Crystallization of sodium sulfate on hydrophilic/hydrophobic surfaces during drying: An NMR study

Sodium sulfate is recognized as a salt with probably the most damaging capabilities when crystallizing in porous media. The three main crystalline phases which can be formed are thenardite (Na2SO4, anhydrous salt), decahydrate (Na2SO4·10H2O) and the thermodynamically metastable heptahydrate (Na2SO4·7H2O). In this study, using a setup in which nuclear magnetic resonance was combined with a digital microscope, we have investigated crystallization by the drying of sodium sulfate droplets on hydrophilic/hydrophobic surfaces in order to see, which crystalline phase is formed.