Evaluation and investigation on the effect of ionic liquid onto PMMA-PVC gel polymer blend electrolytes

1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl imide), BmImTFSI based poly(methyl methacrylate)-poly (vinyl chloride), PMMA-PVC gel polymer electrolytes were prepared by solution casting technique. These ionic liquid-based gel polymer electrolytes exhibit Arrhenius type temperature dependence of ionic conductivity. The highest ionic conductivity of (8.08 ± 0.01) × 10^− 4 Scm⁻¹ was achieved at 80 °C upon addition of 60 wt.% of BmImTFSI. X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies revealed the amorphous nature and morphology of these polymer electrolytes, respectively. The lower coherence length of the peak inferred the higher amorphous degree in these polymer matrices. Decreases in T_g and T_m indicate the flexibility of polymer backbone. The amorphous behavior of these ionic liquid-based gel polymer electrolytes are also enhanced as shown in differential scanning calorimetry (DSC) analysis. On the contrary, thermogravimetric analysis (TGA) divulges that the thermal stability of polymer electrolytes has been improved upon impregnation of BmImTFSI.     

Defect-mediated self-diffusion in calcium aluminosilicate glasses: A molecular modeling study

The mechanism of self-diffusion in calcium aluminosilicate glasses is investigated at the atomistic level using molecular dynamics (MD) simulations. We study nine glass compositions having the fixed ratio R = [CaO]/[Al₂O₃] = 1 and the concentration of SiO₂ varied from 11.8 to 76.5 mol%. The diffusion coefficient is calculated for each composition at different temperatures from 300 to 6000 K in steps of 300 K. The self-diffusivities of the various elements are found to be close to each other in magnitude, signifying the cooperative nature of the atomic movement. Network “defects” such as miscoordinated cations, non-bridging oxygen, and oxygen triclusters are also studied as a function of temperature and composition. We find that the behavior of self-diffusion correlates well with the concentration of network defects. A model of self-diffusion in calcium aluminosilicate glasses is proposed where diffusion is considered as a defect-mediated process resulting from bond-switching reactions at high temperature.     

Thermodynamics of the Cu/Cu-redox equilibrium in soda-silicate and soda-lime-silicate melts

The thermodynamics of the redox equilibrium of Cu⁺/Cu²⁺ were determined by square-wave voltammetry in glass melts with the base mol% compositions x Na₂O · (100 − x) SiO₂ (x = 15, 20, 26 and 33) and (26 − x) Na₂O · x CaO · 74 SiO₂ (x = 0, 5, 10 and 15) doped with 1 mol% CuO in the temperature range from 850 to 1150 °C. All recorded voltammograms showed two maxima attributed to the reductions of Cu²⁺ to Cu⁺ and Cu⁺ to metallic copper. Both peaks are shifted to smaller potentials with decreasing temperature. With increasing melt basicity, the [Cu⁺]/[Cu²⁺]-ratio first increases, and remains constant for optical basicities >0.56. The effect of composition on the redox equilibrium is explained by the incorporation of both Cu⁺ and Cu²⁺ in octahedral coordination into the melt structure.     

Redox freezing temperature and Bartenev equation in a 25Na2O-15B2O3-60SiO2 glass doped with chromium and manganese

In a melt with the base mol% composition 25Na₂O-15B₂O₃-60SiO₂, doped with chromium and manganese, a redox reaction takes place during cooling the melt. This reaction was studied using high temperature UV-vis spectroscopy. Above 600 °C, the reaction is in equilibrium and shifted during cooling to the Cr³⁺ and Mn³⁺ species. At temperatures between 500 and 600 °C, the kinetics of the redox reaction is decisive and the cooling rate plays an important part. At temperatures < 500 °C, the reaction is frozen in. The smaller the cooling rate, the smaller is the Cr⁶⁺ concentration and the lower is the fictive redox temperature.The kinetics of the reaction was described by a differential equation assuming Arrhenian behaviour. The equation was numerically solved and fictive temperatures were calculated. These temperatures depended on cooling rate similar to Bartenev equation. Activation energies calculated hereof were around 38 kJ?mol⁻¹ larger than those inserted into the kinetic equation. The experimentally determined activation energy is 565 kJ?mol⁻¹, a value much larger than the activation energies of diffusion of the polyvalent elements. The rate determining step in the case of the Cr³⁺/Cr⁶⁺/Mn²⁺/Mn³⁺ system is the electron transfer reaction, because a notable structural rearrangement is necessary during the course of the electron transfer reaction (Cr³⁺ and Cr⁶⁺ occur in octahedral and tetrahedral coordination, respectively). The latter leads to a large inner reorganisation energy and to an activation energy similar to that of the viscous flow. In the case of the redox reaction between copper and arsenic, the activation energy is much smaller (210 kJ?mol⁻¹), because here the coordination numbers do not change during the course of the redox reaction.     

Condensation of aluminosilicate gels—model system for geopolymer binders

The reaction of geopolymer binders can be subdivided into two more or less parallel reactions, (1) the dissolution of reactable silicate and aluminate monomers from the reactive solid material and (2) the condensation to an aluminosilicate gel. Due to the wide range of possible raw materials, the question arises whether the Si/Al ratio of the hardened aluminosilicate network is predominated by the Si/Al ratio of the raw materials, or a gel with preferred Si/Al ratio wants to condense. Therefore, aluminosilicate gels were synthesized with pure alkali silicate and alkali aluminate solutions. Two measurement series were started to investigate the influence of hydroxide concentration as well as the influence of Si/Al in the model system. The gels were characterized by chemical analysis, FT-IR spectroscopy, X-ray diffraction as well as ²⁹Si and ²⁷Al MAS NMR spectroscopy.     

A low silica, barium borate glass-ceramic for use as seals in planar SOFCs

A low silica, barium borate glass-ceramic for use as seals in planar SOFCs containing 64 mol%BaO, 3 mol%Al₂O₃ and 3 mol%SiO₂ was studied. Coefficient of thermal expansion (CTE) between 275-550 °C, glass transition temperature (T_g), and dilatometric softening point (T_s) of the parent glass were 11.9 × 10⁻⁶ °C⁻¹, 552 °C, and 558 °C, respectively. Glass-ceramic was produced by devitrification heat treatment at 800 °C for 100 h. It was found that nucleation heat treatment, seeding by 3 wt%ZrO₂ as glass-composite and pulverization affected the amount, size and distribution of crystalline phases. SEM-EDS and XRD results revealed that crystalline phases presented in the devitrified glass-ceramic were barium aluminate (BaAl₂O₄), barium aluminosilicate (BaAl₂Si₂O₈) possibly with boron associated in its crystal structure, and barium zirconate (BaZrO₃). CTE of the devitrified glass-ceramic was in the range of (10.1-13.0) × 10⁻⁶ °C⁻¹. Good adhesion was obtained both in the cases of glass and devitrified glass-ceramic with YSZ and AISI430 stainless steel. Interfacial phenomena between these components were discussed.     

In situ gravimetric monitoring of surface reactions between sapphire and NH3

Surface reactions between a (0 0 0 1) C-plane sapphire and NH₃, with He as an inert carrier gas, were investigated at high temperatures over 1200 °C using the in situ gravimetric monitoring method. Although the sapphire substrate was stable up to 1400 °C under a He atmosphere, decomposition started to occur at 1300 °C under a 0.1 atm NH₃+He and the decomposition rates were found to be lower than those in 0.1 atm H₂+He at each temperature. These results imply that sapphire can be decomposed by NH₃ and/or hydrogen generated by the decomposition of NH₃ over 1300 °C. The decomposition rate in NH₃+He was decreased with increase in NH₃ flow time, and the decomposition rate became constant after 60 min of NH₃ flow. Moreover, the activation energy for sapphire decomposition before 60 min of NH₃ flow was different from that after 60 min of NH₃ flow time, which indicates that the surface reaction between sapphire and NH₃ and/or hydrogen generated from NH₃ changes depending on the time of NH₃ flow. The dependence of the surface reactions and rate-limiting reactions between sapphire and NH₃ on the time of NH₃ flow is discussed.     

Influence of high temperature deformation on the fracture behavior of a bulk Zr-based metallic glass

Nanocrystalline/amorphous matrix composites obtained by isothermal compression at high temperatures and low strain rates were characterized using transmission electron microscopy. To study the influence of high temperature deformation on the fracture behavior and room temperature plasticity, compression tests with a constant strain rate of 1 × 10⁻⁴ s⁻¹ were applied to the deformed samples. Fracture features of as-cast alloy and deformed samples were analyzed using scanning electron microscopy. Compared with the as-cast alloy, the room temperature plasticity of deformed sample is not destroyed both in the range of 370-395 °C at 1 × 10⁻³ s⁻¹ and at 395 °C in 1 × 10⁻² to 1 × 10⁻³ s⁻¹, and deteriorated at higher temperatures and lower strain rates. Corresponding to the TEM images, the homogenously dispersed nanocrystals with small size contribute to the compressive plasticity, and the aggregated large nanoparticles destroy the plasticity of the sample after high temperature deformation.     

Structural order and crystallization of an iron-rich aluminosilicate liquid under oxidizing condition

An iron-rich aluminosilicate liquid is studied in different atmospheres by using differential scanning calorimetry. The results show that the oxidation state of iron and the maximum temperature of the scan have an effect on the liquid structure and on the crystallization behavior of the liquid during both cooling and reheating processes. Increase in Fe²⁺/Fe³⁺ enhances crystallization and favors formation of a stable crystal structure. The structural order conserved in the liquid is an intrinsic phenomenon, which is not related to the oxidation state of iron.     

Low-temperature growth of epitaxial (1 0 0) silicon based on silane and disilane in a 300 mm UHV/CVD cold-wall reactor

Epitaxial (1 0 0) silicon layers were grown at temperatures ranging from 500 to 800 °C in a commercial cold-wall type UHV/CVD reactor at pressures less than 7×10⁻⁵ Torr. The substrates were 300 mm SIMOX SOI wafers and spectroscopic ellipsometry was used to assess growth rates and deposition uniformities. High-resolution atomic force microscopy (AFM) was employed to verify the atomic terrace configuration that resulted from epitaxial step-flow growth. Deposition from disilane exhibited a nearly perfect reaction limit for low temperatures and high precursor flow rates (partial pressures) with measured activation energies of ≈2.0 eV, while a linear dependence of growth rate on precursor gas flow was found for the massflow-controlled regime. A similar behavior was observed in the case of silane with substantially reduced deposition rates in the massflow-limited regime and nearly a factor of 2 reduced growth rates deep in the reaction limited regime. High growth rates of up to 50 μm/h and non-uniformities as low as 1σ=1.45% were obtained in the massflow-limited deposition regime. Silicon layers as thin as 0.6 nm (4.5 atomic layers ) were deposited continuously as determined using a unique wet chemical etching technique as well as cross-sectional high-resolution transmission electron microscopy (HRTEM). In contrast, epitaxial silicon deposited in RPCVD at 10 Torr using disilane within the same temperature range showed imperfect reaction limitation. While activation energies similar to that of UHV/CVD were found, no partial pressure limitation could be observed. Furthermore, layers deposited using disilane in RPCVD exhibited a large number of defects that appeared to form randomly during growth. We attribute this effect to gas phase reactions that create precursor fragments and radicals—an effect that is negligible in UHV/CVD.     

Properties of gallium- and aluminum-doped bulk ZnO obtained from single-crystals grown by liquid phase epitaxy

Bulk properties of gallium (Ga)- and aluminum (Al)-doped zinc oxide (ZnO) were studied using bulky single-crystalline thick films grown by liquid phase epitaxy (LPE). The highest possible dopant concentration was 1×10¹⁹ cm^–3 for LPE growth at around 800 °C. The electron concentration was nearly same to the Ga and Al concentrations. The donor binding energy decreased to nearly zero with an increase in dopant concentration, and electron mobility of the sample with relatively high dopant concentration (1×10¹⁹ cm^–3) was more than 60 cm² V^–1 s^–1 at room temperature. The LPE technique is a potential solution for the production of ZnO for optical applications because the well-defined excitonic luminescence could be seen from the LPE-grown-doped single-crystals.     

Tin valence and local environments in silicate glasses as determined from X-ray absorption spectroscopy

X-ray absorption spectroscopy (XAS) was used to characterize the tin (Sn) environments in four borosilicate glass nuclear waste formulations, two silicate float glasses, and three potassium aluminosilicate glasses. Sn K-edge XAS data of most glasses investigated indicate Sn⁴⁺O₆ units with average Sn-O distances near 2.03 Å. XAS data for a float glass fabricated under reducing conditions show a mixture of Sn⁴⁺O₆ and Sn²⁺O₄ sites. XAS data for three glasses indicate Sn-Sn distances ranging from 3.43 to 3.53 Å, that suggest Sn⁴⁺O₆ units linking with each other, while the 4.96 Å Sn-Sn distance for one waste glass suggests clustering of unlinked Sn⁴⁺O₆ units.     

Polyvinyl alcohol cross-linked macroporous polymeric hydrogels: Structure formation and regularity investigation

A series of novel polyvinyl alcohol (PVA) hydrogels were synthesized by cross-linking of acrylate-modified PVA in aqueous solutions. Hydrogels were prepared at a temperature range −7.5 to −25 °С, macromer concentration 4-12 wt.%, and initiator concentration 0.4 to 1.6 mg/ml. The swelling behavior of polymeric hydrogels in aqueous media with different pH and ionic strength values was investigated. It was shown that they possess a high level of water absorption. The influence of different factors (porosity, pore size, and pore size distribution) and reaction conditions on the hydrogel structure was studied. The interior morphology of the hydrogel networks exhibits a complicated structure filled by fibrillar, lamellar and dendritic formations consisting of cross-linked polymer. The dispersed pores which are randomly distributed can be observed inside these formations and between them.     

Rheological and thermodynamic behaviors of different calcium aluminosilicate melts with the same non-bridging oxygen content

The relationships between the chemical composition and the derivative rheological and thermodynamic values have been determined for two melt series in the anorthite-wollastonite-gehlenite (An-Wo-Geh) compatibility triangle. The melt series have 0.5 and 1 non-bridging oxygens per tetrahedrally coordinated cation (NBO/T), respectively. The influences of the ratio Si/(Si + AlCa_1/2) and NBO/T on the fragility and the configurational entropy at T_g are evaluated. Linear dependencies of the viscosity, the glass transition temperature and the fragility on the ratio Si/(Si + AlCa_1/2) are found for the two melt series. A crossover in the viscosity-temperature relationship is observed for both series, i.e. an inverse compositional dependence of viscosity in the high and low viscous range. The crossover presumably reflects different responses of the adjustment of melt structure to the substitution of Al³⁺ + 1/2Ca²⁺ for Si⁴⁺ in the low versus the high viscous ranges. The crossover shifts to higher temperature with increasing NBO/T.     

On the correlation between solidified microstructures and liquid structural states in Bi-40 wt%Te alloy

The compound-forming alloy Bi-40 wt%Te was selected to explore effects of the temperature-induced liquid–liquid structure transition (TI-LLST) on solidification. The resistivity–temperature pattern of the molten alloy suggested that an irreversible TI-LLST occurred from 694.6 to 723.2 °C as temperature elevated. When solidified from the melt undergoing the TI-LLST, the solidification undercooling of the primary phase Bi₂Te₃ was enlarged and its growth manner was obviously changed, resulting in the spirally curling refined branches, contrary to the orientated thick rod-like crystals solidified from the melt failed to undergo the TI-LLST. Moreover, the volume fraction of the peritectic phase increased from 30.6% to 56.4%, which implied that the phase competition behavior during the peritectic reaction was also changed.     

HVPE growth of semi-polar (1 1 2¯ 2)GaN on GaN template (1 1 3)Si substrate

The hydride-vapour-phase-epitaxial (HVPE) growth of semi-polar (1 1 2¯ 2)GaN is attempted on a GaN template layer grown on a patterned (1 1 3) Si substrate. It is found that the chemical reaction between the GaN grown layer and the Si substrate during the growth is suppressed substantially by lowering the growth temperatures no higher than 900 °C. And the surface morphology is improved by decreasing the V/III ratio. It is shown that a 230-μm-thick (1 1 2¯ 2)GaN with smooth surface is obtained at a growth temperature of 870 °C with V/III of 14.     

Investigation on the crystal growth process of spherical Si single crystals by melting

Spherical Si single crystals with a diameter of approximately 1 mm were grown by melting for solar cell applications. The start sources were spherical Si multicrystals fabricated by a dropping method, which had various irregular shapes. Spherical Si multicrystals were melted into droplets and recrystallized on a quartz plate sample holder that was coated with Si₃N₄. It was found that a surface coating of SiO₂ layer on the start sources and oxygen atmosphere during melting and recrystallization were essential to achieve almost perfect spherical shape. Defect-free single crystalline spherical Si could be obtained at recrystallization temperature ranging from 1400 to 1330 °C, corresponding to an undercooling ranging from 14 to 84 °C, with a yield of nearly 100%. At recrystallization temperatures higher than 1380 °C, the recrystallized spherical Si crystals were almost perfect spheres, whereas small protuberances were formed when the recrystallization temperature was lower than 1360 °C. It was also found that that melting at a temperature close to the melting point of Si (at ~1414 °C), a slow cooling rate of ~1 °C/min before recrystallization and relatively fast cooling rate of ~20 °C/min after recrystallization were important for achieving high carrier lifetime. The average carrier lifetime was greatly improved from lower than 2.5 μs of start sources up to ~7.5 μs by melting at optimized conditions. The influences of residual oxygen on the carrier lifetime of recrystallized spherical Si are discussed based on the measurement results with Fourier transform infrared spectrometer.     

Electrical, structural and optical properties of SnO2 thin films prepared by spray pyrolysis

This study investigated the effect of the substrate temperature on the structural, optical, morphological, and electrical properties of undoped SnO₂ films prepared by a spray deposition method. The films were deposited at various substrate temperatures ranging from 300-500 °C in steps of 50 °C and characterized by different optical and structural techniques. X-ray diffraction studies showed that the crystallite size and preferential growth directions of the films were dependent on the substrate temperature. These studies also indicated that the films were amorphous at 300 °C and polycrystalline at the other substrate temperatures used. Infrared and visible spectroscopic studies revealed that a strong vibration band, characteristic of the SnO₂ stretching mode, was present around 630 cm⁻¹ and that the optical transmittance in the visible region varied over the range 75-95% with substrate temperature, respectively. The films deposited at 400 °C exhibited the highest electrical conductivity property.     

Conversion of batch to molten glass, II: Dissolution of quartz particles

Quartz dissolution during the batch-to-glass conversion influences the melt viscosity and ultimately the temperature at which the glass forms. Batches to make a high-alumina borosilicate glass (formulated for the vitrification of nuclear waste) were heated at 5 K min^− 1 and quenched from temperatures of 400 to 1200 °C at 100 K intervals. The batches contained quartz as a silica source, with particles ranging from 5 to 195 μm in diameter. The content of unreacted quartz in the samples was determined with X-ray diffraction. Most of the fine quartz dissolved during the early batch reactions (at temperatures < 800 °C), whereas coarser quartz dissolved mostly in a continuous glass phase via diffusion. The mass-transfer coefficients were assessed from the data as functions of the initial particle sizes and the temperature. A series of batches were also tested that contained nitrated components and additions of sucrose, known to accelerate melting. While sucrose addition had no discernible impact on quartz dissolution, nitrate batches melted somewhat more slowly than batches containing carbonates and hydroxides in addition to nitrates.     

A glass with high crack initiation load: Role of fictive temperature-independent mechanical properties

The crack initiation load of a series of calcium aluminosilicate glasses and selected commercial glasses were evaluated using Vickers indentation. The results showed that a calcium aluminosilicate glass containing 80 mol% SiO₂, 10 mol% Al₂O₃ and 10 mol% CaO exhibited a high crack initiation load comparable to that of the less-brittle glass (LB glass) developed by Asahi Glass Co., Ltd. It has previously been determined that glasses experience a fictive temperature increase by indentation. The indented region of a glass, therefore, acquires, in general, different mechanical properties, such as hardness and elastic moduli, from the original, unindented glass. The extent of these mechanical property changes depends upon the glass composition and a certain glass composition with fictive temperature-independent mechanical properties can have the deformed region with matching mechanical properties to those of the undeformed region of the glass. It was found that the calcium aluminosilicate glass having no fictive temperature dependence on elastic moduli gave the highest crack initiation load. However, this composition did not coincide with fictive temperature-independence of hardness or density.