Heat flux, differential scanning calorimetry

Figure 7.53. Differential scanning calorimetry (DSC). Shown are (a) schematic of the heat-flux sample chamber (b) an example of a DSC thermogram, showing endothermic eventsbDf (c) DSC thermogram of a poly(vinyUdene fluoride)-ethyl acetoacetate polymer-solvent system, showing two melting events for the polymer due to its intermolecular interactions with solvent molecules. The inset shows a comparison between the pure polymer (b) and the polymer-solvent (a). Reproduced with permission from Dasgupta, D. Mahk, S. Thierry, A. Guenet, J. M. Nandi, A. K. Macromolecules 2006, 39,6110.

Figures 21 14) and 22 show the weight increase and heat of reaction due to chemisorption of oxygen on fresh char determined by thermogravimetry (TG) and differential scanning calorimetry (DSC). In low-density fibrous cellulosic materials where the heat loss is restricted but oxygen can penetrate by diffusion, the heat flux from chemisorption could play a significant role in the ignition of the active...

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.)...

Pyda, M. Kwon, Y.K. Wunderlich, B. Heat capacity measurements by saw-tooth modulated standard heat-flux differential scanning calorimetry with sample temperature control. Thermochim. Acta 2001, 367 (8), 217-227. 

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. 

In calorimetry techniques, enthalpy changes accompanying physical or chemical events, whether they are exothermic or endothermic, are measured and monitored either as a function of temperature or time. Thus, a calorimeter is able to collect a heat flux exchanged between the sample and the sensible part of the apparatus, generally made of thermocouples, and to register it. The result is a profile of the rate of enthalpy change, either as a function of temperature as the sample is heated at a known linear rate in differential scanning calorimetry (DSC), or as a function of time when the calorimeter is held at constant temperatnre in isothermal differential calorimetry (DC). 

Chater M., G. Chataing, and J.M. Vergnaud. 1985. Enhanced study of differential scanning calorimetry with determination of heat flux-time curves, profiles of temperature and state of cure. Thermochim. Acta. 90 135-47. 

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. 

Differential scanning calorimetry (DSC) is a thermoanalytical technique used to study the thermal properties of the polymer using a differential scanning calorimeter. In this process, the difference in the amount of heat required to increase the temperature of a sample and reference is measured as a function of temperature. Sample and reference will be maintained at same temperature throughout the experiment. DSC curves were plotted based on heat flux versus temperature or time. Thermal transitions of polymer can be determined by this technique. DSC is widely used for the decomposition behavior determination of the polymer. Figure 17.8 shows the DSC curves of PHB. 

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. 

Heat d or heat flux d Differential scanning calorimetry DSC... 

The investigation of the initial stages of reaction-diffusion in multilayers, carried out during recent years, by differential scanning calorimetry (DSC), proved that the stage of intermediate phase nucleation at solid-state reaction does take place. DSC experiments [6-8] have shown that the formation of a new phase in multilayers can involve two stages. For example, the curve illustrating the dependence of heat flux on time at formation of NbAls in multilayers Nb/Al (obtained by deposition) has two maxima. X-ray analysis and electron microscopy confirmed that both peaks correspond to the formation of the phase NbAls. Similar curves with two peaks are obtained for such systems as Co/Al, Ni/Al, Ti/Al, Ni/amorphous Si, and V/amorphous Si. 

Differential scanning calorimetry (DSC) is a thermal method commonly used to determine the hquid crystal phase transition during heating and cooling of a sample at controlled rate [5]. The DSC method measures the flux between the sample and a reference (an inert material - aluminum oxide, gold, etc.) subjected to the same (isothermal and dynamic) temperature program. There are two types of differential scanning calorimetry ... 

This leads to quantitative or heat-flux differential scanning calorimetry... 

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