Phase Morphology Research Articles

Mechanism of Fe-rich phase supercooling induced by CDS process to regulating microstructure and strengthen properties of Al-Si-Fe alloy

Excessive iron in aluminum alloys forms compounds that weaken their strength and workability. Therefore, controlling the morphology of the Fe-rich phase is vital for developing strong, high-quality aluminum alloys. This research explores the controlled diffusion solidification (CDS) process, an innovative approach designed to optimize the morphology and distribution of the Fe-rich phase, thereby enhancing the alloy properties beyond what conventional methods can achieve. Specifically, the CDS process uniquely modifies the solidification behavior of the alloy, suppressing the growth of the primary Fe-rich phase and enhancing the overall properties. This demonstrating the ability of process to refine microstructural characteristics effectively. The experimental results confirm the presence of primary Si and Al3Fe in the CDS process samples. Consequently, the nucleation of Al3Fe in the precursor alloy leads to the concentration of Fe solutes reduce, impeding the nucleation and growth of the primary Fe-rich phase during the subsequent solidification process. The key factors are temperature difference between two mixed alloy and mass ratio of precursor alloys. The mass ratio influences the precipitation sequence of the precursor alloys, while the difference of temperature and concentration induces the undercooling necessary for nucleation. The study reveals that an optimal mass ratio of 4:1 in the CDS process achieves the best mechanical properties with a 73.78 % increase in ultimate tensile strength (UTS) and a 107.77 % increase in elongation (UL) compared to conventional casting. The findings provide a theoretical basis for controlling the Fe-rich phase evolution, significantly augmenting the performance of Al-Si-Fe alloys. The findings not only enhancing the optimizing fundamental reactions in the CDS process for other alloy systems but also enriching the broader field of materials science.

Synthesis of porous Mg2MnO4 spinel microspheres and enhanced lithium storage properties

Porous Mg2MnO4 spinel microspheres were synthesized by a facile solvothermal method. Various techniques such as X-ray powder diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, were used to characterize the phase composition, morphology and electronic structure of materials. The results show that Mg2MnO4 spinel material was obtained at the temperature of 600–800 °C and has a microsphere structure. The microspheres were assembled by nanoparticles, and the particle size increases with the increase of annealing temperature. Analyses of XPS spectra reveal that Mn exists in multiple valence states (+2, +3, +4) in Mg2MnO4 materials, and all the materials are mixed spinel with Mg2+ and Mn2+/3+/4+ ions occupy both tetrahedral and octahedral sites of spinel structure, and the degree of inversion decreases with increasing annealing temperature. Mg2MnO4 microspheres exhibit excellent lithium storage performance, the first discharge specific capacity of M2MO-8 is 835.3 mAh g−1 under a voltage window of 0–3 V and with a current density of 100 mA g−1, and after 100 cycles the discharge capacity of the material is as high as 406.5 mAh g−1. In addition, this material shows high cyclic reversibility. The enhanced lithium storage properties of the material can be attributed to its porous structure, which promote the transport of lithium ions and reduce the damage to the structure caused by the volume change during the charge and discharge process.

3D X-ray Tomography Analysis of Mg–Si–Zn Alloys for Biomedical Applications: Elucidating the Morphology of the MgZn Phase

Temporary metal implants, made from materials like titanium (Ti) or stainless steel, can cause metabolic issues, raise toxicity levels within the body, and negatively impact the patient’s long-term health. This necessitates a subsequent operation to extract these implants once the healing process is complete or when they are outgrown by the patient. In contrast, medical devices fabricated from absorbable alloys have the advantage of being biodegradable, allowing them to be naturally absorbed by the body once they have fulfilled their role in facilitating tissue healing. Among the various absorbable alloy systems studied, magnesium (Mg) alloys stand out due to their biocompatibility, mechanical properties, and corrosion behavior. The existing literature on absorbable Mg alloys highlights the effectiveness of silicon (Si) and zinc (Zn) additions in improving mechanical properties and controlling corrosion susceptibility; however, there is a lack of comprehensive quantitative morphological analysis of the intermetallic phases within these alloy systems. The quantification of the complex morphology of intermetallic particles is a challenging task and has significant implications for the micromechanical properties of the alloys. This study, therefore, aims to introduce a robust set of morphometric parameters for evaluating the morphology of intermetallic phases within two as-cast Mg alloys with Si and Zn additions. X-ray Computed Tomography (XCT) was used to capture the 3D tomographic data of the alloys, and a novel pair of morphological parameters (ratio of convex hull to particle volume and convex hull sphericity) was applied to the 3D tomographic data to assess the MgZn phase formed in the two alloys. In addition to the impact of composition, the effect of solidification rate on the morphological parameters was also studied. Furthermore, Scanning Electron Microscopy (SEM) and Energy-Dispersive Spectroscopy (EDS) were employed to gather detailed 2D microstructural and compositional information on the intermetallics. The comprehensive characterization reveals that the morphological complexity and size distribution of the MgZn phase are influenced by both compositional changes and the solidification rate. However, the change in MgZn intermetallic particle morphology with size was found to follow a predictable trend, which was relatively agnostic of the chosen casting conditions.

Phase-Field Modeling of Kinetics of Diffusive Phase Transformation in Compositionally-Graded Ni-Based Superalloys

AbstractKinetics of the $$\gamma$$ γ /$$\gamma ^{\prime}$$ γ ′ phase transformation and the interdiffusion phenomena in single-crystal Ni-based superalloys, under isothermal annealing and composition gradient, is investigated through the phase-field and continuum diffusion models. The employed models in the present work exploit CALPHAD-based thermodynamics and kinetics databases, in order to perform realistic simulations. We specifically predict the interdiffusion of elements for a hypothetical alloy AlCoCrTaNi/Ni diffusion couple, equivalent to the CMSX-10/Ni diffusion couple, at 1323 K. Accordingly, the phase fraction and morphology of $$\gamma ^{\prime}$$ γ ′ precipitations in the $$\gamma$$ γ matrix is simulated as well. The implemented multi-component diffusion model takes into account vacancies and pore formation, reflecting Kirkendall effect. Furthermore, the time evolution of morphology parameters of the precipitate-depleted zone in the diffusive region (i.e., the position and the size) are estimated.

High Milling Time Influence on the Phase Stability and Electrical Properties of Fe50Mn35Sn15 Heusler Alloy Obtained by Mechanical Alloying.

Fe50Mn35Sn15 Heusler alloy, obtained by mechanical alloying, was subjected to larger milling times in the range of 30-50 h to study the phase stability and morphology. X-ray diffraction studies have shown that the milled samples crystallise in a disordered A2 structure. The A2 structure was found to be stable in the milling range studied, contrary to the computation studies performed on this composition. Using Rietveld refinements, the lattice parameter, mean crystallite size, and lattice strain were computed. The nature of the obtained phases by milling was found to be nanocrystalline with values below 50 nm. A linear increase rate of 0.00713 (h-1) was computed for lattice strain as the milling time increased. As the milling time increases, the lattice parameter of the cubic Heusler was found to have a decreasing behaviour, reaching 2.9517 Å at 50 h of milling. The morphological and elemental distribution-characterised by scanning electron microscopy and energy-dispersive X-ray spectroscopy-evidenced Mn and Sn phase clustering. As the milling time increased, the morphology of the sample was found to change. The Mn and Sn cluster size was quantified by elemental line profile. Electrical resistivity evolution with milling time was analysed, showing a peak for 40 h of milling time.

Antisolvent crystallization of rare earth sulfate hydrates: Thermodynamics, kinetics and impact of iron

The thermodynamics and kinetics of ethanol antisolvent crystallization of rare earths from sulfate solutions has been explored, with a view towards separating the rare earths as part of a NdFeB magnet recycling process. The solubility of single and binary metal (Nd, Pr, Fe) phases in aqueous ethanol solutions has been determined. The impact of Fe and Pr on the crystallization of Nd is evaluated, the oxidation kinetics of Fe(II) to Fe(III) quantified, and the influence of Fe oxidation state on the thermodynamics and kinetics of crystallization investigated. Oxidation to Fe(III) is slow, with a half life of approx. 600 h. For pure Nd, the solubility of the obtained, stable sulphate octahydrate decreases exponentially with increased molar organic:aqueous (O/A) ratio, and is well described by the OLI model until O/A=0.2. Pr crystallizes as an isostructural octahydrate with similar solubility. Fe(II) precipitates as a mixed solid phase, with a solubility approximately 40 times higher than the rare earths at O/A=0.2. Fe(III) solutions exhibit liquid–liquid phase separation without precipitation at all evaluated concentrations. Nd and Pr coprecipitate together in proportion to their relative concentrations, with Pr precipitating at concentrations well below its pure component solubility. Fe(II) does not precipitate with Nd at O/A≤0.2 even at high concentration, with significant precipitation as separate particles at higher O/A for all concentrations. The crystallization kinetics and the morphology of the Nd phase is affected by the Fe oxidation state. The work highlights the potential of antisolvent crystallization for selective and efficient separation of REE from Fe.

Study on solidification organization and phase formation of Fe-6.5wt.%Si high silicon steel by arc melting and heat treatment

Abstract The solidification microstructure and phase formation behavior of Fe-6.5wt.%Si high silicon steel was investigated using arc melting and heat treatment. The alloy phase composition and microstructure were analyzed by XRD and SEM. The magnetic performance was measured at a high- and low-temperature vibration sample magnetometer. The results show that the temperature gradient causes alloy ingot to be roughly divided into three layers. With the decrease in temperature, from the bottom to the top, the phase morphology is fine crystals, columnar internal dendrites, and isoaxial internal dendrites. In the annealing ring ingot, the inner dendrites disappeared, and from the bottom to the top of the sample, the microstructure changed from fine crystal, columnar crystal, and isoaxial crystal, to micro-cracks, which first increased and then reduced. The hysteresis loop curve width of the alloy is narrow, the slope is large, the hysteresis is 0.126 emu/g, and the magnetic utilization after annealing decreases to 0.0667 emu/g, but the coercive force increases to 2.8 Oe/g, and the annealed alloy is more sensitive to the magnetic field and has a high magnetic conductivity coefficient.

Ti2NTx MXene Materials Derived from Ti2AlN MAX Phases: Their Characterization and Electrocatalytic Activity Toward Hydrazine Electrooxidation

Nitride-based MXenes materials are promising for advancing technological developments, especially in popular scientific fields such as energy storage and conversion. This study successfully synthesized 2D lamellar Ti2NTx MXenes via selective etching of Al from the Ti2AlN MAX phase. Synthesized Ti2NTx MXene was characterized by field emission scanning electron microscope with energy-dispersive X–Ray spectroscopy attachment (FESEM-EDX), X-ray diffraction (XRD), X–Ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), and Brunauer–Emmett–Teller (BET) analyses techniques in details. 2D lamellar morphology of MXene phase was observed with FESEM, while distinctive diffraction peaks were confirmed with XRD analyses. While the BET surface area of the MAX phase was 0.5375 m2/g, it was measured as 2.0867 m2/g with Ti2NTx MXene which increased by 3.88 times. Ti–O–N, Ti–N, and surface functional groups (Tx: –OH, –F, –O) of Ti2NTx MXenes were revealed with XPS analyses. (112) crystal plane associated interplanar d-space (0.243 nm) was observed with HRTEM results. The electrocatalytic activity of synthesized Ti2NTx MXene was investigated by hydrazine electrooxidation. The Ti2NTx electrocatalyst exhibited a specific activity of 2.739 mA/cm2 and mass activity of 44.1 mA/mg for hydrazine electrooxidation. Ti2N also showed long-term stability compared to Ti2AlN.

Er3+ activated BaLaGaO4 multifunctional green phosphors for optical thermometers and WLEDs

Er3+-doped BaLaGaO4 green phosphors was synthesized through a high-temperature solid-state reaction technique. The phase structure and morphology test results of the phosphor indicate that the BaLaGaO4 material was successfully synthesized and Er3+ ions were successfully doped into the main lattice. This doping does change the basic structure of the crystal. BaLaGaO4:Er3+ phosphor exhibits bright green emission centered at 545 nm when excited by 381 nm ultraviolet light or 980 nm near-infrared light. The optimal doping concentration is found to be x = 0.04. To quantify the temperature sensitivity of the phosphor, the fluorescence intensity ratio method was used. Within the temperature range of 298–473 K, the maximum relative sensitivities are 1.35%/K (298 K, 381 nm) and 1.45%/K (298 K, 980 nm), respectively. The maximum absolute sensitivities are 0.67%/K (473 K, 381 nm) and 0.69%/K (473 K, 980 nm), respectively. Finally, white light-emitting diodes (WLEDs) with a high colour index of Ra = 82 and a relatively low correlated colour temperature of CCT = 5064 K are obtained by integrating the synthesized BaLaGaO4:0.04Er3+ green phosphor into warm WLEDs devices. These results suggest that Er3+-activated BaLaGaO4 multifunctional phosphors hold considerable promise in the areas of optical temperature sensing and WLEDs phosphor conversion.

Approach towards the Purification Process of FePO4 Recovered from Waste Lithium-Ion Batteries

The rapid development of new energy vehicles and Lithium-Ion Batteries (LIBs) has significantly mitigated urban air pollution. However, the disposal of spent LIBs presents a considerable threat to the environment. Recycling these waste LIBs not only addresses the environmental issues but also compensates for resource shortages and generates substantial economic benefits. Current recycling processes primarily focus on the extraction of valuable metals, often overlooking the treatment of residual waste post-extraction. This project targets the iron phosphate (FePO4) derived from waste lithium iron phosphate (LFP) battery materials, proposing a direct acid leaching purification process to obtain high-purity iron phosphate. This purified iron phosphate can then be used for the preparation of new LFP battery materials, aiming to establish a complete regeneration cycle that recovers lithium carbonate and iron phosphate from waste LFP materials for the production of LFP. The study investigates process parameters such as acid types and concentrations, leaching time, and the number of leaching cycles. The results demonstrate that, after purification, the levels of impurity metals decrease while the iron content increases correspondingly. Under optimized experimental conditions, the dilute sulfuric acid leaching rates of Al, Cu, Ca, and Ni reached 36.0%, 51.4%, 89.5%, and 90.9%, respectively. Furthermore, hydrothermal treatment in dilute phosphoric acid achieved leaching rates of 87.9%, 85.8%, 98.4%, and 99.1% for Al, Ca, Cu, and Ni, respectively. The microstructure characterization revealed significant changes in phase and grain morphology during the leaching process in dilute phosphoric acid, which are likely associated with the liberation of impurity atoms from the lattice. These findings indicate that acid leaching is highly effective in removing impurities from the iron phosphate recycled from waste LIBs.

Influence of heat treatment on the structure and mechanical properties of pseudo α-titanium alloy in a welded joint

The object of this study was the weld material of a new Ti-6.1Al-6.0Zr-6.3Sn-3.2Mo-1.1Nb-1.2Si alloy, which was obtained by electron beam welding. Electron beam welding (EBW) provides rapid melting and cooling with crystallization under significant temperature gradients. For the pseudo α-titanium alloy, this leads to the appearance of significant residual stresses in the joint and determines the specificity of the dispersion decay of the β-phase. Residual stresses are reduced by preliminary heating, removed by heat treatment. Such processing exerts a critical influence on the formation of the structure and phase composition of the weld and the zone of thermal influence of the electron beam; it can form macro defects, undesirable phases, and structural states. The conditions of heat treatment have been determined to bring the welded joint from complex alloyed pseudo α-titanium alloy to the required level of mechanical characteristics. The structure, phase morphology, elemental composition, and mechanical characteristics of welded joints without additional heat treatment have been compared, with preliminary local heating of 400 °C, with additional post-weld local annealing at ТТ=750 °С, tT=4 minutes and sequential annealing in the furnace at ТТ=850 °C, tT=60 minutes. It has been established that a full cycle of heat treatment of a welded joint provides the highest characteristics of strength and plasticity, but local heat treatment also makes it possible to obtain a defect-free joint with satisfactory characteristics for less responsible products. It is shown how heat treatment of pseudo α-titanium alloy makes it possible to get rid of unwanted phase formations (Zr,Ti)5Si3Al and transform them into (Zr,Ti,Nb,Mo)3SiAl. The results are promising for use in the production of aircraft engine parts

Pt nanoclusters as co-catalysts for efficient photocatalytic hydrogen evolution

Photocatalytic water splitting for hydrogen production is an ideal strategy to relieve the energy crisis. In this work, Pt nanoclusters are employed as a co-catalyst to modify g-C3N4 for optimizing the photocatalytic hydrogen evolution performance. Compared with the pristine g-C3N4, the Pt nanoclusterss/g-C3N4 nanocomposites exhibit dramatic enhancement toward H2 production, where the H2 evolution rate of CN-Pt-C2 is nearly 425.1 times higher than pristine g-C3N4. The phase structure, morphology, optical properties, and surface chemical states of the fabricated samples are fully investigated. Based on the systematical characterizations, the reason for the enhanced H2 generation performance is disclosed. It is expected this work can provide a valuable reference for the fabrication of a co-catalyst-based photocatalytic system.

Effects of residual Laves phase on microstructural evolution and mechanical properties of wire arc additive manufactured GH4169 Ni-based superalloy

The GH4169 Ni-based superalloy is prepared by wire arc additive manufacturing and the sizes and morphologies of Laves phases under different heat treatment strategies are obtained to further investigate the influence of residual Laves phases on the tensile properties of the superalloy. After the solution treated at a higher 1150 °C and followed by aging, the Laves phase is completely dissolved, with limited δ phase with varying sizes distributed at the grain boundaries. While for lower 1020 °C solid solution heat treatment temperature, the Laves phase in the sample changes from chain-like to particle-like shapes by partially dissolving, and the needle-like δ phase exists around the particle-like Laves phase. Such residual "Laves + δ" impede high-temperature tensile crack propagation, significantly enhancing plasticity. This mechanism makes the lower temperature solid solution treated sample exhibit similar tensile stress but ∼2 times of elongation when compared to the sample treated by higher solid solution.

Role of Minor Phase Morphology on Mechanical and Shape-Memory Properties of Polylactide/Bio-Polyamide Nanocomposite.

In situ-generated nanofibrillar polymer-polymer composites are excellent candidates for the production of polymer materials, with high mechanical and SME properties. Their special feature is the high degree of dispersion of the in situ-generated nanofibers and the ability to form entangled nanofiber structures with high aspect ratios through an end-to-end coalescence process, which makes it possible to effectively reinforce the polymer matrix and, in many cases, increase its ductility. The substantial interfacial area, created by the in situ formed fiber/matrix morphology, significantly strengthens the interfacial interactions, which are crucial for shape fixation and shape recovery. Using the polylactide/bio-polyamide (PLA/PA) system as an example, it is shown that in situ PA fibrillation improves the mechanical and shape-memory properties of PLA. The modulus of elasticity increases by a factor of 1.4, the elongation at break increases by a factor of 30, and the shape-strain/fixity ratio and shape recovery increase from 80.2 to 97.4% and from 15.5 to 94.0%, respectively. The morphology of the minor PA phase is crucial. The best result is achieved when a physically entangled nanofibrous network is formed.

Eggshell derived scaffold of hydroxyapatite-ammonium bicarbonate nano-composite: Bioactivity and cytotoxicity studies

This work investigated the facile synthesis of porous scaffold eggshell derived hydroxylapatite (ESHAp) as a composite with ammonium bicarbonate (AMB) for potential biomaterial in tissue engineering application. The phase purity, composition, size, functional groups and morphology of the apatite were elucidated using high resolution transmission electron microscopy (HTEM), X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR) and scanning electron microscopy (SEM). The results showed that hydroxylapatite (HAp) nanoparticles have round morphologies with average diameters between 20 nm and 80 nm, FT-IR analysis confirmed significant hydroxylapatite functional groups like carbonate, phosphate, and hydroxyl groups, while XRD analysis revealed a well crystalline monophasic HAp powder. The scaffold samples containing 10, 20, 25 and 30 % of AMB withstood a compressive stress up to 5, 20, 30 and 42 N/mm2 respectively which indicates that the compressive stress increased with the AMB content introduced as the pore forming agent. MTT assay performed using MG63 osteosarcoma cell lines showed that on comparing the sample of ESTHAp which contained 0 % AMB with other samples in the range of 0.01–1 mM, viability of above 85 % MG63 cells was achieved except for ESTHAp with 40 % AMB, which showed some level of toxicity. The cell adhesion studies of sintered ESTHAp porous scaffold with different weight percent of the pore forming agents using inverted microscopic images of MG 63 cells incubated with ESTHAp samples and treated with heat at 1000 °C appeared to be unstable in the media used with particle leaching observed, and no cells observed near to the samples.

Accelerated hydrolytic degradation of poly(l-lactide) by blending with poly(ether-block-amide)

A continuing challenge in the most common biodegradable polyester of poly(l-lactide) (PLLA) is to improve the degradation rate in the environment, though it has been widely used in packaging and medical applications. In this study, PLLA/poly(ether-block-amide) (PEBA) blends are prepared by melt blending to investigate the effect of PEBA component on the phase morphology, thermal behavior, mechanical properties, and hydrolytic degradation of the blends. The incorporation of PEBA component is beneficial to the improved toughness and increased water absorption of the blends, and accelerated hydrolytic degradation of PLLA. The blend exhibits the optimal mechanical and hydrolytic degradation properties when the blend mass ratio of PLLA/PEBA is 80/20. The toughness of the blend is increased by 390 % compared to that of pure PLLA. After being hydrolyzed at 58 °C for 240 h, the water absorption, the mass loss and the decrease of molecular weight of the blend is increased by 138 %, 160 % and 40 %, respectively, indicating faster hydrolytic degradation rate of the blend than that of pure PLLA. Furthermore, the accelerated hydrolytic degradation mechanism of PLLA in the blend is revealed. The amorphous region of PLLA is hydrolyzed initially at the phase interface of the blend, and subsequently the crystalline structure of PLLA is degraded. The hydrolysis process causes a change in the relative content of crystalline regions in the system, resulting in an increase in crystallinity of PLLA first and then decrease. These findings provide a new strategy for the design of novel degradable PLLA materials for practical applications.

Influence of grain size and grain edge phase on the flexural strength of aluminum nitride ceramics with Y2O3 sintering additive

The necessity for efficient heat dissipation compels AlN packaging materials towards a thinner profile. In response to the ensuing concerns regarding the reliability of strength, the effects of the grain edge phases and grain size on flexural strength are investigated in this study. Different preparation processes, including (hot-pressed sintering, pressureless sintering, and annealing) are employed to prepare AlN ceramics with different grain edge phases and grain sizes. After classifying the morphology of the grain edge phases and fitting the Hall-Petch relationship, it is found that the grain edge phases had a more significant influence on the flexural strength. Depending on the morphology, the negative effects can be divided into three degrees. While the finer grain size proves advantageous for the flexural strength. Consequently, in the non-additive system, the flexural strength of AlN ceramic is 422 MPa, with an average grain size of 8.47 μm. For the additive-doped system, the maximum flexural strength can reach 532 MPa, which can be attributed to the limited average grain size resulting from the hot-pressed sintering process, approximately 1.32 μm. These results could potentially be employed in the microstructural design of high-strength AlN ceramics.

Effect of La on the Microstructures and Mechanical Properties of Al-5.4Cu-0.7Mg-0.6Ag Alloys.

The effects of the rare earth element La on the microstructure and mechanical properties of cast Al-5.4Cu-0.7Mg-0.6Ag alloys have been investigated through metallographic observation, scanning electron microscopy analysis, transmission electron microscopy, X-ray diffraction, and tensile testing. The present form and action mechanism of La have been analyzed. The findings indicate that the inclusion of trace amounts of La markedly diminishes the grain size in the Al-Cu-Mg-Ag alloy. Furthermore, as the La content increases, the alloy's strength is significantly improved. When the La concentration reaches 0.4 wt.%, the mechanical properties of the alloy, both at room temperature and at 350 °C, surpass those of the alloy lacking rare earth elements. When the added rare earth La content exceeds 0.2 wt.%, the emergence of the Al6Cu6La phase causes the alloy structure to exhibit a skeletal morphology, altering the morphology and distribution of excess second phases along grain boundaries, thereby impacting the alloy's overall performance. Incorporating La leads to a reduction in the size of the strengthening precipitate phase Ω while also enhancing its precipitation density, but an excess of La leads to the emergence of Al6Cu6La, depleting the available Cu and suppressing the precipitation of the Ω phase, ultimately affecting the mechanical properties of the alloy.

Effect of Al–Zr and Si–Zr atomic pairs on phases, microstructure and mechanical properties of Si-alloyed (Ti28Zr40Al20Nb12)100-xSix(x=1, 3, 5, 10) high entropy alloys

The phases, microstructure, and mechanical properties of Si-alloyed (Ti28Zr40Al20Nb12)100-xSix(x = 1, 3, 5, 10) high entropy alloys are studied. Although silicides were not detected in the as-cast 1 at. % Si-alloyed sample, after annealing all the four alloys have the same phase composition: the Zr5Al3-type phase, Zr5Si3-type silicides, and the BCC/B2 dual-phase matrix, indicating that 1 at. % Si addition is adequate for the formation of silicides in equilibrium. The phase morphologies show a dependence on the Si content and the cooling rate, which changed from the occurrence of columnar grain zones together with coarse dendrites of the as-cast 1 at. % Si-alloyed alloy to four different cooling-rate-related morphologies in the other three as-cast alloys. After heat treatment, differently shaped precipitates tend to aggregate and spherize, and a three-step-shaped phase morphology is observed when the Si content is above 5 at. %. All precipitates are rich in Zr due to either the strong Si–Zr pair or Al–Zr pair, but heterogeneous distributions of Si and Al exist. An increase of the Si content led to a gradual decrease of the compressive strength in both as-cast and annealed samples, yet the total fracture strain does not show monotonously decrease trend. 5 at. % Si-alloyed samples possessed a higher total fracture strain than the 3 at. % Si-alloyed samples.

Photocatalytic degradation of low-concentration gaseous benzene in air via bifunctional tin-doped titanium dioxide catalyst

Benzene, a common volatile organic compound (VOC) detected in indoor environments, poses challenges for its removal because of its stable molecular structure and low-concentration. In this study, we successfully synthesized tin-doped titanium dioxide (Sn-TiO2) using a simple hydrothermal method. Various characterization techniques including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunner–Emmet–Teller (BET) and molecular probes were employed to analyze the phase composition, structure and morphology, as well as photocatalytic properties of TiO2 and Sn-TiO2. The characterization results showed that moderate addition of tin doping not only effectively enhanced the capture ability of benzene molecules but also promoted hydroxyl radicals (·OH) generation, which was further validated by in-situ diffuse reflectance infrared Fourier transform (DRIFT) spectra and density function theory (DFT) calculations. Degradation experiments on gaseous benzene revealed that under 15 W ultraviolet (UV) light irradiation in humid and closed conditions for 60 min, 1 % Sn-TiO2 achieved a benzene degradation efficiency of 93.14 %, with almost complete mineralization. Furthermore, flow system experiments demonstrated efficient decomposition of trace amounts of benzene (∼10 mg/m3) in the air to satisfy emission standards when employing 1 % Sn-TiO2 at a flow rate of 100 L/min.