Polymorphic Mode

The polymorphic mode of nucleation is characterized by the conservation of the concentration profile, which is a reasonable assumption if the system has no time to redistribute atoms inside and outside the nucleus in the process of lattice transformation. For the polymorphic mode, we also consider the two cases discussed earlier (i) without shape optimization (rp = 1) and (ii) with shape optimization. 

For each value of the curvature parameter a one finds a critical zone width Kcr, at which nucleation by the polymorphic mode becomes possible. We define this critical width by postulating that the nucleation barrier becomes lower than bOke for all fC Kci a) (nucleation allowed). No direct measurements of the curvature of the Gibbs potential of the AI9C02 phase are known. Therefore, we first determine 

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Figure 4.2 Nucleation at polymorphic mode and frozen-in concentration profile (a) dependence of the Gibbs free energy per atom on the compositions of the old and new phases and (b) frozen-in profile in the diffusion couple, approximately linear in the nucleation region.

Thermodynamics of the Polymorphic Mode of Nucleation in a Concentration Gradient... 

The basic results of the analysis for the polymorphic mode of nucleation are as... 

Therefore, the transversal mode with shape optimization gives us the same qualitative results as the polymorphic mode ... 

Yet, in most cases, soHd-state reactions proceed in diffusion couples with low mutual solubihty even in the metastable state (Figure 4.15b). In the case of phase 1 nucleating between a and p, in the absence of phase 1, these phases have metastable solubilities c and 1 — c . Interdiffusion must yield a steplike profile with a concentration gap (c, c ), which does not contain the concentration interval of phase 1. Here the polymorphic mode cannot be reaUzed. 

Figure S.6 Section through the AC(N,Cx) surfaces for the polymorphic mode without shape optimization at a composition Cy = 15 at.% (a = 8 X 10 J/atom, calculation for different diffusion zone widths /f) = 3 nm K2 = 3.5 nm ...

Figure 5.7 Polymorphic mode with shape optimization at a = 4 x 10 J/atom ...

Thus, it turns out that the curvature parameter required for the numerical calculation to obtain critical gradients in the order of the experiment is quite reasonable and corresponds to the thermodynamic situation of the Al-Co system. Especially, for the polymorphic nucleation mode without shape optimization, we find almost exact agreement. The value of a = 8 x 10 J/atom for the polymorphic mode without... 

Typically this technique includes the preparation of the base material that involves the blending of film-forming excipients and therefore the API mixed along in a very appropriate solvent or solvent system. The choice of solvent basically depends on the API to be incorporated into the film/strip. The physicochemical properties of the API like heat sensitivity, shear sensitivity, the polymorphic mode of the API utilized, compatibihty of the API with solvent and different strip excipients are to be critically studied. The several components during this are liquid rheology, desired mass to be forged and content uniformity. Solvents used for the preparation of solution or suspension ought to ideally be elite ones from the ICH 3 solvent list [2]. 

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