Thermally decarboxylated sodium bicarbonate: Interactions with water vapour, calorimetric study
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- 作者：Natalia Volkova ; Henri Hansson ; Lennart Ljunggren
- 关键词：Isothermal titration calorimetry ; Sodium bicarbonate ; Sodium carbonate ; Trona salt ; Wegscheider's salt ; Enthalpy ; Relative humidity ; Pyrolytic decarboxylation
- 刊名：Journal of Pharmaceutical Analysis
- 出版年：2013
- 出版时间：June, 2013
- 年：2013
- 卷：3
- 期：3
- 页码：193-199
- 全文大小：647 K
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>.