Formation Of Primary Particles Research Articles

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).

Mechanism of ultrasound-induced microstructure modification in Al–Zr alloys

This work probes the effect of ultrasonic melt treatment (UST) on primary intermetallic particles and α-Al using pure Al and Al–Zr alloys (Al–0.3Zr–0.1Ti, Al–0.5Zr, Al–0.5Zr–0.5Mg–0.9Si) solidified at various cooling rates of 0.2–70 K s−1. The application of UST is shown to decrease the size and increase the number density and volume fraction of D023-structured primary Al3Zr and Al3(Zr,Ti) particles with a high nucleation potency for α-Al formation. High-resolution transmission electron microscopy analysis reveals that the cavitation-induced wetting and dispersion of γ-Al2O3 inoculant particles contribute to the refinement of primary intermetallic particles. The grain size of Al–Zr alloys increases with increasing cooling rate because of the concomitantly reduced formation of primary intermetallic inoculant particles. The UST-induced refinement of primary Al3Zr particles and the increased number density lead to grain refinement in Ti-free Al–Zr alloys. For the Ti-containing Al–Zr alloy, UST-induced grain refinement is achieved only at a very low cooling rate of 0.2 K s−1, possibly because of the side effects of UST on the growth-restricting influence of Ti. The fast cooling–induced solidification enables significant age-hardening by L12-Al3Zr nanoprecipitation (~5 nm) and is not affected by UST. Thus, this study shows that UST can be used to reduce the degree of grain coarsening of age-hardenable Al–Zr alloys at high cooling rates.

Zinc Phosphate Nanoparticles Produced in Saliva

This paper reports the formation of zinc phosphate nanoparticles from the artificial digestion of zinc chloride. Initially, the formation of amorphous primary particles with a mean radius of 1.1 nm is observed, alongside the formation of larger, protein stabilized aggregates. These aggregates, with a radius of gyration of 37 nm, are observed after 5 minutes of exposure to artificial saliva and are shown to be colloidally stable for a minimum time of two weeks. The initially formed primary particles are thought to consist of amorphous zinc phosphate, which is then transformed into crystalline Zn3(PO4)2·4H2O over the course of two weeks. Our results demonstrate that the interaction of inorganic salts with bodily fluids can induce the formation of de novo nanoparticles, which in turn, provides insights into how zinc‐enriched foods may also facilitate the formation of nanoparticles upon contact with saliva. As such, this may be considered as an undesirable (bio)mineralization.

Synthesis of Al2O3-ZrO2-MxOy (M = Mg, La) complex oxide systems using electrogenerated reagents and their physicochemical properties

A method for the synthesis of metal oxide precursors based on the electrogeneration of reagents in a coaxial electrochemical reactor without a membrane with electrodes substantially different in the surface area was proposed. The electrogeneration is accompanied by the subsequent hydrolysis of the products, the formation of primary particles due to the polycondensation of aquahydroxo complexes, and their further enlargement. In the coaxial electrolyzer-reactor, the flow of gas and electrolyte bubbles moves up and to the sides from the central electrode to form a vortex in the confined space. This makes it possible to distribute the components of the reaction mixture and to suspend more uniformly the formed particles of the solid phase in the liquid bulk due to the appeared turbulence. The introduction of Zr4+, Mg2+, and La3+ ions favors the formation of stable positively charged particles. The average particle size of alumina modified with oxides of other metals (Zr, Mg, and La) obtained using electrogenerated reagents was found to be 20-50 nm. Under thermal treatment of the synthesized systems (1100°C), complex phase transformations lead to the formation of spinel Al2MgO4 and stabilization of α-Al2O3 and tetragonal t-ZrO2 stable at high temperatures up to 1600°C

Synergistic coupling effect of single crystal morphology and precursor treatment of Ni-Rich cathode materials

The precursor was treated by KMnO4 and combined with the formation of single crystal primary particles to improve the electrochemical performance of LiNi0.8Mn0.1Co0.1O2 in this study. The single crystal primary morphology of the cathode material can not only shorten the migration path of lithium ions, but also maintain the integrity of particle morphology and avoid the generation of cracks in particles after circulation. Some Mn4+ from KMnO4 incorporated into the crystal lattice, causing a small amount of Ni2+ act as pillars in the lithium layer and thus avoiding its collapse in the delithium state. Besides that, a thin MnO2 layer is also formed on the cathode material, which inhibit side reactions between electrolyte and cathode material. The results show that the synergistic coupling effects of single crystal morphology and precursor treatment are realized to improve the electrochemical properties of the Ni-rich cathode materials.

Constitutive Behavior of an AA4032 Piston Alloy with Cu and Er Additions upon High-Temperature Compressive Deformation

Aluminum piston alloys of the AA4032 type are produced by direct-chill (DC) casting and subsequent forging; therefore, it is important to understand their thermomechanical behavior. In recent years, it was shown that additions of Cu and Er could improve mechanical properties of these alloys at room and high temperatures. In this work, we studied the constitutive behavior of AA4032-type alloys with and without Cu and Er additions. The experimental true stress–true strain curves were obtained by compression tests under various temperatures [683 K to 723 K (410 °C to 450 °C)] and strain rates (0.01 to 10 s−1) to determine constitutive parameters [strain-rate sensitivity, activation energy, and Zener–Hollomon (Z) parameter] for the hot deformation behavior of AA4032-type piston alloys with and without additions of Cu and Er. The flow stress decreased with increasing deformation temperature and decreasing strain rate. The results also showed that increasing the Cu content increased the flow stress over the applied range of deformation conditions due to solid-solution strengthening and the formation of primary Si particles, which led to an increase in the activation energy during hot deformation. Moreover, the main microstructural damage in the AA4032 alloy with 3.5 pct Cu was predominantly due to the cracking of primary Si particles. Additions of 0.4 pct Er and 3.5 pct Cu lower the activation energy of deformation, Q, as compared to the base alloy and the alloy with 3.5 pct Cu. The microstructures in the deformed specimens consisted of subgrains, recrystallized grains, and fine eutectic phases. The alloys containing Er demonstrated more polygonized grains at a low strain rate than the alloys without Er, indicating that Er hindered recrystallization development. The peak stress of the AA4032 alloy with 3.5 pct Cu alloy was higher than for the base AA4032 alloy and for the AA4032 alloy with 3.5 pct Cu and 0.4 pct Er additions, which was attributed to the prevalence of the work-hardening mechanism over the softening mechanism.

Crystallization by particle attachment is a colloidal assembly process.

The nucleation of crystals has long been thought to occur through the stochastic association of ions, atoms or molecules to form critical nuclei, which will later grow out to crystals1. Only in the past decade has the awareness grown that crystallization can also proceed through the assembly of different types of building blocks2,3, including amorphous precursors4, primary particles5, prenucleation species6,7, dense liquid droplets8,9 or nanocrystals10. However, the forces that control these alternative pathways are still poorly understood. Here, we investigate the crystallization of magnetite (Fe3O4) through the formation and aggregation of primary particles and show that both the thermodynamics and the kinetics of the process can be described in terms of colloidal assembly. This model allows predicting the average crystal size at a given initial Fe concentration, thereby opening the way to the design of crystals with predefined sizes and properties.

Оптимальная пара ридберговских атомов щелочных металлов в несимметричных пеннинговских процессах ионизации

Penning ionization (PI) processes for cold Rydberg alkali metal atoms are investigated. Contrary to the reference case of a hydrogen atom, the corresponding autoionization widths demonstrate a sharp dependence (by orders of magnitude) on the orbital quantum numbers of the atoms exposed to long-range dipole-dipole interaction. An important feature of PI is the nontrivial dependence of its efficiency on the size of Rydberg particles. For all types of alkali atoms, the existence of optimal Rydberg pairs has been demonstrated (highly asymmetric configurations of Rydberg pairs), which lead to an explosive intensification (by several orders of magnitude) of the formation of free electrons due to PI processes. This property makes PI an important source of the formation of primary charged particles during the formation of cold Rydberg plasma. The presented numerical data for potassium atomic pairs demonstrate a significant effect of the Förster resonance on the values of PI rate constants.

Nitrogen-doped porous carbon via ammonothermal carbonization for supercapacitors

In this study we demonstrate a cheap and sustainable ammonothermal approach towards nitrogen-doped porous carbons. Sodium borate (borax) is employed as a catalyst during the synthesis resulting in the formation of small interconnected primary particles of 99%. Comparison of different pore systems indicates that a continuous pore size distribution may explain improved rate performances.

Chemical nature of PM2.5 and PM10 in Xi'an, China: Insights into primary emissions and secondary particle formation

In Xi'an, a city that frequently experiences serious PM pollution in northern China, 1476 PM10 and 1464 PM2.5 valid daily filter samples were collected at six sites from December 2014 to November 2015 and analyzed for 29 species. The annual mean PM10 and PM2.5 concentrations were 149.4 ± 93.1, 108.0 ± 70.9 μg/m3, respectively. Organic carbon (OC) is the predominant PM2.5 component while crustal material predominated in PM10. Sulfate concentrations, which was the largest component in Xi'an PM in previous studies, were lower than nitrate. Winter sulfate, OC, and elemental carbon (EC) have decreased since 2003, while nitrate remained constant in recent years and the ratio of NO3−/SO42− increased from 0.4 in 2006 to 1.3 in 2014. This result suggests that the motor vehicle contribution to PM has increased relative to coal-fired power plant emissions over the past decade. The mass fractions of crustal material, sulfate, and EC in PM2.5 decreased as the PM2.5 concentrations increased from “clean” days (<50 μg/m3) to the highest values, while nitrate significantly increased. Despite forming through secondary reactions, the high concentrations of SOC and SO42− in winter are attributed to primary emissions and particularly to residential heating and cooking with coal. Primary SOC and SO42− accounted for 33% and 42% of their total PM2.5 concentrations in winter, respectively. Therefore, control measures applied to these primary sources can substantially improve air quality.

Formation mechanism of Pd/PVP nanoparticles: effect of ultrasonic irradiation time

The effects of ultrasonic irradiation time on the palladium nanoparticles (Pdns) formation mechanism have been investigated using UV-Visible spectroscopy, Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). Pdns colloids have been prepared by ultrasonic irradiation of Pd(NO3)2 solutions at different irradiation times (from 30 to 180 minutes). The obtained results show that the rate of sonochemical reduction of Pd(II) ions has been found to be dependent upon the irradiation time. The kinetic of Pdns formation can also be correlated with the rate of sonochemical reduction ofPd(II) ions, as well as with the role of PVP molecules. The results suggest a three-step mechanism to describe the Pdns formation as a function of ultrasound irradiation time. During the first step, the Pd(II) ions are rapidly reduced to Pd(0) atoms, and when the concentration of Pd(0) atoms is sufficient for nucleation, the formation of primary particles occurs which are stabilised by a maximal number of PVP molecules. During the second step, these particles grow progressively by adsorption of the Pd(0) atoms and the obtained particles are coordinated to all available PVP molecules. The third step corresponds to decrease of the bounded PVP to the particle surface and the growth of the large particles at the expense of the unstable small ones. Keywords: Palladium nanoparticles, ultrasound irradiation, formation mechanism, UV-visible spectroscopy, FT-IR spectroscopy, TEM.

Hydrogen-assisted spark discharge generated metal nanoparticles to prevent oxide formation

There exists a demand for production of metal nanoparticles for today's emerging nanotechnology. Aerosol-generated metal nanoparticles can oxidize during particle formation due to impurities in the carrier gas. One method to produce unoxidized metal nanoparticles is to first generate metal oxides and then reduce them during sintering. Here, we propose to instead prevent oxidation by introducing the reducing agent already at particle formation. We show that by mixing 5% hydrogen into the nitrogen carrier gas, we can generate single crystalline metal nanoparticles by spark discharge from gold, cobalt, bismuth, and tin electrodes. The non-noble nanoparticles exhibit signs of surface oxidation likely formed post-deposition when exposed to air. Nanoparticles generated without hydrogen are found to be primarily polycrystalline and oxidized. To demonstrate the advantages of supplying the reducing agent at generation, we compare to nanoparticles that are generated in nitrogen and sintered in a hydrogen mixture. For bismuth and tin, the crystal quality of the particles after sintering is considerably higher when hydrogen is introduced at particle generation compared to at sintering, whereas for cobalt it is equally effective to only add hydrogen at sintering. We propose that hydrogen present at particle generation prevents the formation of oxide primary particles, thus improving the ability to sinter the nanoparticles to compact and single crystals of metal. This method is general and can be applied to other aerosol generation systems, to improve the generation of size-controlled nanoparticles of non-noble metals with a suitable reducing agent. (Less)

Nanoparticle formation and growth in turbulent flows using the bimodal TEMOM

A developed bimodal Taylor-series expansion method of moments (B-TEMOM) is first coupled with a large eddy simulation (LES) model to investigate nanoparticle formation and subsequent growth due to nucleation, coagulation and condensation processes in turbulent flows. An incompressible gas mixture containing sulfuric acid and water vapor is injected into a stationary flow field with background aerosols. The spatial and temporal particle size distribution (PSD), particle number and mass concentrations, and competition between the formation of primary and secondary particles in turbulent flows are studied. The instantaneous results demonstrate that the large coherent structures strongly affect the particle number and mass concentration distributions as well as particle polydispersity. This finding also verifies that the coherent structures enhance diffusion in the flows and finally increases particle transfer between the two modes of particles. Furthermore, the numerical simulation results obtained by the B-TEMOM are validated with those obtained by the sectional method with excellent agreement.

Dicarboxylic Acid Emissions from Aftertreatment Equipped Diesel Engines.

Dicarboxylic acids play a key role in atmospheric particle nucleation. Though long assumed to originate from primary sources, little experimental evidence exists directly linking combustion to their emissions. In this work, we sought definitive proof that dicarboxylic acids are produced in diesel engines and that they can slip through a modern aftertreatment system (ATS) at low exhaust temperatures. One difficulty in measuring dicarboxylic acid emissions is that they cannot be identified using conventional mass spectroscopy techniques. In this work, we refined a derivatization gas chromatography-mass spectroscopy technique to measure 11 mono- and dicarboxylic acids from plain and KOH impregnated quartz filters. Filters were loaded with exhaust from a modern passenger car diesel engine on a dynamometer sampled before and after an ATS consisting of an oxidation catalyst and diesel particulate filter. Our findings confirm that dicarboxylic acids are produced in diesel engine combustion, especially during low temperature combustion modes that emit significant concentrations of partially combusted hydrocarbons. Exhaust acids were largely removed by a fully warmed-up ATS, mitigating their environmental impact. Our results also suggest that dicarboxylic acids do not participate in primary particle formation in dilute engine exhaust as low quantities were collected on unimpregnated filters.

Physicochemical and Additive Controls on the Multistep Precipitation Pathway of Gypsum

Synchrotron-based small- and wide-angle X-ray scattering (SAXS/WAXS) was used to examine in situ the precipitation of gypsum (CaSO4·2H2O) from solution. We determined the role of (I) supersaturation, (II) temperature and (III) additives (Mg2+ and citric acid) on the precipitation mechanism and rate of gypsum. Detailed analysis of the SAXS data showed that for all tested supersaturations and temperatures the same nucleation pathway was maintained, i.e., formation of primary particles that aggregate and transform/re-organize into gypsum. In the presence of Mg2+ more primary particle are formed compared to the pure experiment, but the onset of their transformation/reorganization was slowed down. Citrate reduces the formation of primary particles resulting in a longer induction time of gypsum formation. Based on the WAXS data we determined that the precipitation rate of gypsum increased 5-fold from 4 to 40 °C, which results in an effective activation energy of ~30 kJ·mol−1. Mg2+ reduces the precipitation rate of gypsum by more than half, most likely by blocking the attachment sites of the growth units, while citric acid only weakly hampers the growth of gypsum by lowering the effective supersaturation. In short, our results show that the nucleation mechanism is independent of the solution conditions and that Mg2+ and citric acid influence differently the nucleation pathway and growth kinetics of gypsum. These insights are key for further improving our ability to control the crystallization process of calcium sulphate.

Comparison of primary and secondary particle formation from natural gas engine exhaust and of their volatility characteristics

Abstract. Natural gas usage in the traffic and energy production sectors is a growing trend worldwide; thus, an assessment of its effects on air quality, human health and climate is required. Engine exhaust is a source of primary particulate emissions and secondary aerosol precursors, which both contribute to air quality and can cause adverse health effects. Technologies, such as cleaner engines or fuels, that produce less primary and secondary aerosols could potentially significantly decrease atmospheric particle concentrations and their adverse effects. In this study, we used a potential aerosol mass (PAM) chamber to investigate the secondary aerosol formation potential of natural gas engine exhaust. The PAM chamber was used with a constant UV-light voltage, which resulted in relatively long equivalent atmospheric ages of 11 days at most. The studied retro-fitted natural gas engine exhaust was observed to form secondary aerosol. The mass of the total aged particles, i.e., particle mass measured downstream of the PAM chamber, was 6–268 times as high as the mass of the emitted primary exhaust particles. The secondary organic aerosol (SOA) formation potential was measured to be 9–20 mg kgfuel−1. The total aged particles mainly consisted of organic matter, nitrate, sulfate and ammonium, with the fractions depending on exhaust after-treatment and the engine parameters used. Also, the volatility, composition and concentration of the total aged particles were found to depend on the engine operating mode, catalyst temperature and catalyst type. For example, a high catalyst temperature promoted the formation of sulfate particles, whereas a low catalyst temperature promoted nitrate formation. However, in particular, the concentration of nitrate needed a long time to stabilize – more than half an hour – which complicated the conclusions but also indicates the sensitivity of nitrate measurements on experimental parameters such as emission source and system temperatures. Sulfate was measured to have the highest evaporation temperature, and nitrate had the lowest. The evaporation temperature of ammonium depended on the fractions of nitrate and sulfate in the particles. The average volatility of the total aged particles was measured to be lower than that of primary particles, indicating better stability of the aged natural gas engine-emitted aerosol in the atmosphere. According to the results of this study, the exhaust of a natural gas engine equipped with a catalyst forms secondary aerosol when the atmospheric ages in a PAM chamber are several days long. The secondary aerosol matter has different physical characteristics from those of primary particulate emissions.

On the Breakdown of SiC during the Selective Laser Melting of Aluminum Matrix Composites

Selective laser melting (SLM) is used to produce a SiC reinforced aluminum metal matrix composite (AMMC, Al–12Si plus 10 vol% SiC) with laser energy densities () between 20 and 80 J mm−3. Microstructural analysis shows that at lower energies, SiC is present in the Al–12Si matrix; however, at higher energies there is a distinct lack of SiC particles and the extensive formation of Al4C3 needles and primary Si particles. XRD analysis confirms a decrease in the volume of SiC and an increase in the amount of Al4C3 and primary Si with increasing . This indicates that a reaction occurs between the Al and SiC during SLM. The underlying mechanism is attributed to the selective absorption of laser energy into the SiC particles, causing regions of extremely high temperatures. The formation of the reaction products cause errors in the theoretical density calculations. Therefore, X‐ray micro tomography (XMT) is used to independently measure the relative density of the samples with a peak relative density ≈97.4%, which is much higher than that (relative density ≈93%) measured using the Archimedes method.

Effects of Sc(Zr) on the microstructure and mechanical properties of as-cast Al–Mg alloys

Both the addition of 0.6% Sc and simultaneous addition of 0.2% Sc and 0.1% Zr exerted a remarkable effect on grain refinement of as-cast Al–Mg alloys, changing typical dendritic microstructure into fine equiaxed grains. Such effect was found to be related to the formation of primary particles, which acted as heterogeneous nucleation sites for α-Al matrix during solidification. Primary particles formed in Al–Mg–Sc–Zr alloy could be identified as the eutectic structure consisting of multilayer of ‘Al3(Sc,Zr) + α-Al + Al3(Sc,Zr)’, with a ‘cellular-dendritic’ mode of growth. In addition, an attractive comprehensive property of as-cast Al–5Mg alloy due to the addition of 0.2% Sc and 0.1% Zr was obtained.

The effect of alloying elements on the ductility of Al-Mg-Si alloys

Experiments were conducted to document the combined effect of different alloying elements on the microstructure and associated stress-strain behavior of extruded Al-Mg-Si alloys, with a special emphasis on the ductility to fracture characteristics. Four alloys with different concentrations and relative amounts of Mg, Si, Fe, Cu, and Mn were selected for examination. In order to obtain an accurate description of the strength-ductility relationship, tensile testing was performed with a laser extensometer, and scanning (SEM) and transmission microscope (TEM) studies were carried out to correlate the microstructure and fracture characteristics with the stress-strain behavior. Excess-Si (Mg/Si<1.73) was found to have a detrimental effect on the ductility of Al-Mg-Si alloys without the presence of additional alloying elements, leading to fracture occurring partly intergranularly. This was linked to the segregation of free Si at grain boundaries, forming coarse Si-particles, and the formation of Mg2Si particles during solution heat treatment. Adding Fe and Cu improved the ductility and strength, which could be attributed to a lower solvus temperature and increased formation of primary particles, resulting in less free Si for embrittlement of grain boundaries. The highest ductility was found by introducing Mn, which in addition to tie up free Si to second-phase particles, suppressed recrystallization by forming dispersoids. The most desirable combination of tensile strength and ductility was found in an excess-Mg alloy (Mg/Si>1.73) with additions of both Mn and Cu.