This instrument is described in detail in the literature
[5±9]. Basically, it consists of two differentially
assembled vessels (reference and measuring) accommodated
in a calorimetric block immersed in a thermostating
liquid (undecane) the temperature of which
is controlled via the Peltier effect. This ensures a
highly uniform temperature and very low thermal
inertia, and allows operation in the scanning mode.
The assembly is placed in an inert atmosphere of dry
nitrogen. The temperature is measured near the vessels,
inside the calorimetric block. The reproducibility
is 0.01 K and the operating range is 253.15±
373.15 K. The calorimeter operation is based on Calvet's
principle: the calorimetric signal is the differential
heat ¯ow rate, which is measured by one
thermopile around each vessel. The detection limit
of the heat ¯ow rate ranges from 0.2 to 2 mW, depending
on the particular conditions. This calorimeter
combines the power of differential scanning calorimetry
and the precision of Calvet calorimetry, so it is
suitable for the precise determination of heat capacities
over a wide temperature range.
Most of the vessels used in conventional calorimeters
are designed in such a way that a vapour phase
is always present; this calls for measurement corrections.
Setaram liquid heat capacity vessels circumvent
this shortcoming by avoiding the presence of the
vapour phase over the liquid (see Fig. 1). Thus, the
calorimeter detection zone is in contact with a small,
constant volume V of about 1 cm3 ®lled with liquid
phase and no vapour phase correction is needed. The
calorimetric signal is proportional to the heat capacity
per unit volume CpV
ÿ1 of the unknown liquid; determining
this quantity per unit mass obviously entails
using density data which, in this work, were measured
by means of an Anton±Paar vibrating tube densimeter.
One of the major advantages of the calorimetric
vessels used is that they do not need to be removed
for cleaning (usually by ¯ushing with an organic
solvent); this allows the system geometry to be preserved
between measurements and calibrations to hold
over long periods.