Soda-lime Aluminoborosilicate Glasses Research Articles

ZrO2 addition in soda-lime aluminoborosilicate glasses containing rare earths: Impact on rare earths environment and crystallization

The effect of adding increasing ZrO2 content on the environment of Nd3+ ions in a glass belonging to the SiO2-B2O3-Al2O3-Na2O-CaO system was investigated both by optical absorption spectroscopy and Nd-EXAFS (LIII-edge). In agreement with the evolution of the structure of the glassy network and more particularly of the distribution of Na+ and Ca2+ ions with ZrO2 addition put in evidence in a previous study, it is shown here that the average NdO distance continuously increases whereas the bond covalency decreases with zirconium content. This result can be explained both by the decrease of the amount of non-bridging oxygen atoms (NBOs) and by the increase of the proportion of Ca2+ ions acting as charge compensators in the neighborhood of neodymium polyhedra in the depolymerized regions of the glass structure. This evolution is due to a competition in favor of zirconium between Zr and Nd for Na+ cations charge compensators. The local structural evolution around neodymium is probably responsible for the evolution of the crystallization tendency - increase of Nd-rich apatite (Ca2Nd8(SiO4)6O2) crystallization in the bulk - observed in this work both during melt cooling and glass heating by increasing ZrO2 content. It is proposed that the nucleating effect of ZrO2 on apatite crystallization put in evidence here is mainly due to the changes that are indirectly induced by zirconium in the neighborhood of Nd3+ ions (destabilization) rather than to the formation of Zr-rich crystals that would then act as nucleating phase for apatite.

ZrO2 addition in soda-lime aluminoborosilicate glasses containing rare earths: Impact on the network structure

The influence of increasing ZrO2 content on the structural features of a rare earths (RE = Nd, La) bearing soda-lime aluminoborosilicate glass was investigated through a multi-spectroscopic approach (Raman, Zr-EXAFS, 29Si, 11B, 27Al and 23Na MAS NMR). Particular attention was paid to the modifications occurring in the glassy network and on the distribution of Na+ and Ca2+ ions. Zr4+ ions were shown to be located in (ZrO6)2− sites, connected to the silicate network, and preferentially charge compensated by Na+ ions. A favorable competition of Zr4+ ions against RE3+ ions and (BO4)− entities for charge compensators was observed, but no effect was detected on the environment of (AlO4)− entities. This competition resulted in a modification of the RE3+ ions environment with the ZrO2 content that may affect their solubility in the glassy network.

Nonlinear relationship between the Product Consistency Test (PCT) response and the Al/B ratio in a soda-lime aluminoborosilicate glass

We have investigated the effect of Al/B ratio on the Product Consistency Test (PCT) response. In an aluminoborosilicate soda-lime glass based on a modified International Simple Glass, ISG-3, the Al/B ratio varied from 0 to 0.55 (in mole fractions). In agreement with various models of the PCT response as a function of glass composition, we observed a monotonic increase of B and Na releases with decreasing Al/B mole ratio, but only when the ratio was higher than 0.05. Below this value (Al/B < 0.05), we observed a sharp decrease that we attribute to B in tetrahedral coordination.

Effect of MoO3, Nd2O3, and RuO2 on the crystallization of soda–lime aluminoborosilicate glasses

The effect of adding Nd2O3, MoO3, and RuO2 separately or simultaneously on the crystallization of a soda-lime aluminoborosilicate glass during cooling from the melt or glass heating was studied by DTA, XRD (at room and high temperature), SEM, Raman, and optical absorption. Nd2O3 addition strongly reduces liquid-liquid phase separation and crystallization of calcium and sodium molybdates (CaMoO4 (powellite) and Na2MoO4) in Mo- rich compositions as long as Nd 3? ions remain solubilized in the glassy network. This suggests that (MoO4) 2- entities and Nd 3? ions are close to each other in the glass structure (Nd 3? ions would prevent the clustering of molybdate entities). The effect of MoO3 addition in Nd-rich compo- sitions is more complex since an increase of the solubility of Nd2O3 is observed, whereas the nucleation rate of an Nd-rich silicate apatite (Ca2Nd8(SiO4)6O2) in the bulk of the glass increases as soon as molybdates crystallized. The addition of RuO2 has a nucleating effect on apatite crys- tallization in the bulk but not on molybdates crystallization.

Effect of boron oxide addition on the Nd 3+ environment in a Nd-rich soda-lime aluminoborosilicate glass

The environment of Nd 3+ ions has been studied using optical absorption spectroscopy and EXAFS at the Nd L 3-edge, in a series of soda lime aluminoborosilicate glasses with increasing B 2O 3 content. The proportion of BO 4 units has been determined by 11B MAS NMR in an equivalent glass series with La 3+ ions replacing the majority of Nd 3+ ions, and complementary information has been obtained by measuring the Nd 3+ decay fluorescence times in these latter glasses. In these glasses with low Al 2O 3 content, the R′ ratio, with R′ = [Na 2O exc ] / [B 2O 3] and [Na 2O exc ] = [Na 2O] − [Al 2O 3] − [ZrO 2], plays a key role in controlling the structural organization and crystallization resistance, in a similar way as the R ratio in the Dell and Bray model of sodium borosilicate glasses. At R′ > 0.5, the Nd 3+ ions are located in a mixed silicate–borate environment and, by slow cooling of the melt, they tend to crystallize within a silicate apatite phase close to the Ca 2Nd 8(SiO 4) 6O 2 composition. At R′ < 0.5, the structural results are compatible with Nd 3+ ions located in a borate-type environment (not excluding Si neighbors), and, by slow cooling of the melt, they segregate with Ca 2+ ions within a Si-depleted separated borosilicate phase.

Effect of neodymium oxide on the solubility of MoO 3 in an aluminoborosilicate glass

High molybdenum and rare earth concentrations in soda–lime aluminoborosilicate glasses may lead to the crystallization of molybdenum-rich phases such as alkali and alkaline-earth molybdates (Na 2MoO 4, CaMoO 4) and also rare earth (RE)-rich phases such as apatite (Ca 2RE 8(SiO 4) 6O 2) during melt cooling that must be controlled particularly during the preparation of highly radioactive nuclear glassy wasteforms. To understand the effect of neodymium addition (from 0 to 16 wt.% Nd 2O 3) on the phase separation and the crystallization tendency of molydbate phases and on the structure of a Mo-bearing nuclear glass belonging to the SiO 2–B 2O 3–Al 2O 3–Na 2O–CaO–MoO 3 system, crystallization and structural studies have been performed by X-ray diffraction, scanning electron microscopy, electron microprobe analysis, Raman and optical absorption spectroscopies. The results obtained show that the addition of an increasing amount of Nd 2O 3 induces a significant increase of the solubility of molybdenum in the glass, characterized by a decrease of the phase separation and of the crystallization tendency of molybdate phases. The increase of chemical disorder in the structure of Mo-bearing glasses when Nd 2O 3 is added – and more precisely in the depolymerized regions where Nd 3+ cations and [MoO 4] 2− entities are located – could be at the origin of the evolution of the molybdenum solubility in the glass.

Observation of two Z 3 exciton resonances in CuCl-doped non-linear optical glass

Non-linear optical properties of CuCl-doped soda-lime aluminoborosilicate glass system have been investigated using the absorption saturation measurement and the degenerate four wave mixing method. The non-linear optical properties were confirmed by the saturation of the absorption coefficient and the blue shift with increase of laser intensity. Two Z 3 exciton resonances of the CuCl crystallites in the samples heat treated at 600 °C for 10 h were observed when the laser intensity was less than 10 3 kW/cm 2 at 77 K. The unique two Z 3 exciton peaks are attributed to a bimodal distribution in sizes of CuCl crystallites due to the phase separation. The third-order non-linear susceptibilities, χ (3), obtained by the absorption saturation measurement showed large peak values at two Z 3 exciton resonances. The χ (3) values of3×10 −8 esu obtained by the absorption saturation method were in good agreement with directly measured values by the degenerate four wave mixing method.;p