In Vitro Dissolution of Na-Ca-P-Oxynitrides.

Sodium-calcium-phosphate based oxynitride glasses and glass-ceramics doped with Mg, Si, and Nb were studied in vitro in simulated body fluid (SBF) under static conditions. The release of ions and pH changes up to 7 days of immersion were investigated. The nitrogen incorporation into phosphate glass matrix was found to notably influence in vitro dissolution only of homogenous glasses. Increasing the nitrogen content in the samples decreased the mean mass loss, while the niobate incorporation increased it. The correlation between the nitrogen content and increase in pH of SBF was also observed. The presence of phosphates crystallites was found to support the dissolution process at the beginning step (up to 3 days).

Microstructure Evaluation and Impurities in La Containing Silicon Oxynitrides.

Oxynitride glasses are not yet commercialised primarily due to the impurities present in the network of these glasses. In this work, we investigated the microstructure and instinctive defects in nitrogen rich La-Si-O-N glasses. Glasses were prepared by heating a powder mixture of pure La metal, Si3N4, and SiO2 in a nitrogen atmosphere at 1650-1800 °C. The microstructure and impurities in the glasses were examined by optical microscopy, scanning electron microscopy, atomic force microscopy, and transmission electron microscopy in conjunction with electron energy-loss spectroscopy. Analyses showed that the glasses contain a small amount of spherical metal silicide particles, mostly amorphous or poorly crystalline, and having sizes typically ranging from 1 µm and less. The amount of silicide was estimated to be less than 2 vol. %. There was no systematic relation between silicide formation and glass composition or preparation temperature. The microstructure examination revealed that the opacity of these nitrogen rich glasses is due to the elemental Si arise from the decomposition reaction of silicon nitride and silicon oxide, at a high temperature above ~1600 °C and from the metallic silicide particles formed by the reduction of silicon oxide and silicon nitride at an early stage of reaction to form a silicide intermetallic with the La metal.

DC and AC Conductivity, Biosolubility and Thermal Properties of Mg-Doped Na2O-CaO-P2O5 Glasses.

Bioactive glasses have recently been extensively used to replace, regenerate, and repair hard tissues in the human body because of their ability to bond with living tissue. In this work, the effects of replacing Na2O with MgO on the electrical, biosolubility, and thermal properties of the target glass 10Na2O-60P2O5-30CaO (in mol%) were investigated. The electrical properties of the glasses were studied with the impedance spectroscopy technique. At 473 K, DC conductivity values decreased from 4.21 × 10-11 to 4.21 × 10-12 S cm-1 after complete substitution of MgO for Na2O. All samples had a similar activation energy of the DC conduction process ~1.27 eV. Conduction mechanisms were found to be due to hop of ions: Na+, Mg2+, and probable H+. FTIR analysis showed that, as the Mg content increased, the Q2 unit (PO2-) shifted towards higher wavenumbers. The proportion of Q3 unit (P2O5) decreased in the glass structure. This confirmed that the replacement of Na+ by Mg2+ was accompanied by concurrent polymerization of the calcium-phosphate glass network. The biosolubility test in the phosphate-buffered saline solution showed that the magnesium addition enhanced the biosolubility properties of Na2O-CaO-P2O5 glasses by increasing their dissolution rate and supporting forming CaP-rich layers on the surface. The glass transition temperature increased, and thermal stability decreased substantially upon substitution of Na2O by MgO.

Anion polarizabilities in oxynitride glasses. Establishing a common optical basicity scale.

Inspired by the work of John Duffy on optical basicity of oxyfluoride glasses, we apply here the concept of optical basicity to oxynitride systems. While in the original work of Duffy and Ingram the basicity of a medium could be probed by s2 ions like Pb2+, the low energy intrinsic absorption edge of nitride-containing systems does not allow the use of such probe ions. This study uses therefore experimental data on refractive index and density of alkaline earth and rare earth containing silicate oxynitride glasses, prepared by the authors or taken from the literature. In addition, literature reports on experimental or calculated refractive index, density and polarizability data are used to compare pure nitride systems, e.g. bulk or thin film materials that are either crystalline or glassy. We compare simple and complex nitride systems with their oxygen counterparts, by calculating their optical basicity using the chemical composition as well as the established relationship between optical basicity, Λ, and electronic polarizability in oxide systems. Our results on oxynitride systems are in good agreement with Duffy's previous work on oxyfluoride glasses and indicate that the optical basicity varies for the isoelectronic anions in nitrides, oxides and fluorides (N3-:O2-:F-) of a cation Mm+ as follows: Λ(MFm) = 1/2Λ(M2Om) = 1/3Λ(M3Nm). Using this relation for CaO, for which the optical basicity was set as unity by Duffy and Ingram, one has Λ(CaF2) = 0.50, Λ(CaO) = 1.00 and Λ(Ca3N2) = 1.50. The optical basicity of complex nitrides can therefore be calculated by the same method established for oxides using the equivalent fractions and the basicity of the constituent nitrides. The relationship between nitride polarizability αN and basicity Λ(nitride) was found to be linear, with Λ(nitride) = 0.39αN- 0.14 where αN is given in Å3.

Dissolution of glass compositions containing no added lead in simulated lung fluid.

Six crystal glass compositions containing no added lead were studied with respect to the potential exposure of workers during the cold-end working of crystal type glasses. During cutting and grinding of crystal glass, fine dusts are produced. These may be inhaled by the workers with subsequent partial dissolution of the dusts in the lung fluid. In order to provide a measure of the degree of dissolution in the case of the six crystal glass compositions produced in this work, the release of antimony, barium, silicon, and bismuth was investigated by passing simulated lung fluid over powdered samples of the crystal having a maximum distribution at a diameter of ca. 0.5 microm for a period of 21 days. The results show that it is possible to produce durable glass containing no added lead. While the leaching and weathering of the glass compositions studied here could be correlated with the mole ratio of alkali/silica and the degree of depolymerisation of the silica network, the dissolution of silica in simulated lung fluid seems to be independent of this property.

Element migration from glass compositions containing no added lead.

Six crystal glass compositions without added lead were used to prepare standard beakers having a volume of ca. 240 ml. The experimentally determined concentrations of the elements in the glass beakers were in satisfactory agreement with the theoretically predicted values. The degree of leaching of selected elements from these beakers was determined using 4% acetic acid as described in the ISO 7086-1:2000 standard test. In addition, to the degree of leaching by 4% acetic acid, migration into cola, red wine, 40% ethanol and 0.3% citric acid was also determined. Elements tested included antimony, barium, bismuth and zinc as these were considered to be of most interest. The results show that it is possible to produce durable glass containing no added lead. The overall quality of the glasses was good and the concentrations of the various elements migrating (leaching) into the various test solutions used was very small and it is clear that they would not present a hazard to consumers in the event that they were to use glasses of any of these compositions for consumption of either alcoholic or non-alcoholic beverages. The original ISO7086-1:2000 test using a 4% acetic acid leaching solution was developed to test for lead migration from crystal containing added lead and ceramic ware containing lead glazes or colouring. This work also shows that it is an excellent leaching agent for assessing the safety of crystal containing no added lead as it gave the highest degree of migration for all the glass compositions and all the elements tested. In the case of glasses containing ZnO, it was shown that the degree of zinc migration was linearly related to the mole-% of ZnO in the glass. With respect to the durability of glasses, it was shown that the degree of attack increases when the degree of silica depolymerisation increases.