Chemistry Reference
In-Depth Information
Fig. 4 Scanning transitiometry setup for in situ simultaneous determination of the thermal and
mechanical derivatives. For convenience, two types of cells are shown: on the
left
is the standard
high pressure cell and on the
right
is a reaction type cell that can accommodate various accessories
(stirrer, reagents feeding, capillaries, optical fibers or probes for UV/Vis/near IR spectroscopic
analysis)
thermocouples (chromel-alumel), are mounted differentially and connected to a
nanovolt amplifier, which functions as a noninverting amplifier, whose gain is
given by an external resistance (with 0.1% precision). The calorimetric detectors
are placed in a metallic block, the temperature of which is directly controlled by a
digital feedback loop of 22 bits resolution (
10
4
K), being part of the transiti-
ometer software. The calorimetric block is surrounded by a cooling/heating
jacket, which is connected to an ultracryostat (Unistat 385 from Huber, Ger-
many). The temperature difference between the block and the heating/cooling
jacket is set at a constant value. In addition, the jacketed calorimetric block is
embedded in an additional electrically heated shield. The temperature difference
between the block and the heated shield is set to a constant value (5, 10, 20, or 30
K) and is controlled by an analogue controller. The temperature measurements,
both absolute and differential, are performed with calibrated 100
Pt sensors; a
Pt100 temperature sensor is placed between the sample and the reference calori-
metric detectors. The heaters are homogeneously embedded on the outer surfaces
of both the calorimetric block and the cooling/heating shield. The whole assembly
is thermally insulated and enclosed in a stainless steel body.
The stainless steel body is fixed on a sliding support (Fig.
5
shows the main
elements of a scanning transitiometer), which can be moved up and down along two
guiding rails. This is part of a mechanical displacement system consisting of a
winch and counterweight that allows the calorimetric body to easily move vertically
O
