Thermochimica Acta, Vol.290, No.1, 1-12, 1997
A Batch-Type Heat-Conduction Microcalorimeter for Immersion Heat Determinations - Design, Calibration and Applications
A batch-type heat conduction microcalorimeter is designed and constructed for the determination of immersion heats of microporous solids in polar and non-polar solvents. The apparatus is of the twin type and uses high sensitivity thermopiles for the detection of thermal effects. The calibration constant of the equipment is determined for the constructed aluminum and Pyrex brand glass cells, at different levels of work and electric power (between 0.25 J and 2 J, and 1 mW and 16 mW, respectively). The values of the calibration constant vary between 18 WV-1 and 22 WV-1. Chemical calibrations are also carried out with the standard systems HCl-NaOH, and THAM-HCl(THAM = trishydroxymethylaminomethane). The results, -56.40 +/- 0.08 kJ mol(-1) for the neutralization heat of aqueous solutions of HCl and NaOH, and -47.40 +/- 0.01 kJ mol(-1) for the protonation heat of THAM with a dilute aqueous solution of HCl, are in good agreement with those reported in the literature and corroborate the correct functioning of the microcalorimeter. The equipment was employed in the determination of surface areas of activated carbons, between 250 and 1500 m(2) g(-1), with an imprecision of 0.45%; the results show better sensitivity with respect to previously reported determinations. Also, immersion heats of activated carbons in 0.1M NaOH and HCl were determined and related to the number of acid or basic groups of the carbon.