Heat Treatment Effect on the Phase Composition of the Silica Electrochemical Coating and the Carbon Fiber Strength

• Main Authors: Sergei Galyshev, Evgeniya Postnova, Olga Shakhlevich, Dmitrii Agarkov, Ekaterina Agarkova, Alexey Nekrasov, Rais Mozhchil
• Format: Article
• Language: English
• Published: MDPI AG 2021-09-01
• Series: Materials
• Subjects: carbon fiber coating; electrochemical sol-gel coating; silica coating; carbon fiber
• Online Access: https://www.mdpi.com/1996-1944/14/18/5209

This work is devoted to the study of the chemical and phase composition of a carbon fiber coating obtained by the electrochemical sol-gel method. The experimental data obtained using several independent complementary methods, including X-ray phase analysis, thermogravimetric and differential thermal analysis, scanning electron microscopy and elemental analysis, and X-ray photoelectron spectroscopy, are in good agreement with each other. It was found that the resulting coating consists of amorphous silicon oxide and crystalline potassium carbonate. Heating above 870 °C leads to the crystallization of cristobalite from amorphous silicon dioxide. At a temperature of about 870 °C, the coating acquires a smooth surface, and heating above 1170 °C leads to its destruction. Thus, the optimum temperature for the heat treatment of the coating is about 870 °C. The loss of strength of carbon fiber at each stage of coating was estimated. A full coating cycle, including thermal cleaning from the sizing, coating, and heat treatment, results in a loss of fiber strength by only 11% compared to the initial state.