Experimental Thermograms Research Articles

Étude de la cinétique de la dégradation thermique du polypropylene et du polystyrène par analyse thermogravimétrique

Kinetic studies on the thermal degradation of polypropylene and polystyrene have been carried out using the thermogravimetric technique. Experimental thermograms have been interpreted by means of a simulation model which takes into account several simultaneous or consecutive reactions. In nitrogen, polypropylene degradation involves two reactions. The activation energy calculated for the second reaction, which corresponds to the main part of the weight loss curve, agrees with values obtained by means of calculation methods based on only one overall reaction. In air, a third reaction is added. Its activation energy is also in agreement with published values. However, for the two studied materials, orders of reaction are different.

Apparent temperature degradation in thermograms of human anatomy viewed obliquely.

A series of experimental thermograms were obtained to determine the significance of body curvature on apparent temperature measurement. Variations of apparent temperature on oblique views, predicted by theory, are discussed. The concern that "hot spots" on thermograms might not be visible in oblique views is unfounded for angles of less than 75° from normal. A minor effect of less than 1° F is seen in relatively large (>75°) angles of incidence.

Determination of kinetic parameters for the thermal degradation of polymers by the quasilinearization technique

The thermal degradation of polymers is explored generally by the experimental technique of thermogravimetry (TG). Existing mathematical methods for processing dynamic TG data to obtain kinetic parameters for non-linear models require data obtained at a constant rate of temperature rise and employ one or more graphical techniques, which are time-consuming and lead to some inaccuracy. A recently developed numercial approach to the determination of kinetic parameters which avoids the forementioned problems and provides a rapid, flexible, systematic, and accurate technique is the Bellman-Kalaba method of quasilinearization. Their general technique is extended and applied to TG data. The method presented utilizes the experimental thermogram(s) directly and selects the kinetic parameters by a least-squares-optimization procedure to best fit the data. The calculations are conveniently carried out on a digital computer. The technique has been applied to data on the thermal degradation of high-temperature polymers including polyphenylene, polyimide and polyquinoxaline.

New developments in breast thermography. High spatial resolution.

Two design trends have become evident in the development of clinical thermo-graphic equipment—higher frame rates which meet the requirements for real-time presentation and novel color and isotherm techniques designed to increase the differential temperature capabilities of display systems. These developments, for the most part, have been accomplished at the expense of spatial resolution. Little has been reported on the characteristics of high spatial resolution thermography. With the rapid developments in detector technology, it has now become possible to retain the desired degree of temperature resolution at clinically acceptable frame rates while increasing spatial resolution. Such a system is presently being tested at the University of Texas M. D. Anderson Hospital and Tumor Institute and its performance compared with commercially developed thermographic units. The criteria for comparison are the diagnostic value of the thermograms and image quality as determined by the modulation transfer function. At the present time, the experimental thermograms indicate that high spatial resolution simplifies the recognition and classification of thermal patterns while decreasing the number of false-positive examinations. Information may also be derived concerning the heat transfer processes involved. The experimental scanner is not suited for routine clinical use and theoretical calculations concerning the development of an optimal clinical scanning device are presented.

Kinetic parameters in polypropylene degradation from DTA traces

AbstractA novel and relatively simple procedure is described for the estimation of kinetic parameters in pyrolyses from DTA traces. The expressions derived are tested by utilizing data from experimental thermograms. Calculated values of parameters agree well with reported values.

Estimation of kinetic parameters from thermogravimetric traces

AbstractA novel and comparatively simple procedure is described for the estimation of values of kinetic parameters from thermogravimetric traces. The expressions derived are assessed for their facility and reliability by utilizing data from theoretical and experimental thermograms. Calculated values of parameters agree well with assumed or reported values.