FEATURES OF SYNTHESIS OF COMPOSITE MATERIAL BASED ON SILICON DIOXIDE AND CARBON NANOTUBES
Today, there are many papers showing the effectiveness of the use of carbon nanotubes as additives to composites. Their use in polymers is especially successful, but the efficiency of their use in ceramics poses many questions. The aim of the work was to study the effect of the addition of carbon nanotubes on the properties of ceramics. For this purpose, pure silica, obtained by the hydrolysis of tetraethoxysilane in an alkaline medium, was taken as a model. The obtained granules of the material were well sintered at 900 ° C and it was decided to compound this material with carbon nano- tubes. Depending on the method of introducing, the result turned out to be diametrically opposite. Nanotubes intro- duced during the synthesis of silica played a role in the formation of silicon dioxide grains and effectively compacted the material, increasing its hardness. On the contrary, nanotubes grown in ceramic pores wedged the grain of silicon dioxide, making the material softer. In the first case, it is important to note that the synthesis of ceramics is not affected by the synthesis of nanotubes. In turn, nanotubes always affect the process of forming ceramics. This influence leads to a change in the structure of the grains of ceramics, and as a consequence of the mechanism of interaction between them, which in turn changes the density and strength of the ceramics. In the second case, in order to grow nanotubes in the pores and cavities of the ceramic material, one must first im- pregnate the ceramic material with a catalyst. Thus, there is a requirement for a precursor of the catalyst - the absence of its interaction with ceramics. The second requirement is for inertness of the ceramics, both to the catalyst and to the entire synthesis process. In addition, it is necessary that the structure of the pores does not change during the synthesis, i.e. they did not close during the synthesis of nanotubes, but provided transportation of the starting materials and reac- tion products. Therefore two mechanisms that affect the formation of a composite ceramic material have been described. The described composite can be used in the rocket and space industry for compounding ceramic fairings and thermal insu- lation.