Scanning power compensated

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

Adiabatic calorimeters are complex home-made instruments, and the measurements are time-consuming. Less accurate but easy to use commercial differential scanning calorimeters (DSCs) [18, 19] are a frequently used alternative. The method involves measurement of the temperature of both a sample and a reference sample and the differential emphasizes the difference between the sample and the reference. The two main types of DSC are heat flux and power-compensated instruments. In a heat flux DSC, as in the older differential thermal analyzers (DTA), the... 

Figure 12.3 Schemeofa power compensation differential scanning calorimeter. A sample furnace Ar reference furnace B temperature sensor of the sample furnace Br temperature sensor of the reference furnace C resistance heater of the sample furnace Cr resistance heater of the reference furnace D cell S sample R reference.

There are two types of differential scanning calorimeters (a) heat flux (AT) and (b) power compensation (AT). Subsequent sections of this experiment will not distinguish between the two types. In either type of calorimeter, the measurement is compared to that for a reference material having a known specific heat [16,17], As AT and AT have opposite signs there is some potential for confusion [3], e.g., at the melting point, Tm, Ts < Tr, and AT < 0, whereas Ts > Tr and AT > 0 because latent heat must be supplied (subscripts s and r refer to the sample and the reference material, respectively) [3]. 

Figure 3.3 Schematic of a power-compensated differential scanning calorimeter.

We stress here that although DSC is in principle a relatively straightforward physical technique, its theoretical thermodynamical and kinetic basis is not trivial but should be well understood as it applies to equilibrium and nonequlibrium thermotropic lipid phase transitions of various types and to either heat conduction or power compensation instruments. Moreover, some care must be taken in sample preparation, selection of sample size, and sample equilibration before data acquisition in the choice of suitable scan rates, starting temperatures, and ending temperatures during data acquisition and in the analysis and interpretation of the DSC thermograms obtained. An adequate treatment of these issues is not possible in this brief... 

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.)...

Kwon, Y.K. Andorsch, R. Pyda, M. Wunderlich, B. Multifrequency saw-tooth modulation of a power-compensated differential scanning calorimeter. Thermochim. Acta 2001, 367 (8), 203-215. 

Differenhal scanning calorimetry (DSC) conshtutes one of the most widely used techniques for the study of polymers, parhcularly those systems that crystallize. Although the term DSC is used in conjunchon with many different instruments, fundamentally, these can be divided into two categories heat flow instruments based upon differenhal thermal analysis (DTA) and those which are true power compensated instruments. 

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... 

Whereas most fixed-cell instruments are power-compensation instruments (because it is possible to place heaters on the base of cells that are not removable), batch-cell instruments are available as either power-compensation or heat-flux designs. One design of a heat-flux, batch-cell instrument is the micro-DSC in (Setaram). The instrument consists of a calorimetric block into which two channels are machined. One channel holds the sample cell, the other holds the reference cell. At the bottom of each channel, between the cell and the block, is a plane-surfaced transducer. The transducers provide a thermal pathway between the cells and the block and are used to maintain the cells at a temperature identical to that of the block. The electrical signal produced by the transducer on the sample side is proportional to the heat evolved or absorbed by the sample. The temperature of the calorimetric block is maintained by a precisely thermostated circulating liquid. The liquid is raised in temperature by a separate heater and is cooled by a supply of circulating water. The precise control of the temperature of the circulating liquid allows scan rates of just 0.001°C min-1 to be attained and ensures that the calorimetric block is insulated from the surrounding environment. 

Figure 11.17. Power-compensated diflerential scanning calorimetry (DSQ apparatus (S - sample R reference)...

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. 

Figure 4. The present evolution of Standard DSC towards a range of low- to high-speed calorimeters [32]. Commercial instruments like heat-flux and power-compensation Standard DSCs work typically at scan rates of 0.1 to 60 C/min High Performance DSC (HPer DSC), using a modified PerkinElmer power-compensation Pyris 1 or Diamond DSC, covers the range 0.1 to 500 C/min thin-film (chip) calorimeters have scan rates from 1000 to 1.2-10 C/min and rates as high as 6-10 C/min are attainable using the high-speed pulse-calorimeter (all numbers are approximate indications).

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. 

Most differential scanning calorimeters fall into one of two categories depending on their operating principle power compensation or heat flux. 

Figure 2 (a) Power-compensation differential scanning calorimeter, (b) Heat flux differential scanning calorimeter... 

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

Kwon YK, Androsch R, Pyda M, Wunderlich B (2001) Multi-frequency Sawtooth Modulation of a Power-compensation Differential Scanning Calorimeter. Thermochim. Acta 367/368 203-215. 

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