Rheological properties of nuclear glass melt containing platinum group metals

2nd International Summer School on Nuclear Glass Wasteform - Structure, Properties and Long-Term Behavior (SumGLASS), FRANCE, SEP 23-27, 2013International audienceDispersions of undissolved palladium or ruthenium in nuclear glass can affect the glass flow during the vitrification process. As a consequence, one of the major challenges in nuclear glass elaboration is to understand and control the rheological behavior of glass melts. In this context, this work aims at describing accurately the rheological behavior of glass melts containing platinum group metals to better model the thermal hydraulics in vitrification process. A Searle viscometer has been used to characterize the non-Newtonian behavior of nuclear glass melt containing these noble metals versus temperature and shear rate. Obtained data have been compared to different reference models (Bingham, Ostwald ... ) in order to find the appropriate relation describing rheological behavior of nuclear glass melts. The specific role of low shear rates on viscosity measurements has been highlighted. Finally, another investigation under a constant low shear rate has been performed at high temperature during a few hours with the view to clarify this role and the associated physical phenomenon

Ionic transport of alkali in borosilicate glass. Role of alkali nature on glass structure and on ionic conductivity at the glassy state

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Drivers of Water Transport in Glass: Chemical or Topological Effect of the Glass Network?

International audienceThe relation existing between water transport in glass, topology, chemical elements (network former and charge compensator), and their structural role in glass were investigated through glass topology modeling, glass and water structure analyses, and water diffusion characterization. Two series of aluminosilicate glasses with and without boron and having various ratios of charge compensators CaO/Na 2 O were used. The glass structure was characterized using Raman spectroscopy and nuclear magnetic resonance. Their topologies, i.e., the density of bottlenecks and the interstitial sites, were obtained by molecular dynamics. For glasses without boron, the substitution of Na by Ca leads to the strengthening of the glass network. The results are similar for glasses with boron except if the amount of Na is not sufficient. In this case, a part of Ca is required as a charge compensator for AlO 4 and BO 4 units. This last result is important since it highlights that the presence of boron and the CaO/Na 2 O ratio drives the roles of Ca inside the glass structure. Moreover, glass topology is driven by boron presence and to a lesser extent by CaO/Na 2 O ratio. Water transport characterized by the duration of the predominance of the hydration/interdiffusion processes, the apparent water diffusion coefficient, and the water structure in the hydrated glass were studied and determined using X-ray reflectivity and attenuated total reflectance infrared spectroscopy. The results show that the duration of the predominance of the hydration/interdiffusion processes is driven by the ability of Si-OX bonds to be hydrolyzed as much as the fraction of free water clusters in hydrated glass. Moreover, for aluminosilicate glasses, we show that water transport is mainly driven by glass topology through the role of Ca and its amount in glass. Indeed, Ca strengthens the glass network by decreasing the density of the bottleneck allowing the diffusion of water molecules. When boron is added to the glass, water transport may be mainly driven by the chemical interactions between the water molecules, Ca, and the network former of glass matrix