article posted 22 March 2016
Tadeáš Gavenda Researcher at the University of Chemistry and Technology in Prague, Department of glass and ceramics. Field of research: Structure of silica and silicate glasses, glass surfaces and coatings - AFM method, glasses irradiated by electrons, Raman spectroscopy of glasses.
Comparison of structural response of glasses irradiated by electrons: Vitreous silica versus binary alkali-silicate glass
Tadeáš Gavenda*1 & Ondrej Gedeon1 & Karel Jurek2
1 Department of Glass and Ceramics, University of Chemical Technology, Technická 5, CZ-166 28 Prague, Czech Republic
2 Institute of Physics, Academy of the Czech Republic, Na Slovance 2, CZ-182 21 Prague, Czech Republic
Electron radiation causes many changes in the structure of the glasses, therefore the study of radiation effects is important in the fields of cosmic research, nuclear industry, vitrification of nuclear waste, in detectors and generally in such cases, where the radiation occurs in any form. Volume and structural changes of glasses under irradiation were observed in this experiment. Three glasses were observed: Suprasil silica glass, Li15 (15Li2
) and K15 (15K2
). Glasses were irradiated by 50 keV electron beam with doses within the range of 0.21 – 318.5 kC/m2 Volume changes induced by electron bombarding were monitored by means of Atomic Force Microscopy (AFM). Low doses caused compaction of all glasses. Volume responses to higher doses were more complex. While glasses containing alkali ions revealed volume expansion, which can be attributed mainly to the migration of alkali ions, silica glass continued in its compaction, due to the additional relaxation of silica backbone. Raman spectra were taken from the irradiated spots to observe structural changes. Broad band, located at 450 cm-1
, is becoming wider due to the wider Si-O-Si angle distribution after electron irradiation. The band is also being shifted towards higher frequencies as result of the decrease of average Si-O-Si angle. The intensity of the D2 defect peak, situated at 602 cm-1
, is increasing with the dose. This effect is attributed to the increase of the three-membered rings in the irradiated volume. In addition, Q-motives band in the spectra of binary glasses changed its shape and position after irradiation. Irradiated glasses were annealed at higher temperatures to study relaxation of the changes induced with irradiation. After annealing, the irradiated spots were again examined by AFM and Raman spectroscopy in order to observe volume and structural relaxation of radiation-induced changes. Full relaxation of both volume and structure was observed between 600 – 900°C for silica glass. Relaxation of binary silicate glasses are more complicated as it was not possible to reverse the induced changes. The departure of alkali ions under irradiation seems to play a crucial role. Evolution of D2 peak under irradiation and subsequent annealing showed that topological changes in glass structure are possible deeply below the glass transition temperature.