Various characterization techniques were used to study the composition of the glass series xAl 2 O 3 -(40 -x)CaO-10Na 2 O-50P 2 O 5 (with 0 ≤ x ≤ 10) in terms of chemical durability, X-ray diffraction, IR spectroscopy and scanning electron microscopy (SEM). The improved chemical durability was attributed to the replacement of easily hydrated P-O-P bonds by covalent and resistant Ca-O-P and Al-O-P bonds. However, the change in the dissolution rate (D R ) versus time showed a marked decrease in chemical durability with increasing the Al 2 O 3 content to the detriment of the CaO content. The X-ray diffraction analysis of glasses annealed at 550˚C and 660˚C for 48 hours indicated the presence of pyrophosphate phases and predominant metaphosphates or cyclic metaphosphate phases when the Al 2 O 3 content was ≤7.5 mol%. Nevertheless, both, X-ray diffraction and IR spectroscopy confirmed the structural tendency change from metaphosphate (Q 2 ) and pyrophosphate structural units (Q 1 ). Toward short isolated orthophosphate units (Q 0 ) when the Al 2 O 3 content above 7.5 mol%. SEM micrographs illustrated that the number of crystallites increased in the glass network when the Al 2 O 3 content increased at the expense of the CaO content. An increase in the Al 2 O 3 content to 10 mol% led to the formation of a larger number of crystallites of different sizes, dominated by small crystallite sizes assigned to short isolated orthophosphate groups. This phenomenon led to a decrease in chemical durability and seems to be a favorable factor for the formation of the apatite layers which enclose the glass, in a SBF solution test, able of regenerating bone tissue in biomedical application.

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Use of the regular melting-quench method allowed the isolation of a small glass domain within the ternary system Li 2 O-P 2 O 5 -Cr 2 O 3 at 1000˚C. Electrical conductivity and dielectric permittivity measures on sample glasses and ceramic glasses of this domain were performed at a frequency of 10 kHz and at temperatures between 25˚C and 300˚C. The values of dielectric permittivity and electrical conductivity increase with increasing Li 2 O content. However, increases of Cr 2 O 3 content, even at low concentrations, induce a change in electrical conductivity behaviour from that of a glass to that of a ceramic glass. The introduction of an increasing amount of Li 2 O content in vitreous phosphorus pentoxide changes its three-dimensional network; rupture of the P-O-P bond then occurs and there is formation of easily polarisable entities with quite high values of r ε ′ . The vibrational spectroscopy technique I.R has allowed an efficient investigation of the structural change versus composition within the above indicated ternary diagram. The maximal dielectric permittivity obtained at 300˚C, both for the glasses and for the ceramic glasses varied in the order 10 4 to 3 × 10 5 , while the maximum electrical conductivity obtained at 300˚C for the ceramic glasses was in the order of 10 −3 Ωcm −1.

The glass series 50P 2 O 5 -25CaO-(25−x)Na 2 O-xCoO (with (0 ≤ x ≤ 25; mol%), has been prepared by direct melting at 1080˚C ± 20˚C. The introduction of cobalt in calcium phosphate glasses is used to compare its effect with calcium in inhibition corrosion. The dissolution rate has been investigated. It indicated an improvement of chemical durability when the cobalt oxide increases in the network glass at the expense of Na 2 O content. Both, IR spectroscopy and X-ray diffraction have confirmed the structure changes when the CoO content increases in the glass. This change results in the disappearance of isolated orthophosphate groups followed of a polymerizing of the structure from isolated orthophosphate towards pyrophosphate chains (Q 1 ) by promoting the formation of olygophosphates (mixed Q 1 -Q 2 ) rich in pyrophosphates. Analysis of the density values, showed an increase of density with the increase CoO content. The covalent radius values of oxygen r cal (O 2− ) indicate a significant decrease and therefore a relatively high reinforcement of the metal-oxygen-phosphorus (Co-O-P) bonds. SEM micrograph confirms the evolution of the glass structural morphology. The sample having a maximum CoO content confirms a homogeneous glass phase with quite crystalline particles. This property is prerequisite for many interesting industrial applications.

The synthesis for glasses series xFe 2 O 3 -(45-x)PbO-55P 2 O 5 , (with 0 ≤ x ≤ 20; mol%) carried out in a temperature (1050 ± 10)˚C, leads to obtaining transparent glasses, brown in color and with a non-hygroscopic appearance. The study of glasses dissolution rate, immersed in distilled water at 90˚C for 24 days, indicates a considerable chemical durability. The increase in the Fe 2 O 3 content in the vitreous network to the detriment of PbO is a favorable factor for the chemical durability improvement. Different techniques have been used such as X-ray diffraction, infrared spectroscopy, DSC, SEM and density for the study of these glasses. These techniques have led to establish correlations between chemical and structural properties. Thus the results obtained confirmed the creation of P-O-M bonds (M = Pb, Fe) with a strongly covalent nature to the detriment of the hydrated P-O-P bonds and led to the formation, mainly, of pyrophosphate groups. The low melting point of Pb-O makes it possible to play an important role, at the same time, on the viscosity, on the equilibrium between the vitreous bath and the crystallites formed. The dissolution rate obtained is 100 times smaller than that of silicate glasses used as an alternative form for the vitrification of radioactive waste.