The Outgassing Characteristics and Dual-mechanism Kinetic Model of 304 Stainless Steel in a Variable-temperature Vacuum Environment

The outgassing rate of stainless steel is a critical parameter in the design of high vacuum systems, as it directly affects the ultimate pressure and pump-down time of the system. To characterize the dynamic outgassing behavior of materials at different baking temperatures, this study investigated the variable-temperature outgassing characteristics of 304 stainless steel within the range of 27℃ to 250℃ using a high-vacuum outgassing rate testing platform based on the dynamic flow method. The area-specific outgassing rate of the 304 stainless steel samples was calculated by real-time monitoring of the pressure difference between the sample chamber and the pump chamber through an orifice with fixed conductance, followed by subtraction of the background outgassing rate measured under the same temperature and pump-down time conditions. The results show that, at room temperature and in the high-temperature region (≥200℃), the single Fick diffusion model can reasonably describe the decay behavior of the outgassing rate, with fitting correlation coefficients R²≥0.87. However, in the transition temperature region of 150℃, the fitting accuracy of the single model decreases significantly, suggesting that the outgassing process in this region may involve a mixed mechanism associated with surface desorption and bulk diffusion. To further describe the outgassing behavior in this temperature region, a dual-mechanism superposition model incorporating a surface desorption exponential decay term and a bulk diffusion power-law term was introduced and verified by fitting the outgassing curves at different temperatures. The results show that this model achieves high fitting correlation coefficients at all tested temperatures, with the most significant improvement observed at 150℃, where R² increases from 0.78 to 0.98. The results provide experimental data and model references for evaluating the outgassing rate of 304 stainless steel vacuum vessels under different temperature conditions and for designing high vacuum systems.