Showing papers in "Journal of Non-crystalline Solids in 2019"

Physical, structural, optical and gamma radiation shielding properties of borate glasses containing heavy metals (Bi2O3/MoO3)

Abstract: In an attempt to develop a novel gamma radiation shielding glasses, we prepared borate glasses contains a high concentration of heavy metals like Bi2O3 and MoO3 with the composition of 20MoO3-(80-x)B2O3-xBi2O3, were x varied from 30 to 45 mol% using tradition melt-quenching-annealing method. A structural investigation such as XRD and FTIR were characterized to confirm the amorphous structure of the prepared glasses and prove the availability of all chemicals included in these compositions after the melting process. Furthermore, optical studies on these glasses were investigated to prove the transparency of the fabricated glasses. Attenuation characteristics (mass attenuation coefficients, radiation protection efficiency, and half value layer) of the prepared glasses with respect to gamma photons (in the range of 0.356–1.33 MeV) were investigated. The mass attenuation coefficients and radiation protection efficiency results increased with increasing the Bi2O3 content and this improves the attenuation ability for the prepared samples. The radiation protection efficiency also revealed that the glasses have the maximum capability in attenuation gamma photons at 0.356 MeV. The mean free path with the prepared glasses was compared with some concretes which is reported in the literature and with some commercial glasses to assess their potential for use in gamma radiation shielding products.

Reducing crystallinity on thin film based CMC/PVA hybrid polymer for application as a host in polymer electrolytes

Abstract: The carboxymethyl cellulose and polyvinyl alcohol (CMC/PVA) based hybrid polymer (HPe) system with different ratio of composition have been prepared via solution casting. The features of interaction between CMC and PVA were investigated using X-ray diffraction (XRD), and infrared (IR) spectroscopy to disclose the reduction of crystallinity of the HPe system. Morphological properties observed by Scanning electron microscopy (SEM) confirmed the homogeneity of the HPe system. Differential scanning calorimetry (DSC) result explains the miscibility of the HPe system which was confirmed by means of variations in the glass transition temperature (Tg). Two degradation mechanisms were revealed by thermogravimetric analysis (TGA) in the HPe system attributed to the decarboxylation in CMC and degradation of bond scission in PVA backbone. The blend of 80:20 compositions of CMC/PVA HPe system was found to be the optimum ratio with an increase in conductivity of CMC/PVA by one magnitude order from 10−7 to 10−6 S/cm with the lowest in crystallinity.

Influence of bismuth oxide on gamma radiation shielding properties of boro-tellurite glass

Abstract: Boro-tellurite glasses have recently been attracting the attention of several researchers as a tremendous optical device and shielding material. In this work, boro-tellurite glasses with bismuth oxide (Bi2O3) have been synthesized by melt quenching technique. The structural and shielding property changes after adding of bismuth oxide in boro-tellurite glass were studied using Fourier Transform Infrared (FTIR) and Lead Equivalent Thickness measurement (LET), respectively. The results show that the bismuth oxide increases glass density, changes the glass structure, and increases the radiation shielding properties. Changes in the glass structure are due to atomic rearrangements and formation of non-bridging oxygen (NBO). The density of boro-tellurite glass system increased up to 97% when Bi2O3 content increased, which is due to the high molecular weight of Bi2O3 and the increasing number of NBO atoms in the glass structure. In addition, the mass attenuation coefficient of the glass system increases as Bi2O3 concentration increases and the half value layer and mean free path show that present glass better than some standard concretes and commercial radiation shielding glasses. Current results demonstrated the advantages of bismuth-boro-tellurite glass as a new candidate of gamma radiation shielding material in selected energy range.

Physical, structural, optical investigation and shielding featuresof tungsten bismuth tellurite based glasses

Abstract: Ternary tellurite glasses with composition 20WO3-xBi2O3- (80-x) TeO2 (x = 10, 15, 20 and 25 mol%) were synthesized by conventional quenching method from pure oxides. Amorphous state of the prepared samples was checked by X-ray diffraction. The variation in the density values (ρ) and molar volume (Vm) oxygen packing density (OPD) and ion concentration (N) showed the influence of Bi2O3 on glass structure. The various optical properties such as optical band gap (Eopt), refractive index (n), molar refraction (Rm), cationic polarizability (αm) and optical basicity (∧) were calculated and are discussed in terms of structural changes. These optical properties have been observed to vary with Bi2O3 concentration. FTIR investigation shows the glasses contain TeO4, BiO6 and WO4 basic structural units. Additionally, different shielding parameters such as effective atomic number, radiation protection efficiency, mean free path, half value layer and exposure buildup factor were calculated in order to effectively use these glasses simultaneously in optical-based devices with high radiation shielding performance. The results showed that the mass attenuation coefficient and effective atomic number values of WTBi4 glass sample which contains the higher Bi2O3 concentration were the maximum at the selected energies. The mean free path of the prepared glasses was compared to different glasses, while the half value layer of the prepared glasses was compared to different types of concretes.

Structural, optical and thermal properties of nickel doped bismuth borate glasses

Abstract: Nickel doped Bismuth Borate glasses with composition (70B2O3-(30-x)Bi2O3-xNiO) where x = 0,0.5,1.0,1.5,2.0 (wt%) have been synthesized by conventional melt quenching technique. X-Ray Diffractograms have confirmed the amorphous nature of the prepared glasses. The calculated physical parameters such as density, molar volume, average boron‑boron separation, ion concentration and inter ionic distance provided the information about the structural stability of glass samples. DTA and OPD confirmed the decrease in glass transition temperature (Tg) with increase in Ni content. The FTIR and Raman studies clearly revealed that the glass network mainly comprises of [BiO3], [BiO6], [BO3] and [BO4] units. It is also observed that the introduction of dopant (Ni) and modifier (Bi) leads to the conversion of [BO3] trigonal units into the [BO4] tetragonal units due to the increase in non-bridging oxygen atoms which results in the increase of degree of disorder in the glass network. The optical absorption measurements (UV) carried out for well polished glass samples show a decrease in optical band gap with the increase in Ni doping. This observation was further supported by the urbach energy calculations and metallization criterion of the prepared glass samples. The electronegativity and electronic polarizability values revealed the ionic character of glass samples.

Effect of Fe nanoparticles on the structure and optical properties of polyvinyl alcohol nanocomposite films

Abstract: Polyvinyl alcohol (PVA) nanocomposite films embedded with iron (Fe) nanoparticles were prepared via the solution cast technique. The effect of Fe nanoparticles on the structural and optical properties of PVA nanocomposite films were investigated using X-ray diffraction, a scanning electron microscope, and UV–Vis spectroscopy. The size of the Fe nanoparticles was calculated using the Debye–Scherrer equation, and it was found that there was an increase in nanoparticle size after dispersion in the polymer matrix due to aggregation. Optical parameters such as optical band gap, Urbach energy, refractive index and extinction coefficient were investigated. The transmittance of a pure PVA film decreases from 82% to 18% after 3 wt% Fe nanoparticle dispersion in a polymer matrix. The direct optical band gap was found to decrease whereas Urbach energy was found to increase with the increase in Fe nanoparticle concentration. In addition, the refractive index and extinction coefficient of polymer nanocomposite films were found to increase compared to those made of pure PVA. Also, the optical dielectric and optical conductivity were observed to increase with an increase in Fe nanoparticle concentration.

Surface modified sodium silicate based superhydrophobic silica aerogels prepared via ambient pressure drying process

Abstract: The silica aerogel was synthesized by simple and cost-effective sol-gel process under ambient pressure drying. The wet gel was modified by using trimethylchlorosilane (TMCS) as silylating agent. The prepared aerogel was characterized by X-ray diffractometer (XRD), thermogravimetric and differential thermal analyzer (TG-DTA), Fourier transform infrared spectrometer (FT-IR), Brunauer-Emmett-Teller (BET) analyzer, field emission scanning electron microscope (FE-SEM) and Ultraviolet-Visible (UV–Vis) spectrophotometer for structural, thermal, functional, surface, morphological and optical properties. The presence of hump in X-ray diffraction pattern revealed the amorphous nature of prepared silica aerogel. Thermal stability of silica aerogel investigated by TG-DTA show a hydrophobic nature up to 478 °C. FE-SEM images confirmed the porous nature of silica aerogel. The surface area and pore radius measured by BET analyzer disclosed as 792.308 m2/g and 5.779 nm respectively while the total pore volume is 2.289 cc/g. Superhydrophobic nature of silica aerogel sample was affirmed by contact angle measurements. The energy band gap calculated from UV–Vis spectra was found to be 4.25 eV confirming the insulating nature of prepared silica aerogel. The resulting silica aerogel possesses high thermal stability, Superhydrophobicity and large specific surface area which can be useful in various applications such as catalysis, coating materials, oil spill cleanup processes and insulating materials.

Machine learning for glass science and engineering: A review

Abstract: The design of new glasses is often plagued by poorly efficient Edisonian “trial-and-error” discovery approaches. As an alternative route, the Materials Genome Initiative has largely popularized new approaches relying on artificial intelligence and machine learning for accelerating the discovery and optimization of novel, advanced materials. Here, we review some recent progress in adopting machine learning to accelerate the design of new glasses with tailored properties.

Structural, UV and shielding properties of ZBPC glasses

Abstract: In the present research work, six glasses with chemical mode (10ZnO-40 B2O3-(50-x) Pb3O4-xCuO), where 0≤ × ≤7.5 wt% have been synthesized by solid state reaction method. X-ray diffraction (XRD) measurements have been achieved to check the amorphous nature of these glasses. UV-visible measurements were performed, the optical energy band gap ( E gap ASF ) and refractive index (n) were determined using the absorption spectrum fitting method (ASF). E gap ASF values were in the range of 2.54-1.24 eV, while (n) in the range of 2.53 to 1.17. Densities (ρ) of the synthesized glasses were measured, and molar volume (Mv) were evaluated. The radiation shielding features like; mass attenuation coefficients (μ/ρ), effective atomic number (Zeff), half value layer (HVL), mean free path (MFP) for the glasses were evaluated using XCOM and MCNPX general purpose Monte Carlo code in the energy range 0.015–10 MeV and compared with some different types of glasses. Results reflected that the (μ/ρ) of the studied glasses decreased with the ratio of CuO increased. ZBPC0 glass has the highest Zeff whereas ZBPC7.5 glass has the lowest. The glass ZBPC7.5 has the highest HVL and MFP values while ZBPC0 glass has the lowest. One can conclude that ZBPC0 has superior gamma radiation shielding effectiveness among the synthesized glasses.

Alkaline fused phosphate mine tailings for geopolymer mortar synthesis: Thermal stability, mechanical and microstructural properties

Abstract: The present study investigates the efficiency of alkaline fusion method to enhance the geopolymeric reactivity of phosphate mine tailings. The effect of sodium hydroxide content and fusion temperature on the mineralogical composition of the fused phosphate sludge was assessed by XRD measurement. The microstructure as well as the mechanical behavior of the prepared geopolymer mortars were investigated using compressive strength test and EDS/SEM analysis. Furthermore, the thermal stability of samples was studied by measuring the mechanical properties after exposure to several cycles of heat treatment at different elevated temperatures (350, 500, 650 and 800 °C). The obtained results showed that the structure of phosphate sludge underwent a significant variation after fusion. Alkali thermal treatment led mainly to the decomposition of illite, palygorskite and dolomite, and the formation of Na-rich crystalline phases. NaOH content as well as temperature of fusion has been proved to be essential factors controlling the transformations of the material structure and hence the development of the geopolymer strength. The optimum conditions of fusion were set at 10 wt% of NaOH and a temperature of 550 °C, providing geopolymer mortars with high compressive strength (40 MPa).

The influence of TiO2 on structural, physical and optical properties of B2O3 –TeO2 – Na2O – CaO glasses

Abstract: B2O3 –TeO2 – Na2O – CaO glasses doped with small concentrations of TiO2, from 0.5 to 3 mol%, were prepared by traditional technique. The changes in the structure of studied glasses were observed by using FTIR technique and it was found that glasses containing different structure units of borate and tellurite groups. The change in the many optical and physical parameters such as density, molar volume, band gap, optical backing density, refractive index and others were studied. The density was found to increase with the addition of TiO2 till 1 mol% then begin to decrease and the opposite trend was observed to molar volume. Energy band gap was measured by two techniques ASF and Tauc's models and their values was very close to each other and to decrease with the addition of TiO2. The refractive index was found to increase with the addition of TiO2 from 2.4 for base glass to 2.59 for glass containing 3 mol% of TiO2. The ionic concentration of Ti, the interionic distance ri, field strength F, dielectric constant, molar refraction index rm, molar polarizability, average electronegativity, and the reflection loss (rL) were rise with increasing TiO2 content. On the other hand, there are some properties such as transmission coefficient (T) was found to decrease with increasing the concentration of Ti ions.

Physical, mechanical and gamma-ray shielding properties of highly transparent ZnO-MoO3-TeO2 glasses

Abstract: Physical, mechanical and radiation shielding properties of ZnO-MoO3-TeO2 glasses were studied. Density, molar volume, oxygen molar volume, oxygen packing density were evaluated for the interpretation of physical properties. Mechanical properties were determined through Vickers hardness measurements. The shielding estimation was accomplished by studying linear attenuation coefficient (LACμ), mass attenuation coefficient (MAC), effective atomic number (Zeff), effective electron density (Neff), mean free path (mfp), exposure buildup factor (EBF) and energy absorption buildup factor (EABF). The glasses were irradiated by 133Ba radioactive source emitting gamma rays in the range of 79.61 keV to 383.80 keV to determine LACs and MACs. mfp values were calculated for present glasses and compared with various concretes and a commercial window glass in energy region 81–384 keV. The glass structure became stronger and mechanical properties showed an increment with increasing MoO3 content. Synthesized glasses have lower mfp values indicating better shielding properties than concretes and window glass.

The impact of Er3+ ions on the spectroscopic scrutiny of Bismuth bariumtelluroborate glasses for display devices and 1.53 μm amplification

Abstract: Er3+ incorporated Bismuth bariumtelluroborate [BTBxEr] glasses were synthesized using the composition, 20TeO2 + (30–x)B2O3 + 30BaO + 20Bi2O3 + xEr2O3, following the traditional melt quenching method. The bonding parameters were calculated using absorption spectra to analyze the dopant-host bonding nature. Ωλ (λ = 2,4,6) intensity parameters are determined from the oscillator strengths employing Judd-Ofelt (JO) theory for the estimation of the radiative parameters. Broad emission transition 4I13/2 → 4I15/2 were observed around 1530 nm, under 980 nm excitation which exhibits outstanding increased intensity with the Er3+ concentration of till it reaches 0.5 wt%. CIE chromaticity coordinates, CCT and Duv have determined to analyze the color of emission and the absorption quality of the glasses. Lifetime for the 4I13/2 excited (at 980 nm excitation) and 4S3/2 (at 488 nm excitation) levels of Er3+ ions were measured using decay measurements. Of all investigations, BTBEr glasses could be an apt material for the fabrication optical amplifiers, display devices and green laser applications.

Predicting Young's modulus of oxide glasses with sparse datasets using machine learning

Abstract: Machine learning (ML) methods are becoming popular tools for predicting and designing novel materials. In particular, neural network (NN) is a promising ML method, which can be used to identify hidden trends in the data. However, these methods rely on a large dataset and often exhibit overfitting when used with a sparse dataset. Further, assessing the uncertainty in predictions for a new dataset or an extrapolation of the present dataset is challenging. Herein, using Gaussian process regression (GPR), we predict Young's modulus for silicate glasses having a sparse dataset. We show that GPR significantly outperforms NN for the sparse dataset while ensuring no overfitting. Further, thanks to the nonparametric nature, GPR provides quantitative bounds for the reliability of predictions while extrapolating. Overall, GPR presents an advanced ML methodology for accelerating the development of novel functional materials such as glasses.

Improved heat insulation and mechanical properties of silica aerogel/glass fiber composite by impregnating silica gel

Abstract: In this paper, a kind of silica gel was applied to improve the mechanical properties of silica aerogel/glass fiber composite without compromising its thermal conductivity The composite was prepared by acid-base catalyzed tetraethylorthosilicate sol-gel followed by supercritical CO2 drying, in which the silica gel was impregnated The effects of the silica gel on the thermal conductivity and strength of the composite were investigated The results indicated that the composite possessed not only ultra-low thermal conductivity of 00179 W·(m·K)−1, but also excellent mechanical strain and low bulk density of 0246 g/cm3, and was dust-free It was demonstrated that the impregnated silica gel filled in the gap between the glass fibers and anchored the silica aerogel on the glass fiber tightly via the –Si-O-Si- network, which not only prevented the heat transfer but also trapped and protected the silica aerogel from collapsing This new approach shed light on solving the big issue of the silica aerogel in practical application due to its brittle and dust-drop

Precipitation of silver nanoparticles in silicate glasses via Nd:YAG nanosecond laser and its characterization

Abstract: This work presents a new route to synthesis nanomaterials for nonlinear optical devices, Nd:YAG laser irradiation is considered as recent technique for precipitation of nanoparticles in glassy matrix. Precipitation of silver nanoparticles (AgNPs) in silicate glasses is achieved by Nd:YAG nanosecond laser irradiation to soda lime silicate glasses doped with silver nitrate (AgNO3) using melt annealing technique. The influences of different concentrations of AgNO3 on the optical and the structural characterization of the precipitated glasses were investigated using; XRD, FT-IR, UV–Vis, and HRTEM. An obvious change in color was observed inside the silicate glasses regions after laser irradiation, which was attributed to the growth of silver nanoparticles in the glass.XRD patterns indicate the presence of sharp diffraction peaks of AgNPs after laser irradiation due to precipitated AgNPs in silicate glasses. FT-IR spectra of the precipitated samples show a little change in intensity for the sample before and after the laser irradiation combined with the identification of a new band that approves the precipitated AgNPs. The optical absorption spectra confirm the formation of the precipitated AgNPs inside the silicate glasses by appearance of Surface Plasmon Resonance (SPR) and the intensity of the absorption peak increases with an increase of the silver nitrate concentration. TEM micrographs confirm the precipitation of silver within the samples after laser irradiation.

Gamma radiation shielding investigations for selected germanate glasses

Abstract: Radiation shielding characteristics of different germanate glasses with compositions of Nd doped Bi2O3–SiO2/GeO2–Nd2O3, Sm3+ doped B2O3–GeO2–Gd2O3, Tb3 doped GeO2–B2O3–SiO2–Ga2O3, TeO2–GeO2–Li2O and Na2O–GeO2–P2O5 glasses have been studied using XCOM program at several photon energies between 0.015 and 10 MeV. Dependencies of their photon attenuation properties with the photon energy and the composition have been investigated. The mass attenuation coefficient values and the effective atomic numbers for Nd doped Bi2O3–SiO2/GeO2–Nd2O3glasses are higher than those of the other samples. 69Bi2O3–30GeO2–1.0Nd2O3 has the highest mass attenuation coefficients among the selected samples. The Zeff results revealed that to increase the photon attenuation ability for the germanate glasses, high Z-elements (such as Bi, Te and Tb) in a suitable concentration must be included. The HVL results for the present germanate glasses suggested that the attenuation capacity of the gamma photons increases as the density of the sample increases, hence, the glass sample with high density must be considered for high attenuation ability. Also, the significant influence of modifier contents on the HVL values namely the attenuation ability has been noticed for Tb3 doped GeO2–B2O3–SiO2–Ga2O3 and TeO2–Li2O–GeO2 glasses. Moreover, the values of the mean free path for the selected samples have been compared with those of different radiation shielding glasses and concrete samples.

Toward clean cement technologies: A review on alkali-activated fly-ash cements incorporated with supplementary materials

Abstract: The consistent development of the waste-minimisation and recycling-oriented technologies in the most resource- and energy-intensive industries is crucial for sustainable development. Chemical activation based on a non-fired or low-temperature approach for the production of binders from glassy aluminosilicates, including a wide range of wastes and by-products from different industries, is an intensively developing and promising clean technology that finds application in construction and building materials, management of hazardous and nuclear waste, etc. Blended binders are designed using a mixture of mineral materials as a tool, through the regulation of composition and structure, to obtain materials with controlled performance. The resulting materials in turn improve engineering performance and aid the valorisation of different types of wastes and by-products. This is one of the main trends in the development of the modern cement industry, including the alkali activation technology. Coal fly ash is one of the large-tonnage wastes that is effectively converted by alkali activation in binders and compatible with many mineral supplementary materials. This paper reviews (i) the supplementary mineral materials of natural and waste origin from different industries for alkali activated fly ash (class F) cements (AAFA); (ii) the composition, structure, and properties formation process of AAFA incorporated with blending and modifying materials, and (iii) the feasibility for improvement of the structures and properties of mixed AAFA.

Investigation ofthe gamma ray shielding parameters of (100-x)[0.5Li2O–0.1B2O3–0.4P2O5]-xTeO2 glasses using Geant4 and FLUKA codes

Abstract: In the present work, the radiation shielding proeprties of lithium borophosphtellurite glass system with the composition of (100-x) [0.5Li2O-0.1B2O3–0.4P2O5]-xTeO2 (x = 0, 10, 20, 30 and 40 mol%) were reported. The mass attenuation coefficient (μ/ρ) of the selected glass system (LiBPTe0, LiBPTe10, LiBPTe20, LiBPTe30 and LiBPTe40) was calculated at 356 keV, 662 keV, 1173 keV and 1330 keV photon energies by using Geant4 and FLUKA codes and the results were compared to the values obtained theoretically using WinXcom software. The correlation theory has been used to calculate the correlation coefficients (R2) between the results from WinXcom and the both simulations codes (Geant4 and FLUKA) for each sample. Moreover, some other radiation shielding parameters such as effective atomic number, photon transmission, mean free path and half value layer were calculated. The gamma photon transmission results showed that the transmission values of the 356 keV photons are lower than those of energies 662, 1173 and 1330 keV. At 356 keV, the transmission value for LiBPTe0 (at 6 cm thickness) is found to be 0.245 while at the same energy and thickness the transmission value is 0.088 for LiBPTe40. Out of all the glasses considered in present work, LiBPTe40 possesses the highest values of effective atomic number (Zeff). The Zeff values for the present glasses are 8.02, 9.55, 11.16, 12.85 and 14.64 for LiBPTe0, LiBPTe10, LiBPTe20, LiBPTe30 and LiBPTe40 respectively at 356 keV. The mass attenuation coefficient and effetive atomic number results showed that utilization 40% mol of TeO2 significantly improves the gamma ray shielding properties of the selected glass system. The shielding effectiveness of the selected samples was compared with other reference materials namely two radiation shielding glasses and four concretes used in different shielding purposes in terms of the mean free path (MFP) at 356 keV. The results revealed that the MFP of RS-253-G18 is lower than LiBPTe0sample. Moreover, the MFP of ordinary concrete is higher than the MFP of all glasses under examination, thus the investigated tellurite glasses have better attenuation features than the ordinary concrete.

Effect of curing temperature on the synthesis, structure and mechanical properties of phosphate-based geopolymers

Abstract: The purpose of this work was to study the effect of curing temperature on the synthesis, structure and mechanical properties of Phosphate-based geopolymers, using two curing temperatures for geopolymers preparation: room temperature and slightly elevated one (60 °C). The main techniques used to achieve this purpose are quasi-isothermal Differential Scanning Calorimetry measurements (DSC), atomic absorption measurements, compressive strength measurements, Fourier Transform Infrared spectroscopy (FTIR), X-ray powder Diffraction (XRD) and 29Si, 27Al and 31P magic angle spinning nuclear magnetic resonance (MAS-NMR). Experimental results showed that the increase of curing temperature activates the dealumination of metakaolin and accelerates the different geopolymeric steps. Moreover, for both considered curing temperatures, the obtained geopolymer presents an amorphous composite material composed of two geopolymeric networks: a first geopolymeric network based on Al-O-P units and another one based on Si-O-T units (with T = Si, Al and P). The only structural difference generated by the variation of curing temperature is in the quantity of the formed phases. In fact, the temperature elevation yields to a geopolymer structure richer in aluminum phosphate phases which enhances the material compressive strength (29.9 MPa).

Physical, structural and optical properties of Sm3+ doped lithium zinc alumino borate glasses

Abstract: Sm3+ doped lithium zinc alumino borate glasses with composition 15ZnF2–12Li2CO3–10BaO–8Al2O3–(55-x) B2O3–xSm2O3 where x=0.1, 0.3, 0.5, 0.7 and 1.1 mol% were prepared by conventional melt quenching technique Their optical, physical, structural, mechanical and luminescence properties are investigated. UV–Vis-NIR absorption spectra showed all possible transitions of samarium ion in this glass matrix. Band gap values for all the glass samples were above 3 eV confirming the insulating nature for the glass. Densities, assessed using the Archimedes rule, were observed to be increasing with increasing samarium concentration. Increase in molar volume with addition of samarium content indicated that the extension of glass network is on account of the increase of number of Non-Bridging Oxygens created by network modifier samarium ions. Scanning Electron Microscopy (SEM) image showed a smooth surface for the synthezied glass. X-Ray Diffraction (XRD) technique was employed to verify the amorphous nature of the glasses. A Makishima and Mackenzie theoretical model gave acceptable approximation of elasticity constants viz. Young's modulus, shear modulus, bulk modulus and Poisson's ratio. The high Vickers hardness values evaluated with mechanical loads of 50, 100, 300, 500, 1000 g force, proved the stability of the glasses. Emission spectra showed a prominent transition 4G5/2→6H7/2 at 598 nm excited with 6H5/2→4P3/2 transition at 401 nm. Luminescence quenching effect was observed beyond 0.3 mol% Sm2O3 addition. The chromaticity coordinates (x, y) clustered in the orange-red region, making these Sm3+ doped lithium zinc alumino borate glasses suitable candidate for applications in LEDs and solid-state lasers.

The effect of cryogenic thermal cycling on aging, rejuvenation, and mechanical properties of metallic glasses

Abstract: The structural relaxation, potential energy states, and mechanical properties of a model glass subjected to thermal cycling are investigated using molecular dynamics simulations. We study a non-additive binary mixture which is annealed with different cooling rates from the liquid phase to a low temperature well below the glass transition. The thermal treatment is applied by repeatedly heating and cooling the system at constant pressure, thus temporarily inducing internal stresses upon thermal expansion. We find that poorly annealed glasses are relocated to progressively lower levels of potential energy over consecutive cycles, whereas well annealed glasses can be rejuvenated at sufficiently large amplitudes of thermal cycling. Moreover, the lowest levels of potential energy after one hundred cycles are detected at a certain temperature amplitude for all cooling rates. The structural transition to different energy states is accompanied by collective nonaffine displacements of atoms that are organized into clusters, whose typical size becomes larger with increasing cooling rate or temperature amplitude. We show that the elastic modulus and the peak value of the stress overshoot exhibit distinct maxima at the cycling amplitude, which corresponds to the minimum of the potential energy. The simulation results indicate that the yielding peak as a function of the cycling amplitude for quickly annealed glasses represents a lower bound for the maximum stress in glasses prepared with lower cooling rates.

Composition – structure – property relationships in alkali aluminosilicate glasses: A combined experimental – computational approach towards designing functional glasses

Abstract: A set of 12 glass compositions with distinct structural features have been designed over a broad composition space in the per-alkaline region of the Na2O – Al2O3 – SiO2 ternary system. As expected from a per-alkaline system, aluminum has been found to be tetrahedrally coordinated in all the glasses using 27Al magic angle spinning – nuclear magnetic resonance (MAS-NMR) spectroscopy and from structure models generated using molecular dynamic (MD) simulations. The physical properties of glasses, for example, density, coefficient of thermal expansion (CTE), glass transition, elastic moduli and Vickers hardness and brittleness have been measured experimentally and their trends have been explained based on the atomic structure of glasses, from both simulations and experiments. A reasonable agreement has been observed between the composition – structure – property relationship trends obtained experimentally when compared with those predicted by MD simulations. This demonstrates that MD simulation is a promising technique for predictive modeling and designing novel glass compositions for functional applications.

Quartz fiber reinforced Al2O3-SiO2 aerogel composite with highly thermal stability by ambient pressure drying

Abstract: A low-cost and high-performance quartz fiber/Al2O3-SiO2 aerogel (QF/ASA) composite insulation material has been successfully prepared by vacuum filtration molding and sol-gel impregnation following surface-modified ambient pressure drying (APD). The macroporous in the quartz fiber perform are filled by Al2O3-SiO2 aerogels with a large amount of mesoporous. The morphology, microstructure, thermal conductivity and thermal stability of the QF/ASA composite were investigated. Compared to the fiber/aerogel materials dried by supercritical drying, the composite exhibits similar low density (0.36 g·cm−3), high specific surface area (580.5 m2·g−1), low thermal conductivity (0.049 W·m−1·K−1) at room temperature. The compressive strength of the composite up to 0.85 MPa which is approximately triple as much as that of fiber perform. After being heated at 600 to 1100 °C, the specific surface area of composite aerogel decrease from 578.0 to 113.6 m2·g−1 and the linear shrinkage is almost zero. The XRD patterns show that mullite (3Al2O3·2SiO2) appeared in the Al2O3-SiO2 aerogel after heat-treatment at 1100 °C, which is consistent with the molar ratio of silica and alumina of 2:3.

Influence of cobalt ions on the structure, phonon emission, phonon absorption and ligand field of some sodium borate glasses

Abstract: To study some effects of cobalt cations on some properties of a glass system, new glass formulation [75% B2O3 – 5% Al2O3 – (20–x) %Na2O – (x) % CoCl2], where x = 0, 1, 2, 3 and 4 mol% was obtained via melt quenching method. X-ray diffraction (XRD) results emphasize the amorphous nature. The glasses' internal structure was examined via Fourier transform infrared (FTIR). The dependence of density (⍴), boron to boron separation (dB-B), molar volume (Vm), optical absorbance (A), Urbach energy (EU) and band gap (Eg) on Co2+ cations content was scrutinized. The trend of density (⍴), molar volume (Vm), optical absorbance (A), and Urbach energy (EU) shows an increasing behavior, while band gap (Eg) exhibits a decrement behavior with CuCl2 content. The optical absorption coefficient was employed to calculate Eg using the phonon emission and absorption. The crystal field (10Dq), Racah parameters (B and C) and the nephelauxetic ratio will be obtained from optical absorption spectra. According to the obtained results, the sample that contains 4% mol. of CoCl2 has the highest density, molar volume and the least band gap.

Dy3+ doped tellurite glasses for solid-state lighting: An investigation through physical, thermal, structural and optical spectroscopy studies

Abstract: In the present work, a series of Dy3+ ion doped tellurite glasses in the (50-x)TeO2-25WO3-25Li2O-xDy2O3 system were synthesized using conventional melt quenching technique to investigate colorimetric and radiative properties of Dy3+ ions in a new and stable host for their evaluation as solid-state lighting materials. Physical and structural properties were studied through density calculations, refractive index measurements, and Fourier-transform IR spectroscopy analysis. Thermal properties of glasses – glass transition (Tg) and crystallization (Tc/Tp) temperatures and temperature difference (ΔT) – were determined using differential scanning calorimetry. Optical absorption spectra of glasses were recorded with Vis-NIR spectrophotometer. CIE color coordinates, correlated color temperature, color rendering index and yellow to blue emission intensity ratio values were obtained through photoluminescence analysis. Radiative properties such as, radiative transition probability, stimulated emission cross-section, branching ratio and optical bandwidth gain were calculated according to Judd-Ofelt theory. The obtained optical spectroscopy results were found to be comparable or better than other reported glass systems. From the derived results, glasses with Dy3+ ion concentration lower than 0.5 mol% were found to show the closest CIE color coordinate values to pure white light and highest CCT and CRI values revealing good potentiality to be used for applications in white LEDs and solid-state lasers.

Characterization of a broad range gamma-ray and neutron shielding properties of MgO-Al2O3-SiO2-B2O3 and Na2O-Al2O3-SiO2 glass systems

Abstract: In this research, the radiation shielding parameters for two glass systems with composition of 20MgO-(20-x)Al2O3-57SiO2-3B2O3-xCr2O3 (x = 0, 0.1, 0.25, 0.5 and 1 mol%) and Na2O-Al2O3 SiO2 glasses were studied. For this purpose, a scintillation detector namely 3 × 3 inch NaI(Tl) has been designed for detection of photons through MCNPX simulation code. Thus, the mass attenuation coefficients (μ/ρ) and some other gamma shielding quantities were calculated. The estimated MCNPX data of all the glasses were compared and approved with those of WinXCOM program. The gamma ray buildup factors for the two glass systems were also determined in a wide energy range of 0.02–15 MeV for penetration depths up to 15 mfp. The results revealed that the mass attenuation coefficients for the glass samples in the first glass system are higher than those in the glasses in the second system and thus the glasses coded as MASBC have more ability in reducing radiation than NAS glasses. Among the selected glasses, C4 has the largest values of μρ and lowest half value layer, and therefore this glass sample has better shielding features than other samples. Besides, 3—1 glass sample has the lowest values; therefore this sample has the least ability to block and reduce the incoming gamma radiation. The results also showed that the effective atomic number (Zeff) of the glasses in the first composition increased with increasing the content of Cr2O3, and Zeff in the second glass system (i.e. NAS) increased with increasing the Al2O3 content. The values of mass removal cross section for neutron (ΣR) vary between 0.09112 and 0.09163 and 0.08415–0.08710 for the first and second glass system respectively. The obtained results from the present investigation can be useful to understanding of influence of Cr2O3 and Al2O3 additive on nuclear radiation shielding properties of tellurite MgO-Al2O3-SiO2-B2O3 and Na2O-Al2O3-SiO2 glasses.

Foam glass using sodium hydroxide as foaming agent: Study on the reaction mechanism in soda-lime glass matrix

Abstract: Foam glasses have potential of using in several fields due to their high porosity. Usually, the foam glasses are prepared though chemical approach where the powdered glass is mixed with foaming agents at high temperatures. However, in such approach, the emission of gaseous pollutants (e.g. CO2) from the most used foaming agents can be harmful to the environment. Thus, understanding the mechanisms of foam formation is quite important to eliminate the drawbacks afore mentioned, as well as, give us more information on the processing steps. Herein, we propose a new chemical route to obtain foam glasses from soda-lime glass waste using sodium hydroxide and borax as foaming and flow agents, respectively. The reaction mechanism was investigated by thermogravimetric and differential thermal analysis, mass spectroscopy, mercury porosimetry, optical dilatometry, X-ray diffraction, and infrared spectroscopy. At the glass transition temperature (587o C), the crystallization of a new phase of hydrated sodium and calcium silicate (Na2CaSi2O6.2H2O) was observed. As demonstrated by mass spectrometry, when the mixture was heated to a temperature above the softening point, the foaming occurred only due to steam released from the hydrated sodium and calcium silicate. This foaming process provided a foam glass with 86% of porosity, low permeability and bulk density of 0.3 g/cm3. The results indicate the proposed approach is environmentally safe, besides being relatively cheap and easy to prepare.

Acid-based geopolymers: Understanding of the structural evolutions during consolidation and after thermal treatments

Abstract: Materials such as ceramic matrix composites are developed for mechanical applications at high temperature, but their cost remains a limitation. Consequently, the use of acid-based geopolymer matrices may be an alternative to reduce costs. In this study, the sample was prepared from metakaolin and phosphoric acid. Fourier Transform InfraRed and Nuclear Magnetic Resonance spectroscopies, X-Ray Diffraction and thermal measurements were used to understand the structural evolution of acid-based geopolymers (binders) during consolidation and after thermal treatments. According to the results, the consolidation of the binder has been divided into four steps: the dissolution of the metakaolin, the polycondensation reactions forming AlPO4 entities and hydrated phases, the breakdown of SiOAl bonds with formation of various hydrated silica networks and finally the completion of the networks. After a thermal treatment at 1000 °C, the binder consists of AlPO4 phases, quartz and vitreous silica.

Development of Eu3+ doped bismuth germanate glasses for red laser applications

Abstract: The intense red-emitting Eu3+ doped bismuth germanate glasses have been prepared by melt quenching technique with the chemical composition of (100-x)(0.2Bi2O3–0.8GeO2)-xEu2O3 (x = 0.5–2 mol%). Spectroscopic analysis have been performed through FTIR, absorption, luminescence and decay time measurements to enlighten the structural and optical properties of these systems. The bonding parameter (δ) and optical band gap (Eg) of prepared glasses have been calculated from the optical absorption spectra. Phonon side band spectroscopy was used to explore the phonon energy, electron-phonon coupling strength and multiphonon relaxation rate of Eu3+ doped bismuth germanate glasses. Under near UV excitation at 393 nm enhanced red emission is observed at 611 nm (5D0 → 7F2) with rising Eu3+ content. The radiative properties including transition probability (A), branching ratio (βR), stimulated emission cross-section (σe) and decay time (τR) for different excited states have been evaluated by using Judd-Ofelt parameters determined from the emission spectra. The calculated values of asymmetric ratio (R/O) and Ω2 suggest high asymmetric environment for Eu3+ ions and high covalency for Eu O bond which are also confirmed by positive values of bonding parameter. The decay curves of 5D0 → 7F2 transition were well fitted to single exponential function for all the concentrations. The slight increase in decay times with rising Eu3+ ion content is due to the increase in the asymmetry of the local environment at the Eu3+ ion site. The CIE color coordinates (x,y) of the prepared glasses are within the range of 0.637–0.648 and 0.347–0.350 and are very close to the standard red color (0.67, 0.33) suggesting pure intense red emission is achieved. The results indicate that BGEx glasses are promising materials for red laser applications.