Measuring the water concentration in glasses with Raman spectroscopy

What is it about?

Raman spectroscopy is a technic that analyses the vibrations of the molecules composing materials such as glasses and crystals. Vibration of water molecules in glasses give a particular Raman signal. This study shows how to take advantage of this signal in order to measure the water concentration in glasses. It establish a calibration between the ratio of water and silicate Raman signals from the glass and its water concentration, which is independent of glass chemistry.

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Why is it important?

Measuring the water concentration in glasses is important because it represents that in the melts at high temperature from which the glasses were formed. Water strongly affects the properties of the melts, such as, for instance, their ability to flow (i.e., their viscosity). This, in turn, influences the dynamic of volcanic eruptions or the manufacturing of technical glasses such as window or cellphone screen glasses. Most methods to measure the glass water content are destructive, need a large amount of sample or a heavy sample preparation. Raman spectroscopy solves those problems, because it allows to analyse samples in a few minutes with only a tiny amount of unprepared material, because of its low spatial resolution of ~1 micron. After analysis, the samples can be retrieved as Raman spectroscopy is non-destructive. Furthermore, it allows to perform analysis in difficult conditions, for instance during experiments at high temperature and high pressure, or directly on volcanoes using portable Raman spectrometers. Raman spectroscopy thus opens new ways to look at volcanic and industrial glasses, to analyse their water concentration, and to solve challenging problems linked to glass-making processes, volcanic eruptions, or the water content of the deep Earth.

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