Induction time of a polymorphic transformation

Abstract

We analyze the processes governing the lifetimes of transient metastable polymorphs, within the context of classical nucleation theory.

Non-Equilibrium Crystallization Pathways of Manganese Oxides in Aqueous Solution

“…4, we construct Pourbaix free-energy orderings of manganese (oxyhydr)oxide phases at three conditions within the equilibrium β-MnO 2 stability window; at pH = 8, 9.5, and 11, with E = +0.5 V and [Mn 2+ ] = 10 −2 M. We compute the oxidation pathway of Mn 2+ (aq) under these conditions, using the procedure we derived in ref. 25 , described here briefly:…”

“…Even if the metastable phase completes crystal growth by consuming Mn 2+ to equilibrium, Ψ Mn2+ is still supersaturated with respect to the more stable phases. The next lowest-barrier phase nucleates, and this process repeats by dissolution-reprecipitation in a recursive, energetically-cascading series of metastable stages down to the equilibrium phase, β-MnO 2 25 . Figure 4a shows the computed Mn 2+ oxidation pathways under the three considered pH conditions.…”

“…According to classical nucleation theory, a metastable phase can precipitate first from a supersaturated solution if it has a lower nucleation barrier than the stable phase [23][24][25] , The nucleation barrier takes the form:…”

Visualising early-stage liquid phase organic crystal growthvialiquid cell electron microscopy

“…However, unlike pXRD, LCEM can be used to probe crystalline particles at their inception and early-stage growth which may be a distinct metastable phase preceding the final stable crystalline product observed at the laboratory or industrial scale. 24 While it should be noted that the nucleation mechanisms present in LCEM are distinct from typical supersaturation induced crystallisation, direct observations of these crucial stages will offer new insights into the missing-steps of organic crystallisation and lead undoubtedly to a better understanding of the processes and thus control over them.…”

Thermodynamic Routes to Novel Metastable Nitrogen-Rich Nitrides

“…41,42 Syntheses of metastable nitrides often require low-temperature reaction conditions, which kinetically inhibit decomposition into gaseous N 2 or transformation to equilibrium phase(s). 43 Under constrained equilibrium, where reactive nitride precursors cannot recombine to form N 2 , phase stability on the nitrogen-rich end should be calculated with respect to the chemical potential of the reactive nitrogen precursor. This may "stabilize" nitrogen-rich metastable nitrides ( Figure 2B), as they are above the convex hull with respect to standard-state gaseous N 2 , but are below the hull connected with the reactive precursor.…”