Simulations of fine ceramics cascade synthesized by the self-propagating high-temperature synthesis method
- PDF / 380,887 Bytes
- 9 Pages / 612 x 792 pts (letter) Page_size
- 94 Downloads / 151 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Simulations of fine ceramics cascade synthesized by the self-propagating high-temperature synthesis method Bai-Wai Chen and Chien-Chong Chena) Department of Chemical Engineering, National Chung Cheng University, Chia-Yi 621, Taiwan (Received 22 September 1996; accepted 23 June 1997)
Due to the convective and radiant heat losses, there exists a maximal converted length of a dense pellet synthesized by the self-propagating high-temperature synthesis (SHS) method. In this paper, we numerically investigate the possibility to increase that maximal converted length by cascading two reactant pellets in series, where an interface is naturally and artificially introduced. First, the impacts of both the bulk and interfacial parameters on the SHS process are estimated. The maximal converted length for a single pellet is computed. Next, by varying the interfacial parameters, it is found that more than 10% of extra converted length is obtained by the proposed cascade arrangement. Effects of the bulk parameters on the same purpose are also addressed. I. INTRODUCTION
The self-propagating high-temperature synthesis (SHS), or the combustion synthesis, initiated in the early 1970s in the former Soviet Union, is emerging as an attractive way to produce advanced materials, because the SHS method has the following advantages1 : lower energy requirement, higher product purity, simpler and cheaper equipment, higher sinterability, and possible nonequilibrium phases in the final products. Also, combined with the pressurized techniques such as explosives,2 HIP,3 and HPCS,4,5 the SHS method is capable of producing very dense products. In the SHS method, a reactant pellet is subject to an external heat source, which can be a heated coil, a torch, and a laser beam, etc., on one end and is then ignited at this end. Due to the highly exothermic nature of reaction, a self-sustained combustion wave propagates from this ignited end to the other, and converts the reactant into the product. A lot of advanced materials2,5–10 such as refractory, intermetallic materials, super alloys, and superconductors, etc., can be manufactured by this method. Besides the successes of producing advanced materials experimentally, theoretical studies on the SHS method are abundant in the literature since the physical and chemical mechanisms involved are rich and complicated. The mechanisms include transport phenomena (momentum, heat, and mass transfer), phase transformations, microstructural organization, and chemical kinetics. Thus, a new research field called structural macrokinetics advocated by Merzhanov11 is created to study the coupling effects of the above mechanisms. From the literature, topics of theoretical studies included determination of combustion velocity,12–14 influences of physical properties on
a)
Author to whom correspondence should be addressed. J. Mater. Res., Vol. 13, No. 5, May 1998
http://journals.cambridge.org
Downloaded: 15 Mar 2015
combustion,15–18 onset of combustion wave (i.e., when to hav
Data Loading...
