Hello,
I purchased a manufactured bottle of PbSO4 from Alfa Aesar and according to the XRD it's 100% PbSO4, however when I ran it through the XPS I have low energy S2p peaks (160.38 eV and 163.26 eV), which remind me of PbS and S. All of the other peaks point to PbSO4 (O1s: 530.59 eV; Pb4f: 138.2 eV and 143.06 eV; S2s: 231.54 eV; S2p: 167.7 eV). The presence of PbS is surprising since PbS oxidizes to PbSO4, particularly when enough time has passed (this bottle has been sitting around for 2-3 yrs).
Can anyone confirm or deny this hypothesis?
Dear Sara Port ,
I agree with you regarding the presence of PbS and that it oxidizes to PbSO4. However, at low temperature, the oxidation process is slow and its rate is inversely proportional to the thickness of the PbSO4 surface layer. Accordingly, assuming that bottle was kept below 60oC, I think that the "enough time has" NOT "passed" yet.
Valuable information regarding the oxidation of PbS are given at:
Article Oxidation of nanocrystalline lead sulfide in air
Article The oxidation of the PbS(001) surface with O2 and air studie...
Oxidation of lead sulfide, Peter John Sleeman, PhD thesis:
https://core.ac.uk/download/pdf/29818687.pdf
XPS is a surface sensitive technique and does not provide a bulk analysis. Almost certainly you'll see around 30% carbon on the surface, fully oxidized species, as well as any components brought to the surface by chemisorption induced segregation. You need to use Ar+ etching to around 15 - 20 atomic layers in order to remove the surface before you can come to any conclusions.
One hypothesis could be selective reduction of PbSO4 to PbS in the presence of carbonaceous materials on the surface: PbSO4 + 2C = PbS + CO2 . Presence of any trace level impurity that is a reductant (including elemental sulfur) could have selectively reduced the PbSO4 to PbS (at the surface level), especially in a tightly closed container. The reduction reaction, if occurs, will be very very slow at room temperature and therefore it is just a surface (mono layer?) reaction.
The observed peaks at 160-164 eV probably result from the plasmon satellites of the intensive Pb4f line. I had a look on spectra of Pb containing samples (but not containing sulfur), and these spectra indeed show some structure in this energy range. The presence of sulfides seems unlikely, because S2p peak in sulfides usually demonstrates more resolved (narrower) doublet than for oxidized sulfur.
- Badges
- Science topic
- Similar topics
- Physics
- Condensed Matter Physics
- Solid State Physics
- PEAKS