Raman Study of Arsenic‐Containing Potassium Silicate Glasses

Abstract

Raman spectra are given of potassium silicate glasses with batch composition xK2CO3‐(100—x)SiO2‐0.5As2O3 in which x varies from 10 to 50. To isolate the contribution of the As2O3 additions to the spectra from that of the silicate network, difference spectra were prepared from spectra of glasses with and without As2O3 added to the batch. To obtain a precision sufficient for this purpose, the spectral data were collected in multiple scans under full computer control using photon counting and a correction for laser‐source fluctuations. It is concluded from the polarized and depolarized difference spectra that arsenic in potassium silicate glasses with x>35 is mainly present in the pentavalent state as AsO43‐ ions. For glasses with x<35 it is concluded that As5+ is present in As2O74‐ or As3O105‐ ions and As3+ as AsmO2m+1‐m‐2 chains of AsO3 pyramids. In these chains, m increases with decreasing x. From the intensity ratio of Raman peaks, caused by arsenite (As3+) and arsenate (As5+) ions in the glasses, it is concluded that there is a significant increase of the As3+/As5+ ratio with x increasing from 50 to 10. The effect of melting temperature on the As3+/As5+ ratio in 30K2O‐70SiO2‐0.5As2O3 glasses at 1300° to 1600°C was also studied. No clear temperature effect could be concluded from the Raman spectra.