TITLE:
Correlation between Chemical Durability Behaviour and Structural Approach of the Vitreous Part of the System 55P2O5-2Cr2O3-(43-x) Na2O-xPbO
AUTHORS:
Nadia Beloued, Zineb Chabbou, Said Aqdim
KEYWORDS:
Phosphate Glasses, Chemical Durability, IR, SEM
JOURNAL NAME:
Advances in Materials Physics and Chemistry,
Vol.6 No.6,
June
24,
2016
ABSTRACT: Various
characterisation techniques were used to study the composition of the glass
series 55-P2O5-2Cr2O3-(43-x) Na2O-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 Na2O
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 Cr2O3, 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 PO3-4 orthophosphate groups at the expense of
pyrophosphate groups. The radical change in the structure from ultraphosphate
groups to pyrophosphate and orthophosphate groups seems to be the cause of the
formation of crystallites. The existence of crystallites in these glasses
results in a marked improvement in their chemical durability. However, when the
crystallites exceed a certain limit, the equilibrium between the glass bath and
these crystallites is no longer maintained; we notice, once, a decrease in the
chemical durability.