Showing papers in "Journal of Non-crystalline Solids in 2011"
TL;DR: In this article, high resolution Na 1s, O 1s and Si 2p core level XPS spectra of six Na2O-SiO2 glasses were collected using the Kratos Ultra Axis instrument with its unique charge compensation system.
Abstract: High resolution Na 1s, O 1s and Si 2p core level XPS spectra of six Na2O–SiO2 glasses ranging in composition from 100 to 45 mol % SiO2 have been collected using the Kratos Ultra Axis instrument with its unique charge compensation system. The O 1s spectra for the glasses are well resolved so that bridging oxygen (BO, Si–O–Si) and non-bridging oxygen (NBO, Na–O–Si) signals can be accurately fitted and quantified without resorting to constraints or assumptions. The same samples were analysed by 29Si MAS NMR to obtain Q-species abundances from which BO and NBO proportions were calculated. Similar BO:NBO ratios were obtained by both methods over the entire compositional range studied. They are also consistent with most previous XPS and NMR results for glasses containing more than ~ 65 mol % SiO2. Our XPS and NMR experimental results, however, differ somewhat from previously published XPS and NMR results for glasses containing less than about 65 mol % SiO2. Na is mobile in the X-ray beam and mobility causes BO:NBO ratios to increase with time of exposure. Na mobility here has been circumvented to yield reliable BO:NBO ratios of the glasses. The ratios are lower than previously reported in XPS studies and are similar to ratios obtained from our 29Si MAS NMR results on the same glasses. The XPS and 29Si MAS NMR results also indicate the presence of a third oxygen species in sodic glasses. As has been proposed for CaSiO3 glass and for sodic and potassic glasses containing La, we suggest that O2− is present in sodic glasses at small concentrations. The O2− content correlates with increased soda content and may be associated with, and instrumental in development of, three dimensional percolation channels in the glasses. The XPS O 1s line width of the BO peak is broader than the NBO peak, indicating more than one contribution to the BO peak. As observed in crystalline Na metasilicate and Na disilicate, BO of Na-silicate glasses may be of two types, one arising from BO bridging two Si atoms, and the second BO signal arising from BO bonded not only to two Si atoms but also to Na.
220 citations
TL;DR: Geopolymer-type coatings prepared by using an industrially available sodium silicate solution (SiO2:Na2O = 3.1) and metakaolin were applied to steel substrates as mentioned in this paper.
Abstract: Geopolymer-type coatings prepared by using an industrially available sodium silicate solution (SiO2:Na2O = 3.1) and metakaolin were applied to steel substrates. The coatings exhibited excellent adhesion to steel substrates achieving greater than 3.5 MPa tensile stress. Dissolution of the coating in water after 72 h of static testing varied between 12.8 and 34.5 wt.% depending on the water content of initial formulations. Coating formulations showed up to 3% thermal expansion after heating to 800 °C. Coatings maintained high structural integrity with steel substrates when subjected to a heat treatment by a gas torch and formulations calcined at 1000 °C for 1 h showed an X-ray amorphous structure.
193 citations
TL;DR: In this paper, the chitosan-PVA-NH 4 I electrolytes were analyzed using Fourier transform infrared (FTIR) spectroscopy in order to determine the interaction between salt and the polymer blend hosts.
Abstract: The (chitosan–PVA)–NH 4 I electrolytes have been prepared by the solution casting method. The prepared electrolytes are analyzed using Fourier transform infrared (FTIR) spectroscopy in order to determine the interaction between salt and the polymer blend hosts which can be deduced from the band shifting. From infrared spectra, shifts are observed at the amine, carboxamide, carbonyl and hydroxyl bands of chitosan and PVA. These shifts indicate that complexation has occurred. The crystallinity/amorphousness of the blended electrolytes has been examined by X-ray diffraction (XRD). XRD pattern shows that the crystallinity of chitosan–NH 4 I electrolyte increases with PVA concentration. Impedance of the electrolytes has been measured using electrochemical impedance spectroscopy (EIS) over the frequency range from 50 Hz to 1 MHz. The highest conducting sample 55 wt.% (chitosan–PVA)–45 wt.% NH 4 I has conductivity of 1.77 × 10 − 6 S cm − 1 . The chitosan:PVA ratio is 1:1. This is higher than the conductivity for the unblended electrolyte 55 wt.% chitosan–45 wt.% NH 4 I which is 3.73 × 10 − 7 S cm − 1 . From ln τ versus 10 3 / T plot, the activation energy for relaxation process is 0.87 eV. This is different from activation energy for dc conductivity which is 0.38 eV. Ion conduction is by hopping.
183 citations
TL;DR: In this article, the authors reviewed the various arguments and models which have been proposed in this context over the last decade and identified the major open questions, and concluded that the optical bandwidth which is provided by Bi-doped glasses and crystals cannot be achieved by any rare earth (RE) based amplifier, or by the combination of multiple rare-earth (RE)-doped devices.
Abstract: Ever since the discovery of ultra-broadband near-infrared (NIR) photoluminescence (PL) from Bi-doped silicate glass, this class of materials and corresponding devices have experienced rapid progress. This is mainly driven by the suggested use in broadband optical amplifiers and novel lasers for future telecommunication networks. Currently, it appears that the optical bandwidth which is provided by Bi-doped glasses and crystals cannot be achieved by any rare-earth (RE) based amplifier, or by the combination of multiple RE-doped devices. However, the nature of the optically active NIR emission centers remains highly debated. The present paper critically reviews the various arguments and models which have been proposed in this context over the last decade. From the overall conclusions, the major open questions are identified.
177 citations
TL;DR: In this article, the authors used the split network model to predict apatite formation in bioactive glasses and showed that the bioactivity enhances monotonically for increasing phosphorus content of the glass.
Abstract: Bioactive glasses (BG) are used as bone substitutes and re-mineralising additives in toothpastes. They work by precipitating apatite on their surface, and the network connectivity (NC) and split network models can be used to predict their bioactivity, i.e. their ability to form apatite. While NC predicts glass degradation and has been used successfully to predict the bioactivity of BG, it does not take into account their phosphate content. Our experimental data confirm predictions using the split network model by Eden [Journal of Non-Crystalline Solids 357 (2011) 1595–1602], that “as long as P remains predominantly as Q P 0 tetrahedra and the average silicate network-polymerisation is ‘favourable’, the bioactivity enhances monotonically for increasing phosphorus content of the BG”. Results show that phosphate plays a key role in bioactivity and apatite formation of BG. This can be explained by the fact that phosphorus does not form part of the silicate network, but instead forms a separate orthophosphate phase. However, NC and split network models are still useful approaches for predicting BG bioactivity and apatite formation, if care is exercised when applying the models to glasses that contain more components than simple SiO 2 –P 2 O 5 –CaO–Na 2 O systems.
150 citations
TL;DR: In this article, a corn starch-lithium hexafluorophosphate (LiPF 6 ) based biopolymer electrolytes were prepared by solution casting technique.
Abstract: Biodegradable corn starch–lithium hexafluorophosphate (LiPF 6 ) based biopolymer electrolytes were prepared by solution casting technique. Ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate (BmImPF 6 ) was doped into the polymer matrix. Upon addition of 50 wt.% BmImPF 6 , the maximum ionic conductivity of (1.47 ± 0.02) × 10 − 4 Scm − 1 was achieved due to its higher amorphous region. This result had been further proven in ATR-FTIR study. Frequency dependence of conductivity and dielectric studies reveal the occurrence of polarization at the electrolyte–electrode interface and thus form the electrical double layer, asserting the non-Debye characteristic of polymer electrolytes. This result is in good agreement with dielectric loss tangent study. Based on the changes in shift, changes in intensity, changes in shape and existence of some new peaks, attenuated total reflectance-Fourier Transform Infrared (ATR-FTIR) divulged the complexation between corn starch, LiPF 6 and BmImPF 6 , as shown in the spectra.
145 citations
TL;DR: In this paper, the formation of a series of high mixing entropy bulk metallic glasses based on multiple major elements, which have unique characteristics of excellent glass-forming ability and mechanical properties compared with conventional BMGs, is reported.
Abstract: Bulk metallic glasses (BMGs) are usually based on a single principal element such as Zr, Cu, Mg and Fe. In this work, we report the formation of a series of high mixing entropy BMGs based on multiple major elements, which have unique characteristics of excellent glass-forming ability and mechanical properties compared with conventional BMGs. The high mixing entropy BMGs based on multiple major elements might be of significance in scientific studies, potential applications, and providing a novel approach in search for new metallic glass-forming systems.
142 citations
TL;DR: In this article, the structure and morphology of the aerogels were investigated by TEM, XRD, FTIR and BET techniques, and the results confirmed that the as-prepared alumina aerogel possessed a network microstructure made up of pseudoboehmite fibers and a surface area of 690 m 2 /g.
Abstract: Alumina aerogels were prepared by a sol–gel method combined with the ethanol supercritical drying technique using aluminum tri-sec butoxide and nitric acid as the precursor and catalyzer respectively. This method affords high-surface-area alumina aerogel monoliths without the use of complexing agents. The structure and morphology of the aerogels were investigated by TEM, XRD, FTIR and BET techniques. The results confirmed that the as-prepared alumina aerogel possessed a network microstructure made up of pseudoboehmite fibers and a surface area of 690 m 2 /g. It was transformed to γ-Al 2 O 3 after heat treatment at 800 °C without a significant loss in surface area. DMA analysis and hotdisk thermal analysis were performed to characterize the mechanical and thermal properties of the samples. The results indicated that the alumina aerogel was robust and exhibited excellent thermal insulating properties. The elastic modulus was up to 11.4 MPa after drying, which is the one of the highest modulus of alumina aerogels ever reported. The thermal conductivities at 30 °C and 400 °C were 0.028 W/mK and 0.065 W/mK respectively.
137 citations
TL;DR: In this article, the authors review half a century of research on radiation-induced point defects in pure and doped glassy silica and its crystalline polymorph α quartz, placing emphasis on trapped-electron centers.
Abstract: This paper reviews half a century of research on radiation-induced point defects in pure and doped glassy silica and its crystalline polymorph α quartz, placing emphasis on trapped-electron centers because the vast majority of all presently known point defects in various forms of SiO2 are of the trapped-hole variety. The experimental technique most discussed here is electron spin resonance (ESR) because it provides the best means of identifying the point defects responsible for the otherwise difficult-to-attribute optical bands. It is emphasized that defects in α quartz have been unambiguously identified by exacting analyses of the angular dependencies of their ESR spectra in terms of the g matrix of the unpaired electron spin and the matrices of this spin's hyperfine interactions with non-zero-nuclear-spin 29Si and 17O nuclides in pure α quartz and/or with substitutional 27Al, 31P, or 73Ge in quartz crystals respectively doped with Al, P, or Ge. Many defects in pure and doped glassy silica can be unambiguously identified by noting the virtual identities of their spin Hamiltonian parameters with those of their far better characterized doppelgangers in α quartz. In fact, the Ge(1) trapped-electron center in irradiated Ge-doped silica glass is shown here to have a crystal-like nature(!), being virtually indistinguishable from the Ge(II) center in Ge-doped α quartz [R.J. McEachern, J.A. Weil, Phys. Rev. B 49 (1994) 6698]. Still, there are other defects occurring in glassy silica that are not found in quartz, and vice versa. Nevertheless, those defects in glasses without quartz analogues can be identified by analogies with chemically similar defects found in one or both polymorphs and/or by comparison with the vast literature of ESR of paramagnetic atoms and small molecules. Oxygen “pseudo vacancies” comprising trigonally coordinated borons paired with trigonally coordinated silicons were proposed to exist in unirradiated B2O3–3SiO2 glasses in order to account for observations of γ-ray-induced trapped-electron-type B- and Si-E′ centers [D.L. Griscom et al., J. Appl. Phys. 47 (1976) 960]. Analogous Al-E′ trapped-electron centers have been elucidated in silica glasses with Al impurities [K.L. Brower, Phys. Rev. B 20 (1979) 1799]). And it has been proposed [D.L. Griscom et al., J. Appl. Phys. 47 (1976) 960] that trapping of a second electron on such oxygen pseudo vacancies accounts for the predominant ESR-silent trapped-electron centers in irradiated silica glasses containing B or Al. The present paper additionally attempts to divine the identities of some of the ESR-silent radiation-induced trapped-electron centers in silica glasses free of foreign network-forming cations. This quest led to the doorstep of the most famous ESR-silent defect of all, the twofold-coordinated silicon, which is found only in silica glasses (not in quartz) and is responsible for the UV/visible optical properties of the oxygen-deficiency center known as ODC(II). The oxygen-deficiency center called ODC(I) is associated with an absorption band at 7.6 eV and, though commonly believed to be a simple oxygen mono-vacancy, is clearly more complicated than that [e.g., A.N. Trukhin, J. Non-Cryst. Solids 352 (2006) 3002]. Certain well documented but persistently enigmatic ODC(I)↔ODC(II) “interconversions” [reviewed by L. Skuja, J. Non-Cryst. Solids 239 (1998) 16] have never been explained to universal satisfaction. An innovative combined ESR/thermo-stimulated-luminescence (TSL) study of a series of pure low-OH silica glasses with oxygen deficiencies of 0.000, ~ 0.015, and ~ 0.030 vol.% [A.N. Trukhin et al., J. Non-Cryst. Solids, 353 (2007) 1560] places new constraints on all future models for ODC(II). Taking this history into account, specific redefinitions of both ODC(I) and ODC(II) are proposed here. The present review also revisits a study of X-ray-induced point defects in an ultra-low-OH, high-chlorine but otherwise ultra-high-purity silica glass [D.L. Griscom, E.J. Friebele, Phys. Rev. B34 (1986) 7524], arguing that (1) most of the reported E′γ and E′δ centers were created via the mechanism of dissociative electron capture at chlorine-decorated oxygen vacancies, (2) the concomitantly created interstitial chloride ions serve as ESR-silent trapped-electron traps, (3) the ESR-detected “Cl0” centers arise from hole trapping on O3≡ Si–Cl units without detachment of the resulting Cl atom, and (4) those chlorine atoms that are detached by homolytic bond fission are ESR-silent. Finally, in chlorine-free, low-OH, high-purity silica glasses, up to 100% of the trapped-electron centers appear to be ESR silent and are tentatively ascribed to electron trapping in pairs below the mobility edge of the conduction band. In such cases, the sum of all trapped-hole centers has been found to decay exponentially with increasing isochronal annealing temperature in the range 100 to ~ 300 K [D.L. Griscom, Nucl. Inst. & Methods B46 (1990) 12]. Overall, this review consolidates a large amount of long-existing but often underappreciated knowledge bearing on the natures of trapped-electron centers in pure and doped glassy silica, proposes new models for some of these, and raises a number of questions that cannot be fully answered without future performance of new experiments and/or ab initio calculations.
134 citations
TL;DR: In this paper, the dynamic rheological behavior of geopolymers, inorganic materials synthesized by activation of an aluminosilicate source by an alkaline solution, is described.
Abstract: The dynamic rheological behavior of geopolymers, inorganic materials synthesized by activation of an aluminosilicate source by an alkaline solution, is described The pastes studied were mixtures of an activation solution (alkali + silica) and metakaolin The influence of the activation solution (NaOH vs KOH), the silica (Aerosil vs Tixosil), and the temperature on the evolution of the elastic modulus (G′) and viscous modulus (G″) over time were studied in the linear viscoelastic range The results show that the nature of the silica has little influence on the viscous and elastic moduli when the geopolymer is activated by KOH, and that the setting time is faster with sodium hydroxide and at higher temperatures regardless of the geopolymer In addition, during geopolymerization the stepwise variation of the modulus values indicates that the formation of the 3D network occurs in several steps Moreover, geopolymers activated by potassium hydroxide exhibit slower kinetics but the interactions between constituents are stronger, as the loss tangent (tanδ = G″/G′) is lower Finally, the maximum loss tangent, tanδ, was also used as a criterion to determine the temperature dependence of the geopolymers synthesized This criterion is a precursor of the transition to the glassy state The activation energies could thus be determined for the geopolymers synthesized with potassium hydroxide or sodium hydroxide
133 citations
TL;DR: In this paper, the behavior of bonding constraints with temperature is analyzed from an atomic scale approach (Molecular Dynamics, MD) combined with partial bond angle distributions (PBAD), which allows to have access to the second moments (standard deviations) of the distributions.
Abstract: The behaviour of bonding constraints with temperature is analyzed from an atomic scale approach (Molecular Dynamics, MD) combined with partial bond angle distributions (PBAD). The latter allows to have access to the second moments (standard deviations) of the distributions. Large (small) standard deviations correspond to large (small) angular excursions around a mean value, and are identified as broken (intact) bond-bending constraints. A similar procedure is used for bond-stretching constraints. Systems examined include glassy and liquid disilicate 2SiO2–Na2O (NS2). In the glass, MD constraint counting closely matches Maxwell enumeration of constraints using the octet binding (8-N) rule. Results show that the standard deviations of the partial bond angle distributions increase with temperature and suggest a softening of bond-bending constraints. A bimodal bonding oxygen distribution is obtained for T> Tg, and the fraction of thermally activated broken bond-bending constraints computed as a function of temperature. Overall, these results provide a microscopic rationale for extending constraint counting from chalcogenides to complex oxides, and also a numerical basis for recent functional forms of temperature-dependent constraints proposed from energy landscape approaches.
TL;DR: In this article, new parameter values are proposed for the empirical potentials used to describe SiO2-B2O3-Na2O alkali borosilicate glass systems.
Abstract: New parameter values are proposed for the empirical potentials used to describe SiO2–B2O3–Na2O alkali borosilicate glass systems. They are based on Buckingham potentials, but include dependence between the fitting parameters and the glass chemical composition to improve the representation of the complex environment around the boron atoms. In particular, the boron anomaly (observed when the [Na2O]/[B2O3] ratio varies) is correctly reproduced. The structural and mechanical properties of a wide range of glass compositions and of reedmergnerite crystals are correctly simulated: bond distances, mean angles, densities, elastic moduli. The deviations from the experimental values are small.
TL;DR: In this paper, the ionic liquid-based gel polymer electrolytes exhibit Arrhenius type temperature dependence of ionic conductivity and the amorphous behavior of these polymer electrolyte is also enhanced as shown in differential scanning calorimetry (DSC).
Abstract: 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.
TL;DR: In this paper, a micro-structural control on sintering is claimed as the rheological behavior of the viscous phase (i.e., the matrix containing both liquid phase and fine-grained crystals of quartz and mullite) is substantially different from that of the liquid phase only.
Abstract: High performance ceramic tiles (ISO 13006 Group BIa, water absorption < 05%) are composed of porcelain stoneware: a compact and light-colored material containing a large amount of vitreous phase, which governs sintering behavior and affects geometrical, mechanical and functional properties of finished products Ninety-three porcelain stoneware tiles were analyzed for bulk chemistry (XRF) and quantitative phase composition (XRD-Rietveld) in order to calculate both chemical composition and physical properties of the vitreous phase; their evolution during the sintering process was followed by lab simulation of industrial firing and quenching in the 1100–1200 °C range Porcelain stoneware tiles contain 40% to 75% wt of a vitreous phase having a quartz-feldspathic composition with an alumina excess coming from clay minerals breakdown Vitreous phase formation by feldspars melting is a fast phenomenon, starting from ~ 1050 °C, that is mostly accomplished before viscous flow begins densification, which goes on involving a slow-rate quartz dissolution Sintering kinetics is expected to be controlled by viscosity and surface tension of the liquid phase, which appear to depend essentially on the alumina content (hence on the mullite stability) along with the Na/K and Na/Ca ratios At any rate, a microstructural control on sintering is claimed as the rheological behavior of the viscous phase (ie the matrix containing both liquid phase and fine-grained crystals of quartz and mullite) is substantially different from that of the liquid phase only
TL;DR: In this paper, the effect of Y 2 O 3 on the structural and optical properties of glasses has been investigated using different characterization techniques and the results are discussed in light of non-bridging oxygens, optical basicity and heat-treatment of glasses.
Abstract: SiO 2 –BaO–ZnO–xB 2 O 3 –(10−x) Y 2 O 3 , (0 ≤ x ≤ 10) glasses are synthesized. The effect of Y 2 O 3 on the structural and optical properties of glasses has been investigated using different characterization techniques. The results are discussed in light of non-bridging oxygens (NBO), optical basicity and heat-treatment of glasses. The band gap has been calculated for as cast and heat-treated glasses. The band gap energy is found to decrease with the increasing content of Y 2 O 3 in the glasses and heat-treatment. The presence of the crystalline phase in the glass matrix showed remarkable effect on band gap which decreases to semiconducting range.
TL;DR: In this paper, the authors used the Middle Infrared (MIR) spectra of simple silicate glasses and their mathematical decomposition to identify the bands characteristic for ring systems as well as those originating from Si −O −, Si = O defects.
Abstract: The aim of the work is to determine the internal structure of simple silicate glasses based on structural studies. Due to the absence of the long-range order, the X-ray methods usually applied in the studies of crystalline materials are of low applicability in the investigations of glasses. Therefore, spectroscopic methods, such as Middle Infrared (MIR), which make it possible to ‘see’ the short- and the middle-range orders are extremely suitable in their studies. MIR investigations have shown that the glasses studied exhibit domain composition, which corresponds to the order of certain crystalline phases. Analysis of the MIR spectra of simple silicate glasses and their mathematical decomposition allowed us to identify the bands characteristic for ring systems as well as those originating from Si–O − , Si = O defects. Appearance of the bands characteristic for pseudolattice ring vibrations (740–600 cm − 1 ) in the MIR spectra of glasses is an evidence of the existence of over-tetrahedral order.
TL;DR: Isotropic soft core potentials with two characteristic length scales have been used since 40-years ago to describe systems with polymorphism as discussed by the authors, but the absence of directional bonding in these isotropic potentials makes them different from water.
Abstract: Isotropic soft-core potentials with two characteristic length scales have been used since 40 years ago to describe systems with polymorphism. In the recent years intense research is showing that these potentials also display polyamorphism and several anomalies, including structural, diffusion and density anomaly. These anomalies occur in a hierarchy that resembles the anomalies of water. However, the absence of directional bonding in these isotropic potentials makes them different from water. Other systems, such as colloidal suspensions, protein solutions or liquid metals, can be well described by this family of potentials, opening the possibility of studying the mechanism generating the polyamorphism and anomalies in these complex liquids.
TL;DR: In this paper, the authors present a split network analysis for assessing the average network polymerization and mean number of bridging oxygen (BO) atoms ( (N) over bar (F)(BO)) for eac...
Abstract: We present a strategy, referred to as “split network” analysis, for assessing the average network polymerization (r(F)) and mean number of bridging oxygen (BO) atoms ( (N) over bar (F)(BO)) for eac ...
TL;DR: In this article, the average activation energy of isothermal and non-isothermal bulk metallic glass calculated using Arrhenius equation is larger than the value calculated by the Kissinger method in nonisothermal conditions.
Abstract: Crystallization transformation kinetics in isothermal and non-isothermal (continuous heating) modes were investigated in Cu46Zr45Al7Y2 bulk metallic glass by differential scanning calorimetry (DSC). In isochronal heating process, activation energy for crystallization at different crystallized volume fraction is analyzed by Kissinger method. Average value for crystallization in Cu46Zr45Al7Y2 bulk metallic glass is 361 kJ/mol in isochronal process. Isothermal transformation kinetics was described by the Johnson–Mehl–Avrami (JMA) model. Avrami exponent n ranges from 2.4 to 2.8. The average value, around 2.5, indicates that crystallization mechanism is mainly three-dimensional diffusion-controlled. Activation energy is 484 kJ/mol in isothermal transformation for Cu46Zr45Al7Y2 bulk metallic glass. These different results were discussed using kinetic models. In addition, average activation energy of Cu46Zr45Al7Y2 bulk metallic glass calculated using Arrhenius equation is larger than the value calculated by the Kissinger method in non-isothermal conditions. The reason lies in the nucleation determinant in the non-isothermal mode, since crystallization begins at low temperature. Moreover, both nucleation and growth are involved with the same significance during isothermal crystallization. Therefore, the energy barrier in isothermal annealing mode is higher than that of isochronal conditions.
TL;DR: In this paper, a new domain of optical waveguide writing with record high refractive index contrast (0.022) is reported in fused silica by strong focusing of a 522 nm wavelength, 500 kHz repetition rate femtosecond laser with oil-immersion optics.
Abstract: A new domain of optical waveguide writing with record high refractive index contrast (0.022) is reported in fused silica by strong focusing of a 522 nm wavelength, 500 kHz repetition rate femtosecond laser with oil-immersion optics. The strongly confining waveguide supports a mode of only 7 μm mode field diameter at 1550 nm wavelength, opening the door for higher density integration in photonic circuits formed by femtosecond lasers. It is found that green and fundamental wavelengths have similar absorption in femtosecond laser waveguide writing in fused silica and that the advantage of the second harmonic is simply from an increased fluence through a smaller focal volume.
TL;DR: In this paper, a polymer blend electrolyte has been prepared with different concentrations of PVA and PVP by solution casting technique using DMSO as solvent and the increase in amorphous nature of the polymer electrolytes has been confirmed by XRD analysis.
Abstract: Several methods such as copolymerization, plasticization and blending etc., have been used to modulate the conductivity of polymer electrolytes. Polymer blending is one of the most important contemporary ways for the development of new polymeric materials and it is a useful technique for designing materials with a wide variety of properties. Polymer blend electrolyte has been prepared with different concentrations of PVA and PVP by solution casting technique using DMSO as solvent. The prepared films have been investigated by different techniques. The increase in amorphous nature of the polymer electrolytes has been confirmed by XRD analysis. The FTIR analysis reveals that the interchain hydrogen bonding within a PVA–PVP blends. The dielectric permittivity (e*) and modulus (M*) have been calculated from the ac impedance spectroscopy in the frequency range 42 Hz– 1 MHz and the temperature range 308–373 K. The maximum conductivity has been found to be 1.58 × 10 − 6 S cm − 1 at room temperature for 70PVA:30PVP concentration. The conductivity has been increased to 5.49 × 10 − 5 S cm − 1 when the temperature is increased to 373 K. The activation energy of all samples was calculated using the Arrhenius plot and it has been found to be 0.53 eV to 0.78 eV.
TL;DR: In this article, the concentration of luminescence centers of bismuth ions (Bi 2+ ions in visible region) decreased by the integration of BaO and also by increasing dopent concentration.
Abstract: Transparent glasses of the composition 10RO.20Bi 2 O 3 .(70 − x) B 2 O 3 .xCuO [R = Ca, Ba] with x = 0, 0.4, 0.8 (wt.%) were prepared via melt-quenching technique and characterized using X-ray powder diffraction. Spectroscopic measurements, viz., optical absorption, EPR, FTIR and photoluminescence (PL) were studied at room temperature. Analysis of the present investigations indicates that the concentration of luminescence centers of bismuth ions (Bi 2+ ions in visible region) decreased by the integration of BaO and also by increasing dopent concentration. It is also observed that addition of CuO decreases stability of the glass network in calcium series and strengthens in barium series.
TL;DR: In this paper, Fourier Transform Infrared (FTIR) spectroscopy has been used for quantitatively determining the presence of various different chemical bonds in gasses, liquids, solids, and on surfaces.
Abstract: Fourier Transform Infrared (FTIR) Spectroscopy has long been utilized as an analytical technique for qualitatively determining the presence of various different chemical bonds in gasses, liquids, solids, and on surfaces. Most recently, FTIR has been proven to be extremely useful for understanding the different types of bonding present in low dielectric constant “low-k” organosilicate materials. These low-k materials are predominantly utilized in the nanoelectronics industry as the interlayer dielectric material in advanced Cu interconnect structures. In this article, we utilize FTIR to perform a detailed analysis of the changes in chemical bonding that occur in Plasma Enhanced Chemically Vapor Deposited (PECVD) low-k a-SiC:H thin films. PECVD low-k a-SiC:H materials are equally important in advanced Cu interconnects and are utilized as both etch stop and Cu diffusion barrier layers. We specifically investigate the changes that occur in low-k a-SiC:H films as the dielectric constant and mass density of these films are decreased from > 7 to 3 respectively. We show that decreases in mass density and dielectric constant are accompanied by both an increase in terminal SiH x and CH x bonding and a decrease in Si C network bonding. At densities of 1.85 g/cm 3 , the concentration of terminal SiH x bonding peaks and subsequent hydrogen incorporation are achieved predominantly via terminal CH 3 groups. Low-k a-SiC:H films with k 3 can be achieved via incorporating larger organic phenyl groups but result in non-stoichiometric carbon rich films. Electron beam curing of these lower density a-SiC:H films results in volatilization of the phenyl groups leaving behind nanoporous regions and production of some C C C chain linkages in the network.
TL;DR: In this paper, the authors investigated the influence of hydroxide concentration as well as Si/Al in the model system of aluminosilicate gels and showed that a gel with a preferred Si-Al ratio wants to condense.
Abstract: 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.
TL;DR: In this paper, an in situ inorganic foam based on alkaline polysialate was achieved at a slightly elevated temperature by alkaline activation of raw minerals and industrial waste based on a geopolymer synthesis process.
Abstract: The synthesis of an in situ inorganic foam based on alkaline polysialate was achieved at a slightly elevated temperature by alkaline activation of raw minerals and industrial waste based on a geopolymer synthesis process. To understand the formation of the foam, the differences induced by the variations in the alkaline element (sodium or potassium) and water content were investigated throughout XRD, in situ FTIR-ATR, volume expansion and thermal analysis coupled with mass spectrometry. The amount of water is the determining parameter for volume expansion but does not interfere with the structure formation of foams. The comparison between geopolymers and foams has elucidated the formation of at least two amorphous networks in the case of sodium foam and three in the particular case of potassium as the alkaline element.
TL;DR: In this article, a local thermal quenching model is proposed to account for the effects of ballistic collisions in glasses, where the core of a displacement cascade is heated by the passage of a single projectile, then rapidly quenched, leading to a process that mimics a local heating.
Abstract: Molecular dynamics simulations of the ballistic effects arising from displacement cascades in glasses have been investigated in silica and in a SiO2-B2O3-Na2O glass. In both glasses the T-O-T′ angle (where T and T′ are network formers) diminishes, despite radiation causes opposite effects: while the ternary glass swells and silica becomes denser. We show that radiation-induced modifications of macroscopic glass properties result from structural change at medium/range, reflecting an increasing disorder and internal energy of the system. A local thermal quenching model is proposed to account for the effects of ballistic collisions. The core of a displacement cascade is heated by the passage of the projectile, then rapidly quenched, leading to a process that mimics a local thermal quenching. The observed changes in both the mechanical and structural properties of glasses eventually reach saturation at 2 1018 α/g as the accumulated energy increases. The passage of a single projectile is sufficient to reach the maximum degree of damage, confirming the hypothesis postulated in the swelling model proposed by J.A.C. Marples
TL;DR: In this paper, the effect of gamma irradiation on the IR spectra is correlated with the intrinsic and extrinsic defects within the various V 2 O 5 -doped phosphate glass systems.
Abstract: Radiation-induced defects generated by successive gamma irradiation have been investigated in V 2 O 5 -doped phosphate glasses of three basic compositions, namely, sodium metaphosphate, lead metaphosphate and zinc metaphosphate. Glasses were prepared from chemically pure materials. Melting was carried at 900°–1100 °C for 1 h and with several stirrings of the melt to achieve homogeneity. The glassy samples were annealed at 200°–250 °C and left to cool to room temperature at a rate of 20 °C/h. Polished samples from undoped and V-doped samples of equal thickness. ~ 2 mm were measured in a double beam UV–visible spectrophotometer at 200–1000 nm before and after gamma irradiation. Induced defects were analyzed for these three phosphate glass systems. Infrared absorption spectra were measured for the prepared undoped and V-doped samples by the KBr technique before irradiation and after being subjected to a high dose of 7 M Rads (7 × 10 4 Gy). The cumulative effects of gamma irradiation on the UV–visible spectra are correlated with the intrinsic and extrinsic defects within the various three glasses. Some shielding behavior for the various glasses towards successive gamma irradiation are observed and realized in relation to the different partner anions studied. The effect of gamma irradiation on IR spectra indicates the persistence of the main characteristic bands due to phosphate network and the minor changes are correlated with the possible changes in the bond lengths and/or bond angles of the building units during the irradiation process. The effect of V 2 O 5 on the IR spectra is correlated with the depolymerization effect of the glass network.
TL;DR: In this paper, the authors show that fluoride was lost as hydrofluoric acid after reaction with atmospheric water during melting, but nominal and analysed CaF2 contents in the glass correlated linearly.
Abstract: Melt-derived bioactive glasses (SiO2–P2O5–CaO–Na2O–CaF2; CaF2 0 to 17.76 mol%) lost fluoride during melting, but nominal and analysed CaF2 contents in the glass correlated linearly. Analysed CaO contents were increased, showing that fluoride was lost as hydrofluoric acid after reaction with atmospheric water during melting. Weight loss on ignition reduced linearly with increasing CaF2, suggesting that CaF2 impedes absorption of atmospheric water. pH changes in tris buffer solution showed that pH is controlled by the silicate matrix (via ion exchange processes), and fluoride release contributes less to the overall pH. Glasses formed apatite in tris buffer; phosphate concentration of the glass was the limiting factor, resulting in fluorite formation for increasing fluoride content in the glass and calcite formation for the fluoride-free composition. These results allow for tailoring of novel fluoride-containing bioactive glasses to address specific needs, particularly in dentistry and for remineralising toothpastes.
TL;DR: In this paper, a SiO 2 -based bioactive glass with high Na 2 O content was used to investigate the real influence of the synthesis route (sol-gel versus melting) on the glass intrinsic properties and then, later, on glass behavior and particularly on bioactivity.
Abstract: New sol–gel experimental conditions were tested to prepare a new SiO 2 -based bioactive glass with high Na 2 O content. The aim of this work is to investigate the real influence of the synthesis route (sol–gel versus melting) on the glass intrinsic properties and then, later, on the glass behavior and particularly on bioactivity. The obtained glass and its melt derived counterpart were characterized from structural and morphological (porosity, specific surface area) point of view. It could be noticed that the synthesis mode has no significant influence on glass structure. Conversely, the synthesis mode greatly influences the glass texture. The sol–gel derived glass exhibits a greatly higher specific surface area and pore volume than melt derived glass. This parameter may be a key factor of glass bioactivity.
TL;DR: In this paper, a three-dimensional multi-scale microstructure model was developed to investigate the effects of non-ideal structures and high temperatures on the insulation performance of aeogel-based composite materials.
Abstract: The multi-scale, temperature related structural characteristics of aerogel-based composite insulation materials that contain nano-scale aerogels, as well as micron-scale fibers, opacifiers and cracks were evaluated using various instruments for 300 to 1423 K. The structural tests were used to develop a three-dimensional multi-scale microstructure model to investigate the effects of non-ideal structures and high temperatures on the insulation performance of aeogel-based composite materials. The predictions agree well with experimental with literature. The model, thus provides theoretic guidelines for manufacturing with optimal parameters, such as the type, loading, and distribution of fibers and opacifiers. The structural analysis shows that the insulation performance of the composite materials degrades significantly with the deformation of the pore structure at high temperatures conditions.