Changes of physical properties of glass surfaces exposed to KNO3 vapors

Modifications of glass surfaces were studied after exposure of samples to an atmosphere resulting from the decomposition of molten KNO₃. The diffusion coefficient of K⁺ ions migrating into the surfaces of float glass and synthesized glasses doped with up to 5 wt% SnO₂ was calculated by the Boltzmann–Matano technique. The Vickers hardness and the refractive index increase with exposure time. Infrared spectra show that the migration of K⁺ is responsible for an increase in the number of non-bridging oxygens in the exposed samples. The spectra of the synthesized glasses present evidences that their surfaces undergo crystallization during the exposure. All results lead to the conclusion that the presence of tin in the glasses hinders the diffusion of K⁺ ions, thus affecting the Vickers hardness, the refractive index and the infrared spectra. It is shown that the exposure method can be used as an alternative process to promote the K⁺ migration into glass surfaces.     

Measurement of diffusion coefficients of Au in liquid Ag with the shear cell technique

Diffusion coefficients of Au in liquid Ag were measured at the temperatures 1300 K and 1500 K by using the shear cell technique. The adopted technique was a modified long capillary method which had a diffusion couple configuration. Obtained diffusion coefficients of Au in liquid Ag were respectively 2.30 × 10⁻⁹ m² s⁻¹ at 1300 K and 3.16 × 10⁻⁹ m² s⁻¹ at 1500 K, which were in good agreement with calculations based on the hard sphere mixture model.     

Reactions between sol–gel coatings and some technical glass substrates during consolidation

SiO₂ and Na₂O–SiO₂ coatings have been applied on float glass and other technical glass substrates by a sol–gel dip-coating process. After drying and baking these films at temperatures up to 500 °C and for times up to 1020 min, the in-depth profiles of the different constituents were measured by secondary neutral mass spectrometry (SNMS). Sn, Al, and Si turned out to be immobile, whereas a diffusion coefficient of ≈10⁻¹⁷ cm²/s could be evaluated for Mg at 500 °C for the transport from float glass into the films. Ca diffused a little faster, however, especially for the Na₂O–SiO₂ films a saddle point and finally a peak occurred in the interface region. This interface peak was even stronger for Na, showing quite anomalous profiles. The mechanism of this peak formation is explained mainly as an up-hill diffusion process. According to this model at the interface non-bridging –O⁻ ions are formed, whose electroneutrality has to be maintained by mobile cations like Na⁺ and Ca²⁺, even diffusing against their own concentration gradient. The other glass substrates, two borofloat glasses and an alkali-poor display glass showed similar but less pronounced effects.     

Cation diffusion in soda-lime-silicate glass melts

Cation diffusion was experimentally investigated in soda-lime-silicate glass melts (composition in mol%: 74SiO₂–16Na₂O–10CaO) at temperatures from 1000 to 1200 °C using the diffusion couple technique. One half of each diffusion couple was doped with 11 trace elements (500 ppm by weight of Rb, Cs, Sr, Zn, Cd, Nd, Eu, In, Sn, Ge and 1000 ppm by weight of Fe). Experiments were performed in an internally heated gas pressure vessel at a confining pressure of 100 MPa to avoid convective fluxes in the diffusion samples. The distribution of major elements was analyzed by electron microprobe. IR spectroscopy was used to quantify concentrations of dissolved water in the run products. Trace element diffusion profiles were measured simultaneously employing synchrotron X-ray fluorescence microanalysis. In all analyzed glasses the highest diffusion coefficients were observed for Rb whereas Nd was always the slowest element, e.g. at 1000 °C the diffusivity decreases from (1.51 ± 0.35) × 10⁻¹¹ m²/s for Rb to (1.29 ± 0.34) × 10⁻¹³ m²/s for Nd. The diffusivity of Nd is close to the chemical diffusivity of network former calculated from viscosity data using the Eyring relationship. Surprisingly, the rare earth elements Nd (3+) and Eu (mixed 2+, 3+) diffuse more slowly than the tetravalent Ge. Activation energies for diffusion increase from (132.1 ± 1.5) kJ/mol for Rb to (205 ± 16) kJ/mol for Eu. Based on the diffusion data for Eu, Sr and Nd we estimated that Eu²⁺/Eu_total ratios in soda-lime-silicate glass melts are below 0.04 both at reducing and oxidizing conditions.     

Properties of sodium-based ternary phosphate glasses produced from readily available phosphate salts

Three series of phosphate glasses were produced by melting together sodium phosphate salt (NaH₂PO₄) and the phosphate salts of either calcium (CaHPO₄), magnesium (MgHPO₄ · 3H₂O) or iron (FePO₄ · 2H₂O) in a 5% gold/95% platinum crucible at 1200 °C. The glass compositions were confirmed by EDX and XRD analysis. Glass transition temperature (T_g), density and durability in water were determined for all the compositions. Maximum metal oxide contents before devitrification were between 55% and 59% for CaO + Na₂O and 59% and 62% for MgO + Na₂O. The normalized equivalent for Fe₂O₃ + Na₂O was between 55% and 61%. Density values for the glasses lay between 2.49 and 2.75 g cm⁻³. T_gs lay between 295 °C and 470 °C. Degradation rates in deionized water at 37 °C lay between 0.03 g cm⁻² h⁻¹ for Na phosphate glasses and 9 × 10⁻⁶ g cm⁻² h⁻¹ for Ca phosphate glasses, 3 × 10⁻⁶ g cm⁻² h⁻¹ for Mg phosphate glasses and <3 × 10⁻⁶ g cm⁻² h⁻¹ for Fe phosphate glasses. The effect of metal addition on properties goes as Fe > Mg > Ca for degradation rates and T_g and Fe > Mg ≈ Ca for density. The change in properties with metal addition was seen to be linear for Fe and Ca additions but not with Mg addition. This is in agreement with the anomalous behavior of magnesium phosphate glasses.     

Nanocalorimetric investigation of light-induced metastable defects in hydrogenated amorphous silicon

The electrical properties of hydrogenated amorphous silicon, a-Si:H, are degraded by light-induced metastable defects after exposure to visible light for extended periods. Using nanocalorimetry, we have directly measured the heat released when these defects are annealed. Although these low level measurements were close to the instrument noise limit, and were affected by extraneous signals from adsorbed gas, a total heat release of only a few tens of nJs could be resolved. For a heating rate of 12 000 K s⁻¹, a single broad peak of heat release, centered at 180 °C, was observed. The integrated heat release indicates that ∼8 × 10¹⁶ defects cm⁻³ h⁻¹ were generated. Polycrystalline Si samples, in which no defects are created by light-soaking, showed no heat release.     

Nonlinear optical properties of PbS quantum dots in boro-silicate glass

PbS quantum dots synthesis in boro-silicate glass is presented. Absorption bleaching of PbS quantum dots of ≈4 and ≈7 nm in diameter dispersed in this glass has been studied. Bleaching relaxation time of 20–30 ps, absorption saturation fluence of ≈5 mJ/cm² and ground-state absorption cross-section of 2 ÷ 6 × 10⁻¹⁷ cm² at the wavelengths corresponding to the first excitonic absorption band maxima are measured.     

Thermal lens study of PbO–Bi2O3–Ga2O3–BaO glasses doped with Yb3+

The aim of this paper is to present a study of the thermal lens technique in quantifying the thermo optical coefficients: ds/dT (optical path change with temperature), thermal diffusivity and conductivity of PbO–Bi₂O₃–Ga₂O₃–BaO glasses doped with Yb³⁺. The thermal lens results indicate that the heat generation, as a function of the incident wavelength, resembles the absorption band ²F_7/2 → ²F_5/2 of Yb³⁺. Thermal diffusivity of 2 × 10⁻³ cm²/s and thermal conductivity of 4.5 × 10⁻³ W/K cm were obtained and are similar to other glasses already reported in previous literature. The results emphasize that the thermal lens technique can be a powerful tool to study the heat generation of new glassy systems.     

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.     

Optical properties and infrared-to-visible upconversion in Er3+-doped GeO2–Bi2O3 and GeO2–PbO–Bi2O3 glasses

Luminescence properties and upconversion studies of germanate glasses in ternary GeO₂–PbO–Bi₂O₃ and binary GeO₂–Bi₂O₃ systems containing Er₂O₃ (0.1–1.0 wt%) are presented for the first time. The Judd-Ofelt parameters found for these glasses are: Ω₂ = 4.50 × 10⁻²⁰ cm², Ω₄ = 1.55 × 10⁻²⁰ cm² and Ω₆ = 0.69 × 10⁻²⁰ cm² for binary glasses and Ω₂ = 4.44 × 10⁻²⁰ cm², Ω₄ = 1.82 × 10⁻²⁰ cm² and Ω₆ = 0.39 × 10⁻²⁰ cm² for ternary glasses. The refractive index of these glasses is found to be ∼2. The transition ⁴I_13/2 → ⁴I_15/2 is peaked at ∼1.53 μm and shows a radiative lifetime around 5 ms. Both systems exhibit similar emission cross-section at 1.53 μm around 0.8 × 10⁻²⁰ cm². Upconverted green emission at ∼530 nm (²H_11/2 → ⁴I_15/2) and ∼550 nm (⁴S_3/2 → ⁴I_15/2) and red emission at ∼668 nm (⁴F_9/2 → ⁴I_15/2) are observed under 980 nm cw excitation. Our results suggest that these glasses are promising candidates for applications in photonics.     

Deformation behaviors of a tungsten-wire/bulk metallic glass matrix composite in a wide strain rate range

Using melt infiltration casting a composite (W-BMG) of Zr_41.25Ti_13.75Ni₁₀Cu_12.5Be_22.5 bulk metallic glass reinforced with tungsten wires has been produced and its quasi-static and dynamic deformations are investigated within the strain rates ranging from 1 × 10⁻⁴ to 2 × 10³ s⁻¹. The lengthwise frozen-in stress of the composite during the fabrication process is also calculated. The quasi-static stress–strain behavior is discussed in detail in light of the observation of the appearances of the specimens. The study reveals that the strain rate sensitivity exponent of 0.022 of the W-BMG composite is half that of the monolithic tungsten, which is a result of the frozen-in stress.     

Vapor growth and characterization of pyrite (FeS2) doped with Co,Ni, and As: Variations in semiconducting properties

Pyrite (FeS₂) crystals doped with As, Ni and Co were synthesized with chemical vapor transport over an 18 cm horizontal gradient of 700–600 °C in evacuated quartz tubes, from a mixture of FeS and S, with FeBr₃ as a transport agent. Sulfur fugacity and thus S:Fe stoichiometry was constrained by the Fe_1−xS/FeS_2−y buffer. As, Ni and Co concentrations were ∼3–800 ppm, ∼200–1500 ppm and ∼ 450–3700 ppm, respectively.Semiconducting properties were measured at room temperature using a van der Pauw and Hall measurement system. Ni and Co-doped pyrite are n-type while As-doped pyrite tends to be p-type. Resistivity for Co-doped pyrite ranged from 0.009 to 0.02 Ω cm while for Ni- and As-doped pyrite, resistivity ranged from 2 to 17 Ω cm. Undoped pyrite resistivity ranged from 15 to 85 Ω cm. Carrier concentration was similar for undoped and Ni-doped pyrite, ranging from 10¹⁵ to 10^16.6 cm⁻³, while for Co-doped pyrite it ranged from 10^18.7 to 10^19.3 cm⁻³ and for As-doped pyrite it ranged from 10¹⁴ to 10¹⁸ cm⁻³. Hall mobility was similar for Co and Ni-doped pyrite ranging from 60 to 270 cm² v⁻¹ s⁻¹ while for undoped pyrite it ranged from 8 to 70 cm² v⁻¹ s⁻¹. Hall mobility for As-doped pyrite ranged from 55.0 to 0.2 cm² v⁻¹ s⁻¹ for electrons and from 0.1 to 11.3 cm² v⁻¹ s⁻¹ for holes with the exception of one sample (of 22). These values should be viewed more as trends than as definitive. The results obtained for Ni, Co, and undoped pyrite are similar to those reported in the literature while results for As-doped synthetic pyrite have not previously been reported.     

Absorption,emission and absorption saturation of Cr4+ ions in calcium aluminate glass

Absorption, luminescence and absorption saturation of Cr ions in a calcium aluminate glass are studied. In the absorption spectrum, the absorption bands of Cr³⁺, Cr⁴⁺ and Cr⁶⁺ ions are revealed. The emission spectrum presents luminescence of Cr³⁺ ions centered at 0.82 μm and that of Cr⁴⁺ ions at 1.3 μm. The luminescence signal demonstrates short decay times of 120 ± 10 ns and 300 ± 20 ns for Cr³⁺ and Cr⁴⁺ ions, respectively. Absorption saturation measurements allowed an estimate of the ground-state absorption cross-sections for Cr⁴⁺ ions at 1.06 μm of 0.7 × 10⁻¹⁸ cm² and at 0.69 μm of 1.5 × 10⁻¹⁸ cm².     

Spectroscopic properties of Tm3+ doped TeO2-R2O-La2O3 glasses for 1.47 μm optical amplifiers

Upon excitation at 808 nm laser diode, an intense 1.47 μm infrared fluorescence has been observed with a broad full width at half maximum (FWHM) of about 124 nm for the Tm³⁺-doped TeO₂-K₂O-La₂O₃ glass. The Judd–Ofelt parameters found for this glass are: Ω₂ = 5.26 × 10^?20 cm², Ω₄ = 1.57 × 10^?20 cm² and Ω₆ = 1.44 × 10^?20 cm². The calculated emission cross-sections of the 1.47 μm transition are 3.57 × 10^?21 cm², respectively. It is noted that the gain bandwidth, σ_e × FWHM, of the glass is about 440 × 10^?28 cm³, which is significantly higher than that in ZBLAN and Gallate glasses, a high gain of 35.5 dB at 1470 nm can be obtained in a TKL glass fiber. TeO₂-R₂O (R = Li, Na, K)-La₂O₃ glasses has been considered to be more useful as a host for broadband optical fiber amplifier.     

Effect of dehydration techniques on the fluorescence spectral features and OH absorption of heavy metals containing fluoride tellurite glasses

Heavy metal containing fluoride tellurite glasses were prepared by different dehydration techniques and the effects of dehydration techniques on fluorescence spectral features, OH content and volatilization of the glass compositions were systematically studied by means of fluorescence spectral measurements FTIR and energy-dispersive X-ray spectrometer. Experimental results indicated that different dehydration induced difference in actual compositions of the glasses that resulted in the variation of their fluorescence spectral features, and melting the glass frits in close environment with mechanical stirring and simultaneous bubbling dry O₂ + CCl₄ mixture in a O₂-rich environment was much more effective to remove the OH groups in the glass matrix, through which an OH absorption coefficient and absorption concentration could be efficiently reduced to as low as 1.09 cm^? 1 and 1.17 × 10¹⁹ cm^? 3, respectively. The low OH content contributed to the increase in fluorescence lifetime, and resulted in the improvement of gain characteristic. The bubbling time of dry O₂ + CCl₄ mixture was optimized via OH absorption concentration investigation.     

Dilithium dialuminium trisilicate phase obtained using coal bottom ash

The Li₂Al₂Si₃O₁₀ glass-ceramics well crystallized and with a regular morphology was produced starting from a mixture of Li₂CO₃, TiO₂, Al₂O₃ and coal bottom ash, after reducing the magnetite phase content. Its measured thermal expansion coefficient in the temperatures range from 25 °C to 300 °C is α_(25–300) = −23.4 × 10⁻⁷ °C⁻¹. This value is ≈18% smaller than that for the commercial lithium glass-ceramics (−23.4 × 10⁻⁷ °C⁻¹ to 50 × 10⁻⁷ °C⁻¹).     

Influence of hydrogen on the thermomechanical properties of a-CNx:H and a-CNx films deposited by glow discharge and ion beam assisted deposition

The coefficient of thermal expansion (CTE), Young’s modulus, Poisson’s ratio, stress and hardness of a-CN_x and a-CN_x:H were investigated as a function of nitrogen concentration. Hydrogenated films were prepared by glow discharge, GD, and unhydrogenated films were prepared by ion beam assisted deposition, IBAD. Using nanohardness measurements and the thermally induced bending technique, it was possible to extract separately, Young’s modulus and Poisson’s ratio. A strong influence of hydrogen, in a-CN_x:H films, was observed on the CTE, which reaches about ∼9 × 10⁻⁶ C⁻¹, close to that of graphite (∼8 × 10⁻⁶ C⁻¹) for nitrogen concentration as low as 5 at.%. On the other hand, the CTE of unhydrogenated films increases with nitrogen concentration at a much lower rate, reaching 5.5 × 10⁻⁶ C⁻¹ for 33 at.% nitrogen.     

Initiation and propagation of shear bands in Zr-based bulk metallic glass under quasi-static and dynamic shear loadings

The effect of strain rate on the initiation and propagation of shear bands in the Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5 bulk metallic glass under shear loading was investigated. The quasi-static (at a strain rate of 1.5 × 10⁻³ s⁻¹) and the dynamic shear tests (at a strain rate of 1.4 × 10³ s⁻¹) were conducted at room temperature using a GATAN Microtest-2000 instrument and a split Hopkinson pressure bar (SHPB) with a specially designed ‘Plate-shear’ specimen, respectively. The complete process of shear band initiation, propagation, and shear band unstable propagation-induced fracture was revealed. The experimental results demonstrated that the macroscopic shear strength is relatively insensitive to the strain rate, whereas shear band initiation and fracture are significantly dependent on strain rate. A dimensionless Deborah number was introduced to characterize the effect of the strain rate on the formation of shear bands. Additionally, the observed numerous liquid droplets and melted belts on the fracture surface at high-strain rates demonstrate that the adiabatic heating exerts a significant effect on fracture behavior of the material.     

Spectroscopic properties and energy transfer in Yb3+–Ho3+ co-doped germanate glass emitting at 2.0 μm

A new kind of germanate glass co-doped with Yb³⁺–Ho3⁺ was prepared. The J-O parameters were calculated to be Ω₂ = (6.59 ± 0.21) × 10^? 20 cm², Ω₄ = (2.77 ± 0.36) × 10^? 20 cm², and Ω₆ = (1.90 ± 0.25) × 10^? 20 cm². The little overlap between the absorption cross section and stimulated emission cross section indicates a non-resonant energy transfer process. The calculation demonstrates that the energy transfer between Yb³⁺ and Ho³⁺ is one-phonon assisted in a great measure. The gain coefficient of Ho³⁺ at 2.0 μm was also calculated. The fluorescence measurement shows the Yb³⁺ co-doping enhances the 2.0 μm emission remarkably.     

Solid–liquid interface energies in the succinonitrile and succinonitrile–carbon tetrabromide eutectic system

The equilibrated grain boundary groove shapes for the commercial purity succinonitrile (SCN) and succinonitrile–carbon tetrabromide (CTB) eutectic system were directly observed. From the observed grain boundary groove shapes, the Gibbs–Thomson coefficients for the solid SCN–liquid SCN and solid SCN–liquid SCN CTB have been determined to be (5.43±0.27)×10⁻⁸ Km and (5.56±0.28)×10⁻⁸ Km, respectively, with numerical method. The solid–liquid interface energies for the solid SCN–liquid SCN and solid SCN–liquid SCN CTB have been obtained to be (7.86±0.79)×10⁻³ J m⁻² and (8.80±0.88)×10⁻³ J m⁻², respectively from the Gibbs–Thomson equation. The grain boundary energies in the SCN and SCN rich phase of the SCN–CTB system have been calculated to be (15.03±1.95)×10⁻³ J m⁻² and (16.51±2.15)×10⁻³ J m⁻², respectively, from the observed grain boundary groove shapes. The thermal conductivity ratios of the liquid phase to the solid phase for SCN and SCN–4 mol% CTB alloy have also been measured.