Narasimharao Dontula

In situ high-temperature X-ray diffraction characterization of silver sulfide, Ag2S

Silver sulfide, Ag 2 S, is most commonly known as the tarnish that forms on silver surfaces due to the exposure of silver to hydrogen sulfide. The mineral acanthite is a monoclinic crystalline form of Ag 2 S that is stable to 176°C. Upon heating above 176°C, there is a phase conversion to a body-centered cubic (bcc) form referred to as argentite. Further heating above 586°C results in conversion of the bcc phase to a face-centered cubic (fcc) phase polymorph. Both high-temperature cubic phases are solid-state silver ion conductors. In situ high-temperature X-ray diffraction was used to better understand the polymorphs of Ag 2 S on heating. The existing powder diffraction file (PDF) entries for the high-temperature fcc polymorph are of questionable reliability, prompting a full Rietveld structure refinement of the bcc and fcc polymorphs. Rietveld analysis was useful to show that the silver atoms are largely disordered and can only be described by unreasonably large isotropic displacement parameters or split site models.

Foamed and Oriented Polypropylene Films

Foamed polypropylene films that are made by extruding mixtures of polypropylene (PP) and a chemical blowing agent are described in this study. The films are prepared by a cast extrusion process, followed by machine direction orientation. This article describes the structure–property relationships of the resultant foamed PP films and the varied applications of the foamed films.