Thermal properties and glass formation in the SiO2–B2O3–Bi2O3–ZnO quaternary system

Lead-free glasses in the SiO₂–B₂O₃–Bi₂O₃–ZnO quaternary system were studied. The glass formation region, as determined by XRD patterns of bulk samples, was limited to glasses having more than 40 mol% of the glass-forming oxides SiO₂ and B₂O₃. Crystalline phases of Zn₂SiO₄ (willemite) were detected in compositions of 30SiO₂ · 10B₂O₃ · 20Bi₂O₃ · 40ZnO and 20SiO₂ · 10B₂O₃ · 25Bi₂O₃ · 45ZnO. Glass transition temperatures (T_g), dilatometric softening points (T_d) and linear coefficients of expansion in the temperatures range of 25–300 °C (α_25–300) were measured for subsystems along the B₂O₃ join of 10, 20 and 30 mol%. For these subsystems, T_g ranged from 411 to 522 °C, and T_d ranged from 453 to 563 °C, both decreasing with increasing Bi₂O₃ content. The measured α_25–300 ranged from 53 to 95 × 10⁻⁷ °C⁻¹, with values increasing with increasing Bi₂O₃ content. The ZnO content had the opposite effect to the Bi₂O₃ content. It appears that Bi³⁺ acts as a glass-modifier in this quaternary system.     

Thermal expansion of glass–ceramics in the system BaO/Al2O3/B2O3

Glasses in the system BaO/Al₂O₃/B₂O₃ with and without the addition of platinum were melted. In one sample series, the BaO-concentration was varied while the ratio [Al₂O₃]/[B₂O₃] was kept constant. In another sample series, the [BaO]/[Al₂O₃]-ratio (= 0.9) was kept constant and the B₂O₃ concentration was varied. The samples were thermally treated at 720 °C for 24 h and subsequently at 780 °C for 4 h. In most thermally treated samples, the crystalline phase BaO · Al₂O₃ · B₂O₃ occurred. At some compositions, the platinum-doped samples showed larger concentrations of the crystalline phases. The most remarkable property of the obtained glass–ceramics is their zero or negative thermal expansion coefficient. Here, notable differences were observed: samples with fine grained microstructures showed thermal expansion coefficients approximately zero up to temperatures of around 80 °C. By contrast, samples with coarser microstructures and large spheroidal crystals exhibit negative expansion coefficients up to temperatures of around 280–375 °C. The thermal expansions of these samples were close to those of the mean thermal expansion of the unit cell of the BaO · Al₂O₃ · B₂O₃ phase. The thermal expansion of the fine grained samples was approximately equal to that of the crystallographic a-axis of the BaO · Al₂O₃ · B₂O₃ phase.     

Mechanism of crystallization of fast fired mullite-based glass–ceramic glazes for floor-tiles

The mechanism of crystallization from a B₂O₃-containing glass, with composition based in the CaO–MgO–Al₂O₃–SiO₂ system, to a glass–ceramic glaze was studied by different techniques. Glass powder pellets were fast heated, simulating current industrial tile processing methods, at several temperatures from 700 to 1200 °C with a 5 min hold. Microstructural study by field emission scanning electron microscopy revealed that a phase separation phenomenon occurred in the glass, which promoted the onset of mullite crystallization at 900 °C. The amount of mullite in the glass heated between 1100 and 1200 °C was around 20 wt%, as determined by Rietveld refinement. The microstructure of the glass–ceramic glaze heated at 1160 °C consisted of interlocked, well-shaped, acicular mullite crystals longer than 4 μm, immersed in a residual glassy phase.     

Preparation and characterization of CuO doped Bi2O3–B2O3–BaO–ZnO glass system for transparent dielectric layer

The electrical, thermal, optical, and morphological properties of CUO doped Bi₂O₃–B₂O₃–BaO–ZnO glasses were studied as a PbO-free, low firing transparent dielectric layer for plasma display panels (PDP). CuO improved the transmittance of Bi₂O₃–B₂O₃–BaO–ZnO by up to 84% in the visible region, eliminating a yellowish color typical of Bi₂O₃–B₂O₃–BaO–ZnO. A slight absorption within the near infrared (NIR) region was also observed. The glass transition temperature (T_g), thermal coefficient of expansion (TCE), and root-mean square (rms) roughness of 0.005 wt% CuO doped Bi₂O₃–B₂O₃–BaO–ZnO were found to be 455 °C, 81.4 × 10⁻⁷/K, respectively, and 162 ± 14 Å, which satisfied the requirements for a transparent dielectric layer for PDP application.     

Precipitation of zinc ferrite nanoparticles in the Fe2O3–ZnO–SiO2 glass system

Glass materials in the ZnO–Fe₂O₃–SiO₂ system, containing zinc ferrite nanoparticles, were prepared by the sol–gel method and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Mössbauer spectroscopy, AC- and DC-magnetization techniques. The gel samples, dried at 130 °C, were further heat treated in air at 500 and 800 °C. At 500 °C zinc ferrite and hematite nanoparticles, with an average size of approximately 24 nm, were precipitated in the brown and opaque 10ZnO–10Fe₂O₃–80SiO₂ and in the ruby colored transparent 5ZnO–5Fe₂O₃–90SiO₂ and 2.5ZnO–2.5Fe₂O₃–95SiO₂ glass matrices. In the 5ZnO–5Fe₂O₃–90SiO₂ sample the nanoparticles exhibited ferro or ferrimagnetic interactions combined with superparamagnetism with a blocking temperature of approximately 14 K. Heating at 800 °C seems to cause partial dissolution of the zinc ferrite and hematite particles in all the investigated compositions. Accordingly at 800 °C the 5ZnO–5Fe₂O₃–90SiO₂ glass shows a paramagnetic behavior down to 2 K.     

Crystallization of KNbO3 in a B2O3 glass network

The ferroelectric material potassium niobate (KNbO₃) has a large number of exceptional electronic and optical properties with important technological applications. Due to the high preparation difficulties and costs of the single crystals, a considerable interest in the preparation of glass-ceramics with the KNbO₃ crystal phase exists. In this work we present the preparation of a glass, with the composition 40B₂O₃–40K₂O–20Nb₂O₅ (% mole), through the melt-quenching method and glass-ceramics obtained by controlled heat-treatments. The samples structure was analyzed using X-ray power diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy. KNbO₃ crystals were detected in the glass sample treated at 500 °C. For treatments at temperatures above 500 °C, other niobium-based crystal phases are present. The behavior of the heat-treatment temperature parameter, in the glass and glass ceramic structure, is discussed.     

PbO–B2O3–SiO2 glass powders with spherical shape prepared by spray pyrolysis

PbO–B₂O₃–SiO₂ glass powders were directly prepared using spray pyrolysis. The powders were spherical and fine-sized. One glass particle was obtained from one droplet by melting the precursors inside a hot wall tubular reactor. The characteristics of these powders were compared with those of the commercial product, which was prepared using the conventional melting process. The spherical powders, which were prepared using spray pyrolysis at 1000 °C, had broad peaks at around 28° in the XRD spectrum. The glass phase was formed during the spray pyrolysis process even within a short residence time of the powders inside the hot wall tubular reactor. The mean size of the prepared glass powders was 1 μm. The dielectric layers formed from the spherical, fine-sized glass powders had a high transparency at firing temperatures above 520 °C. The maximum transparency of the dielectric layer formed from the glass powders obtained from spray pyrolysis was 95.3% at the firing temperature of 560 °C. The dielectric layer formed from the spherical, fine-sized glass powders had a smooth surface and no void inside the dielectric layer.     

ESR dosimeter based on P2O5–CaO–Na2O glass system

This paper presents the results of a study of thermal properties, solubility and response to ⁶⁰Co γ-rays by electron spin resonance of the P₂O₅–CaO–Na₂O glass system. The sample compositions were selected by fixing the P₂O₅ mol% content at 50 mol%, and varying the CaO mol% at 30 and 40 mol%. The spectrum is characterized by hyperfine doublet from ³¹P isotope (nuclear spin = 1/2), and its stability and response to the γ-ray dose were studied to establish the suitability of this glass as a γ-ray dosimeter.     

In2O3 and tin-doped In2O3 nanocrystals prepared by glass crystallization

Glasses in the system Na₂O/B₂O₃/Al₂O₃/In₂O₃/(SnO₂) were melted and subsequently tempered in the range from 540 to 700 °C. This led to the crystallization of In₂O₃, besides also NaBO₂ and Na₂Al₂B₂O₇ were formed. The crystallite sizes were in the range from 12 to 34 nm, depending on the temperature of thermal treatment, as calculated from XRD-line broadening. Crystal sizes determined by TEM were in the same range. Particle size histograms show a narrow crystal size distribution. After crystallization, the glass matrices and the non indium-containing crystalline phases were dissolved in diluted acetic acid. Spectra of the obtained suspensions containing tin-doped In₂O₃ nanocrystals exhibited a sharp UV-cut off, high transmission in the visible range and strongly decreasing transmission at wavelengths >1000 nm.     

Properties and structure of (1 − x)Li2O–xNa2O–Al2O3–4SiO2 glass systems

(1 − x)Li₂O–xNa₂O–Al₂O₃–4SiO₂ glasses were studied for the progressive percentage substitution of Na₂O for Li₂O at the constant mole of Al₂O₃ and SiO₂. The crystallization temperature at the exothermic peak increased from 898 to 939 °C when the Na₂O content increases from 0 to 0.6 mol. The coefficient of thermal expansion and density of these as-quenched glasses increase from 6.54 × 10⁻⁶ °C⁻¹ to 10.1 × 10⁻⁶ °C⁻¹ and 2.378 g cm⁻³ to 2.533 g cm⁻³ when the Na₂O content increases from 0 to 0.4 mol, respectively. The electrical resistivity has a maximum value at Na₂O · (Li₂O + Na₂O)⁻¹ = 0.4. The activation energy of crystallization decreases from 444 to 284 kJ mol⁻¹ when the Na₂O content increased from 0 to 0.4 mol. Moreover, the activation energy increases from 284 kJ mol⁻¹ to 446 kJ mol⁻¹ when the Na₂O content increased from 0.4 to 0.6 mol. The FT-IR spectra show that the symmetric stretching mode of the SiO₄ tetrahedra (1035–1054 cm⁻¹) and AlO₄ octahedra (713–763 cm⁻¹) exhibiting that the network structure is built by SiO₄ tetrahedra and AlO₄.     

Evolution of nanocrystalline BaBi2Nb2O9 in Li2B4O7–BaO–Bi2O3–Nb2O5 glass system

Transparent glasses and glass nano crystal composites (GNCs) of various compositions in the system (100 − x)Li₂B₄O₇–x(BaO–Bi₂O₃–Nb₂O₅) (where x = 10, 20, and 30 in molar ratio) were fabricated via splat-quenching technique. The glassy nature of the as-quenched samples was established by differential thermal analyses. X-ray powder diffraction and transmission electron microscopic (TEM) studies confirmed the formation of layered perovskite BBN via a fluorite like phase. TEM studies revealed the presence of 10 nm sized spherical crystallites of fluorite like BaBi₂Nb₂O₉ phase in the glassy matrix of Li₂B₄O₇ (LBO). The influence of composition on the dielectric and the optical properties (transmission, optical band gap) of these samples has been investigated.     

Non-isothermal crystallization kinetic studies on MgO–Al2O3–SiO2–TiO2 glass

Thermal stability and crystallization kinetics of the glass 21% MgO, 21.36% Al₂O₃, 53.32% SiO₂ and 4.11% TiO₂ (mol%) has been studied using differential thermal analysis (DTA), dilatometry and X-ray diffraction (XRD). Glass in both bulk and frit forms were produced by melting in platinum crucible at 1600 °C for 1–2 h. From variation of DTA peak maximum temperature with heating rate, the activation energies of crystallization were calculated to be 340 kJ mol⁻¹ and 498 kJ mol⁻¹ for first and second crystallization exotherms, respectively. Crystallization of bulk glass was carried out at various temperatures and for different time durations in the range of 850–1000 °C. The influence of the addition of TiO₂ on the crystallization sequence of the glass was experimentally determined and discussed.     

Structure and properties of Sb2O3-containing zinc borophosphate glasses

ZnO–B₂O₃–P₂O₅ glasses formulated with Sb₂O₃ were investigated in the series 50ZnO–10B₂O₃–40P₂O₅ + xSb₂O₃ (x = 0–70 mol%). With increasing Sb₂O₃ content, the values of glass transition temperature decrease from 492 °C down to 394 °C. The dissolution rate of the glasses reveals a maximum for the glass with x = 15 mol% Sb₂O₃. Raman spectra with increasing Sb₂O₃ content reflect the depolymerisation of phosphate chains. Antimony at low Sb₂O₃ content forms individual SbO₃ pyramids manifested in the Raman spectra by a broad vibrational band at ∼520–690 cm⁻¹. In the glasses with a higher Sb₂O₃ content SbO₃ units link into chains and clusters with Sb–O–Sb bridges manifested in the Raman spectra by a strong broad band at 380–520 cm⁻¹. The ³¹P MAS NMR spectra with increasing Sb₂O₃ content reflect the depolymerisation of phosphate chains at low Sb₂O₃ content and only small changes in the PO₄ coordination at a high Sb₂O₃ content. ¹¹B MAS NMR spectra reveal a steady transformation of B(OP)₄ units into B(OP)_4−x(OSb)_x units, accompanied by the transformation of BO₄ into BO₃ units with increasing Sb₂O₃ content.     

Microstructural characteristics and crystallization of CaO–P2O5–Na2O–ZnO glass ceramics prepared by sol–gel method

Porous phosphate-based glass ceramics prepared by the sol–gel method were characterized using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and differential thermal analysis (DSC). The 48CaO–45P₂O₅–2ZnO–5Na₂O glassy system can remain fully amorphous up to 550 °C. After heat treated at 650 °C, the obtained porous bodies consisted of dense struts and macropores where β-Ca₂P₂O₇ and Na₂CaP₂O₇ phases crystallized from the glass matrix. When treated at 750 °C, Ca₄P₆O₁₉ and NaZn(PO₃)₃ precipitated homogeneously as new phases among the residual glass matrix. The material was assessed by soaking samples in phosphate-based buffer solution (PBS) solution to determine the solubility and observe apatite formation.     

Bond character,optical properties and ionic conductivity of Li2O/B2O3/SiO2/Al2O3 glass: Effect of structural substitution of Li2O for LiCl

A glass of composition (20 ? x)Li₂O–xLiCl–65B₂O₃–10SiO₂–5Al₂O₃ where 0 ? x ? 12.5 wt% is prepared using the normal melt-quenching technique. The optical constants and electrical conductivity and their correlation are investigated, furnished and discussed with the substitution of Li₂O for LiCl. The mechanism of the optical absorption and the calculated Urbach energy follow the rule of phonon-assisted transitions. The ionic conduction mechanism is determined by activation energy process. Substitution up to 10 wt% LiCl provides high ionic conductivity (1.9 × 10^?2 Ω^?1 m^?1) due to the high average electronegativity of LiCl which increases the polarizability of lithium ions. The small cation–anion distance approach confirmed the enhancement in ionic conductivity of LiCl containing glass compared to that of Li₂O. Due to the large size of Cl^? ions, there is an expansion of the lattice which in turn broadens the available path windows. For 12.5 wt% LiCl, anomalous density behavior is observed and a reduction in conductivity is occurred, σ = 5.4 × 10^?3 Ω^?1 m^?1. Owing to the model of bond fluctuation, the reduction is attributed to the increase in the alkali halide concentration which creates bottlenecks that hinder the motion of Li⁺ ions. The ionic conductivity character is strongly supported by the behavior of the glass ionicity factor, density, molar volume, refractive index, average boron–boron separation, molar refraction, metallization criterion and non-bridging oxygen concentration of the studied glass.     

Effect of OH-content on thermal and chemical properties of SnOP2O5 glasses

Glasses with 55–60 mol% SnO and 40–45 mol% P₂O₅ have shown extremely large differences in the chemical and thermal properties depending on the temperature at which they were melted. Glasses prepared at low melting temperature, 450–550 °C, had low T_g, 150–200 °C, and low chemical stability. Glasses prepared at high melting temperature, 800–1200 °C, had much higher T_g, 250–300 °C, and much higher chemical stability. No significant differences were found by ¹¹⁹Sn Mössbauer and ³¹P Nuclear Magnetic Resonance spectroscopy. Large differences in the OH-content could be detected as the reason by infrared absorption spectroscopy, thermal analyses, and ¹H Nuclear Magnetic Resonance spectroscopy. In samples with low T_g, a broad OH – vibration band around 3000 nm with an absorption intensity >20 cm^?1, bands at 2140 nm with intensity ～5 cm^?1, at 2038 nm with intensity ～2.7 cm^?1, and at 1564 nm with intensity ～0.4 cm^?1 were measured. These samples have shown a mass loss of 3–4 wt% by thermal gravimetric analyses under argon in the temperature range 400–1000 °C. No mass loss and only one broad OH-band with a maximum at 3150 nm and low absorption intensity <4 cm^?1 could be detected in samples melted at high temperature, 1000–1200 °C, which have much higher T_g, ～300 °C, and much higher chemical stability.     

Phase evolution on heat treatment of sodium silicate water glass

Heat treatment of sodium silicate water glass of the nominal composition Na₂O/SiO₂ = 1:3 was carried out from 100 °C up to 800 °C and the advancement of the resulting phases was followed up by powder X-ray diffraction, scanning electron microscopy and thermogravimetry along with differential thermal analysis. The water glass, initially being an amorphous solid, starts to form crystals of β-Na₂Si₂O₅ at about 400 °C and crystallizes the SiO₂ modification cristobalite at about 600 °C that coexists along with β-Na₂Si₂O₅ up to 700 °C. At 750 °C Na₆Si₈O₁₉ appears as a separate phase and beyond 800 °C, the system turns into a liquid.     

The effect of fluoride on the Fe2+/Fe3+-redox equilibrium in glass melts in the system Na2O/NaF/CaO/Al2O3/SiO2

Liquids with the base compositions (16 − x/2)Na₂O · xNaF · 10CaO · 74SiO₂ (x = 0, 1, 3, and 4) and (10 − x/2) · Na₂O · xNaF · 10CaO · yAl₂O₃ · (80 − y)SiO₂ (x = 0, 1, 3, 5 and y = 5 and 15) doped with 0.25 mol% Fe₂O₃ were studied by means of square-wave voltammetry in the temperature range from 1000 to 1500 °C. With increasing temperature, the redox equilibria were shifted to the reduced state. Also while increasing the alumina concentration, the Fe²⁺/Fe³⁺-redox equilibrium is shifted to the reduced state. In the soda-lime–silica melt the addition of fluoride shifts the equilibrium to the oxidized state, while in the aluminosilicate melts with 15 mol% Al₂O₃, the equilibrium is shifted to the reduced state. In the aluminosilicate melts with 5 mol% Al₂O₃, the equilibrium was not affected by the fluoride concentration. This is explained by the structure of the respective glass compositions.     

Synthesis and characterization of Cr4+-doped CaO–GeO2–Li2O–B2O3(Al2O3) transparent glass-ceramics

Synthesis and devitrification behavior of Cr-doped CaO–GeO₂–Li₂O–B₂O₃(Al₂O₃) glasses have been studied. A range of glass compositions was found to yield transparent glass-ceramics after devitrification. The size of crystallites is below 1 μm. Glass-ceramic samples exhibit 1050–1600 nm broad-band emission with a maximum around 1260 nm, very similar to the emission of Cr⁴⁺:Ca₂GeO₄ bulk crystals. X-ray diffraction measurements indicate that the structure of crystallites exhibiting near infrared emission in glass-ceramics may be assigned to Cr⁴⁺:Ca₂GeO₄ with increased lattice parameters.     

Crystallization of amorphous Al2O3–SiO2 precursors doped with nickel

The crystallization of amorphous diphasic Al₂O₃–SiO₂ precursors doped with nickel has been studied by differential scanning calorimetry (DSC), XRD diffraction (XRD) and scanning and transmission electron microscopy (SEM, TEM) equipped with energy dispersive X-ray spectroscopy (EDS). Diphasic gels with constant atomic ratio (Al + Ni)/Si = 3:1, where 0, 1, 2 and 3 at.% of aluminum were replaced by nickel, have been prepared by hydrolyzing of TEOS in aqueous solution of aluminum nitrate. Crystallization of Ni-containing γ-Al₂O₃ preceded the crystallization of Al–Si spinel. Activation energy of 603 ± 16 kJ mol⁻¹ for crystallization of Ni-containing γ-Al₂O₃ was obtained in non-isothermal conditions. Ni-incorporated γ-Al₂O₃ transforms gradually with the temperature increase into Ni aluminate spinel, while Al–Si spinel reacts with amorphous silica forming mullite at about 1200 °C. Rietveld structure refinement of phases present in the samples annealed at 1600 °C and SEM-EDS and TEM-EDS analyses of related phases have shown that nickel predominantly crystallizes as NiAl₂O₄, but small amount of nickel is incorporated in mullite structure, as well as, dissolved in the glassy phase of the system.