Structural Study of PbO–B2O3 Glasses by X-ray Diffraction and 11B MAS NMR Techniques

The structure of PbO–B₂O₃ glasses has been investigated in the composition range of 25–80 mol% PbO by using X-ray diffraction and ¹¹B NMR techniques. The well-separated peaks due to Pb–O and Pb–Pb pairs were first observed in the radial distribution function, and peak deconvolution was performed by using a pair function method. The average coordination number of lead atoms was determined to be about 6 in the low-PbO-content region and about 3 in the high-PbO-content region. With an increase of PbO content, the peaks at 0.24 and 0.40 nm shifted to shorter distances, and especially the latter peak drastically increased in intensity in the composition range >50 mol% PbO. It was suggested that PbO is a main glass former in the high-PbO-content region. Based on the results obtained, we propose structural models of lead borate glasses.     

Reaction of CaTiO3 with PbO–B2O3 and PbO–SiO2 Glasses

Interfacial and powder reactions between CaTiO₃ and 90PbO–10B₂O₃ and 75PbO–25SiO₂ binary glasses were studied. The reaction has been analyzed as the effect of B₂O₃ and SiO₂ additions on the interaction between CaTiO₃ and PbO, and discussed from thermodynamic and kinetic points of view. For a fixed CaTiO₃/PbO ratio₂ the product perovskite phase became enriched with lead as the amount of additives increased, which is more pronounced with B₂O₃ addition. The reaction of CaTiO₃ with the lead–boron glass was controlled by a dissolution-precipitation mechanism, and that with the lead-silica glass by a diffusion mechanism.     

Energetics of La2O3–HfO2–SiO2 Glasses

A series of La₂O₃–HfO₂–SiO₂ glasses, approximately along the join 0.73SiO₂–0.27( x HfO₂–(1− x )La₂O₃), 0< x <0.3), was prepared using containerless processing techniques (aerodynamic levitation combined with laser heating in oxygen). The enthalpy of formation and enthalpy of vitrification at 25°C were obtained from drop solution calorimetry of these glasses and appropriate crystalline compounds in a molten lead borate (2PbO–B₂O₃) solvent at 702°C. The enthalpy of formation from crystalline oxides was exothermic and became less exothermic with increasing HfO₂ content. Heat contents were measured by transposed temperature drop calorimetry and depended linearly on the HfO₂ content. Differential scanning calorimetry showed that both the onset glass transition and the onset crystallization temperature of these glasses increased with increasing HfO₂ content. Upon slow cooling in air, the glasses crystallized to a mixture of baddeleyite, cristobalite, lanthanum disilicate, and hafnon.     

Effect of Sb2O3 on Thermal Properties of Glasses in Bi2O3–B2O3–SiO2 System

Glasses with compositions 50Bi₂O₃– x Sb₂O₃–10B₂O₃–(40– x ) SiO₂ ( x =0, 1, 3, 5, 8, 10) have been prepared by conventional melt quench technique. Substitution of Sb₂O₃ for SiO₂ exerted an obvious effect on properties of glasses, especially, increased glass transition temperature ( T _g) and crystalline temperature ( T _c) greatly. Results of infrared transmission spectra attributed the effect to the formation of new bridging bonds of Sb–O–B and Sb–O–Si in glass network.     

11B and 27Al Nuclear Quadrupole Interactions in SiO2-B2O3-Al2O3-R2O Glass Systems

Quadrupole interactions of ¹¹B and ²⁷Al in SiO₂-B₂O₃-Al₂O₃-R₂O glass systems were investigated to determine the structure of these glasses, which should be amenable to chemical strengthening. The ratio of BO₄ units to BO₃ units approached unity as the R₂O/Al₂O₃ ratio for compounds having fixed B₂O₃ contents approached unity. Nuclear quadrupole coupling constants ( e²Qq/h =2.73 to 2.93 MHz) were measured for the NMR spectra of ¹¹B triangles. The line shapes of ²⁷Al spectra varied with chemical composition, but a few glasses exhibited ²⁷Al line shapes similar to those of the AlO₄ triclusters in SiO₂-Al₂O₃-Na₂O glasses. Compositional trends in the formation of BO₄ and AlO₄ were deduced from the NMR spectra.     

Proton Conductivity in Zr4+-Ion-Doped P2O5–SiO2 Porous Glasses

The effect of zirconium ions on glass structure and proton conductivity was investigated for sol-gel-derived P₂O₅–SiO₂ glasses. Porous glasses were prepared through hydrolysis of PO(OCH₃)₃, Zr(OC₄H₉)₄, and Si(OC₂H₅)₄. Chemical bonding of the P⁵⁺ ions was characterized using ³¹P-NMR spectra. The phosphorous ions, occurring as PO(OH)₃ in the ZrO₂-free glass, were polymerized with one or two bridging oxygen ions per PO₄ unit with increased ZrO₂ content. The chemical stability of these glasses was increased significantly on the addition of ZrO₂, but the conductivity gradually decreased from 26 to 12 mS/cm at room temperature for 10P₂O₅·7ZrO₂·83SiO₂ glass. A fuel cell was constructed using 10P₂O₅·5ZrO₂·85SiO₂ glass as the electrolyte; a power of ∼4.5 mW/cm² was attained.     

Interaction between Barium Titanate and Binary Glasses

Interactions between BaTiO₃, and three binary glasses were studied through the reaction of BaTiO₃, powder with glass powder. For PbO–B₂O₃ and PbO–SiO₂ glasses, the reaction led to stable compound formation, the substitution of Pb in the BaTiO₃ structure, and noticeable grain growth of BaTiO₃. The interaction phenomena for these two glass systems were very similar. The substitution of Pb into BaTiO₃ is assisted by chemical reactions in which BaB₂O₄ or Ba₂SiO₄ is formed. The substitution into BaTiO3 also seems to be closely related to the grain growth of BaTiO₃. On the other hand, only compound formation was observed during the processing of BaTiO₃ with Bi₂O₃–B₂O₃ glass. Neither BaTiO₃ grain growth nor Bi substitution took place with the Bi₂O₃–B₂O₃ glass system. Based on the observed reactions and the glass viscosity, several sintering aids for BaTiO₃ ceramic products are suggested in this paper.     

Properties of Sm2O3─Al2O3─SiO2 Glasses for In Vivo Applications

The compositional range for glass formation below 1600°C in the Sm₂O₃─Al₂O₃─SiO₂ system is (9–25)Sm₂O₃─(10–35)Al₂O₃─(40–75)SiO₂ (mol%). Selected properties of the Sm₂O₃─Al₂O₃─SiO₂ (SmAS) glasses were evaluated as a function of composition. The density, refractive index, microhardness, and thermal expansion coefficient increased as the Sm₂O₃ content increased from 9 to 25 mol%, the values exceeding those for fused silica. The dissolution rate in 1 N HCl and in deionized water increased with increasing Sm₂O₃ content and with increasing temperature to 70°C. The transformation temperature ( T _g ) and dilatometric softening temperature ( T _d ) of the SmAS glasses exceeded 800° and 850°C, respectively.     

Characterization and Sintering of a Porous Glass-Ceramic in the System Na2O-B2O3-Sc2O3

Clear glasses which included droplet-like microphases were produced when SiO₂ in sodium borosilicate glasses was replaced by Sc₂O₃. Phase separation and/or crystallization occurred after heat treatment. The porous skeleton of leached glasses consisted of hexagonal ScBO₃. The specific surface areas and pore radii are comparable to those of porous SiO₂ glass. The sintering temperature of porous Sc-based material is higher than that of porous SiO₂. Alumina contamination influenced the structure of the porous material.     

125Te, 27Al, and 71Ga NMR Study of M2O3–TeO2 (M = Al and Ga) Glasses

The structures of M₂O₃–TeO₂ (M = Al and Ga) glasses have been investigated by means of ¹²⁵Te, ²⁷Al, and ⁷¹Ga NMR spectroscopies. The structural units of respective cations in M₂O₃–TeO₂ glasses were quantitatively analyzed. The fractions of TeO₄ trigonal bipyramid, AlO₆ and GaO₆ octahedra decreased and those of TeO₃ trigonal pyramid, AlO₄, AlO₅, and GaO₄ polyhedra increased with increasing M₂O₃ content. Based on the local structures around Te, Al, and Ga atoms, the structure models of M₂O₃–TeO₂ glasses were proposed.     

SiO2–PbO–CaO–ZrO2–TiO2–(B2O3–K2O), A New Zirconolite Glass–Ceramic System: Crystallization Behavior and Microstructure Evaluation

Zirconolite (CaZrTi₂O₇) is a mineral that has a high containment capacity for actinides and lanthanides and is considered to be a good candidate for the immobilization of radioactive wastes. The glass–ceramic technique seems to be a very suitable and convenient method to produce zirconolite crystals by precipitating them in a specific glass matrix. In this study, development of a new zirconolite-based glass–ceramic belonging to SiO₂–PbO–CaO–ZrO₂–TiO₂–(B₂O₃–K₂O) system was investigated. The presence of PbO, together with B₂O₃ and K₂O, allowed the preparation of a X-ray diffraction (XRD) amorphous glass with a relatively high concentration of ZrO₂ and TiO₂, which was successfully converted to a glass–ceramic containing 34 wt% of zirconolite after heating at 770°C for 4 h. Differential thermal analysis, XRD, scanning electron microscope, and energy dispersive X-ray spectroscopy were used to determine the crystallization conditions, identify the crystallized phases, determine their compositions and quantities and observe and analyze the microstructures. The zirconolite crystals showed a platelet morphology with a monoclinic structure characterized by a =1.246 nm, b =0.7193 nm, c =1.128 nm, and β=100.508°.     

Properties and Structure of Glasses in the System Bi2O3-SiO2-GeO2

In the system Bi₂O₃-SiO₂-GeO₂, good glasses can be formed only from limited compositional regions consisting of 2 narrow strips along the lines x Bi₂O₃-(100-:t) GeO₂ ( x ≤40) and 40Bi₂O₃ y SiO₂ (60- y )GeO₂ (mol%); such glass is dark brown. Compositions from a large region (Bi₂O₃ content <40 mol%) showed immiscibility. In the binary system Bi₂O₃-GeO₂, density and refractive index vary linearly with composition (mol%). Negative deviations of molar volume from ideality suggest that the coordination of a significant number of Ge ions is changing from 4-fold to 6-fold. Thermal expansion and electrical resistivity data are also reported.     

Effect of Molybdenum on the Structure and on the Crystallization of SiO2–Na2O–CaO–B2O3 Glasses

Crystallization of the poorly durable Na₂MoO₄ phase able to incorporate radioactive cesium must be avoided in SiO₂–Al₂O₃–B₂O₃–Na₂O–CaO glasses developed for the immobilization of Mo-rich nuclear wastes. Increasing amounts of B₂O₃ and MoO₃ were added to a SiO₂–Na₂O–CaO glass, and crystallization tendency was studied. Na₂MoO₄ crystallization tendency decreased with the increase of B₂O₃ concentration whereas the tendency of CaMoO₄ to crystallize increased due to preferential charge compensation of BO₄⁻ entities by Na⁺ ions. ²⁹Si MAS NMR showed that molybdenum acts as a reticulating agent in glass structure. Trivalent actinides surrogate (Nd³⁺) were shown to enter into CaMoO₄ crystals formed in glasses.     

Compound Formation and Phase Equilibria in the System PbO-SiO2

Compound formation in the system PbO-SiO₂ was studied; the results are contrasted with those previously reported. Fifteen binary phases, 4 of which had not been reported, were prepared in the present study. The new phases include Pb₅Si₈O₂₁, an orthorhombic polymorph of PbSiO₃, Pb₃SiO₅, and a high-SiO₂ phase containing ∼ 60 mol% SiO₂. It was shown that Pb₃SiO₅ is thermodynamically stable relative to Pb₂SiO₄ and 4PbO.SiO₂ below 640±5°C. A revised phase equilibrium diagram is presented.     

Optical and NMR Studies on Interdiffusion of Silver in SiO2-B2O3-AI2O3-R2O Glasses

Interdiffusion of silver ions in SiO₂-B₂O₃-AI₂O₃-R₂O glasses where R=Na or K was investigated, using optical transmission, ESR, and wet chemical methods to determine concentration and the chemical state of silver, and NMR spectra as a probe of the glass structure. The concentration of silver introduced by ion exchange increased monotonically, as the line widths of²⁷AI NMR spectra decreased. The sharp and narrow features of ²⁷Al line shapes were broadened and the amount of colloidal silver produced by ion exchange decreased, as R₂O/B₂O₃ approached unity with fixed AI₂O₃. The BO₄ to BO₃ ratio approached unity and the quadrupole coupling constant of BO₃ units varied from 2.70 to 2.96 MH_Z, as R₂O/AI₂O₃, approached unity for fixed B₂O₃. These diverse data suggest a relation between silver diffusion and glass structure, although the phenomena of phase separation and the mixed-alkali effect could also influence silver-colloid formation in the glasses studied.     

Leaching of Glasses with Molar Composition 20Na2O · 10RO ·x Al2O3· (70-x)SiO2

Sodium depth profiles were determined in water-leached glass samples with molar composition 20Na₂O · 10RO · x Al₂O₃· (70 - x)SiO₂ (RO = CaO, MgO, and ZnO) using secondary ion mass spectrometry. The leaching of sodium ions decreases with increasing Al₂O₃ content in all three glass systems. For x = 0 the leaching is hardly affected by the nature of the divalent cation. For x = 5 and 10 the corrosion resistance is highest for the glass containing ZnO, and for the glasses containing ZnO and MgO, respectively. These glasses correspond to those with the smallest fraction of NBOs. From all these results it is concluded that the nonbridging oxygen atoms play an important role in promoting the leaching of a glass.     

Preparation of NiAl2O4/SiO2 and Co2+-Doped NiAl2O4/SiO2 Nanocomposites by the Sol–Gel Route

NiAl₂O₄/SiO₂ and Co²⁺-doped NiAl₂O₄/SiO₂ nanocomposite materials of compositions 5% NiO – 6% Al₂O₃– 89% SiO₂ and 0.2% CoO – 4.8% NiO – 6% Al₂O₃– 89% SiO₂, respectively, were prepared by a sol–gel process. NiAl₂O₄ and cobalt-doped NiAl₂O₄ nanocrystals were grown in a SiO₂ amorphous matrix at around 1073 K by heating the dried gels from 333 to 1173 K at the rate of 1 K/min. The formations of NiAl₂O₄ and cobalt-doped NiAl₂O₄ nanocrystals in SiO₂ amorphous matrix were confirmed through X-ray powder diffraction, Fourier transform infrared spectroscopy, differential scanning calorimeter, transmission electron microscopy (TEM), and optical absorption spectroscopy techniques. The TEM images revealed the uniform distribution of NiAl₂O₄ and cobalt-doped NiAl₂O₄ nanocrystals in the amorphous SiO₂ matrix and the size was found to be ∼5–8 nm.     

Thermal, Dielectric, and Optical Properties of Neodymium Borosilicate Glasses for Thick Films

Because of their thermal, dielectric, and optical properties, new glass compositions and thick-filmed transparent dielectrics containing neodymium oxide (Nd₂O₃) were studied as a source of purer images in plasma display panels. In the present study, PbO–B₂O₃–SiO₂ and PbO–B₂O₃–SiO₂–ZnO–Al₂O₃ were used as starting glass compositions, to which up to 25 wt% of Nd₂O₃ then was added. Increased amounts of Nd₂O₃ increased the glass transition temperature and dielectric constant of the bulk glasses and decreased the coefficient of thermal expansion. The fired thick films (around 30 μm) allowed selectively visible light to penetrate and showed deep absorption properties at 585 nm that were related to an extraneous gas from neon discharge.     

Structural Analysis of SiO2-Al2O3 Glasses

The structure of SiO₂-Al₂O₃ glasses with up to 60 wt% Al₂O₃ was investigated using the radial distribution function together with the correlation method based on X-ray scattering intensity data. Radial distribution curves are interpreted on the basis of glass-in-glass separation with the constituents of SiO₂-rich and Al₂O₃-rich glasses. The structure of the Al₂O₃-rich glass has a short-range ordering similar to the crystal structure of mullite. The calculated S- i (S) curve of this model gives good agreement with the observed one.     

Oxidation of Tetragonal PbO in Air

Isothermal oxidation of tetragonal PbO in air produced multiphase assemblages with apparent equilibrium compositions which varied linearly with temperature from PbO_1.548 at 286°C to PbO_1.333 at 351°C. Oxidation at each temperature was relatively rapid to PbO_1.40 and very slow from PbO_1.40 to apparent equilibrium values. Pseudocubic PbO_{1+ x} , with compositions between PbO_1.41 and PbO_1.57, was indexed on a cubic unit cell at the lower O/Pb ratios and on a tetragonal unit cell at the higher ratios. Linear changes in lattice parameters and deviation from cubic symmetry accompanied reversible oxidation and reduction of the phase. Pseudocubic PbO_{1+ x} was reduced irreversibly to Pb₃O₄ below the composition PbO_1.41. Hexagonal PbO_{1+ x} , with compositions between PbO_1.333 and PbO_1.41, developed to a maximum of 60% at intermediate temperatures. The hexagonal phase oxidized irreversibly to pseudocubic PbO_{1+ x} at lower temperatures and reduced irreversibly to Pb₃O₄ at higher temperatures. The extent of oxidation at a given temperature was greater in PbO with a mean diameter of 0.52 μm than in PbO with a mean diameter of 2.89 μm, indicating a metastable assemblage. Linear variation of oxidation limits with temperature across the composition boundary between the PbO_{1+ x} phases suggests that the free energies are equal at PbO_1.41, with the lower limit of pseudocubic PbO_{1+ x} determined by tolerance of the structure for oxygen vacancies.