Number Of Bridging Oxygens Research Articles

Experimental and numerical assessment on Pb-free alkaline mixed borate glasses for radiation resisting applications

Melt quenching technique has been used to fabricate calcium boro-phosphate glasses doped with praseodymium oxide ions. With increased P2O5 content, structural parameters like oxygen molar volume (Vo) and oxygen packing density (OPD) indicate an opposing trend. In addition to optical factors like optical electronegativity, absorption edge, and direct and indirect bandgap values being estimated and discussed, optical absorption spectra have been recorded for all the glasses. The presence of ionic bond behaviour confirms the strong structural and optical property changes caused by the P2O5 content. Using the Phy-X software application, the radiation shielding parameters were investigated. The incorporation of B2O3, CaCO3, and P2O5 offers more number of bridging oxygens which further leads to closely packed nature. Considering the glass sample B0PCM:Pr, the highest linear attenuation coefficient (LAC) is determined. The LAC results showed that at high energy levels, the glass's shielding performance became more consistent. The results of the effective atomic number analysis demonstrated the impact that CaCO3 has on the glass's shielding effectiveness, with a higher concentration of CaCO3 improving the material's defence against gamma radiation. For B0PCM:Pr glass, the half value layer (HVL) rises from 2.101 to 3.444 cm at 0.284–1.333 MeV. Certainly, it has been observed that the glass tends to have a smaller HVL when it contains more CaCO3 with lesser P2O5 content.

Effect of Bi2O3 on the physical, structural and gamma ray shielding properties of phosphate glasses inside the ternary P2O5-SrO-Bi2O3 system

Strontium phosphate glasses containing bismuth oxide were prepared using conventional melt-quenching technique. X-ray diffraction and differential scanning calorimetry (DSC) analysis suggests that stable ternary glasses of composition 70 P2O5-(30-x)SrO-xBi2O3 can be obtained for x = 5–25 mol%. This study examines such physical properties as the density, molar volume (Vm), glass transition temperature (Tg), and structural properties in the interest of explaining the effect on these glasses of Bi-Sr substitution. An almost linear increase in the density when the concentration of bismuth increases between x = 5 and x = 10 mol% followed by monotonic decreasing is noted. However, the calculated molar volume (Vm) behaves in exactly the opposite way. DSC curves showed that the glass transition temperature (Tg) decreases by 555 °C down to 490 °C as the concentration of Bi2O3 increases, due to the increase in the number of bridging oxygens. Structural investigations performed using IR spectroscopy revealed that the structure of the phosphate network contains predominately meta-phosphate (Q2) units, with contributions from pyrophosphate (Q1) and orthophosphate (Q0). The infrared spectra also revealed depolymerization of the phosphate chains in the glass system, with increased Bi2O3 concentration and the formation of P–O–Bi bonds. The study of the gamma ray shielding parameters showed that the prepared glasses can be used for shielding radiation applications.

Nb5+-doped SrTiO3-based glass-ceramics: Insight into crystallisation kinetics, microstructure, and dielectric properties

Nb5+-doped SrTiO3-based glass-ceramics composed of SrO–B2O3–SiO2–TiO2 were modified by Nb2O5 doping and prepared via a melt-quenching process accompanied by controlled crystallisation. The effect of the Nb2O5 concentration on the crystallisation, microstructure, and dielectric properties of the glass-ceramics was investigated. Surface analysis conducted by XPS revealed that with the addition of Nb2O5, the number of non-bridging oxygens (NBO) decreased while the number of bridging oxygens (BO) increased, increasing the interconnection of the structural units. The crystallisation activation energies of the samples tended to decrease from 376.06 kJ/mol to 271.50 kJ/mol (Kissinger model), and the crystal growth modes changed from two-dimensional to three-dimensional (Avrami indexes n: 2.38–4.23) with increasing Nb2O5 concentration. The XRD, SEM, and EDS analyses showed that the addition of Nb5+ promoted the growth of crystals (0.44–1.35 μm). The dielectric properties show that an appropriate amount of Nb2O5 greatly improves the dielectric constant of the glass-ceramics. The dielectric constant of the glass-ceramic doped with 1.5 mol% Nb2O5 is 178.1 (300 K, 1 MHz), which is approximately 6.7 times higher than that of the undoped Nb2O5-doped glass-ceramics (26.5). The introduction of Nb2O5 reduced the activation energy of glass devitrification, promoted crystal development, and improved the dielectric properties of the glass-ceramics.

Structures and transport properties of supercritical SiO2-H2O and NaAlSi3O8-H2O fluids

Abstract Speciation and transport properties of supercritical fluids is critical for understanding their behavior in the Earth’s interior. Here, we report a systematic first principles molecular dynamics simulation study of the structure, speciation, self-diffusivity (D), and viscosity (η) of SiO2 melt, NaAlSi3O8 melt, SiO2-H2O and NaAlSi3O8-H2O fluids at 2000–3500 K with 0–70 wt% H2O. Our calculations show that as the water content increases, the proportion of Q0 species (Qn species, where n is the number of bridging oxygens in an individual Si/Al-O polyhedra) increases while Q4 decreases. The proportions of Q1, Q2, and Q3 species first increase and then decrease with increasing water content. The diffusivity sequence for the supercritical SiO2-H2O fluids is DH >DO >DSi, and for the supercritical NaAlSi3O8-H2O fluids, on the whole, is DNa ≈ DH >DO >DAl ≈ DSi. The viscosities of the two systems decrease drastically at the beginning of the increase in water content, and then decrease slowly. We demonstrate that the exponential decrease in the viscosity of polymerized silicate melt with increasing water content is due to a sharp decrease in the proportion of Q4 species and increase in Si-O-H. The typical structural feature of supercritical fluid is that it contains a large amount of easy-to-flow partially polymerized or depolymerized protonated silicate units, which leads to a low viscosity while being enriched in silicate. This feature provides supercritical fluids the potential to transport elements that are hard to migrate in aqueous fluids or hydrous silicate melts, such as high field strength elements.

Development of coarse-grained potential of silica species

ABSTRACT Understanding the molecular transformation of silica aggregates during silica polymerisation is crucial to control the properties of final products such as zeolite, nanoparticles, mesoporous silica and other polymorphs. Nevertheless, molecular events during synthesis are challenging to probe using experimental techniques. Computational tools are beneficial to probe molecular length and time scales; however, the complex systems with significant degrees of freedom require significant computational resources. In this work, we have developed coarse-grained (CG) potentials for silica system wherein every silica tetrahedron (Si(OH)O) having ‘z’ number of bridging oxygen is mapped to a unique CG silica bead (). Different composition of these CG silica beads represent a polymerised silica system with varying degrees of condensation. We performed molecular dynamics (MD) simulations of all-atom silica system to obtain reference radial distribution functions between various silica species (), which was used in Monte Carlo simulations of the CG system to obtain CG potentials. We iteratively refined the CG potentials using iterative Boltzmann inversion and inverse Monte Carlo techniques. We found two attractive minima in the CG potential between arising due to direct and indirect interactions of species representing first and second coordination shells. The strength of CG potential increases for both of minima with increasing number of bridging oxygen in species. We performed MD simulations of CG silica beads using developed CG potentials at two degree of condensations and found equilibrium structure of spherical silica nanoparticle. We found that and species are predominantly located at the centre of nanoparticles, whereas species are present uniformly.

Effect of the Initial P Content on Dephosphorization of Hot Metal with Low Basicity Slag at 1623 K

The effect of the initial P content ranging from 0.057% to 0.292% in hot metal on dephosphorization with low basicity (CaO/SiO2) slag at 1623 K is investigated using high‐temperature laboratorial experiments. With increasing initial P content in the hot metal, the dephosphorization ratio increases first and then decreases, with the highest dephosphorization ratio of 83.2% at the initial P content in the hot metal of 0.173%. The phases in dephosphorization slags are basically consistent, which are mainly composed of nCa2SiO4‐Ca3(PO4)2, Ca2SiO4, metal oxide, Ca3(PO4)2, Ca3Mg(SiO4)2, Ca2Fe2O5, and MgAl2O4. The compositions of all the P‐rich phases are close to the connection line between Ca2SiO4 and Ca3(PO4)2 in the phase diagram. In addition, with increasing the initial P content in hot metal, the viscosity and activation energy values of the dephosphorization slag increases at the present dephosphorization temperature of 1623 K and the values of the activation energy of the dephosphorization slags increase gradually. The area fractions of Q0 + Q1 (Qi, i is the number of bridging oxygen per silicon atom) units decrease, whereas those of the Q2 + Q3 units increase. The average number of nonbridging oxygen per silicon atom (NBO/Si) value decreases, indicating that the degree of the polymerization (DOP) of the corresponding dephosphorization slag increases resulting in the increased viscosity.

Improved empirical force field for multicomponent oxide glasses and crystals

In this paper, the self-consistent PMMCS force fields (FFs) [Pedone et al., J. Phys. Chem. B 110, 11780 (2006)] widely used for the simulation of a large variety of silicates, aluminosilicate and phosphate crystals, and multicomponent oxide glasses have been revised and improved by the inclusion of two types of three-body interactions acting between T-O-T bridges ($T=\mathrm{Si}$ and P) and network former-network former repulsive interactions. The FFs named Bertani--Menziani--Pedone (BMP)-harm and BMP-shrm better reproduce the T-O-T bond angle distributions (BADs) and network former-oxygen distances. Consequently, the prediction of ${Q}^{n}$ distributions (Q stands for quaternary species, and $n$ is the number of bridging oxygens around it), neutron total distribution functions, solid-state nuclear magnetic resonance spectra of spin active nuclei ($^{29}\mathrm{Si}$, $^{17}\mathrm{O}$, $^{31}\mathrm{P}$, $^{27}\mathrm{Al}$), and the density have also been hugely improved with respect to the previous version of our FF. These results also highlight the strong correlation between the T-O-T BADs and the other short and intermediate structural properties in oxide glasses, which have been largely neglected in the past. In addition to the improvement of the structure, the FF has been revealed to reproduce well the ionic conductivity in mixed alkali aluminosilicate glasses and the elastic properties. The systematic comparison with other interatomic potential models, including the polarizable core-shell model, carried out in this paper showed that our potential model is more balanced and effective for simulating a vast family of crystalline and amorphous oxide-based systems.

Impact of sodium oxide, sulfide, and fluoride-doped vanadium phosphate glasses on the thermoelectric power and electrical properties: structure analysis and conduction mechanism

Four glasses of the (13.5%X– 32.5%V2O5–54%P2O5) mol%, X = Na2O, Na2S, and NaF, and (13.5% Na2S – 32.5%V2S5–54%P2S5) mol% were prepared. DSC, density, molar volume, XRD, thermoelectric power, and glass transport properties of the prepared glasses were reported. Density was found to increase with decreasing the molar volume, Vm, of glasses containing sulfur. Replacing oxygen with sulfur results in less number of bridging oxygen; this decrease leads to less compactness and molar volume increase of the host network. Thermoelectric power (S) of present samples was reported and the fraction C of reduced transition metal ions (C = V4+/Vtotal or V3+/Vtotal ) was calculated. Moreover, the conductivity data temperature dependence has been studied in two distinct polaronic models. Above θD/2 (high temperature region), the conductivity data are compatible with Mott SPH model between the nearest neighbors, but in the intermediate temperature extent, the appropriate model was Greaves VRH model. Dc conductivity values have a positive relation with C results calculated from thermoelectric power. The dc conductivity of the formed sulfur-containing glasses is enhanced owing to the increase of V4+–V5+ or V3+–V4+ ion pairs as sulfur worked as a reducing agent, which resulted in reduction of the vanadium ions from high valence (V4+ and/or V5+) to low valence states (V3+ and/or V4+). From inspecting the conduction mechanism nature and type, the current work displayed was proved to be in accord with non-adiabatic case of SPH. The hopping carrier mobility is very small in order of 10− 5 cm2 V− 1 s− 1 at 393 K satisfying the localized condition for hopping electrons.

Structural densification of lithium phosphoaluminoborate glasses

AbstractLithium aluminoborate glasses have recently been found to undergo dramatic changes in their short‐range structures upon compression at moderate pressure (~1 GPa), most notably manifested in an increase in network forming cation coordination number (CN). This has important consequences for their mechanical behavior, and to further understand the structural densification mechanisms of this glass family, we here study the effect of P2O5 incorporation in a lithium aluminoborate glass (with fixed Li/Al/B ratio) on the pressure‐induced changes in structure, density, and hardness. We find that P2O5 addition results in a more open and soft network, with P‐O‐Al and P‐O‐B bonding, a slightly smaller fraction of tetrahedral‐to‐trigonal boron, and an unchanged aluminum speciation. Upon compression, the cation‐oxygen CNs of both boron and aluminum increase systemically, whereas the number of bridging oxygens around phosphorous (Qn) decreases. The glasses with higher P2O5 content feature a larger decrease in Qn (P) upon compression, which leads to more non‐bridging oxygen that in turn fuel the larger increase in CN of B and Al for higher P2O5 content. We find that the CN changes of Al and B can account for a large fraction (around 50% at 2 GPa) of the total volume densification and that the extent of structural changes (so‐called atomic self‐adaptivity) scales well with the extent of volume densification and pressure‐induced increase in hardness.

Structure Dependence of Poisson's Ratio in Cesium Silicate and Borate Glasses.

In glass materials, Poisson’s ratio (ν) has been proposed to be correlated with a variety of features, including atomic packing density (Cg), liquid fragility (m), and network connectivity. To further investigate these correlations in oxide glasses, here, we study cesium borate and cesium silicate glasses with varying modifier/former ratio given the difference in network former coordination and because cesium results in relatively high ν compared to the smaller alkali modifiers. Within the binary glass series, we find positive correlations between ν on one hand and m and Cg on the other hand. The network former is found to greatly influence the correlation between ν and the number of bridging oxygens (nBO), with a negative correlation for silicate glasses and positive correlation for borate glasses. An analysis based on topological constraint theory shows that this difference cannot be explained by the effect of superstructural units on the network connectivity in lithium borate glasses. Considering a wider range of oxide glasses from the literature, we find that ν generally decreases with increasing network connectivity, but with notable exceptions for heavy alkali borate glasses and calcium alumino tectosilicate glasses.

The structure of model glasses of the amorphous phase of glass-ceramic glazes from the SiO2[sbnd]Al2O3[sbnd]CaO[sbnd]MgO[sbnd]Na2O[sbnd]K2O[sbnd]ZnO system

In this work, particular attention was paid to the structural characteristics of the amorphous phase in glass-ceramic glazes from the SiO2Al2O3CaOMgONa2OK2OZnO system. The study was carried out on model glasses whose chemical composition corresponds to the chemical composition of the vitreous phase of the glazes determined on the basis of electron probe micro-analyzer (EMPA). Structural investigations of the obtained model glasses were carried out using the mid-infrared (MIR) and solid-state magic-angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy. The solid-state MAS-NMR study carried out on 27Al and 29Si nuclei showed that all aluminum and silicon ions have tetrahedral coordination and thus form the glass network. The results of the 29Si solid-state MAS-NMR measurements also showed that with the increase of ZnO content in the glass chemical composition, the number of Q3 and Q2 silicon-oxygen units increases at the expense of Q4 (where n is the number of bridging oxygens), thus indicating an increase in the degree of depolymerization of the alumino-silico-oxygen network of studied of glasses. Analysis of the MIR spectra of the obtained glasses confirmed the conclusions from the solid-state MAS-NMR research, i.e. that Zn2+ ions cause depolymerization of the glass network of glazes. The weakening of the network of glasses resulted in lowering of the transformation and dilatometric softenings temperature. The tests carried out on model glasses allow drawing conclusions about the structure and properties of the vitreous phase of real glazes.

The effect of boron substitution for aluminium on the microstructure of calcium fluoro-aluminosilicate glasses and glass-ceramics

Calcium fluoro-aluminosilicate (4.5SiO2-3Al2O3-1.5P2O5-3CaO-2CaF2) glasses have significant applications in the medical and dental fields. However, due to the biological hazard of aluminium in the human body, this study focused on the influence of boron substitution for aluminium on the structure and properties of a series of substituted glasses and their correlated glass-ceramics. The results indicated that by increasing the amount of boron, the density of glasses and their glass-ceramics both decreased, whereas the number of bridging oxygens in the glasses increased. The glass transition temperature and the crystallization temperature remained almost unchanged for the glasses with a boron substitution of less than 25 mol%. Boron formed oxygen bridges in all glasses in the form of BO3 triangles and BO4 tetrahedra. Reducing the Al content in glasses, had an effect on the morphology and orientation of the fluorapatite crystal phase formed.

Composition dependence of the short range order structures in 0.2Na2O + 0.8[xBO3/2 + (1-x)GeO2] mixed glass formers

The atomic level structures of ternary 0.2Na2O + 0.8[xBO3/2 + (1-x)GeO2] glasses have been carefully examined for the first time using a combination of Raman, infrared (IR) and 11B magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopies. It was found that, like in other mixed glass former (MGF) systems, there is an unequal sharing of the sodium oxide between the two glass formers, B and Ge, across this series 0 < x < 1. It is found that for all x > 0, the Na2O preferentially reacts with boron to create a larger number of tetrahedral boron, BO4/2−1 ≡ B4, units than would be found for a binary sodium borate glass of the same mole fraction, 0.20, of Na2O. In addition to this higher than expected fraction of B4 units as determined by the 11B MAS-NMR measurements, the Raman spectra further suggest the presence of high concentrations of octahedrally coordinated GeO6/2−2, Ge6, units in the GeO2 rich end of this compositional series, x ≤ 0.2. Across this series, it is found that there are at most five short range order (SRO) structural units present in these glasses, BO3/2 (B3), B4, GeO6/2−2 (Ge6), GeO3/2O−1 (Ge3), and GeO4/2 (Ge4), where the superscript gives the number of bridging oxygens (BOs) bonded to the central atom. The composition, x, dependence of all of these SRO structural units were determined by combining the results all of these spectral techniques and requiring that the total sum of all the negatively charged SRO units balance the positive (+0.4) charges from the Na+ ions and that the total amount of B balance to 0.8×, the total amount of Ge balance to 0.8*(1-x), and the total amount of oxygen balance to1.8–0.4× as required by the stoichiometry of this compositional series.

Investigation the influences of B2O3and R2O on the structure and crystallization behaviors of CaO–Al2O3based F-free mold flux

The influences of B2O3and R2O on the structure and crystallization of CaO–Al2O3based F-free mold flux were investigated by Raman Spectroscopy and Differential Scanning Calorimetry Technique, respectively, for developing a new type of F-free mold flux. The results of structural investigations showed that B3+is mainly in the form of [BO3]. And [BO3] appears to form BIII–O–Al linkage which will produce a positive effect on forming [AlO4] network. The number of bridging oxygen and the degree of polymerization of [AlO4] network structure for CaO–Al2O3system were also increased with the increasing of B2O3. On the contrary, with the addition of R2O into CaO–Al2O3–B2O3system, the number of bridging oxygen and the degree of polymerization of [AlO4] network were decreased. DSC results showed that the crystallization process became more sluggish with the increase of B2O3, which indicated that the crystallization ability was weakened. While the quenched mold fluxes crystallized more rapidly when introducing R2O. In other word, the crystallization rates of CaO–Al2O3based slags were accelerated by the introduction of R2O. The liquidus temperature and crystallization temperature were decreased with the increasing amount of B2O3or by addition of R2O into CaO–Al2O3system. Only one kind of crystal was precipitated in 8% B2O3and %R2O-containing samples, which was CaAl2O4identified by SEM-EDS. When the content of B2O3increased from 8% to 16%, Ca3B2O6is clearly observed, demonstrating that the crystallization ability of Ca3B2O6is enhanced by the increasing concentration of B2O3in mold flux. The Ca/Al ratio of the generated calcium aluminate has been altered from 1:2 to 1:4 with the increasing of B2O3. The size of CaAl2O4crystal is gradually increased with the addition of R2O. The crystallization ability of CaAl2O4is promoted by R2O.

Molecular structure, configurational entropy and viscosity of silicate melts: Link through the Adam and Gibbs theory of viscous flow

The Adam and Gibbs theory depicts the viscous flow of silicate melts as governed by the cooperative re-arrangement of molecular sub-systems. Considering that such subsystems involve the silicate Qn units (n=number of bridging oxygens), this study presents a model that links the Qn unit fractions to the melt configurational entropy at the glass transition temperature Tg, Sconf(Tg), and finally, to its viscosity η. With 13 adjustable parameters, the model reproduces η and Tg of melts in the Na2O-K2O-SiO2 system (60≤[SiO2]≤100mol%) with 1σ standard deviations of 0.18 log unit and 10.6°, respectively.The model helps understanding the links between the melt chemical composition, structure, Sconf and η. For instance, small compositional changes in highly polymerized melts generate important changes in their Sconf(Tg) because of an excess of entropy generated by mixing Si between Q4 and Q3 units. Changing the melt silica concentration affects the Qn unit distribution, this resulting in non-linear changes in the topological contribution to Sconf(Tg). The model also indicates that, at [SiO2]≥60mol%, the mixed alkali effect has negligible impact on the silicate glass Qn unit distribution, as corroborated by Raman spectroscopy data on mixed Na-K tri- and tetrasilicate glasses. Such model may be critical to link the melt structure to its physical and thermodynamic properties, but its refinement requires further high-quality quantitative structural data on silicate and aluminosilicate melts.

Structural Investigation of Phosphorus in CaO-SiO2-P2O5 Ternary Glass

The system of CaO-SiO2-P2O5 ternary glass is not only among the major constituents of steelmaking slags in iron and steel industry, but also play a significant role in other industrial process, such as chemical engineering and glass industry. In the present study, the structure of CaO-SiO2-P2O5 ternary glass with varying P2O5 content from 0 to 15 wt pct at a fixed CaO/SiO2 = 1.4 was investigated using molecular dynamics (MD) simulation combined with X-ray photoelectron spectroscopy and Raman spectra techniques. The results indicated that P5+ ions have a higher affinity to Ca2+ ions which are then stripped away from the silicate network with the addition of P2O5, resulting in the formation of Ca-O-P and Si-O-Si linkages. In addition, almost all P5+ ions displayed as $$ {\text{Q}}_{\text{P}}^{0} $$ ( $$ {\text{Q}}_{\text{P}}^{n} $$ , n is the number of bridging oxygen in one [PO4]-tetrahedra units) and a small fraction of P5+ ions behave as $$ {\text{Q}}_{\text{P}}^{1} $$ (P-O-P) and P-O-Si. The enhanced degree of polymerization can be detected from the increase of $$ {\text{X}}_{\text{Si}}^{3} $$ and $$ X_{\text{P}}^{1} /X_{\text{P}}^{0} $$ (mole fraction of $$ {\text{Q}}_{\text{Si}}^{i} $$ or $$ {\text{Q}}_{\text{P}}^{i} $$ ). Furthermore, the ratio of Raman scattering coefficients for $$ Q_{\text{Si}}^{i} /Q_{\text{Si}}^{1} $$ and $$ Q_{\text{P}}^{i} /Q_{\text{P}}^{1} $$ were determined by combining MD simulated result with Raman spectra, which were considered to be suitable to the present study.

Experimental, in-situ carbon solution mechanisms and isotope fractionation in and between (C–O–H)-saturated silicate melt and silicate-saturated (C–O–H) fluid to upper mantle temperatures and pressures

Our understanding of materials transport processes in the Earth relies on characterizing the behavior of fluid and melt in silicate–(C–O–H) systems at high temperature and pressure. Here, Raman spectroscopy was employed to determine structure of and carbon isotope partitioning between melts and fluids in alkali aluminosilicate–C–O–H systems. The experimental data were recorded in-situ while the samples were at equilibrium in a hydrothermal diamond anvil cell at temperatures and pressures to 825 °C and >1300 MPa, respectively.The carbon solution equilibrium in both (C–O–H)-saturated melt and coexisting, silicate-saturated (C–O–H) fluid is 2CO3 + H2O + 2Qn + 1 = 2HCO3 + 2Qn. In the Qn-notation, the superscript, n, is the number of bridging oxygen in silicate structural units. At least one oxygen in CO3 and HCO3 groups likely is shared with silicate tetrahedra. The structural behavior of volatile components described with this equilibrium governs carbon isotope fractionation factors between melt and fluid. For example, the ΔH equals 3.2 ± 0.7 kJ/mol for the bulk 13C/12C exchange equilibrium between fluid and melt. From these experimental data, it is suggested that at deep crustal and upper mantle temperatures and pressures, the δ13C-differences between coexisting silicate-saturated (C–O–H) fluid and (C–O–H)-saturated silicate melts may change by more than 100‰ as a function of temperature in the range of magmatic processes. Absent information on temperature and pressure, the use of carbon isotopes of mantle-derived magma to derive isotopic composition of magma source regions in the Earth's interior, therefore, should be exercised with care.

Influence of SiO2 on the Luminous Properties of Nd3+-Doped Barium Silicophosphate Nanostructured Glasses

Barium phosphate glasses with high glass transition temperature, which belong to alkali-free glasses, are valuable candidates for application in high-power laser glasses. With the introduction of SiO2 content, the thermal properties, refractive index, and mechanical properties of these glasses can be improved, while the effects that silica exerts on the structure and luminous properties of the glasses are still in need of further study. Herein, the structure and the luminous properties, containing transmittance and fluorescence properties, of Nd3+-doped barium silicophosphate glasses are studied. It is notable that both the maximum values of luminous intensity and luminous decay time appear at the composition of 26.7 mol% of SiO2, a composition which also possesses the largest ultraviolet end edge redshift. The maximum percentage of bridging oxygen (BO) is also found at this composition, which is quantified by X-ray photoelectron spectroscopy (XPS). And both the luminous intensity and luminous decay time of these glasses appear in positive correlations with the number of bridging oxygen of the glass matrix. Thus, a method to improve the luminous properties of the barium phosphate glasses through changing the local chemistry state of the dopants by introducing SiO2 content is proposed. The optimized composition found in this paper would be useful throughout the wide field of optics.

Structural investigation of calcium borosilicate glasses with varying Si/Ca ratios by infrared and Raman spectroscopy

Si/Ca ratio-dependent structure of borosilicate.

Calcium/strontium substituted phosphate based glasses for orthopaedic applications

Event Abstract Back to Event Calcium/strontium substituted phosphate based glasses for orthopaedic applications Uresha Patel1*, Kazi Md Zakir Hossain1, Andrew Kennedy1, Alex Hannon2, Emma Barney1 and Ifty Ahmed1 1 University of Nottingham, Faculty of Engineering,, United Kingdom 2 Rutherford Appleton Laboratory, ISIS Facility, United Kingdom Introduction: Phosphate based glasses (PBGs) are an ideal material to act as “carriers” of therapeutic ions such as strontium (Sr), since their degradation rate can be tailored to range over orders of magnitude [1] by altering the glass composition. Sr substitution is of particular interest for orthopaedic applications due to the dual effect of Sr on bone metabolism: osteoblast activation and osteoclast inhibition[2]. This study aims to investigate the effect of the substitution of CaO with SrO in a PBG system with a fixed glass former content of 40mol%. By investigating the glass structure at an atomic level the inter-relationship between glass composition, structure and durability can be understood, enabling optimisation of an ideal therapeutic glass with controlled release rates. Materials and Methods: SrO was substituted for CaO in a series of PBGs (mol%(P2O5)40 (CaO)16-x (MgO)24 (Na2O)20 (SrO)x where x= 0, 4, 8, 12 and 16, denoted P40, Sr4, Sr8, Sr12 & Sr16 respectively). All glass samples were fabricated via a melt quench route involving drying of precursors at 350ºC for 30min, followed by melting at 1150ºC for 1.5h. Structural characterisation was carried out using 31P NMR (spectra obtained at the EPSRC UK National Solid-state NMR Service, Durham) and neutron diffraction (ND) studies (GEM diffractometer at ISIS spallation neutron source, Rutherford Appleton Laboratory, UK). The ND results were interpreted using fitting and simulation techniques. Dissolution studies were conducted in distilled water at 37ºC for 28d. Results and Discussion: The ND study revealed that CaO substitution with SrO had little effect on the well-ordered, short range structure of the glasses. This is thought to be due to the similarities in charge and field strength of Ca2+ and Sr2+ ions. The coordination numbers (CN) derived from ND showed that all P atoms are 4-coordinated (Table 1) which is consistent with previous studies[3]. The modifier environments for each glass composition also did not vary considerably as shown in Figure 1A & B. Solid state 31P NMR indicated little change in Qi­­ species for all compositions except for Sr16. These glasses showed an approximate 1:1 ratio of Q1:Q2 species, suggesting a network connectivity (number of bridging oxygens (BO) per network forming tetrahedral) of around 1.5. From these results it can be assumed the glass network consists of an average chain length of 4 tetrahedral units. The larger increase in Q1 species for Sr16 indicated that Q1 units may also be present as dimers i.e. pyrophosphates. Dissolution studies showed that Sr free glasses degraded at a faster rate than those with Sr, which contradicted previous studies [4][5]. In addition, no significant difference was observed between the Sr containing glasses (p>0.05) suggesting it may be possible to deliver varying concentrations of Sr without affecting the rate of the glass degradation. Conclusion: Replacing CaO with SrO exerted little effect on the overall glass structure. A consistent Qi distribution and network connectivity was observed along with little change in modifier environments (CN and percentage of BO). The dissolution studies showed that the Sr content had an insignificant effect on degradation rate, hence controlled release of a suited amount of Sr may be delivered posing these glasses beneficial for therapeutic use in bone related diseases such as osteoporosis. Funding body: Science and Technology Facilities Council (STFC ref. no. ST/L502583/1); EPSRC UK National Solid-state NMR Service at Durham