Oxide Coating on Carbon Surface and Mechanism of Antioxidation

为了探索在碳材料上涂覆氧化物膜的条件，本文对溶胶-凝胶法涂覆氧化物膜和金属碳化物氧化机理进行了基础研究，通过选择合适的金属醇盐，采用简单的浸渍工艺，在碳材料上涂覆了ZrO_2、SiO_2和ZrSiO_4膜。醇盐溶液的粘度被发现支配的氧化膜的厚度。为了得到均匀的ZrSiO_4膜，必须控制各醇盐的水解速率，TiC和ZrC的氧化动力学研究表明，氧的扩散是一个速率控制过程。对于这两种碳化物，观察到在碳化物和氧化物之间形成中间层。对于TiC，该中间层应该由钛的碳氧化物和低价氧化物组成。对于ZrC，预期碳的偏析，可能是金刚石结构。实验结果表明，这些中间层具有良好的碳化物和氧化物之间的粘附的重要性。

In order to find out the conditions for antioxidation coating of some oxide films on carbon materials, the fundamental studies on the following two points were carried out; 1) oxide coating by using sol-gel method and 2) oxidation mechanism of metal carbides.By selecting the suitable metal alkoxides and employing a simple dipping process, the films of ZrO_2, SiO_2 and also ZrSiO_4 were coated on the carbon materials. The viscosity of the alkoxide solutions was found to govern the thickness of oxide films. In order to get homogeneous film of ZrSiO_4, it was found to be essential to control the hydrolysis rates of each alkoxide.From the kinetic studies of oxidation of TiC and ZrC the diffusion of oxygen was found to be a rate-determining process. For both carbides, a formation of intermadiate layer between carbide and oxide was observed. For TiC, this intermediate layers are supposed to consist of titanium oxycarbide and suboxides. For ZrC, the segregation of carbon was expected, possibly diamond structure. The experimental results suggest the importance of these intermediate layers for having good adhesion between carbide and oxide.