Sulfur void formation

In 2004, void formation in spherical samples was rediscovered at the nanolevel and discussed in [4-6]. HoUow nanosheUs of cobalt and iron oxides and sulfides have been obtained by means of reaction of metaUic nanopowders with oxygen or sulfur. Contrary to [2, 3], these results have been explained by the Frenkel effect - out-diffusion of metal through the formation of a spherical layer of the compound is faster than in-diffusion of oxygen or sulfur through the same phase. This inequahty of fluxes generates the inward flux of vacancies, meeting inside and forming the void in the internal part of the system. 

Such a methodology is also useful for the chemoselective functionalization of internal voids of dendrimers. This can be accomplished for example by adding 2 equiv. of allyl, propargyl or phosphonate trifluoromethane sulfonate on the dendrimer of generation 1 71-lGj] (Scheme 34). Functionalization occurs on the sulfur atom of the two P=N-P(S) units with the quantitative formation of the... 

Organic sulfur is the dominant form in peats described in these studies. Pyrite, however, is abundant in brackish and marine peats, occurring in void spaces in or between plant debris (3). In a study of pyrite formation in freshwater peats, Altschuler et al. (5) determined parallel decline in ester sulfate with increases in pyrite as depth increased and concluded that pyrite formed at the expense of organic sulfur. In general, framboidal morphology is present at all salinities. Altschuler et al. (5) and Lowe and Bustin (10) found monosulfides to be minor in peats. 

The areas concerning monolithic intermetallics which have been studied in recent years are (i) the formation of mctastable aluminas, and their transformation to stable a-alumina, (ii) the formation of interfacial voids and scale adherence and how these are influenced by reactive elements and sulfur, and (iii) accelerated oxidation at intermediate temperatures. Additionally the applications oriented areas of (iv) coatings, (v) oxidation of composites, and (vi) life predictions have received attention. 

The Formation of Interfacial Voids and Scale Adherence and how these are Influenced by Reactive Elements and Sulfur... 

An important result of the present analytical study is the detection of S in Y-rich precipitates within the alloy. This observation supports the sulfur effect model", which proposes that reactive elements getter the S [16,17]. The presence of S reduces the surface energy of the metal and thereby promotes the formation of interfacial voids, as has been shown by Grabke ct al. [18]. Although no S-rich particles have been found in NiAl - 0.2 wt% Zr. it is possible that the Zr can lower the activity of S by solute - solute interaction. Further work is necessary in order to study the interaction between reactive elements and S. 

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