Advanced Thermal Analysis System

Advanced Thermal Analysis System (ATHAS) Polymer Heat Capacity Data Bank... 

Pyda et al. (1998) studied in detail the heat capacity of PTT by adiabatic calorimetry, standard DSC and temperature-modulated differential scanning calorimetry (TMDSC) for this measurement. The computation of the heat capacity of solid PTT is based on an approximate group vibrational spectrum and the general Tarasov approach for the skeletal vibrations, using the well-established Advanced Thermal Analysis System (ATHAS) scheme. The experimental heat capacity at constant pressure is first converted to heat capacity at constant volume using the Nemst-Lindemann approximation... 

Heat capacity is the basic quantity derived from calorimetric measurements, as presented in Sects. 4.2-4A, and is used in the description of thermodynamics, as shown in Sects. 2.1 and 2.2. For a full description of a system, heat capacity information is combined with heats of transition, reaction, etc. hi the present section the measurement and the theory of heat capacity are discussed, leading to a description of the Advanced THermal Analysis System, ATHAS. This system was developed over the last 30 years to increase the precision of thermal analysis of linear macromolecules. 

Conclusions. The heat capacity is one of the few macroscopic quantities with a well-understood link to the microscopic molecular motion. The Advanced Thermal Analysis System displayed in Fig. 2.76 allows to establish empirical addition schemes... 

The Advanced THermal Analysis System was developed in the 1980 s to be able to interpret the heat capacities of linear macromolecules more precisely. In the solid state, the heat capacity is described by contributions from the vibrations of an approximate spectrum. Any deviation is a sign of additional processes, usually conformational disordering or motion. In the liquid state extensive addition schemes based on group contributions have been developed to judge heat of fusion baselines and increases in heat capacity on devitrification at Tg. 

Fig. 2. Heat capacity contributions of the skeletal and group vibrations of solid poly-oxymethylene, calculated by the Advanced Thermal Analysis System (ATHAS). A, C B, C C, group vibrations D, skeletal vibrations. To convert J to cal, divide by 4.184.

ZHO 00] Zhou X., He J., Liao L.S. et al, Real-time observation of temperature rise and thermal breakdown processes in organic LEDs using an IR imaging and analysis system ". Advanced Materials, vol. 12, no. 4, pp. 265-269, 2000. 

More advanced techniques are now available and section 4.2.1.2 described differential scanning calorimetry (DSC) and differential thermal analysis (DTA). DTA, in particular, is widely used for determination of liquidus and solidus points and an excellent case of its application is in the In-Pb system studied by Evans and Prince (1978) who used a DTA technique after Smith (1940). In this method the rate of heat transfer between specimen and furnace is maintained at a constant value and cooling curves determined during solidification. During the solidification process itself cooling rates of the order of 1.25°C min" were used. This particular paper is of great interest in that it shows a very precise determination of the liquidus, but clearly demonstrates the problems associated widi determining solidus temperatures. 

The initi findings of the Tg depression in PLLA were ex situ characterization by thermal analysis. In the remainder of this section the use of advanced characterization methods is illustrated to provide additional insight into the novel behavior. The methods used to address the polymer were those appropriate to provide in situ, real-time information on morphology via SALS, and on segmental dynamics via DRS. The rationale for the use of these tools is that the dipolar loss peak in the frequency domain (from DRS) is closely related to the glass transition of a given polymer system — hence, under isothermal conditions, a change in the loss peak frequency is... 

Flotherm. Advanced thermal analysis of packaged electronic systems. Flomerics, Inc., Westborough, MA. Higgins, C. 1991. Signetics Corp. presentation, Nov. 

Compilation based on four sources Keith, F. 1973. Heat Transfer. Harper Row, New York. Rohsenow, W.M. and Choi,H. 1961. Heat, Mass, and Momentum Transfer. Prentice-Hall, Englewood Cliffs, NJ. Kraus, AD. and Bar-Cohen, A. 1983. Thermal Analysis and Control of Electronic Equipment. Hemisphere, New York. Moffat, R.J. and Ortega, A 1988. Direct air coohng in electronic systems. In Advances in Thermal Modeling of Electronic Components and Systems, ed. A. Bar-Cohen and A.D. Kraus, Vol. 1, pp. 129-282. Hemisphere, New York.)... 

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