FROM THE VIBRATIONAL DYNAMICS OF GLASSES TO THE MELT VISCOSITY AND BACKWARD TO GLASSES

There is a growing evidence of nanoscale modifications in silicate and volcanic melts both during viscosity measurements and during eruptions. This challenges the possibility of being able to quantify the contribution to the measured viscosity of the crystal-free melt phase. This doctoral project deals with Raman spectroscopy investigation of glasses having a wide range of compositions. Central here is the derivation of the viscosity of volcanic and of technical melts from the vibrational properties of their parental glasses. We developed and further validate a crossed Raman-Brillouin model (in synergy with the BGI of Bayreuth), in a chemical domain encompassing virtually the whole magmatism on Earth. Our results provide an alternative method to derive viscosity, bypassing the complex procedures of the typical measurements at high temperature. Moreover, the study provides a new way in which to develop further studies of the nanoscale dynamics of natural melts and its impact on the style of volcanic eruptions. Concluding, our results support the link between acoustic modes and the boson peak, adding new insights about its long-debated nature.