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.

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.