Formation Of Intermediate Phase Research Articles

Combustion Synthesis and Reactive Spark Plasma Sintering of Non-Equiatomic CoAl-Based High Entropy Intermetallics

The present work reports the direct production of a high-entropy (HE) intermetallic CoNi0.3Fe0.3Cr0.15Al material with a B2 structure from mechanically activated elemental powder mixtures. Fast and efficient combustion synthesis (CS), spark plasma sintering (SPS), and reactive SPS (RSPS) methods were used to synthesize the HE powders and bulks. The formation of the main B2 phase along with some amounts of secondary BCC and FCC phases are reported, and L12 intermetallic (CS scheme) and BCC based on Cr (CS + SPS and RSPS schemes at 1000 °C) were observed in all samples. The interaction between the components during heating to 1600 °C of the mechanically activated mixtures and CS powders has been studied. It has been shown that the formation of the CoNi0.3Fe0.3Cr0.15Al phase occurs at 1370 °C through the formation of intermediate intermetallic phases (Al9Me2, AlCo, AlNi3) and their solid solutions, which coincidences well with thermodynamic calculations and solubility diagrams. Compression tests at room and elevated temperatures showed that the alloy obtained by the RSPS method has enhanced mechanical properties (σp = 2.79 GPa, σ0.2 = 1.82 GPa, ε = 11.5% at 400 °C) that surpass many known alloys in this system. High mechanical properties at elevated temperatures are provided by the B2 ordered phase due to the presence of impurity atoms and defects in the lattice.

The Algorithm to Predict the Grain Boundary Diffusion in Non-Dilute Metallic Systems

The analysis of grain boundary (GB) diffusion in metallic systems based on Cu, Ni, Ag and Al was made to set demonstrate the common behavior. It was shown that the slow penetration for 11 systems can be connected with negative segregation or specific interatomic interaction. Two energetic parameters such as energy of interaction with GB and energy of interatomic interaction are proposed as main characteristics. The analysis of a tendency toward segregation and tendency of intermediate phase formation in these terms allows us to divide the systems on four groups and formulate a qualitative way to predict the behavior of the diffusing elements in a non-dilute solution. Mathematical formulation of GB diffusion problem and typical solutions are presented.

The Role of Intermediate Phases in the Crystallization of Aluminophosphate Sieves on Examples of AlPO-11 and AlPO-41

The formation of intermediate phases during aging of the reaction gel composition 1.0Al2O3•1.0P2O5•1.5DPA•40H2O and its subsequent crystallization into molecular sieves AlPO-11 and AlPO-41 was studied in this work. The initial gels and crystallization products were characterized by XRD; MAS NMR 27Al and 31P; scanning electron microscopy (SEM); transmission electron microscopy (TEM); and N2-physical adsorption. It has been found that the nature of the aluminum source used to prepare the gel has a significant effect on the properties of the resulting intermediate phases. It is shown that by changing the chemical and phase composition of the intermediate aluminophosphate, it is possible to control the morphology and characteristics of the secondary porous structure of the AlPO-11 molecular sieve. The formation of the intermediate phases with a layered structure opens the possibility to synthesize high-phase purity AlPO-41 at the di-n-propylamine/Al2O3 ratio = 1.5. The formation mechanisms of AlPO-11 and AlPO-41 are proposed depending on the phase composition of the intermediate phases.

Effect of pressure on the evolution of vitrinite graphitized mesophases: An experimental study on anthracite under high temperature and pressure

In this study, the influence of pressure on the evolution of the intermediate phase of graphitization of vitrinite was determined. Using samples of Taixi anthracite from the Rujigo Coal Mine (Ordos Basin, China), experiments were conducted in a piston cylinder press at a constant temperature of 1073 K and pressures from 500 MPa to 1 GPa. Raman spectroscopy, high-resolution transmission electron microscopy, selective electron diffraction, and electron loss energy spectra were used to characterise the microcrystalline morphology, structural order, and atomic valence states of the samples. Under confined conditions, pressure significantly promoted the graphitization process; however, the effect of different pressures on such process in vitrinite varied. Low pressure (<700 MPa) promoted an ordered growth of aromatic rings; meanwhile, a medium pressure (700–800 MPa) destroyed the microporous structure of vitrinite, leading to a less-ordered carbon layer and a sp3 metastable carbon structure resembling nano-diamond. Notably, high pressure (>900 MPa) promoted the condensation and directionalisation of the carbon layer of the vitrinite by destroying the microporous structure, resulting in a rapid growth of microcrystalline graphite. This suggests a transition to the key stage of anthracite graphitization, which may be an important feature in the formation of intermediate phases. In fact, pressure has been shown to exert an important role in the rupture of microporous structures in vitrinite, whose mechanism may be related to the sp3 metastable carbon formed between the basic structural units in different high-pressure environments. These findings provide insight into the formation mechanism of coal graphite, bringing new understanding of the transition from multi-faceted nanocrystals to graphitization in an orogenic metamorphic zone (e.g., in high-pressure schist and hornblende).

A review of the oxygen vacancy ordering in surrogate structures simulating Pu-based nuclear ceramics

Advanced nuclear power systems and nuclear fuel cycles will require nuclear fuels capable of higher burnup and with higher transuranic concentrations than those previously developed for current nuclear power plants. Expensive qualification tests are required to validate the thermal and mechanical performance of fuels in normal and accident-scenario operations. Research of surrogate systems with specific properties and characteristics of advanced nuclear fuels can be an effective way to frame the problem, reduce costs, and support the technical development of future research. From this perspective, lanthanide counterparts like mixed oxides of Ce and Nd can provide replica systems for many technological properties of the actual fuels. These ceramic systems can lead to a better understanding of the fundamental irradiation processes responsible for the evolution of their microstructures, the interplay with charge and defect localisation, and the evolution of their mechanical properties. In non-stoichiometric MO2−x binary systems (M = Ce, Pr, and Tb), there is evidence of systematic ordering of vacancies resulting in a deviation from the ideal fluorite structure and the formation of several intermediate fluorite-related phases. Substitution of the 4+ cations with 3+ cations in these systems drives the formation of oxygen vacancies as a charge compensation mechanism. By analogy with MO2−x systems, a variety of similar intermediate phases would also be expected to form in the MO2:Ln2O3 (Ln = La, Nd, Gd … etc). However, in order to achieve chemical homogeneity and charge ordering, prolonged annealing just above the charge ordering transition temperature is required, covering a time-scale determined by the chemical diffusion coefficient. Achieving these conditions with powder metallurgy techniques, commonly employed in literature, is practically impossible. This paper reviews the transport properties and structural features found in these surrogate systems which may be helpful in addressing challenges facing advanced nuclear fuels. We present results of a recent diffraction experiment investigating the structure of neodymium doped ceria synthesised using soft chemical methods. The sample shows a deviation from previous literature as the diffraction data is best described by a monoclinic Ln6O11-type structure (SG P21/c), often referred to as “β phase” in PrO2−x.

Impact of two-step calcination on microstructure, phase, electronic, and dielectric properties of KCa2Nb3O10 bulk layered perovskite

ABSTRACT The effects of varying calcination temperature, K content, and the number of calcination steps in the dielectric performance of KCa2Nb3O10 synthesized via solid-state reaction are investigated. Adding an extra calcination step at 500°C followed by another calcination at 1100°C suppressed the formation of secondary phases while maximizing the relative density (95%) and the average grain area (2.12 μm2). The first calcination at 500°C ensures the formation of intermediate phases (KNbO3 and Ca2Nb2O7), which are prerequisites for single-phase KCa2Nb3O10 synthesis. A significantly high dielectric constant of 352 at 100k Hz is achieved in the two-step calcined sample despite the low sintering temperature of 1250°C. The highest resistivity of the two-step calcined sample (2 × 108 Ω cm) obtained from complex impedance analysis supports its lowest dielectric loss (0.034 at 100k Hz). When the two-step calcined KCa2Nb3O10 powder is exfoliated, much higher dielectric properties of Ca2Nb3O10 nanosheets are expected.

Phase and structural evolution of zirconolite ceramics prepared by solid-state reaction sintering

The evolution of phase assemblage and microstructure of stoichiometric zirconolite (CaZrTi 2 O 7 ) ceramics, prepared by a solid-state reaction sintering route, was systematically investigated as a function of sintering temperature. Using powder XRD and quantitative phase analysis data, it was determined that the formation of zirconolite was a one-step reaction, without formation of intermediate phases. The accompanying fractions of secondary CaTiO 3 and ZrO 2 phases were reduced to approximately 2 wt % each after sintering at 1200 °C, with zirconolite formed as the major phase (> 99 wt%) after reaction at 1300 °C. Notable product densification only occurred at T ≥ 1400 °C, at which it was possible to achieve a relative density of 96.97% which is highly desirable for applications as a nuclear wasteform. The zirconolite-2M polytype structure (space group: C2/c) was formed in all products as expected, confirmed by combined high resolution TEM-ED analyses.

Crystal engineering of SAPO-11 sieves by forming intermediate phases

New opportunities to control the morphology and size of SAPO-11 molecular sieve crystals through the preliminary formation of intermediate phases.

Precipitation behavior and microstructural evolution during thermo-mechanical processing of precipitation hardened Cu-Hf based alloys

A recently found precipitation hardened Cu-Hf alloy is a promising candidate for the fabrication of novel high strength and high electrical conductivity materials. However, the precipitation behavior and microstructural evolution during thermo-mechanical processing remain poorly recognized. The present paper focuses on the crystallography, thermodynamics and kinetics of precipitation process during isothermal aging and the interaction between nano-precipitates and nano-twins during liquid nitrogen temperature (LNT) rolling in Cu-Hf alloys. The isothermal aging precipitation procedure of Cu-Hf alloys was identified as supersaturated FCC-Cu → coherent Cu5Hf phase → incoherent Cu51Hf14 phase. The coherent Cu5Hf is oriented with respect to the Cu matrix: (111)Cu//(311)Cu5Hf, [0−11]Cu//[0−11]Cu5Hf. According to thermodynamic assessment and kinetic analysis, the formation of intermediate Cu5Hf phase is due to the lower accommodation energy and interfacial free energy of coherent nano-precipitates, and the change of the growth mode results in shape change in nano-precipitates. Based on molecular dynamics simulations, the significant improvement in the twinning ability of Cu-Hf alloys by the pre-existing nano-precipitates leads to the formation of plenty of nano-twin bundles during LNT-rolling. Finally, a new type of Cu-Hf based alloys with an excellent combination of high strength, high electrical conductivity, as well as high heat-resistance were fabricated by routine process.

Effect of Impregnation with Ammonia vs Silica Support Textural Properties on Ni Nanoparticle Catalysts for Dry Reforming of Methane

In this work, Ni(0) nanoparticles (3.5 and 5 wt %) highly dispersed on silica were obtained by reducing the calcined solid resulting from the impregnation of a nonporous siliceous support (here Aerosil-380) by aqueous nickel(II) nitrate in the presence of aqueous ammonia. The great effect of that base could be emphasized by the comparison with the solid prepared in the absence of ammonia. It was also clearly shown to be superior to the physical barrier effect induced by SBA-15, a mesostructured silica support, impregnated, using a “two-solvents” method, with a similar amount of aqueous precursor (5 wt % of Ni) in the absence of ammonia. In the protocol involving NH3, nickel phases could be hardly detected by X-ray diffraction (XRD) before and after reduction. However, the presence of Ni could be confirmed by X-ray photoelectron spectroscopy (XPS) and H2-TPR. After reduction, transmission electron microscopy (TEM) observations as well as H2 chemisorption highlighted the important dispersion of Ni(0) nanoparticles (up to 42% for 3.5 wt % of Ni). Aerosil-380-based catalysts prepared in the presence of NH3 revealed great performances in the dry reforming of methane at 650 °C for 12 h using a gas hourly space velocity of 960 L g–1 h–1 and an equimolar ratio of CH4 and CO2 reactants. Moreover, they showed a great resistance toward sintering and coke deposition. The formation of Ni phyllosilicate intermediate phases, which are at the origin of this excellent stability, could be evidenced by Fourier transform infrared (FTIR) and 29Si solid-state nuclear magnetic resonance (NMR).

Strong metal-support interaction of Pd/CeO2 enhances hydrogen production from formic acid decomposition

Strong metal support interaction (SMSI) between metals and oxides is considered an efficient manner to promote catalytic performance by the electron transfer, stabilizing the active metals, and the formation of intermediate phases, etc. Herein, we synthesized Pd NPs on cube and truncated cube ceria (Pd/CeO2-c and Pd/CeO2-tc) to study the effect of SMSI on formic acid (HCOOH) decomposition (FAD) to H2. Pd/CeO2-tc exhibited the excellent catalytic performance for FAD with a turnover frequency of 2850 h−1 at 323 K, which was 3.41 times than that of Pd/CeO2-c. Detailed studies demonstrated that the enhanced FAD performance of Pd/CeO2-tc was due to SMSI between Pd NPs and CeO2-tc, with lower electron cloud density of the surface Pd species, higher surface oxygen vacancies (OV) ratio, and more Pd0–OV–Ce3+ species than Pd/CeO2-c. Mechanistic studies indicated that Pd/CeO2-tc with SMSI facilitated the generation of bidentate formate complex with HCOOH (HCOOH–HCOO*) and the evolution from HCOOH–HCOO* to HCOO*, CO2, and H2, where HCOOH–HCOO* should be the more critical intermediate than HCOO* for FAD.

Fabrication of Ti-6Al-4V alloy powder by a novel sintering-deoxygenation process

Given the high cost of fabricating the Ti-6Al-4V alloy powder by the traditional hydriding-dehydriding and atomization methods, a novel sintering-deoxygenation process was proposed and studied in this research. With the help of the developed deoxygenation treatment, value-added raw materials such as Ti sponge can be substituted by low-cost and low-grade materials with high oxygen content. In addition, sintering in a solid state saves a significant amount of processing energy compared to alloying above the melting point of Ti in the conventional alloy production process. This paper prepared six sintering precursors with different initial compositions and oxygen contents using the low-valued raw materials of crude titanium, crude vanadium, V2O3, Al powder, and Al2O3 powder. These precursors' sintering performances on shrinkage, phase composition, microstructure, and porosity were investigated. The results show that the sintering shrinkage is positively correlated with the sintering temperature and holding time and is also affected by the raw materials. The pellet made by mixed crude titanium and AlV master alloy showed the largest shrinkage and the densest bulk. The various combinations of the raw materials led to the changes in the oxygen contents in the precursors, the alpha-beta phase ratio, and the shift of the diffraction peaks of the α-phase. The dissolving of the AlV master alloy and the formation of the Ti3Al intermediate phase took place during sintering due to diffusion. Sintering at 900–1000 °C is critical for elemental diffusion and densification, and sintering at higher temperatures is decisive for microstructure homogenization and further densification. Using the hydrogen-assisted Mg deoxygenation method, all the sintered samples could be treated to an oxygen level of around 0.4 wt% regardless of oxygen content in precursors. The contents of Ti, Al, V, and Fe in the obtained Ti-6Al-4V powders met the requirements of GB/T 34486-2017. This research has demonstrated the feasibility of fabricating Ti-6Al-4V alloy powder by the novel sintering-deoxygenation process.

From Solid-Solution MXene to Cr-Substituted Na3V2(PO4)3: Breaking the Symmetry of Sodium Ions for High-Voltage and Ultrahigh-Rate Cathode Performance.

Stabilizing Na+ accessibility at high voltage and accelerating Na+ diffusivity are pressing issues to further enhance the energy density of the Na3V2(PO4)3 (NVP) cathode for sodium-ion batteries (SIBs). Herein, by taking a V/Cr solid-solution MXene as a precursor, a facile in-situ reactive transformation strategy to embed Cr-substituted NVP (NVCP) nanocrystals in a dual-carbon network is proposed. Particularly, the substituted Cr atom triggers the accessibility of additional Na+ in NVCP, which is demonstrated by an additional reversible redox plateau at 4.0 V even under extreme conditions. More importantly, the Cr atom alters the Na+ ordering at the Na2 sites with an additional intermediate phase formation during charging/discharging, thus reducing the energy barriers for Na+ migration. As a result, Na+ diffusivity in NVCP accelerates to 2-3 orders of magnitude higher than that of NVP. Eventually, the NVCP cathode exhibits extraordinarily high-rate capability (78 mA g-1 at 200 C and 68975 W kg-1), outstanding cycle stability (over 1500 cycles at 10 C), excellent low-temperature property, and full cell performance.

Choice and ambiguity of diffusion paths during formation and growth of intermediate phases and two-phase zones in ternary systems

Choice and ambiguity of diffusion paths during formation and growth of intermediate phases and two-phase zones in ternary systems

Formation of Intermediate Phases in Decomposition of Metastable B-Phase in Titanium Alloys of Transition Class

Formation of Intermediate Phases in Decomposition of Metastable B-Phase in Titanium Alloys of Transition Class

Principles of pyrometallurgical processing of quartz-leucoxene concentrates with the formation of a pseudobrookite phase. Part 2. Phase transformations

Quartz-leucoxene ore and its processing concentrates are valuable titanium-containing raw materials, however a comprehensive processing technology for the ore is yet to be developed. This paper studies the high-temperature processes occurring in a system containing quartz-leucoxene concentrate with an iron-containing additive. It has been established that, depending on the atmosphere of the pyrometallurgical processing and the type of the iron-containing additive, phases of ilmenite (in an inert atmosphere) or pseudobrookite (in an oxidizing atmosphere) may be obtained. The possibility of using heat treatment and forging scale (a common large-tonnage metallurgical production waste) as an iron-containing additive has been studied. It has been established that pseudobrookite will be the final product. For all concentrate/iron-containing additive systems studied, depending on the thermal effects, the possibility of intermediate reduction/oxidation reactions for iron oxides and of the formation of Fe2TiO4 intermediate phases (followed by their transition to the pseudobrookite phase) was identified. The minimum triggering temperatures for the conversion process of quartz-leucoxene concentrate Fe2TiO5 and FeTiO3 have been established, as well as the main thermal effects, mass losses, and melt crystallization parameters, which allows optimizing the conditions for pyrometallurgical conversion. The data obtained enables effective process scaling. It has been established that impurity components in the concentrate (up to 7&ndash;9 wt% on average) enter into intrasystem reactions with the formation of calcium titanates (sphene CaSiTiO5) and magnesium (MgTiO3, MgTi2O5, Mg2TiO2).This is a continuation of the article titled &laquo;Principles of pyro-hydrometallurgical&nbsp;processing of quartz-leucoxene concentrates with the&nbsp;formation of a pseudobrookite phase&raquo; (&laquo;Obogashchenie Rud&raquo;, 2021,&nbsp;No. 3).

Different Stages of Phase Transformation in the Synthesis of Nanocrystalline Sr-Hexaferrite Powder Prepared by a Gaseous Heat Treatment and Re-Calcination Method.

In this paper, the phase transformation in a gaseous heat treatment and re-calcination (GTR) process for preparing nanocrystalline Sr-hexaferrite powder using methane (CH4) was studied. The process included gaseous heat treatment and subsequent re-calcination. Phase composition of the powder and its physical properties were changed significantly owing to formation of different intermediate phases. Sr-hexaferrite powder was prepared by the conventional route as the precursor. The results were represented in a phase transformation map that showed the intermediate phases and clarified the transformation path during the process. As evidenced by the map, the process had four general stages: decomposition of hexaferrite, reduction of iron oxides to pure iron, re-oxidation of iron, and re-formation of hexaferrite with different properties and structure.

Room-Temperature Fabrication of p-Type SnO Semiconductors Using Ion-Beam-Assisted Deposition.

Over the past decade, SnO has been considered a promising p-type oxide semiconductor. However, achieving high mobility in the fabrication of p-type SnO films is still highly dependent on the post-annealing procedure, which is often used to make SnO, due to its metastable nature, readily convertible to SnO2 and/or intermediate phases. This paper demonstrates a fully room-temperature fabrication of p-type SnOx thin films using ion-beam-assisted deposition. This technique offers independent control between ion density, via the ion-gun anode current and oxygen flow rate, and ion energy, via the ion-gun anode voltage, thus being able to optimize the optical band gap and the hole mobility of the SnO films to reach 2.70 eV and 7.89 cm2 V-1 s-1, respectively, without the need for annealing. Remarkably, this is the highest mobility reported for p-type SnO films whose fabrication was carried out entirely at room temperature. Using first-principles calculations, we rationalize that the high mobility is associated with the fine-tuning of the Sn-rich-related defects and lattice densification, obtained by controlling the density and energy of the oxygen ions, both of which optimize the spatial overlap of the valence bands to form a continuous conduction path for the holes. Moreover, due to the absence of the annealing process, the Raman spectra reveal no significant signatures of microcrystal formation in the films. This behavior contrasts with the case involving the air-annealing procedure, where a complex interaction occurs between the formation of SnO microcrystals and the formation of SnOx intermediate phases. This interplay results in variations in grain texture within the film, leading to a lower optimum Hall mobility of only 5.17 cm2 V-1 s-1. Finally, we demonstrate the rectification characteristics of all-fabricated-at-room-temperature SnOx-based p-n devices to confirm the viability of the p-type SnOx films.

Clay mineral evolution and formation of intermediate phases during pedogenesis on picrite basalt bedrock under temperate conditions (Yunnan, southwestern China)

In order to better understanding clay mineral evolution coupled with geochemical changes during weathering of igneous rocks under temperate conditions, the picrite basalt-derived soil in Dali (South China) was investigated using X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscope (SEM), and high-resolution transmission electron microscopy (HRTEM) methods. Our results show that smectite and mixed-layer clays occur throughout the weathered soil profile, while discrete kaolinite and illite phases are absent in the soil. From saprolite to topsoil, smectite decreases sharply, while mixed-layer kaolinite/smectite (K/S) and illite/smectite (I/S) clays increase markedly. Clay minerals in the saprolite consist of both dioctahedral and trioctahedral species, while those of the middle to upper profile display a uniform dioctahedral structure. I/S phases are characterized by interstratification of 12-Å smectite and 10-Å illite layers, and K/S phases by interstratification of 12-Å smectite and 7-Å kaolinite layers, with I/S/K clays containing all three layer types. Kaolinization of smectite occurs at the initial stage of weathering, earlier than that of smectite illitization. Desilication and K-fixation of smectite take place simultaneously during advanced weathering, resulting in formation of illitic and kaolinitic phases continuously throughout the developmental history of the soil. Notably high K concentrations in the weathering profile may be related to K-fixing in the interlayer of illite due to smectite illitization in response to more advanced weathering and pedogenic processes, while the increasing K content in the topsoil may be ascribed to fertilizer in land use and uptake of K by plants from deeper soil horizons. Fe2O3 and TiO2 accumulation in the topsoil is probably mediated by microorganisms.

Reconfiguring Sodium Intercalation Process of TiS2 Electrode for Sodium-Ion Batteries by a Partial Solvent Cointercalation

Titanium disulfide (TiS2), a first-generation cathode in lithium batteries, has also attracted a broad interest as a sodium-ion battery electrode due to fast sodium intercalation kinetics and large theoretical capacity. However, the reversibility of sodium de/intercalation is far inferior to that of lithium because of the unfavorable intermediate phase formation. Herein, we demonstrate that reconfiguring sodium intercalation via partial solvent cointercalation alters the phase-transition paths for the entire reactions of NaxTiS2 (0 < x < 1), detouring the formation of the unfavorable intermediates. Additionally, it unexpectedly results in a remarkable enhancement of sodium intercalation reversibility, boosting the cycle stability (1000 cycles) accompanying high power capability (10C rate). Comparative investigations reveal that the sodium intercalation in ether-based electrolyte involves a preintercalation of solvent molecules, which is subsequently dissimilar to the bare sodium intercalation in conventional electrolytes. Rediscovery of the intercalation behavior of TiS2 offers a new insight in revisiting the reversibility and kinetics of the commonly known electrodes for batteries.