TITLE:
Relationship between Chemical Durability, Structure and the Ionic-Covalent Character of Me-O-P Bond (Me = Cr, Fe), in the Vitreous Part of the System 60P2O5-2Cr2O3-(38 - x) Na2O-xFe2O3 (with 3 ≤ x ≤ 33 mol%)
AUTHORS:
Nadia Beloued, Radouane Makhlouk, Yassine Er-Rouissi, M’hammed Taibi, Mohammed Sajieddine, Said Aqdim
KEYWORDS:
Chemical Durability, Phosphate Glasses, Chromium and Iron Oxides, IR, XRD, Nuclear and Chemical Wastes
JOURNAL NAME:
Advances in Materials Physics and Chemistry,
Vol.9 No.10,
October
12,
2019
ABSTRACT: The structure and chemical
durability in the vitreous part of the system 60P2O5-2Cr2O3-xFe2O3-(38 - x)Na2O
phosphate glasses (with 3 ≤ x ≤ 33 mol%) were investigated using various
techniques such as IR spectroscopy, X-ray diffraction and M?ssbauer
spectroscopy. The presence of Cr2O3 and the increase of
Fe2O3 at the expense of Na2O in the glass
network lead to a large number of covalent and rigid Fe-O-P and Cr-O-P bonds.
The infrared and XRD spectra indicate a radical change of structure and show that
the increase of the Fe2O3 content favors the depolymerization
of the vitreous network towards pyrophosphate chains. The presence of Cr2O3 in the glass seems to favor the covalent Cr-O-P bonds linked to the most
probable cyclic metaphosphate chains. However, when the Fe2O3 content increases (≥23 mol%), its impact on the glass network is stronger than
that of Cr2O3. The infrared and XRD spectra indicate a radical change of structure and
show that the increase in Fe2O3 content favors the depolymerization
of the vitreous network to short pyrophosphate chains. The results of M?ssbauer
spectroscopy indicate the presence of both Fe (III) and Fe (II) ions which
occupied more or less deformed octahedral sites. The growth of the glass
transition temperature (Tg) with the increase of the iron oxide in the vitreous
network, leads to an improvement of the glass rigidity. This explains the decrease of the ionic radius of the iron and the
reinforcement of the interconnection of the chains of vitreous networks. The
structure of sodium-chromium-iron phosphate glasses can be considered largely
as pyrophosphate units linked to ferric and ferrous ions in octahedral or
deformed octahedral coordination. The dissolution rate is 200 times lower than
that of the silicate glasses.