Thermal decomposition of the calcium salts of several carboxylic acids

A systematic study of thermal decomposition of the calcium salts of eight carboxylic acids, using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), is presented. Synthesized calcium salts of carboxylic acids with 3-13 carbon atoms in the aliphatic chain exist as monohydrates that transform into anhydrous salts at about 110°C, changing their structures and diminishing their crystallinity. Beginning at temperatures between 160 and 315°C, the salts decompose, forming carbonates as final solid products. From a qualitative point of view, the studied salts show a thermal stability that exponentially decreases with the aliphatic chain length growth. In the temperature interval between dehydration and decomposition, some of the samples suffer a recrystallization process, while others melt. The conclusions possible from thermal analysis were confirmed by monitoring the changes in salt crystallinity with temperature and the appearance of new phases by X-ray powder diffraction (XRD). Infrared (IR) spectroscopy also suggests these conclusions.