Formation Of New Phase Research Articles

Phase equilibria in the La2O3-Y2O3-Nd2O3 system at 1500 °C

The phase equilibria in the ternary La2O3-Y2O3-Nd2O3 system at 1500 °C were studied by X-ray diffraction, petrography, and electron microscopy in the overall concentration range. The samples of different compositions have been prepared from nitrate acid solutions by evaporation, drying, and calcination at 1100 and 1500 °C. The solid solutions based on various polymorphous forms of source components and ordered phase of LaYO3 were revealed in the system. The isothermal section of the phase diagram for the La2O3-Y2O3-Nd2O3 system has been developed. It was established that in the ternary La2O3-Y2O3-Nd2O3 system there exist fields of solid solutions based on hexagonal (A) and monoclinic (B) modifications of La2O3 and Nd2O3, cubic (C) modification of Y2O3, as well as perovskite-type structure of LaYO3 (R) with rhombic distortions. The systematic study that covered the whole composition range excluded the formation of new phases. The refined lattice parameter of the unit cell and the boundaries of the homogeneity fields for solid solutions were determined.

Osteogenesis and biofilms formation on titanium surfaces submitted to oxygen plasma immersion ion implantation

The objectives of this study were to characterize titanium (Ti) surfaces treated by ion implantation by immersion in oxygen plasma (O-PIII) at different temperatures, correlating these implanted layers with therapeutic effects and with osteogenesis, as well as the formation of monotypic biofilms microbial. The groups were divided into: a) Ti (pre-treatment) b) Ti O-PIII at 400 ° C. c) Ti O-PIII at 500 ° C. d) Ti O-PIII at 600 ° C. The properties and surface characteristics were evaluated according to the roughness, texture, corrosion resistance, formation of new phases and the identification of chemical compounds present. Cellular analyzes investigated cell interaction, viability, total protein content, alkaline phosphatase and quantification of mineralized nodules using MG-63 cells. The formation of monotypic microbial biofilms, including P. aeruginosa, S. aureus, S. mutans and C. albicans were evaluated. The increase in surface roughness, corrosion resistance and oxygen content, leading to the formation of TiO2-rutile with more intense peaks and in greater numbers according to the increase in the substrate temperature, ionic implanted Ti samples was observed. There was also a significant increase in cell viability, total protein production, alkaline phosphatase activity and formation of mineralization nodules for the group treated with O-PIII at 600ºC compared to other groups, in addition to a reduction of microorganisms in the groups treated with O- PIII. Therefore, treatment with O-PIII at 600ºC in Ti grade IV showed favorable results for its use.

Phase Transitions and Structural Changes in DPPC Liposomes Induced by a 1-Carba-Alpha-Tocopherol Analogue.

Steady-state emission spectroscopy of 1-anilino-8- naphthalene sulfonate (ANS) and 1,6-diphenyl-1,3,5-hexatriene (DPH), fluorescence anisotropy, and DSC methods were used to characterize the interactions of the newly synthesized 1-carba-alpha-tocopherol (CT) with a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) membrane. The DSC results showed significant perturbations in the DPPC structure for CT concentrations as low as 2 mol%. The main phase transition peak was broadened and shifted to lower temperatures in a concentration-dependent manner, and pretransition was abolished. Increasing CT concentrations induced the formation of new phases in the DPPC structure, leading to melting at lower temperatures and, finally, disruption of the ordered DPPC structure. Hydration and structural changes of the DPPC liposomes using ANS and DPH fluorescent probes, which are selectively located at different places in the bilayer, were studied. With the increased concentration of CT molecules in the DPPC liposomes, structural changes with the simultaneous formation of different phases of such mixture were observed. Temperature studies of such mixtures revealed a decrease in the temperature of the main phase transition and fluidization at decreasing temperatures related to increasing hydration in the bilayer. Contour plots obtained from concentration–temperature data with fluorescent probes allowed for identification of different phases, such as gel, ordered liquid, disordered liquid, and liquid crystalline phases. The CT molecule with a modified chromanol ring embedded in the bilayer led to H-bonding interactions, expelling water molecules from the interphase, thus introducing disorder and structural changes to the highly ordered gel phase.

Pressure-induced electrides and metallic phases in the Y–Cl system

Pressure can profoundly change the electronic structure, leading to the formation of new phases and materials with exotic properties. Herein, using evolutionary algorithms and density functional theory, we systematically investigate the behaviour of materials in the yttrium–chlorine binary system under pressure. Electrons are found to be spatially confined at low pressures in yttrium chlorides and tend to form new electrides. In particular, a novel yttrium chloride, Y3Cl2, is predicted to be thermodynamically and lattice dynamically stable at approximately 10 GPa. Further analyses of the electron localization function and partial charge density identify trigonal Y3Cl2 as a new 2D high-pressure electride with partially localized electrons contributing to the conduction. By further increasing the pressure, electrons in the yttrium–chlorine binary system tend to delocalize with the electrides decomposing into two new compounds (Y2Cl and YCl2) and a new YCl phase (space group P63/mmc) above 20 GPa. These newly discovered phases are all metallic in their stable pressure range according to band structure simulations without interstitial electron localization. The discovery of these unconventional yttrium chlorides may inspire strategies to search for low-pressure electrides in other rare-earth halogenide systems.

Phase evolution and structural modulation during in situ lithiation of MoS2, WS2 and graphite in TEM

Li-ion batteries function by Li intercalating into and through the layered electrode materials. Intercalation is a solid-state interaction resulting in the formation of new phases. The new observations presented here reveal that at the nanoscale the intercalation mechanism is fundamentally different from the existing models and is actually driven by nonuniform phase distributions rather than the localized Li concentration: the lithiation process is a ‘distribution-dependent’ phenomena. Direct structure imaging of 2H and 1T dual-phase microstructures in lithiated MoS2 and WS2 along with the localized chemical segregation has been demonstrated in the current study. Li, a perennial challenge for the TEM, is detected and imaged using a low-dose, direct-electron detection camera on an aberration-corrected TEM and confirmed by image simulation. This study shows the presence of fully lithiated nanoscale domains of 2D host matrix in the vicinity of Li-lean regions. This confirms the nanoscale phase formation followed by Oswald ripening, where the less-stable smaller domains dissolves at the expense of the larger and more stable phases.

Controlled preparation of undoped Zn2GeO4 microcrystal and the luminescent properties resulted from the inner defects

Zn2GeO4 microcrystals were prepared by hydrothermal method. Two synthesis routes were tried and the products were studied by analyzing the morphology and the crystalline phases. According to the experimental phenomenon and the XRD spectra of the products obtained at different stages in the preparation process, the possible chemical reactions in the synthesis process were analyzed. Homogeneous dispersion system is needed for preparing well dispersed nanometer or micron Zn2GeO4. PH value of the reaction system and the synthesis route affect the particle size and the morphology of the samples deeply. Heat treatment changes the optical properties of the samples and too high temperature leads to the formation of new phase. With the increase of annealing temperature, the emission spectrum first becomes wider and then narrower. This is because the defect kind and the defect intensity vary with sintering temperature. As a result, the CIE Chromaticity coordinates correspond to the emission spectra move from white area to green area. This change is the inevitable result of defect luminescence mechanism.

Characterization of AlScN-Based Multilayer Systems for Piezoelectric Micromachined Ultrasound Transducer (pMUT) Fabrication

Scandium-alloyed aluminum nitride (AlScN) is a potential material for micro-electromechanical systems because of its unique advantages, such as strong piezoelectric effect and high thermal stability. However, issues related to its stability and interaction with other materials in multilayer systems require investigation. The formation of new phases at the interface between piezomaterial and electrode material can lead to the device failure. In this study, multilayer structures Si substrate/AlN/Ti-Mo/Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.8</sub> Sc <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.2</sub> N/top electrode (TE) were studied after annealing at a wide range of temperatures and durations. Four different TE materials (i.e. Al, AlSi (1%), Mo/Al, and Mo) were examined to determine the most reliable electrode material for the structure. The phase stability, interfacial quality, and piezoelectric response of the multilayer systems after thermal annealing were investigated. The structure with Mo TE layer was stable after annealing at 800 °C for 300 h and at 1000 °C for 100 h. None of the structures formed any new phases at the interface between the electrode layer and AlScN. The transverse piezoelectric coefficient (e <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">31,f</sub> ) was determined for Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.8</sub> Sc <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.2</sub> N before and after annealing. The absolute value of the e <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">31,f</sub> was -1.39 C/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for as-deposited structure and -1.67 C/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for the same structure annealed for 300 h at 800 °C. [2020-0361]

A Short Review on the Phase Structures, Oxidation Kinetics, and Mechanical Properties of Complex Ti-Al Alloys.

This paper reviews the phase structures and oxidation kinetics of complex Ti-Al alloys at oxidation temperatures in the range of 600–1000 °C. The mass gain and parabolic rate constants of the alloys under isothermal exposure at 100 h (or equivalent to cyclic exposure for 300 cycles) is compared. Of the alloying elements investigated, Si appeared to be the most effective in improving the oxidation resistance of Ti-Al alloys at high temperatures. The effect of alloying elements on the mechanical properties of Ti-Al alloys is also discussed. Significant improvement of the mechanical properties of Ti-Al alloys by element additions has been observed through the formation of new phases, grain refinement, and solid solution strengthening.

Dependence of Thermal Expansion of Zr-Based Products on their Crystallographic Texture

The accident at Fukushima Daiichi in 2011 highlighted the increased interest in predicting the materials properties under extreme conditions. In this work, it is considered the behaviour of cubic samples cut from the wall of channel tubes made of Zr-2.5% Nb alloy during heating and cooling in the temperature range of 20-1200 °C. The anisotropy of changes in the dimensions of cubic samples in different structural states has been studied. Thermal tests were carried out in three mutually perpendicular directions: radial, tangential and axial. The structural state of tubes was estimated from the features of their crystallographic texture. The significant anisotropy of the size change is observed in the Zr-2.5%Nb alloy product with an unstable crystallographic texture of deformation due to the α↔β-phase transformation inhomogeneity. In the case of complete recrystallization and orientation of the <1120> axes along the tube axis, the anisotropy of the dimensions change is minimal, due to uniform nuclei formation of new phases in different orientations.

Remarkable improvement in high temperature oxidation resistance of WC-12Co by the addition of CrSi2

WC-Co has excellent mechanical properties at a temperature below 700 °C, but above it, the mechanical properties of WC-Co decrease severely because of the oxidation effect. In the present study, the addition of metal silicide of CrSi2 was considered to enhance the oxidation resistance of cementite carbide. The WC-12Co compacts containing 0, 12.5, and 25 wt% CrSi2 were prepared using mechanical alloying and spark plasma sintering techniques at 1150 °C. According to the results of metallographic characterization, the sintered WC-12Co is composed mainly of WC and Co phases. The addition of CrSi2 leads to the formation of new phases as CrSi, CoSi, Co6W6C, and SiC depending on the compact composition. It is found that the WC-12Co compact with 12.5 wt% CrSi2 content exhibits a lower measured density and higher hardness compared to that of CrSi2-free compact. After the first cycle of exposure at 900 °C, the WC-12Co is severely oxidized, forming porous and crack oxide scales. On the contrary, the addition of 12.5 wt% CrSi2 shows the lowest mass gain and displays the most resistance to oxidation attributed to the formation of mainly SiO2 scales. Further increase in CrSi2 concentration, however, the alloy compact experiences breakaway oxidation after the fifth cycle of exposure. Accordingly, it can be proposed that the addition of 12.5 wt% CrSi2 is the most promising composition to allow the cemented carbide used at high temperatures and oxidizing atmospheres.

Formation of short-range magnetic order and avoided ferromagnetic quantum criticality in pressurized LaCrGe3

LaCrGe$_3$ has attracted attention as a paradigm example of the avoidance of ferromagnetic (FM) quantum criticality in an itinerant magnet. By combining thermodynamic, transport, x-ray and neutron scattering as well as $\mu$SR measurements, we refined the temperature-pressure phase diagram of LaCrGe$_3$. We provide thermodynamic evidence (i) for the first-order character of the FM transition when it is suppressed to low temperatures and (ii) for the formation of new phases at high pressures. From our microscopic data, we infer that short-range FM ordered clusters exist in these high-pressure phases. These results suggest that LaCrGe$_3$ is a rare example, which fills the gap between the two extreme limits of avoided FM quantum criticality in clean and strongly disordered metals.

Improving of shaft steel materials properties using ion nitriding

During operation, shaft steel always contacts with other components, so this material will erode gradually and will be accelerated if this component used in corrosive environment. Finally, the performance of the components to be worse. To improve the quality of the surface components, an ion nitriding technique can be applied. In this research, ion nitriding process was carried out at 300°C, 350°C, 400°C, 450°C and 1.6 mbar for 4 hours. It can be concluded that generally by increasing the temperature, the hardness increases and at 450°C reached the highest value in order of 297.86 VHN, while the hardness of raw materials is 98.66 VHN or increases by factors 3, the wear decreases from 60.3 × 10−9 mm2/kg to 26.8 × 10−9 mm2/kg or there is an increasing in wear resistance by factor 2.25, and corrosion rate decreases from 4.2465 mpy to 0.6748 mpy.From XRD analysis, it is observed the formed phase are Fe2N and Fe3N. The formation of new phase contributes in improving of hardness, wear, and corrosion resistance.

A simultaneous improvement of both hardness and ductility of Ti-6Al-4V alloy by Nb addition

Some mechanical properties of treated Ti-6Al-4V alloy such as micro hardness and ductility were investigated. Ti-6Al-4V-xNb (x = 1, 2 and 5 wt.%) alloys were produced. The influence of Nb contents on microstructure characteristics and mechanical properties showed that the addition of Nb in Ti-6Al-4V alloy persuaded the formation of new phase distributing at grain boundaries. When the Nb content increases from 0 wt% to 5 wt%, the existence of fine precipitates postponed dynamic recrystallization and refined dynamically recrystallized. The average grain size of treated titanium alloy decreased significantly from ∼20 to ∼5 µm as a function of Nb contents increasing from 0 to 5 wt%, which can be attributed to the greater number of recrystallization nucleation sites due to grain refinement of the billet. The addition of Nb simultaneously improved the microstructural homogeneity, hardness, and ductility of the extruded alloys. The significant increase of microhardness was mainly ascribed to refined microstructure and dynamic precipitates.

Study on the formation mechanism of Y-Ti-O oxides during mechanical milling and annealing treatment

Y-Ti-O nano-scale oxides play important roles in ensuring the excellent performance of oxide dispersion strengthened (ODS) steels. In this study, a model powder system of Y2O3 and Ti was designed to investigate the formation and evolution mechanism of Y-Ti-O oxides. The morphology of powders tended to be stable after high energy ball milling for 240 min in Ar. X-ray diffraction (XRD) results suggested that there was no formation of new phase after mechanical milling. Thermo-gravimetric and differential thermal analysis (TG-DTA) was applied to analyze physical and chemical reactions of milled powders respectively in Ar and air. The corresponding annealing and XRD were performed to study the types and structures of oxides at different temperatures. It shows that oxygen concentration and temperature are the critical factors affecting the formation of oxides. Ti was evolved into Ti6O, Ti3O and TiO2 in turn with temperature increasing. Then only TiO2 was reacted with Y2O3 to form Y2Ti2O7. The formation of Y2Ti2O7 began at around 500 ℃ and was completed around 1004 ℃. A maximum formation rate occurred at about 779 ℃. High resolution transmission electron microscopy (HRTEM) suggested that the main phase in powders sintered at 1100 ℃ was identified as pyrochlore structure Y2Ti2O7.

Precipitation kinetics in heavily deformed CoCrFeNiMn high entropy alloy

The present research was conducted on the bcc Cr-rich precipitation kinetics in a heavily deformed CoCrFeNiMn HEA. Activation energy calculation of ~ 226 kJ.mol−1 suggests that precipitation is controlled by grain boundary diffusion of Ni during post deformation annealing using Johnson–Mehl–Avrami–Kolmogorov equation. This value is smaller than the activation energy for the diffusion of Co, Cr, Fe, Ni and Mn in homogenized CoCrFeNiMn HEA. It can be due to the large number of defects such as dislocations and non-equilibrium grain boundaries which serve both as fast diffusion pathways and also as preferential nucleation sites for the formation of new phases.

The effect of high energy milling and high thermal treatment on the structure and thermal decomposition of minerals from natural CaO-SiO2-P2O5 ceramic system

The major issue studied in this paper is a natural mineral aggregate of quartz, calcite, and fluorapatite (the raw material originated from Bulgaria) before and after high energy milling and thermal treatment, in the order to investigate the properties of natural CaO-SiO2-P2O5 ceramic system. The activation effects are monitored by chemical analysis, X-ray powder diffraction, Fourier transformed infrared spectroscopy, and Thermal analysis (TG/DTG).The activation effect study shows: (i) change of chemical bond strength; (ii) deformation of structural polyhedrons with the formation of new isomorphic phases; (iii) the prolonged time of HEM activation leads to lower raw mineral stability and to the formation of new phases; iv) increased SiO2 reactivity resulting in solid-phase crystallization.The obtained results can be used in the study of ceramic and cement materials (ancient and modern), soil conditioners, etc.

Tuning of surface characteristics of composite (WO3/BiVO4) zinc phosphate coatings for industrial applications

The paper reports about a simple strategy for improvements of zinc phosphate coated steel for protection from corrosion with an added advantage of energy saving by enhanced NIR reflectance. In this work, WO3/BiVO4 composite was synthesized by a simple double precipitation method with a tuned composition of 1:4 WBV. Accordingly, the band gap energy, electronic transitions, particle size, stability and color characteristics were effectively controlled to enhance the NIR reflectance efficiency. The weight percentage of the tuned composite (1:4 WBV) additive was optimized to achieve NIR reflectance as high as 64% as compared to the galvanized steel (25%). The addition of an optimum amount (0.2 wt%) of the tuned composite (1:4 WBV) into the phosphating bath could effectively act as a nucleating agent for the formation of zinc phosphate crystals by reducing the activation energy for the formation of new phases resulting in the development of more compact and dense phosphate coating. The resultant coating yielded very high surface coverage and thereby enhanced NIR reflectance (64%), chemical stability and high corrosion resistance (0.0753 mmpy) as compared to other coatings. The developed composite zinc phosphate coating (BP-0.2WBV) with enhanced NIR reflectance can be used as an energy saving ‘cool coating’ for structural engineering materials such as roofing and automotive body parts.

Tracing the ionic evolution during ILG induced phase transformation in strontium cobaltite thin films

Ionic liquid gating (ILG) that drives the ions incorporate into or extract from the crystal lattice, has emerged as a new pathway to design materials. Although many intriguing emergent phenomena, novel physical properties and functionalities have been obtained, the gating mechanism governing the ion and charge transport remains unexplored. Here, by using the model system of brownmillerite SrCoO2.5 and the corresponding electric-field controlled tri-state phase transformation among the pristine SrCoO2.5, hydrogenated HSrCoO2.5 and oxidized perovskite SrCoO3−δ through the dual ion switch, the ionic diffusion and electronic transport processes were carefully investigated. Through controlling gating experiment by design, we find out that the collaborative interaction between charge transport and ion diffusion plays an essential role to prompt the hydrogen or oxygen ions incorporate into the crystal lattice of SrCoO2.5, and therefore leading to formation of new phases. At region closer to the electrode, the electron can shuttle more readily in (out) the material, correspondingly the incorporation of hydrogen (oxygen) ions and phase transformation is largely affiliated. With the compensated charge of electron as well as the reaction front gradually moving away from the electrode, the new phases would be developed successively across the entire thin film. This result unveils the underlying mechanism in the electric-field control of ionic incorporation and extraction, and therefore provides important strategy to achieve high efficient design of material functionalities in complex oxide materials.

Dynamic Evolution of a Cathode Interphase Layer at the Surface of LiNi0.5Co0.2Mn0.3O2 in Quasi-Solid-State Lithium Batteries.

Intensive understanding of the surface mechanism of cathode materials, such as structural evolution and chemical and mechanical stability upon charging/discharging, is crucial to design advanced solid-state lithium batteries (SSLBs) of tomorrow. Here, via in situ atomic force microscopy monitoring, we explore the dynamic evolution process at the surface of LiNi0.5Co0.2Mn0.3O2 cathode particles inside a working SSLB. The dynamic formation process of the cathode interphase layer, with an inorganic-organic hybrid structure, was real-time imaged, as well as the evolution of its mechanical property by in situ scanning of the Derjaguin-Muller-Toporov modulus. Moreover, different components of the cathode interphase layer, such as LiF, Li2CO3, and specific organic species, were identified in detailat different stages of cycling, which can be directly correlated with the impedance buildup of the battery. In addition, the transition metal migration and the formation of new phases can further exacerbate the degradation of the SSLB. A relatively stable cathode interphase is key to improving the performance of SSLBs. Our findings provide deep insights into the dynamic evolution of surface morphology, chemical components and mechanical properties of the cathode interphase layer, which are pivotal for the performance optimization of SSLBs.

Mineralogical and Leaching Characteristics of Altered Ilmenite Beach Placer Sands

In order to have a good understanding of the treatment process and improvement on the market value of ilmenite beach placer sands, knowledge of its mineral composition and phase distribution is fundamental. In this study, a combination of characterization techniques including high-resolution scanning electron microscopy (HR-SEM), high-resolution transmission electron (HR-TEM) microscope, and X-ray diffraction (XRD) techniques was used to understand the mineralogical characteristics of ilmenite beach placer sands obtained from Richards Bay, South Africa. The mineral phase constituents of the ilmenite beach placer sands were studied before pre-oxidation and additive leaching in a chloride environment. During observations using XRD and HR-SEM, the ilmenite beach placer sands exhibited signature rhombohedral crystal form and crescentic pits with evidence of alteration phases. The characterized pre-oxidized ilmenite showed the presence of a ferric oxide film deposit of the particles. The leaching characteristics of both raw and pre-oxidized ilmenite was studied in the presence of additives. The leaching efficiency of the pre-oxidized ilmenite in the presence of additives increased by 20% at atmospheric conditions. The characterized residues show the improved amenability of pre-oxidized leach in chloride media. The formation of new phases containing pseudo-rutile indicated crystallographic disintegration by the movement of atoms during dissolution. Some particles retained the crescentic pit and the subangular grain structure; however, the phase changes were observed at the grain boundaries and grain edges. The leached residue’s EDS results still indicated the presence of pseudo-rutile and some minor unreacted oxides such as SiO2, Al2O3, and other trace metals. The trace metals impurities present in the as-received ilmenite were reduced by 80% in the final residue after the leaching.