The most common glasses are made by brutally cooling a bath of molten oxides. These glass casting processes are supposed to provide very homogeneous glassy materials with large dimensions (10x10x3cm for about 1kg, see figure). But are they really so homogeneous? This is what scientists from the laboratory Extreme conditions and materials: high temperature and irradiation (CNRS) and the laboratory Glass surface and interfaces (CNRS/Saint Gobain Research) wanted to verify.
The thermal memory of glass reveals its history
glass temperature Published by Adrien on 20/04/2021 at 09:00
Source: CNRS INC
The most common glasses are made by brutally cooling a bath of molten oxides. These glass casting processes are supposed to provide very homogeneous glassy materials with large dimensions (10x10x3cm for about 1kg, see figure). But are they really so homogeneous? This is what scientists from the laboratory Extreme conditions and materials: high temperature and irradiation (CNRS) and the laboratory Glass surface and interfaces (CNRS/Saint Gobain Research) wanted to verify.
As part of a fundamental study on the diffusion mechanisms in glass, they studied by Raman imaging samples of sodium and calcium aluminosilicates obtained by this casting process. Surprising images revealed macroscopic scrolls on the surface of the glass, a kind of surface inhomogeneities, which are a memory of the casting process and testify to the thermal history of the glass.
Indeed, during the casting process, the liquid jet cools down progressively and falls on a surface with an evolving temperature: cold at the beginning, then hotter and hotter because the molten liquid flows on the cooling glass. The cooling rate varies strongly during the process and the glass structure keeps a topological trace of these thermal variations. This work, to be found in the Journal of Raman Spectroscopy, also shows the extreme sensitivity of Raman imaging to reveal small inhomogeneities in glass structures.
