Differential Scanning Calorimetry specific heat

In addition to DTA, other techniques used to detect thermal activity in PVC include differential scanning calorimetry, specific heat, thermal conductivity, and thermal diffusity. 

Difl erential thermal analysis (DTA) and differential scanning calorimetry (DSC) are the other mainline thermal techniques. These are methods to identify temperatures at which specific heat changes suddenly or a latent heat is evolved or absorbed by the specimen. DTA is an early technique, invented by Le Chatelier in France in 1887 and improved at the turn of the century by Roberts-Austen (Section 4.2.2). A... 

Although there are other ways, one of the most convenient and rapid ways to measure AH is by differential scanning calorimetry. When the temperature is reached at which a phase transition occurs, heat is absorbed, so more heat must flow to the sample in order to keep the temperature equal to that of the reference. This produces a peak in the endothermic direction. If the transition is readily reversible, cooling the sample will result in heat being liberated as the sample is transformed into the original phase, and a peak in the exothermic direction will be observed. The area of the peak is proportional to the enthalpy change for transformation of the sample into the new phase. Before the sample is completely transformed into the new phase, the fraction transformed at a specific temperature can be determined by comparing the partial peak area up to that temperature to the total area. That fraction, a, determined as a function of temperature can be used as the variable for kinetic analysis of the transformation. 

M. J. Richardson. The Application of Differential Scanning Calorimetry to the Measurement of Specific Heat. In Compendium of Thermophysical Properties Measurement Methods, vol 2 K. D. Maglic, A. Cezairliyan, V E. Peletsky, Eds. Plenum New York, 1992 chapter 18. 

Thanks to the extensive literature on Aujj and the related smaller gold cluster compounds, plus some new results and reanalysis of older results to be presented here, it is now possible to paint a fairly consistent physical picture of the AU55 cluster system. To this end, the results of several microscopic techniques, such as Extended X-ray Absorption Fine Structure (EXAFS) [39,40,41], Mossbauer Effect Spectroscopy (MES) [24, 25, 42,43,44,45,46], Secondary Ion Mass Spectrometry (SIMS) [35, 36], Photoemission Spectroscopy (XPS and UPS) [47,48,49], nuclear magnetic resonance (NMR) [29, 50, 51], and electron spin resonance (ESR) [17, 52, 53, 54] will be combined with the results of several macroscopic techniques, such as Specific Heat (Cv) [25, 54, 55, 56,49], Differential Scanning Calorimetry (DSC) [57], Thermo-gravimetric Analysis (TGA) [58], UV-visible absorption spectroscopy [40, 57,17, 59, 60], AC and DC Electrical Conductivity [29,61,62, 63,30] and Magnetic Susceptibility [64, 53]. This is the first metal cluster system that has been subjected to such a comprehensive examination. 

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] ... 

Differential scanning calorimetry is applicable to the measurement of transition temperatures, specific heats, and heats of transition or reaction for all nonvolatile materials that do not evolve significant amounts of volatiles by reaction. The usual temperature range covered is -150 to 725°C. 

Next, the thermal properties of the dye must be such that absorption of the laser energy will result in dye diffusion but not in decomposition. The melting temperature Tm, the latent heat of fusion, AH, and the specific heat for these dyes were determined by differential scanning calorimetry using a DuPont 990 Thermal Analyzer. The data are given in Table II. No thermal decomposition products for these dyes were detected upon heating to 600 °C for 20 msec. 

ASTM E1269, 2004. Standard test method for determining specific heat capacity by differential scanning calorimetry. 

The specific heat as a function of temperature is measured by calorimetry, usually with DSC (differential scanning calorimetry). At Tg a jump to a higher level is found. 

This would not be problematic if standardized, reliable, reproducible, and inexpensive laboratory tests were available to estimate each of the required properties. Although several specialized laboratory tests are available to measure some properties (e.g., specific heat capacity can be determined by differential scanning calorimetry [DSC]), many of these tests are still research tools and standard procedures to develop material properties for fire modeling have not yet been developed. Even if standard procedures were available, it would likely be so expensive to conduct 5+ different specialized laboratory tests for each material so that practicing engineers would be unable to apply this approach to real-world projects in an economically viable way. Furthermore, there is no guarantee that properties measured independently from multiple laboratory tests will provide accurate predictions of pyrolysis behavior in a slab pyrolysis/combustion experiment such as the Cone Calorimeter or Fire Propagation Apparatus. 

The result for the thermal expansion coefficient, a, which is equal to (dV/dT)/V, is shown in Fig. 13.36 for the cooling and heating process. In the cooling process a decreases gradually from tq to ag. Hysteresis in the volume causes in the subsequent heating process an anomalous effect in the thermal expansion coefficient, depicted by undershoot and overshoot, as also shown in Fig. 13.36. A similar effect occurs in enthalpy H and accordingly in cp, the specific heat capacity, equal to dH/dT. This effect is frequently observed in DSC (Differential Scanning Calorimetry) experiments. 

Similarly, if a quantity such as the volume exhibits an abrupt change in slope, which occurs at the T, then there is a discontinuity in quantities associated with first derivatives of this parameter, or second derivatives of the free energy (with respect to appropriate thermodynamic variables), such as the specific heat (Figure 10-19). Accordingly, the Tg may be related to a second-order phase transition, but this remains in dispute. The experimentally observed transition is clearly governed by kinetics and the standard method of measuring this transition is by differential scanning calorimetry (DSC), which measures the specific heat. 

Differential scanning calorimetry (DSC) The method to measure the heat flow to a sample as a function of temperature. It is used to measure, for example, specific heats, glass transition temperatures, melting points, melting profiles, degree of crystallinity, degree of cure, and purity. 

In this section, some case studies will be presented on the characterization of CMP pad and slurry [17-20] using such advanced analytical techniques as dynamic mechanical analysis (DMA), modulated differential scanning calorimetry (MDSC), thermal gravimetric analysis (TGA), thermal mechanical analysis (TMA), dynamic rheometry, dual emission laser induced fluorescence (DELIF), and the dynamic nuclear magnetic resonance (DNMR). More specifically, these techniques were used to characterize (a) the effect of heat... 

Differential scanning calorimetry measures the thermodynamic parameters associated with thermally induced phase transitions. Here, the sample of interest and an inert reference are heated or cooled independently at a programmed rate, and in tandem, such that their temperatures change in unison and the differential temperature is maintained at zero. If the sample undergoes a thermally induced transition, heat must be applied to or withdrawn from the sample in order to maintain the same temperature in both sample and reference compartments. The instrument measures the heat flow into the sample relative to the reference and this dijferential heat flow (or excess specific heat) is recorded as a function of temperature, resulting in a trace, as shown in Fig. 1... 

Many relatively slow or static methods have been used to measure Tg. These include techniques for determining the density or specific volume of the polymer as a function of temperature (cf. Fig. 11-1) as well as measurements of refractive index, elastic modulus, and other properties. Differential thermal analysis and differential scanning calorimetry are widely used for this purpose at present, with simple extrapolative eorrections for the effects of heating or cording rates on the observed values of Tg. These two methods reflect the changes in specific heat of the polymer at the glass-to-rubber transition. Dynamic mechanical measurements, which are described in Section 11.5, are also widely employed for locating Tg. 

For the specific case of tetramethyl-l,2-dioxetane, the heat of reaction was determined experimentally by differential scanning calorimetry (DSC) to be A/fg = — 61 kcal/mole. Its activation enthalpy is about 25 kcal/moleThus, a total of... 

Thermal analysis techniques (differential thermal analysis (DTA), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and evolved gas analysis (EGA)) provide qualitative, semiquantitative, and in special cases, quantitative measurements of the energetic evolution of nanophase materials on heating. Variation of the heating rate and the atmosphere surrounding the sample provide additional information. Some examples are given below in the context of specific systems. 

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