Heating temperature effect on the hygroscopicity of expanded vermiculite

Abstract

The hygroscopicity of expanded vermiculite is one of major influence factors for thermal insulating performance. To explore the water absorption properties of expanded vermiculite prepared via electrical heating method, heating temperature effect on the hygroscopicity of expanded vermiculite was investigated under various humidity circumstances. The influencing mechanisms were analyzed by means of Thermogravimetric Analysis-Differential Scanning Calorimeter technique (TG-DSC), Fourier-Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), and the Brunauer–Emmett–Teller technique (BET) for the measurement of the specific surface area. The results of water absorption experiments indicated that the hygroscopicity of vermiculite showed an inversely proportional relationship to heating temperature and the water absorption content of EV-900 was only 6.206 mg/g with a dramatic decline of 91.5% in comparison with that of RV. This decline of water absorption capacity was mainly attributed to the decrease of interlamellar spacing and specific surface area. In addition, environment humidity had a significant effect on water absorption capacity and velocity. The water absorption content of EV-400 sample increased dramatically from 48.414 mg/g at the humidity of 55%–72.929 mg/g at the humidity of 95%, and the equilibrium time reduced from 3 h to 0.5 h. This study will provide a new perspective and theoretical guidance for the development of vermiculite based thermal insulating materials.