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.     

Preparation and ionic conductivity of transparent glass−ceramics containing a large quantity of lithium−mica

In order to crystallize a large quantity of the lithium?mica in glass?ceramics, 5.1 mass% MgF₂ was added to the starting materials of the parent glasses having chemical compositions of Li_(1+x)Mg₃AlSi_3(1+x)O_10+6.5xF₂ (x = 0.5 and 1.0). Transparent glass?ceramics, in which a large quantity of lithium?mica with particle size of <50 nm was separated, could be prepared from the MgF₂-added parent glass with x = 0.5. While the parent glass, which had a binodal phase separation structure, did not exhibit electrical conductivity, the transparent glass–ceramic was given conductivity by the formation of an interlocking structure of mica. As the separated mica formed a tighter interlocking structure, the conductivity increased and reached a value of 2.0 × 10^?3 S/cm at 600 °C. The MgF₂-added parent glass with x = 1.0 was not transparent because of coarse spinodal phase separation. The conductivity was 4.3 × 10^?4 S/cm at 600 °C but was significantly decreased by the separation of mica.     

Growth improvement and quality evaluation of ZnGeP2 single crystals using vertical Bridgman method

ZnGeP₂ single crystals were grown using two-temperature zone vertical Bridgman method. The effect of crucible material, crucible shape, and cooling program on the growth of the ZnGeP₂ crystal was investigated. The qualities of the crystals were evaluated by high resolution X-ray diffraction, X-ray fluorescence spectrometry, and IR transmittance spectra. The results show that the full width at half maximum of the rocking curves for (200), (004), and (220) faces are 45″, 37″, and 54″, respectively. The concentration of the P, Zn and Ge are almost homogeneous along the growth axis, but P and Zn are slightly deficient compared with Ge in the as-grown ZnGeP₂ crystals. The increase of annealing temperature from 600 °C to 700 °C has little effect on the reduction of the absorption losses in ZnGeP₂ powders, and has negative effect on the reduction of the absorption losses in ZnP₂ powders. Annealed in ZnP₂ powders at 600 °C for 300 h, the optical absorption loss at 2.05 μm reduce by 37%, compared with that of 27% reduction annealed in ZnGeP₂ powders.     

Manufacturing of porous niobium phosphate glasses

Niobium phosphate glasses with composition 33P₂O₅ · 27K₂O · 40Nb₂O₅ are usually very stable with regard to crystallization resistance, with a relatively high glass transition temperature (T_g ∼ 750 °C), and are potentially suitable for nuclear waste immobilization. Porous niobium phosphate glasses were prepared by the replication method. The porous glasses were produced via the dip-coating of an aqueous slurry containing 20 wt% powdered glass into commercial polyurethane foams. The infiltrated foams were oxidized at 600 °C for 30 min to decompose the polymeric chains and to burn out the carbon, leading to a fragile glass skeleton. Subsequent heating above the glass transition temperature in the range of 780–790 °C for 1 h, finally resulted in mechanically stable glass foams, which maintained the original interconnected pore structure of the polyurethane foam. The struts showed the neck formation between particles, evidencing the initial stage of sintering. The open and interconnected porosity of the glassy foams lies in the range of 85–90 vol.%. It was concluded that porous niobium phosphate glasses are potential candidates for immobilizing liquid nuclear waste.     

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.     

Effect of preparation procedure on redox states of iron in soda-lime silicate glass

The redox state of iron in soda-lime silicate glass was determined by analysis of the optical absorption bands due to Fe²⁺ and Fe³⁺ states. When raw materials containing Fe₂O₃ were heated gradually to 1400 °C, the total-Fe content of the glass was 9.4% Fe²⁺, but rapid heating at 1400 °C increased the Fe²⁺ content to 11.7%. The oxygen activity (aO₂) in the corresponding melts was measured using zirconia and Pt electrodes. The value increased with increasing temperature in the gradually heated sample and reached log(aO₂) = 0.03 at 1400 °C, but was about 2.5 times lower in the rapidly heated sample at log(aO₂) = ?0.37. After SnO addition to the raw material, oxygen activity depended strongly on heating speed: log(aO₂) at 1400 °C fell as low as ?1.8 with rapid temperature increase but was about ?0.2 or higher with gradual heating. The Fe²⁺ content of the cooled glass was consistent with the oxygen activity of the melts. The effect of heating speed was attributed to the formation of a melt layer on the surface of the raw material.     

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.     

Performance investigation of Li2O–Al2O3–4SiO2 based glass–ceramics with B2O3, Na3AlF6 and Na2O fluxes

Influence of single fluxes (10 wt.% B₂O₃), bi-component fluxes (4 wt.% B₂O₃ + 6 wt.% Na₃AlF₆), and complex fluxes (4 wt.% B₂O₃ + 4 wt.% Na₃AlF₆ + 2 wt.% Na₂O) on the thermal kinetic parameters, microstructure, flexural strength and coefficient of thermal expansion (CTE) of Li₂O–Al₂O₃–4SiO₂ (LAS) glass–ceramics was investigated through differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscope (SEM). The results showed that complex fluxes could efficiently decrease transition temperature (T_g) and crystallization temperature (T_p), and accelerate the formation of needle-like β-spodumene crystals which benefit high flexural strength. The homogeneous LAS glass–ceramic (sample C₃) which has a high strength of 132.4 MPa and low CTE (100–650 °C) of 2.74 × 10^? 6/°C is obtained by doping of the initial LAS glass by complex fluxes of 4 wt.% B₂O₃, 4 wt.% Na₃AlF₆, and 2 wt.% Na₂O, nucleating at 630 °C/120 min and then crystallized at 780 °C/120 min. It is worthy of further investigation as a bonder of diamond composite material due to its outstanding prosperities.     

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.     

Silver release from hydroxyapatite self-assembling calcium–phosphate glasses

The in vitro behavior of xAg₂O (100 ? x)[50P₂O₅ · 30CaO · 20Na₂O] glasses (0.14 ? x ? 20 mol%) is investigated in simulated body fluid (SBF) mainly with respect to bioactivity and silver ions release. In order to estimate the biodegradability and bioactivity, the samples were soaked in SBF, which has almost equal ions concentration to those of human blood plasma, and kept at 37 °C for fixed periods of time up to 18 days. After the fixed periods of time analyses were performed on the SBF solutions. Calcium and silver ions concentration of SBF after different soaking times of the glass samples were primarily examined. Conductivity data support the assumption that the released silver ions are reduced in SBF and their release is obstructed by growth of the bioactive layer on the glass surface. X-ray diffraction and infrared analysis attest the development on glass surface of a hydroxyapatite type layer.     

Preparation of transparent lithium-mica glass-ceramics

In order to fabricate transparent and machinable mica-type glass-ceramics, parent glasses having chemical compositions corresponding to Li_(1+x)Mg₃AlSi_3(1+x)O_10+6.5xF₂ (x = 0.15, 0.5, 0.65, 1.0 and 1.2) were crystallized. Lithium-micas were precipitated in all the specimens as the main crystal at 650 °C though the content was little. And the micas were changed from trisilicic type to tetrasilicic type as the x increased. After the precipitation of the micas, a large amount of β-eucryptite solid solution was precipitated as the main crystal at higher temperatures and even at 650 °C after a certain period of time. The parent glasses having the spinodal phase separation, of which the x was 1.0 and 1.2, were transparent and colored in light blue. And at 650 °C, the fine mica crystals with size of about 20 nm were precipitated in one continuous glass phase of the spinodal phase separation, which made the phase separation structure become finer. Consequently, the heated specimens showed higher transmittance of visible ray and became colorless. Moreover, because the mica crystals formed the continuous phase, the specimens showed the machinability.     

Influence of Bi2O3 content on the crystallization behavior of TeO2–Bi2O3–ZnO glass system

Glass ceramic materials with composition 75TeO₂–xBi₂O₃–(25-x)ZnO (x = 13, 12, 11) possessing transparency in the near- and mid-infrared (MIR) regions were studied in this paper. It was found that as the Bi₂O₃ content increased in the glass composition, the observed crystallization tendency is enhanced, and high crystal concentrations were obtained for the glasses with high Bi₂O₃ content while maintaining transparency in the MIR region. Crystal size in the glass ceramic was reduced by adjusting the heat treatment conditions; the smallest average size obtained in this study is 700 nm. Bi_0.864Te_0.136O_1.568 was identified using X-ray Diffraction (XRD) and found to be the only crystal phase developed in the glass ceramics when the treatment temperature was fixed at 335 °C. The morphology of the crystals was studied using Scanning Electron Microscopy (SEM), and crystals were found to be polyhedral structures with uniform sizes and a narrow size distribution for a fixed heat treatment regime. Infrared absorption spectra of the resulting glass ceramics were studied. The glass ceramic retained transparency in the infrared region when the crystals inside were smaller than 1 μm, with an absorption coefficient less than 0.5/cm in the infrared region from 1.25 to 2.5 μm. The mechanical properties were also improved after crystallization; the Vickers Hardness value of the glass ceramic increased by 10% relative to the base glass.     

Characterization of thermo-optical and mechanical properties of calcium aluminosilicate glasses

In this work several different compositions of CaO:Al₂O₃:SiO₂ were prepared under vacuum atmosphere to study the glass forming ability of this system as a function of the SiO₂ content. Samples containing 25–45 wt% of Al₂O₃, 31–44 wt% of CaO, 14–39 wt% of SiO₂ and 4.1 wt% of MgO were prepared in graphite crucibles, for approximately 2 h at ∼ 1600 °C. The influence of silica content is discussed in terms of the mechanical properties, glass transition temperature, crystallization temperature, transmittance spectrum, refractive index, mass density, specific heat, thermal diffusivity, thermal conductivity and the temperature coefficient of optical path length change. The results reinforce the idea that these glasses are strong materials, having useful working-temperature range, good combination of thermal, mechanical and optical properties that could be exploited in many optical applications, in particular, as glass laser materials.     

Effect of Al2O3 addition on the formation of perovskite-type NaNbO3 nanocrystals in silicate-based glasses

The crystallization behavior of 30Na₂O–25Nb₂O₅–(45 ? x) SiO₂–xAlO_1.5 (x = 0, 2.5, and 5) (mol%) glasses was examined and the effect of Al₂O₃ addition on the formation of perovskite-type NaNbO₃ crystals was clarified. It is found from X-ray diffraction analyses and transmission electron microscope observations that NaNbO₃ nanocrystals are formed in all glasses and the size of NaNbO₃ crystals decreases with the substitution of Al₂O₃ for SiO₂. A crystallized (heat-treated at 684 °C for 5 h) glass with x = 5, which contains NaNbO₃ nanocrystals with an average size of 50 nm, shows good optical transparency in the wavelength region of 500–2000 nm and a small hysteresis loop in the polarization–electric field curve. The lines containing NaNbO₃ crystals were patterned on the surface of NiO-doped glass with x = 5 by irradiations (power: 1.3–1.4 W, scanning speed: 10 μm/s) of Yb:YVO₄ fiber laser (wavelength: 1080 nm). The formation mechanism of NaNbO₃ nanocrystals in aluminosilicate glasses was also discussed.     

Systematic study of spectroscopic properties and thermal stability of lead germanate glass doped with rare-earth ions

Glasses with composition 50GeO₂–(50?x)PbO–5PbF₂–xLnF₃ (Ln = Pr³⁺–Yb³⁺) were prepared from commercial raw materials. The content of PbF₂ was constant and amounted to 5 mol% whereas the concentration of luminescent ions was diverse (0.2 and 2 mol%). Thermal stability of the glasses were monitored by differential thermal analysis (DTA). It has been found that increase of rare-earth fluoride content from 0.2 mol% to 2 mol% brings about a shift of the glass crystallization onset from 450 °C to 487 °C for Nd-doped samples and from 466 °C to 482 °C for Tm-doped samples. Optical absorption and emission spectra of Ln active ions in oxyfluoride glass have been investigated at room temperature in the ultraviolet (UV), visible (VIS) and near-infrared (NIR) region. Oscillator strengths, phenomenological Judd–Ofelt intensity parameters Ω_2,4,6, radiative transition probabilities, branching ratios and radiative lifetimes of luminescent levels have been estimated. Analysis of decay curves of luminescence revealed that the increase of rare-earth fluoride content from 0.2 mol% to 2 mol% shortens the lifetime of the ⁴F_3/2 level of Nd³⁺ from 224 μs to 90 μs.     

Pyrolytic conversion studies of blended polycarbosilane and polyaluminasilazane

Multinuclear solid-state NMR spectroscopy, FTIR and Raman experiments are employed to investigate the pyrolytic conversion of blended polycarbosilane and polyaluminasilazane (denoted CA) up to 800 °C, with the aim of studying structural evolutions and interactions between polycarbosilane and polyaluminasilazane during the pyrolysis process. Vinyl and SiCH₃ units can react with Si–H, SiCH₃ and Si–CH₂–Si groups below 400 °C. These crosslinking reactions can increase the ceramic yield of the blended precursors. At 500 °C aromatic carbon is formed, and N–H and Si–H groups vanish at 600 °C and 700 °C, respectively. At 600 °C, SiCH₃ and Si–H units can further react with SiCN₃, SiC₂N₂, N–H and C–H units. An amount of amorphous carbon and CSi₄ and CSi₃H groups are detectable at 800 °C. Even at this temperature there are still many aromatic protons. In addition, there are also SiC₄, SiC₃N, SiCN₃ and SiN₄ units. Silicon forms SiN₄ more readily than SiC₄. Many AlN₅ groups transform into AlN₆ groups. The D and G bands of graphite are observed in CA pyrolyzed at 1400 °C. According to the XRD patterns, the reflection of crystalline β-Si₃N₄ vanishes at 1700 °C, and the residue pyrolyzed at 1800 °C mainly contains a large number of 2H-SiC/AlN solid solution crystals and a few β-SiC crystals.     

Magnetite nanoparticles prepared by the crystallization of Na2O–Fe2O3–B2O3–SiO2 glasses

A glass with the composition of 35Na₂O–24Fe₂O₃–20B₂O₃–20SiO₂–1ZnO (mol%) was melted, quenched, using a twin roller technique, and subsequently heat treated in the range 485–750 °C for 1–2 h. This led to the crystallization of magnetite as the sole or the major crystalline phase.Heat treatment at lower temperatures resulted in the crystallization of magnetite crystals 7–20 nm in diameter, whereas heat treatment at higher temperatures produced higher quantities of magnetite and much larger crystals. The room temperature magnetization and coercive force values were in the range of 6–57 emu g^? 1 and 0–120 Oe, respectively for the heat treated glasses.     

Improving the performance of amorphous and crystalline silicon heterojunction solar cells by monitoring surface passivation

The influence of thermal annealing on the crystalline silicon surface passivating properties of selected amorphous silicon containing layer stacks (including intrinsic and doped films), as well as the correlation with silicon heterojunction solar cell performance has been investigated. All samples have been isochronally annealed for 1 h in an N₂ ambient at temperatures between 150 °C and 300 °C in incremental steps of 15 °C. For intrinsic films and intrinsic/n-type stacks, an improvement in passivation quality is observed up to 255 °C and 270 °C, respectively, and a deterioration at higher temperatures. For intrinsic/n-type a-Si:H layer stacks, a maximum minority carrier lifetime of 13.3 ms at an injection level of 10¹⁵ cm^? 3 has been measured. In contrast, for intrinsic/p-type a-Si:H layer stacks, a deterioration in passivation is observed upon annealing over the whole temperature range. Comparing the lifetime values and trends for the different layer stacks to the performance of the corresponding cells, it is inferred that the intrinsic/p-layer stack is limiting device performance. Furthermore, thermal annealing of p-type layers should be avoided entirely. We therefore propose an adapted processing sequence, leading to a substantial improvement in efficiency to 16.7%, well above the efficiency of 15.8% obtained with the ‘standard’ processing sequence.     

Characteristics of ITO films fabricated on glass substrates by high intensity pulsed ion beam method

Transparent conductive oxides such as indium tin oxide (ITO) are interesting materials due to their wide-band gaps, high visible light transmittance, high infrared reflectance, high electrical conductivity, hardness and chemical inertness. ITO films were fabricated on soda lime glass substrates by using high-intensity pulsed ion beam (HIPIB) technique. The as-deposited films comprised of partially crystallized In₂O₃ and after annealing at 500 °C for 1 h the film changed to polycrystalline phase. After annealing carrier concentration and Hall mobility increased while specific resistance and sheet resistance decreased quickly; and this trend was also observed when film thickness increased up to 300 nm for the post-annealed samples. Further increase in thickness of the film changed the electrical properties slightly. Atomic force microscopy (AFM) revealed that roughness decreased after 500 °C annealing for 1 h in air, except for the film of 65 nm thick. The thickness of the film which relates to the carrier concentration and mobility, degree of crystallization, size of the grain, and connections among grains in film are main factors to determine film’s electrical properties.     

Kinetics of crystal growth of mirabilite in aqueous supersaturated solutions

The crystallization of sodium sulfate decahydrate (Na₂SO₄·10H₂O, mirabilite) from supersaturated solutions was investigated using stable supersaturated solutions seeded with mirabilite seed crystals. The experiments were done in batch, stirred reactors in which the supersaturated solutions were prepared either by dissolution of sodium sulfate anhydrous at 32 °C followed by cooling to 18 or 20 °C or by mixing equal volumes of equimolar ammonium sulfate and sodium hydroxide solutions at 20 °C. Inoculation of the solutions supersaturated only with respect to mirabilite with seed crystals was accompanied with temperature increase of the thermostated solution. Despite the fact that crystal growth was initiated with seed crystals, the process started past the lapse of induction times inversely proportional to the solution supersaturation. The rates of crystal growth were measured both from the temperature rise and from the concentration–time profiles, which were linearly correlated. The measured crystal growth rates showed a parabolic dependence on supersaturation at low supersaturations. For higher values this dependence changed to linear, a behavior consistent with the BCF spiral crystal growth model. The morphology of the crystals growing at 20 °C showed typical prismatic habit, while at 18 °C when crystallized from cooled sodium sulfate solutions changes in the crystal habit to a leaf like morphology were observed.