An Investigation of Isothermal Thermogravimetric Profiles in the Low Temperature Range (60°C–200°C)

Knowledge about the isothermal thermogravimetric (TG) profiles of soils within the low-temperature range (60°C–200°C) and their relationship to physicochemical properties are limited. The isothermal TG profiles of three typical clay minerals and eight mineral soils with varying clay contents (6%–47%) and clay mineralogies were measured within the temperature range of 60°C–200°C. Except for kaolinite, which showed a linear increase in mass loss (ML) with temperature, the ML of all other samples showed a logarithmic increase with temperature. For clay minerals, the ML was in the order of montmorillonite > illite > kaolinite at different temperature levels. For minerals soils, the cation exchange capacity (CEC) was the important factor affecting soil ML at different temperatures. Soil water content decreased linearly with increasing pF (logarithm of negative water potential) within the temperature range of 60°C–200°C, and the relationship between water content and pF can be well described with the Campbell and Shiozawa (1992) model (R² = 0.98–1.00). The reciprocal of model parameter SL had a very significant correlation with CEC or specific surface area determined from water vapour adsorption ((Formula presented.)). Our results implied that the easily measured isothermal TG data have the potential to be used to estimate some important soil properties (e.g., CEC and (Formula presented.)).