Overheating Interface Effect

In the case of embedded nanosolids, the coefficient of surface energy will be replaced by the interfacial energy if surfaces are completely saturated with atoms of the surrounding matrix. Nanda et al. [47] introduced the ratio as a perturbation of surface energy between the matrix and the embedded specimen, 

If the surface energy of the matrix yMat T. the core nanosohd melts at a temperature that is higher than its bulk counterpart. This expression matches the experimental data of Pb particles embedded in an Al matrix but overestimates the Tn, for Indium particles embedded in an Al matrix by some 10-20 K using the known y and yj i values. 

The models of LSN, HMG and LNG suit only the cases of suppression (ATiji 0) while the liquid-drop and the RMSD models cover both the undercooling and the overheating. For particles larger than several nanometers, all the models worked sufficient well despite the disputable mechanisms. 

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The existence of the so-called microwave effect has not been proved. It does, however, seem to have been demonstrated that overheating of polar liquids [17] occurs and that hot spots are present in heterogeneous systems, especially at the interface [38]. Similarly, microwave irradiation results in an increase in the molecular mobility in solids [5 b]. 

The substantial effect of secondary breakup of droplets on the final droplet size distributions in sprays has been reported by many researchers, particularly for overheated hydrocarbon fuel sprays. 557 A quantitative analysis of the secondary breakup process must deal with the aerodynamic effects caused by the flow around each individual, moving droplet, introducing additional difficulty in theoretical treatment. Aslanov and Shamshev 557 presented an elementary mathematical model of this highly transient phenomenon, formulated on the basis of the theory of hydrodynamic instability on the droplet-gas interface. The model and approach may be used to make estimations of the range of droplet sizes and to calculate droplet breakup in high-speed flows behind shock waves, characteristic of detonation spray processes. 

At the mixed interface, the n may not change substantially, so we can introduce the interfacial bond energy as Sint = yEb and the interfacial atomic cohesive energy as Sc,int = yzSb, and then, all the equations for the surface effect are adoptable to the interface properties. A numerical fit of the size dependence of overheating for In/Al [61], Ag/Ni [62], and Pb/Al and Pb/Zn [63] core-shell nanostructures, presented in Fig. 14.3(i) has led to a y value of 1.8, indicating that an interfacial bond is 80 % stronger than a bond in the bulk of the core material [64]. If one took the bond contraction to be 0.90-0.92 as determined from the As- and Bi-doped CdTe compound [46] into consideration, the m value is around 5.5-7.0. 

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