Correlation between Chemical Durability Behaviour and Structural Approach of the Vitreous Part of the System 55P<sub>2</sub>O<sub>5</sub>-2Cr<sub>2</sub>O<sub>3</sub>-(43-x) Na<sub>2</sub>O-xPbO

Abstract

Various characterisation techniques were used to study the composition of the glass series 55-P 2 O 5-2Cr 2 O 3-(43-x) Na 2 O-xPbO (with 8 ≤ x ≤ 38; mole %) in terms of chemical durability, IR spectroscopy and scanning electron microscopy (SEM). The change in the dissolution rate as a function of time when the studied glasses were kept submerged in distilled water at 90˚C for 20 days showed an improvement in the chemical durability when Na 2 O content was substituted to PbO content. IR spectroscopy revealed a structural change from ultraphosphate groups to pyrophosphate, orthophosphate and probably ring metaphosphate groups. SEM revealed the existence of two phases: a vitreous phase and a crystalline phase. The presence of Cr 2 O 3 , even in small amounts, seems to play an important role in the formation of crystallites in the glass network. The improved chemical durability is attributed to the replacement of the easily hydrated Na-O-P and P-O-P bonds by covalent and resistant Pb-O-P bands. Both the increase in PbO content and in the Pb + Cr/P ratio causes an increase in the number of covalent Pb-O-P and Cr-O-P bonds, making the glass structure more rigid. The increase of the covalent Pb-O-P bands leads to a clear evolution of the structure and chemical resistance, caused by grain-boundary resistance as a result of glass crystallisation. The IR spectra indicate that the increase in PbO content favours the formation of isolated 3 4 * Corresponding author. N. Beloued et al. 150 limit, the equilibrium between the glass bath and these crystallites is no longer maintained; we notice, once, a decrease in the chemical durability.

Chemical Durability, Structure Properties and Bioactivity of Glasses 48P<SUB>2</SUB>O<SUB>5</SUB>-30CaO-(22−x)Na<SUB>2</SUB>O-xTiO<SUB>2</SUB>(With 0 < x ≤ 3; mol%)

“…The number of peaks and their intensities increase, while the peak intensity of the A deep analysis of the spectra obtained seems to suggest that the tricalcium phosphate layer is more important than the hydroxyapatite phase when the TiO 2 content reaches 3 mol%. [20]. This series of reactions constitutes the mechanism of bioactivity.…”

“…the glass due to the radical change of structure by the formation, of isolated ortho phosphate groups, confirmed , both, by IR spectroscopy and XRD[12] [15][20]. The increase of isolated short orthophosphate chains in the glass network, at the expense of olygophosphate chains, when the Ti 2 O content exceeded 2 mol%, can be explained by the fact that we were close to the border area between crystal and glass[15] [20]. The number of crystallites of different sizes generally increased and exceeded the equilibrium that must be established between the glass bath and the crystallites; hence, we note a significant decrease in chemical durability.…”

“…When the TiO 2 content beyond 2 mol%, the chemical durability undergo a slow decrease and the structure evolve toward majority isolated short orthophosphate units (Q 0 ), confirmed by IR spectrum and X-Ray diffraction, SEM micrographs illustrated that the number of crystallites increased in the glass network when the TiO 2 content increased at the expense of the Na 2 O content. This indicates that we are near the border between the glass and the crystal [15] [19] [20]. The chemical reactivity of these materials was evaluated after immersion in the simulated body fluid (SBF) at 37˚C for 15 days.…”

Study of Chromium-Lead-Phosphate Glasses by XRD, IR, Density and Chemical Durability

“…4PO −[6] [19]. The decrease of chemical durability observed, can be also explained by the existence of the critical concentrations between the cation ions beyond which each ion seeks, by competition, to…”

Elaboration and Characterization of Glasses and Ceramic-Glasses within Theternary Diagram Li<sub>2</sub>O-Cr<sub>2</sub>O<sub>3</sub>-P<sub>2</sub>O<sub>5</sub>

“…Due to their low chemical durability, phosphate glasses have gained less attention. However, several phosphate glasses with high aqueous corrosion resistance have been reported [5]- [12]. The electrical engineering field constitutes one of the numerous fields of application of glasses.…”