Heating modes, scanning calorimetry

Differential Scanning Calorimetry (DSC) This is by far the widest utilized technique to obtain the degree and reaction rate of cure as well as the specific heat of thermosetting resins. It is based on the measurement of the differential voltage (converted into heat flow) necessary to obtain the thermal equilibrium between a sample (resin) and an inert reference, both placed into a calorimeter [143,144], As a result, a thermogram, as shown in Figure 2.7, is obtained [145]. In this curve, the area under the whole curve represents the total heat of reaction, AHR, and the shadowed area represents the enthalpy at a specific time. From Equations 2.5 and 2.6, the degree and rate of cure can be calculated. The DSC can operate under isothermal or non-isothermal conditions [146]. In the former mode, two different methods can be used [1] ... 

The latest development (1992) is the Modulated Differential Scanning Calorimetry (MDSC). Here the linear heating rate is superimposed by a sinoidal modulation. The following advantages of this mode are claimed direct measurement of heat capacity improved resolution of adjacent or superimposed effects improved sensitivity for weak transition effects separation of reversible from irreversible effects... 

To better assess heat losses, twin calorimeters have been developed that permit measurement in a differential mode. A continuous, usually linear, temperature change of calorimeter or surroundings is used in the scanning mode. The calorimetry, described in Sect. 4.3 is scanning, isoperibol twin-calorimetry, usually less precisely called differential scanning calorimetry (DSC). 

Differential scanning calorimetry (DSC) data were recorded on a Du Pont DSC (mod. 2940) in the dynamic mode with a heating rate of 10 C/min or in isothermal mode pre-selecting the final curing temperature. Nitrogen was used as purge gas. 

Differential scanning calorimetry (DSC) A technique in which the difference in energy inputs into a substance and a reference material is measured as a function of temperature whilst the substance and reference material are subjected to a controlled temperature program. Two modes, power-compensation DSC and heat-flux DSC, can be distinguished, depending on the method of measurement used. Usually, for the power-compensation DSC curve, heat flow rate should be plotted on the ordinate with endothermic reactions upwards, and for the heat-flux DSC curve with endothermic reactions downwards. 

Vanden Poel, G. and Mathot, V.B.F. (2006) High-speed/high performance differential scanning calorimetry (HPer DSC) Temperature calibration in the heating and cooling mode and minimization of thermal lag. Thermochim. Acta, 446,... 

Much of the intrinsic difficulties with DSC measurements and the tedious data collecting process of traditional adiabatic calorimetry can be avoided by adiabatic scanning calorimetry. In this technique a measured heating power is continuously applied to (or extracted from) the sample and sample holder. It was used in the 1970s for the study of liquid-gas [17] and liquid-liquid critical points [18] and first applied to liquid crystals by us [19] and later also by Anisimov et al. [20]. In the dynamic modes the total heat capacity Cj is now given by ... 

An identical result is obtained with calorimetry driven in scanning mode, the integration of the heat flux being made with respect to temperature. 

The calorimetry techniques have been used for many purposes in the cure of rubber, including to measure the heat of the overall cure reaction, but also for evaluating the kinetics of the heat evolved from the overall reaction. The only question at first was what way to use the calorimetry In the early eighties, it seemed to a majority of the authors that the isothermal condition would be preferable, but finally the operation in scanning mode was preferred. 

FIGURE 3.6 Calorimetry in scanning mode. Effect of the heating rate on the heat flux-temperature history. (With permission of Elsevier, Figure 9, Thermochim. Acta 1987. 116 111-24. J.Y. Armand and J.M. Vergnaud.)... 

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