Theoretical investigation of Fe–Rh binary nanoalloys: Chemical ordering and magnetic behavior

Gupta and Density Functional Theory (DFT) calculations were performed to investigate of structural and magnetic behaviors of 19 atom FenRh[Formula: see text] ([Formula: see text]–19) nanoalloys. A double icosahedron structure was considered for FenRh[Formula: see text] ([Formula: see text]–19) nanoalloys. Significantly, the effects of Fe atom addition on the chemical ordering, stability and total magnetic moments of the nanoalloys were investigated. Local optimization results at the Gupta level show that the Fe atoms are located in the center of the double icosahedron structure and finally in the equatorial region on the surface. The mixing energy analysis obtained that Fe[Formula: see text]Rh7 and Fe4Rh[Formula: see text] nanoalloys are the most stable compositions at Gupta and DFT levels, respectively. It was found that FenRh[Formula: see text] ([Formula: see text]–19) nanoalloys are energetically suitable for mixing at both Gupta and DFT levels. Also, the bond order parameter result is compatible with the mixing energy analysis result. The total magnetic moments of the FenRh[Formula: see text] ([Formula: see text]–19) nanoalloys increase with the addition of the Fe atom, which is a ferromagnetic metal.

INFLUENCE OF THE SIZE EFFECT ON THE REGULARITIES OF THE STRUCTURE FORMATION IN BIMETALLIC Au-Co NANOPARTICLES

В данной работе методом молекулярной динамики с использованием потенциала сильной связи исследовались биметаллические наночастицы Au - Co трёх стехиометрических составов различного размера. Установлены закономерности структурообразования, описаны их характерные особенности. В частности, в составах с 50ат.% и 75ат.% содержанием Au образуются множественные малые ядра локальной икосаэдрической симметрии. Только в составе Co -25ат.% Au с увеличением размера частиц преобладают кристаллические фазы. Выявлены составы, в которых внутренняя симметрия наночастицы определена наличием одного икосаэдра, либо сверхструктуры из нескольких икосаэдров. Рассчитаны концентрационные зависимости энергии смешения биметаллической наночастицы Au - Co. Показано, что в определённом диапазоне размеров существуют концентрационные составы, при которых биметаллический наносплав может проявлять нестабильность. С использованием калорических кривых потенциальной части внутренней энергии определены температуры кристаллизации. Установлено, что температура кристаллизации демонстрирует умеренный, либо существенный, в зависимости от состава, рост с увеличением размера биметаллических наночастиц Au - Co. This work studied bimetallic Au - Co nanoparticles of three stoichiometric compositions of various sizes by the molecular dynamics method using the tight-binding potential. The regularities of structure formation are established, their characteristic features are described. In particular, in compositions with 50at% and 75at% Au content, multiple small nuclei of local icosahedral symmetry are formed. Crystalline phases prevail only in the Co - 25 at% Au composition with an increase in the particle size. Compositions are revealed in which the internal symmetry of a nanoparticle is determined by the presence of one icosahedron or a superstructure of several icosahedrons. The concentration dependences of the mixing energy of a bimetallic Au - Co nanoparticle are calculated. It is shown that there are concentrations of compositions at which bimetallic nanoalloys can exhibit instability in a certain size range. Crystallization temperatures were determined using the caloric curves of the potential part of the internal energy. It was found that the crystallization temperature demonstrates a moderate or significant, depending on the composition as well as growth with an increase in the size of bimetallic Au - Co nanoparticles.

REGULARITIES OF STRUCTURE FORMATION IN BIMETALLIC NANOPARTICLES WITH DIFFERENT CRYSTALLIZATION TEMPERATURES

В данной работе исследуются закономерности структурообразования на примере биметаллических наночастиц Au - Ag, Ti - Al, Ti - V. Данные биметаллические наночастицы обладают различным размерным несоответствием и различной температурой кристаллизации. Проведены серии молекулярно-динамических экспериментов, по результатам которых проанализированы конечные конфигурации с наименьшей энергией и получены концентрационные зависимости энергии смешения. Анализ концентрационных зависимостей энергии смешения позволяет прогнозировать составы и размеры биметаллических наночастиц, которые могут проявлять нестабильность, как например для биметаллических наночастиц Ti - V. Асимметричность отдельных концентрационных зависимостей энергии смешения свидетельствуют о специфических структурных превращениях, характерных именно для данного состава и размера. Установлено, что для биметаллических наночастиц Au - Ag, Ti - Al характерна структурная сегрегация, и она активно проявляется при малых концентрациях более легкоплавкого компонента. Конкурирующими фазами в данном случае выступают ГЦК и ГПУ фазы. Кроме того, для средних из рассматриваемых в статье размеров исследована зависимость температуры кристаллизации от состава биметаллических наночастиц. In this work, of the structure formation was investigated using Au - Ag, Ti - Al, Ti - V bimetallic nanoparticles as the patterns. These bimetallic nanoparticles have different atomic size mismatches and different crystallization temperatures. A series of molecular dynamics experiments was carried out. Based on their results, the final configurations with the lowest energy were analyzed and the concentration dependences of the mixing energy were obtained. An analysis of the concentration dependences of the mixing energy makes it possible to predict the compositions and sizes of bimetallic nanoparticles, which can exhibit instability, such as for Ti - V bimetallic nanoparticles. The asymmetry of individual concentration dependences of the mixing energy is evidence of specific structural transformations characteristic for the given composition and size. It has been established that structural segregation is characteristic for Au - Ag,Ti - Al bimetallic nanoparticles and it is actively manifested at low concentrations of a more low-melting component. The competing phases in this case are fcc and hcp phases. In addition, for the average sizes considered in the article, the dependence of the crystallization temperature on the composition of bimetallic nanoparticles was investigated.

Impact of Microplastics on Oil Dispersion Efficiency in the Marine Environment

Oil spill and microplastics (MPs) pollution has raised global concerns, due to the negative impacts on ocean sustainability. Chemical dispersants were widely adopted as oil-spill-treating agents. When MPs exist during oil dispersion, MP/oil-dispersant agglomerates (MODAs) are observed. This study explored how MPs affect oil-dispersion efficiency in oceans. Results showed that, under dispersant-to-oil volumetric ratio (DOR) 1:10 and mixing energy of 200 rpm, the addition of MPs increased the oil droplet size, total oil volume concentration, and oil-dispersion efficiency. Under DOR 1:25 and mixing energy of 120 rpm, the addition of MPs increased the oil droplet size but resulted in a decrease of total oil volume concentration and dispersion efficiency. Compared with the oil volume concentration, the oil droplet size may no longer be an efficient parameter for evaluating oil-dispersion efficiency with the existence of MODAs. A machine learning (ML)-based XGBRegressor model was further constructed to predict how MPs affected oil volume concentration and oil-dispersion efficiency in oceans. The research outputs would facilitate decision-making during oil-spill responses and build a foundation for the risk assessment of oil and MP co-contaminants that is essential for maintaining ocean sustainability.

Theoretical assessment for the mixing properties of AlMg liquid alloys at 1073K

The alloying behavior of AlMg alloy in the liquid form at 1073 K has been theoretically investigated in the framework of four-parameter model which is based on Maclaurin series. The analytical expressions for thermodynamic functions such as excess free mixing energy, free mixing energy, enthalpy of mixing and entropy of mixing and microscopic functions such as concentration fluctuations at the long wavelength limit and Warren-Cowley chemical short range order parameter have been derived. These expressions have been used to compute the excess Gibbs free energy of mixing, Gibbs free energy of mixing, activity, enthalpy(heat) of mixing, excess entropy of mixing, entropy of mixing, concentration fluctuations in long wavelength limit and Warren-Cowley short range order parameters of AlMg liquid alloys at 1073 K. The investigation shows the excellent concurrence between the experimental and theoretical measurements of the mixing properties of AlMg liquid alloys at 1073 K. Interaction parameters of energy depends on temperature.

Specific Mixing Energy of Cemented Paste Backfill, Part II: Influence on the Rheological and Mechanical Properties and Practical Applications

The rheological properties (yield stress, flow index and infinite dynamic viscosity) and mechanical properties (unconfined compressive strength, UCS) of different cemented paste backfill (CPB) recipes must be determined during the laboratory optimization phase. However, the influence of the mixing procedure on these properties has scarcely been studied so far. The objective of this paper is to assess to what extent these properties depend on the specific mixing energy (SME) for a given type of mixer. CPB recipes were prepared based on two types of tailing (CPB-T1 and CPB-T2, also referred to as T1 and T2) at a fixed solid percentage for each type of tailing using the Omcan laboratory mixer. A mixture of 80% slag and 20% GU was used as a binder. The mixing time and the rotation speed of the mixer were successively varied. For each recipe prepared, we determined the SME, the rheological properties of fresh CPB (at the end of mixing) and the UCS at 7, 28 and 90 days of curing. The results show that yield stress and infinite viscosity decreased when SME increased in an interval going from 0.3 to 3.8 Wh/kg and 0.6 to 6 Wh/kg for CPB-T1 and CPB-T2, respectively. An increasing trend in UCS with increasing SME was also observed. Empirical equations describing the change of the rheological properties with the SME are used to estimate the change in rheological properties of CPB along the distribution system, considering the specific energy dissipation during CPB transportation. A mixing procedure for obtaining CPB mixtures that are representative of CPB deposited in underground mine stopes is suggested for laboratories who currently use a same mixing procedure, irrespective of the variable field specific energy.

Specific Mixing Energy of Cemented Paste Backfill, Part I: Laboratory Determination and Influence on the Consistency

Slump determination is widely used to assess the consistency and transportability of fresh cemented paste backfill (CPB). CPB consistency can depend on the mixing procedure for CPB preparation. In this paper, a method was developed to determine the specific mixing energy (SME) that is dissipated during the preparation of CPB mixtures and to analyze its effect on CPB consistency. For this purpose, CPB recipes were prepared using two tailings and the mixing parameters (mixing time and speed and load mass) were successively varied. SME was determined for each mixture using a power meter equipped with an energy recording system mounted on a laboratory Omcan mixer. Slump was also determined for each mixture. A semi-empirical model was then developed to predict SME as a function of the mixing parameters. Results showed that predicted SME compared well with measured SME during CPB preparation. Results also showed that slump increased with increasing SME. The influence of SME on the rheological and mechanical properties of CPB and practical applications are presented in a companion paper.

Resonance of mixing energy and energy of elastic deformations during spinodal decomposition and the composition modulation effect in ZnхCd1-ХTe solid solutions

The Cahn-Hilliard equation is adapted to consider the spinodal decomposition of A2B6 semiconductor solid solutions. This approach is used to analyze the process of spinodal decomposition of ZnхCd1-хTe solid solution, which is accompanied by the appearance of the composition modulation effect during its low-temperature synthesis. Numerical simulations of the spinodal decomposition of the ZnхCd1-хTe solid solution are performed. It is shown that micro-variations of the material composition are related by the resonance phenomenon between the excess mixing energy and the energy of elastic strains arising in the inclusions of the new phase, which are coherently conjugated with the initial crystal lattice. It is revealed that such resonance phenomena are most intense when the conditions for the material synthesis are located in close proximity to the spinodal curves on the phase state diagram of the system.

Optimal Combination of Mixing Units Using the Design of Experiments Method

A passive micromixer was designed by combining two mixing units: the cross-channel split and recombined (CC-SAR) and a mixing cell with baffles (MC-B). The passive micromixer was comprised of eight mixing slots that corresponded to four combination units; two mixing slots were grouped as one combination unit. The combination of the two mixing units was based on four combination schemes: (A) first mixing unit, (B) first combination unit, (C) first combination module, and (D) second combination module. The statistical significance of the four combination schemes was analyzed using analysis of variance (ANOVA) in terms of the degree of mixing (DOM) and mixing energy cost (MEC). The DOM and MEC were simulated numerically for three Reynolds numbers (Re = 0.5, 2, and 50), representing three mixing regimes. The combination scheme (B), using different mixing units in the first two mixing slots, was significant for Re = 2 and 50. The four combination schemes had little effect on the mixing performance of a passive micromixer operating in the mixing regime of molecular dominance. The combination scheme (B) was generalized to arbitrary mixing slots, and its significance was analyzed for Re = 2 and 50. The general combination scheme meant two different mixing units in two consecutive mixing slots. The numerical simulation results showed that the general combination scheme was statistically significant in the first three combination units for Re = 2, and significant in the first two combination units for Re = 50. The combined micromixer based on the general combination scheme throughout the entire micromixer showed the best mixing performance over a wide range of Reynolds numbers, compared to other micromixers that did not adopt completely the general combination scheme. The most significant enhancement due to the general combination scheme was observed in the transition mixing scheme and was negligible in the molecular dominance scheme. The combination order was less significant after three combination units.

Recycling EVA Waste: An Opportunity For The Footwear Industry - Rheological Properties of EVA Waste Composites Using Torque Rheometry

Ethylene vinyl acetate blends (EVA-B) (at 19 and 28wt% vinyl acetate) were supplied by the footwear industry, along with an industrial (reference) compound labeled EVA-ref. EVA waste is an industrial sub-product crosslinked (injection sprues and unused midsoles), that was particulate through a micronization process and labeled as EVA-w. The objective of the present work was to evaluate processability and rheological parameters (using torque rheometry) when adding EVA-w to EVA-B. The EVA-w particle size distribution was bimodal, with an average diameter of 53.06 μm, and volume (%) D (10), D (50), and D (90) respectively equal to 12.47, 31.83, and 135.18 μm. However, this ample size distribution did not affect the composite mixing. FTIR-ATR analysis showed that no new crosslinking occurred after processing the composites. Low unit mixing energy (Wu), and mechanical work (as represented by DT values: torque stabilization temperature (Tstab) - test temperature (Ttest)) were required to mix the composites. Consequently, the dispersion of the EVA-w particles within the molten EVA-B occurred during the first 3 min of mixing, making it easier. The sensibility to shear-thinning behavior was more pronounced when adding EVA-w, especially at 25 phr. The m parameter was smaller in the composites as compared to the EVA-ref, and when adding EVA-w at 35 phr, it showed a tendency to increase. The average shear stress (E) of the 15 phr composite was similar to that of the EVA-ref compound. Yet for 25 phr, a higher value was observed. The adding of EVA-w made the non-Newtonian behavior of EVA-B less pronounced. For all samples, the average viscosity (t) decreased with average shear rate (h), revealing a pseudoplastic behavior.