底上制备了三种类型的二氧化硅薄膜。这些样品在高温下氧化，以评估膜中氧的扩散率。由于薄膜的热扩散系数不同， 关于我们 e微观结构。氧压的氧化速率的依赖性表明，在二氧化硅膜中的氧的溶解度是成比例的氧压和扩散率是独立的压力。（B）薄膜热导率测量新技术的开发开发了一种称为“点脉冲法”的新技术，在该技术中，脉冲激光束聚焦在薄膜上，并测量表面温度的变化。该技术被证明适用于厚度大于25 μ m的薄膜。(2)（a）钼上铝的包埋渗层通过包埋渗法将铝涂覆在钼上。在Mo_3O_8和Mo之间形成一层Mo_3Al薄膜。涂层在冷却过程中产生了许多裂纹。裂纹沿垂直于表面方向发展，部分裂纹到达Mo基体。Mo_3O_8本身具有很高的抗氧化性，形成连续的Al_2O_3层，但由于裂纹到达基体，涂层抗氧化性较差。（B）Si和Al的两阶段涂覆开发了Si和Al的两阶段涂覆，其中在铝化物涂覆之前涂覆少量Si。两段式涂层的显微组织与铝化物涂层基本相同，但裂纹的形成受到明显抑制。没有裂纹到达Mo基底提供了极强的抗高温氧化性。少

Improvement of energy efficiency requires materials for high temperature use in oxidizing atmospheres. The coating of oxidation-resistant films on materials is one of the most favorable ways without the degradation of their mechanical properties. Silica and alumina are the potential materials for oxidation-resistant films at temperatures higher than 1000 C in oxidizing conditions. This research dealt with the physical chemistry involving in the preparation or formation of silica and alumina on the surface of high temperature materials, and the protective property against oxidation.(1) Physicochemical Study on Silica Films on Silicon (a)Mechanism of thermal oxidation of silicon Three kind of silica films were formed on silicon substrates by thermal oxidation, chemical vapor deposition and spin-on glass techniques. These samples were oxidized at elevated temperatures to evaluate the diffusivity of oxygen in the films. The diffusivity varied among the films because of the difference in th … More e microstructure. Oxygen pressure dependence of the oxidation rate indicated that the solubility of oxygen in the silica film was proportional to the oxygen pressure and that the diffusivity was independent of the pressure. (b)Development of a new technique for measurement of thermal conductivity of thin films A new technique named "Spot-Pulse Method" was developed, in which technique a pulsed laser beam was focused on the film and the change in surface temperature was measured. This technique proved to be applied the films with thickness more than 25mum.(2) Aluminide Coatings on Molybdenum for High Temperature Use (a)Pack-cementation coating of aluminum on molybdenum Aluminum was coated on molybdenum by pack-cementation. A thick film of Mo_3O_8 was formed and thin film of Mo_3Al existed between Mo_3O_8 and Mo. The coating layer contained many cracks which formed during cooling. The cracks were developed perpendicularly to the surface, and some of them reached the Mo substrate. The oxidation resistance of the coated Mo was poor because of the crack reaching the substrate although Mo_3O_8 itself exhibited the high resistance to oxidation forming a continuous Al_2O_3 fayer. (b)Two-stage coating of Si and Al Two-stage coating of Si and Al was developed, in which a small amount of Si was coated prior to the aluminide coating. Mirostructure of the two-stage coating was basically same as that of the aluminide coating but the marked suppression of the formation of cracks. The absence of cracks reaching the Mo substrate provided the extremely strong resistance to high temperature oxidation. Less