Studies on the Coprecipitation of Cadmium and Mercuric Sulfides.

Abstract

It has long been known that the quantitative separation of cadmium and mercury by procedures which depend upon the different solubilities of their sulfides is in many cases impossible (3,4,5,6). Because of the near equality in atomic radii of the two metals, it is to be expected that substitutional solid solutions should easily be formed. The investigations of Bottger and Druschke (3) and of Ahrens (1) point strongly to the occurrence of solid solutions in the zinc blende structure as the explanation of the induced precipitation of cadmium sulfide by mercuric sulfide and the failure of boiling dilute nitric acid to extract all the cadmium from a mixed precipitate of these sulfides. Since both sulfides are polymorphous, solid solutions might be expected to exist in any one of the crystal structures exhibited by the pure components. It therefore appeared of interest to us to study the structures of the phases obtained by coprecipitation of the two sulfides under a variety of conditions, and to compare them with the structures formed by the separate precipitation of each substance under the given conditions. During the course of the investigation, observations were made bearing on the polymorphism of both sulfides.CADMIUM SULFIDE Cadmium sulfide is dimorphous (8), crystallizing in a hexagonal form (wurtzite structure) and also in a cubic form (zinc blende structure). Milligan (7) has reported some of the conditions under which each modification is precipitated by hydrogen sulfide from neutral or acid solutions of various cadmium salts.No data on the stability relations of the two modifications have been heretofore available. By direct observation of the transition

Stacking fault in precipitated cadmium sulphide

“…Therefore, what are being observed in this study are atomic structures as grown of the precipitates. Although c~-CdS is said to be the stable modification at room temperatures (Rittner & Schulman, 1943), fl-CdS seems also to be practically stable at the temperatures. Since, moreover, the specimens are not subjected to any mechanical works, the theories to be considered for interpretation of the results do not seem to lie in those regarding 'deformation faults', but those regarding 'growth faults'.…”

Polymorphism, band-structure, band-lineup, and alloy energetics of the group II oxides and sulfides MgO, ZnO, CdO, MgS, ZnS, CdS

“…The energy difference between the two tetrahedral polymorphs (ZB and WZ) is comparatively small, both in DFT and RPA, as expected. Notably, the RPA predicts that the ZB structure of CdS is slightly lower in energy than the WZ phase, which is generally considered to be the ground state [29], even though the zinc-blende modification of CdS is well known. However, the energy difference of 8 meV/fu is small enough to be considered essentially degenerate within the limits of the calculations, which do not include zero point motion and finite temperature effects.…”

Nicht-VSEPR-Strukturen und chemische Bindung in d0-Systemen

“…Es wurde festgestellt, dass Rumpfpolarisation und d-Orbitalbeteiligung an s-Bindungen die Nicht-VSEPR-Strukturen begünstigen, Ligandenabstoûungen und p-Bindungen jedoch in die entgegengesetzte Richtung wirken. [135] Demnach kann, wie in Abbildung 11 gezeigt ist, ein groûes, Abbildung [136] auf eine quantitativere Basis gestellt, [137] und es wurde auch von anderen Gruppen getestet. Rumpfpolarisation und s-Bindungen sowie die üblicherweise zu ihrer Behandlung verwendeten Modelle werden in den Abschnitten 3.1 ± 3.6 beschrieben.…”