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 hi gh 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 Na2CO3. The enthalpy value co rresponding to the heat of solution of Na2CO3 was also applicable to a phys ical mixture of NaHCO3/Na2CO3. However, from the characteristic peaks of th e heat flow versus time curve, pyrolytically formed Na2CO3 could be disting uished 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 b e inferred that a decarboxylation of up to 4.5% could be allowed without an y significant effect on the stability of bicarbonate at 54%. (C) 2000 Elsev ier Science B.V. All rights reserved.