Abstract
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.
Highlights
The development of carbon fiber oxide coatings is an urgent task, primarily for metal matrix composites
Heating to 1170 ◦ C leads to the destruction of the coating, the coating material coagulates as droplets on the fiber surface, indicating an active mass transfer
The chemical and phase composition of the coating of carbon fiber obtained by electrochemical deposition from an aqueous-alcoholic solution of tetraethoxysilane has been studied
Summary
The development of carbon fiber oxide coatings is an urgent task, primarily for metal matrix composites. Sol-gel methods are the most promising since they do not require specialized equipment or any special conditions, such as a high temperature and/or a pressure level different from the atmospheric one These methods consist of forming a thin layer of sol on the surface of the substrate, for example, by immersion. During the drying process, a thin layer of sol, due to the evaporation of the liquid, first undergoes gelation, and dries completely, forming a porous coating Such a coating is usually further heat treated to eliminate porosity [6]. It works well for rigid flat substrates; it has a number of limitations when it comes to carbon fiber coatings. These limitations are associated with the capillary structure of the fiber that leads to the formation of bridges between the fibers in the interfiber space
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