No abstract

Glasses gradually dissolve and corrode when they are exposed to aqueous solutions, and for many applications it is necessary to understand and predict the kinetics of the glass dissolution. Despite the recent progress in understanding the impact of chemical composition on the dissolution rate, a detailed understanding of the structural and topological origin of chemical durability in solutions of different pH is still largely lacking. Such knowledge would enable the tailoring of glass dissolution kinetics as a function of chemical composition. In a recent study focusing on silicate minerals and glasses, a direct relation was demonstrated between the dissolution rate at high pH and the number of chemical topological constraints per atom (n) acting within the molecular network [Pignatelli, I.; Kumar, A.; Bauchy, M.; Sant, G. Langmuir 2016, 32, 4434-4439]. Here, we extend this work by studying the bulk dissolution rate (D) of a wider range of oxide glasses in various acidic, neutral, and basic solutions. The glass compositions have been selected to obtain a wide range of chemistries and values of n, from flexible phosphate glasses to stressed-rigid aluminosilicate glasses. We show that, in flexible glasses, the internal modes of deformation facilitate the hydration of the network, whereas, in stressed-rigid glasses, the high number of constraints largely inhibits hydration in basic, neutral, and acidic solutions. Our study of chemical dissolution also allows establishing the kinetic mechanisms, which is controlled through an effective activation energy and depends on pH and glass topology. The energy barrier that needs to be overcome to break a unit atomic constraint is approximately constant for pH > 2, but then decreases at lower pH, indicating a change in dissolution mechanism from hydrolysis to ion exchange at low pH. Thus, with this research and existing topological models, the atomistic design of new oxide glasses with a specific chemical durability for a determined pH could become possible.

Alkali aluminoborate glasses have recently been shown to exhibit a high threshold for indentation cracking compared to other bulk oxide glasses. However, to enable the use of these materials in engineering applications, there is a need to improve their hardness by tuning the chemical composition. In this study, we substitute alkaline earth for alkali network-modifying species at fixed aluminoborate base glass composition and correlate it with changes in the structure, mechanical properties, and densification behavior. We find that the increase in field strength (i.e., the charge-to-size ratio) achieved by substituting alkaline earth oxide from BaO to MgO manifests itself in a monotonic increase in several properties, such as atomic packing density, glass-transition temperature, densification ability, indentation hardness, and crack resistance. Although the use of alkaline earth oxides as modifier enables higher hardness values (increasing from 2.0 GPa for Cs to 5.8 GPa for Mg), their crack resistance is generally lower than that of the corresponding alkali aluminoborate glasses. We discuss the origin of this compromise between hardness and crack resistance in terms of the ability of the glass networks to undergo structural transformations and self-adapt under stress. We show that the extent of volume densification scales linearly with the number of pressure-induced coordination number changes of B and Al.

The relationships between structure and electrical properties of nitrided lithium phosphate glasses (LiPON) used as electrolytes for lithium batteries are key issues for better understanding and design of these materials. For the first time, the effect of nitrogen introduction in the structure of lithium phosphorus oxynitride glasses, formulated over a wide range of composition 38-55 mol.% of Li 2 O, has been studied through 31 P 1D/2D MAS NMR experiments. Information obtained from 2D 31 P/ 31 P correlation maps has been used to deconvolute the 1D 31 P NMR spectra and allowed establishing the percentage of oxide phosphate groups (PO 4 ) and phosphorus species with nitrogen (P(O,N) 4 ) as well as the connectivity scheme of the phosphate network. Finally, it has been demonstrated that the lithium content affects the structural changes induced by the introduction of nitrogen. In particular, the lower the lithium content is, the lower the total percentage of nitrided P(O,N) 4 species is. *fmunoz@icv.csic.es

Alkali and alkaline earth aluminoborate glasses feature high resistance to cracking under sharp contact loading compared to other oxide glasses. However, due to the high content of hygroscopic B2O3, it is expected that applications of these glasses could be hindered by poor chemical durability in aqueous solutions. Indeed, the compositional and structural dependence of their dissolution kinetics remains unexplored. In this work, we correlate the dissolution rates of aluminoborate glasses in acidic, neutral, and basic solutions with the structural changes induced by varying the aluminum‐to‐boron ratio. In detail, we investigate a total of seventeen magnesium, lithium, and sodium aluminoborate glasses with fixed modifier content of 25 mol%. We show that the structural changes induced by alumina depend on the network modifier. We also demonstrate a correlation between the chemical durability at various pH values and the structural changes in Mg‐, Li‐ and Na‐aluminoborate glasses. The substitution of alumina by boron oxide leads to a general decrease in chemical corrosion in neutral and acidic solutions. The lowest dissolution rate value is observed in Mg‐aluminoborate glasses, as a consequence of the intermediate character of magnesium which can increase the network cross‐linking. For basic solutions, the chemical durability is almost constant for the different amount of alumina in the three series, likely because B2O3 is susceptible to nucleophilic attack, which is favored in high‐OH− solutions.