Systems for Simulation of Reactant Interaction

The spatial structure of a heterogeneous reactant powder mixture with its random distribution of reactant particles is too complex for a study of the elemental stages of structure formation mechanisms. This problem has been overcome by the development of experimental techniques that utilize reactants with simpler geometries, such as wires and foils. These methods isolate the reactant interaction, thus yielding additional information. 

To provide a well-defined boundary between reactants, experiments have been conducted using ensembles of laminated Ni and Al metallic foils (Anselmi-Tamburini and Munir, 1989). These experiments were motivated by modeling efforts that used a foil geometry to understand interactions between powder reactants (Hardt and Phung, 1973 see Section IV,B). In the experimental technique, nickel (12.5 and 125 tm) and aluminum (12.5 fim) foils were laminated in specific stoichiometric amounts corresponding to the NiAl and NiAls compounds. These ensembles were then ignited in a chemical oven consisting of Ni-I-Al pow- 

In both the electrothermographic and foil assembly methods, the rapid heating rates associated with combustion synthesis are reproduced. However, the powder reactant contact found in a compacted green mixture of particulate reactants is not adequately simulated. One way to overcome this is to investigate interactions of particles of one reactant placed on the surface of the coreactant in the form of a thin foil. The physical simulation corresponds to the reaction of a powder mixture where the particle size of one reactant is small while that of the coreactant is relatively large. Two methods have been used to initiate the interaction. 

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