Eq 3

where AJJ f is the heat of formation for the compound at a reference temperature, T, such as the reaction initiation temperature or 298 K. CPad and CPd are the heat capacity of the compound, AB, and the diluent, D, phase, ttT

respectively. The values for ^ f , O"1 ad. and CPad are obtained from thermodynamic handbooks. From Eq 3, the mole fraction of the product phase AB, (x), can be determined using numerical integration techniques. The reaction utilizing prealloyed NiAl powder as the diluent for the combustion synthesis of nickel and aluminum powders is as follows:

XM + XA1 + (1 - x)NiAlprealloyed ' >xMAl reaction

The subsequent energy balance is:

Using Eq 4b, x was determined to be 78 mol%, which corresponds to 22% NiAl prealloyed powder required to prevent slumping during combustion synthesis of NiAl. This is consistent with experimental results (Fig. 7, Ref 25). In practice, it is important not to overdilute the reaction as this will inhibit liquid formation and impede densification.

Augmenting Liquid Phase Formation by Alloying. The addition of alloying elements that melt during combustion synthesis prolongs the duration, distribution, and amount of the liquid phase during processing. These elements may or may not participate in the actual reaction. An example of the former is the reactive synthesis of aluminum-modified MoSi2, from the following reaction:

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