文摘
Isothermal titration calorimetry (ITC) was used to study interactions between water vapour and the surface of thermally converted sodium bicarbonate (NaHCO<sub>3sub>). The decarboxylation degree of the samples was varied from 3 % to 35 % and the humidity range was 54-100 % . The obtained enthalpy values were all exothermic and showed a positive linear correlation with decarboxylation degrees for each humidity studied. The critical humidity, 75 % (RH<sub>osub>), was determined as the inflection point on a plot of the mean?¦¤H kJ/mole Na<sub>2sub>CO<sub>3sub> against RH. Humidities above the critical humidity lead to complete surface dissolution. The water uptake (m) was determined after each calorimetric experiment, complementing the enthalpy data. A mechanism of water vapour interaction with decarboxylated samples, including the formation of trona and Wegscheider's salt on the bicarbonate surface is proposed for humidities below RH<sub>osub>.