SiO2 Glass System Research Articles

Viscosity and Liquidus Temperature of Ternary Glasses Close to the Eutectic Composition in the CaO–Al2O3–SiO2 System

Thermal properties of ternary glass‐forming systems within the known CaO–Al2O3–SiO2 system were evaluated. Different glass compositions near the lowest eutectic composition (around a liquidus temperature of 1170°C) within the CaO–Al2O3–SiO2 system were melted from pure raw materials. The investigated target range of compositions in wt% was between 60.5 and 63.5 SiO2, 13.1 and 16.1 Al2O3, and 21.4 and 25.4 CaO. The chemical compositions, the glass transition temperatures, and the temperatures attributed to viscosities of 10³ dPa*s were determined experimentally. It was of special interest to obtain information of all these properties of the glasses and the effect of small composition changes hereon. The liquidus temperature changed less than expected for a composition close to the eutectic composition. Temperatures at a viscosity of 10³ dPa*s varied between 1263 and 1363 °C ± 6°C. A liquidus temperature of 1157°C ± 7°C (with a confidence interval of 95%) of the eutectic composition was found. The results reported here may be useful for understanding and improvement of the modeling within the CaO–Al2O3–SiO2 glass system.

Microstructural design of phlogopite glass-ceramics

Fluorophlogopite glass-ceramics in the MgO–Al2O3–SiO2 glass systems were crystallized by two stages thermal treatments. Obtained glass-ceramics were characterized by DTA, X-ray diffraction and scanning electron microscopy. The heat treated samples at 705°C/3 h + 1000°C/15 min showed 2570.32 ± 98 MPa microhardness. The effect of heat treatment and preparation methods on microhardness and microstructure were studied. The microstructure of samples showed phlogopite and forsterite phases and solved or soft edge in the semi-rod like crystals was recorded which can explain the small value of microhardness. The various microhardness were determined in the range between 1591.61 to 9610 ± 147 MPa.

Contribution of some divalent oxides replacing Li2O to crystallization characteristics and properties of magnetic glass–ceramics based on Li2O–Fe2O3–Al2O3–SiO2

Magnetic glass–ceramics based on the Li2O–Fe2O3–Al2O3–SiO2 glass system, were prepared through controlled heat treatment regimes. The effect of MO/Li2O replacements (MO=MgO, MnO, ZnO, CdO) on the crystallization process, physical and magnetic properties of the glasses and glass–ceramics were investigated. The crystalline phases formed in the glass–ceramic were lithium metasilicate (Li2SiO3), β-quartz solid solution (ss) (LiAlSi2O6), lithium ferrite (LiFe5O8), Magnesioferrite (MgFe2O4), Jacobsite (MnFe2O4), Franklinite (ZnFe2O4), lithium zinc orthosilicate (γ-Li2ZnSiO4) and lithium ferrite solid solution Li(Fe,Cd)5O8. The density of the prepared glass samples ranged from 2.69 to 2.88g/cm3, whereas the corresponding crystalline materials had a density between 2.77 to 2.95g/cm3. The microhardness of the glass samples ranged from 4665MPa to 5586MPa and increased to a range of 6268–7042MPa after crystallization. The saturation magnetization (Ms), remanence magnetization (Mr), and coercivity (Hc) of the glass–ceramics varied from 0.83 to 8.24emu/g, 0.11 to 0.97emu/g and 112 to 211G, respectively. The formation of different MFe2O4 spinel ferrite magnetic phases instead of LiFe5O8 led to a greatly enhanced saturation magnetization of the glass–ceramics. Possible use of the prepared glass–ceramics may be realized in microwave and magnetic recording applications as well as in tumors therapy.

Spectroscopic features of Ni2+ ion in PbO–Bi2O3–SiO2 glass system

Glasses of the composition (30-x)PbO–5Bi2O3–65SiO2: xNiO (with x ranging from 0 to 1.0mol%) were synthesized. A variety of spectroscopic studies, viz., IR, Raman optical absorption and luminescence properties of these glasses have been carried out as a function of NiO concentration. The analysis of results of all these studies has indicated that the nickel ions occupy both octahedral and tetrahedral positions. However, with the increase of NiO concentration the octahedral occupancy of Ni2+ ions prevailed over the tetrahedral ions. The luminescence spectra of these glasses have exhibited a broad NIR emission band in region 1100–1500nm. This band is identified as being due to 3T2(3F)→3A2(3F) octahedral transition of Ni2+ ions. The luminescence efficiency and cross section have been found to be the highest for the glass containing the highest concentration of NiO. The reasons for such high luminescence efficiency have been discussed in the light of structural variations taking place in the host glass network.

Barium Borosilicate Sealing Glasses Synthesized by a Sol–Gel Process: Chemical Interactions with a Stainless Steel and Gas‐Tightness of a SOFC

AbstractSeveral glasses synthesized by sol–gel route and based on the BaO–B2O3–X–Al2O3–SiO2 (X = CaO, MgO) glass system have been investigated to evaluate their applicability as sealant for solid oxide fuel cell (SOFC). Chemical interactions with K41X stainless steel and hydrogen‐tightness of these materials were evaluated after operations at high temperatures over 1,000 h in air atmosphere. Formation of a new phase at the steel–glass interface and formation of porosity in the glass were observed and determined as critical problems over mid‐term operations. The role of MgO is important to obtain a gas‐tight sealing. Application of the glass paste without binder addition was performed in order to avoid possible residual porosity related problems. The best glass was finally used as sealant between anodic and cathodic compartments in complete SOFCs operated at 760 and at 800 °C. Open circuit voltages and power densities of the cells were recorded during the first hours of operation.

The effect of aluminum and germanium oxides on the crystallization process and magnetic properties of Li2O–Fe2O3–SiO2 glass system

The crystallization behavior of Li2O–Fe2O3–SiO2 glasses containing Al2O3 and GeO2 has been studied using differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The crystalline phases identified by XRD were lithium metasilicate (Li2SiO3), Li-aegirine (LiFeSi2O6), lithium ferrite (LiFe5O8), and varieties of β-quartz solid solution. The partial swap of Al2O3 instead of SiO2 has led to the formation and growth of β-quartz solid solution with formula LiAlSi2O6. However LiFe5O8 phase has been formed instead of LiFeSi2O6. In the case of GeO2/SiO2 replacement β-quartz ss has the preferential tendency to accommodate GeO2 in its structure to form different formulas of LiAl(Six, Ge1−x)2O6 phases. The magnetic property of the prepared glass-ceramics was characterized using a vibrating sample magnetometer (VSM). The evolutions of magnetic parameters in the crystallized glasses were greatly dependent on the amount and size of iron containing phases present in the material. The coercive force and remnant of the glass-ceramic materials have increased by decreasing the size of iron magnetic phase. Under applied magnetic field of ±20kOe, the saturation magnetization (Ms), remanance magnetization (Mr), and coercivity (Hc) varied from 0.46 to 0.83emu/g, 0.056 to 0.16emu/g and 118 to 204G, respectively. The high coercivity values of the prepared glass-ceramics are expected to be useful as permanent magnets.

Unexpected behavior of the 1.54 μm luminescence in Er-doped silica films

Materials such as Er:glass are still of great interest in optical communication technology for their applications in photonic devices operating at the standard telecommunication wavelengths. The 1.54μm emission properties of the Er3+ ions embedded in glassy systems depend on several factors, as for instance the synthesis technique and the thermal history of the material. A photoluminescence investigation, made on Er:SiO2 thin films deposited by PVD for a wide range of different Er concentration and subsequently annealed in the range 50–1200°C (with 50°C step), was done to investigate in which way both Er concentration and thermal annealing influence the 1.54μm emission performance of the Er:SiO2 glass system. For low Er concentration, we evidenced an unexpected 1.54μm activity also after annealing at temperatures much lower than the usual ones. We suspect that this behavior could be related to the medium/long-range order around the Er3+ ions, as a possible consequence of local silica polymorphs formation.

Effects of lanthanum oxide on the properties of barium-free alkaline-earth borosilicate sealant glass

We have explored the effects of lanthanum oxide (La2O3) on the properties of barium-free SrO–CaO–ZnO–B2O3–SiO2 glass system varying its content from 0 to 6mol%. The coefficient of thermal expansion and glass transition temperature of the glasses are found to be in the ranges 10.6–10.8×10−6/K (50–600°C) and 650–690°C respectively. Differential scanning calorimetric studies revealed an increase in crystallization peak temperature and thermal stability of the glasses up to 4mol% and then decrease on further addition. A monotonic increase in characteristic shrinkage temperature of glass powder compact is observed on addition of La2O3 as revealed in the heating stage microscopic study. X-ray diffraction studies revealed reduced crystallization peak intensity in La2O3 added glasses. Fourier transformed infrared spectra disclosed that the addition of La2O3 stabilized the glass structure by reducing the number of non-bridging oxygens. Vickers micro hardness of the glasses varied in the range 2.6–5.6GPa. Scanning electron microscopy revealed the formation of particulate nature of microstructures in parent glass which is not observed in the La2O3 added glasses. Activation energy of crystallization has increased from 331 to 361kJ/mol determined by Kissinger and Augis–Bennett models. Above properties of these glasses clearly advocate their applicability as solid oxide fuel cell sealants.

Effect of magnesium additive on structure and properties of Al2O3–B2O3–SiO2 glass system

Printed wiring board is an important component of electronic devices. Low dielectric constant materials are expected to reduce the time delay of signal propaganda and dielectric loss. E-glass fibre as reinforcing material of printed wiring board does not meet the requirements. To reduce the operating temperature of glass, bivalent metal oxides must be introduced, often at the expense of dielectric properties. Aluminoborosilicate glass is a typical glass system with low dielectric constant. Al2O3–B2O3–SiO2 glasses that replaced Al2O3 by MgO were melted, and their microstructure, some physical properties and chemical durability were investigated. In addition, the role of Al2O3 in borosilicate glasses was investigated. The glass system was characterised with lower dielectric constant (4·8–5·7) and loss tangent (10−3) at 1 MHz. By replacing Al2O3 with MgO, the density and viscosity–temperature characteristic points of the studied glasses showed a decreasing tendency. The average dissolution rate of the studied glasses was <4·51×10−8 g cm−2 min−1. When the molar ratio of RO/Al2O3 is >2·5 (R = Ca2+, Mg2+), the trivalent, tetrahedral [BO4] and [AlO4] network units increased at the same time as indicated by infrared spectra. The paper has designed a group of glasses that has both satisfactory processing properties and dielectric properties. The present glass system could substitute E-glass and be a possible candidate for many applications.

Absorption spectroscopic studies on gamma irradiated bismuth borosilicate glasses

FT-IR spectroscopic measurements have been employed to investigate the structural changes in quaternary xBi2O3–15 Na2O–(70−x) B2O3–15 SiO2 glass system with x=5, 10, 15, 20 and 25 (mol%). The effect of gamma irradiation in the dose range of 0.1–60kGy on the infrared absorption spectra of these glasses is also reported. The IR spectra of the prepared samples show characteristic bands related to the sharing of triangular and tetrahedral borate and silicate groups together with Bi–O groups. The effect of the heavy metal oxide Bi2O3 on the glass composition is also studied.

Gamma ray irradiation effects on the optical properties of BaO–Na2O–B2O3–SiO2 glasses

This paper reports the effect of gamma radiation on the optical absorption spectra of xBaO–Na2O–(70−x) B2O3–SiO2 glass system with x=0, 5, 10, 15, 20, 25 (mol%) recorded in spectral range from 200 to 900nm at room temperature. The optical absorption edge, optical band gap and Urbach energy were determined from the absorption spectra before and after irradiation. Changes occurring in the optical parameters of these glasses have been associated with radiation induced structural defects and compositional changes.

Manifestation of up-conversion in Yb3+/Tm3+ doped Li2O–Y2O3–SiO2 glass system

In this study, we have investigated the principal role of Y2O3 on the emission features of Tm3+ ion and up-conversion phenomenon in Tm3+ and Yb3+ co-doped Li2O–Y2O3–SiO2 glass system. The concentration of Y2O3 is varied from 0 to 5 mol% while that of Yb3+ and Tm3+ is fixed. When the glasses are doped with Tm3+ ions, the intense blue and red emissions were observed, whereas Yb3+ doped glasses exhibited NIR emission at about 980 nm. When the glasses are co-doped with Tm3+ and Yb3+ ions and excited at 900 nm, the blue and red emission lines were observed to be reinforced and strengthened with increase in the concentration of Y2O3. The IR emission band detected at about 1.8 μm due to 3F4 → 3H6 transition of Tm3+ ions is also observed to be strengthened due to co-doping. The reasons for enhancement in the intensity of various emission bands due to co-doping have been identified and discussed with the help of rate equations for various emission transitions.

Influence of CeO2 on structural properties of glasses by using ultrasonic technique: Comparison between the local sand and SiO2

Comparison between the local sand and SiO2 with different compositions of CeO2 on the structural properties of glasses was carried out by using ultrasonic technique. The ultrasonic velocities were measured by the pulse echo technique with a frequency of 4MHz and at room temperature. From these obtained velocities and densities, various elastic moduli, micro-hardness and Poisson’s ratio were calculated. The interesting point of the bulk modulus (SiO2 glass system) decreases at x = 1.25mol.% initially before it turns to increase between x = 3.75 and x = 5.00mol.%. While the bulk modulus of the local sand glass system is near constant. FTIR spectra were used to study the structural properties of the prepared glass system. The results supported our discussion of the formation of non-bridging oxygens (NBO) and bridging oxygens (BO).

Phase evolution and electrical properties of copper-electroded BaTi4O9 materials with BaO–ZnO–B2O3–SiO2 glass system in reducing atmosphere

BaTi4O9 (BT4) microwave dielectric ceramics using a copper electrode and containing 10wt% BaO–ZnO–B2O3–SiO2 (BZBS) glass frit were sintered under reducing atmosphere at 950°C and were investigated on the phase evolutions, microstructures and dielectric properties of BT4 with various BaO/SiO2 and ZnO/SiO2 ratios of BZBS glasses. Experimental results show that the BaO/SiO2 ratio contributes to wettability of glass with BaTi4O9 ceramics, and ZnO/SiO2 ratio determines the densification of BaTi4O9 ceramics. The different Ba–Ti–O and Ba–Cu–O phases with various Ba/Ti and Ba/Cu ratios can be attributed to the contents of BaO in glass. Ba4Ti13O30 and Ba2Cu3O5+X may form when BaO contents are too high, and inducing copper diffusion due to the reactions of BaO and Cu, accompanying with degrading of the dielectric characteristics. If the ZnO contents of BZBS glasses were raised, a little bit of ZnSiO3 and Ba2Cu3O5+X phases appear without Cu diffusion due to non-reaction of ZnO and CuO. The high ZnO/SiO2 ratio of glass reveals the lower softening point, indicating that the high ZnO glass could enhance the density and therefore increase the dielectric constant and quality factor.

Enhanced Photoluminescence at λ = 1.54 μm in the Cu-Doped Er:SiO2 System

The radiofrequency magnetron sputtering codeposition is a versatile technique to obtain Er-doped glass films, i.e., optical materials characterized by the emission of an intense photoluminescence signal at λ = 1.54 μm, the most exploited wavelength for optical telecommunications through fiberglass. After the optimization of this radiative emission in the Er:SiO2 systems, strong sensitizing effects in Cu-doped Er:SiO2 glass systems were evidenced and investigated. Experimental findings suggested that the main energy-transfer mechanism in the metal-doped Er:SiO2 system could be related only to the very small size (less than 1–2 nm) of the doping aggregates and not dependent on their composition.

High resolution X-ray Photoelectron Spectroscopy (XPS) study of K2O–SiO2 glasses: Evidence for three types of O and at least two types of Si

High resolution O 1s, K 2p and Si 2p XPS Spectra were collected for a series of potassium silicate glasses ranging in composition from 10mol% to 35mol% K2O. The mole fraction of bridging oxygen (BO) has been accurately evaluated from the O 1s spectra. BO mole fractions of K-silicate glasses were calculated from Q-species distributions previously reported by 29Si MAS NMR data. The mole fractions of BO are identical for the two techniques (within experimental error) in glasses containing 13mol% to 25mol% K2O but in the compositional range between 25mol% and 35mol% BO mole fractions obtained by XPS are slightly greater than values derived from NMR data. The slight discrepancies between the two techniques at higher K2O content have not been resolved. The experimental data between 13mol% and 25mol% K2O indicate the presence of a third type of oxygen, O2−, in these glasses. A thermodynamic analysis indicates O2− is present at a few mol% in the glasses of low K2O content, but increases monotonically with increased K2O content.The O 1s XPS line widths for the BO peaks are highly variable. The variation in line widths may result from two types of BO contributing to the BO peak. As in the Na2O–SiO2 glass system, one type probably bridges two Si atoms (SiOSi) and the second type is O bonded to two Si atoms and one K atom.The Si 2p XPS spectra are distinctly non-symmetric, with low binding energy shoulders commonly present on the major peak, suggesting two contributions to the Si 2p signal. There is a strong correlation of Si 2p XPS peak and shoulder intensities with the abundances of the Q4 and Q3 species in glasses of the same composition suggesting that, with additional resolution, XPS may be capable of resolving individual Q-species in this system.

Spherical Cavity Glass Lasers for Multiwavelength Emission

This review takes a look at small-sized resonators, especially, spherical glass lasers of micrometer size. Two optical coupling techniques developed in our laboratories are described: (1) terrace microspheres (high-refractive index glass spheres having a light entrance portion made from organic–inorganic hybrid materials) and (2) a half-polished fiber coupler. We tried to pump several tens of micrometer-sized high-index glass spheres (nD=1.93) in BaO–TiO2–SiO2 glass system and containing a few ppm of Nd3+ for laser demonstrations. Using two optical coupling techniques with CW Ti:sapphire laser, we carried out overlapped emission of both of the wavelength regions originating from Raman scattering (840–890 nm) and fluorescence of Nd3+ (860–940 nm). A potential for a multiwavelength laser having >100 emission peaks was demonstrated with thresholds of several mW order.

Gd&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Added Glass-Ceramic Composite for the Improvement of Energy Storage Density through Controlled Crystallization

Crystallization of a glass containing high dielectric performance components can be controlled in the nucleation and growth processes in order to meet the requirements of enabling the glass-ceramic dielectric composites to obtain the desired high electric energy storage densitiy. In this paper, the controlled crystallization technique was employed to synthesize glass-ceramic composites with addition of Gd2O3 in BaO-Na2O- Nb2O5- SiO2 glass system. The results show that both the dielectric constant and the breakdown strength of the glass-ceramic composites demonstrate an increasing tendency with the addition of Gd2O3 from 0 mol% to 7 mol% (relative to SiO2), being responsible for remarkable improvement of the energy storage density of the glass-ceramic composites from 1.7 J/cm3 to 4.7 J/cm3.

Influence of aluminum ions on fluorescent spectra and upconversion in codoped CaF2–Al2O3–P2O5–SiO2:Ho3+ and Er3+ glass system

The glasses of the composition 20CaF2–xAl2O3–(59−x)P2O5–20SiO2:1.0Ho2O3/1.0Er2O3 and 20CaF2–xAl2O3–(59−x)P2O5–20SiO2:(0.6Ho2O3+0.4Er2O3) with x varying from 2 to 10 mol % have been synthesized. Optical absorption and fluorescence spectra (in the spectral range 350–2100 nm were studied at ambient temperature. The Judd–Ofelt theory was applied to characterize the absorption and luminescence spectra of Ho3+ and Er3+ ions in these glasses. Following the luminescence spectra, various radiative properties like transition probability A, branching ratio β, and the radiative life time τ for blue (B), green (G), and red (R) emission levels of these glasses have been evaluated. The radiative life times for these transitions of Ho3+ and Er3+ have also been measured. The variations observed in these parameters were discussed in the light of varying coordinations (tetrahedral and octahedral positions) of Al3+ ions in the glass network. The energy transfer between the two rare earth ions (Ho3+ and Er3+) in codoped CaF2–Al2O3–P2O5–SiO2 glass system in the visible and near infrared (NIR) regions has also been investigated as a function of varying concentration of Al2O3. A significant enhancement in the intensities of B, G, and R lines has been observed due to codoping. The quantitative analysis of these results (with the aid of the data on IR and Raman spectral studies) has indicated that the glasses mixed with around 6.0 mol % of Al2O3 is the optimum concentration for yielding the highest quantum efficiency and for maximum energy transfer with low phonon losses.

Effect of Artificial Saliva with Fluoride Ions on the Color of Ti-Porcelain

In the acidic oral environments containing fluoride ions, hydrofluoric acid (HF) would form and affect the color of Titanium porcelain crown, but there is a lack of information on how color is affected by this oral fluid. The purpose of this study was to investigate the effects of various artificial saliva simulating oral environments in the presence of fluoride ions with different pH value on the color of self-made dental opaque, body porcelain, belonging to the Na2O-K2O–MgO–CaO–Al2O3–SiO2 glass system. Disc-shaped specimens, 5 mm diameter and a 2-mm thickness, were made by firing. Specimens were immersed in artificial saliva in the presence of fluoride ions with different pH value for 7, 14, 21 days, and then the color of the specimens was compared with the color of the initial specimen. The interactions were present in L*a*b* values between pH value and the day of immersion. The changes in L*a*b* color data as the day of immersion and pH value increased were revealed, which can resulted in perceptual color changes in L*a*b* color parameters.