The regular melting-quenching method allowed isolating very large vitreous domains within the ternary system Li 2 O-P 2 O 5-Fe 2 O 3 at 1100˚C. The vitrification and crystallization effects are discussed in terms of phosphorus pentaoxide concentration (mol%). In the course of the present study, we analyzed chemical durability along the glass domain and many sample glasses were isolated. We noticed that our compounds demonstrated very high chemical resistance to attack, even with very highly concentrated mineral acid solutions. This behavior can be assigned to the presence of poorly crystalline phases in these glasses, which tended to increase as the Fe 2 O 3 content increased. This property is a prerequisite for many interesting industrial applications. XRD, IR spectroscopy and SEM micrographs allowed an efficient investigation of the structural changes versus composition within ternary diagrams. The results were found to be consistent with the regular structural changes of phosphate glasses.

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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.

Glasses in the ternary system Cr 2 O 3-PbO-P 2 O 5 were prepared by direct melting of the mixture with stoichiometric proportions of the reagents Cr 2 O 3 , PbO and (NH 4) 2 HPO 4 at 1080˚C. The glasses obtained are transparent in colour and have a non-hygroscopic appearance. The study of the dissolution rate was carried out on ternary glasses xCr 2 O 3-(45-x)PbO-55P 2 O 5 with (1 ≤ x ≤ 4; mol%), immersed in distilled water at 90˚C for 24 days, indicating a maximum of chemical durability when the level of chromium oxide passed through 2 mol%. Both, IR spectra and X-ray diffraction have indicated the predominance of metaphosphate or cyclic metaphosphate groups with some traces of isolated orthophosphate groups when the Cr 2 O 3 content is equal to x = 2. Analysis of the density values also, has showed a maximum density for x = 2 mol%. The covalent radius values of oxygen have indicated that the minimum value rcal (O 2−) is observed for x = 2 mol% and therefore a relatively high reinforcement of the metal-oxygen-phosphorus (Cr-O-P) bonds. SEM Micrographs have exhibited two phases, a vitreous phase and a crystalline phase. The radical change in the structure from ultraphosphate Q 3 groups to ring metaphosphate Q 2 and orthophosphate groups Q 0 seems to be the cause of the formation of crystallites. Beyond 2 mol% of Cr 2 O 3 , the structure of the glass changed relatively and the orthophosphate phases increased to the detriment of the metaphosphate phases. We observed a decrease in chemical durability. However, it was confirmed that the dissolution rate (D R) of the S 2 analysed compound is comparable to the values of borosilicate glasses which are used as alternative materials for the immobilisation of nuclear waste substances.

Chromium iron phosphate glass was investigated for use as waste form because of its improved chemical durability. The introduction of chromium in sodium-iron-phosphate glass is used to compare its effect with iron in inhibition of corrosion. The sodium-chromium-iron phosphate glass of composition 10Na 2 O-30Fe 2 O 3 -5Cr 2 O 3 -55P 2 O 5 (mol%) was produced by melting batches of (99, 98% pure) Cr 2 O 3 , Fe 2 O 3 , Na 2 CO 3 , and (NH 4 ) 2 HPO 4 at 1080˚C for one hour and pouring the liquid into steel mold. The sample was annealed at 680˚C for 48 h. We have performed the measurement of X-Ray Diffraction (XRD), Scanning Electronic Microscopy (SEM), Infra-Red spectroscopy (IR), and the chemical durability. The IR of the glass studied, contains two dominant bands, which were characteristic of pyrophosphate groups, (P-O) stretching mode of P-O non bridging oxygen at 1055 cm −1 and sym stretching mode of bridging oxygen at 444 cm −1 respectively. There is also a band at 603 cm −1 attributed to isolated tetrahedral units (PO 4 ) 3− . The chemical durability of the glass was investigated by measuring the weight loss in distilled water at 90˚C for 22 days.