Papers by Keyword: Glass Structure

Abstract: Tantalum-containing phosphate invert glasses were prepared using a liquid phase method under ambient conditions. In our previous study, the ion-releasing behavior (i.e. chemical durability) of phosphate glasses was controlled by the amount of intermediate oxides. In this work, Ta₂O₅ (intermediate oxide) was used to improve the chemical durability of the glasses. Ta-containing phosphate invert glasses were prepared and their structures were characterized. X-ray diffraction (XRD) patterns of the glasses exhibited broad halos, indicating an amorphous state. The amount of P₂O₅ in the glasses increased with increasing Ta₂O₅ content, while the amount of CaO decreased. The glasses prepared with a nominal P : Ta molar ratio of 2 : 1 showed a value of 1.87 : 1. Thus, almost all the Ta used in the synthesis was contained in the resulting glass. Raman spectra showed bands corresponding to short phosphate units such as ortho-and pyrophosphate, and the P-O-P peak was blue-shifted with increasing Ta₂O₅ content. The P-O-Ta bonds were formed with TaO₄ tetrahedra, as new peaks at 970 cm^-1 (P-O-Ta bonds) and 825 cm^-1 (observed in YTaO₄) were observed. The glasses containing higher amounts of Ta₂O₅ exhibited TaO₆-rich phases, as shown by the Raman band at 630 cm^-1 (Ta-O-Ta bonds) and broad XRD peaks at 2θ = 5 ~ 10°. Therefore, Ta in the phosphate invert glasses prepared by the liquid-phase method crosslinks phosphate units in the form of TaO₄ tetrahedra, and the excess Ta exists in the form of TaO₆ octahedra as a network modifier and/or Ta₂O₅-rich phase.

Abstract: Phosphate invert glasses are mainly composed of ortho-and pyro-phosphate units and can stimulate cellular functions by releasing inorganic ions. Our group has succeeded in the synthesis of titanium-containing phosphate invert glasses with the liquid phase method at room temperature. ZnO is classified as an intermediate oxide in the glass network structure and improves the chemical durability of phosphate invert glasses. In addition, zinc ion exhibit a wide range of antibacterial ability. However, excess amounts of zinc ions can be toxic to cells. Hence, the dissolution behavior of zinc ions must be controlled for biomedical applications. In this work, ZnO-containing phosphate invert glasses (PIG-Zn) were prepared using the liquid phase method. The phosphate groups of PIG-Zn were composed of ortho-and pyro-phosphate groups, and the peaks were blue-shifted with increasing the ZnO content due to the field strength of Zn²⁺ being larger than that of Ca²⁺. Thus, phosphate groups may be cross-linked by Zn²⁺ to form P-O-Zn bonds. Meanwhile, ion-releasing amounts from PIG-Zn were decreased with increasing ZnO content. This is because the formation of P-O-Zn bonds can increase the chemical durability of PIG-Zn. In addition, PIG-Zn showed excellent antibacterial ability. Therefore, PIG-Zn is expected to exhibit antibacterial ability with controlled Zn²⁺ ion-releasing behavior for biomedical applications.

Abstract: The effect of additives of P₂O₅ on the solubility of molybdenum in the amorphous part of glass and on the phase composition of the crystallized part of the highly alkaline glasses of the Li₂O–(Na₂O–K₂O)–B₂O₃-SiO₂ system was studied. The comparison of the phase composition of samples with or without phosphorus prior and after annealing allowed to determine the change of solubility of molybdenum in the amorphous part of the samples and to evaluate the thermal stability of the synthesized glass-ceramic materials. It was found, that for the compositions without phosphorus and the samples without lithium, when molybdenum is added at the synthesis stage, almost all of the molybdenum is included only in the crystalline molybdates. The study has shown an increase in the solubility of molybdenum only in the structure of lithium-containing glasses with phosphorus.

Abstract: The effect of substitution of alkaline earth metals for sodium on the structure of alkali borosilicate glasses had been studied using the solid-state ¹¹B and ²⁹Si NMR spectroscopy. NMR spectra enable to evaluate the relative mole fractions of different silicon and boron structural units in studied samples. The obtained results demonstrate that alkaline earth metals increase the polymerization degree of the silicon structural units at the expense of de-polymerization of the boron units. The reason for these changes is preferential coordination of sodium and alkaline earth metals to the boron units, that increases strongly for the studied alkaline earth metals.

Abstract: Glassy solid electrolytes are important integral components for all-solid-state devices for energy storage and conversion. The use of multiple network formers is an important part of their design strategy for specific applications. In many glass systems the interaction between the different network formers results in strongly non-linear variations in physical properties (network former mixing (NFM) effects), requiring a detailed understanding on a structural basis.The issues to be addressed involve both the structural organization and connectivities within the framework, the local environments and spatial distributions of the mobile ions, and the dynamical aspects of ion transport, to be discussed in relation to possible phase separation or nano-segregation effects. Besides Raman and X-ray photoelectron spectroscopies, solid state nuclear magnetic resonance (NMR) methods are particularly useful for providing detailed answers to such issues. The present review introduces the basic principles of modern solid state NMR methods and their applications to glass structure, with a particular focus on the characterization of network-former mixing effects in the most common lithium and sodium conducting oxide and chalcogenide glass systems. Based on the current state of the literature reviewed in the present work, some emerging general principles governing structure/property correlations are identified, to be tested by further experimenteation in the future.

Abstract: Abstract. Neodymium doped sodium bismuth borate (Na2O-Bi2O3-B2O3) glasses were prepared by melt quenching method. Amorphous nature of the glass is confirmed through the X-ray diffraction study. Density of the investigated glasses increases systematically with Bi2O3 concentration. Glass transition temperature decrease slightly with increase of Bi2O3 content and could be due to increase in the number of weaker Bi-O linkages by stronger Nd-O linkages. Fourier Transform - Infrared (FTIR) spectroscopy has been carried out. The IR spectra of the glasses reveal that the strong network consisting of diborate units and is unaffected by the variation of Nd3+ concentration. UV-Visible absorption studies have been performed on these glasses to examine the optical spectra and the optical band gap energy has been calculated. The intensity of the absorption band increases with the increase of Nd3+ concentration. This is due to the formation of non-bridging oxygens (NBO’s) in the structure.

Abstract: The structure of silicate glasses gets its charge stability through SiO₂, R₂O₃, R²⁺ and R⁺ groups arrangement. In these glassy structures, transition metals are usually used as dopants in small amounts. However, in soda-lime glass systems, transition metals can take part in the glassy network in larger quantities as secundary former or modifier, insted R²⁺ groups, if the charge balance conditions are made favorable by R₂O₃ groups additions. This paper studies transition metals (Cr, Ni, Fe, Cu, Zn, Pb, Ru) soda-lime-borosilicate glass network incorporation. This process was applied for many kinds of toxic metals containing vitrification waste. The glasses were obtaind by melt at temperature of 1300°C, and characterized by FT-IR and XRD techinics. The chemical stability was evaluated by hydrolytic attack test. The glasses showed a high chemistry and environmental stability like the soda-lime glass. Keywords: glass structure, electroplating waste, e-waste, nanowaste.

Abstract: SnO-B₂O₃-SiO₂ glass powders, in which the different contents of SnO and B₂O₃ were 35% ~ 70%wt and 26% ~ 61% wt respectively, were prepared through high-temperature melting, water quenching and Ball milling. XRD showed that the performance of forming glass was very good and the range of extension was very wide. The effect of the contents of SnO and B₂O₃ on Tg, acidoresistant and density of prepared glass was studied. IR showed that it generates the heavy metal oxide generated glass. The density of glass powder decrease with increase of B₂O₃ content, but increase with increasing SnO content. SnO-B₂O₃-SiO₂ glass had excellent chemical stability. Differential thermal analysis (DTA) shown that, with increasing SnO content, glass transition temperature first lower and then decreased.

Abstract: Fluoride is an important mineral for hard tissues in the body and appropriate fluoride exposure and usage are beneficial to bone and tooth integrity. Fluoride increases both bone density and bone mass due to stimulation of bone formation and it is used as a treatment for osteoporosis. Bioactive glasses have the capacity to form an intimate bond with living bone tissue due to formation of a mixed hydroxycarbonate apatite layer (HCA) in vitro and in vivo. This makes fluoride-containing bioactive glasses attractive biomaterials. In order to design fluoride-containing bioactive glasses, we need to understand the role of fluorine within the glass structure. A series of bioactive glasses with increasing fluoride content was prepared by a melt-quench route. Characterisation included differential scanning calorimetry (DSC), density measurements, MASNMR spectroscopy and studies in simulated body fluid (SBF). DSC results showed a linear decrease in glass transition temperature (Tg) with increasing amounts of fluoride. Density of the glasses increased with increasing amounts of fluoride. This may indicate an expansion of the silicate glass network accompanying incorporation of CaF2. 19F MAS-NMR spectroscopy showed broad peaks at chemical shifts between -135 and -120 ppm. As sodium fluoride gives a chemical shift of -223 ppm and calcium fluoride of -108 ppm, this indicated possible formation of mixed calcium sodium fluoride species. HCA and calcium phosphate layers were found on the glasses after one week of immersion in SBF showing the bioactivity of the glass series.

Abstract: The structure of a seven oxide aluminoborosilicate simplified nuclear glass, bearing a high amount of neodymium or lanthanum oxide (16 wt%), alkali and alkaline earth cations is studied. Nd3+ or La3+ are supposed to simulate the trivalent lanthanides and minor actinides present in nuclear wastes. In the studied glass composition, lanthanide ions have a modifying role and are located in highly depolymerized regions of the structure as shown by neodymium optical absorption and EXAFS spectroscopies. Both alkali and alkaline earth cations are present around Nd3+ ions enabling their stabilization in glass structure near non-bridging oxygen atoms (NBOs). We show that both the nature of alkali R+ and alkaline earth R'2+ cations and the K = [R'O]/([R2O]+[R'O]) ratio can greatly influence the structure of the aluminoborosilicate glass network. Three glass series were prepared for which: (i) K ratio was varied from 0 to 0.5 (Na+ and Ca2+ being respectively the only alkali and alkaline-earth cations), (ii) the nature of R+ cation was varied from Li+ to Cs+ (Ca2+ being the only alkaline earth cation and K = 0.3), (iii) the nature of R'2+ cation was varied from Mg2+ to Ba2+ (Na+ being the only alkali cation and K = 0.3). 27Al MAS NMR spectroscopy results show that (AlO4)- units are preferentially charge compensated by alkali cations rather than by alkaline-earth cations. Both R+ and R’2+ cations can compensate (BO4)- units. Nevertheless, whereas the proportion N4 of (BO4)- units increases with the size of R'2+ cations, the evolution of N4 with R+ cation size for glasses of the R series is not monotonous. The evolution of sodium ions distribution trough glass structure is followed by 23Na MAS NMR spectroscopy.