Spectroscopic studies of oxygen speciation in potassium silicate glasses and melts

Abstract

To resolve discrepant results between O1s XPS and 29 Si and 17 O NMR techniques, O1s XPS spectra were collected and fitted for 15 potassium silicate glasses containing 10−37 mol% K 2 O. The effects of melting on the compositions of the glasses are documented and quantified, as are uncertainties associated with fitting the O1s spectra. These spectra are well resolved into two symmetric peaks: a narrow peak due to NBO (Si−O−K) plus “free oxide” (O 2– or K−O−K) and a broader peak due to BO (Si−O−Si). Values of mol% BO (uncertainties of ±1%) are obtained from the computed peak areas and indicate 2.2 (±0.8) mol% O 2– for glasses containing 32 (±1) mol% K 2 O. Reassignment of Q species for previously published 29 Si NMR spectra leads to BO and O 2– values in good agreement with these O1s XPS spectra. A recent 17 O NMR study on potassium silicate glasses concluded that there is <1 mol% O 2– in these glasses based mainly on the assumption that the 17 O chemical shift for O 2– should be similar in the glasses and the oxide in crystalline K 2 O. This assumption is questionable. Free oxide in these glasses should be highly reactive toward gases such as CO 2 (via CO 2 + O 2– → CO 3 2– ) and it seems likely that the reactive species in silicate glasses is O 2– rather than NBO as often assumed. The small amounts of CO 2 found in reacted glasses are qualitatively consistent with the abundance of O 2– obtained from these O1s XPS spectra of silicate glass.