Electron spectroscopic studies of galena and its oxidation by microwave-generated oxygen species and by air

Abstract

The reaction of (100) surfaces of PbS crystals (natural galena) with reactive oxygen species generated by microwave discharge in NO has been compared with aerial oxidation in studies using angle-resolved X-ray and ultraviolet photoelectron spectroscopies. Reaction with the discharge products was much faster, facilitating the study of this process in a controlled environment. The final products of the two processes were similar.Initial attack by atomic oxygen at Pb sites led to the formation of oxide species with the liberation of free sulphur, most of which was lost from the surface. Some, however, remained trapped under an oxidized layer. Sulphate species were also formed, probably by direct attack on PbS. Surfaces of good crystallinity (assessed via their photoelectron diffraction patterns) and chemical purity could be regenerated from oxidized surfaces by 800 eV argon-ion bombardment followed by annealing at ca. 350 O C .Core-level binding energies (&) for bulk PbS, PbSO,, PbO, PbCO,, PbS,O, and 5Pb(OH), * Pb(NO,), were obtained via gold decoration and confirmed by reference to adventitious carbon. The Eb of the surface sulphate and oxide differed from those of the individual bulk lead salts, and they were inferred to coexist in an intimate mixture which probably also contained hydroxide. After the oxidized surfaces were heated to ca. 350 O C only the sulphate and some of the oxide remained.

Controlling Nanocrystal Superlattice Symmetry and Shape-Anisotropic Interactions through Variable Ligand Surface Coverage

“…For extensive air exposures, planar PbS is known to form sulfate species, which would be observed at ∼7 eV above the sulfide component. 41 However, this was not observed in our NC films. Notably, the S/Pb ratio was found to be 0.35 for the air-aged and 0.52 for the N 2 -aged NCs.…”

Surface Termination Control in Chemically Deposited PbS Films: Nucleation and Growth on GaAs(111)A and GaAs(111)B

“…This peak which appears at 137.9 eV in the case of PbS/GaAs(111)A and at 138.4 eV in the case of PbS/GaAs(111)B can be attributed to different forms of oxidized lead species such as PbO for the former and such as PbS 2 O 3 or PbSO 3 for the latter. Furthermore, this chemical state can also be assigned to Pb(OH) 2 , that was reported to be formed on the surface of metal oxides and metal sulfides in aqueous solution, rendering them hydrophilic. , However, the existence of Pb(OH) 2 in the UHV environment is questioned since it is thought to exist only in aqueous solutions. , The corresponding S2p spectra shown in Figure , panels c and d further elucidate the origin of the differences observed in the photoelectron emission values of the oxidized lead species for GaAs(111)A and GaAs(111)B. The S2p peak at 160.2 eV is characteristic for the Pb–S bond .…”

X-ray Photoelectron Spectroscopy in Mineral Processing Studies

“…Brion [41] has compared oxidation of main sulfide minerals in air and water and found sulfate and, in the case of Fe-bearing minerals, Fe(III) (hydr)oxides as the main surface products, with the rate of sulfation decreasing in the order FeS 2 > CuFeS 2 ≥ PbS > ZnS, which looks debatable at present [10,[35][36][37][38][39]. Evans and Raftery [42] have studied the initial surface oxidation of natural PbS crystals using angle-resolved photoelectron spectroscopy and pointed out that elemental sulfur tends to be lost in vacuum but some S remained trapped under an oxidized layer. Luttrell and Yoon [43] have characterized chalcopyrite surfaces with a focus on the formation of elemental sulfur as a hydrophobizing agent under collectorless flotation conditions and suggested that the presence of polysulfide species could explain some contradictions between XPS and other methods.…”