Showing papers in "Journal of Non-crystalline Solids in 2009"
TL;DR: In this article, a study of the structure and bonding configuration of sol-gel silicate glasses by Raman and infrared spectroscopies is presented, and a review of the Raman lines and infrared bands assignment, the identification of the non-bridging silicon-oxygen groups and the ring structures are also demonstrated.
Abstract: A study of the structure and bonding configuration of sol–gel silicate glasses by Raman and infrared spectroscopies is presented. Moreover, a review of the Raman lines and infrared bands assignment, the identification of the non-bridging silicon–oxygen groups and the ring structures are also demonstrated. The evolution of the changes of the bonding configuration in the composition and the stabilization temperature of the bioactive glasses is discussed in terms of the structural and textural characteristics of the glasses. Raman and infrared analyses contribute to the improvement in understanding of the local symmetry for sol–gel silicate glasses. infrared spectroscopy has allowed to identify the vibration bands of the hydroxyl groups associated with various configurations of the terminal silanol bonds on the glass surface and the free molecular water in the glass matrix. Raman analysis has provided an alternative method of quantifying the network connectivity grade and predicting the textural properties of the sol–gel silicate glasses.
495 citations
TL;DR: It has been shown that the release rate depends primary on the properties of the matrix and the preparation method and chemical nature of the gel phase, which demonstrates for the first time the high potential of polysaccharide aerogels for pharmaceutical applications.
Abstract: The application of aerogels as drug delivery system was successfully demonstrated for silica aerogels previously However, being biocompatible silica matrices are not biodegradable, which is a certain disadvantage for a number of pharmaceutically oriented applications For these purposes biodegradable materials are beneficial Supercritical drying of polysaccharide gels results in highly porous biodegradable aerogel matrices with large surface areas Structural properties of the polysaccharide aerogels depend on the preparation method and chemical nature of the gel phase In this work different polysaccharide precursors (starch, alginate) were used to produce aerogels, which later on were loaded with the drugs ibuprofen and paracetamol Furthermore release kinetics was studied in vitro Thereby it has been shown that the release rate depends primary on the properties of the matrix The presented results demonstrate for the first time the high potential of polysaccharide aerogels for pharmaceutical applications
248 citations
TL;DR: In this article, the role of divalent cations in the structure of B2O3 glasses has been investigated using sound velocity measurements at 4 MHz and IR spectroscopic analysis of IR spectra.
Abstract: Studies on xRO · 30Bi2O3 · (70−x)B2O3 glasses have been carried out (0 ⩽ x ⩽ 30 mol%, R = Zn, Ba). Elastic properties and Debye temperature have been investigated using sound velocity measurements at 4 MHz. The ultrasonic parameters along with the IR spectroscopic studies have been employed to explore the role of divalent cations in the structure of the studied glasses. Analysis of infrared spectra indicates that RO is preferentially incorporated into the borate network, forming BO4 units. It is assumed that Bi2O3 enters the structure in the form of BiO6 only. The change of density and molar volume with RO content reveals that BO4 units linked to R2+ cations are denser than those linked to positive sites in the Bi2O3 network. Predicted values of four co-ordinated boron put forward questions about the reliability of assignment of structural units that Bi2O3 may form.
227 citations
TL;DR: In this article, the aging of glass and basalt fibers with different chemical constitutions in NaOH and cement solutions was investigated and the strength distributions have been evaluated using a Weibull distribution function.
Abstract: In alkaline solutions, the reaction of hydroxyl ions with Si–O–Si-groups of the glass network leads to the formation of hydrated surfaces and dissolved silicate. The rate of this corrosion depends on the chemical constitution of the fiber and the alkaline solution as well as on time and temperature. The investigation of the aging of glass and basalt fibers with different chemical constitutions in NaOH and cement solutions shows that the corrosion mechanism changes due to the inhibiting effect of calcium ions. The strength distributions have been evaluated using a Weibull distribution function. The mechanical behavior strongly depends on the chemistry of the solution and determines the parameters of the Weibull distribution function in terms of either single or mixed distributions. The corrosion in NaOH solution leads to a strong dissolution of the outer layer of the glass and basalt fibers, whereas during aging in cement solution at the same pH-value a limited, local attack was revealed.
168 citations
TL;DR: In this article, the authors focus on characterizing PVA: NH4X (X = Cl, Br, I) proton conducting polymer electrolyte prepared by solution casting technique using XRD, FTIR and ac impedance spectroscopic studies.
Abstract: The present study focuses on characterizing PVA: NH4X (X = Cl, Br, I) proton conducting polymer electrolyte prepared by solution casting technique using XRD, FTIR and ac impedance spectroscopic studies. The XRD patterns of all the prepared polymer electrolytes reveal the amorphous nature of the films. The FTIR spectroscopic study indicates the detailed interaction of PVA with proton. From ac impedance spectroscopic studies, it has been found that PVA doped with NH4I have high ionic conductivity (2.5 × 10−3S cm−1) than PVA doped with NH4Br (5.7 × 10−4S cm−1) and NH4Cl (1.0 × 10−5S cm−1) polymer electrolytes. This is due to the large anionic size and low lattice energy of NH4I (in comparison with NH4Br and NH4Cl).The temperature dependence of ionic conductivity for all the PVA: NH4X (X = Cl, Br, I) polymer films obey Arrhenius equation. Ionic transference number measured has been found to be in the range of 0.93–0.96 for all the polymer electrolytes proving that the total conductivity is mainly due to ions.
164 citations
TL;DR: In this paper, the structure, thermal properties, chemical durability and redox state of modified iron phosphate glasses have been characterized, and it has been shown that the addition of divalent cations has a less deleterious effect on glass stability than alkali additions.
Abstract: Modified iron phosphate glasses have been prepared with nominal molar compositions [(1−x)·(0.6P2O5–0.4Fe2O3)]·xRySO4, where x = 0–0.5 in increments of 0.1 and R = Li, Na, K, Mg, Ca, Ba, or Pb and y = 1 or 2. In most cases the vast majority or all of the sulfate volatalizes and quarternary P2O5–Fe2O3–FeO–RyOz glasses or partially crystalline materials are formed. Here we have characterized the structure, thermal properties, chemical durability and redox state of these materials. Raman spectroscopy indicates that increasing modifier oxide additions result in depolymerization of the phosphate network such that the average value of i, the number of bridging oxygens per –(PO4)– tetrahedron, and expressed as Qi, decreases. Differences have been observed between the structural effects of different modifier types but these are secondary to the amount of modifier added. Alkali additions have little effect on density; slightly increasing Tg and Td; increasing α and Tliq; and promoting bulk crystallization at temperatures of 600–700 °C. Additions of divalent cations increase density, α, Tg, Td, Tliq and promote bulk crystallization at temperatures of 700–800 °C. Overall the addition of divalent cations has a less deleterious effect on glass stability than alkali additions. 57Fe Mossbauer spectroscopy confirms that iron is present as Fe2+ and Fe3+ ions which primarily occupy distorted octahedral sites. This is consistent with accepted structural models for iron phosphate glasses. The iron redox ratio, Fe2+/ΣFe, has a value of 0.13–0.29 for the glasses studied. The base glass exhibits a very low aqueous leach rate when measured by Product Consistency Test B, a standard durability test for nuclear waste glasses. The addition of high quantities of alkali oxide (30–40 mol% R2O) to the base glass increases leach rates, but only to levels comparable with those measured for a commercial soda-lime-silica glass and for a surrogate nuclear waste-loaded borosilicate glass. Divalent cation additions decrease aqueous leach rates and large additions (30–50 mol% RO) provide exceptionally low leach rates that are 2–3 orders of magnitude lower than have been measured for the surrogate waste-loaded borosilicate glass. The P2O5–Fe2O3–FeO–BaO glasses reported here show particular promise as they are ultra-durable, thermally stable, low-melting glasses with a large glass-forming compositional range.
152 citations
TL;DR: In this article, a series of glasses and melts along the GeO2-SiO2 join using in situ Raman spectroscopy were investigated, and the results for both the glass and melts were consistent with a continuous random network in which there are regions that are SiO2like, GeO 2-like, and mixed geO2 and SiO 2 -SiO 2 like.
Abstract: We have investigated a series of glasses and melts along the GeO2–SiO2 join using in situ Raman spectroscopy. The results for both the glasses and melts are consistent with a continuous random network in which there are ‘regions’ that are SiO2-like, GeO2-like and mixed GeO2–SiO2-like. Incorporation of GeO2 into the SiO2 network is initially accommodated via the 3- and 4-membered SiO4 rings which are lost as they convert to larger mixed Ge/Si rings. The LO–TO mode behavior is also consistent with a network that is composed of different ‘regions’ and is similar to that expected from the Bruggeman effective media model. At the highest temperatures there are indications that the mixed Ge/Si rings convert back to small 3-membered GeO4 rings and large SiO4 rings; the small 3- and 4-membered SiO4 rings are not reformed.
146 citations
TL;DR: The position of the absorption edge and hence the values of the optical band gap was found to depend on the glass composition using the Tauc model as mentioned in this paper, which requires only the measurement of the absorbance spectrum of the sample.
Abstract: Glasses with compositions (60−x) V2O5–40TeO2–xSb2O3 with 0 ⩽ x ⩽ 10 (in mol%) have been prepared using usual melt quenching method. The position of the absorption edge and hence the values of the optical band gap was found to depend on the glass composition. Using the Tauc model, the absorption spectrum fitting method (ASF) was employed to obtain the optical band gap. This method requires only the measurement of the absorbance spectrum of the sample. For each sample, the width of the band tail was determined. Also, the density and glass transition temperature values indicate that the rigidity and packing of the samples increase with increase in Sb2O3 concentration.
138 citations
TL;DR: In this article, the fabrication, glass-forming ability, polyamorphism, elastic, thermal, and physical properties of rare earth-based bulk metallic glasses are summarized and discussed, which have implications for seeking novel metallic glasses with controllable properties and for understanding the nature of glass formation.
Abstract: Recently, the rare earth based bulk metallic glasses (REBMGs) have attracted increasing interest due to their unique properties and potential applications as functional glassy materials. These REBMGs display many fascinating properties such as heavy fermion behavior, thermoplastic properties near room temperature, excellent magnetocaloric effect, hard magnetism, and polyamorphism, all of which are of interest not only for basic research but also for metallurgy and technology. These characteristics and properties are ascribed to the unique electronic, magnetic and atomic structures of the REBMGs. In this review paper, the fabrication, glass-forming ability, polyamorphism, elastic, thermal, and physical properties are summarized and discussed. Owing to the unique electronic structure of rare earth elements, the electric and magnetic properties of the REBMGs are especially addressed. The works have implications for seeking novel metallic glasses with controllable properties and for understanding the nature of glass formation. The development of REBMGs as functional materials might promote and extend the commercial applications of metallic glasses.
131 citations
TL;DR: In this paper, the effects of HF/NH4F, wet chemical etching on the morphology of individual surface fractures and of an ensemble of surface fractures (ground surfaces) on fused silica glass has been characterized.
Abstract: The effects of HF/NH4F, wet chemical etching on the morphology of individual surface fractures (indentations, scratches) and of an ensemble of surface fractures (ground surfaces) on fused silica glass has been characterized. For the individual surface fractures, a series of static or dynamic (sliding) Vickers and Brinnell indenters were used to create radial, lateral, Hertzian cone and trailing indentation fractures on a set of polished fused silica substrates which were subsequently etched. After short etch times, the visibility of both surface and subsurface cracks is significantly enhanced when observed by optical microscopy. This is attributed to the increased width of the cracks following etching, allowing for greater optical scatter at the fracture interface. The removal of material during etching was found to be isotropic except in areas where the etchant has difficulty penetrating or in areas that exhibit significant plastic deformation/densification. Isolated fractures continue to etch, but will never be completely removed since the bottom and top of the crack both etch at the same rate. The etching behavior of ensembles of closely spaced cracks, such as those produced during grinding, has also been characterized. This was done using a second set of fused silica samples that were ground using either fixed or loose abrasives. The resulting samples were etched and both the etch rate and the morphology of the surfaces were monitored as a function of time. Etching results in the formation of a series of open cracks or cusps, each corresponding to the individual fractures originally on the surface of the substrate. During extended etching, the individual cusps coalesce with one another, providing a means of reducing the depth of subsurface damage and the peak-to-valley roughness. In addition, the material removal rate of the ground surfaces was found to scale with the surface area of the cracks as a function of etch time. The initial removal rate for the ground surface was typically 3.5× the bulk etch rate. The evolving morphology of ground surfaces during etching was simulated using an isotropic finite difference model. This model illustrates the importance that the initial distributions of fracture sizes and spatial locations have on the evolution of roughness and the rate at which material is removed during the etching process. The etching of ground surfaces can be used during optical fabrication to convert subsurface damage into surface roughness thereby reducing the time required to produce polished surfaces that are free of subsurface damage.
116 citations
TL;DR: In this article, a revision of the YBD model is proposed to take into account more recent experimental results, and in particular the formation of Na2O·B2O3·2SiO2 danburite-like units in borosilicate glasses.
Abstract: Within the framework of structural studies of borosilicate glasses, a revision of the Yun, Bray and Dell (YBD) model is proposed here. The YBD model is slightly modified in order to take into account more recent experimental results, and in particular the formation of Na2O·B2O3·2SiO2 danburite-like units in borosilicate glasses. The following more general formula is proposed for R∗, the threshold value of R (R = [Na2O]/[B2O3]), beyond which glass depolymerisation begins upon addition of modifier to the glass: R ∗ = 0.5 + K 2 N where N is the average number of SiO2 units included in the borosilicate groups (reedmergnerite and danburite-like), and K = [SiO2]/[B2O3].
TL;DR: In this paper, an immersion model was built up to study the effect of immersion on the thermal insulation and hydrophobic properties of a silica aerogel/epoxy composite.
Abstract: Silica aerogel/epoxy composite was prepared by dry mixing hydrophobic aerogels with epoxy powders and heat pressing method. The composite materials show a serviceability temperature up to 250 °C with low thermal conductivity (0.11–0.044 W/m k) and hydrophobic property (water contact angle of 117–140°). Transmission electron microscope photos proved that part of silica aerogels nanopores had been immersed by epoxy. Based on this phenomenon, an immersion model was build up to study the effect of immersion on the thermal insulation and hydrophobic properties. In addition a thermal conductivity prediction equation of aerogel/polymer system was obtained and confirmed by comparing the experimental data.
TL;DR: In this article, the authors determined the details of structural changes caused by variations in the ratio CaO/Na2O in two series of aluminoborosilicate glasses with different contents of boron oxide.
Abstract: Among the most important adjustable compositional variables in controlling glass and glass-melt properties are the relative proportions of network modifiers with varying cation field strength (ratio of charge to radius). Here we determine the details of structural changes caused by variations in the ratio CaO/Na2O in two series of aluminoborosilicate glasses with different contents of boron oxide. Using high-resolution, high field 11B and 27Al MAS NMR, we report precise values of contents of three- and four-coordinated boron (N4) and of four- and five-coordinated aluminum ([5]Al), and calculate fractions of non-bridging oxygens (NBOs). Increasing CaO/Na2O dramatically lowers N4 and increases NBO and [5]Al, but effects are non-linear with composition. Boron content affects these trends because of energetic constraints of mixing of various network cations. 23Na spectra reveal slight but systematic increases in the mean Na–O distance with increasing CaO/Na2O, suggesting that in Ca-rich glasses, Na+ has a higher ratio of bridging to non-bridging oxygens in its coordination shell. All of these changes can be understood by the tendency of higher field strength modifier cations to promote the concentration of negative charges on non-bridging oxygens in their local coordination environment, systematically converting four- to three-coordinated boron.
TL;DR: In this article, bismuth borate glasses were prepared by devitrification of glasses and characterized by X-ray diffraction, FTIR and 11B MAS-NMR studies, showing that the fraction of tetrahedrally coordinated borons (N4) is maximum at 42 −mol% of Bi2O3 and that there is a local maxima in N4 at Bi 2O3 concentration of 50 −mol%.
Abstract: Glasses of the system: xBi2O3–(100−x)B2O3 (x = 20 to 66 mol%) were prepared and characterized by density, DSC, UV–visible absorption and 11B MAS-NMR spectroscopy. Glass molar volume increases while the glass transition temperature decreases with Bi2O3 concentration. Densities of some bismuth borate glasses are found to be greater or very close to those of single crystal phases with equal composition. B11 MAS-NMR studies determined that the fraction of tetrahedrally coordinated borons (N4) is maximum at 42 mol% of Bi2O3 and that there is a local maxima in N4 at Bi2O3 concentration of 50 mol%. Glasses containing Bi2O3 concentration of 33 mol% and higher show an unusual, intense absorption band just below the optical band gap. Two crystalline phases: Bi3B5O12 and Bi4B2O9 were prepared by devitrification of glasses and characterized by X-ray diffraction, FTIR and 11B MAS-NMR studies. Both crystalline phases contained significantly lower N4 than glasses with equal composition.
TL;DR: The authors conducted a critical analysis of the existing data in terms of the different glass-forming criteria and concluded that the available parameters cannot satisfactorily predict the GFA and explain all the observed data.
Abstract: Several empirical rules have been proposed during the past few years to synthesize bulk metallic glasses But, the real reasons for the improved glass-forming ability of these alloys are still not clear and the ability to design alloy compositions to enable synthesis of larger diameter rods has not improved The present work conducts a critical analysis of the existing data in terms of the different glass-forming criteria and concludes that the available parameters cannot satisfactorily predict the GFA and explain all the observed data Reasons for this failure have been suggested
TL;DR: SiO2-CaO-P2O5 ternary bioactive glass ceramic nanoparticles were prepared via the combination of sol-gel and coprecipitation processes.
Abstract: SiO2-CaO-P2O5 ternary bioactive glass ceramic nanoparticles were prepared via the combination of sol-gel and coprecipitation processes. Precursors of silicon and calcium were hydrolyzed in acidic solution and gelated in alkaline condition together with ammonium dibasic phosphate. Gel particles were separated by centrifugation, followed by freeze drying, and calcination procedure to obtain the bioactive glass ceramic nanoparticles. The investigation of the influence of synthesis temperature on the nanopartilce's properties showed that the reaction temperature played an important role in the crystallinity of nanoparticle. The glass ceramic particles synthesized at 55 degrees C included about 15% crystalline phase, while at 25 degrees C and 40 degrees C the entire amorphous nanopowder could be obtained.
TL;DR: In this paper, a two-stage process was used to synthesize a CeO 2 -Bi 2 O 3 composite with different molar ratios through the hydrothermal process, and then was completed by carrying out the precursors for 4h at 600°C under flowing air atmosphere.
Abstract: CeO 2 –Bi 2 O 3 composite was synthesized via a two-stage process. The precursors were prepared from Ce(NO 3 ) 3 ·6H 2 O, Bi(NO 3 ) 3 ·5H 2 O and CO(NH 2 ) 2 with different molar ratio through the hydrothermal process, and then was completed by carrying out the precursors for 4 h at 600 °C under flowing air atmosphere. Techniques of X-ray diffraction (XRD), transmission electron microscopic (TEM) and diffuse reflectance ultraviolet–vis spectra (UV-DRS) were employed to characterize the as-synthesized materials. The results showed that the microstructure and morphology of CeO 2 –Bi 2 O 3 composite were similar in spite of different inverse proportion. We also investigated improved photocatalytic activity in the case of CeO 2 –Bi 2 O 3 composite catalyst compared to the catalytic activity of pure Bi 2 O 3 or CeO 2 powder. The suppression of charge recombination in the composite CeO 2 –Bi 2 O 3 catalyst led to higher catalytic activity for the degradation of RhB. The CeO 2 10%/Bi 2 O 3 photocatalyst exhibited maximum photocatalytic activity. The photocatalytic activity is in close relation with the inverse proportion between reactants.
TL;DR: In this paper, a Li1.5[Al0.5Ge1.3] glass composition was subjected to several crystallization treatments to obtain glass-ceramics with controlled microstructures.
Abstract: A Li1.5[Al0.5Ge1.5(PO4)3] glass composition was subjected to several crystallization treatments to obtain glass–ceramics with controlled microstructures. The glass transition (Tg), crystallization onset (Tx) and melting (Tm) temperatures of the parent glass were characterized by differential scanning calorimetry (DSC). The glass has a reduced glass transition temperature Tgr = Tg/Tm = 0.57 indicating the possibility of internal nucleation. This assumption was corroborated by the similar DSC crystallization peaks from monolithic and powder samples. The temperature of the maximum nucleation rate was estimated by DSC. Different microstructures were produced by double heat treatments, in which crystal nucleation was processed at the estimated temperature of maximum nucleation rate for different lengths of time. Crystals were subsequently grown at an intermediate temperature between Tg and Tx. Single phase glass–ceramics with Nasicon structures and grain sizes ranging from 220 nm to 8 μm were then synthesized and the influence of the microstructure on the electrical conductivity was analysed. The results showed that the larger the average grain size, the higher the electrical conductivity. Controlled glass crystallization allowed for the synthesis of glass–ceramics with fine microstructures and higher electrical conductivity than those of ceramics with the same composition obtained by the classical sintering route and reported in literature.
TL;DR: The Adam–Gibbs model’s theoretical bases as well as its reported experimental model confirmations are discussed; in the process of doing this a number of problems with the model are identified.
Abstract: This paper critically discusses the entropy model proposed by Adam and Gibbs in 1965 for the dramatic temperature dependence of glass-forming liquids’ average relaxation time, which is one of the most influential models during the last four decades. We discuss the Adam–Gibbs model’s theoretical bases as well as its reported experimental model confirmations; in the process of doing this a number of problems with the model are identified.
TL;DR: In this paper, the structural, magnetic and mechanical properties of co-based magnetic microwires and their composites were investigated and it was found that annealing amorphous microwires at 600 C caused a drastic variation in the amorphized structure due to crystallization and consequently degraded the soft magnetic properties of the microwires.
Abstract: Structural, magnetic and mechanical properties of Co-based magnetic microwires and their composites had been investigated. It was found that annealing amorphous microwires at 600 C caused a drastic variation in the amorphous structure due to crystallization and consequently degraded the soft magnetic properties of the microwires. The tensile tests on the single microwires of different size with and without glass-coated layer revealed a coherent correlation between the mechanical properties and the wire geometry. When compared with single magnetic microwires, the magnetic and magneto-impedance properties of composites were much improved. The strong field dependence of the effective permittivity and transmission/reflection parameters in the Gigahertz range of the composites containing short wires or arrays of continuous wires indicated that these new composites are promising candidate materials for a variety of self-sensing applications.
TL;DR: In this paper, the photoluminescence properties of glass and glass ceramics containing CaF 2 nanocrystals were investigated and Decay lifetime measurements were also carried out for all the observed Sm 3+, Dy 3+, and Tm 3+ -doped glass-ceramic emission bands.
Abstract: Photoluminescence properties of Sm 3+ , Dy 3+ , and Tm 3+ -doped transparent oxyfluoride silicate glass ceramics containing CaF 2 nanocrystals were reported. Emission bands of 4 G 5/2 → 6 H 5/2 (562 nm), 4 G 5/2 → 6 H 7/2 (598 nm), 4 G 5/2 → 6 H 9/2 (645 nm) and 4 G 5/2 → 6 H 11/2 (706 nm) for the Sm 3+ : glass and glass ceramic, with an excitation at 6 H 5/2 → 4 F 7/2 (402 nm) have been recorded. Of them, 4 G 5/2 → 6 H 7/2 (598 nm) has shown a bright orange emission. With regard to the Dy 3+ : glass, a bright fluorescent yellow emission at 575 nm ( 4 F 9/2 → 6 H 13/2 ) and blue emission at 481 nm ( 4 F 9/2 → 6 H 15/2 ) have been observed, apart from 662 nm ( 4 F 9/2 → 6 H 11/2 ) emission transition with an excitation at 386 nm ( 6 H 15/2 → 4 I 13/2 + 4 F 7/2 ) wavelength. Emission bands of 1 G 4 → 3 F 4 (650 nm) and 1 G 4 → 3 H 5 (795 nm) transitions for the Tm 3+ : glass and glass ceramic, with an excitation at 3 H 6 → 1 G 4 (467 nm) have been observed. Of them, 1 G 4 → 3 F 4 (650 nm) has shown bright red emission. Decay lifetime measurements were also carried out for all the observed Sm 3+ , Dy 3+ , and Tm 3+ -doped glass and glass ceramic emission bands.
TL;DR: In this paper, the authors reported the production and characterization of silica nano-particles by Californian red worms through a bio-digestion process of rice husk; the worms were fed gradually with rice hull and water during 5 months to clean the worm's digestive system from other types of food.
Abstract: It is reported the production and characterization of silica nano-particles by Californian-red worms through a bio-digestion process of rice husk; the rice husk contains, naturally, high concentrations of silica (22%). The worms were fed gradually with rice husk and water during 5 months to clean the worm’s digestive system from other types of food. The humus was collected, dried at room temperature, pH neutralized and calcined at different temperatures (500, 600 and 700 °C) to remove the organic matter. The calcined humus was digested to remove traces of inorganic compounds. The size of the silica particles was in the range from 55 to 250 nm depending on calcination temperatures. The efficiency in the production of the particles was 88%. These results were compared with those obtained using other agro-industrial wastes that contain silica: coffee (12%) and cane (8%) husk. The samples were characterized by XRD, FTIR, EDS, DLS, SEM and TEM.
TL;DR: In this article, a study on the structure, microstructure and properties of 50Li2O·xB2O3·(50−− ǫx)P2O5 glasses is presented.
Abstract: This work presents a study on the structure, microstructure and properties of 50Li2O·xB2O3·(50 − x)P2O5 glasses. The structure has been studied through NMR spectroscopy and the microstructure by TEM. The properties of the glasses are discussed according to their structure and microstructural features. The introduction of boron produces new linkages between phosphate chains through P–O–B bonds, whose amount increases with boron incorporation; at the same time, a depolymerisation of the phosphate chains into Q1-type phosphate units takes place. The introduction of boron produces an increase in Tg together with a decrease in the molar volume. The room temperature electrical conductivity increases with boron content as well. However, B2O3 contents higher than 20 mol% lead to crystallisation of lithium orthophosphate which contributed to hinder ionic conduction of the glasses.
TL;DR: In this article, a phase separation domain appears for composition around Te40Ge20Se40.% and Te80-xGe20Sex glasses with 1 < x < 5 at.%.
Abstract: Te80-xGe20Sex glasses have been prepared along the GeSe4-GeTe4 axis using the classical method in silica tube under vacuum. A phase separation domain appears for composition around Te40Ge20Se40. Our attention was turned toward the Te-rich compositions corresponding to 1 < x < 5 at.%. These glasses are transparent from 4 to about 20 μm without any purification of the starting elements. Furthermore the difference ΔT between the crystallization temperature Tx and the vitreous transition temperature Tg lies at about 110 °C that is to say 30 °C higher than for the GeTe4 reference glass. Finally the introduction of a few percentages of Se makes the glasses much easier to prepare and more stable against crystallization, making them drawable as optical fibers for example. Taking into account their transparency window, encompassing the CO2 absorption band around 15 μm, the Te80-xGe20Sex with 1 < x < 5 at.% could become matchless composition for the CO2 infrared detection as planed by the Darwin mission of the European Space Agency. © 2009 Elsevier B.V. All rights reserved.
TL;DR: In this article, the authors used Raman spectroscopy to investigate sulfate content in borosilicate glasses and verified the results using electron probe micro analysis (EPMA) with an accuracy of approximately 0.1 wt% depending on the composition of the glass.
Abstract: Raman spectroscopy is used here as an innovative technique to investigate sulfate content in borosilicate glasses. Using Raman spectroscopy after having heated the material, the evolution of sulfate amounts can be followed as a function of temperature, time and chemical composition of the starting matrix. The accu- racy of this technique was verified using electron probe micro analysis (EPMA), on two systems of glasses (SiO2-B2O3-Na2O (SBNa) and SiO2-B2O3-BaO (SBBa)) in order to compare the effect of alkaline or alka- line-earth elements on sulfur speciation and incorporation. To quantitate sulfate content with Raman spectroscopy, the integrated intensity of the sulfate band at 990 cm � 1 was scaled to the sum of the inte- grated bands between 850 and 1250 cm � 1 , bands that are assigned to Q n silica units. Calibration curves were then determined for different samples. The determination of sulfate contents with Raman spectros- copy analysis is possible with an accuracy of approximately 0.1 wt% depending on the composition of the glass. It mainly allows us to follow sulfate removal during the elaboration process and to establish kinetic curves of sulfate release as a function of the viscosity of the borosilicate glass.
TL;DR: In this article, a self-consistent data evaluation showed that at moderate departure from equilibrium, volume and enthalpy in amorphous selenium relax in the same way as expressed by Tool-Naraynaswamy-Moynihan (TNM) and Adam-Gibbs-Scherer (AGS) models.
Abstract: Volume and enthalpy relaxation studies of amorphous Se have been performed in the glass transition region by mercury dilatometry and differential scanning calorimetry. For simple temperature jump experiments, as well as for more complex thermal history the volume and enthalpy relaxation data can be described by a single set of kinetic parameters for Tool-Naraynaswamy-Moynihan (TNM) model [Δh∗/R = 42.8 kK, ln(ATNM/s) = −133]. Slightly different non-linearity and non-exponentiality parameter were found for volume [x = 0.42, β = 0.58] and enthalpy [x = 0.52, β = 0.65] relaxation data. Similar results were obtained also for Adam-Gibbs-Scherer (AGS) model. The activation energy of viscous flow in the glass transition range is identical with the effective activation energy for relaxation process. A self-consistent data evaluation shows that at moderate departure from equilibrium, volume and enthalpy in amorphous selenium relax in the same way as expressed by TNM and AGS models. Both volume and enthalpy change can be interpreted within the same fictive temperature concept.
TL;DR: In this paper, a spin-coating technique for the deposition of thin chalcogenide glass was proposed, and the dissolution mechanisms of Ge23Sb7S70 in different solvents were studied in order to select the optimal solvent for film deposition.
Abstract: Thin film Ge23Sb7S70 chalcogenide glass has emerged as an important material system for photonic applications due to its high non-linear refractive index. However, one of the challenges is developing low-cost methods to deposit films of glassy material while retaining glass stoichiometry and high film quality. In this paper, we demonstrate a spin-coating technique for the deposition of such films. The dissolution mechanisms of Ge23Sb7S70 in different solvents are studied in order to select the optimal solvent for film deposition. We show that the use of amine-based solvents allow the deposition of stoichiometric films in contrast to alkaline solutions. Films with low surface roughness (RMS roughness <5 nm) and controlled thickness (100–600 nm) can be deposited from solutions. We also show that annealing the films in vacuum decreases the amount of residual solvent, the presence of which is expected to lead to variation in optical properties of the thin films. 2009 Published by Elsevier B.V.
TL;DR: In this article, undoped and transition metals (TM 3d)-doped lead phosphate glasses were measured in the range 200-1100 nm before and after successive gamma irradiation.
Abstract: Undoped and transition metals (TM 3d)-doped lead phosphate glasses were prepared. Ultraviolet–visible absorption spectra were measured in the range 200–1100 nm before and after successive gamma irradiation. Experimental results indicate that the undoped lead phosphate glass reveals before irradiation strong and broad ultraviolet absorption which is related to the co-sharing of absorption due to both trace iron impurities and lead ions (Pb2+). In the TM-doped glasses, characteristic absorption bands are obtained in both the UV and/or visible regions due to each respective TM ion in addition to that observed by the base undoped UV absorption. Gamma irradiation produces with the undoped glass a prominent induced ultraviolet broad band centered at about 300 nm originating mostly from the contribution of trace iron impurities and the visible spectra reveal markedly high shielding behavior towards successive gamma irradiation, due to the presence of both high content of heavy Pb2+ ions and the sharing of phosphate as a partner. With TM-doped samples, the observed induced bands are virtually varying and related to the type of the sharing TM ions. Infrared absorption spectra reveal in the undoped and TM-doped glasses characteristic structural phosphate groups mainly consisting of metaphosphate and pyrophosphate units. Transition metals are assumed to cause depolymerization of the phosphate glass network with different ratios but the changes in IR spectral data are limited due to the low doping level. Gamma irradiation of the samples is assumed to cause changes in the bond angles or bond lengths of the structural phosphate units within network as evident in the variation of the intensities of the IR bands.
TL;DR: In this article, the fragility of a liquid is linked to the ratio between the energy barrier (E eq ) for the equilibrium viscous behavior and that (E iso ) for non-equilibrium iso-structural viscous behaviour.
Abstract: This paper describes how the fragility of a liquid is linked to the ratio between the energy barrier ( E eq ) for the equilibrium viscous behavior and that ( E iso ) for the non-equilibrium iso-structural viscous behavior. Using the concept of iso-structural viscosity, two functions describing the variation of the configurational entropy ( S c ) with temperature ( T ) are obtained from the Avramov-Milchev (AM) and the Vogel-Fulcher-Tammann (VFT) viscosity equations, respectively. The two S c ( T ) functions exhibit different relations to the liquid fragility. The AM S c ( T ) function is a power function with the exponent of F − 1, where F is the AM fragility index. In this case, S c vanishes at T = 0 K. For the VFT function, S c vanishes as T is lowered to a finite temperature T 0 , whereas it reaches the maximum value S c,max at infinitively high T . S c,max is proportional to the VFT fragility index. Thus, the VFT equation is not only a dynamical, but also a thermodynamic model. It is proved that for oxide liquids, the VFT equation describes viscosity data better than the AM equation, provided the pre-exponential factor η 0 is fixed to a generally accepted value, e.g., 10 −3.5 Pa s.
TL;DR: In this article, the growth processing, interfacial structure and electrical properties of the La2O3 gate dielectric films were investigated by various techniques, including XRD results, XPS results, and atomic force microscopy image.
Abstract: Ultrathin La2O3 gate dielectric films were prepared on Si substrate by ion assistant electron-beam evaporation. The growth processing, interfacial structure and electrical properties were investigated by various techniques. From XRD results, we found that the La2O3 films maintained the amorphous state up to a high annealing temperature of 900 °C for 5 min. From XPS results, we also discovered that the La atoms of the La2O3 films did not react with silicon substrate to form any La-compound at the interfacial layer. However, a SiO2 interfacial layer was formed by the diffusion of O atoms of the La2O3 films to the silicon substrate. From the atomic force microscopy image, we disclosed that the surface of the amorphous La2O3 film was very flat. Moreover, the La2O3 film showed a dielectric constant of 15.5 at 1 MHz, and the leakage current density of the La2O3 film was 7.56 × 10−6 A/cm2 at a gate bias voltage of 1 V.