Теплові режими високотемпературного окислення вольфрамових дротиків

Research on tungsten oxidation is essential for creating functional oxide materials, developing next-generation photocatalysts, and constructing modern models of high-temperature heat and mass transfer and phase formation. Heat and mass transfer processes during tungsten oxidation significantly influence the properties of tungsten oxides at virtually all levels — from phase composition to electrophysical characteristics. It is heat and mass transfer that determines the morphology of oxides and surface self-organization. This work is dedicated to a detailed analysis of the influence of various heat and mass transfer mechanisms and phase transitions on the low- and high-temperature steady-state and critical regimes of tungsten oxidation. Physical and mathematical modeling was carried out to study the heat and mass transfer processes and the oxidation kinetics of tungsten wires heated by an electric current in air. The conducted studies showed that in steady-state low-temperature oxidation regimes, as well as near the critical current value corresponding to the ignition of the tungsten wire, heat losses due to the evaporation of the oxide layer are negligible and can be omitted. However, at wire temperatures exceeding 1500 K, oxide evaporation processes become crucial and significantly affect the formation of dendritic branched structures of tungsten trioxide on the conductor surface. The role of radiative heat loss from the surface of the heated wire to the walls of the reaction chamber was investigated in steady-state and critical regimes corresponding to wire ignition and extinction. It was established that for wires with a diameter of less than 100 μm, thermal radiation to the apparatus walls can be neglected. For wires with a diameter exceeding 100 μm, accounting for radiative heat losses in the physical and mathematical model leads to an increase in the critical current value at which high-temperature oxidation regimes occur. It is demonstrated that natural convection substantially influences the stable and critical oxidation regimes of tungsten wires. It was found that the intensification of heat transfer due to natural convection causes an increase in the critical current value by approximately 20%.