Phase Structural Characteristics Research Articles

Scientific and technological bases for creation of cold-resistant steel with a guaranteed yield strength of 315–750 MPa for the Arctic. Part 1: Principles of alloying and requirements for sheet metal structure

The results of the choice of rational alloying and microalloying of cold-resistant steels with a guaranteed yield strength of 315–750 MPa are presented on the basis of the established interrelationship of phase transformations, structure, mechanical properties and performance characteristics when varying the content of basic alloying elements. Quantitative requirements for various structural parameters and their maximum permissible difference in sheet metal thickness up to 100 mm have been developed, depending on the strength category, manufacturing technology (thermomechanical treatment with accelerated cooling, hardening from separate furnace or rolling heating with high temperature tempering), which provide guaranteed characteristics of strength, cold resistance (impact work KV at test temperature –60 ... –80°С, critical temperatures of viscousbrittle transition Ткand zero ductility NDT) and crack resistance under the criterion of the critical opening in the top CTOD fracture.

Preparation and characterization of nano SiO2@CeO2 extracted from blast furnace slag and uranium extraction waste for wastewater treatment

Nowadays, ceramic oxides such as SiO2, CeO2 and their hybrid SiO2@CeO2 are considered as interesting materials for many applications. In the present work, SiO2 nanoparticles (NPs) were extracted from blast furnace slag (waste material derived from iron industry) by chemical method. On the other hand, CeO2 NPs were also extracted from radioactive nitrate solution waste using tris(2-ethylhexyl) phosphate solvent (TEHP). A simple precipitation and calcination method was used to prepare silica functionalized by ceria i.e. SiO2@CeO2 core-shell nanoparticles. In order to examine phase composition, structural characteristics, morphological, surface area and physical properties, the prepared NPs were characterized by various techniques. These techniques were XRF, XRD, Raman spectroscopy, Nitrogen adsorption–desorption isotherms, DLS, TEM, and Zeta potential. The activity of prepared SiO2 and hybrid SiO2@CeO2 materials towards the adsorption and photocatalytic degradation of methylene blue dye (MB) was investigated in absence (dark) or presence of UV–visible light. The results revealed that CeO2, SiO2 and SiO2@CeO2 nanoparticles having high surface area, high pore volume and small particle sizes were successfully prepared using the aforementioned waste materials. SiO2 NPs exhibited higher absorption capacity for MB in dark due to its higher negative surface charge as indicated by its zeta potential result. On the other hand, enhanced photocatalytic activity was obtained after coating CeO2 on SiO2 nanoparticles as compared with that of single SiO2. The overall adsorption efficiencies for MB in dark followed by UV light using SiO2 and SiO2@CeO2 were 94% and 99.1%, respectively. The kinetic studies indicated that the reaction proceeded as a pseudo-second order reaction.

Effect of Heating on the Structure, Phase Composition, and Micromechanical Properties of the Metastable Austenitic Steel Strengthened by Nanostructuring Frictional Treatment

The influence of heat treatment in the 100–900°С temperature range on the phase composition, structure, and micromechanical characteristics of the surface layer of the 12Kh18N10T steel subjected to nanostructuring frictional treatment (FT) with a sliding indenter has been studied. This study considered opportunities for strengthening metastable austenitic steel using combined thermomechanical treatments. Annealing at 400–450°C allows for the retention of nanocrystalline martensitic–austenitic structures formed in the surface layer of the steel and a significant increase in the micromechanical characteristics owing to the strengthening of the strain-induced martensite. The annealing of the steel at 650°C leads to the formation in the surface layer of an austenitic predominantly submicrocrystalline and nanocrystalline structure with a hardness of 630 HV 0.025, which is almost 3 times higher than the hardness of steel in the initial quenched state. The transmission electron-microscopic studies of the surface layer of the austenitic steel deformed by FT made it possible to reveal the retention of highly dispersed austenitic regions in addition to the recrystallized regions upon heating to 800°C, as well as the absence of abnormal growth of recrystallized austenite grains upon heating to 900°C.

Phase evolution, structural characteristics and mechanism of vesicle formation from a synthetic amphiphile: Controlled morphology by tuning solution phase parameters

We report herein, the aggregation behavior of 3, 4-di(dodecyloxy)benzoic acid-4-hydroxy phenyl ester (DDBE), a synthetic amphiphile and a true non-ionic surfactant system as per the geometrical considerations. The true surfactant nature of the system stems from its hydrophilic-lipophilic-balance (HLB = 4.7), comparable to that of Span-60, also a true non-ionic surfactant. This compound undergoes spontaneous vesicle formation in THF:water binary solvent mixtures which further underwent fission at lower DDBE concentrations and fusion at higher concentrations, leading to giant vesicles of the order of 3000 nm. These vesicles are sensitive to the polarity of their environment. The predominant mode of interaction as observed from the molecular dynamics simulations were found to be π-π stacking with the phenyl rings of the molecule. Further, the system, upon complete extraction into water, formed spherical aggregates of size 50 nm based on the good solvent-poor solvent combination as the necessary condition for the vesicle formation.GRAPHICAL ABSTRACT

Вплив ультразвукового оброблення в кульовому млині на фазово-структурні характеристики високодисперсних порошкових сумішей міді з залізом і кобальтом

Вплив ультразвукового оброблення в кульовому млині на фазово-структурні характеристики високодисперсних порошкових сумішей міді з залізом і кобальтом

Magnesium and silicon co-doped LiNi0.5Mn1.5O4 cathode material with outstanding cycling stability for lithium-ion batteries

The magnesium (Mg) and silicon (Si) co-doped LiNi0.5Mn1.5O4 sample has been obtained by sol-gel method. The effects of co-doping with magnesium and silicon ions on the phase structure, morphology and electrochemistry characteristics of LiNi0.5Mn1.5O4 are investigated by a series of physico-chemical characterizations. XRD results demonstrate that the magnesium and silicon ions successfully enter into the spinel structure and make the lattice parameter slightly increased. Moreover, the magnesium and silicon ions co-doped sample presents superior cycling stability. When cycled at 0.5 C, this sample still delivers 121 mAh g−1 after 100 cycles with outstanding retention of 98.86%, while the undoped LiNi0.5Mn1.5O4 sample only exhibits 104.5 mAh g−1 after 100 cycles with low retention of 79.17%. In addition, the Mg2+ and Si4+ co-doped sample shows outstanding rate capability and low charge transfer resistance.

Multilayer-Structured Poly-Vanadium Acid/Polyaniline Composite: Synthesis and Properties for Humidity Sensing

A high-performance humidity sensor based on multilayer-structured poly-vanadium acid/polyaniline (V/PANI) composite was reported in this paper. Two-layer-structured V/PANI composite was fabricated by dip-coating poly-vanadium acid and electrochemically polymerizing PANI onto the interdigitated gold electrode in sequence, and then the process could be repeated to prepare the second two-layer-structured V/PANI composite. The crystalline phase properties and structural characteristics of the poly-vanadium acid, PANI, and V/PANI composite were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy, and UV-visible spectroscopy, respectively. The morphological characteristics of the first two-layer-structured V/PANI composite and multilayer-structured V/PANI composite were characterized by scanning electron microscopy. Additionally, sensors based on the multilayer-structured V/PANI composite showed good humidity sensing properties. For instance, its impedance changed linearly for approximately four orders of magnitude in a wide range of 11-97% RH. Furthermore, it displayed small hysteresis (~5% RH), fast response (t90% of 8 s and 12 s for adsorption and desorption processes, respectively), good stability. The possible sensing mechanism was analyzed by considering the special multilayer structure and using complex impedance spectra and the corresponding equivalent circuit of the sensor. The measurement results highlight the multilayer-structured V/PANI composite film is a candidate material for constructing humidity sensors.

Sol-gel synthesis and luminescence properties of Ba2SiO4:Sm3+ nanostructured phosphors

Ba2SiO4:Sm3+ nanostructure phosphors have been synthesized by a simple sol-gel method. Phase evaluation, structural characteristics and photoluminescence properties of the synthesized Ba2SiO4:Sm3+ powders were studied using field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG-DTA), Fourier transform infrared spectroscopy (FTIR), and photoluminescence spectroscopy (PL). X-ray diffraction results showed that all synthesized samples were single-phase barium silicate (Ba2SiO4) and samarium (Sm) ions were incorporated into the lattice of Ba2SiO4. Adding samarium to barium silicate changed the microstructure from vermicular to spherical structures. The Photoluminescence spectrum of Ba2SiO4:Sm3+ phosphors exhibited characteristic emission peaks at 562 nm which is due to the 4G5/2 →6H7/2 transition of samarium ions and corresponds to the orange region. The results showed that the barium silicate activated with 0.08 mol samarium exhibited the highest PL intensity.

Magnetic Properties and Structural Characteristics of BaFe12O19 Hexaferrites Synthesized by the Zol-Gel Combustion

The phase structure, structural parameters, and basic magnetic characteristics of BaFe12O19 hexaferrites prepared by the zol-gel combustion method with subsequent annealing at a temperature of 850°С for 6 h are investigated. The influence of the organic fuel type on the properties of synthesized materials is analyzed. Values of the saturation magnetization and the anisotropy field are determined. It is established that they depend on the organic fuel type. It is shown that powders synthesized with citric acid used as a fuel have the largest particle sizes and the highest saturation magnetization.

Crystallization characteristic and scaling behavior of germanium antimony thin films for phase change memory.

Amorphous Ge8Sb92 thin films with various thicknesses were deposited by magnetron sputtering. The crystallization kinetics and optical properties of the Ge8Sb92 thin films and related scaling effects were investigated by an in situ thermally induced method and an optical technique. With a decrease in film thickness, the crystallization temperature, crystallization activation energy and data retention ability increased significantly. The changed crystallization behavior may be ascribed to the smaller grain size and larger surface-to-volume ratio as the film thickness decreased. Regardless of whether the state was amorphous or crystalline, the film resistance increased remarkably as the film thickness decreased to 3 nm. The optical band gap calculated from the reflection spectra increases distinctly with a reduction in film thickness. X-ray diffraction patterns confirm that the scaling of the Ge8Sb92 thin film can inhibit the crystallization process and reduce the grain size. The values of exponent indices that were obtained indicate that the crystallization mechanism experiences a series of changes with scaling of the film thickness. The crystallization time was estimated to determine the scaling effect on the phase change speed. The scaling effect on the electrical switching performance of a phase change memory cell was also determined. The current-voltage and resistance-voltage characteristics indicate that phase change memory cells based on a thinner Ge8Sb92 film will exhibit a higher threshold voltage, lower RESET operational voltage and greater pulse width, which implies higher thermal stability, lower power consumption and relatively lower switching velocity.

Structural characteristics and microwave dielectric properties of a new Sm2O3-Nd2O3-MgO-CeO2 ceramic system

Sm2O3-Nd2O3-MgO-CeO2 ceramic systems of the form Sm1-xNdx(Mg0.5Ce0.5)O3 (0.0 ≤ x ≤ 1.0) were synthesized by a conventional solid-state reaction method, and the phase structural characteristics, microstructures, sintering behaviors and microwave dielectric properties were investigated systematically. X-ray diffraction analyses revealed that a cubic fluorite-type structure with Fm-3m (225) space group was identified as the main crystalline phase in the composition range of x = 0.0–1.0, while some secondary phases were also detected in all the Sm1-xNdx(Mg0.5Ce0.5)O3 samples. The phase structural characteristics of Sm2O3-Nd2O3-MgO-CeO2 quaternary ceramic systems were significantly affected by a certain amount of Mg2+ ion volatilization, detected by the typical EDS data. Additionally, both an example of EDS analysis in the second phases regions and some details of the diffraction peaks implied that the unknown phases were mainly composed of MgO phase. Furthermore, for the microwave characteristics, the relative permittivity (εr) was closely related to the dense degree and phase compositions, and also, the quality factor (Q × f) had been strongly depended on the compactness and lattice defects in these investigated ceramics. Wherein, after sintering at 1450 °C for 4 h, the x = 0.0 sample demonstrated the excellent microwave dielectric performance: εr ∼16.6, Q × f ∼111,280 GHz (at 7.938 GHz) and τf ∼ −56.7 ppm/°C. These results also indicated that the Ce1-xLnxO2-δ (Ln = Sm and Nd) solid solutions could be a good candidate for dielectric resonators, filters and other microwave electronic device applications.

Preparation of dense La0.9Sr0.1Ga0.8Mg0.2O3-δ with high ionic conductivity by solid-state synthesis

The results of a systematic investigation on the effects of processing steps, via solid-state reactions, on structural phase characteristics and ionic conductivity of La0.9Sr0.1Ga0.8Mg0.2O3-δ solid electrolyte are reported. The main purpose of this work is to establish an optimized route for obtaining good densification and high ionic conductivity of this solid electrolyte. Processing routes with three successive calcinations at 1250 °C followed by attrition milling (R1), and with two sequences of calcination at 1350 °C with intermediary attrition milling (R2) give rise to near full density at 1450 °C sintering temperature. The rate of grain growth is fast when the relative density reaches 95%. Elemental mapping reveals uniform distribution of the constituents in the matrix along with La4Ga2O9, LaSrGa3O7 and sub-micrometer MgO grains at grain boundaries. The ionic conductivity of grains remains unchanged with the processing route and sintering profile. The blocking effect of charge carriers at grain boundaries decreases with increasing the dwell temperature.

Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS) with Raman Imaging Applied to Lunar Meteorites.

Lunar meteorites provide a more random sampling of the surface of the Moon than do the returned lunar samples, and they provide valuable information to help estimate the chemical composition of the lunar crust, the lunar mantle, and the bulk Moon. As of July 2014, ∼96 lunar meteorites had been documented and ten of these are unbrecciated mare basalts. Using Raman imaging with multivariate curve resolution-alternating least squares (MCR-ALS), we investigated portions of polished thin sections of paired, unbrecciated, mare-basalt lunar meteorites that had been collected from the LaPaz Icefield (LAP) of Antarctica-LAP 02205 and LAP 04841. Polarized light microscopy displays that both meteorites are heterogeneous and consist of polydispersed sized and shaped particles of varying chemical composition. For two distinct probed areas within each meteorite, the individual chemical species and associated chemical maps were elucidated using MCR-ALS applied to Raman hyperspectral images. For LAP 02205, spatially and spectrally resolved clinopyroxene, ilmenite, substrate-adhesive epoxy, and diamond polish were observed within the probed areas. Similarly, for LAP 04841, spatially resolved chemical images with corresponding resolved Raman spectra of clinopyroxene, troilite, a high-temperature polymorph of anorthite, substrate-adhesive epoxy, and diamond polish were generated. In both LAP 02205 and LAP 04841, substrate-adhesive epoxy and diamond polish were more readily observed within fractures/veinlet features. Spectrally diverse clinopyroxenes were resolved in LAP 04841. Factors that allow these resolved clinopyroxenes to be differentiated include crystal orientation, spatially distinct chemical zoning of pyroxene crystals, and/or chemical and molecular composition. The minerals identified using this analytical methodology-clinopyroxene, anorthite, ilmenite, and troilite-are consistent with the results of previous studies of the two meteorites using electron microprobe analysis. To our knowledge, this is the first report of MCR-ALS with Raman imaging used for the investigation of both lunar and other types of meteorites. We have demonstrated the use of multivariate analysis methods, namely MCR-ALS, with Raman imaging to investigate heterogeneous lunar meteorites. Our analytical methodology can be used to elucidate the chemical, molecular, and structural characteristics of phases in a host of complex, heterogeneous geological, geochemical, and extraterrestrial materials.

Fabrication of duplex coatings on biodegradable AZ31 magnesium alloy by integrating cerium conversion (CC) and plasma electrolytic oxidation (PEO) processes

In the present study, two types of duplex coatings were fabricated on pre-treated biodegradable AZ31 magnesium alloy by a combination of cerium conversion (CC) and plasma electrolytic oxidation (PEO) coating processes, namely CC followed by PEO coating (CCPEO) and PEO followed by CC coating (PEOCC). PEO coating was fabricated with an electrolyte system consisting of 7 g/l sodium silicate (Na2SiO3·10H2O) and 3 g/l potassium hydroxide (KOH). All the PEO coatings were formed using a pulsed DC power source at a constant current density of 60 mA/cm2 and a treatment time of 15 min. An electrolyte containing 10 g/l cerium nitrate hexahydrate (Ce (NO3)3·6H2O) with a pH of 3 adjusted by using H2O2 was used for the conversion coating process with the treatment time of 4 h. The phase composition, surface roughness, surface morphology, elemental composition and structural characteristics of the coatings were assessed by X-ray diffraction (XRD), an optical profilometer, scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) techniques. The electrochemical corrosion behavior of substrate and coatings was analyzed under a Kokubo 7.4 pH simulated body fluid (SBF) solution by open circuit potential (OCP) measurement, electrochemical impedance spectroscopy (EIS) with an equivalent circuit modelling and potentiodynamic polarization (PDP) methods. The scratch resistance and wettability of the coatings were analyzed by performing a scratch test using a Rockwell C diamond indenter and contact angle goniometer, respectively. The apatite forming ability of all the coatings and the substrate was studied after immersing in SBF solution for 14 days. Among all the coatings under this investigation, the CCPEO coating showed higher corrosion resistance in the SBF environment (icorr = 1.18 × 10−3 μA/cm2 and higher scratch resistance (Lc = 32.5 N). The high corrosion and scratch resistances of the CCPEO coating is attributed to its higher coating thickness and less surface porosity. The CCPEO coated sample also showed good apatite forming ability under physiological environment, making it a good candidate material for biodegradable implant applications.

Graphene and related two-dimensional materials: Structure-property relationships for electronics and optoelectronics

The exfoliation and identification of the two-dimensional (2D) single atomic layer of carbon have opened the opportunity to explore graphene and related 2D materials due to their unique properties. 2D materials are regarded as one of the most exciting solutions for next generation electronics and optoelectronics in the technological evolution of semiconductor technology. In this review, we focus on the core concept of “structure-property relationships” to explain the state-of-the-art of 2D materials and summarize the unique electrical and light-matter interaction properties in 2D materials. Based on this, we discuss and analyze the structural properties of 2D materials, such as defects and dopants, the number of layers, composition, phase, strain, and other structural characteristics, which could significantly alter the properties of 2D materials and hence affect the performance of semiconductor devices. In particular, the building blocks principles and potential electronic and optoelectronic applications based on 2D materials are explained and illustrated. Indeed, 2D materials and related heterostructures offer the promise for challenging the existing technologies and providing the chance to have social impact. More efforts are expected to propel this exciting field forward.

Domain Evolution and Piezoelectric Response across Thermotropic Phase Boundary in (K,Na)NbO3-Based Epitaxial Thin Films.

Recent research progress in (K,Na)NbO3 (KNN)-based lead-free piezoelectric ceramics has attracted increasing attention for their applications to microsystems or microelectromechanical systems (MEMS) in the form of thin films. This work demonstrates that high-quality KNN-based epitaxial films can be synthesized by a conventional sol-gel method, whose phase structure and domain characteristics have been investigated with emphasis on the temperature effect. A monoclinic MC structure is observed at room temperature in KNN-based epitaxial films, which is close to but different from the orthorhombic phase in bulk counterparts. Piezoresponse force microscopy (PFM) at elevated temperatures reveals continuous changes of ferroelectric domains in KNN films during heating and cooling cycles between room temperature and 190 °C. A distinct change in domain morphology is observed upon heating to 110 °C, accompanied by a clear variation of dielectric permittivity suggesting a thermotropic phase transition, which is revealed to belong to a MC-MA phase transition on the basis of structural and PFM analysis on local ferroelectric and piezoelectric behaviors. Enhanced piezoelectric response at the thermotropic phase boundary is observed, which is attributed to active domains and/or nanodomains formed across the boundary. Domain engineering by utilizing the phase transition should be important and effective in KNN-based films not only for property enhancement but also for its textured ceramics.

Electrochemical synthesis and the physicochemical properties of a nanodispersed system based on iron and aluminum oxides

An Al2O3–Fe2O3 dispersed oxide system has been obtained electrochemically in aqueous solutions containing chloride ions with the subsequent thermal treatment. The phase and elemental composition and structural characteristics of the samples have been studied using X-ray phase analysis, Mossbauer spectroscopy, and scanning electron microscopy. The effect of the electrolysis mode and thermal treatment on the characteristics of the samples which were synthesized is shown. It is found that a high-temperature treatment (1100°C) facilitates the formation of a complex oxide material whose phase composition is a combination of the α-Al2O3 (corundum) and α-Fe2O3 (hematite) crystalline phases and whose particles have nanometer sizes.

Template-assisted hydrothermally synthesized iron-titanium binary oxides and their application as catalysts for ethyl acetate oxidation

Iron-titanium binary oxides were synthesized by template-assisted hydrothermal method. The effect of the variation in the Fe/Ti ratio and the temperature of hydrothermal treatment on the phase composition, structural, textural and redox characteristics of thus obtained materials was studied by Nitrogen physisorption, XRD, SEM, HRTEM, XPS, Raman, UV–vis, FTIR and Moessbauer spectroscopy and TPR with hydrogen. The contribution of various features of the samples on their catalytic behaviour in total oxidation of ethyl acetate as a representative VOC was in the focus of the discussion. The binary materials represent a complex mixture of pure and substituted anatase and/or hematite phases with different dispersion and proportion, which can be controlled by both the variation in the Fe/Ti ratio and the temperature of hydrothermal treatment. The stabilization of finely dispersed hematite-like particles in the vicinity of Fe3+ substituted in titania was considered as an important factor for the improvement of the catalytic activity and selectivity in total oxidation of ethyl acetate and it is favoured by the lower Fe/Ti ratio and the lower temperature of the hydrothermal treatment.

Rare earth and transition metal doped BiFeO3 ceramics: structural, magnetic and dielectric characterization

Here we studied the effect of rare earth (Y) and transition metal (Co, Ni) substitution on the structure, magnetic and dielectric properties of the BiFeO3 (BFO) multiferroic ceramic. The samples were synthesized by modified rapid liquid phase sintering method. The phase purity and structural characteristics of the ceramics were investigated by X-ray diffraction and scanning electron microscope. The results revealed the uniform micro-structure with reduced grain size due to the rare earth doping in the BFO. Compared to the pure BFO, enhanced coercivity and resistivity were observed for the co-doped ceramics with Y and Co. The improvement of temperature stability of magnetism and electrical conductivity was found for ceramic co-doped with Y+3 and Ni+2 ions. The possible origin of the improvement in these properties has been discussed on the basis of the size effect and nature of the dopants.

Changes of Asphaltenes’ Structural Phase Characteristics in the Process of Conversion of Heavy Oil in the Hydrothermal Catalytic System

The composition of heavy crude oil from the Ashal’cha field (Volga-Ural Basin, Republic of Tatarstan) and the peculiarities of the changes of its asphaltenes’ structural phase characteristics in the model hydrothermal–catalytic system have been studied very thoroughly. It has been established that in the water vapor media the process of destruction of the heavy crude oil high-molecular-weight components with the new light fraction formation in the presence of a natural catalyst, namely, hematite, containing iron oxide and at the temperatures of 210, 250, and 300 °C respectively, takes place which has an effect on the changes in its component hydrocarbon, fractional, and structural group composition as well as in the structural parameters of its asphaltenes. As the experiments temperature increases and the water content in the reaction system decreases, the general tendency of growth the asphaltene associates aromaticity factor revealed that in turn it is accompanied by the extension (increase) of the distance between the aromatic layers and polymethylene chain fragments under the reduction of the size of associates and the number of their aromatic layers; this results from the destructive processes course, taking place along/on the most stable asphaltene heteroatomic bonds with/accompanied by further peripheral alkyl fragments breaking off, which has been confirmed by the molecular mass of the fragments above as well as destruction of vanadyl–porphyrin complexes and increase of free radicals concentration. A significant ability of asphaltene associates to immobilize their maltenes has been revealed. Within the process of oxidation cracking at the temperature of 300 °C and under the low water content in the reaction system, the increase in aromaticity and in the degree of association asphaltenes transform to carben–carboids and then to coke and are precipitated out of the oil in the solid form.