Na2SO4·10H2O dehydration in view of thermal storage

The idea of using hydrated salts as working media for thermal energy storage has increased the interest in understanding their phase transitions. During studying the phase transition of mirabilite into thenardite, the crystal structure and water content are monitored by three experimental techniques. With the help of NMR, homogeneous drying of mirabilite crystals over the entire grain is observed. According to the drying behavior, the mobility of water molecules should be high inside the grain during dehydration. XRD experiments show that during this phase transition no disordered phase or other metastable phases like Na2SO4·7H2O or phase III appear. With Raman spectroscopy, these experiments are repeated at several relative humidities and again no metastable phases are observed

The mode of formation of thecotrichite, a widespread calcium acetate chloride nitrate efflorescence

The widespread occurrence of thecotrichite, Ca3(CH3COO) 3Cl(NO3)2·7H2O, in the museum environment is explained theoretically by construction and examination of its phase diagram. Thecotrichite formation was simulated in the laboratory to identify the key factors involved in its production. This efflorescence occurs on porous limestone or calcareous artefacts such as pottery, stored in wooden cabinets that generate acetic acid vapour. Salt production depends on the moisture content of the object and the concentration of acetic acid in its surroundings. Furthermore, for thecotrichite to form the artefact must contain soluble chloride and nitrate salts