Compositional effects on the crosslink density of Ca–(Mg)–(Y)–Si–Al–oxyfluoronitride glasses

The effects of fluorine and nitrogen substitution for oxygen in aluminosilicate glasses, effectively oxyfluoronitride (OFN) glasses, modified by calcium, calcium–yttrium or calcium–magnesium on thermal and physical/mechanical properties have been compared. Thus, 42 glasses in the Ca–(Mg)–(Y)–Si–Al–O–(N)–(F) system have been prepared and characterized with respect to density (ρ), molar volume (MV), compactness (C), free volume (FV), glass transition temperatures measured by DTA (T_g,DTA) and dilatometry (T_g,dil), dilatometric softening point (T_DS), microhardness (μHv) and Young's modulus (E). Gradients of property variation with nitrogen or fluorine substitutions for oxygen are similar for all three different oxyfluoronitride glass systems and are comparable with those reported for other OFN glasses, again indicating independent and additive effects of nitrogen and fluorine. In attempting to further understand how fluorine affects the cross‐link density (CLD) in OFN glasses, it becomes apparent that it is necessary to allow for a greater contribution by aluminum in a modifier role as fluorine content is increased. This modified calculation of CLD values results in good linear fits between T_g and CLD values. This analysis clearly demonstrates and endorses the concepts that thermal properties are related to CLD while physical/mechanical properties are dependent on glass compactness.     

Melt Processing and Properties of Barium-Sialon Glasses

Bulk oxynitride glasses in the system Ba-Sialon were prepared by cooling homogenized melts from ∼1740°C at ∼50°C/min. The microchemistry, microstructure, and properties of these materials were studied by DTA, dilatometry, electron microscopy, and energy dispersive X-ray analysis. Up to ∼ 7 at.% nitrogen was retained in the glasses by the conventional glass-processing techniques used. Microscopically homogeneous glasses were obtained despite macroscopic segregation of millimeter-sized metallic spheres consisting of Si and Fe. Incorporation of nitrogen in the glass network led to decreasing thermal expansion coefficients, higher glass-transition temperatures, and greater values of indentation hardness with increasing nitrogen content.     

Effect of fluorine and nitrogen content on the properties of Ca-Mg-Si-Al-O-(N)-(F) glasses

X-ray amorphous glasses of composition (in equivalent percent) 15Ca:15Mg: 55Si:15Al:(100-x-y)O:xN:yF with x=0, 10, 15 and y=0, 1, 3, 5, were prepared by melting and casting. The effects of oxygen substitution by fluorine and/or nitrogen on the physical, mechanical, thermal and optical properties of the glasses have been investigated. Molar volume, fractional glass compactness, microhardness, Young's Modulus, glass-transition temperature, dilatometric-softening point and refractive index increased linearly with nitrogen substitution for oxygen, whereas molar volume and thermal expansion coefficient decreased linearly with nitrogen increase. In contrast, all properties except glass-transition temperature and dilatometric-softening point, are virtually unaffected by fluorine substitution for oxygen. Significant and linear, decreases in thermal properties occurred with increasing fluorine substitution level. All the data collected and its analysis clearly showed that the substitution effects of fluorine for oxygen on the studied properties of the glasses of the system with general formula Ca-Mg-Si-Al-O-(N)-(F) are totally independent and additive with respect to the substitution effects of nitrogen for oxygen on glass properties.     

Independent Effects of Nitrogen Substitution for Oxygen and Yttrium Substitution for Magnesium on the Properties of Mg-Y-Si-Al-O-N Glasses

Glasses of composition (in equivalent percent) (28 − x )Mg: x Y:56Si:16Al:(100 − y )O: y N, with x = 0, 14, or 28 for y = 0 and 15 and with x = 0, 7, 14, 21, or 28 for y = 10, were prepared by melting and casting. For glasses where the nitrogen content was varied for a constant cationic ratio, the glass molar volume (MV), compactness ( C ), Young's modulus ( E ), glass-transition temperature ( T _g), and dilatometric-softening temperature ( T _ds) varied linearly as the nitrogen content increased, with MV decreasing and the other properties increasing. From the incremental changes in these properties with nitrogen content, for glasses with x = 0, 14, and 28, good linear fits ( R ² > 0.99) were obtained, and best-fit slopes are reported here. The property changes and their linearity were consistent with the increased cross-linking of the glass network by tricoordinated nitrogen. The replacement of magnesium by yttrium led to a nonlinear decrease in glass compactness and to nonlinear increases in MV, T _g, and T _ds. However, linear correlations were found for MV and ionic volume and for T _g, T _ds, and the coordination of (Si,Al)(O,N) tetrahedra of the glass structural units to the modifier cations not involved in charge compensating aluminum ions in fourfold coordination. The replacement of magnesium by yttrium had little effect on Young's modulus, and this result was related to similar changes in the compactness, C . The present results showed that the effects of substituting nitrogen for oxygen and yttrium for magnesium are independent and additive; thus, no synergistic effects of anion and cation substitutions were observed.     

Review: Elaboration,structure, and mechanical properties of oxynitride glasses

Oxynitride glasses are glasses where threefold coordinated nitrogen atoms substitute for twofold oxygen ones, hence resulting in a larger interatomic cross-linking degree. Such glasses were first observed at the grain boundary in silicon nitride ceramics, where they govern the high-temperature behavior. Later, they were prepared as bulk materials and motivated numerous researches, thanks to their large viscosity, glass transition range, elastic moduli, hardness, and fracture toughness among inorganic and non-metallic glasses. In different chemical systems that were investigated, the synthesis routes and the sources for these exceptional mechanical properties are reviewed. Oxynitride glasses are not easy to process and suffer from the loss of transparency as nitrogen is incorporated over some critical content. Nevertheless, they are attractive “specialty” glasses in various niche areas, thanks to their large refractive index and dielectric constant, improved chemical durability, high softening point, etc., and majorly to their exceptional mechanical properties.     

Viscosities, Glass Transition Temperatures, and Microhardness of Y-Si-A1-O-N Glasses

Y-Si-A1-O-N glasses containing up to 15 at.% nitrogen were prepared. Comparisons of properties of glasses with the same cation composition but with varying N:O ratios show that glass transition temperature, viscosity, and microhardness all increase with increasing nitrogen content.     

Enhanced Thermostability,Thermo‐Optics,and Thermomechanical Properties of Barium Gallo‐Germanium Oxyfluoride Glasses and Glass‐Ceramics

Serial substitutions of BaF₂ for BaO in BaO–Ga₂O₃–GeO₂ glasses were performed, and the effects of the substitutions on the glass properties were investigated. The glass transition temperature, density, refractive index, thermo‐optics coefficient, and figure of merit for thermal shock decreased with the replacement of oxygen by fluorine. On the other hand, the glass‐forming ability increased. Fluorine substitution removed the absorption band of hydroxyl near 2.9 μm. Raman scattering spectroscopy was used to characterize the fluorogermanate glasses. The crystallization process of the glass‐ceramics under different heat‐treatment conditions was also investigated using differential scanning calorimetry, X‐ray diffraction, scanning electron microscopy, and atomic force microscopy. The thermal and mechanical properties were improved by controlling the crystal size of the near‐ and middle‐infrared transparent glass‐ceramics.     

Preparation and Properties of Nitrogen-Containing Na2O-B2O3 Glasses

Up to 3.3 wt% nitrogen can be incorporated into Na₂O-B₂O₃ glass melts. The melting procedure is described, and structure models are given. In contrast to N-containing silicate glasses, the borate glasses were transparent; however, micrographs of their fracture surfaces showed some crystallinity. Properties were determined as a function of the N and Na₂O contents of the glasses. Compared with N-containing silicate glasses, the properties of borate glasses are much less changed by the nitrogen introduced.     

Compositional effects on the properties of high nitrogen content alkaline-earth silicon oxynitride glasses, AE = Mg, Ca, Sr, Ba

A series of alkaline-earth element containing high nitrogen content oxynitride glasses (AESiON), with AE = Mg, Ca, Sr, Ba, were prepared in order to investigate the compositional effects on the physical properties of the alkaline-earth element. The physical properties were found to change linearly with the concentration of AE elements. The density of the glasses increases substantially with an increase in the AE atomic mass and slightly with an increase in nitrogen ratio. Ba containing glasses shows the value of density 4.16 g/cm³. Glass transition temperatures are found to be higher for Mg glasses, ca. 1020 °C, in comparison with Ba glasses, ca. 895 °C. The hardness of Mg containing glasses shows high values, up to 12.2 GPa and decreases for Ca, Sr and Ba containing glasses. Ba, containing glasses shows high values of refractive index in comparison with the Sr, Ca and Mg containing glasses.     

Properties of BaO–R2O3– Ga2O3–GeO2 (R = Y, Al, La, and Gd) Glasses

Barium gallogermanate glasses were prepared with substitutions of Al₂O₃, Y₂O₃, La₂O₃, and Gd₂O₃ for Ga₂O₃. The effects of these substitutions on the glass transformation temperature, viscosity, thermal expansion, and molar volume have been determined. The changes in properties associated with each substitutional ion are consistent with structural roles reported for these ions in other glasses. Aluminum acts as an intermediate with [AlO₄^–] tetrahedra substituting directly for [GaO₄^–] tetrahedra. Yttrium and gadolinium act as "atypical" modifier ions because of their large field strengths. Finally, the properties of the La₂O₃-substituted glasses indicate a possible dual structural role for La³⁺ ions in these glasses.     

Structure–Property Correlations in Y–Ca–Mg–Sialon Glasses: Physical and Mechanical Properties

The physical and mechanical properties of 12 glasses from the Y–(Mg,Ca)–Si–Al–O–N and (Mg,Ca)–Si–Al–O–N systems were investigated. The effect of the substitution of magnesium for calcium through two series of glasses, one consisting of oxides glasses and the other of glasses containing 6 at.% of nitrogen (15 e/o N), was considered. The change of the glass transition temperature through the glass series provides evidence for a mixed-alkaline-earth effect between magnesium and calcium species. The indentation hardness ( H ), Young's modulus ( E ), and indentation fracture toughness ( K _C) were found to increase significantly with either the magnesium or the nitrogen content, and nitrogen also seems to enhance the effect of magnesium on the properties. The network structure was analyzed both by ²⁹Si and ²⁷Al Magic Angle Spinning Nuclear Magnetic Resonance and by neutron scattering experiment, which allows for the estimation of some atomic bond lengths in such complex glasses. Nitrogen was found to have a significant structural effect on the magnesium environment and on the glass polymerization degree, and hence on the glass properties.     

Surface nitrogen doping of optical glasses (a review)

The need is demonstrated for improvement in the service properties of the surfaces of optical components fabricated from chemically unstable glasses. A number of solid and gaseous reagents are proposed for surface nitrogen doping of optical glasses and the requirements they should meet are defined. The process variables involved in the nitrogen doping of glass at temperatures belowt _g are examined. The service properties of lead-containing, phosphate and borate glasses with a nitrogen-doped surface are listed. Translated from Steklo i Keramika, No. 1, pp. 6–8, January, 1997.     

Mechanical properties of oxynitride glasses

Oxynitride glasses combine a high refractoriness, with Tg typically >850°C, and remarkable mechanical properties in comparison with their parent oxide glasses. Their Young's modulus and fracture toughness reach 170 GPa and 1.4 MPa m^.5, respectively. Most reports show good linear relationships between glass property values and nitrogen content. There is a clear linear dependence of Young's modulus and microhardness on fractional glass compactness (atomic packing density). They also have a better resistance to surface damage induced by indentation or scratch loading. The improvements stem from the increase of the atomic network cross-linking—because of three-fold coordinated nitrogen—and of the atomic packing density, despite nitrogen being lighter than oxygen and the Si–N bond being weaker than the Si–O bond. For constant cation composition, viscosity increases by ∼3 orders of magnitude as ∼17 eq.% oxygen is replaced by nitrogen. For rare earth oxynitride glasses with constant N content, viscosity, Young's modulus, Tg, and other properties increase with increasing cation field strength (decreasing ionic radius). Research continues to find lighter, stiffer materials, including glasses, with superior mechanical properties. With higher elastic moduli, hardness, fracture toughness, strength, surface damage resistance, increased high temperature properties, oxynitride glasses offer advantages over their oxide counterparts.     

THE EFFECTS OF ADDITIONS OF ZINC OXIDE AND CADMIUM OXIDE ON SIMPLE GLASSES1

The glass consisted of the composition SiO₂ 58%, PbO 22%, and Na₂O 20%. Zinc oxide was introduced in increments of 5% up to a maximum of 20% as a substitute for equivalent parts of Na₂O. Similar substitutions were made with cadmium oxide. The following physical properties were studied: thermal expansions, solubilities in hydrochloric acid, indices of refraction, and annealing conduct. Analyses of the glasses were made. The suitability of these glasses as vitreous enamels is discussed. A vacuum electric furnace for melting and fining glass under reduced pressures is described.     

Microscopic Origins of Compositional Trends in Aluminosilicate Glass Properties

Revealing and understanding the microscopic origins of the macroscopic properties of aluminosilicate glasses is important for the design of new glasses with optimized properties. In this work, we study the composition‐structure‐property relationships in 20 MgO/CaO sodium aluminosilicate glasses upon Al₂O₃‐for‐SiO₂ and MgO‐for‐CaO substitutions. We find that some properties (density, molar volume, Young's modulus, and shear modulus) are linear through the investigated range of Al₂O₃ compositions, while others (refractive index, coefficient of thermal expansion, Vickers hardness, isokom temperatures, and liquid fragility index) exhibit a change in the slope around the composition with [Al₂O₃] = [Na₂O], which is especially pronounced for the glasses containing MgO. We discuss these phenomena based on structural information obtained by NMR spectroscopy and topological considerations.     

Enhancement of mechanical properties and chemical durability of Soda-lime silicate glasses treated by DC gas discharges

We report for the first time a study on non-contact thermal poling of soda lime silicate glasses using DC gas discharge. In this work, the formation of a glow discharge is evidenced during the thermal poling treatment (longer than 30 minutes). The hardness and the chemical durability of glasses poled under different conditions (contact or non-contact) and atmospheres (nitrogen or air) are measured and compared to that of un-poled reference glass. The results reveal enhanced mechanical and chemical properties for samples poled under nitrogen as compare to air poled or soda lime silicate glass samples. A structural and chemical analysis of surface of the glass using IR-reflectance measurement and ToF-SIMS is also presented. The formation of a “silica-like” layer on the surface of nitrogen poled glasses is observed, which is likely associated with the enhancement of surface properties. On the other hand, the introduction of protons beneath the surface of glasses poled under air leads to the formation of a hydrated alkaline earth silica layer. Based on the observations a mechanism behind the sustainability of the plasma under DC conditions is proposed.     

Oxyfluoronitride Glasses with High Elastic Modulus and Low Glass Transition Temperatures

The preparation and properties of novel calcium aluminosilicate glasses containing both nitrogen and fluorine are reported. Nitrogen increases Young's modulus and microhardness of oxide glasses by ∼25%. However, one of the major disadvantages of the use of oxynitride glasses for high-stiffness applications is the fact that nitrogen also increases glass viscosity. Melting temperatures of the order of ∼1700°C are required to achieve sufficiently low viscosities for glass forming and drawing processes. Fluorine substitution for oxygen in Ca–Si–Al–O–N glasses yields significant decreases in glass transition temperature and glass melting temperature as well as increasing nitrogen solubility to levels much higher than that previously reported for glasses made by melting CaO, SiO₂, Si₃N₄, and Al₂O₃ powder mixtures. The important effect that N results in increased elastic modulus is not diminished by the addition of fluorine. Thus, it is possible to produce novel oxyfluoronitride glasses with a high elastic modulus but melting and working can be carried out at more conventional glass processing temperatures.     

Effect of boron oxide on mechanical and thermal properties of bioactive glass coatings for biomedical applications

Bioactive glass coatings can improve the osteo integration of metallic implants with the host tissue, thereby increasing their lifespan and overall success rate. However, complex composition-structure-property relations in phosphosilicate-based bioactive glasses make experimental determination of these relations and related composition design of bioactive coatings challenging. By applying molecular dynamics (MD)-based atomistic simulations with recently developed effective potentials, this work addresses the challenge by using a material genome approach to obtain the composition and structure effects on various key properties for bioactive coating applications. A series of potential bioactive glass compositions were studied and the composition effects on the mechanical and thermal properties that are critical to these bioactive glasses as a coating to metallic implants were calculated. Particularly, by varying the level of B₂O₃ to SiO₂ substitutions, the effect of composition on various key properties was elucidated. It was found that by using cation in a 1 to 1 ratio (BO_3/2 to SiO₂) instead of the commonly used substitutions (B₂O₃ to SiO₂), the composition effect can be more clearly expressed and, hence, recommended in future composition designs. Together with careful structural analysis, the origin of property changes can be elucidated. The atomistic computer simulation-based approach is, thus, an effective way to guide future bioactive glass designs for bioactive coatings and other applications.     

Nitrogen Coordination in Oxynitride Glasses

Soda-silica and soda-lime-silica glasses were prepared with varying amounts of Si₃N₄, to produce oxynitride glasses with nitrogen contents up to 3.23 mol%. The glasses were analyzed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, and evidence for the formation of tricoordinated nitrogen groups in the glasses was obtained.     

Properties of Ca–(Y)–Si–Al–O–N–F Glasses: Independent and Additive Effects of Fluorine and Nitrogen

Thirty glasses of composition (in equivalent percent) 20‐xCa:xY:50Si:30Al:(100‐y‐z)O:yN:zF, with x = 0, 10; y = 0, 10, 20, and z = 0, 1, 3, 5, 7 were prepared by melting and casting. All glasses were X‐ray amorphous. Glass molar volumes (MV) decreased with nitrogen substitution for oxygen for all fluorine contents and, correspondingly, glass fractional compactness increased. Fluorine substitution of oxygen had virtually no effect on molar volume or fractional glass compactness for the three nitrogen contents tested. Young's modulus and microhardness were virtually unaffected by fluorine substitution for oxygen while nitrogen substitution for oxygen caused increases in these two properties. Glass‐transition temperature and dilatometric‐softening point values all decreased with increasing fluorine substitution levels, while increasing nitrogen substitution caused values for these thermal properties to increase. Correspondingly, the thermal expansion coefficient increased with fluorine and decreased with nitrogen substitution levels. Using property value differences between glasses containing fluorine and the corresponding glass containing 0 eq.% F enabled 24 data points to be used to determine the effect of fluorine on T_g,dil and T_DS. The trends were linear with a gradient for both properties of the order of ?22°C (eq.% F)^?1. For the nitrogen effect, 20 data points were analyzed for trend effects. As expected from earlier work, all trends had good linearity. Gradients were for T_g,dil and T_DS +2.5°C (eq.% N)^?1, which are fairly similar to previous results in oxynitride systems. All of the data collected and its analysis clearly shows that the substitution effects of fluorine for oxygen and nitrogen for oxygen are independent and additive with the fluorine substitution. The property trends of the glasses are discussed in terms of their implications for glass structure.