Nano-sized Dust Research Articles

ЭВОЛЮЦИЯ СТРУКТУРЫ МЕДНЫХ ПОКРЫТИЙ, ОСАЖДЕННЫХ ИЗ ПЛАЗМЫ ИМПУЛЬСНОЙ ВАКУУМНОЙ ДУГИ

The work is devoted to the study of the structure of metal layers deposited from vacuum arc plasma. Under conditions of high gradients of temperature fields and thermal plasma density of the arc, coatings are formed with a non-uniform structure, porous, with drops of metal on the surface. The study of metal layers deposited from thermal plasma is relevant due to the unusual properties and unique structure of these coatings. The purpose of our study is to trace the evolution of the structure of a copper coating deposited from the plasma of a vacuum arc in a pulsed operating mode. The peculiarity of the method is that the pulsed mode involves low energy consumption, so it is more economical than a stationary arc, however, the characteristic physical features of arc plasma are preserved. The practical goal is to deposit a thin layer of copper on aluminum for energy applications. As a result of the experiments, during the deposition time of 15-40 minutes, a process of significant compaction of the copper layer on the surface of the aluminum substrates was observed. The influence of deposition time on the size of surface defects was analyzed. Before 30 min of deposition, the formation of a highly dispersed nanosize structure of spherical clusters was observed in the coating; after 30 min, the transformation of the coating structure into a thick layer with high homogeneity was observed. This behavior can be explained by the initial formation of a coating of layers of nano-sized dust. When the substrate temperature changes, nanoscale clusters enlarge and disintegrate, accompanying phase transitions. An accompanying undesirable factor was the precipitation of metal oxide phases. The development of this area of research is necessary due to the fact that in pulsed arcs a high rate of layer deposition is achieved, therefore it is necessary to improve the properties of coatings by developing this method

Explosion mechanism of nano-sized dust cloud in interconnected vessels

Explosion mechanism of nano-sized dust cloud in interconnected vessels

Progress in Studies of Surface Nanotextures and Coatings with Nanomaterials on Glass for Anti-Dust Functionality.

Dust pollution presents a wide range of adverse effects to product functionalities and the quality of human life. For instance, when dust particles deposit on solar photovoltaic panels, sunlight absorption is significantly reduced, and solar-to-electrical energy conversion yield may be lowered by 51%- Conventional (manual) dust removal methods are costly, consume significant material resources, and cause irreparable damage to the solar glass surface. Therefore, it is critical to develop glass surfaces that can clean themselves or are easily cleaned by natural forces. Many approaches have been attempted to reduce dust deposition, such as developing superhydrophobic surfaces and preparing anti-static surfaces. This paper reviews the recent progress in studies of anti-dust and cleaning mechanisms or methodologies, which include investigation into micro- and nano-sized dust properties, dust deposition processes and adhesion mechanisms to surfaces, and the state-of-the-art approaches to anti-dust and easy-cleaning functions that tailor surface micro-/nanotextures, lowering surface energy via nanocoatings, and enhancing anti-static properties with nanomaterials. We compare the advantages and disadvantages of various approaches and discuss the research prospects. We envision that future research will be focused on developing transparent surfaces with multiple dust-proof functions to cope with dust-burdening operating environments.

Combining Rosetta’s GIADA and MIDAS data: morphological versus dynamical properties of dust at 67P/Churyumov–Gerasimenko

ABSTRACT We related morphological (size/shape) and dynamical properties of the dust ejected from the 67P/Churyumov–Gerasimenko comet by combining data from two instruments onboard the ESA's Rosetta mission, i.e. the MIDAS atomic force microscope and the GIADA dust detector. The two instruments detected dust of different size (10−6–10−5 and 10−4–10−3 m, respectively). MIDAS detected dust in four periods, three during the inbound orbit arc (2014 September–November; 2014 December– 2015 February; 2015 February–March) and one corresponding to a post-perihelion outburst (2016 February 19). For these periods, we analysed the dust particles’ spatial distribution on the MIDAS targets to obtain the number of parent particles hitting the instrument by means of an empirical procedure and to measure the corresponding dust flux. For the same periods, we retrieved the dust flux measured by GIADA. The ratio between the two dust fluxes is constant. By coupling this result with activity models, we inferred that the particles detected by MIDAS are fragments of hundreds-micron- to mm-sized particles detected by GIADA. In addition, the similar dust flux ratios between nominal activity and outburst indicates that the outburst did not include micro- and nano-sized dust, differently from other outbursts previously observed. Dust and surface properties were related by applying a traceback algorithm to GIADA data to retrieve the source regions of dust ejected in different periods. We did not detect variations of morphological properties between dust ejected from more and less processed terrains, concluding that compact dust particles (detected by MIDAS) have the same properties across the comet surface.

On the Role of Electron Quantum Tunneling in Charging of Dust Grains in Complex Plasma

The role of the quantum tunneling effect in the electron accretion current onto a negatively charged grain immersed in isotropic plasma is analyzed, within the quasiclassic approximation, for different plasma electron distribution functions, plasma parameters, and grain sizes. It is shown that the contribution of the quantum tunneling into the grain charging is small (negligible) for relatively large (micron-sized) dust grains in plasmas with electron temperatures of the order of a few eV, but becomes important for nano-sized dust grains (tens to hundreds nm in diameter) in cold and ultracold plasmas (electron temperatures ~ tens to hundreds of Kelvin degrees), especially in plasmas with depleted high-energy "tails" in the electron energy distribution.

Seed traits linked to differential survival of plants during the Cretaceous/Paleogene impact winter

In past investigations the pattern of differential survival of plants across the K/Pg boundary has been viewed as incompatible with severe asteroid impact winter scenarios (i.e., an impact winter lasting more than a few months), particularly the enigmatic survival of coryphoid palms and Pandanus (screw pine). Stateof- the-art climate models based on soot, sulfate and nano-sized dust aerosols predict a global impact winter that drastically reduced precipitation and resulted in a transient period of total darkness and permafrost conditions. This suggests that the plants most likely to have been affected by the global mass-extinction event were tropical phanerophytes that produce recalcitrant seeds, which by definition are desiccation-intolerant, survive less than a year, and cannot survive freezing. However, this hypothesis has never been tested. In this study I sampled over 100 plant species from the global fossil record that have a high probability of having produced either recalcitrant seeds/disseminules (n1 = 58) or orthodox seeds (n2 = 59), based on their phylogenetic relationships with extant taxa that either are monomorphic for these traits or specifically exhibit a genetic marker for abscisic acid inhibition associated with seed dormancy and recalcitrance. A one-tailed z-test for the difference between two proportions revealed that plant taxa with a high probability of having produced recalcitrant seeds had significantly lower survivorship than plant taxa with a high probability of having produced orthodox seeds (p < 0.0001). Based on these data, it can be concluded that plants which formed a frost-tolerant seed bank during the latest Maastrichtian were significantly more likely to survive the K/Pg impact winter than plants which did not (including palms). These data clearly indicate that the K/Pg impact winter probably lasted longer than a year and that it selected for seed-based traits that effectively sorted correlated functional traits of mature plants (i.e., leaf physiognomic features). This novel hypothesis stands as an alternative to J.A. Wolfe’s classic hypothesis that a mild K/Pg impact winter selected for fast-growing angiosperms with deciduous leaves and did not affect the plant communities of the Southern Hemisphere. Potential mechanisms for the rare survival of tropical, recalcitrant-seeded plants are discussed.

The effects of secondary emission on the sheath structure in an electrostatic dusty plasma containing energetic electrons and charged nanoparticles

Multi-fluid numerical simulations are utilized to explore the effects of secondary emission by nanosize dust particles on the structure of a dusty plasma sheath in the presence of a beam of fast, mono-energetic electrons. It was found that the sheath dynamics depends strongly on the magnitude of the secondary emission yield δm. For δm smaller than unity, the secondary emission is weak, and the sheath width always increases with increasing beam flux, such that it experiences a sharp transition from the regime of thin sheath to the regime of thick sheath, at a given beam flux. For δm larger than unity, the secondary emission dominates the dust dynamics, and the sheath width always decreases with increasing beam flux. The sheath thickness decreases very quickly with the secondary emission yield, but increases with Em, the characteristic energy corresponding to the maximum secondary emission. As δm is increased, the absolute dust charge and hence the accelerating ion drag force are reduced. Then, the dust is decelerated and as a result the dust number density is enhanced. Increasing the dust radius and/or the dust number density leads to an enhanced secondary emission effect and thus to a narrower sheath width.

Simulation study of the photoemission effects in an electrostatic plasma sheath containing charged nanoparticles

Numerical simulations of the multi-fluid equations are utilized to investigate the effects of a directed photon flux on the structure of an electrostatic plasma sheath in the presence of nano-sized dust grains. The results revealed that the sheath width decreases with an increase in the photon flux as well as the photoelectric efficiency, and that the effect is prominent at high plasma number densities. With the increase in the incident flux, the absolute dust charge decreases immediately until it changes sign and becomes positive at moderate fluxes and then increases quite slowly. The ion drag is also reduced by the photoemission, while the electric force is enhanced. The net effect is an enhancement of the total force on the dust grains towards the sheath edge, leading to a significantly reduced dust speed and consequently an increased dust number density throughout the sheath.

Release of monomers from composite dust

Dental personnel are more at risk to develop asthmatic disease, but the exact reason is so far unknown. During abrasive procedures, dental personnel are exposed to nano-sized dust particles released from dental composite. The aim of this study was to investigate whether respirable composite dust may also release monomers. Respirable (<5μm) composite dust was collected and the release of methacrylate monomers and Bisphenol A (BPA) in water and ethanol was evaluated by liquid chromatography/mass spectroscopy (LC-MS/MS). The dust was ultra-morphologically and chemically analyzed by transmission electron microscopy and energy-dispersive X-ray spectroscopy (TEM-EDS). LC-MS/MS analysis revealed that, irrespective of the type of composite, the respirable fraction of composite dust may release relatively high concentrations of unpolymerized methacrylate monomers, both in water and ethanol. Higher release was observed in ethanol. The endocrine disruptor BPA also emanated from the composite dust particles. TEM showed that most particles were nano-sized, although particle size ranged between 6nm and 5μm with a mode value between 12 and 39nm. Most particles consisted of several filler particles in resin matrix, although single nano-filler particles could also be observed. Elemental analysis by TEM-EDS proved that the particles collected on the filters originated from the dental composites. Theoretically, composite dust may function as a vehicle to transport monomers deeply into the respiratory system. The results of this study may shed another light on the increasing incidence of respiratory disease among dental personnel, and more care should be taken to prevent inhalation of composite dust. Special care should be taken to prevent inhalation of composite dust, as the dust particles may release methacrylate monomers.

Dynamic Behavior of Nano-Size Dust Particles in a Magnetic Field Channel.

Removal of very small dust from indoor public spaces, such as metro subway stations, is a challenge. A large proportion of subway dust, particularly that of submicron sizes, contains iron compounds. This study sought to understand the dynamic behavior of such fine iron dust in a magnetic field. The computer aided fluid dynamics (CFD) calculation revealed that the design and configuration of a rectangular flow channel with magnets determine the dynamic motion of particles. An attractive magnetic emitter arrangement produced higher magnetic flux density than a repulsive arrangement. Additional ferromagnetic wire mesh inserted into the duct channel could provide a more systematic magnetic field and collect more dust. The field gradient for 0.3 mm thick wire was more than twice that of 0.5 mm wire. The provision of a magnetic field could contribute a 20% increase in 100 nm particle collection and an increase of 5% in 10 nm.

Possible observation of charged nanodust from comet 67P/Churyumov–Gerasimenko: An analysis for the ROSETTA mission

Abstract Nanodust particles are ubiquitous in the solar system; we may expect that comet 67P/Churyumov–Gerasimenko, the target of the upcoming ROSETTA mission, is also a source of nanodust, that is dust particles of nanometer size. Due to their small size and mass, the dust detectors cannot observe them directly neither on the orbiter nor on the Philae lander. However, if nanodust grains get charged, the ion and electron sensors on board of the orbiter might detect them. In this study we investigate whether this is a realistic option. We show that when the comet activity is low between 3.25 and 2.7 AU, the cometary surface and a part of the dust particles get charged due to the charging currents of the solar wind and photoionization as a result of solar radiation. The nucleus׳ surface potential depends on the solar wind density, and it is higher than +4 V for solar zenith angle between 0° and 50° for solar wind density n(d=1 AU)=4×10−6 m−3, and nano-size dust gets immediately accelerated when it collected Q=+1e positive charge due to photoelectron emission. The energy of this charged nanodust is higher than 4 eV and it could be detected not far from the subsolar region by the ion and electron sensor (IES) of the Rosetta Plasma Package. In this paper we examine this process in detail.

Fluid simulation of the sheath formation in a multi-component plasma containing charged dust nanoparticles

Abstract Numerical simulations of the multi-fluid equations are utilized to study the sheath structure in an acetylene plasma consists of electrons, different species of positive and negative ions, and charged nanosize dust particles. It is found that in the presence of negative ions spatially periodic fluctuations are developed in the profiles of the plasma and dust parameters. The fluctuations are enhanced with increasing the electronegativity, ion Mach number and neutral number density, while they are suppressed with increasing the dust Mach number. As the electronegativity increases, the incident dust flux on the wall decreases, whereas the positive ion flux increases. The sheath width is a descending function of the electronegativity, plasma number density, ion Mach number, and dust radius but increases monotonically with the neutral number density.

Nanoparticle release from dental composites

Dental composites typically contain high amounts (up to 60 vol.%) of nanosized filler particles. There is a current concern that dental personnel (and patients) may inhale nanosized dust particles (<100 nm) during abrasive procedures to shape, finish or remove restorations but, so far, whether airborne nanoparticles are released has never been investigated. In this study, composite dust was analyzed in real work conditions. Exposure measurements of dust in a dental clinic revealed high peak concentrations of nanoparticles in the breathing zone of both dentist and patient, especially during aesthetic treatments or treatments of worn teeth with composite build-ups. Further laboratory assessment confirmed that all tested composites released very high concentrations of airborne particles in the nanorange (>10(6)cm(-3)). The median diameter of airborne composite dust varied between 38 and 70 nm. Electron microscopic and energy dispersive X-ray analysis confirmed that the airborne particles originated from the composite, and revealed that the dust particles consisted of filler particles or resin or both. Though composite dust exhibited no significant oxidative reactivity, more toxicological research is needed. To conclude, on manipulation with the bur, dental composites release high concentrations of nanoparticles that may enter deeply into the lungs.

Investigation of the sheath formation in a dusty plasma containing energetic electrons and nano-size dust grains

Numerical simulations of the stationary multi-fluid equations are used to study the structure of a dusty plasma sheath in the presence of a beam of energetic electrons. It is found that even a small number of energetic electrons can strongly modify the sheath parameters, specially the sheath thickness. Depending on the magnitude of the beam flux, two different regimes of sheath thickness can be recognized; At small beam fluxes, the sheath is in the regime of thin sheath and its thickness grows linearly with the beam flux. As the beam flux increases, at a certain beam energy or beam number density, the sheath demonstrates a sharp transition to the regime of thick sheath where the width is almost three times larger. The beam parameters corresponding to the transition between the two regimes depend on the parameters of the background plasma. The beam transition energy increases with the electron temperature and dust number density while decreases with the dust radius. On the other hand, the beam transition number density is a non-monotonic function of the background plasma number density. The localization of dust particles above the substrate is intensified by the increase in the beam number density.

Numerical study of an electrostatic plasma sheath containing two species of charged dust particles

A multi-fluid model is used to study the dynamics of a dusty plasma sheath consists of electrons, ions, and two species of charged dust particles, i.e., nano-size and micron-size particles. It is found that, when the sheath is dominated by the nano-size dust grains, spatially periodic fluctuations are developed in the profiles of the sheath potential, and the number density and velocity of the plasma and dust particles. Due to inertial effects, the fluctuations in the parameters of the micron-size grains are much lower than those of the other parameters. The competition between the electric and ion drag forces plays the primary role in development of the fluctuations. The spatial period of the fluctuations is approximately a few Debye lengths and their amplitude depends on the plasma and dust parameters. The fluctuations are reduced by the increase in the radius, mass density, and Mach number of the nano-size particles, as well as the density and Mach number of the ions. But, they are enhanced by the increase in the plasma number density and the electron temperature. The sheath thickness demonstrates a non-monotonic behavior against variation of the nanoparticle parameters, i.e., it first decreases quickly, shows a minimum, and then increases. However, the sheath width always decreases with the plasma number density and ion Mach number, while grows linearly with the electron temperature.

Nanostructures in controlled thermonuclear fusion devices

It is shown that the presence of nano-sized and nano-structured erosion products not only affects the operation of thermonuclear devices but also, to a large extent, determines the safety and economy of future thermonuclear reactors. The formation mechanisms and the characteristics and properties of deposited films and nano-sized dust that form in tokamaks are reviewed.

The magnetized sheath of a dusty plasma with nanosize dust grains

The magnetized sheath of a dusty plasma is investigated via numerical simulations of stationary multifluid equations by taking into account the electric, magnetic, gravitational, ion drag, neutral drag, and thermophoretic forces. Dependence of the sheath properties on the characteristics of the magnetic field and plasma parameters is explored. The sheath dynamics is mainly governed by the electric and ion drag forces and the effect of gravitation is negligible. The sheath demonstrates a nonmonotonic behavior against variations of the magnetic intensity and its angle of incidence. The sheath thickness and the maximum of dust density distribution decrease with increasing the ion to electron density ratio at the sheath edge, but increase with growing electron temperature and the positive temperature gradient of the neutrals. The effects of ion drag are similar to those of the gravitational force as both of them accelerate the dust to the wall. By a suitable configuration of the temperature gradient in the neutral gas, thermophoretic force can be utilized to deposit the building units of nanostructures on a substrate or remove any unwanted contaminant from its neighborhood.

Modelling of carbon dust formation by cluster growth in argon plasmas

In tokamaks with carbon plasma-facing components, one can observe the presence of nano-sized dust particles. Understanding such dust particle formation is a prerequisite to any attempt to limit or avoid this dust that may be responsible for tritium retention and pollution of the plasma. We report on coupled modeling of carbon chemistry and dust particle nucleation , growth, and transport in a plasma discharge . The chemical model used for carbon cluster dust growth is described in detail. The results are consistent with measurements made at LPIIM from low-pressure argon DC discharges in a stainless steel reactor with a graphite cathode [C. Arnas, C. Dominique, P. Roubin et al., J. Nucl. Mater. 337–339 (2005) 69], serving as a proxy for the tokamak plasma edge. The time evolution of the ‘large’ dust particles consists of a nucleation phase followed by an accretion phase. These reach a dust grain size of 40 nm on a timescale comparable to the experimental observations (minutes to hours).