Amorphous configurational contributions

The Cp s curve of the reheated (control) sample is unaffected by thermal changes and consists of configurational contributions as well as those arising from purely thermal vibrations. Therefore, the vibrational specific heat, Cp,v, for the amorphous alloy is extrapolated from the Cp values in the low-temperature region and is a linear function of temperature, viz.,... 

Fig. 3. Plot of logio normalized ion-exchange rate at amorphous silica saturation vs. the amount of excess alkalis (Na, K), denoted by the molar ratio XAlk/(Al + IVB + FeT). All boron is treated as four-fold coordinated (IVB) and total iron (FeT) is regarded as ferric. The ion-exchange rate subtracts out the contribution of alkalis to solution from matrix dissolution. As the amount of excess alkali increases, the ion-exchange rate increases. This increase in rate reflects the increasing amount of alkalis in non-bridging oxygen (NBO) configurations. Error bars represent 2-

In both cases the reference state ( ) is pure unmixed components S = S + S and U =U +U, where S and U are the entropy and energy of n moles of pure solvent, and Sj and U refer to moles of polymer in pure amorphous polymer. The energy Uln (5.2.12) becomes a Helmholtz energy if x contains an entropic contribution. However, this Helmholtz energy only includes those entroplc contributions which are proportional to (for example, those originating from orientations of the solvent molecules, as in hydrophobic bonding), and not the configurational entropy of the chains as embodied in (5.2.111. 

The long-pathway rearrangement processes expected for fragile materials at low temperatures are expected to be rare, to involve a local disruption of the otherwise well-structured amorphous medium, and to be relatively long-lived on the usual molecular time scale. These features all contribute to a substantial lengthening of the mean relaxation time /rci(7 ), Eq. (36), with declining temperature. Furthermore, the landscape diversity of deep traps and of the configuration space pathways that connect them should produce a broad spectrum of relaxation times, just as required by stretched-exponential relaxation functions, Eq. (34). 

Other researchers have focused on the thermodynamic contributions to physical stability and have investigated if these parameters could be exploited for stability predictions. The configurational heat capacity (Cpconf) is defined as the difference between the heat capacity of the amorphous and crystalline forms of a material (Eq. 2.23) ... 

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