Low-pressure adsorption isotherms of CO₂ on low-temperature surface measured on a quartz crystal microbalance

Attitude-control engine plume will generate a low pressure area on spacecraft surface. The low pressure gas adsorbed on cryogenic surface could cause contamination effect and affect the performance of spacecraft. Low pressure adsorption theory at low surface temperature is conducive to analyze contamination effect. Therefore, it is necessary to investigate the low pressure adsorption theory. In this paper, an experimental system was designed for low gas pressure and low surface temperature control. Low-pressure carbon dioxide adsorption equilibrium isotherms less than 100Pa on a gold-plated quartz crystal microbalance were experimentally measured at nine surface temperatures from 213 K to 273 K. The experimental results showed that each isotherm was consistent with type I isotherm. However, the maximum adsorption capacities of the isotherms under different temperatures were different and decreased exponentially with the increase of surface temperature. This phenomenon indicates that multilayer adsorption occurred in these experimental conditions and the traditional Langmuir model was not suitable for the isotherms in this experiment. Therefore, a Multi-Langmuir isotherm model was proposed based on the isotherms to describe carbon dioxide adsorption isotherm under low pressure and low surface temperature. The error between the Multi-Langmuir model and the experimental results is basically less than 20%.