Power compensation, differential scanning calorimetry

Power-compensated differential scanning calorimetry (DSC) apparatus (S = sample R = reference). 

Differential scanning calorimetry (DSC) is a calorimetric method that finds widespread use in many fields, including protein dynamics, polymers, pharmaceuticals, and inorganic materials. DSC measures energy (heat) flow into a sample and a reference substance as a function of controlled increase or decrease of temperature. In a typical power-compensated DSC (Fig. 3.2), the sample and reference are placed on metal pans in identical furnaces each containing a platinum resistance thermometer (thermocouple) and heater. During a thermal transition (e.g., when a physical change in the sample occurs),... 

Figure 10.4 Differential scanning calorimetry (DSC) instrumentation design (a) heat flux DSC and (b) power compensation DSC. A, furnace B, separate heaters and C, sample and reference holders. (Reproduced with permission from E.L. Charsley and S.B. Warrington, Thermal Analysis Techniques and Applications, Royal Society of Chemistry, Cambridge, UK. 1992 Royal Society of Chemistry.)...

Differential scanning calorimetry was introduced in the 1960s as a means of overcoming the difficulties associated with DTA. Fundamentally, there are two different types of DSC instruments heat flux and power compensation. In common with DTA, DSC involves the measurement of the temperature difference between a... 

The term differential scanning calorimetry has become a source of confusion in thermal analysis. This confusion is understandable because at the present time there are several entirely different types of instruments that use the same name. These instruments are based on different designs, which are illustrated schematically in Figure 5.36 (157). In DTA. the temperature difference between the sample and reference materials is detected, Ts — Tx [a, 6, and c). In power-compensated DSC (/), the sample and reference materials are maintained isothermally by use of individual heaters. The parameter recorded is the difference in power inputs to the heaters, d /SQ /dt or dH/dt. If the sample is surrounded by a thermopile such as in the Tian-Calvet calorimeter, heat flux can be measured directly (e). The thermopiles surrounding the sample and reference material are connected in opposition (Calvet calorimeter). A simpler system, also the heat-flux type, is to measure the heat flux between the sample and reference materials (d). Hence, dqjdi is measured by having all the hot junctions in contact with the sample and all the cold junctions in contact with the reference material. Thus, there are at least three possible DSC systems, (d), (c), and (/), and three derived from DTA (a), [b), and (c), the last one also being found in DSC. Mackenzie (157) has stated that the Boersma system of DTA (c) should perhaps also be called a DSC system. 

Thermal analysis is not really one subject, because the information gained and the purposes for which it can be used are quite varied. The main truly thermal technique is differential scanning calorimetry (DSC). The heat input and temperature rise for the material under test are compared with those for a standard material, both subjected to a controlled temperature programme. In power compensation DSC the difference in heat input to maintain both test pieces at the same temperature is recorded. In heat flux DSC the difference in heat input is derived from the difference in temperature between the sample and the reference material. Heat losses to the surroundings are allowed but assumed to depend on temperature only. 

Calorific Values Obtained Using Power Compensated Differential Scanning Calorimetry... 

The crystallization and melting behaviors of polymers are conventionally measured by the method of differential scanning calorimetry (DSC). One can obtain the heat flow or compensation power dQ/dt as a function of temperature, which is in principle proportional to the heat capacity of materials Cp and the scanning rate q, as given by... 

Differential thermal analysis (DTA) and differential scanning calorimetry (DSC) are similar techniques. They measure change in the heat capacity of a sample. These techniques can be used to determine various transition temperatures (T , Tg, T , Tp, etc.), specific heat, heat of fusion, percent crystallinity, onset of degradation temperature, induction time, reaction rate, crystallization rate, etc. A DSC instrument operates by compensating electrically for a change in sample heat. The power for heating is controlled in such a way that the temperature of the sample and the reference is the same. The vertical axis of a DSC temperature scan shows the heat flow in cal/s. 

Differential scanning calorimetry (DSC) is a method to determine phase transition temperamres and enthalpies [3]. In this thesis a power compensation DSC of the Perkin Elmer Corporation (DSC 8000) was used. 

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. 

The first commercial DSC instrument was introduced by Watson and his co-workers at Perkin-Elmer (Model DSC-1) in 1964.1 1 Watson, et al., also appear to be the first to have used the nomenclature differential scanning calorimetry. Their instrument, a power-compensating DSC, maintained a zero temperature difference between the sample and the reference by supplying electrical energy (hence, the term power-compensation) either to the sample or to the reference, as the case may be, depending on whether the sample was heated or cooled at a linear rate. The amount of heat required to maintain the sample temperature and that of the... 

DSC (Differential Scanning Calorimetry) has also been used in cement science investigations to some extent. It is based on a power compensated system. In this technique the reference and the sample imder investigation are maintained at a constant temperature throughout the heating schedule. The heat energy required to maintain the isothermal condition is recorded as a function of time or temperature. There are some similarities between DTA and DSC ineluding the appearance of thermal curves. DSC can be used to measure the heat capacities of materials. DSC measures directly the heat effects involved in a reaction. 

Differential scanning calorimetry (DSC) Two types of DSC are found in commercial instrumentation, namely, power-compensation DSC and heat-flux DSC. 

Figure 1 Different types of differential scanning calorimeters, (a) Three-dimensional cylindrical calorimeter (Tian-Calvet). (b) Three-dimensional calorimeter with power compensation, (c) Two-dimensional plate-like calorimeter, (d) Scheme of a twin-chip sensor (Mettler Toledo Flash 1 DSC ) for fast scanning calorimetry.

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