Formation Of Primary Particles Research Articles

Изучение влияния содержания гафния и эрбия на формирование микроструктуры при литье алюминиевого сплава 1590 в медный кокиль

Introduction. High-magnesium aluminum alloys are widely used in the automotive, building and aerospace industries due to its low specific gravity and high strength. The characteristics of such alloys can be improved by small additions of scandium and zirconium. However, scandium is very expensive, so in new generation alloys its amount is tended to be reduced. In the recently developed 1590 aluminum alloy, this was achieved by addition of erbium and hafnium. The objective of the paper is to study the effect of erbium and hafnium concentrations on the modification of the cast structure in 1590 aluminum alloy at high solidification rates. Research Methods. The paper investigates the microstructure, chemical composition and size of intermetallic compounds in specimens from ten alloy 1590 modifications with different hafnium and erbium contents cast into a copper chill mold with a solidification rate of 10 °C/sec. The grain structure was studied using an optical microscope. The chemical composition and size of the intermetallic phases were studied using a Tescan Vega 3 scanning electron microscope. Results and discussion. It is established that as the amount of hafnium and erbium increases, the cast structure is modified. In general, grain refinement with the addition of hafnium and erbium can be explained by a higher degree of supercooling between the solid and liquid phases. At a hafnium content of 0.16 %, the dendritic structure begins to transform into an equiaxed grain structure. This transformation can be explained by the appearance of primary intermetallic compounds of the Al3Sc type in the liquid phase. Such intermetallic compounds are identified at a concentration of erbium and hafnium equal to 0.16 %. Moreover, in all alloys eutectic intermetallic compounds are identified that contained manganese and iron and had no effect on the cast structure. Comparison with previously obtained results on the grain size of specimens cast into a steel mold shows that with higher solidification rate, the structure modification in 1590 alloy is getting less efficient. This is explained by an increase in the concentration of transition elements in the solid solution, primarily scandium, necessary for the formation of primary intermetallic particles.

Regulating the Si/Al ratio of GIS zeolite with bulky primary particles for selective CO2 capture from hydrocarbons

Carbon dioxide (CO2) capture from hydrocarbons using low-energy adsorption separation techniques is a promising alternative to conventional low-temperature distillation, but limited by the shortness of low-cost and efficient physical adsorbent, especially for the direct acetylene (C2H2) purification because of their very similar size and physiochemical properties. In this work, GIS zeolites with tunable Si/Al ratio were synthesized in an unusual acid co-hydrolysis route to enable the formation of large-sized primary particles, which greatly reduce the outside surface adsorption to enhance the sieving effect of 8-membered ring microchannels. The obtained GIS zeolites afforded high CO2 uptake (3.5 mmol g-1 and 128 cm3 cm-3) while negligible adsorption towards other gases including C2H2, N2, CH4, C2H4, and C2H6, showing the remarkable selective CO2 adsorption from a CO2-C2H2(N2 or CH4) mixture with the CO2/C2H2 (50/50 v/v) selectivity up to 8.5 × 1010. Breakthrough experiments revealed the favorable dynamic separation behavior with better performance on the sample with the comparatively high Si/Al ratio of 3.1. The CO2 adsorption at 195 K and structural refinement results demonstrated that the excellent separation performance was attributed to the less Na+ ions inside the microchannels providing more inner space for the accommodation of guest molecules.

Formation of primary intermetallic phases in the interaction of Fe-containing melts of recycled Al-Si alloys with Al2O3 and Al2O3-C filter materials: A µ-CT study

Fe is the most detrimental impurity element in recycled Al-Si alloys due to the formation of brittle, primary, Fe-containing, intermetallic particles during solidification. Their removal from the Al-Si melts e.g. by filtration can reduce the Fe content. New active filter materials can facilitate the formation of these particles for their removal and contribute to the production of high-quality, recycled Al-Si alloys. The interaction of the alloy with the filter material can lead to modification of the thermodynamics of the alloy or of the kinetics of the particle formation. Time-resolved, three-dimensional microstructural investigations have been carried out to study the formation of primary intermetallic particles in Al7.1Si1.5Fe and Al7.1Si0.75Fe0.75Mn alloy melts in contact with Al2O3 and Al2O3-C filter substrate material during a melt conditioning treatment at 620 °C. The microstructures, in particular the primary intermetallic particles αc and αh, have been characterized by computed tomography (CT) and supplementary scanning electron microscopy (SEM). As expected by thermodynamics, the total volume fraction of primary particles remains unchanged by the interaction with the substrate materials. However, kinetic advantages for Fe-removal efficiency can be achieved by an accelerated and preferred selective particle formation in contact with the Al2O3-C material. Furthermore, particle formation is discussed in view of its different stages: nucleation, growth, and ripening.

Large eddy simulation of iron oxide formation in a laboratory spray flame

Iron oxide nanoparticles are very interesting for many applications in different industrial sectors. A promising process to manufacture these nanoparticles is flame spray pyrolysis (FSP). A lack of understanding of the individual sub-processes in FSP makes it challenging to tailor nanoparticle properties. This work provides insights into the formation of iron oxide nanoparticles in a turbulent spray flame using Large Eddy Simulations (LES), which are based on a comprehensive model, including customized submodels. Highlights are the adaption of a turbulent combustion model and a bivariate hybrid method of moments for modeling nanoparticle dynamics. The work focuses on the SpraySyn burner, which is a standardized laboratory burner and was operated with a precursor-solvent mixture of ethanol and iron(III) nitrate nonahydrate. For studying the relevance of precursor chemistry, LES using an evaporation-limited precursor chemistry model is compared with a model that includes detailed iron chemistry. A further novelty is the inclusion of adsorption in the simulation, which defines a third model for comparison. Sufficient validation is achieved for the undoped LES using experimental data from the literature. A strong impact of the detailed iron chemistry and adsorption is found on the precursor consumption and the aggregate and primary particle formation. Comparing the particle diameters with experimental measurements from the literature and data generated for this work is found unsuitable to asses the precursor chemistry model and revealed an urgent need for future experimental and numerical research. This work serves as a step forward in realizing a reliable model.

The surface structure of nanosilica produced from sodium silicate by the carbonation process

CO2 was used to prepare nanosilica particles through a carbonization reaction in a Na2SiO3 solution, aiming to convert CO2 into value-added products. The relationship between the specific structure of the as-prepared nanosilica and the sodium silicate concentration, reaction temperature, reaction time, and aging time was explored by TEM, BET, and XRD analysis. The growth process of nanosilica particles was relatively slow with the increase in the Na2SiO3 concentration, which resulted in the formation of large primary particles, reducing the specific surface area. The decreasing temperature reduced the polymerization of Si(OH)4 and SiOSi(OH)3, reducing the specific surface area. Meanwhile, the effects of reaction time and aging time on the surface structure of silica nanoparticles were studied. Different surface structure of nanosilica particles were synthesized by controlling the carbonization process conditions, which expand the application of nanosilica products. At present, the research on the carbonization preparation of nanosilica mainly focused on the carbonization process conditions and modification technology, but the research of control mechanism of nanosilica surface structure and properties was insufficient. This study focused on the relationship between surface structure evolution and properties, and provided a theoretical basis for the mechanism of the influence factors of preparation process on the structure evolution of prepared nanosilica. And the process reduced CO2 emission, which had important environmental protection value.

The morphology and electrochemical properties of LiNi0.8Co0.1Mn0.1O2 cathode material prepared by the assistance of CTAB surfactant

The effect of hexadecyl trimethyl ammonium bromide (CTAB), as a surfactant, on morphology and electrochemical properties of LiNi0.8Co0.1Mn0.1O2 cathode materials was systematically investigated. Ni0.8Co0.1Mn0.1(OH)2 precursors were obtained through co-precipitation method using CTAB as a surfactant, then sintered with lithium salt to synthesize LiNi0.8Co0.1Mn0.1O2 cathode materials. XRD and TEM results show that the materials possess rhombohedral α-NaFeO2 layered structure (space group R3¯m), and Ni/Li mixing degrees reduce and the (003) crystal plane spacing enlarges to some degree upon the assistance of CTAB. SEM images prove that the formation of columnar primary particles of can be promoted by the assistance of CTAB. The discharge capacity for the samples reaches the maximum 186.9 mAh∙g−1 at 0.1C while the content of CTAB increases to 0.2%, and NCM 0.2 sample also shows better high-rate charge/discharge ability and preferable cycling performance. Furthermore, NCM 0.2 sample exhibits lower charge transfer impedance and faster diffusion rate of Li+ than that of the blank.

Sensitivity of pollutant concentrations in urban streets to asphalt and traffic-related emissions

The higher concentrations of atmospheric particles, such as black carbon (BC) and organic matter (OM), detected in streets compared to the urban background are predominantly attributed to road traffic. The integration of this source of pollutant in air quality models nevertheless entails a high degree of uncertainty and some other sources may be missing. Through sensitivity scenarios, the impacts on pollutant concentrations of sensitivities related to traffic and road-asphalt emissions are evaluated. The 3D Eulerian model Polair3D and the street network model MUNICH are applied to simulate various scenarios and their impacts at the regional and local scales. They are coupled with the modular box model SSH-aerosol to represent formation and aging of primary and secondary gas and particles. Traffic emissions are calculated with the COPERT methodology. Using recent volatile organic compound speciations for light vehicles with more detailed information pertaining to intermediate, semi- and low-volatile organic compounds (I/S/LVOCs) leads to limited reductions of OM concentrations (10% in streets). Changing the method of estimating I/S/LVOC emissions leads to an average reduction of 60% at emission and a decrease of the OM concentrations of 27% at the local scale. An increase in 219% of BC emissions from tire wear, consistent with the uncertainties found in the literature, doubles the BC concentrations at the local scale, which remain underestimated compared to observations. I/S/LVOC emissions are several orders of magnitude higher when considering emissions from road asphalt due to pavement heating and exposure to sunlight. However, simulated concentrations of PM at the local scale remain within acceptable ranges compared to observations. These results suggest that more information is needed on I/S/LVOCs and non-exhaust sources (tire, brake and road abrasion) that impact the particle concentration. Furthermore, currently unconsidered emission sources such as road asphalt may have non-negligible impacts on pollutant concentrations in streets.

INFLUENCES OF P AND Sr ON MICROSTRUCTURE AND ITS EFFECTS ON MACHINABILITY AND MECHANICAL PROPERTIES OF HYPEREUTECTIC Al-20%Si

Hypereutectic Al-Si alloys are widely utilized in the automotive industry due to their high strength-to-weight ratio, minimal thermal expansion, and superior castability. The downside of hypereutectic Al-Si alloys is the formation of coarse primary silicon particles. The primary Si phases were controlled by the growth-hindering agents, phosphorus (refiner), and strontium (modifier) by using a conventional stir casting technique at room temperature. The microstructural changes were observed through an optical microscope and SEM analysis. The additions of 0.08% P have ensured the formation of the uniformly distributed fine-grained particles in the alloy. The primary silicon particle size was reduced from 220[Formula: see text][Formula: see text]m to 150[Formula: see text][Formula: see text]m as compared to the untreated alloy. The tensile and yield properties of the treated alloy were increased by 12.7% when compared to the untreated alloy with a hardness of 131 BHN. The treated alloy imparted better impact toughness, ensuring a ductile mode of failure through the fractography studies. The influence of the microstructure on the machinability of the alloy was investigated in a dry environment with uncoated and coated inserts (code: CCGT 09T304 FL K10) by varying the process parameters, i.e. speed, feed rate, and depth of cut (DoC). Modification of the primary and eutectic Si phases of an Al-20Si hypereutectic alloy increases machinability with coated inserts as well as its mechanical properties.

Restraining the escape of lattice oxygen enables superior cyclic performance towards high-voltage Ni-rich cathodes.

Layered Ni-rich cathodes, operating at high voltage with superior cyclic performance, are required to develop future high-energy Li-ion batteries. However, the worst lattice oxygen escape at the high-voltage region easily causes structural instability, rapid capacity fading and safety issues upon cycling. Here, we report a dual-track strategy to fully restrain the escape of lattice oxygen from Ni-rich cathodes within 2.7-4.5V by one-step Ta doping and CeO2 coating according to their different diffusion energy barriers. The doped Ta can alleviate the charge compensation of oxygen anions as a positive charge centre to reduce the lattice oxygen escape and induce the formation of elongated primary particles, significantly inhibiting microcrack generation and propagation. Additionally, the layer of CeO2 coating effectively captures the remaining escaped oxygen and then the captured oxygen feeds back into the lattice during subsequent discharge. The resultant Ni-rich cathode enables a capacity of 231.3mAhg-1 with a high initial coulombic efficiency of 93.5%. A pouch-type full cell comprising this cathode and a graphite anode exhibits >1000 times life cycles at 1C in the 2.7-4.5V range, with 90.9% capacity retention.

Microstructure and mechanical properties of Ti–45Al–2W–xC alloys

The microstructure and mechanical properties of five alloys with nominal compositions of Ti–45Al–2W–xC (in at.%), where x is ranging from 0.4 to 2.0 at.%, were studied. The alloys were prepared by vacuum induction melting in graphite crucibles, followed by centrifugal casting into a graphite mould. The as-cast alloys were subjected to hot isostatic pressing and heat treatment consisting of solution annealing, cooling at a constant rate and stabilisation annealing. The microstructure of the heat-treated alloys consists of equiaxed α2(Ti3Al) + γ(TiAl) lamellar grains surrounded by γ grain boundaries with a small amount of β/B2 particles. The α2-α2 interlamellar spacing λ decreases with increasing carbon content until a solubility limit of carbon is achieved. The increase in carbon content above the solubility limit leads to the formation of primary Ti2AlC particles during solidification and an increase in the amount of γ phase at grain boundaries. Vickers microhardness of lamellar grains depends on the carbon content and interlamellar spacing λ. The studied Ti–45Al–2W–0.8C and Ti–45Al–2W–1.2C alloys show improved creep resistance at 800 °C compared to that of the reference carbon-free TiAl–W and carbon-containing TiAl–Nb based alloys with fully lamellar, nearly lamellar, convoluted or pseudo-duplex microstructure.

Complexation in Aqueous Solution of a Hydrophobic Polyanion (PSSNa) Bearing Different Charge Densities with a Hydrophilic Polycation (PDADMAC).

In this work the electrostatic complexation of two strong polyelectrolytes (PEs) was studied, the hydrophilic and positively charged poly (diallyldimethylammonium chloride) (PDADMAC) and the hydrophobic and negatively charged poly (styrene-co-sodium styrene sulfonate) (P(St-co-SSNa)), which was prepared at different sulfonation rates. The latter is known to adopt a pearl necklace conformation in solution for intermediate sulfonation rates, suggesting that a fraction of the P(St-co-SSNa) charges might be trapped in these hydrophobic domains; thus making them unavailable for complexation. The set of complementary techniques (DLS, zetametry, ITC, binding experiment with a cationic and metachromatic dye) used in this work highlighted that this was not the case and that all anionic charges of P(St-co-SSNa) were in fact available for complexation either with the polycationic PDADMAC or the monocationic o-toluidine blue dye. Only minor differences were observed between these techniques, consistently showing a complexation stoichiometry close to 1:1 at the charge equivalence for the different P(St-co-SSNa) compositions. A key result emphasizing that (i) the strength of the electrostatic interaction overcomes the hydrophobic effect responsible for pearl formation, and (ii) the efficiency of complexation does not depend significantly on differences in charge density between PDADMAC and P(St-co-SSNa), highlighting that PE chains can undergo conformational rearrangements favoring the juxtaposition of segments of opposite charge. Finally, these data have shown that the formation of colloidal PECs, such as PDADMAC and P(St-co-SSNa), occurs in two distinct steps with the formation of small primary complex particles (<50 nm) by pairing of opposite charges (exothermic step) followed by their aggregation within finite-size clusters (endothermic step). This observation is in agreement with the previously described mechanism of PEC particle formation from strongly interacting systems containing a hydrophobic PE.

Carbonaceous aerosols in five European cities: Insights into primary emissions and secondary particle formation

Carbonaceous material is an important component of atmospheric aerosol particles, which plays a significant role in air quality and climate, and also has potentially negative impacts on human health. There is a lack of data reported in the literature regarding the carbonaceous fraction of aerosol in the North-West European ‘air pollution hotspot’ and this work reports a comprehensive one-year intensive measurement campaign, where organic carbon (OC) and elemental carbon (EC) fractions of PM10 (particulate matter of diameter ≤ 10 μm) were measured. Owing to the importance of carbonaceous aerosols in understanding particulate pollution sources, ~2000 PM10 samples were simultaneously collected across North-West Europe at four urban background sites located in Amsterdam (AD), Antwerp (AP), Leicester (LE) and Lille (LL), and one industrial site at Wijk aan Zee (WZ). PM10 samples were chemically analysed by OC-EC analyser for carbonaceous species (OC, and EC) and trends were identified. OC accounted for 12.8%, 13.9%, 15.3%, 15.1% and 9.8%, and EC accounted for 2.4%, 4.9%, 4.4%, 4.0%, and 2.4% of total PM10 mass for AD, AP, LE, LL and WZ, respectively. Secondary organic carbon (SOC) contributions were higher in warmer months compared to colder months, and SOC concentration levels were similar at all five locations, with SOC contributing more than primary organic aerosol (POC) in each city. The lower effective carbon ratio (ECR) values (≤0.3) at all five sites in October, November, and February can be attributed to higher combined POC and EC concentrations and lesser contributions from SOC, meaning that SOC with a greater relative formation has a greater tendency to disperse solar radiation. Higher ECR values in April, May, and July, on the other hand, indicate that more absorbing types of carbonaceous aerosols are also present. More than 90% of the air-mass trajectories were from the north and northeast. This paper details atmospheric processes and sources influencing the seasonal variability of the carbonaceous components of PM10.

Effect of trace boron on grain refinement of commercially pure aluminum by Al–5Ti–1B

The effect of boron content on grain refinement of commercially pure aluminum by Al–5Ti–1B was quantitatively assessed. When the boron content is less than 0.03 wt.%, the refining performance of Al–5Ti–1B gradually is weakened as the boron content increases, which is attributed to the reaction of boron with the Al3Ti interlayer on TiB2 and the consumption of solute Ti. On the contrary, when the boron content exceeds 0.03 wt.%, the refining performance of Al–5Ti–1B gradually recovers with increasing boron content, which is related to the formation of primary AlB2 particles that provide additional nucleant substrates.

Indigo-A New Tribological Substance Class for Non-Toxic and Ecological Gliding Surfaces on Ice, Snow, and Water.

The biogenic substance E-indigo can form supramolecular, hydrophobic structures using self-organization. These structures show a low coefficient of friction as a gliding layer against polar surfaces. The formation of primary particles with platelet morphology based on hydrogen-bonded E-indigo molecules is ideal to produce the gliding layer. Structures with excellent gliding properties can be achieved by means of directed friction and high pressure, as well as through tempering. The resulting hard, thin gliding layer of E-indigo does not easily absorb dirt and, thus, prevents a rapid increase in friction. Field tests on snow, with cross-country skis, have shown promising results in comparison to fluorinated and non-fluorinated waxes. Based on quantitative structure–activity relationship (QSAR) data for E-indigo, and its isomers and tautomers, it has been demonstrated that both the application and abrasion of the thin indigo layers are harmless to health, and are ecologically benign and, therefore, sustainable.

Influence of the Small Sc and Zr Additions on the As-Cast Microstructure of Al–Mg–Si Alloys with Excess Silicon

This research is devoted to the study effects of complex alloying of Al-0.3 wt. % Mg-1 wt. % Si and Al-0.5 wt. % Mg-1.3 wt. % Si alloys by small additions of Sc and Zr on the microstructure in the as-cast condition. The effect of small additions of these elements on the microhardness, electrical conductivity, grain size and phase composition of the indicated alloy systems was studied. The methods of optical and electron microscopy were used for the study. Moreover, the phase composition was calculated using the Thermo-Calc software package. The study showed a strong effect of the chemical composition of investigated alloys on the size of the grains, which, with a certain combination of additives, can decrease several times. Grain refinement occurs both due to supercooling and formation of primary Al3Sc particles in the liquid phase. Alloys based on Al-0.5 wt. % Mg-1.3 wt. % Si are more prone to the formation of this phase since a lower concentration of Sc is required for it to occur. In addition, more silicon interacts with other elements. At the same time, Al-0.3 wt. % Mg-1 wt. % Si requires lower temperature for complete dissolution of Mg2Si, which can contribute to more efficient heat treatment, which includes reducing the number of steps. TEM data show that during ingot cooling (AlSi)3ScZr dispersoid precipitates. This dispersoid could precipitate as coherent and semi-coherent particles with L12 structure as well as needle-shaped particles. The precipitation of coherent and semi-coherent particles during cooling of the ingot indicates that they can be obtained during subsequent multistage heat treatment. In addition, in the Al0.5Mg1.3Si0.3Sc alloy, metastable β″ (Mg5Si6) are precipitated.

Small-sized biomass-derived hydrothermal carbon with enriched oxygen groups quickens benzene hydroxylation to phenol with dioxygen

Metal-free carbon materials have attracted growing attention in terms of green and sustainable catalysis processes that could avoid potential metal leaching but usually suffered from inferior activity to metal-loaded counterparts. In this work, we constructed an efficient carbon catalyst via hydrothermal carbonization of biomass-derived feedstock glucose under relatively low temperature (180 °C). The resultant carbon material possessing abundant surface oxygen species effectively catalyzed the benzene hydroxylation with dioxygen (O2), a desirable but very difficult alternative process for producing the important bulk chemical phenol. A considerably high phenol yield of 13.1% was achieved within 4 h, a reaction time much shorter than all the previous metal-free catalysts and even shorter than most efficient metal-based catalysts. The fast reaction is determined by the formation of small-sized primary carbon particles with the abundant surface oxygen species, for which the adsorption enhancing effect in the media of this heterogeneous process was experimentally evidenced.

Simulation of an Industrial Carbon Black Reactor Using Collision Kinetics

Purpose: Objective of the work was to test efficacy of the proposed flame chemistry and collision kinetics for prediction of process parametres through determination of the effect of basic process parameters on yield (which includes but not limited to grade of carbon black produced).&#x0D; Methodology: The research methodology in this work was simulation of an industrial Carbon Black Reactor based on reaction kinetics from flame chemistry which assumes that primary particle formation and particle growth is strictly by collision of molecular nuclei with gas molecule as proposed by the collision theory. Decant oil from the Fluid Catalytic Cracking Unit (FCCU) of the Warri Refinery and Petrochemical Company Limited of Nigeria represented by naphthalene was used as feedstock in the simulation while methane gas is the fuel for combustion needed to attain the reaction temperature.&#x0D; Findings: Results showed an excellent quantitative prediction of trends by models. Qualitative predictions gave far higher parameter values, something easily attributable to the excessively high values of kinetic data used for model testing. &#x0D; Recommendation: The simplifying assumptions of these models completely ignored microscopic phenomena such as interface mass and heat transfer and other similar processes. Consequently, the model can be improved upon by introducing some of these processes as identified.

In situ suspension polymerization of vinyl chloride/3-(trimethoxysilyl) propyl methacrylate (MPTMS)-intercalated Mg-Al-hydroxide layered double hydroxide: I. Grain properties

Suspension polymerization of vinyl chloride (VCM) was carried out in the presence of particle of both pristine Mg-Al layered double hydroxide (LDH) and LDH intercalated by 3-(trimethoxysilyl) propyl methacrylate (MPTMS-LDH) in a pilot-scale reactor. The experiments were conducted at different concentrations of each type of the particles (0, 1, 3, 5, 7 wt. % of VCM). The pure LDH and MPTMS-intercalated LDHs were used as co-monomer for fabrication of LDH or MPTMS-LDH/PVC nanocomposites; the particles were directly pre-dispersed in monomer phase before dispersing in the continuous aqueous phase and starting the suspension polymerization. The basal spacing obtained from the X-ray powder diffraction (XRD) showed that the reaction between VCM and MPTMS-LDH was effective, with a further intercalation of PVC chains in the interlayer space. The molecular characterization showed that the polydispersity index (PDI) and molecular weight of the poly (vinyl chloride) (PVC) resin do not change in the presence of the pristine LDH. The MPTMS-LDH, however, decrease the molecular weight and increase the PDI of PVC resin. Also, from the morphological point of view, scanning electron microscopy (SEM) showed that PVC grains produced with high particles content had a smoother surface with more regular shape. Moreover the incorporation of nanoparticles in the VCM suspension polymerization, made particles with a narrower size distribution. The LDH results in the formation of smaller primary particles with higher internal porosity whereas, the larger primary particles with lower internal porosity in the presence of modified particles was observed.

Microbial dynamics of elevated carbon flux in the open ocean’s abyss

In the open ocean, elevated carbon flux (ECF) events increase the delivery of particulate carbon from surface waters to the seafloor by severalfold compared to other times of year. Since microbes play central roles in primary production and sinking particle formation, they contribute greatly to carbon export to the deep sea. Few studies, however, have quantitatively linked ECF events with the specific microbial assemblages that drive them. Here, we identify key microbial taxa and functional traits on deep-sea sinking particles that correlate positively with ECF events. Microbes enriched on sinking particles in summer ECF events included symbiotic and free-living diazotrophic cyanobacteria, rhizosolenid diatoms, phototrophic and heterotrophic protists, and photoheterotrophic and copiotrophic bacteria. Particle-attached bacteria reaching the abyss during summer ECF events encoded metabolic pathways reflecting their surface water origins, including oxygenic and aerobic anoxygenic photosynthesis, nitrogen fixation, and proteorhodopsin-based photoheterotrophy. The abundances of some deep-sea bacteria also correlated positively with summer ECF events, suggesting rapid bathypelagic responses to elevated organic matter inputs. Biota enriched on sinking particles during a spring ECF event were distinct from those found in summer, and included rhizaria, copepods, fungi, and different bacterial taxa. At other times over our 3-y study, mid- and deep-water particle colonization, predation, degradation, and repackaging (by deep-sea bacteria, protists, and animals) appeared to shape the biotic composition of particles reaching the abyss. Our analyses reveal key microbial players and biological processes involved in particle formation, rapid export, and consumption, that may influence the ocean's biological pump and help sustain deep-sea ecosystems.

Effect of artificial ageing treatment and precipitation on mechanical properties and fracture mechanism of friction stir processed MgZn2 and Al3Sc phases in aluminium alloy

Aluminium alloy (7075 series) contains scandium (Sc) promoting fine grains due to their potent inoculation effects formation of homogeneous primary particles, Al3Sc (L12) during solidification and subsequent age- hardening phenomenon. A supersaturated aluminium matrix can ensure the driving force for the coherent precipitates, and high density (∼0.45 wt% Sc) nanoparticles Al3Sc and further enhanced by raising the ageing temperature. FSP is a solid-state surface modification technique via frictional heat and tool stirring during processing. The effects of double-pass friction stir processing (DP-FSP) on the microstructure, and nano-sized particle (MgZn2, Al3Sc) distribution, as well as the microstructural evolution after T6 heat treatment, were investigated by OM, FESEM, TEM, SEM, Vicker’s hardness measurement, and tensile properties. Zn vaporization is a primary defect in the stirring zone which hinders the high strength even though having fine grain microstructures. SEM fractography revealed coarse precipitates, defects, and propagation of fracture plane of the alloy. The present investigation aims to study the enhancement of strength and ductility for nano-sized precipitates in the matrix by a combination of T4 + DP-FSP and subsequent post ageing treatment at 140 °C for 2 h (T6 treatment).