Amorphous Composition Research Articles

Will mixing rule or chemical reactions dominate the ash behavior of biomass mixtures in combustion processes on laboratory and pilot scales?

Mixing biomasses has a good potential to solve operational problems in thermochemical valorization processes related to ash behavior. Chemical reactions within the ash of the blend, and not only a mixing effect without reaction, need to take place to form new solid phases in the mixture at the expense of getting rid of the problematic liquid one to decrease the slagging tendency. The present work focuses on assessing the presence of a chemical reaction in comparison with a simple mixing effect within the ash of mixtures of wheat straw - oak bark biomass and ash in two laboratory setups and in a fixed and in a moving bed pilot combustion reactors. The operating conditions were varied to study their effects on the reactivity of the ash within the mixtures. This aimed to optimize the ash reactivity and to assess the capabilities of the laboratory test to predict the ash behavior in pilot-scale reactors.Mixing without reaction effect was more evident when mixtures of biomass were used on both laboratory and pilot scales. In this case, the simple mixing rule was able to simulate the general ash behavior of biomass mixture to a certain extent that exact prediction was always limited by the presence of certain chemical reactions. However, chemical reactions effect was dominant when mixtures of ash of biomass were applied as feedstock. Solid crystalline phases K2Ca2Si2O7 and K2Ca6Si4O15 were the direct end products of these chemical reactions. Their relative proportion was inversely proportional to the problematic amorphous phase in the final ash. Hence, optimizing the blend proportion to increase their concentrations has the potential to solve slagging problematic. These two compounds were mostly stable at 1000 ℃, at which equilibrium was reached after 6 h. However, they existed at a lower proportion at 850℃ and disappeared at 1200℃. The developed laboratory pellet test was also able to predict very efficiently the pilot ash behavior of both individual biomasses and their mixture in terms of crystalline and amorphous composition and proportion along with agglomeration distribution.

Optimal removal of diclofenac and amoxicillin by activated carbon prepared from coconut shell through response surface methodology

Agricultural residues like coconut shell are widely available in Benin Republic and can be used as adsorbent. In this study, we determine the limits of pharmaceutical substances adsorption by activated carbon from coconut shells. The synthesis of this adsorbent was optimized by the Response Surface Methodology (RSM) with two factors: the impregnation ratio IR and activation temperature. The iodine value was considered as the performance (response) parameter of this synthesis. After characterizing the prepared activated carbon, adsorption tests were performed on diclofenac sodium (DCF) and amoxicillin (AMX) by varying the contact time and the adsorbate-adsorbent ratio Rads. The synthesis results showed that the optimal physicochemical properties of the activated carbon were observed at 740 °C with phosphoric acid (IR = 1.66). Under these optimal conditions, the activated carbon from the coconut shells presented a large microporous specific surface (SBET = 437 m2/g and Vmicro = 0.21 cm3/g), optimal iodine adsorption (930.28 mg/g), amorphous and low heterogeneous chemical composition. In addition, the prepared activated carbon was an excellent adsorbent for the removal of the pharmaceutical substances studied. The experimental adsorption data followed the Langmuir isotherm and the pseudo first-order kinetic model. However, the efficiency varied depending on the nature of the adsorbate and the adsorbate-adsorbent ratio was the main limiting factor in the adsorption process. Optimal elimination greater than 98% was noticed with Rads = 0.10 and a contact time of 15 min (90 min) for DCF (AMX). However, we noticed the complete elimination of AMX (DCF) for Rads ≤ 0.075 (Rads ≤ 0.040). It was observed that the removal efficiency of pollutant was not defined by the adsorption rate constant but the reactivity with the adsorbent.

Developing a multilateral-based neural network model for engineering of high entropy amorphous alloys

Due to a great number of composition-processing factors, it is very difficult to design high entropy amorphous alloys without performing manifold trial-and-error experimentations. To solve this problem, in this study we developed a machine learning-based approach, namely multilateral-based neural network, which is able to predict new high entropy amorphous compositions through estimating the highest glass forming ability and the critical casting thickness. In this approach, the entropy parameters were individually correlated to each input, which leads to the improvement of predictive model in evaluating the high entropy glassy alloys. As a case study, Ti20Zr20Hf20Be20Co20 high entropy metallic glass (MG) was considered and the effects of added elements such as Y, Ni, Cr and V and Cu on the glass formation and critical casting thickness were investigated. According to the results, it is determined that the Y addition acts as a microalloying process in the base composition, while other elements improve the configurational entropy and the total negative heat of mixing, which lead to the engineering of equi-atomic high entropy MGs.

Magnetic properties of the composition of nanocrystals and amorphous matrix in an alloy of the Fe-Nb-Si-B-Cu system

It is shown that amorphous alloys of the Fe-Nb-Si-B-Cu system are practically not used as soft-magnetic materials in the initial (freshly quenching) state. It is proposed to perform post-quenching annealing of products to improve the soft-magnetic properties. Annealing modes, which remove winding and quenching stresses are studied. Is established the optimal annealing mode, in which a favorable structure is formed. It is an amorphous alloy-nanocrystal composition. This composition can significantly increase the magnetic permeability, reduce the coercive force and the loss of magnetization reversal. This treatment will provide optimal performance characteristics for the amorphous alloy used. The paper studies and compares the magnetic properties of the amorphous alloy-nanocrystal composition obtained at different annealing temperatures. It is shown that the most significant comparison is the dependence of the magnetic induction B (Tl) by the magnetic field strength H (A/m).

Designer Glasses—Future of Photonic Device Platforms

AbstractThe intentional inclusion of key atomic elements in a purpose designed glass helps to achieve unprecedented control over the ultrafast laser written circular waveguide morphology and refractive index change. Behavioral response of glass constituents to ultrafast laser in 14 different commercial silicate glasses having various compositions are studied. Viscosity, aluminum to alkaline earth+alkali ratio, and total silicon content within the glass are the prime control factors for producing waveguides with high circularity and refractive index change. Drawing on this knowledge, the designer glass is successfully fabricated from an empirical formula that facilitates maintaining circular waveguide morphology, high refractive index over fast feed rates, and amorphous composition.

Structural and optical properties of amorphous Si\u2013Ge\u2013Te thin films prepared by combinatorial sputtering

The lack of order in amorphous chalcogenides offers them novel properties but also adds increased challenges in the discovery and design of advanced functional materials. The amorphous compositions in the Si–Ge–Te system are of interest for many applications such as optical data storage, optical sensors and Ovonic threshold switches. But an extended exploration of this system is still missing. In this study, magnetron co-sputtering is used for the combinatorial synthesis of thin film libraries, outside the glass formation domain. Compositional, structural and optical properties are investigated and discussed in the framework of topological constraint theory. The materials in the library are classified as stressed-rigid amorphous networks. The bandgap is heavily influenced by the Te content while the near-IR refractive index dependence on Ge concentration shows a minimum, which could be exploited in applications. A transition from a disordered to a more ordered amorphous network at 60 at% Te, is observed. The thermal stability study shows that the formed crystalline phases are dictated by the concentration of Ge and Te. New amorphous compositions in the Si–Ge–Te system were found and their properties explored, thus enabling an informed and rapid material selection and design for applications.

Nanoscale Variations in Natural Amorphous and Nanocrystalline Weathering Products in Mafic to Intermediate Volcanic Terrains on Earth: Implications for Amorphous Detections on Mars

AbstractSedimentary amorphous and nanocrystalline materials are abundant on Mars, but their formation conditions are poorly understood due in part to instrument limitations and the lack of knowledge about terrestrial sedimentary amorphous and nanocrystalline material compositions and structures. Additionally, it is surprising that the Curiosity rover finds these metastable phases preserved in ancient (3–4 Gya) rocks in Gale crater. Here, we use X‐ray diffraction and high‐resolution transmission electron microscopy to investigate the X‐ray amorphous weathering products found in soils, sediments, and paleosols from Mars‐relevant mafic to intermediate volcanic terrains altered under different climates. The X‐ray amorphous components of our samples are often complex mixtures of amorphous and nanocrystalline materials with compositions that vary at the nanometer‐scale, but are dominated by iron‐oxide, Al2O3, and SiO2, the proportions of which reflect large‐scale weathering conditions, such that those formed in warm and wet climates are deficient in more mobile cations, and those formed under cooler climates reflect restricted cation leaching. We also find high abundances (∼40 wt.%) of X‐ray amorphous weathering products in lithified and diagenetically altered volcanic soils that have been preserved over time scales of ∼107 years. These results have wide‐reaching implications for soil property and paleoclimate investigations on Earth and Mars, and suggest that amorphous and nanocrystalline materials are important, but overlooked components of some sedimentary rocks on Earth. Future investigations are needed to better understand the kinetics behind the transformation from amorphous and nanocrystalline to crystalline materials and the factors that allow their preservation on Earth and Mars.

Electrical conductivity and effects of mechanical bending of flexible amorphous transparent conducting CdO-Ga2O3 films synthesized by room temperature sputtering

Recently, amorphous ionic oxide semiconductors (AIOSs) have attracted much attention as materials for a wide range of next-generation flexible and transparent optoelectronic devices. Despite their amorphous nature, AIOSs are highly conducting due to their high mobility (>10 cm2/V-s) and electron concentration. Typically, they are grown at low temperature with large area uniformity, and hence are compatible with the fabrication of flexible and organic devices. In this study, we synthesize a new class of AIOS, CdO-Ga2O3 alloys on both glass and polyethylene terephthalate (PET) substrates by radio frequency magnetron sputtering at room temperature and explore their properties for flexible electronic applications. Our experimental results show that Cd1−xGaxO1+δ alloy films are amorphous with Ga content x>0.3 and within the amorphous composition range of 0.3<x<0.4 the films exhibit a high electron mobility of ~20 cm2/V-s and a low resistivity of ~2 × 10-3 Ω cm with a wide optical gap of ~3.4 eV. In order to determine if the Cd1−xGaxO1+δ alloy films are suitable for flexible electronic applications, the behaviors of their electrical resistivity after mechanical bending were also evaluated as a function of the bending radius Rb and number of bending cycles. We find that amorphous Cd1−xGaxO1+δ films are more resistant to repeated compressive (inner) bending than that of crystalline film. When Rb ≥ 10 mm, essentially no change in the electrical resistivity of the amorphous films is observed for compressive bending. On the other hand, crystalline films experience much less electrical degradation after tensile (outer) bending. SEM and AFM studies confirm that crystalline films with large grain size easily delaminate from the substrate under compressive bending, giving rise to severe electrical degradation. On the other hand, amorphous films degrade most likely through developing microcracks under repeated tensile bending. Our results suggest that amorphous Cd1−xGaxO1+δ alloy films with 0.3<x<0.4 have the desired electrical, optical and mechanical properties as transparent conductors for flexible optoelectronic devices.

Fabrication of Amorphous ZnO TFT with Tunable Channel Length

The paper discusses the fabrication of amorphous zinc oxide (a:ZnO)-top gate top contact (the gate is situated on the top and the contacts are taken from the top) thin-film transistor (TFT) using spin-spray pyrolysis (SSP) unit. The solutions of ZnO and poly-vinyl-alcohol (PVA) are synthesized separately by the sol–gel method. The ZnO and PVA solution are coated over glass substrate using the SSP unit and drop-cast technique, respectively. These films are characterized using an optical profilometer, X-ray diffractometer, energy dispersive X-ray analysis, ultraviolet–visible spectrophotometry and Keithley measurement system. The XRD and EDAX measurement confirm the amorphous nature and composition respectively. The thickness of the ZnO and PVA film are 460 nm and 600 nm, respectively. The resistance of ZnO film is 100 KΩ. Using the absorption spectrum, we calculate the bandgap of ZnO and PVA thin film samples which are 3.05 eV and 3.9 eV respectively. The metal–insulator–metal (MIM) structure is fabricated using fluorine-doped tin oxide, PVA and silver paste. The MIM structure is characterized for the electrical parameters such as capacitance and dielectric constant $$(\upvarepsilon r)$$ which is found to be 0.4 μF and 8 respectively at 40 Hz frequency. The TFT is fabricated by depositing the aluminium as electrode, ZnO as channel layer and and PVA as insulator layer of TFT with different W/L ratios. The TFT parameters such as threshold voltage (Vth), on/off current ratio (Ion/off) and mobility are studied and presented. The results confirm that Vth decreases with the shrinking of channel length. Current ratio Ion/off increases with the reduction of the channel length due to the increase in on-current value.

The Umov effect in cosmic dust analogue fluffy aggregates

ABSTRACT We investigate the effect of porosity in the Umov effect for the first time using the aggregate dust model. The Umov effect is an inverse correlation between the reflectivity (or geometric albedo) of an object and the degree of linear polarization of light scattered by it. Three different types of fractal aggregates: ballistic agglomeration (BA), ballistic agglomeration with one migration (BAM1), and ballistic agglomeration with two migrations (BAM2) having porosities 0.87, 0.74, and 0.64, respectively (which have the same characteristic radius ∼1 μm), are considered in our simulations. Using the multisphere T-matrix (mstm) code, maximum positive polarization (Pmax) and geometric albedo (A) are calculated for three different fractal aggregated structures considering amorphous silicate composition. Then Pmax and A are plotted against each other in logarithmic scale that shows a linear inverse correlation and a strong porosity dependence. This study shows that the porosity of the aggregates plays a crucial role in the Umov-law diagram. Further, we explore the effect of aggregate size parameter and the effect of composition in the Umov diagram for particles larger than the wavelength of incident radiation. A systematic study is presented in this paper.

Structural investigations on inorganic Al2O3–ZnO composites

The present work deals with the preparation and characterization of Al2O3/ZnO composites under the effect of structural and temperature changes. A sol–gel method of preparing Al2O3/ZnO composites with different concentrations of ZnO and Al2O3 was used. Materials with the extremely high Al2O3 concentration (80 mol%) have been simply prepared by the sol–gel technique. 27Al NMR spectroscopy, X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM) examined the structural features of all the samples. 27Al NMR showed a significant improvement in the product composition with the change of the Al2O3 to ZnO molar ratios. The main units that existed in the Al2O3 rich sample (80 mol%) are the structured groups AlO6, AlO5 and AlO4. The main unit in the lower Al2O3 concentration (20 mol%) is only AlO4 coordination. Through adding Al2O3, the crystalline configuration in the pure ZnO matrix is fully transformed into one of the amorphous forms. The amorphous composition of Al2O3/ZnO is retransformed into crystalline forms after calcination. The presence of different Al2O3 coordination such as AlO6, AlO5 and AlO4 is considered as the main cause for mismatching between different structural units that leads to transformation of crystalline into non-crystalline structure.

Structure of the amorphous titania precursor phase of N-doped photocatalysts.

Amorphous titania samples prepared by ammonia solution neutralization of titanyl sulphate have been characterized by chemical and thermal analyses, and with reciprocal-space and real-space fitting of wide-angle synchrotron X-ray scattering data. A model that fits both the chemical and structural data comprises small segments of lepidocrocite-type layer that are offset by corner-sharing as in the monoclinic titanic acids H2TinO2n+1·mH2O. The amorphous phase composition that best fits the combined chemical and scattering data is [(NH4)3H21Ti20O52]·14H2O, where the formula within the brackets is the cluster composition and the H2O outside the brackets is physically adsorbed. The NH4+ cations are an integral part of the clusters and are bonded to layer anions at the corners of the offset layers, as occurs in the alkali metal stepped-layer titanates. The stepped-layer model is shown to give a consistent mechanism for the reaction of aqueous ammonia with solid hydrated titanyl sulphate, in which the amorphous product retains the exact size and shape of the reacting titanyl sulphate crystals.

Structural stability of mechanically alloyed amorphous (FeCoNi)70Ti10B20 under high-temperature and high-pressure

Nanostructured (FeCoNi)70Ti10B20 (at%) alloy was synthesized by mechanical alloying from elemental powder mixture of Fe, Co, Ni, Ti and B using ball milling. The effect of ball milling time on the evolution of structure and morphology was investigated by X-ray diffraction, scanning and transmission electron microscopy and differential thermal analysis. It was observed that the formation of solid solution of (FeCoNi)70Ti10B20 started from the very onset of the milling process. Crystallite size and lattice strains seemed to be leveled off after 20 h of milling with no further major changes. The milling process for longer periods introduced severe plastic deformations causing formation of amorphous phase of (FeCoNi)70Ti10B20. The amorphous alloy composition was confirmed by energy dispersive X-ray spectroscopy analysis that showed an excellent homogeneity of the alloying elements. The phase stability of the mechanically alloyed amorphous sample was further verified by employing high-temperature and high-pressure studies. The alloy samples heat-treated at 700 °C revealed crystallization of the amorphous phase. However, synchrotron-based high-pressure ambient temperature X-ray diffraction studies confirmed that the amorphous phase of the alloy remained stable up to the pressure of 30 GPa. The 50 h milled sample after being annealed at 350 °C showed improvement in the soft magnetic properties of the alloy, which was due to the probable elimination of the residual stress in the amorphous phase of the alloy powders.

Microstructure Characterization of Amorphous Phase of Polypropylene Impact Copolymers

AbstractIn this work, three polypropylene impact copolymers (ICPs) with different chemical compositions are characterized using gel permeation chromatography (GPC) with triple detection: infrared (IR), viscometer (VIS) and multi angle light scattering (MALS), crystallization analysis fractionation (CRYSTAF), thermal gradient interaction chromatography (TGIC), nuclear magnetic resonance (13C‐NMR) and atomic force microscopy (AFM). The average rubber composition is determined and correlated with the ICP morphology and final mechanical properties. GPC‐IR is used to analyze the ethylene content and distribution along the molecular weight distribution (MWD). The amorphous phase composition distribution is analyzed as a function of temperature by TGIC. The microstructure and morphology of ICP amorphous phase are studied in detail by 13C‐NMR, GPC 3D, TGIC, SEM and AFM allowing to differentiate the samples.

Ефекти пасивації поверхні аморфних композицій на основі Fe внаслідок бомбардування йонами Ar$^+$ низьких енергій

Ефекти пасивації поверхні аморфних композицій на основі Fe внаслідок бомбардування йонами Ar$^+$ низьких енергій

Effect of aluminium concentration on phase formation and radiation stability of Cr2AlxC thin film

Near-stoichiometric and under-stoichiometric Cr2AlxC (x = 0.9 and 0.75) amorphous compositions were deposited onto a silicon substrate at 330 K in a layer-by-layer fashion using magnetron sputtering from elemental targets. The film thickness was found to be 0.9 µm and 1.2 µm for the near- and under-stoichiometric compositions respectively. A transmission electron microscope (TEM) heating holder was used to heat thin sample lamellae prepared using focused ion beam milling. Near-stoichiometric Cr2AlC thin films consisted of nano MAX phase after crystallization at 873 K. Under-stoichiometric Cr2AlxC (x = 0.75) thin films contained MAX phase along with nanocrystalline chromium aluminides after crystallization at 973 K. Irradiations with 320 keV xenon ions was performed at 623 K using a TEM with an in-situ ion irradiation (MIAMI) facility. Nanocrystalline films of near-stoichiometric Cr2AlC irradiated up to 83 displacements per atom (dpa) showed no observable changes. Also, irradiation of under-stoichiometric nanocrystalline thin films up to 138 dpa did not show any observable amorphization, and recrystallization was observed. This radiation resistance of near- and under-stoichiometric thin films is attributed to the known self-healing property of Cr2AlxC compositions further enhanced by nanocrystallinity.

Amorphous silicates as a record of solar nebular and parent body processes—A transmission electron microscope study of fine‐grained rims and matrix in three Antarctic CR chondrites

AbstractRenazzo‐type (CR) carbonaceous chondrites belong to one of the most pristine meteorite groups containing various early solar system components such as matrix and fine‐grained rims (FGRs), whose formation mechanisms are still debated. Here, we have investigated FGRs of three Antarctic CR chondrites (GRA 95229, MIL 07525, and EET 92161) by electron microscopy techniques. We specifically focused on the abundances and chemical compositions of the amorphous silicates within the rims and matrix by analytical transmission electron microscopy. Comparison of the amorphous silicate composition to a matrix area of GRA 95229 clearly shows a compositional relationship between the matrix and the fine‐grained rim, such as similar Mg/Si and Fe/Si ratios. This relationship and the abundance of the amorphous silicates in the rims strengthen a solar nebular origin and rule out a primary formation mechanism by parent body processes such as chondrule erosion. Moreover, our chemical analyses of the amorphous silicates and their abundance indicate that the CR rims experienced progressive alteration stages. According to our analyses, the GRA 95229 sample is the least altered one based on its high modal abundance of amorphous silicates (31%) and close‐to‐chondritic Fe/Si ratios, followed by MIL 07525 and finally EET 92161 with lesser amounts of amorphous silicates (12% and 5%, respectively) and higher Fe/Si ratios. Abundances and chemical compositions of amorphous silicates within matrix and rims are therefore suitable recorders to track different alteration stages on a submicron scale within variably altered CR chondrites.

Lithiation-induced fracture of silicon nanowires observed by in-situ scanning electron microscopy

Silicon is expected to be a useful anode material in lithium ion batteries for future energy storage applications, because of its high theoretical charge storage density of Li+ ions. However, volume expansion due to lithiation fractures the Si anode material, leading to poor cycle stability of battery operation. The approaches to overcome the problem include using Si nanowires to relieve the stress induced by volume expansion and coating a protective layer on the Si anode to prevent delamination. In this study, we use in-situ scanning electron microscopy to monitor the morphological changes of 90 nm thick pristine Si nanowires and the Si nanowires coated with amorphous TiO2, respectively, during electrochemical lithiation. The results of in-situ observation show that both kinds of Si nanowires exhibit a larger thickness after 10 h lithiation and suffer fracture after 25 h. It is also found that the TiO2 layer is not strong enough to prevent Si nanowires from fracture. Since the TiO2 layer can not be elastically deformed, this surface shell fractures earlier in the lithiation process than pristine Si nanowires. Transformation of the crystalline Si nanowires to an amorphous phase and lithium composition detected in the nanowires support that the observed fracture indeed results from lithiation.

Synergistic effects of stretching/polarization temperature and electric field on phase transformation and piezoelectric properties of polyvinylidene fluoride nanofilms

This study aims to investigate the dependence of crystalline structure and piezoelectric properties of polyvinylidene fluoride stretched films (up to four times their initial length) as a function of temperature, polarization under constant field as well as varying electric field at constant polarization temperature. X-ray diffraction analysis indicates that α → β phase transformation occurs below 80 °C; meanwhile, the crystallinity is improved with stretching temperature reaching 44% compared to 32% for un-stretched. FTIR analysis confirms the results obtained by XRD, as new functional groups, shift of peaks position as well as reduction in their relative intensity are observed. It is found that the piezoelectric coefficient (d33) decreases with increasing temperature, while it increases with the electric field. The obtained results are discussed on the basis of the dependence of (d33) as a function of phase (α + β + amorphous) composition and the degree of crystallinity associated with various vibrational modes and the arrangement of hydrogen and fluorine atoms (corresponding charge H+ and F−) from either sides of PVDF skeleton chains arising upon the influence of thermomechanical treatment, polarization and electric field.

Molecular dynamics and experimental study of the growth, structure and properties of Zr–Cu films

Extensive molecular dynamics simulations of the atom-by-atom growth of Zr–Cu films were performed in a wide range of compositions, energies and growth templates. The results are correlated with and used to explain experimental results obtained using magnetron sputtering of the same films. After the identification of compositional ranges corresponding to crystalline and amorphous films, we particularly focus on the evolution of characteristics of the amorphous compositions. The quantities of interest include resputtering during the film growth, surface composition, densification, crystallinity, homogeneity, short-range order (bonding statistics and coordination numbers), medium-range order (ring statistics and common neighbor statistics) and functional properties (hardness and glass transition temperature). The results are important for understanding the structures and properties of Zr–Cu films in general and Zr–Cu metallic glasses in particular, and for the design of pathways for their preparation.