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

Glasses in the ternary system Cr2O3-PbO-P2O5 were prepared by direct melting of the mixture with stoichiometric proportions of the reagents Cr2O3, PbO and (NH4)2HPO4 at 1080℃. 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 xCr2O3-(45-x)PbO-55P2O5 with (1 ≤ x ≤ 4;mol%), immersed in distilled water at 90℃ 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 Cr2O3 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 (O2–) 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 Q3 groups to ring metaphosphate Q2 and orthophosphate groups Q0 seems to be the cause of the formation of crystallites. Beyond 2 mol% of Cr2O3, 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 (DR) of the S2 analysed compound is comparable to the values of borosilicate glasses which are used as alternative materials for the immobilisation of nuclear waste substances.

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%)

Phosphate glasses of composition 48P2O5-30CaO-(22−x)Na2O-xTiO2 (with 0 < x ≤ 3, mol%) were prepared by direct melting at 1080°C ± 20°C. The chemical durability of these glasses shows an improvement when the TiO2 content varies from 0 to 2 mol%. The measurements of differential thermal analysis and density, both, indicate the increase of the glass transition temperature and the density. The increase of Tg leads to an improvement of glass rigidity. X-ray diffraction analysis of the glasses annealed at 650°C for 48 h, indicates the appearance of a mixture of metaphosphate and pyrophosphate phases when the TiO2 content varies from 0 to 2 mol%, the last become majority when the TiO2 content rich 2 mol%. Nevertheless, when the TiO2 content exceeds 2 mol%, the analysis, both, by infrared spectroscopy and X-ray diffraction, reveals a radical change of structure with the formation of majorities isolated orthophosphate groups. SEM micrographs illustrated that the number of crystallites increased in the glass network when the TiO2 content increased at the expense of the Na2O content. An increase in the TiO2 content beyond 2 mol% led to the formation of a larger number of crystallites of different sizes, dominated by small crystallite sizes assigned to majority isolated short orthophosphate groups. This phenomenon led to a decrease in chemical durability and seems to be the main cause promoting the bioactivity of glasses. The results of the bioactivity, after a test in an SBF physiological solution within 15 days, shows, both, the formation of hydroxyapatite and tricalcium phosphate layers, in addition to the layer Ca2P2O7, known by its bioactivity, in some samples. The results obtained on the glasses studied make them potential candidates for an application in tissue engineering.

Chemical Durability and Structural Properties of Al₂O₃-CaO-Na₂O-P₂O₅Glasses Studied by IR Spectroscopy, XRD and SEM

Various characterization techniques were used to study the composition of the glass series xAl2O3-(40 - x)CaO-10Na2O-50P2O5 (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 (DR) versus time showed a marked decrease in chemical durability with increasing the Al2O3 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 Al2O3 content was ≤7.5 mol%. Nevertheless, both, X-ray diffraction and IR spectroscopy confirmed the structural tendency change from metaphosphate (Q2) and pyrophosphate structural units (Q1). Toward short isolated orthophosphate units (Q0) when the Al2O3 content above 7.5 mol%. SEM micrographs illustrated that the number of crystallites increased in the glass network when the Al2O3 content increased at the expense of the CaO content. An increase in the Al2O3 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.

Structural Features and Properties of the Vitreous Part of the System 50P₂O₅-25CaO-(25-x)Na₂O-xCoO (with 0 ≤ x ≤ 25;mol%)

The glass series 50P2O5-25CaO-(25-x)Na2O-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 Na2O 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 (Q1) by promoting the formation of olygophosphates (mixed Q1-Q2) rich in pyrophosphates. Analysis of the density values, showed an increase of density with the increase CoO content. The covalent radius values of oxygen rcal (O2-) 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.

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%)

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.