Kinetics thermal analysis system

An Automated Thermal Analysis System for Reaction Kinetics," A.F. Kah, M.E. Koehler, T.H. Grentzer, T.F. Niemann, and T. Provder, Computer Applications... 

Kah, A. F. Koehler, M. E. Grentzer, T. H. Niemann, T. F. Provder, T. "An Automated Thermal Analysis System for Reaction Kinetics" in "Computer Applications in Applied Polymer Science" Provder, T., Ed. ACS SYMPOSIUM SERIES No. 197, American Chemical Society Washington, D.C., 1982 pp. 197-311. 

An Automated Thermal Analysis System for Reaction Kinetics... 

We have used in this work, the Mettler TA2000B thermal analysis system and the supplied Kinetic and Applied Kinetic Programs. This instrument and associated software is capable of analyzing on-line the nth-order equation (1.1). 

Instrumental. The Mettler TA2000B thermal analysis system is equipped with an interface system, and Hewlett-Packard 9815 desk top calculator and 7225 plotter. Samples, weighing 5-10 mg, sealed in aluminum pans and under a nitrogen blanket, were heated in the calorimeter at a rate of 10 deg/min from -35 or 10 deg C to 180 deg C respectively, for specific heat and kinetic scans. Specific heat measurements were calibrated with alumina to an accuracy of 3%. Temperatures and enthalpies were calibrated with an Indium sample. The accuracies were .02 deg C and 2% (Indium 28.5 J/g), respectively. 

Such a differential heating program leads to increased sensitivity and resolution in TGA but also to a much increased time-frame for the analysis. Dynamic rate TG appears to have addressed both of these features and hence has much potential as a high resolution/ rapid thermal analysis system, which, unlike SCTA, can be applied for rapid and reproducible thermal analysis of a wide range of complex materials. Finally, modulated temperature thermogravimetrie analysis has enhanced potential for the kinetic analysis of thermal decomposition reactions over conventional TGA because of its greater resolution of thermal events. 

Due to the rapid changing technology in microcomputers and microprocessors, data and control systems have evolved rapidly a life time of 3-4 years is about the maximum for such a system. Thus, only the most current computer system will be described here for a particular type of thermal analysis system. No attempt will be made to give details on the software programs in use these can be obtained from the commercial vendor of the system, if desired. Almost all the commercially available thermal analysis instrumentation employs a microprocessor for operating system control or a microcomputer for data processing. Either a proprietary or a commercially available microcomputer is employed to process the experimental data into conventional thermal analysis plots or to perform more sophisticated kinetics or purity determination calculations. 

Any compd or mixt whose heat of formation is smaller by 500 J/g (or more) than the sum of the heats of formation of its reaction products must be regarded with suspicion and handled with more than usual care. The hazards involved in working with a potentially expl system are directly proportional to the amount and to the rate of energy release. Because the reaction kinetics cannot be predicted, the propensity of a new system for expl reaction must be determined. The sensitivity of the system can be evaluated by means of impact, friction, shock and electrostatic discharge. Appropriate methods are reviewed in the Experimental and Hazard Assessment section of this article. Sensitivity to heat or elevated temp may be evaluated by use of differential thermal analysis (DTA)... 

Thermogravimetric analysis (TGA) has been used to study the kinetics of feedstock pyrolysis. In this work, a Seiko 220 TG/DTA thermal balance system was used. The sample mass was 10.0 0.1 mg. The heating rate was 10 C/min. For each test, the nitrogen gas was first introduced in the furnace to remove the air. Then the pressure in the furnace was lowered by a vacuum pump to 13 kPa absolute. 

A DuPont Model 990 Thermal Analysis Console with Model 910 DSC accessory was interfaced to a minicomputer system by means of a microcomputer for automated data collection. A program to provide the analysis of reaction kinetics data by the single dynamic scan method for DSC kinetics was developed. Features of this program include a fit of the data to a single equation by multiple regression techniques to yield the reaction order, the energy of activation and the Arrhenius frequency factor. The rate constant k(T) is then calculated and conversion data as a function of time and temperature can be generated at the operator s option. 

Water molecules are constantly in motion, even in ice. In fact, the translational and rotational mobility of water directly determines its availability. Water mobility can be measured by a number of physical methods, including NMR, dielectric relaxation, ESR, and thermal analysis (Chinachoti, 1993). The mobility of water molecules in biological systems may play an important role in a biochemical reaction s equilibrium and kinetics, formation and preservation of chemical gradients and osmotic pressure, and macromolecular conformation. In food systems, the mobility of water may influence the engineering processes — such as freezing, drying, and concentrating chemical and microbial activities, and textural attributes (Ruan and Chen, 1998). 

MetastabiUly - a common feature in both macromolecular and pharmaceutical systems - is a second major challenge for the coming years. For a thorough understanding of die kinetics of all lands of temperature- and time-dependent processes related to metastability, there is now an urgent need for new and better-matching thermal analysis and calorimetry techniques. 

Temperature may not always be raised in a linear fashion. In the case of CRT A (Controlled Rate Thermal Analysis), the heating rate is varied in such a manner as to produce a constant rate of mass loss. Alternatively a sinusoidal temperature rise is superimposed on the linear rise this is known as Modulated TG and allows the continuous calculation of activation energy and pre-exponential factor during a run. Sometimes a Temperature Jump (or stepwise isothermal) " is used, where temperature is held constant for a time, then jumped rapidly to a higher constant temperature (usually quite close in temperature). All of these procedures are supposed to help in the determination of kinetics of reaction. Another system accelerates the temperature rise when no mass loss is experienced, i.e. between reactions. The rate is slowed to a low value during mass loss. Some manufacturers call this High Resolution TG and an example follows. 

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