Chemical Durability of Lanthanum‐Enriched Borosilicate Glass

Abstract

The role of lanthanum in the alteration kinetics at different degrees of reaction progress was investigated at 90°C and pH 7 by complementary chemical (SIMS), morphological (SAXS), and structural (NMR, Raman, and EXAFS spectroscopy) approaches. In the first step of alteration, the forward dissolution rate diminishes with the addition of lanthanum, resembling to the behavior previously observed for zirconium. Over longer alteration time, the glasses with the highest lanthanum concentrations reach silicon saturation more slowly, but unlike zirconium, do not result in larger quantities of altered glass. Lanthanum is entirely retained in the alteration layer and is uniformly distributed; it undergoes hydrolysis and recondensation mechanisms, and its coordination number increases from 6 to 9 during leaching. Reconstruction of the alteration layer occurred more slowly at higher REE concentrations, with a slowdown in repolymerization of the silicate network and structuring of its porosity.

Phase separation and crystallization effects on the structure and durability of molybdenum borosilicate glass

“…The initial alteration rate regime is the most likely to be directly influenced by the structural organization of a glass, in particular through polymerization of the vitreous network [56], the insertion of network formers of different natures [57], or the distribution of network modifiers [58]. These structure-reactivity correlations are however often complex to demonstrate, as numerous factors vary simultaneously when the chemical composition of the glass changes [32,59].…”

Linear release of strontium ions from high borate glasses via lanthanide/alkali substitutions

“…Demonstrating that upon extraction, La and Si reorganized to form Si-O-La bonds that resided in the alteration layer while the majority of other ions, B, Na and Ca leached out the glass network [26]. This ability of La to consolidate itself and other glass components of the network against 6.…”

“…Contrary to this, Angeli et al demonstrated that additions of La did not cause the formation of O 2− ions or polymerization of the network. However, La ions were confirmed by 17 O NMR and extended X-ray absorption fine structure (EXAFS) to be homogeneously dispersed within borosilicate networks and surrounded by approximately 6 NBO in mixed cation areas containing Na and Ca [25,26]. These modifying cations compensated the charge deficit surrounding La ions due the excess number of NBO.…”

“…La), depending on the composition, may reduce the amount of BO 4 and alter the intermediate groups present. However, in doing this it may also provide a structural mechanism to mediate TMI release and control material degradation characteristics [25,26,40]. It is the combination of such structural units that can effect glass properties, such as T g , density, and chemical durability [19,20,41].…”

“…lanthanum (La)) may provide a mechanism to stabilize a high borate glass and yield a biomaterial with appropriate resorption characteristic and linear Sr release kinetics for bone augmentation. While the precise role of REEs on borate glass structure has not been well defined, this hypothesis is on the basis that trivalent ions result in a more negatively charged local environment and as a consequence may have more pronounced structural effects on borate networks than alkalis [16,18,25,26].…”