Phase Separation Of Borosilicate Glasses Research Articles

Liquid-liquid phase separation in borosilicate glass enriched in MoO3 – experimental investigations and thermodynamic calculations

Phase separation in sodium borosilicate glasses containing molybdenum oxide has been studied in a compositional range of interest for nuclear glasses. Two series of quaternary compositions (63.5SiO2-19.6Na2O-16.9B2O3)1-x(MoO3)x with 0 ≤ x ≤ 3 mol.% MoO3 have been synthesized and characterized, by a range of complementary experimental techniques both in situ in temperature, by viscometry and hot stage SEM, and ex-situ, by HRTEM, PXRD, EPMA and dissolution calorimetry. The phase separation temperatures between silicate and molybdenum oxide rich liquids were determined for each composition. Molybdenum oxide solubility limits were established for quenched and annealed glasses.For molybdenum oxide contents exceeding these limits, crystalline sodium mono-molybdate precipitates in the glasses as shown by XRD results and the fractions of precipitates were indirectly quantified by MoO3 mole balance and enthalpy balance relying on solution calorimetry experiments. The experimental results were compared with thermodynamic calculations performed with Thermo-Calc software and a CALPHAD database of the SiO2-Na2O-MoO3 ternary system. The ternary model allows the calculation of the nature and quantity of the precipitated phases in reasonable agreement with the experiments, even if, in the current state of development of the thermodynamic database, the absence of boron restricts the relevance of the calculations. Thus, for the construction of a predictive thermodynamic calculation tool, the addition of boron to the database is the most promising prospect.

Experimental borosilicate bioactive glasses: Pulp cells cytocompatibility and mechanical characterization.

To assess in vitro the effect of two novel phase separated borosilicate glasses (PSBS) in the system SiO2 -B2 O3 -K2 O-CaO-Al2 O3 on dental pulp cells; and to compare their bioactivity and mechanical properties to a conventional fluoroaluminosilicate glass ionomer cement namely FUJI IX. The cytocompatibility assessment of the two novel borosilicate glasses, one without alumina (PSBS8) and one containing alumina (PSBS16), was performed on cultured primary human pulp cells. Alamar blue assay was used to assess cell metabolic activity and cell morphology was evaluated by confocal imaging. The bioactivity in Stimulated Body Fluid was also evaluated after 1 and 3 weeks of immersion using SEM-EDX analysis. Vickers microhardness and flexural strength were assessed after incorporating the glass particles into a commercial glass ionomer cement (GIC) liquid containing both polyacrylic and polybasic carboxylic acid. The data revealed that the two borosilicate glasses enhanced cell viability ratios at all-time points in both direct and indirect contact assays. After 3 days of contact, PSBS8 without alumina showed higher viability rate (152%) compared to the PSBS16 containing alumina (145%) and the conventional glass ionomer particles (117%). EDX analysis confirmed an initial Ca/P ratio of 2.1 for 45S5K and 2.08 for PSBS8 without alumina after 3 weeks of immersion. The cement prepared using PSBS8 showed significantly higher Vickers hardness values (p=.001) than that prepared using PSBS16 (46.6 vs. 36.7 MPa). After 24 h of maturation, PSBS8 (without alumina) exhibited a flexural strength of 12.9 MPa compared to a value of 16.4 MPa for the commercial control. PSBS8 without alumina had a higher strength than PSBS16 with alumina, after 1 and 7 days of maturation (p=.001). The present in vitro results demonstrated that the borosilicate bioactive glass without alumina enhanced pulp cell viability, spreading and acellular bioactivity better than the conventional GIC and the experimental borosilicate glass containing alumina.

Liquid-Liquid Phase Separation in Borosilicate Glass Enriched in Moo3 – Experimental Investigations and Thermodynamic Calculations

Liquid-Liquid Phase Separation in Borosilicate Glass Enriched in Moo3 – Experimental Investigations and Thermodynamic Calculations

Radiophotoluminescence of Cu-doped silica glass derived from phase-separated sodium borosilicate glass

Radiophotoluminescence, one of the most interesting phenomena induced in materials by ionizing radiation, is expected to be applied for radiation measurements in various fields. The radiophotoluminescence of silica glasses doped with a small amount of copper was investigated after exposure to x rays and 60Co γ rays. The Cu-doped silica glasses were prepared from porous silica glass, obtained from a phase-separated borosilicate glass, through impregnation of the porous glass in Cu(NO3)2 solutions and sintering it. Among various types of defects generated in the glass by the irradiation, boron oxygen hole centers (BOHCs), i.e., holes trapped in oxygen bonded to fourfold-coordinated boron, were observed in electron spin resonance spectra. Before irradiation, a photoluminescence band attributed to the 3d94s1 → 3d10 transition of Cu+ ions was observed at 2.5 eV. The luminescence intensity increased remarkably after irradiation, and in addition, a new luminescence band at 2.1 eV appeared. The intensities of both bands increased proportionally with the irradiation dose. This was due to the conversion of Cu2+ to Cu+ ions by the capture of electrons generated by the irradiation. The luminescent decay was measured, which revealed that the lifetimes of the 2.5-eV and 2.1-eV emissions were 38 µs and 125 µs, respectively. The induced photoluminescence increased after heat treatment up to a temperature of 300 °C and decreased above 350 °C. The effects of heat treatment on the photoluminescence after irradiation and the thermal stability are discussed for BOHCs. A heat treatment of above 500 °C returned the glass near its initial state before irradiation.

Ion release characterization in phase separated borosilicate glass powders

A series of novel borosilicate ionomer glasses composed of varying amount of SiO2–B2O3–K2OCaO–Al2O3 were investigated. The influence of the thermal treatment was evaluated in terms of ion release and glass microstructure. Inductively coupled plasma optical emission spectrometry (ICP-OES) and scanning electron microscopy (SEM) were the main analytical techniques used in this study. The results show that all the glasses samples were amorphous according to the XRD and the SEM results before and after the heat-treatment. However, whilst the as-quenched samples appeared consistently transparent and colourless, the thermal treatment at 700 °C for 20 h induced some of the samples to turn opalescent. The ion concentration profiles suggest that the dissolution rate of Ca and B were enhanced by the heat treatment in all cases. Moreover, it was confirmed that different leaching rates exist between the opal and clear samples

Phase Separation in Borosilicate Glasses Synthesized in the Material System Soda – Colemanite – Quartz Sand

A thorough study of phase separation in borosilicate glasses synthesized in the material system soda – colemanite – quartz sand was performed. The ranges of crystallization-resistant glasses and phase separation prone glasses were determined. It is shown that the complex raw material colemanite can be used to obtain glasses that are transparent or opaque in the bulk. The limiting content of raw materials in the material makeup of glass batches are recommended.

Rice Husk Derived Porous Silica as Support for Pd and CeO2 for Low Temperature Catalytic Methane Combustion

The separation of Pd and CeO2 on the inner surface of controlled porous glass (CPG, obtained from phase-separated borosilicate glass after extraction) yields long-term stable and highly active methane combustion catalysts. However, the limited availability of the CPG makes such catalysts highly expensive and limits their applicability. In this work, porous silica obtained from acid leached rice husks after calcination (RHS) was used as a sustainable, cheap and broadly available substitute for the above mentioned CPG. RHS-supported Pd-CeO2 with separated CeO2 clusters and Pd nanoparticles was fabricated via subsequent impregnation/calcination of molten cerium nitrate and different amounts of palladium nitrate solution. The Pd/CeO2/RHS catalysts were employed for the catalytic methane combustion in the temperature range of 150–500 °C under methane lean conditions (1000 ppm) in a simulated off-gas consisting of 9.0 vol% O2, and 5.5 vol% CO2 balanced with N2. Additionally, tests with 10.5 vol% H2O as co-feed were carried out. The results revealed that the RHS-supported catalysts reached the performance of the cost intensive benchmark catalyst based on CPG. The incorporation of Pd-CeO2 into RHS additionally improved water-resistance compared to solely Pd/CeO2 lowering the required temperature for methane combustion in presence of 10.5 vol% H2O to values significantly below 500 °C (T90 = 425 °C).

Shrinkage of Bismuth-Containing Porous Glass During the Sintering Process and the Viscosity of Quartz-Like Glass Based on Them

Shrinkage during the sintering of porous glass (PG) of different backgrounds and the viscosity of quartz-like glass (QG) sintered until the pores collapse are measured. The samples are obtained as a result of acid leaching of phase-separated sodium borosilicate glass. The initial PG and the samples that are doped with bismuth nitrate from a water-salt solution are studied. It is found that the heat treatment of the matrices at 750°C leads to an increase in their thermal stability. The viscosity of the matrices sintered at 870°C is practically independent of their pretreatment temperature. The viscosity of bismuth-containing quartz-like glass (BQG) decreases with an increase in the matrices’ treatment temperature.

Carbon Nanofibers Grown <i>In Situ </i>on Porous Glass

Carbon nanofibers (CNFs) were grown in situ on porous glass at different temperatures and times using a Ni acetate catalyst and CH4/N2 as a carbon source. The porous glass was obtained by acid leaching of phase separated borosilicate glass, which generates a broad size distribution of mesopores (≈20 nm). Subsequent impregnation with Ni acetate reduces the pore size to ≈ 4 nm but also creates new micropores, thus increasing the surface area. During thermal treatment the surface area decreases as temperature rises, mainly due to shrinkage of the glassy matrix; however new pores are created at ≈ 70 nm (mainly at 600 oC) associated to the generation of CNFs on the glass surface, indicating this temperature offers the best conditions. The CNFs grow inside and fill in the micro-mesopores in the porous glass. They do not grow at 500 oC as the Ni acetate is not transformed into metallic Ni. Ni deactivation occurs at temperatures over 700 oC, thus reducing the formation of CNFs. At 1000 oC the degradation of CH4 leads to a thickening of the CNFs. The thermal degradation of the CNFs occurs in two steps, the first (360-416oC) corresponding to CNFs grown on the glass surface and the second (518-649oC) to CNFs grown inside the glass pores. Treatment times over 2 h lead to the deactivation of Ni, pore shrinkage and hence lower CNF yields.

Effect of the relative volume of the conducting phase on the electroconductivity of glasses in the Na2O–B2O3–SiO2 system

The effect of the relative volume of the conducting phase on the electroconductivity of phase-separated glasses in the ternary system Na2O–B2O3–SiO2, whose compositions are on the same glass transition isotherm at 550°C, is investigated. It is demonstrated that the electroconductivity of phase-separated sodium borosilicate glasses does not depend on the relative volume of the conducting phase (within the limits from 0.3 to 0.9) under the condition that its composition invariable.

Reintroducing sborgite: Crystallization through exposure of sodium borosilicate glasses to moisture

Sborgite (Na[B5O6(OH)4]·3H2O) is a rare mineral, naturally occurring in only 2 known locations worldwide: California, USA and Larderello, Italy. Little is known of this mineral given its rarity in the natural world as well the inability, until now, to be produced in a single crystalline product. For the first time, we reported a single crystalline sborgite crystallization phenomenon caused by exposure of two different sodium borosilicate glasses to moisture. In this study, two homogeneous and two phase separated borosilicate glasses were prepared and exposed to moisture at room temperature (~25°C) for up to 1 month. The powders were characterized by X-ray diffraction (XRD) and environmental scanning electron microscopy (ESEM). The results showed that exposure of all sodium borosilicate glasses to moisture can lead to crystallization of sborgite micro-crystals with a column-like morphology. In addition, it is shown that exposure of homogeneous glasses to humidity results in the formation of more highly crystalline sborgite than phase separated glasses of equal composition.

A generalized domain approach for describing the stress relaxation in a phase separated borosilicate glass

In this work we propose a generalized domain approach for modeling the stress relaxation behavior of phase õseparated borosilicate glasses. The generalization of the domain approach is done by taking two fundamental steps. First, we assume the boron groups to be the soft boundaries in the borosilicate glasses. Second, we introduce the time-dependent power law into the Kohlrausch function. Using the generalized domain approach, we explained why the value of the stretched exponent of the stress relaxation in borosilicate glasses anomalously deviates from the converged exponent value of 3/5. In addition, we introduce a pre-time, i.e., the time for glass to reach the structural equilibrium, into the generalized domain approach in order to compensate the variation of viscosity caused by phase separation. It is found that the pre-time is closely correlated with the time for borosilicate glasses to reach structural equilibrium before stress relaxation experiment.

Exploring Internal Structure of Nanoporous Glasses Obtained by Leaching of Phase‐Separated Alkali Borosilicate Glasses

AbstractMesoporous glasses – the leaching products of phase‐separated alkali borosilicate glasses – are widely used in fundamental research and practical applications. In this work, the option to control their internal mesopore structure by varying the conditions of microphase separation has been studied. Structure and transport characterization of a family of nanoporous glasses obtained under different conditions has been performed using a combination of several experimental techniques, including gas adsorption, nuclear magnetic resonance cryoporometry and diffusometry.

Li+for Na+ion-exchange-induced phase separation in borosilicate glass

Abstract

Effect of additives on the distribution of phosphorus associated with phase separation of borosilicate glasses

Effect of additives on the distribution of phosphorus associated with phase separation of borosilicate glasses

Sassolite Formation in Glass Powders: A Novel Method to Study Phase Separation in Alkali Borosilicate Glass Compositions

This paper reports, for the first time, observation of sassolite (crystalline B(OH)3) formation in alkali borosilicate glass (BSG) powder due to hydration during aging. Correlation between hydration behavior, sassolite formation, and phase separation has been established and hydration‐resistant low‐alkali BSG powders were successfully prepared. The glass composition exhibited very low moisture absorption of <3 wt% in powder form, for an aging duration of 6000 h. This has been achieved by carefully tailoring the glass transition temperature (Tg) and critical immiscibility temperature (Tc). We also report a new, simple, and effective sample preparation method for detecting phase separation in BSG, using transmission electron microscopy.

Quantitative AFM analysis of phase separated borosilicate glass surfaces

Phase separated borosilicate glass samples were prepared by applying various heat treatments. Using selective chemical etching we performed AFM measurement on the phase separated glass surfaces. A quantitative roughness analysis allowed us to measure precisely the dependence of the characteristic size of the phase domains on heating time and temperature. The experimental measurements are very well described by the theoretically expected scaling laws. Interdiffusion coefficients and activation energy are estimated from this analysis and are consistent with literature data.

Spectral hole burning in Sm 2+-doped alkaliborate glasses and Tb 3+-doped silicate and borate glasses

Preparation of Sm 2+-doped borate glasses for persistent spectral hole burning is studied experimentally. The influence of different metallic reducing agents on the reduction of Sm 3+ to Sm 2+ in borate glasses is discussed as well as the influence of phase separation in borosilicate glasses on the spectroscopic properties of Sm 2+ ions. In Tb 3+-doped silicate and borate glasses we demonstrate persistent spectral hole burning in the 7 F 6 – 5 D 4 excitation line at temperatures below 50 K. The hole-burning properties and mechanism are discussed.

Redrawn Phase-Separated Borosilicate Glasses: A TEM Investigation

Redrawn Phase-Separated Borosilicate Glasses: A TEM Investigation

Origin of Viscosity Increase of Phase‐Separated Borosilicate Glasses

The viscosity of some borosilicate glasses increases with heat‐treatment time for phase separation. The viscosity increase in the initial stage of phase separation is attributed to the composition change of the separated phases. The origin of the viscosity increase in the later stage of phase separation is the subject of controversy. Namely, the viscosity increase has been attributed to two different mechanisms: (1) environmental relaxation and (2) the increase of silica content in the high‐viscosity silica‐rich continuous phase. Analyses are presented to show that the latter model is consistent with the experimental data.