Formation Of Atoms Research Articles

Influence of Graphite Nodules on the Microstructure and Mechanical Properties of Hollow Ductile Iron Pipe after Austempering Treatment

Herein, the microstructure and mechanical properties of ductile iron with different numbers of graphite nodules before and after austempering treatment are systematically investigated. The results show that the amounts of graphite nodules affect the microstructure and resulting mechanical properties of ductile iron. The ferrite fraction in an as‐cast matrix decreases with the increase in graphite nodules; this outcome is mainly attributed to the cooling rate. The matrix of ductile iron after austempering treatment is composed of acicular ferrite and retained austenite. The acicular ferrite is refined with the increase in graphite nodules, because the increase in interface between graphite/austenite provides more nucleation sites during austempering treatment. Meanwhile, the formation of ferrite causes carbon atoms to diffuse into the surrounding matrix, giving rise to the increase in carbon concentration of untransformed austenite and further stabilizing the retained austenite. Hence, the volume fraction of retained austenite and the carbon content in it both increase with the increase in graphite nodules. The amounts in graphite nodules affect the mechanical properties significantly after austempering treatment; this outcome is related to the phase constituents of ductile iron after austempering treatment. Herein, the detailed mechanisms are discussed.

Thermodynamics and kinetics of 1-fluoro-2-methoxypropane vs Bromine monoxide radical (BrO): A computational view

CFCs containing volatile compounds are detrimental to atmospheric environment and to all living organisms. These compounds are frequently reported to be chemically stable/inert. Also their photodissociation reaction results to reasonable amount of Chlorine atoms formation in the stratospheric part of atmosphere. This eventually bring out depletion of Ozone (lives and properties protecting compound) in the stratosphere. In order to cope this environmental havoc, there is need to find substitutable compounds for CFCs and possibly predict their atmospheric effects. Ethers when fluorinated can serve as CFCs substitute. Therefore, in this work, an Insilco investigation was conducted on the thermochemistry, mechanism and kinetics of the Hydrogen abstraction reactions of partially fluorinated isopropyl methyl ether (1-fluoro-2-methoxypropane i.e. (CH2FCH(OCH3)CH3)) with Bromine monoxide radical (BrO.) using the Density Functional Theory (DFT) based M06-2X/6-311++G** strategy. To computationally refine/improve the energy data, the single-point calculations (DFT/M06-2X/6-311++G(2df,2p) were immediately executed on the reacting species involved. The Monte Carlo search on the investigating CH2FCH(OCH3)CH3 showed nine conformers with the lowest global minimum configuration being studied. The results of this investigation showed that the atmospheric oxidation reaction of CH2FCH(OCH3)CH3 with the BrO radical proceeded in four (4) plausible reaction routes. The computed total theoretical rate of 7.95*〖10〗^(-11) M-1 sec-1, the first of its kind with BrO radical was recorded. The atmospheric lifetime/global warming potential of 1.35*10-2 days/72.8 were also reported. The potential energy surface (PES) for each reaction route with the BrO radical was constructed at absolute temperature of 298.15 K.

Shipborne measurements of ClNO<sub>2</sub> in the Mediterranean Sea and around the Arabian Peninsula during summer

Abstract. Shipborne measurements of nitryl chloride (ClNO2), hydrogen chloride (HCl) and sulfur dioxide (SO2) were made during the AQABA (Air Quality and climate change in the Arabian BAsin) ship campaign in summer 2017. The dataset includes measurements over the Mediterranean Sea, the Suez Canal, the Red Sea, the Gulf of Aden, the Arabian Sea, the Gulf of Oman, and the Arabian Gulf (also known as Persian Gulf) with observed ClNO2 mixing ratios ranging from the limit of detection to ≈600 pptv. We examined the regional variability in the generation of ClNO2 via the uptake of dinitrogen pentoxide (N2O5) to Cl-containing aerosol and its importance for Cl atom generation in a marine boundary layer under the (variable) influence of emissions from shipping and the oil industry. The yield of ClNO2 formation per NO3 radical generated was generally low (median of ≈1 %–5 % depending on the region), mainly as a result of gas-phase loss of NO3 dominating over heterogeneous loss of N2O5, the latter being disfavoured by the high temperatures found throughout the campaign. The contributions of ClNO2 photolysis and OH-induced HCl oxidation to Cl-radical formation were derived and their relative contributions over the diel cycle compared. The results indicate that over the northern Red Sea, the Gulf of Suez, and the Gulf of Oman the formation of Cl atoms will enhance the oxidation rates of some volatile organic compounds (VOCs), especially in the early morning.

Nanoassembly Growth Model for Subdomain and Grain Boundary Formation in 1T′ Layered ReS2

AbstractGrain boundaries (GBs) significantly affect the electrical, optical, magnetic, and mechanical properties of 2D materials. An anisotropic 2D material like ReS2 provides unprecedented opportunities to explore novel GB properties, since the reduced lattice symmetry offers greater degrees of freedom to build new GB structures. Here the atomic structure and formation mechanism of unusual multidomain and diverse GB structures in the vapor phase synthesized ReS2 atomic layers are reported. Using high‐resolution electron microscopy, two major categories of GBs are observed in each ReS2 domain, namely, the joint GB including three structures, and the GBs formed from a reconstruction of Re4‐chains including seven different structures. Based on the experimental observations, a novel “nanoassembly growth model” is proposed to elucidate the growth process of ReS2, where three types of Re4‐chain reconstruction give rise to a multidomain structure. Moreover, it is shown that by controlling the thermodynamics of the growth process, the structure and density of GB in the ReS2 domain can be tailored. First‐principles calculations point to interesting new properties resulting from such GBs, such as a new electron state or ferromagnetism, which are highly sought after in the construction of novel 2D devices.

A conceptual approach to the formation of paramagnetic nanospecies of noble metals

Abstract The general concepts are analyzed regarding the approach for the formation of paramagnetic species of noble metals, with a non-rigid (labile) molecule being used as a supporting matrix. The formation of the metal nanospecies follows three stages: (i) the metal ions are captured by the matrix, (ii) the reducing agent causes formation of individual atoms separated by the matrix fragments, (iii) the individual atoms agglomerate due to conformational transformations of the labile molecule-matrix. This algorithm is realized in two distinct systems: Ag-containing nanospecies embedded within the system of polyacrylic acid (PAA) chains grafted to the film of fluorinated ethylene propylene copolymer (FEP) and Au-containing nanospecies in the free matrix of tannin-citrate- oxo-hydroxo aluminate. The evolution of the electron paramagnetic resonance (EPR) spectra while cooling down demonstrates the appearance of the exchange interaction which is suppressed at higher temperatures by the vibrational modes of the molecule-matrix. The role of the oxo-hydroxo aluminate form is one of a molecular motor sorting the individual nanospecies by their size and charge state.

Coarse-graining molecular dynamics: stochastic models with non-Gaussian force distributions

Incorporating atomistic and molecular information into models of cellular behaviour is challenging because of a vast separation of spatial and temporal scales between processes happening at the atomic and cellular levels. Multiscale or multi-resolution methodologies address this difficulty by using molecular dynamics (MD) and coarse-grained models in different parts of the cell. Their applicability depends on the accuracy and properties of the coarse-grained model which approximates the detailed MD description. A family of stochastic coarse-grained (SCG) models, written as relatively low-dimensional systems of nonlinear stochastic differential equations, is presented. The nonlinear SCG model incorporates the non-Gaussian force distribution which is observed in MD simulations and which cannot be described by linear models. It is shown that the nonlinearities can be chosen in such a way that they do not complicate parametrization of the SCG description by detailed MD simulations. The solution of the SCG model is found in terms of gamma functions.

MUSIC Speciation of γ-Al2O3 at the Solid Liquid Interface: How DFT Calculations Can Help with Amorphous and Poorly Crystalline Materials.

Transition aluminum oxides, such as γ-Al2O3 or alumina, are widely used in many different technical applications that rely on the surface reactivity of this material at the solid liquid interface. The speciation of surface sites of this material confronts several obstacles. On the one hand, alumina is a poorly crystalline oxide, thus allowing for a limited amount of empirical structural information for an important number of surface sites with different trends in reactivity and, on the other hand, it is a metastable material. In this work, we show several ways in which the multisite complexation model, combined with atomistic information from density functional theory and ab initio molecular dynamics (AIMD), can manage to perform speciation calculations of γ-Al2O3 surface sites at the solid liquid interface. Although the results are in good qualitative agreement with experimental titration curves, and they can serve as a guide for the interpretation of the reactivity of this material at the initial stages of an impregnation experiment and chemical weathering phenomena, this work highlights the need of more complex AIMD simulations to accurately model these phenomena in γ-Al2O3 surface/liquid interfaces.

Rearrangement of interstitial defects in alpha-Fe under extreme condition

In this study, by theoretical means, we reveal the main mechanisms that underpin the microstructure evolution driven by the formation of self-interstitial atoms (SIAs) clusters in body centered cubic iron under extreme conditions. Using Frenkel pairs accumulation simulations we point the complex interplay between the two families of interstitial defects, the dislocation loops with Burgers vectors <100> and ½<111> and the tridimensional C15 clusters. We reconcile the previous sparse understanding of microstructure evolution that put in opposition various mechanisms of defects formation by showing that both ½ <111> loops self-interactions and C15 clusters transformations produce <100> loops. Moreover, we exhibit the fact that these tri-dimensional clusters can form under irradiations with only the Frenkel pair accumulation that mimics electron irradiation and not only in high-energy cascades as it was previously stated. Finally, we show that the tridimensional C15 clusters even precede production of loops under irradiation.

Atomic Sulfur Formation Mechanism on 3-Mercaptopropanoic Acid Derivative Self-Assembled Monolayers: Understanding the C–S Bond Cleavage

Self-assembled monolayers (SAMs) of ω-carboxylic acid thiols are very important in the surface modification of metals, especially on gold surfaces. Indeed, the 3-mercaptopropanoic acid (MPA) and its ester or amide derivatives are widely used for SAM-based sensor design. It was already shown that MPA does not suffer C–S bond scission when adsorbed on Au. On the other hand, in this work we demonstrate that its simplest derivative, methyl 3-mercapto propionate (Me-MPA), is prone to form significant amounts of atomic sulfur when adsorbed on Au. The MPA derivatives are more sensible than MPA itself to alkaline solutions, and its SAM-based sensors will rapidly degrade given atomic sulfur. In this work, we study the simplest MPA derivative Me-MPA SAMs on preferentially oriented Au(111) surfaces by XPS and electrochemical measurements. It was found that the desulfuration of Me-MPA depends on its preparation conditions (grown from ethanol or toluene solution) and on its post-treatment with alkaline solution. In or...

Comparative Study on in-situ Ellipsometric Monitoring of III-Nitride Film Growth via Plasma-Enhanced Atomic Layer Deposition

In this paper a comparative in-situ ellipsometric analysis is carried out on plasma-assisted ALD-grown III-nitride (AlN, GaN, and InN) films. The precursors used are TMA, TMG, and TMI for AlN, GaN, and InN respectively, while Ar is used as purge gas. For all of the films N2/H2/Ar plasma was used as the co-reactant. The work includes real-time in-situ monitored saturation curves, unit ALD cycle analysis, and &gt;500 cycle film growth runs. In addition, the films are grown at different substrate temperatures to observe the impact of temperature not only on the growth rate but on how it influenced the precursor chemisorption, ligand removal, and nitrogen incorporation surface reactions. All three nitride films confirm fairly linear growth character. The growth rate per cycle (GPC) for each film is also measured with respect to rf-plasma power to obtain the surface saturation conditions during ALD growth. The real-time in-situ monitoring of the film growth can really be beneficial to understand the atomic layer growth and film formation in each individual ALD cycle.

Generation of Heteroatom Stereocenters by Enantioselective C–H Functionalization

C–H functionalization has been established as an efficient way to generate molecular complexity. The formation of stereogenic carbon atoms by asymmetric C–H functionalization has seen tremendous pr...

Oxygen Atom Function: The Case of Methane Oxidation Mechanism to Synthesis Gas over a Pd Cluster

A dimer model Pd2 was established to study the adsorption of CHx (x = 1–4) and CH4 dehydrogenation, as well as syngas formation using density functional theory (DFT) at the atomic level. Meanwhile, insight into understanding the role of the oxygen atom on the partial oxidation of methane (POM) was also calculated based on a trimer model of Pd2O. For the adsorption of CHx, results showed that the presence of an oxygen atom was a disadvantage to the adsorption of CHx (x = 1–3) species. For CH4 dissociation, the process of CH2→CH + H was found to be the rate-limiting step (RSD) on both Pd2 and Pd2O. H2 was formed by the reaction of CH2 + 2H→CH2 + H2. For CO formation, it was primarily formed in the process of CH + O→CHO→CO + H on both the Pd2 and the Pd2O catalyst. Thermodynamic and kinetic calculations revealed that formation and maintainance of the oxygen atom on the Pd surface could promote a POM reaction to achieve high H2 and CO yield and selectivity. Our study provides a helpful understanding of the effect of an adsorbed oxygen atom on a POM reaction with a Pd catalyst.

Direct Observation of Yolk-Shell Transforming to Gold Single Atoms and Clusters with Superior Oxygen Evolution Reaction Efficiency.

Noble metal particles and atoms tend not to react with other media even at elevated temperatures due to their inert nature. Herein, we report surprising findings of Au diffusion and dissolution in a Ni2P matrix, forming single Au atoms and tiny clusters. The dynamic atomic diffusion process was directly probed by in situ heating scanning transmission electron microscopy (STEM). The Au yolks can diffuse and dissolve completely into the Ni2P shell at temperatures of 350 °C or higher, resulting in an inward volume expansion of the Ni2P shell and formation of single Au atoms and tiny Au clusters in Ni2P. The resulting structure exhibited outstandingoxygen evolution reaction (OER) efficiency that is 16-fold that of commercial IrO2. The in situ STEM finding explains its drastically improved catalytic performance after annealing, confirming Au single atoms and clusters on a Ni2P surface as active OER sites. Our finding emphasizes the role of dynamic structural changes during simple heat treatment to enhance catalysis efficiency.

Box modelling of gas-phase atmospheric iodine chemical reactivity in case of a nuclear accident

A new atmospheric iodine gas-phase mechanism containing 248 reactions combined to the RACM air quality mechanism was implemented into a 0D box model in order to evaluate the behaviour of iodine fission products released in the atmosphere. Different simulation scenarios were performed unravelling the influence of several parameters on the iodine speciation (season, day/night, low/medium/high iodine concentration release, nature of the injected iodine species). The main outcomes of our work are the following: (i) the I2 reactivity is faster than that of CH3I, (ii) iodine nitroxides INOx are mainly formed during night with low and medium releases in winter, (iii) iodine oxides are promoted with a high release of I2 during summer, (iv) the formation of organic iodine compounds can be highlighted only in the case of a low I2 release. In this work, I2O, I2O5, and HOIO2 are the most abundant iodine oxides because their atmospheric removal pathways in the gas-phase are not yet known. The main iodinated organic species is CH3OOI arising from the reaction between I atom and the methyl peroxy radical. In case of a CH3I release, before the I atom formation, the reaction mechanism leads to either the formation or the destruction of several other organic iodinated compounds such as CH2IOH and CH2IOO.

Ethanol droplet formation, dynamics and combustion mode in the flame of the SpraySyn-nozzle

The synthesis of nanoparticles via flame spray pyrolysis (FSP) is based on a couple of physicochemical steps such as precursor atomization, droplet evaporation, fuel combustion, particle nucleation and growth. Most recent studies on FSP are focused on the particle formation without taking the antecedent precursor atomization and spray formation into account. In the present work, the atomization characteristics under burning and non-burning conditions are investigated by means of laser sheet Mie-scattering images and phase Doppler anemometry. The influence of the gas to liquid volume ratio on the spray formation, jet morphology and scales of turbulence in the nozzle far-field are studied to assess the performance of the external-mixing gas-assisted SpraySyn-nozzle. The turbulent flame spray is characterized by the Kolmogorov length scale and the Kolmogorov shear rate. The droplet–droplet interaction and group combustion behaviour, enabling clouds of merely vaporizing droplets surrounded by a flame sheath, are investigated. The experimentally determined droplet velocities, turbulence length scales and the analysis of group combustion modes allow a deeper insight into the spray flame dynamics and droplet mixing zones.

Surface active flexible palladium nano-thin-film electrode development for biosensing

Metal atoms on surface edges or with specific coordinates possess high surface potentials, and serve as core atoms for organic molecule bonding. However, these active metal atoms may lose their activity by self-diffusion on the surface. A polyethylene terephthalate (PET) substrate provided a stable rough surface in nanoscale for metal atoms absorption and formation of a stable and active nano-thin-film (NTF) surface. However, the NTF surface roughness decreased with increasing thickness of palladium (Pd) granules, indicating that the surface growth of the Pd film followed a Stranski-Krastanov-like growth model. Therefore, the proper thickness of Pd-NTF on PET substrate (Pd NTF-PET) was developed for electrochemical impedance spectroscopy (EIS). Protein was immobilized on the Pd NTF-PET electrodes within 15 min and its biosensing sensitivity was as low as 0.1 ng per-test in 1 μl. We expect that the developed Pd NTF-PET electrode can be used for other biosensing applications as well.

스월 노즐의 분무 미립화 및 실린더 내 혼합기 형성 특성

본 연구는 스월 노즐 인젝터가 분무 미립화 및 실린더내 혼합기 형성에 미치는 영향을 수치해석적 연구한 논문이다. 본 연구에 적용한 스월 노즐 인젝터는 노즐 출구에서 접선 방향으로 20deg 기울여서 분사가 되도록 설정하였으며, 분사 압력은 40MPa과 80MPa로 변경하였다. 해석에 사용된 분열 모델은 Wave 모델을 적용하였으며, 분무 도달 거리, SMD, 스월 비, 혼합기 분포 특성 결과를 비교 분석하였다. 연구 결과, 스월 노즐 인젝터가 기존 노즐 인젝터보다 동일한 통전기간 조건에서 스월 비가 최대 6배 높은 것으로 나타났다. 스월 노즐 인젝터의 작은 노즐 직경으로 인하여 액적이 갖는 모멘텀이 감소하여 기존 노즐 인젝터보다 짧은 분무 도달 거리와 작은 SMD 값을 가졌다. 스월 노즐 인젝터에 의해 발생한 높은 스월 비로 인하여 중심부의 혼합기가 지속적으로 공기와 혼합되어 적은 양의 Soot이 배출될 것으로 기대된다.

Matter-Antimatter Physics at Low Energy

The main objective of the present paper is to discuss the consequences of matter-antimatter interaction at low energy. The production of large number of cooled antimatter in laboratory and the formation of exotic atoms composed of particles and antiparticles are reviewed. Particularly, the quantum mechanical treatment of Four-Body exotic molecules is shortly discussed. The main goal of the paper is to shed light on possible novel discoveries and applications based on the coexistence of matter and antimatter.

METHODS FOR DESCRIBING THE SHAPE OF DEFECTIVE NANOSTRUCTURED FORMATIONS IN MATERIALS UNDER IRRADIATION

Within the framework of the program of using modern computer methods in the task of developing radiation-resistant materials for IV-generation reactors, several methods for describing the form of local atomic segregations or compact radiation defects of the nanometer range have been considered. A numerical method for measuring the shape of an arbitrary atomic formation possessing a well-defined external boundary is proposed. The shape of the sequence of equilibrium clusters is measured, the interaction of the particles in which is described by the Lennard-Jones potential. It is shown that the proposed method correctly reproduces the oscillations of size effects and the sequence of magic numbers for these clusters. The possibility of replacing geometric moments by the moments of Zernike 3D functions is considered. Such a replacement allows us to get rid of the ill-posed nature of the inverse problem in the transition from the source space of clusters form to the space of their descriptors.

Development of R-Group Fingerprints Based on the Local Landscape from an Attachment Point of a Molecular Structure.

Molecular fingerprints are indispensable in medicinal chemistry for quantifying chemical structures. Fingerprints can be calculated for substructures with attachment points, which are positions where a substructure and a corresponding core structure connect. Because structures with attachment points can be crucial for understanding structure-activity relationships, fingerprints specialized for representing this structural feature are required. R-group fingerprints and R-group descriptors were proposed previously for this purpose; however, these molecular representations have limitations. Current R-group fingerprints do not emphasize information about attachment points, and R-group descriptors are too sensitive to changes in the topological path length from an attachment point. In the present work, we developed novel R-group fingerprints, termed R-path fingerprints, which contain substituent information from an attachment point without being sensitive to small differences in topological distances. The concept of the R-path fingerprints is to describe a chemical substructure from the viewpoint of an attachment point, to distinguish atomistic information around the attachment point and other parts of the substructure. This was achieved by considering all the paths on the shortest path between the attachment point and each atom in a substituent. Benchmark testing was conducted, including comparisons of similarity distributions and potency prediction for R-group substituents. The results showed that R-path fingerprints should be useful for classifying and comparing substructures with attachment points.