Use of two-color array pyrometry for characterization of combustion synthesis waves
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Use of two-color array pyrometry for characterization of combustion synthesis waves U. Anselmi-Tamburini,a) F. Maglia, and G. Spinolo Department of Physical Chemistry and C.S.T.E./CNR, University of Pavia, V. le Taramelli, 16, 27100 Pavia, Italy
Z.A. Munir Department of Chemical Engineering and Materials Science, University of California, Davis, California 95616-5294 (Received 27 June 1999; accepted 29 October 1999)
A two-color array pyrometer was used to investigate morphological developments on the surface of materials undergoing self-propagating high-temperature reactions. Time sequences of temperature spatial profiles during wave propagation were found to be complex in their nature and dynamics. They contain features that are interpreted in terms of morphological changes during the process. These features include formation of cracks or voids, expansion of the sample, and formation of droplets of metals on the surface. The use of the array pyrometer for determination of the activation energy of the combustion reaction between Zr and NiO is reported. I. INTRODUCTION
Among the more commonly used approaches in solidstate synthesis in recent years is one that takes advantage of the propensity of some reactions to self-sustain. The process, self-propagating high-temperature synthesis (SHS), has been used to synthesize a large number of material.1–5 It is characterized by several features that have made it attractive for synthesis of monolithic, composite, functionally graded, and metastable materials. However, the method is restricted to reactions that generate a significant amount of heat. Such reactions can propagate in the form of fronts able to advance at relatively high velocities through the reactants without the need for additional external energy. The reaction fronts show several macroscopic similarities to gas-phase combustion; hence the process is commonly referred to as combustion synthesis. Furthermore, these fronts are characterized by high temperatures (1500 < T < 3500 °C) and steep thermal gradients (103–106 K cm−1). Details of these and other characteristics of the process have been reported in several review papers.1–5 Despite the large number of investigations on this process, a complete understanding of the mechanisms involved is not at hand. This is largely due to the intrinsically complicated nature of the process, as indicated above, as well as to experimental difficulties arising from the heterogeneous nature of the reactions. Investigations on the mechanisms of these processes generally rely on
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J. Mater. Res., Vol. 15, No. 2, Feb 2000 Downloaded: 16 Mar 2015
indirect evidence. The only real-time method for investigating the mechanistic steps of the process is by synchrotron time-resolved x-ray diffraction. However, because of experimental difficulties, results of such studies have not provided unambiguous interpretations of the sequence of reactions.6,7 Another
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