Calorimetry a method to be used to characterise pyrolytically decarboxylated bicarbonate and assess its stability at elevated humidities.

Microcalorimetry was used to characterise bicarbonate after treatment at high temperatures. By measuring the heat flow from a sample of bicarbonate at 100% relative humidity, the net exothermic contribution could be used to estimate the fraction of pyrolytically formed Na(2)CO(3). The enthalpy value corresponding to the heat of solution of Na(2)CO(3) was also applicable to a physical mixture of NaHCO(3)/Na(2)CO(3). However, from the characteristic peaks of the heat flow versus time curve, pyrolytically formed Na(2)CO(3) could be distinguished from that present in the physical mixture. The different bicarbonate batches of varying degree of pyrolytic decarboxylation were also observed at an elevated relative humidity of 54%. From these measurements it could be inferred that a decarboxylation of up to 4.5% could be allowed without any significant effect on the stability of bicarbonate at 54%.