The influence of diol addition on water crystallization kinetics in mesopores

Solidification of liquid occupying material's pores is one of the main reasons of its skeleton deterioration. So far, it has been usually assumed that confined water undergoes phase transitions more rapidly than temperature changes, which indicates that the kinetic effects are negligible. However, this assumption is often infringed. The main object of this paper is to analyse the crystallization of commonly applied antifreeze, i.e. ethylene as well as propylene glycol, in water solutions contained in voids of mesoporous silica gel with average pore size equal to 11 nm. In case of both solutions, two concentrations are analysed, 5% and 10%. Additionally, the analysis is conducted also for deionized water. The experimental research has been conducted by means of differential scanning calorimetry with multiple cooling rate program applied. The activation energy is estimated according to the differential Friedman method. In order to pick the most appropriate kinetic model to analysed phenomenon, two approaches are applied: the one introduced by Málek as well as the one described by Perez-Maqueda et al., the so-called model-fitting method. The former indicates the Šesták–Berggren model, whereas the latter points to nth reaction order model. Both equations demonstrate high accordance with the experimental data. The Šesták–Berggren equation is an empirical formula, which does not provide any explanation about antifreeze solidification. However, the nth reaction order model belongs to the group of geometrical extension/contraction models.