Galena stability to 26 kbar

Publication Type  Journal Article
Year of Publication  2007
Authors  Wheeler, K. T.; Walker, D.; Johnson, M. C.
Journal Title  American Journal of Science
Volume  307
Issue  3
Pages  590-611
Journal Date  Mar
ISBN Number  0002-9599
Accession Number  ISI:000247394000002
Key Words  high-pressure; silver-halides; melting points; sulfur system; fe-fes; pbte; pbs; temperatures; polymorphism; density

The melting point of galena was measured by differential thermal analysis to 25 kbar. The meltingpoint is 1191 degrees C at 5.9 kbar and increases to similar to 1315 degrees C by 25 kbar along a concave-down trajectory. The form of the PbS melting curve resembles those of similarly structured compounds that show a range of initial slopes and curvatures. Initial liquidus slopes of several Bl-structured compounds including PbS correlate well with melting volume change. However, the roughly 25 J/mol*K entropy of melting required for PbS by the volume of melting, initial liquidus slope, and Clapeyron equation is approximately double literature estimates. Similar discrepancies exist for the other B1-structured compounds. Liquidus curvature correlates well with the initial ratio of liquid to solid compressibility. PbS liquid compressibility of similar to 12*10(-12) cm(2/) dyne is estimated from galena compressibility and initial melting slope. The transformation of galena from cubic to orthorhombic structure with pressure was determined by electrical resistance measurements up to 1000 degrees C and occurs at about 26 kbar with little temperature variation. Galena's maximum stability is at the inferred triple point among galena, liquid, and orthorhombic-structured PbS at similar to 26 kbar and similar to 1315 degrees C.


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URL  <Go to ISI>://000247394000002
DOI  Doi 10.2475/03.2007.02