Formation Of Precipitates Research Articles

Understanding precipitation during in-situ and post-heat treatments of Al-Mg-Sc-Zr alloys processed by powder-bed fusion

This study investigates the evolution of Sc-rich precipitates in Scalmalloy® processed using Powder Bed Fusion (PBF) additive manufacturing. By combining microstructural analysis, thermodynamic calculations, and an adapted precipitation model, we examine how precipitates change during solidification, in-situ heat treatment (IHT), and post-heat treatment (PHT). We establish a comprehensive classification system for primary and secondary Sc-rich precipitates based on their origin, location, morphology, composition, interaction with other precipitates, and size. Notably, primary precipitates are observed within the fine-grained (FG) zone, and their characteristics suggest further modification during IHT and PHT. The developed precipitation model, coupled with multi-scale thermal simulations, accurately predicts the formation of small homogeneous secondary L12-Al3Sc precipitates during PBF and PHT, showcasing its potential as a powerful tool for optimizing PBF processes for components with complex geometries and different thermal conditions. Our findings reveal that while the employed IHT conditions did not induce secondary precipitation, subsequent PHT at 400°C for 1 hour led to the formation of secondary precipitates via both continuous and discontinuous mechanisms. Addressing limitations in understanding primary precipitate formation during PBF and incorporating both homogeneous and heterogeneous mechanisms in future models are crucial for a deeper understanding of Scalmalloy® precipitation behavior and PBF process optimization.

Dissolution behaviour of WC particles and evolution of precipitated phases in the plasma transfer arc Ni-based composite coating reinforced by 30 wt% WC particles

Ni-WC composite coating was prepared on Q235 steel substrate by plasma transfer arc (PTA) with welding current ranging from 70 A to 85 A. The results show that the dissolution behaviour of WC particles and the elemental diffusion at the interface promoted by the increased welding current promote the formation and evolution of precipitates, including M7(B, C)3 and M6C. The increased current reduced the volume fraction of WC particles in the coating, but increased that of the precipitates. At welding currents of 75 A and 80 A, dendritic-like M7(B, C)3 presented a regular distribution at the bottom of the coating. At a welding current of 80 A, M6C phase began to form at the bottom of the coating. When the welding current reached 85 A, the dendritic structure was broken, and the M6C phase aggregated and grew. The Ni-WC coating had visible delamination. WC particles at the upper part of the coating dissolved more severely compared to those at the middle and bottom of the coating. Ni3Si compound was formed at the upper and middle of the coating, and it had a crystal orientation relationship of [011]Ni3Si∥[011]γ-Ni, (11-1)Ni3Si∥(11-1)γ-Ni, (−200)Ni3Si∥(-200)γ-Ni, (-11-1)Ni3Si 1.3° from (-11-1)γ-Ni with γ-Ni. The average hardness of the coating decreased slightly due to the dissolution of WC, but the hardness at the interface increased, showing an improved bonding of the interface. The newly formed high hardness precipitates can share the load coming from the friction paired ball, thus reducing CoF and wear loss of the coating.

Impact of geomagnetic activity on stratosphere and upper troposphere

During active geomagnetic conditions, a large amount of energy is deposited in the polar atmosphere in the form of particle precipitation that leads to Joule heating creating circulation of intense currents in the auroral region. It can affect the existing background pressure fluctuations in the stratospheric and tropospheric heights, leading to anomalous changes in the vertical temperature (T), zonal (u) and meridional (v) wind. In this study, we demonstrate the effect of active geomagnetic conditions on these atmospheric variables in different longitudinal regions. The investigation involves daily, monthly and seasonal variation of active geomagnetic conditions. Active geomagnetic conditions are selected using geomagnetic activity indices like auroral activity index |AL|>1000 nT, Disturbed Storm time index Dst < -150 and polar cap index PC > 5. Events are identified during November to March for 1990 to 2020 period. Among them 99 active geomagnetic conditions occurred in the month of March which are considered for further investigation. Composite analysis of T, u and v reflects that the temperature shows an increase in the entire atmospheric column; the anomalies in u (u′) and v (v′) show a regional dependence and strengthen in their amplitudes. It is seen from the monthly investigation of March that the Western Pacific, Canadian and East Pacific sectors respond to the active geomagnetic conditions at upper atmospheric pressure levels (approximately 40–70 km altitude) in the polar region. This is indicative of a vertical translation of energy to lower atmosphere during active geomagnetic conditions.

Boosting the visible-light-driven photocatalytic efficiency in porous Cu/TiO2 ceramic coatings

In this study, we examined how current density, sodium phosphate concentration, and the addition of copper sulfate to the supporting electrolyte affect PEO coatings on pure titanium. The chemical composition, morphology, and optical behavior of PEO coatings were extensively analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and UV–Vis diffuse reflectance spectroscopy (DRS). With an increase in current density from 6 to 18 A/dm2, the coating's pore size enlarges and the rutile phase content within the coatings increases. The coating created at 12 A/dm2 shows the highest photocatalytic activity and triggers a unique three-stage behavior in the voltage-time diagram. Adding 4 g/l of CuSO4 to the electrolyte resulted in the formation of an unwanted Cu-based precipitates, causing electrolyte instability. To stabilize it, potassium hydroxide was removed, and the base electrolyte concentration was adjusted. To address this issue, potassium hydroxide was eliminated from the supporting electrolyte. Subsequently, the concentration of the base electrolyte was optimized. Also, the synergistic influence of CuSO4 addition (4 g/l) to the supporting electrolyte at different concentrations of 5, 10, and, 15 g/l of trisodium phosphate on PA was investigated. The superior photocatalytic performance of the optimum coating created in the electrolyte containing 5 g/l trisodium phosphate and 4 g/l CuSO4 is attributed to its enhanced porous structure, along with the heterojunction between the anatase and rutile phases. These features significantly boost the available surface area and facilitate the efficient separation and transfer of photogenerated charge carriers. Ultimately, a mechanism for MB photodegradation was proposed based on the findings from Mott-Schottky analysis and DRS.

3D printing of shape memory Alloys for complex architectures of smart structures

Shape Memory Alloys (SMA) are materials used to design smart structures with intrinsic functional properties and improved efficiency. This is a key aspect of aerospace industry and makes SMA good candidates in this field. One of the most widespread SMA is the equiatomic NiTi alloy which, however, has the strong limitation of poor machinability, so only simple shapes can be obtained. Additive Manufacturing processes allow to overcome this limit and to design complex shapes. Compared to other metallic materials, the optimization of the process for NiTi alloy is complicated because, beside mechanical properties and presence of defects, considerable attention needs to be dedicated to the material functionality. The high temperatures involved in the additive process significantly affect the material properties due to possible evaporation of Ni and formation of precipitates that enable a shift of the phase transformation temperatures. This paper is focused on the optimization of the process parameters of the NiTi alloy printed through the Laser Powder Bed Fusion (L-PBF) to ensure optimal pseudo-elastic behaviour, which is essential for the design of structural dampers. This was accomplished starting from simple structures and then designing a damper that couples the pseudoelasticity of NiTi with load support capacity.The L-PBF is a powder-bed technique that selectively melts layers of micrometric metal powder. A pseudoelastic NiTi powder with 50.8 at. % of Ni content was selected and characterized through scanning electron microscope (SEM) and observations connected to an Energy Dispersive X-ray Spectroscopy (EDX) probe. After that, some cubic samples were manufactured, with the dimension of 3 × 3 × 15 mm3. A set of different laser powers and scanning speeds were used to find the set of process parameters that optimize the functional properties of the printed parts. Near fully dense specimens with density higher than 99.5 % were selected for further investigations. Differential scanning calorimetry (DSC) and mechanical tests were performed on as-built and heat-treated samples.Quasi-static mechanical tests were accomplished in compression mode, at different strains, up to 8 %. It was observed that the residual strain for cyclic loading at 4 % is lower than 1 %, so good recovery of the deformation was shown. Moreover, numerical analyses that mimic the pseudoelastic behaviour in compression tests were implemented.Finally, the best set of parameters was selected on the basis of the material's ability to recover deformations and its loss factor.

Effect of heat treatment on microstructure and mechanical characteristics of laser powder bed fusion (LPBF) produced CuCrZr alloy

In this work, the CuCrZr alloy was fabricated by employing the laser powder bed fusion (LPBF) process. For elevating the mechanical characteristics offered by the LPBF parts, heat treatment was performed and three cooling pathways such as water quenching, air cooling and furnace cooling were adapted. The obtained results showed that the water quenching leads to the formation of more craters in its microstructure compared to the air cooled and furnace cooled samples. The nanoindentation analysis revealed that the furnace cooled sample had higher hardness (1.56 GPa) which is attributed to the precipitation of Cu-Zr intermetallic precipitates. Moreover, this sample tends to have a low wear rate and higher tensile characteristics due to the formation of intermetallic precipitates.

Influence of inorganic compounds on self-repairing capability and frost resistance of concrete incorporating ion chelating agent

Cracks can decrease the durability of concrete structures. The ion chelating agent (ICA) can repair concrete cracks through precipitates formed by chelation crystallization reactions. However, its capacity to repair internal damage in concrete is limited, and the chelation crystallization reaction slows down in cold environments. Some inorganic compounds (magnesium fluosilicate and sodium silicate) can promote precipitation formation within concrete, potentially enhancing its self-repairing capability. This study explores the synergistic effects of ICA and these inorganic compounds on the self-repairing capability and frost resistance of concrete. To achieve this research objective, parameters such as visual crack closure, compressive strength reserved ratio, pore structure change, chloride diffusion coefficient, and the microstructure and composition of the repair products were investigated. Sodium silicate and ICA demonstrated significant improvements in the self-repairing capability and frost resistance of concrete. Concrete containing 0.5 wt% sodium silicate and 0.5 wt% ICA, after 28 d of standard curing, fully repaired surface cracks with a width of 0.49 mm. After 300 freeze-thaw cycles, the chloride diffusion coefficient increase rate and harmful pores proportion in the concrete containing 0.5 wt% sodium silicate and 0.5 wt% ICA were reduced by 51.7 % and 76.6 %, respectively, compared to the control concrete. Following 28 d of curing after freeze-thaw damage, the compressive strength reserved ratio of concrete with 0.5 wt% sodium silicate and 0.5 wt% ICA increased by 38.5 %, while the chloride diffusion coefficient increase rate and the harmful pores proportion decreased by 68.5 % and 84.9 %, respectively, compared to the control concrete. Furthermore, SEM-EDS analyses revealed significant amounts of calcium carbonate and some calcium silicate within the cracks of the concrete containing ICA and sodium silicate, and that the internal damage was primarily repaired by a combination of calcium carbonate and calcium silicate.

Evaluation of microstructure heterogeneity in INCONEL 625 thin-wall fabricated by Laser Powder Bed Fusion additive manufacturing

This study provides a thorough investigation of microstructural heterogeneity and its relationship to the mechanical properties of Inconel 625 (IN625) alloy in as-built Laser Powder Bed Fusion (LPBF) parts. Specifically, detailed high-resolution electron microscopy coupled with thermodynamic simulation, finite element analysis, and nano-hardness testing were carried out. Through the combination of these methods, a new method is proposed to develop a process-structure–property map to illustrate the complex relationship between spatial thermal conditions, microstructure, and mechanical properties in various areas of an LPBF IN625 sample. Different precipitates, including γ′′, Laves, NbC, and Al2O3 oxide were observed along the build direction from the bottom to the top layers of the LPBF part as a function of build height. The hardness value was shown to be minimum in the middle layers while attaining maximum values in the bottom (near the substrate) and top (near the surface) layers of the build’s height. The mechanism for the formation of precipitates during multi-layer additive manufacturing and the dependency of the mechanical properties on the type and distribution of these precipitates are discussed.

Differential effects of Fe, Ti and Fe + Ti addition on the discontinuous precipitation and properties of cu-Ni-Sn alloys

Controlling discontinuous precipitation is crucial for improving the microstructure and mechanical properties of Cu-Ni-Sn alloys. Through the utilization of various characterization techniques such as transmission electron microscopy, scanning electron microscopy, optical microscopy, and mechanical testing, we have successfully demonstrated that the introduction of either Ti or a combination of Fe and Ti elements effectively inhibits the formation of discontinuous precipitation. Notably, the combined addition of Fe and Ti elements showcases superior suppression of the discontinuous precipitation structure. Consequently, we have developed a novel alloy, namely Cu-15Ni-7.5Sn-0.5Fe-0.5Ti, which exhibits remarkable resistance to over-aging. Our analysis indicates that the mechanism of inhibiting discontinuous precipitation is multifaceted. The main effect is believed to be the reduction in nucleation sites and the pinning effect of the D024-Ni3Ti phase on grain boundaries, resulting in a significant decrease in the nucleation rate and growth of the DP reaction. The secondary impact may be due to the distribution of D024-Ni3Ti phase at grain boundaries, which leads to a decrease in grain boundary energy. Meanwhile, the formation of D019-Ni3Sn phase reduces the chemical driving force required for DP growth.

Characteristics of perfluoromethyl vinyl ether: A new eco‐friendly alternative gas for SF6

AbstractThe exploration of eco‐friendly insulating gas to substitute the most potent greenhouse gas sulphur hexafluoride (SF6) has consistently garnered significant attention. Herein, the authors evaluated the feasibility of utilising perfluoromethyl vinyl ether (PMVE, C3F6O) as a new branch of eco‐friendly insulating gas for the first time. The primary dielectric and stability characteristics of PMVE regarding AC breakdown, partial discharge, dielectric recovery, and decomposition properties were revealed under various gas pressure and electrical field conditions. It was found that PMVE demonstrated superior dielectric strength, with the AC breakdown and PD inception voltage (PDIV) 1.10 and 1.14 times that of pure SF6. Furthermore, the dielectric strength of PMVE exhibits stability even after undergoing 100 cycles of AC breakdowns, and there is no observable formation of solid precipitation on the electrode surface. The discharge decomposition of PMVE mainly generates fluorocarbon (CF4, C2F6, C3F6, C3F8, etc.) and CO. Overall, the exceptional insulation stability and no absence of solid precipitation features endow PMVE to be utilised as a new eco‐friendly gas for SF6‐free gas‐insulated equipment.

Ferric nitrate-induced phase transformation of Bi2O3 with ion exchange property for enhanced chloride removal from high-salinity wastewater

The bismuth oxide (Bi2O3)-based method for removing chloride (Cl−) ions has garnered considerable interest because of its superior selectivity and efficiency in removing Cl−. However, the slow release of Bi3+ poses a challenge to the effectiveness of Bi2O3. In this study, a novel chloride removal agent composed mainly of Fe3+-doped Bi5O7NO3 (BF-x) was synthesized through the phase transformation of Bi2O3 by ferric nitrate. By optimizing the Fe/Bi mass ratio to 3 %: 1 (BF-3), a remarkable Cl− removal efficiency of 86.4 % was achieved, representing a substantial improvement compared to the 31.2 % removal efficiency observed for pure Bi2O3. The investigation of the mechanism and formation energy calculation revealed the inherent instability of Bi5O7NO3 in comparison to that of Bi2O3, which facilitated the release of Bi3+ and enabled the direct formation of BiOCl precipitate through ion exchange of NO3– with Cl−. The synergistic effect of chemical precipitation and ion exchange contributes to the excellent Cl− removal performance of BF-3. The final Cl− removal product, comprised of BiOCl and FeOOH, exhibited significant photocatalytic efficacy in the decomposition of organic contaminants. This study proposes a novel strategy for designing and preparing high-efficiency Cl− removal agents.

Synergistic Removal of Nitrogen and Phosphorus in Constructed Wetlands Enhanced by Sponge Iron

Insufficient denitrification and limited phosphorus uptake hinder nitrogen and phosphorus removal in constructed wetlands (CWs). Sponge iron is a promising material for the removal of phosphorus and nitrogen because of its strong reducing power, high electronegativity, and inexpensive cost. The influence of factors including initial solution pH, dosage, and the Fe/C ratio was investigated. A vertical flow CW with sponge iron (CW-I) was established, and a traditional gravel bed (CW-G) was used as a control group. The kinetic analysis demonstrated that for both nitrogen and phosphorus, pseudo-second-order kinetics were superior. The theoretical adsorption capacities of sponge iron for nitrate (NO3−-N) and phosphate (PO43−-P) were 1294.5 mg/kg and 583.6 mg/kg, respectively. Under different hydraulic retention times (HRT), CW-I had better total nitrogen (TN) and total phosphorus (TP) removal efficiencies (6.08–15.18% and 5.00–20.67%, respectively) than CW-G. The enhancing effect of sponge iron on nitrogen and phosphorus removal was best when HRT was 48 h. The increase in HRT improved not only the nitrogen and phosphorus removal effects of CWs but also the reduction capacity of iron and the phosphorus removal effect. The main mechanisms of synergistic nitrogen and phosphorus removal were chemical reduction, ion exchange, electrostatic adsorption, and precipitation formation.

The Microstructure characteristic and Its influence on the stray grains of Nickel-based single crystal superalloys prepared by Laser directed energy deposition

The microstructure adjustment and the stray grains inhibition are important for the preparation of Nickel-based single crystal (SX) superalloys by laser directed energy deposition (L-DED). In this work, the single channel monolayer and single channel five-layers DD6 SX superalloys have been prepared by L-DED. The macroscopic simulations in the deposition processing and multiscale characterizations of deposition structure were used to analyze the formation and evolution mechanisms of unique precipitations and stray grains. Results shows that the larger laser power and higher powder feed rate have a positive impact on the epitaxial growth of columnar dendrite and the elimination of stray grains. The residual stress caused by the complex thermal cycles is not the direct reason that induce the formation of SGs, but the rapid movement of dislocations result in the formation of sub-grain boundary. According to the columnar transition to equiaxed theory (CET), temperature field simulation and analysis of element segregation behaviors, the element segregation results in the unique microstructure, include petal-shaped γ/γ′ eutectic and demarcation band with a thickness of a single γ/γ′ eutectic. Besides, the geometric size of γ/γ′ eutectic decrease with respect to the deposition height. With the change of height at deposition region, dendritic orientation deviations affect the uniformity of element segregation, resulting in variations in γ′ phase and γ/γ′ eutectic dimensions between dendritic core and the inter-dendrite zone at the microscopic level and manifesting as grain boundaries at the mesoscale. At the same time, the formation mechanisms of carbide and adjacent γ/γ′ eutectic leads to the misorientations between the dendrite core and the inter-dendrite zone, which also appears as stray grains at the mesoscopic scale.

Omniphobic/superhydrophobic surface effect on oil and gas flow: A critical review

AbstractFlow assurance in the petroleum business of the oil and gas industry ensures the efficient and continuous flow of hydrocarbons from production facilities to consumers. Impurities in oil and gas can cause corrosion and erosion, hydrate formation, scaling, and fouling, resulting in flow limits and reduced operating efficiency. The significant flow assurance issues must be managed through systematic exploration of effective mitigation and management approaches. The objective of this paper is to highlight the latest research in the field of flow assurance, including the application of superhydrophobic or omniphobic coatings to prevent scale growth, asphaltene precipitation, wax deposition, and hydrate formation. This review will provide new perspectives into the basic mechanistic mechanisms of deposition and blockage in oil and gas production systems, assisting in the development of novel methods compared to the employment of commercial chemical or mechanical techniques. Overall, the flow assurance engineers will gain new perspectives from this study regarding how to deal with the risk of pipeline blockage caused by the problems mentioned earlier.

Strategy for co-enhancement of corrosion resistance-strength of Cu-7Ni-3Al-1Fe-1Mn alloy: Rare earth Sm microalloying

Both high strength and superior corrosion resistance are necessary for Cu-Ni alloys when serving in marine engineering. We discover that the corrosion resistance and strength of Cu-7Ni-3Al-1Fe-1Mn alloy can be enhanced via rare earth Sm microalloying. When Sm content is 33 ppm, the alloy exhibits not only the lowest corrosion rate, which is 40% lower than the Sm-free alloy, but also the maximum tensile strength, which is 6% higher than the Sm-free alloy. After alloying 33 ppm Sm, the average grain size of Cu-7Ni-3Al-1Fe-1Mn alloy is reduced by 42%, from 205 μm to 118 μm. In addition, CuSm phase and (Sm2S3-Al2O3) composite phase appear in the alloy after alloying 33 ppm Sm. The improvement of corrosion resistance is primarily due to the formation of Cu-Sm precipitates, leading to a positive shift of the corrosion potential. Further analysis indicates that the increased strength can be mainly attributed to grain refinement and the formation of Sm-S precipitations. This work promotes a new method for enhancing the strength and corrosion resistance simultaneously of copper alloy.

Effect of Artificial Aging in the Microstructure and Corrosion Performance of Superduplex UNS S32750 Stainless Steel

Superduplex stainless steels have great mechanical and corrosion properties. However, its chemical composition makes it prone to intermetallic phase precipitation during thermal processing. Sigma (σ), chi (χ), and chromium nitrides (Cr2N) remove Cr and Mo from the matrix, reducing the corrosion and mechanical resistance. Understanding the effects of thermal processing on the secondary phase’s precipitation and depletion of the material’s performance is crucial to its applications. Thus, this work aims to analyze the behavior of the corrosion performance of the UNS S32750 after thermal treatment at 800°C, for 60, 180, 300, and 420 minutes, in comparison to the as-received material. Optical emission spectrometry, X-ray diffraction, and SEM with backscattered electrons (BSE) were used to evaluate the material. The corrosion performance was evaluated with the cyclic potentiodynamic polarization technique. The main results and conclusions obtained in the study were a decomposition of the ferrite phase into the χ and σ phases, with the formation of the χ phase being predominant in shorter times, while for longer aging times σ formed in greater quantities. It was also possible to verify a more aggressive corrosion trend for aged samples in the regions adjacent to the formation of the χ and σ phases. It was also possible to observe that the losses generated in corrosion resistance were greater for aging times longer than 60 minutes. The aging treatment significantly reduced the material’s corrosion resistance in conjunction with the formation of precipitates.

Microstructure and properties of oxide-reinforced FeCrAl matrix alloy manufactured by selective laser melting

In this work, nano-Y2O3 dispersed FeCrAl powders (NYD-Fe) were used to produce oxide dispersion strengthened (ODS) alloy by selective laser melting (SLM), and their microstructures and properties were investigated in detail by the kinds of characterization techniques. The results indicate that the Y2O3 particles adhered to the surface of FeCrAl powder absorb more laser, thus increasing the laser energy demand. High quality ODS deposits can be obtained at 600 mm/s and 180 W parameters. The ODS samples deposited by SLM exhibit coarse columnar grains with [001] texture. The Ti-rich nanoparticles and core-shell structured nanoparticles (Y- and O-rich core surrounded by a Ti-rich shell) are observed in ODS alloys. The precipitation formation of core-shell structured nanoparticles involves ball milling amorphization and dissolution reprecipitation. The ODS-180 alloy exhibits a higher ductility compared to FeCrAl-180 alloy, which is caused by the cellular structure with high density dislocations and the nano-sized precipitates inhibit the dislocation motion. The wear rate of the ODS-180 alloy is 51% lower than that of FeCrAl-180 alloy, which is mainly ascribed to the hardness and interface oxide layer resulting from its specific microstructural features.

Layer‑by‑layer assembled binder-free hydrated vanadium oxide-acetylene black electrode for flexible aqueous zinc ion battery

Vanadium oxides are potential positive electrode materials for aqueous zinc ion batteries (ZIBs) owing to their advantages of high theoretical capacity, low cost, and so on. Developments of methods for preparing binder-free vanadium oxide electrodes on a large scale and further investigation of their Zn2+ storage mechanisms are essential for expanding their uses in large-scale energy storage systems and wearable electronics. In this work, binder-free electrodes with hydrated vanadium oxide (V2O5·nH2O, denoted as VOH)-acetylene black (AB) on carbon cloth (VOH-AB/CC) are fabricated by a simple and scalable method which combined low-temperature hydrothermal treatment with layer-by-layer drop/spray-coating process. The AB can greatly improve the electrical conductivity of VOH, thereby enhancing the electrochemical performance. The as-prepared electrode with 20 wt% of AB (VOH-AB2/CC) delivers a high capacity of 280 mA h g−1 at 1 A/g and a good rate capability of 205 mA h g−1 at 4 A/g, which is better than many of the reported binder-free vanadium base electrodes. Besides, excellent cycling performance with 89 % retention rate after 3000 cycles at 4 A/g is achieved on the VOH-AB2/CC electrode. Furthermore, a storage mechanism of Zn2+/H+/H2O insertion accompanied by the formation of basic zinc salt precipitate during the discharging process is proposed by the aid of ex-situ XRD and XPS techniques. Additionally, the flexible Quasi-Solid-State ZIB constructed using VOH-AB/CC as positive electrode can work well at different bending states and two ZIBs connected in series can lighten a light-emitting diode even under bending state. This work provides a low-cost, time-saving, environmental-friendly and scalable method to fabricate binder-free hydrated vanadium oxide electrodes for flexible aqueous ZIBs.

Simulating the seeder–feeder impacts on cloud ice and precipitation over the Alps

Abstract. The ice phase impacts many cloud properties as well as cloud lifetime. Ice particles that sediment into a lower cloud from an upper cloud (external seeder–feeder process) or into the mixed-phase region of a deep cloud from cirrus levels (internal seeder–feeder process) can influence the ice phase of the lower cloud, amplify cloud glaciation and enhance surface precipitation. Recently, numerical weather prediction modeling studies have aimed at representing the ice crystal number concentration in mixed-phase clouds more accurately by including secondary ice formation processes. The increase in the ice crystal number concentration can impact the number of ice particles that sediment into the lower cloud and alter its composition and precipitation formation. In the Swiss Alps, the orography permits the formation of orographic clouds, making it ideal for studying the occurrence of multi-layered clouds and the seeder–feeder process. We present results from a case study on 18 May 2016, showing the occurrence frequency of multi-layered clouds and the seeder–feeder process. About half of all observed clouds were categorized as multi-layered, and the external seeder–feeder process occurred in 10 % of these clouds. Between cloud layers, ≈60 % of the ice particle mass was lost due to sublimation or melting. The external seeder–feeder process was found to be more important than the internal seeder–feeder process with regard to the impact on precipitation. In the case where the external seeder–feeder process was inhibited, the average surface precipitation and riming rate over the domain were both reduced by 8.5 % and 3.9 %, respectively. When ice–graupel collisions were allowed, further large reductions were seen in the liquid water fraction and riming rate. Inhibiting the internal seeder–feeder process enhanced the liquid water fraction by 6 % compared to a reduction of 5.8 % in the cloud condensate, therefore pointing towards the de-amplification in cloud glaciation and a reduction in surface precipitation. Adding to the observational evidence of frequent seeder–feeder situations, at least over Switzerland, our study highlights the extensive influence of sedimenting ice particles on the properties of feeder clouds as well as on precipitation formation.

THERMOPHYSICAL PROPERTIES OF HYPOEUTECTIC, EUTECTIC AND HYPEREUTECTIC Al-Si AUTOMOTIVE ALLOYS UNDER AGEING TREATMENT

Influence of different levels of silicon under a variety of thermal treatment is investigated on the thermophysical behaviour of Al-Si-Cu-Mg automotive alloys. Conventional cast alloys are subjected to T6 heat treatment for age hardening. Hardness values, thermal conductivity along with microstructural observation under different heat-treated conditions are well thought-out to comprehend the ageing performance and the precipitation behaviour of the alloys. From these investigational results it is indicated that two successive hardening peaks take place in the agedalloys. Ageing sequence consists of different phases like a supersaturated solid solution, GP zones, intermediate βʹʹ, intermetallic βʹ, equilibrium β and the Q phase but GP zones and the metastable phases are most likely responsible for these ageing peaks. Thermal conductivity decreases for these precipitates formation during ageing and increases for relieving the internal stress, dissolution of metastable phase and coarsening the precipitation of the alloys. Addingup of Si to the alloy showed earlier ageing peaks with higher intensities intended for its increasing properties of heterogeneous nucleation and diffusion kinetics. After ageing around at 200°C for four hours the alloys offer the height hardness. Microstructural study reveals that eutectic silicon makes the grain boundary coarsen and beyond the eutectic composition the star-shaped blocky primary Si is formed. Subsequent to ageing at 350oC for one hour the alloys reach completely recrystallized state.