Вивчення закономірностей росту оксидних структур на поверхні вольфраму при нагріванні

The paper presents the results of studies of the features of the formation of oxide structures on the surface of tungsten wires heated by electric current in air. Stationary high-temperature oxidation modes of tungsten wires with diameters of 210 and 300 μm were studied by the electrothermographic method. It was established that at an average temperature of a tungsten wire of about 900 K, filamentous crystals appear on its surface, which grow rapidly and subsequently acquire a plate and branched shape. The dispersed composition, shape and surface density of the obtained tungsten trioxide microcrystals depend on the temperature and oxidation time. The growth rates of individual crystals in the longitudinal and transverse directions were determined. It was established that the crystals initially grow more actively in the longitudinal direction (in height), and then grow faster in width. Usually, the final size of the crystal in the transverse direction is larger than in the longitudinal direction. A linear law of growth of the maximum size of dendrites with time has been proved. Calculations of the fractal dimension of dendritic structures of tungsten oxide have been carried out. The obtained values ​​of fractal dimension indicate that the growth mechanism is diffusion-limited aggregation (DLA) with the participation of the vapor phase WO₃. When tungsten is heated to high temperatures, the oxide partially turns into vapor and condenses on the surface in the form of dendrites.