Hydrodynamic coarsening in phase-separated silicate melts

Abstract

Using in-situ synchrotron tomography, we investigate the coarsening dynamics of barium borosilicate melts during phase separation. The 3-D geometry of the two interconnected phases is determined thanks to image processing. We observe a linear growth of the size of domains with time, at odds with the sublinear diffusive growth usually observed in phase-separating glasses or alloys. Such linear coarsening is attributed to viscous flow inside the bicontinuous phases, and quantitative measurements show that the growth rate is well explained by the ratio of surface tension over viscosity. The geometry of the domains is shown to be statistically similar at different times, provided that the microstructure is rescaled by the average domain size. Complementary experiments on melts with a droplet morphology demonstrate that viscous flow prevails over diffusion in the large range of domain sizes measured in our experiments (1 -80 µm).

Long‐Term Heat Treatment of Phase Separating Sodium Borosilicate Glass

“…In samples heat treated at 730 °C very thin parts of the silica skeleton can be seen, appearing to be similar to the structure gained by hydrodynamic coarsening as discussed by Bouttes et al Average pore sizes up to 2 μm at 680 °C and between 7 and 8 μm at 730 °C were reached. The latter pore sizes are already larger than the limits proposed in the literature .…”

“…Generally, there are two different views on the microstructure formation at long heat treatment times. In some reports it was shown, that all size relevant mechanisms follow phase size time laws according to Equation . For these laws lim d P ( t → ∞) = ∞ is valid, although, for β < 1, the growth rate will decrease with time.…”

“…Bouttes et al proposed a mechanism of hydrodynamic coarsening during phase separation in barium borosilicate glasses based on their interpretation of in situ X‐ray microtomography in the time regime after equilibrium compositions are reached . They found an interconnected silica‐rich skeleton increasing in size during heat treatment with a self‐similar appearance.…”

Le verre ne se cache plus pour mûrir

“…… on peut tomographier leur croissance en trois dimensions… Profitant des progrès récents de la microtomographie X à l'ESRF, nous avons pu suivre in situ le mûrissement d'un verre démixé à haute température [6,7,8] L'imagerie 3D donne ainsi accès aux détails de la morphologie et à l'évolution dans le temps des domaines, dont la taille varie de quelques microns à quelques centaines de microns en quelques minutes. L'intérêt de la technique est particulière-ment marqué lorsqu'à la séparation de phase se sont formés des domaines interconnectés (ce qui est typiquement le cas suite à une décomposition spinodale avec un rapport volumique des phases à l'équilibre de l'ordre de 0,5).…”

Structural inhomogeneities in glasses via cavitation

“…Recent work has explored such interplay via thermal quenches of a glass-forming liquid into the two-phase region [18,19], investigating the resultant morphologies. In a silicate system, novel experimental techniques have been recently used to visualise the spatio-temporal evolution of such structures during similar thermal quenches leading to phase separation [20,21], with the possibility that such studies can be extended to the glassy regimes.…”