Phase Composition Research Articles

Effects of liquid accelerators on long-term mechanical strength development and microstructural changes of wet-mixed shotcrete

The significant long-term strength loss of shotcrete can greatly affect the safety and stability of underground shotcrete structures. Developing high-quality liquid accelerators remains an indispensable research direction and a viable approach to mitigate challenge. This study synthesizes three distinct kinds of liquid accelerators - alkali-free fluorine-free (GJ), alkali-free fluorine-containing (MJ), and low-alkaline (JJ) and investigates their effects on the long-term mechanical strength of wet-mixed shotcrete. Moreover, changes in the phase composition and microstructure of accelerated shotcrete were explored utilizing X-ray diffraction, thermogravimetric analysis, mercury intrusion porosimetry, and scanning electron microscopy techniques to reveal underlying mechanisms. Results indicate that accelerated cement paste and mortar with a 6 wt% fixed dosage of liquid accelerators exceeded the prescribed basic performance indices (setting time and 28-day compressive strength ratio) for shotcrete applications. Among the accelerators, the alkali-free fluorine-containing type exhibited the most beneficial effect on long-term strength, attributed to increased C-(A)-S-H formation from added Al and Si into the system. Morphological and crystal composition changes in hydrate phases, notably the transformation of ettringite to AFm and additional formation of monosulfate and hemicarbonate, increased the solid volume, refined pore structure and reduced total porosity, thus enhancing long-term strength. This study offers valuable insights into the synthesis and optimization of main accelerator components to mitigate long-term strength loss in shotcrete for practical engineering applications.

Effect of adding Sr(OH)2 on the formation process of 2024 aluminum alloy micro-arc oxidation coatings

Micro-arc oxidation coatings with oxidation times of 15 S, 30 S, 60 S, 120 S, 240 S and 1800 S were prepared on 2024 aluminum alloy using silicate-phosphate electrolytes containing 0 g/L and 0.5 g/L Sr(OH)2, respectively. The effects of adding Sr(OH)2 on the oxidation voltage, surface morphology and phase composition of the 2024 aluminum alloy MAO coatings formation process were investigated using SEM, XRD and XPS. The results show that adding Sr(OH)2 increases and then decreases the oxidation voltage compared with that of the unadded Sr(OH)2, which has little effect on the morphology of the oxide coatings, the Sr2+ and PO43- in the solution are jointly involved in the formation of the MAO coatings. The main phase composition of the coating is γ-Al2O3, and the Sr element is uniformly distributed as SrCO3 in the coating.

Investigation of the Influence of the Oxygen Flow Rate on the Mechanical, Structural and Operational Properties of 86WC-10Co-4Cr Coatings, as Determined Using the High-Velocity Oxyfuel Spraying Method

The structural-phase composition and tribological and performance properties of coatings based on an 86WC-10Co-4Cr composition obtained by the HVOF method at varying (150 L/min, 170 L/min, 190 L/min) oxygen flow rates were studied. The results showed that the coefficient of friction of coatings in gear oil remained almost unchanged with the variation in oxygen flow rate. However, microhardness increased significantly with an increasing oxygen flow rate, reaching a maximum at 190 L/min. An increasing oxygen flow rate was also accompanied by an increase in roughness and coating thickness, with a decrease in porosity, particularly notable at 190 L/min. Adhesion strength reached the maximum values for the A2 and A3 coatings under high loads. The phase composition of the coatings included WC, W2C and CoO phases irrespective of the oxygen flow rate, and their microstructure was characterized by a more homogeneous and dense structure. Thus, this study confirmed that the optimal oxygen flow rate for achieving an improved performance and tribological characteristics of 86WC-10Co-4Cr coatings is 190 L/min.

Effect of Cr content on the high temperature oxidation behavior of FeCoNiMnCrx porous high-entropy alloys

FeCoNiMnCr porous high-entropy alloys were prepared using the activation reaction sintering method with Fe, Co, Ni, Mn, and Cr as raw materials. The oxidation behaviors of FeCoNiMnCrx porous high-entropy alloys with different Cr contents, such as pore structure, the surface oxide film phase composition, structure, and morphology, were characterized by X-ray diffraction (XRD), electron probe micro analysis (EPMA), energy dispersive X-ray spectroscopy (EDS), and pore tester after high-temperature oxidation at 800–1000 °C. The results indicate that the initial porous high-entropy alloy comprises a single FCC solid solution phase. With the increase in Cr content, the average pore diameter, average porosity, and air permeability of the porous high-entropy alloy also increase. The oxidation kinetics of the porous high-entropy alloy after exposure to temperatures between 800 °C and 1000 °C follows a single-stage parabolic evolution law. At the same oxidation temperature, With the increase of Cr content, the oxidation gains gradually increased, at the same Cr content at different temperatures, the antioxidant performance of 1000 °C was the weakest, followed by 800 °C, and 900 °C showed excellent antioxidant performance. The oxidation products are mainly Mn2O3, Mn3O4, (Mn, Cr)3O4, Cr2O3and Fe2O3.

Synergistic modulation of SrTiO3-TiO2 colossal permittivity system by internal lattice defects and phase composition: Experimental and theoretical investigations

The SrTiO3–TiO2 composite ceramics with different contents of La doping were fabricated by traditional solid-state sintering methods. The performance of the colossal permittivity ceramics was enhanced by the synergistic design of the internal defect structure and phase composition. When the doping content is 2%, SrTiO3–TiO2 composite ceramics possessed a colossal permittivity (ԑr ∼ 1.1 × 105), low dielectric loss (tanδ ∼ 0.050) and favorable thermal stability (−70 °C-150 °C, ΔC/C25°C ≤ ±15%). Phase structure analysis suggested that a TiO2 secondary phase was induced at the grain boundaries of SrTiO3 phase with the addition of La3+ ions. XPS and dielectric behavior analyses revealed that oxygen vacancies and lattice defects formed by inhomogeneous ion-doping act to modulate the dielectric behavior in ceramics. The IBLC interfacial effects in relation to semiconductor grains and insulation grain boundaries are the main contributors to the colossal permittivity (CP) properties of ceramics, and the contribution of the IBLC effects becomes more prominent with increasing doping content. On the basis of first-principles analysis, the ceramic lattice undergoes severe deformation when the La content is increased, and the gathering of electrons at oxygen vacancies and defects is evident. As a result, it leads to enhanced grain semiconducting properties and interfacial effects, which facilitate colossal permittivity and low dielectric loss for ceramics. The results are prospective in the application of CP ceramics.

Structure and properties of powders obtained by electrodispersion of pure Nickel metal waste in distilled water

Purpose. Investigation of the composition, structure and properties of powder materials obtained by electrodispersion of nickel waste of the PNK-0T1 brand in an oxygen-containing medium – distilled water.Methods. To determine the composition, structure and properties of powder materials, samples of powders obtained from waste nickel grade PNK-0T1 were studied. The powder material was obtained by electroerosive dispersion in distilled water. Microanalysis of powder particles was carried out using a scanning electron microscope, an analysis of the size distribution of powder particles was obtained using a particle size analyzer, an X-ray spectral microanalysis of powder particles was carried out using an energy-dispersive X-ray analyzer embedded in a scanning electron microscope, an analysis of the phase composition of powder particles was carried out using X-ray diffraction on the diffractometer.Results. During the study, it was revealed that the shape of the particles obtained from nickel powders is spherical and elliptical, and agglomerates of smaller particles are also noted on the increase. Oxygen and nickel are present in the composition of powder materials. The phases of pure nickel and nickel oxide NiO are marked in the phase composition. From the analysis of the granulometric histogram, it follows that the particle size spread varies in the range of 0.26...18.62 microns, the average volume diameter of the particles was 5.2 microns.Conclusion. The obtained research results can be used to develop a new heavy pseudo-alloy using metal waste from expensive raw materials by the method of electroerosive dispersion, followed by improvement and optimization of the composition and structure of the alloy.

Effect of calcination temperature on the activity of basalt tailings for the lightweight geopolymer from microwave curing

Basalt, the most widely distributed alumino-silicate volcanic rock on Earth, is commonly utilized in construction aggregate area. The challenge lies in how to utilize the tailings produced during mining processes to create high-value products through energy-efficient and environmentally-friendly means. A previous study has already shown the use of basalt tail powder as raw material for lightweight geopolymer materials supported microwave curing, without an extensive focus on mechanical properties, in turn known to be significantly affected by the reactivity of constituents. Here, calcination operations are discussed in their impact on the activity of basalt for lightweight geopolymer from microwave curing. Additionally, the thermal characteristics of basalt during temperature were analyzed using differential scanning calorimetry, scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction analyses were employed to examine the micromorphology, chemical structure, phase compositions, and reaction degree of basalt and its alkali activated products. The results prove that basalt is a sustainable raw material for geopolymers, with properties already optimized without calcination, in turn determining a slight increase only at 750 °C (resulting in compressive strength >7 MPa, with a porosity of 30 %). The effect mechanism of calcination temperature on the activity of basalt tailings for the lightweight geopolymer from microwave curing is also discussed.

Phase Composition of AlTiNbMoV, AlTiNbTaZr and AlTiNbMoCr Refractory Complex Concentrated Alloys: A Correlation of Predictions and Experiment

Phase Composition of AlTiNbMoV, AlTiNbTaZr and AlTiNbMoCr Refractory Complex Concentrated Alloys: A Correlation of Predictions and Experiment

Enhanced thermal conductivity of wood-based phase change materials with copper for thermal management and solar-thermal conversion

Polyethylene glycol (PEG) has been regarded as a promising thermal management material for next-generation building materials due to its high energy storage density and phase change performance. However, its practical application has been limited by some issues such as easily leakage and low thermal conductivity. In this work, a high-thermal-conductivity wood-based composite phase change material (Cu-DW/PEG) was fabricated by impregnating copper (Cu) precursor solution and PEG into delignified wood (DW). The incorporation of Cu nanoparticles increased the thermal conductivity of Cu-DW/PEG by 105 % and 64 % compared to pure PEG and DW/PEG composite, respectively. This also endow the Cu-DW/PEG good photo-thermal conversion capability, achieving a conversion efficiency of 76.5 %. Meanwhile, the Cu-DW/PEG exhibits relatively high latent heat (132.93 J/g), good shape stability and thermal cycling stability. Considering these excellent performances, the Cu-DW/PEG is a promising material for thermal management, building energy conservation, and solar thermal harvesting.

Laser and thermal control over structure and magnetic properties of PrDy-FeCo-B microwires

Magnetic microcombs are necessary in microrobotics, MEMS technologies, actuator and magnetic flow analyzer industries. Usually, magnetic microcombs are artificial linear magnets of periodic shape. We propose another type of microcombs based of microwires, where periodicity of magnetization is caused by equidistant alternation of natural domains. We have demonstrated the presence of quasi-periodic radial magnetization and the effect of temperature and magnetic field on magnetic relief in PrDyFeCoB microwires. Accurate analysis of chemical, phase and structural composition of the microwires allowed us to reveal necessary conditions for the creation of periodical magnetic relief. Annealing affects magnetic relief and changes structure of initially amorphous microwires. Crystal structure of inclusions enriched with Fe and Co instead of Dy and Pr is body-centered cubic (BCC), while the bulk of the microwire has tetragonal structure. We have found laser stimulated amorphization of surface of PrDy-FeCo-B microwires. Partial restoration of the amorphous structure in polycrystalline microwires under single laser pulse of irradiation of 1mJ power and 120 ns duration has been found in 1–2 μm depth.

Synthesis, phase composition, electronic and spectroscopic properties of cobalt-doped aluminum oxynitride

The article presents a comprehensive study of the synthesis, phase formation, electronic structure, and optical properties of cobalt-doped aluminum oxynitride Al5O6N (AlON) in the concentration range of 0.01–5 at%. The solubility limit of cobalt in AlON is found to be 0.1–0.2 at% compared to Al. No corundum is detected even at the lowest cobalt content (0.01 at%), but a low amount of AlN and Co or Co4N is observed. Cobalt ions are incorporated into AlON with the typical oxidation state of Co2+ and form Co–O and Co–N bonds in a ratio of 92/8. The bandgap (Eg) and lattice parameters of AlON:Co are found to be in the range of 5.72–5.84 eV and 7.9411–7.9539 Å, respectively, and are influenced by the oxygen content. Pulsed cathodoluminescence spectra show five emission bands, with some attributed to (VAl–ON)-type defects. The luminescence intensity of AlON:Co decreases with higher contents of cobalt ions.

Corrosion mechanism of alkali-activated slag/metakaolin materials under carbonic acid solution

For promoting the application of alkali-activated slag/metakaolin (AASM) materials in karst areas, it is crucial to understand the corrosion properties of AASM materials in carbonic acid solutions. This paper systematically investigates the evolution of mechanical properties, phase composition, and microstructure of AASM materials in carbonic acid solution environments. The research results indicate that the corrosion mechanism of AASM in carbonic acid solution environments can be summarized as four stages: the dissolution stage, the C-(N)-A-S-H gel decalcification and calcium carbonate formation stage, the further corrosion of calcium carbonate stage, and the slow corrosion stage. Depending on the degree of Ca2+ leaching, the corrosion layers can be divided from the outermost to the innermost layers into the gel layer, the carbonation layer, and the un-corrosion layer. In carbonic acid solution environments, significant leaching of Na+ and OH− occurs in pore solution, which hinders the development of strength. Additionally, the diffusion of CO32− and HCO3− ions dissolved in water into the C-(N)-A-S-H gel, which react with the gel to form calcium carbonate, leads to gel decomposition. Moreover, the generated calcium carbonate is further corrosion into soluble calcium bicarbonate, resulting in substantial leaching of Ca2+, deterioration of pore structure, and increased aggregation degree of C-(N)-A-S-H gel structure. As the MK content increases, the calcium content in the system decreases, leading to a higher crosslinking degree and enhanced resistance of the C-(N)-A-S-H gel to carbonic acid solution corrosion, thereby reducing the corrosion rate of AASM materials. The research results provide new insights into the application of AASM materials in karst areas.

Simulation of bench-scale CO2 injection using a coupled continuum-discrete approach

Unintended releases of CO2 from carbon capture and storage operations presents the risk of atmospheric emissions and groundwater or surface water quality impacts. Given the potential impacts, it is valuable to have tools capable of predicting groundwater concentrations and likely pathways of CO2 migration in the subsurface. Traditional multiphase flow models struggle to simulate the discontinuous flow expected at leakage sites. This work applied a coupled continuum-discrete model, ET-MIP, to simulate a bench-scale injection of CO2. Results demonstrate the capability of ET-MIP to accurately capture gas fingering behaviour, and the complexity of multicomponent mass transfer observed in the experiment. Simulations were computationally efficient, allowing for the use of multiple displacement pressure realizations. CO2 migration in the subsurface was shown to be sensitive to mass transfer, as i) increased groundwater velocity can dissolve leaked CO2 prior to reaching the surface and ii) background dissolved gases in the subsurface can impact the rate of upwards gas movement, gas distribution, and the composition and persistence of the gas phase. The sensitivity to mass transfer suggests it may be preferable to monitor for low-solubility gases in the source mixture rather than CO2. These findings are applicable to other gases in the subsurface, such as hydrogen or methane migrating from geoenergy wells.

Optimization of microstructure and high-temperature mechanical properties of Ti4822/Ti2AlC composites through multiple solution-aging treatments

In this paper, a Ti-48Al-2Cr-2Nb (Ti4822, at%) based composite with uniformly distributed Ti2AlC nano-micro precipitates was prepared by powder metallurgy followed by a multiple solution-aging treatment. Multiple solution treatments eliminated the equiaxial γ grains in the sintered composites and refined the coarse-grained primary Ti2AlC phases, resulting in a fully lamellar microstructure with fine Ti2AlC precipitates embedded between the α2/γ lamellae. The high-temperature ultimate tensile strength of the heat-treated Ti4822/Ti2AlC composites reached 543 MPa at 800 ℃, and the elongation was 7.7 %, increased by 9.7 % and 0.8 % correspondingly compared to that of the sintered composite. The enhancement of the properties of Ti4822/Ti2AlC composite in the heat-treated state was due to the elimination of γ grains in the microstructure to transform the full lamellar microstructure on the one hand, and the refinement and dispersion of agglomerated Ti2AlC precipitates on the other hand. This study provided a valuable reference for the refinement and dispersion of the second phase in TiAl composites.

Using artificial neural networks to elucidate retention interactions on stationary phases with amine moieties dedicated to supercritical fluid chromatography

The retention mechanisms of small molecules on a wide range of stationary phases using different mobile phase compositions are one of the most discussed topics in current state-of-the-art supercritical fluid chromatography (SFC). Although various theories have been published on retention behavior, prediction, and stability over time, an in-depth insight into the mechanisms is still lacking. Our study focused on the description of the retention mechanisms on columns with amine moieties, i.e., 2-ethylpyridine, 2-picolylamine, 1-aminoanthracene, and diethylamine, dedicated to SFC, using three different compositions of organic modifier, i.e., methanol, methanol + 10 mmol/L NH3, and methanol + 2 % H2O, in CO2. An extensive set of analytes characterized by more than 200 molecular descriptors was used. The importance of the effect of each molecular descriptor on the retention behavior was determined by artificial neural networks. Thus, the descriptors increasing and/or decreasing retention on individual columns using different mobile phase compositions were defined. The data collected over one year of column use were statistically evaluated to describe the retention behavior of small molecules on the tested stationary phases using three organic modifiers and to describe the changes in retention behavior over time.As the development of the SFC method can be laborious and time-consuming, this publication offers a detailed description of the interactions taking place between the analyte and the SFC stationary phase. Understanding these fundamental processes will enable faster development of SFC methods using quality-by-design principles.

STUDY OF THE STRUCTURAL AND ELECTROMAGNETIC CHARACTERISTICS OF FERROMAGNETIC-DIAMAGNETIC COMPOSITES OBTAINED BY THE METHOD OF MODIFIED CHEMICAL CO PRECIPITATION

The microwave electromagnetic properties of ferromagnetic-paramagnetic and ferromagnetic-diamagnetic composites can be changed by varying the concentration of diamagnetic (paramagnetic) and ferromagnetic components. To implement the task of introducing such composites into production, research is required to find effective and simple synthesis technologies that make it possible to vary the content of components with different magnetic characteristics. This work demonstrates a simple method for the synthesis of ferromagnetic ((NiZn)Fe2 O4 )- diamagnetic (ZnO) composites by modified chemical deposition followed by annealing. Also, a comprehensive study of the structural and electromagnetic characteristics of experimental samples was carried out. Using the powder X-ray diffraction method, it was revealed that the phase composition of the final samples is represented exclusively by diamagnetic and ferromagnetic phases. Using scanning electron microscopy, it was found that after thermal annealing the powders have submicron sizes with an average size of 100–137 nm. Using vibration magnetometry, magnetic hysteresis loops were measured, the analysis of which showed that an increase in the concentration of the diamagnetic phase leads to an increase in the coercive force of the composites. The measured microwave spectra of complex magnetic permeability show that by changing the ratio between the ferromagnetic and paramagnetic phases, it is possible to realize a frequency shift of natural ferromagnetic resonance. Also, through the calculation of the reflection coefficient on a metal plate, it is shown that the resulting composites can be used as the basis for new radio-absorbing materials. In addition, the synthesized powders can also be used to create microwave devices and microwave antennas.

Initial investigation of catalyst pack for 98 %+ hydrogen peroxide satellite monopropellant thruster

This study aimed to assess the decomposition rate of highly concentrated hydrogen peroxide on catalyst samples, based on the various materials and the geometry of the supporting structures. The drop test method was used and involved delivering a droplet of hydrogen peroxide to a catalyst sample in a sealed chamber, and then measuring the pressure rise. Different sample groups showed various pressure increase rates, indicating differences in catalytic performance. The drop tests were followed by a material investigation to compare the morphology of the active layer produced on various substrates and the effects of the high-test peroxide (HTP) interaction with the surface after the tests. Qualitative tests of phase composition and chemical composition were also performed. Different substrates resulted in varying morphology based on material type, chemical composition, and porosity. The study was treated as a screening test to choose the best catalytic pack option for testing under thruster-like conditions.

Phase composition of sputter deposited tungsten thin films

Sputter deposited tungsten thin films are studied by X-ray diffraction. Two phases can be identified: α-W and β-W based on the observed (110), and (200) and (210) Bragg reflections, respectively. With increasing film thickness (50 to 200 nm), the phase composition shifts from β-W towards α-W. No influence of the base pressure (3 × 10−3 – 3 × 10−5 Pa) on the phase composition is observed. Also the influence of the argon pressure (0.3 to 0.7 Pa) is rather weak. The strongest shift towards α-W composed thin films is obtained by increasing the discharge power (50 to 250 W). This trend is further studied by energy flux measurements using a calorimetric probe. These measurements rule out a strong change of the substrate temperature, and an impact of the energy flux scaled by the deposition rate (total energy per deposited atom). Test particle Monte Carlo simulations reveal the importance of the momentum of the reflected argon neutrals on the phase composition. The maximum energy of these species is mainly defined by the discharge voltage, and is higher than the directional dependent displacement energy of W. Despite the significant correlation between phase composition and the number of displacement per deposited atom, there is a strong scatter of the phase composition. As the deposition conditions were varied in random way, changes of the target erosion profile, and the changing discharge voltage over each series are probably partially responsible for the observed scatter. This scatter is also enhanced by the long term changes in the phase composition towards the more thermodynamic stable α-W phase.

Self-generated B-MAX phase composites: The effect of sintering temperature on surface morphology and phase composition

The use of metal-based MAX phase composites is widespread in the production of high-temperature structural materials, anticorrosive materials and electrode materials. Herein, novel B-Ti3AlC2 and B-Ti4AlN3 composites were prepared using the hot-pressing method at varying sintering temperatures ranging from 950 °C to 1325 °C. This study also explores the effect of sintering temperature on the surface morphology and phase composition of both B-MAX phase composites. The morphological and crystal phase composition of MAX phase composites were investigated through SEM coupled with EDS, FE-SEM, AFM, and XRD test analysis. The results revealed that higher sintering temperatures increase the clear formation of MAX phases and composites as compared to lower temperatures. The findings also expose that the in-situ formation of B-MAX composites significantly changes the structure, contributing to transforming the overall performance and making it suitable for high-stress applications like electronics, aerospace, and cutting tools.

The microstructure and mechanical property of W-TiC/Ti composites via chemical-mechanical milling method

Carbide dispersion strengthened W(CDS-W) has attracted much attention as a plasma-facing material (PFM). However, the carbide tends to segregate at W grain boundaries and has poor interface properties with W due to the large difference in the bond structure. In this work, nanometer Ti was added to improve the performance of the W/TiC interface, and nanoscaled W-TiC-x%Ti (x=0.1,0.5 and 1.0) composites were prepared by chemical-mechanical milling and ordinary sintering method. The effects of Ti on powder morphology, phase composition, microstructure and mechanical properties were systematically investigated using XRD, SEM, EDS, TEM and HADDF technologies. Simultaneously, the existence form and distribution of Ti elements, and W/TiC interface characteristics of powders and composites were analyzed. Moreover, the microstructure evolution and strengthening mechanism were preliminarily discussed. Results show that the W-TiC/Ti powder has an obvious core-shell multilayer structure with a particle size range of 50-120 nm. The addition of Ti exists in the forms of TiC, Ti, and TiO2, and has no effect on the morphology and phase composition. Besides, the phase transformation and solution-precipitation of the Ti-added occurs during the sintering process. Part of Ti precipitates on the W/TiC surface to form Ti rich region, which significantly promotes the dispersion of TiC and improves the W/TiC interface, as well as prevents the growth of W grains, and the average grain size is 2.90 μm. Moreover, the orientation relationship of [013]( 00)TiCFCC||[ 13]( 0)WBCC exists at the W/TiC interface, especially the coherent phase interface is formed. The tensile strength and microhardness at room temperature are 520 MPa and 850 HV0.2, respectively, which is attributed to the synergistic effect of fine-grained strengthening, dispersion strengthening and interface strengthening. This work can provide a new strategy and direction for preparing high-performance CDS-W materials.