Microstructure And Self-Humidity-Control Performance Of Mineral Material Sepiolite

In this work, aimed at the problems of low amount and speed of water adsorption/desorption, process complexity and few theoretical research of self-humidity-control material (SHCM), sepiolite SHCM with good performance were prepared by acid-activation and heat-activation. Experimental parameters optimization, study on relationship between sepiolite microstructure and its self-humidity-control performance were carried out as well as study on sepiolite self-humidity-control theory.Sepiolite SHCM was made through optimizing raw sepiolite, kind of acid, acid concentration, acid-activation time and temperature, gravimetric ratio of sepiolite to acid, heat-activation temperature and time, drying mode. And the maximum amount of water adsorbed is 0.7400 g/g while the maximum amount of water desorbed is 0.6886 g/g. The fastest adsorbing speed in the first 5 hours is 0.0264 g/(g·h) and the fastest desorbing speed in the first 30 hours is 0.0132 g/(g·h).Mechanism of acid-activation and heat-activation and their effect on sepiolite were studied. The results show that acid-activation can distinctly improve its surface area and pore volume. Its main function is increasing the number of both micropore and mesopore. Heat-activation over 150℃ will reduce its surface area and pore volume. And the higher the heat-activated temperature is, the smaller the surface area and pore volume are. Effect of heat-activation on sepiolite is mainly in micropore. The performance of sepiolite SHCM was tested. The results show that the best humidity-control field of Sepiolite SHCM is 74%~98%RH where it has high amount of water adsorbed/desorbed, steep adsorption/desorption isotherms of water vapour and small hysteresis loop of adsorption/desorption isotherms. And its adsorption/desorption isotherms are close to ideal adsorption/desorption isotherms most. Study on the relationship between sepiolite's microstructure and its self-humidity-control performance shows that the main factors influencing the performance of sepiolite are microcosmic appearance, surface area, pore volume and pore distribution. The slenderer and shorter fibre can improve desorption but has litte effect on adsorption. At low relative humidity (RH) (<43%), the performance is mainly influenced by surface area. At medium and high RH (>43%), the main factor is pore volume. And at medium RH (43% - 74%), which is suitable for human most, the pore distribution ataperture 35.8 - 86.0A determines the performance.The self-humidity-control mechanism of sepiolite SHCMs: At low RH, it is monolayer and multilayer adsorption, and surface area is the main factor influencing its performance. At medium and high RH, it is capillary condensation, and the main factor is pore volume. And at medium RH, the pore distribution at apertures according to the RH determines the performance. And in this field, the ideal SHCM is a material with both big pore distribution at apertures according to the RH and hole with only one side opened.