Dispersion Of Fine Particles Research Articles

Mechanical Behavior of Oxide Dispersion Strengthened Steel Directly Consolidated by Rotary Swaging.

Among the main benefits of powder-based materials is the possibility of combining different constituents to achieve enhanced properties of the fabricated bulk material. The presented study characterizes the micro- and sub-structures and related mechanical properties of ferritic steel strengthened with a fine dispersion of nano-sized Y2O3 oxide particles. Unlike the typical method of preparation via rolling, the material presented herein was fabricated by direct consolidation from a mixture of powders using the versatile method of hot rotary swaging. The mechanical properties were evaluated at room temperature and also at 1300 °C to document the suitability of the prepared steel for high-temperature applications. The results showed that the imposed shear strain, i.e., swaging ratio, is a crucial parameter influencing the microstructure and, thus, material behavior. The workpiece subjected to the swaging ratio of 1.4 already exhibited a sufficiently consolidated structure with ultra-fine grains and featured high room-temperature microhardness values (up to 690 HV0.5), as well as a relatively high maximum flow stress (~88 MPa) when deformed at the temperature of 1300 °C with the strain rate of 0.5 s-1. However, the dispersion of oxides within this sample exhibited local inhomogeneities. Increasing the swaging ratio to 2.5 substantially contributed to the homogenization of the distribution of the Y2O3 oxide particles, which resulted in increased homogeneity of mechanical properties (lower deviations from the average values), but their lower absolute values due to the occurrence of nucleating nano-sized recrystallized grains.

The Deep Removal of Mercury in Contaminated Acid by Colloidal Agglomeration Materials M201

The high-temperature roasting/smelting process of copper and zinc concentrates will cause the mercury in the concentrate to evaporate into the flue gas, and most of the mercury in the flue gas will eventually enter the waste acid in its ionic form. A highly efficient mercury removal agent M201 with long carbon chains and loaded active functional groups can adsorb and disperse fine particles for mercury removal in the system. Through bridging, the linear structure is woven into a network to achieve large-scale capture and dispersion of fine particles and colloidal substances. The recommended operating conditions for developing mercury deep purification technology are as follows: M201 reagent concentration of 50 g/L, 6 mL/L added acid solution, room temperature, mixing time of 5 min, air flotation time of 10 min, ventilation rate of 0.1 L/min, H2SO4 concentration of 33.67 g/L, and the residual mercury content of 2 mg/L (the mercury content reaches 0.01 mg/L after two-stage mercury removal treatment). Meanwhile, the residual arsenic content is 21.9 mg/L. This study shows a better separation of arsenic and mercury and achieves one-step mercury removal.

ПЛАНИРОВАНИЕ И РЕАЛИЗАЦИЯ СТРОИТЕЛЬНЫХ РАБОТ ПРИ ТОЧЕЧНОЙ ЗАСТРОЙКЕ ДЛЯ ОПРЕДЕЛЕНИЯ УДЕЛЬНЫХ ПЫЛЕВЫХ ВЫБРОСОВ

Abstract. The construction industry is one of the significant sources of environmental damage. The effects of dust pollution have an impact on all stages of the building's life cycle, from the start of work on the construction site to completion, operation and demolition. Despite the fact that the stage of work implementation does not last long in comparison with other stages of the life cycle of an investment and construction project, the construction stage has a number of significant impacts on the environment. The development of the construction industry requires the comprehensive assessment and investigation of the construction site as a source of pollu-tion, identification and evaluation of all sources of dust pollution on the construction site, the processes of dust pollution propagation in an urban environment. 
 The article offers an analysis of data on field studies of the degree of atmospheric air pollution in the territory of Rostov-on-Don, an analysis of the volume of construction dust emissions from construction works, a method for calculating control over the implementation of construction processes and the spread of dust pollution generated in the atmospheric air, indi-cators of the maximum, average daily emission concentration of fine dust PM2.5 and PM10 formed from construction production and the ability to control the level of pollution on the construction site. There are no fundamental studies on the calculation of dust emission from construction works during spot construction. Based on the field studies conducted earlier using the Handheld 3016 particle counter, data on dust emissions from construction processes under various climatic influences were obtained.
 Subject: analysis of data on field studies of the degree of atmospheric air dustiness in the territory of Rostov-on-Don, the volume of emissions of construction dust from construction work on construction sites in urban conditions.
 Materials and methods: conducting systematic measurements of the degree of dust in Rostov-on-Don using the Lighthouse Handheld 3016 IAQ manual particle counter, taking into account typical climatic, heterogeneous factors of the territory on which the city is located. Systematic monitoring of several construction sites where residential complexes similar in technology and conditions were built in the most dusty area of Rostov-on-Don and the selection of five construction sites for the development of a calendar schedule for construction and installation work, taking into account specific emissions of dust particles and climatic conditions for calculating the dust pollution factor.
 Results: an effective approach that can be usefully applied to the determination of dust emissions on the construction site, to calculate the gross emission of dust released on the site from construction work, daily indicators of the maximum single and average daily concentration, as well as to dust dispersion with the determination of zones exceeding the MPC indicators is the use of network modeling with further calendarization to predict these types of indicators during the design and implementation of construction production.
 Conclusions: based on the data obtained, it can be concluded that with the existing implemented organization and technology of work, the concentration of fine dust particles are within the MPC, but given the background concentrations of atmospheric air in Rostov-on-Don, these indicators in a particular area will exceed the permissible MPC. The process of using existing SMR models taking into account specific dust emissions, the development of a schedule of dust pollution of a specific territory taking into account natural and climatic factors and the determination of zones of excess of MPC indicators in the process of modeling the dispersion of fine dust particles beyond the fence boundaries of the construction site will make it possible to draw up a passport of environmental safety of the nearby urbanized territory during spot development. Daily determination of dust pollution indicators will allow you to adjust the schedule of construction work. Modeling the dispersion of construction dust, taking into account the direction and speed of the wind, will make it possible to monitor the zones of exceeding the MPC of the neighboring territory on a daily basis and adjust measures to extinguish dust emissions at the construction site.

Investigation on Friction Stir Welding Parameters: Mechanical Properties, Correlations and Corrosion Behaviors of Aluminum/Titanium Dissimilar Welds

In industrial applications, welding of dissimilar metals such as aluminum (Al) and titanium (Ti) is a prerequisite for the development of hybrid components with improved mechanical and corrosion properties. However, dissimilar welding of the Al/Ti system is highly challenging due to differences in the physical and thermal properties of the two materials. In the present investigation, an attempt has been made to fabricate a dissimilar friction stir weld (FSW) of commercially pure Al and Ti and to elucidate the mechanism associated with superior joint formation. The process parameters, such as tool rotation speed, traverse speed and tool offset position have been optimized using Taguchi’s optimization technique. A detailed investigation of the weld with optimum process parameters has been carried out to reveal the mechanism of joint formation. The superior mechanical properties (24% higher ultimate tensile strength and 10% higher ductility than that of base Al) of the weld are attributed to the fabrication of a defect-free joint, formation of intercalated particles and an Al/Ti interlocking interface, homogeneous distribution of fine second-phase (Ti and/or intermetallics) particles in the weld nugget, reduction in the evolution of brittle Al3Ti intermetallic compounds (IMCs) and recrystallization and grain refinement of Al in the weld nugget. The potentio-dynamic polarization test indicated that the optimized Al/Ti weld has ~47% higher corrosion resistance than Al; it had a very mild corrosion attack due to the homogeneous dispersion of fine particles. The method and mechanism could have an immense influence on any dissimilar weld and metal matrix composites, improving their mechanical properties and corrosion resistance.

Самоочищение атмосферного воздуха от пылевых частиц в условиях прибрежного морского климата

The intensity of air pollution depends on the characteristics of pollution sources, distance from the sea, terrain, density of residential buildings and the presence of a green zone. The influence of climatic conditions on the distribution of suspended particulate matter in the atmospheric surface layer of Vladivostok was studied. The aim of the study was to determine the particle size distribution of suspended particulate matter in the atmospheric surface layer and to assess the conditions for self-purification of urban air under the influence of the coastal maritime climate. The assessment of the urban air pollution with suspended particulate matter was carried out in two areas with different levels of pollution. The human breathing zone was examined. The temperature, humidity, air pressure, wind direction and speed at sampling points were determined. We used monitoring of meteorological data (dew point, wind gusts, clouds, fog) from the nearest regional meteorological stations. Statistical processing included the “Canonical Analysis” module. In the polluted area of the city the atmospheric circulation (direction, speed and gusts of wind) greatly affect the distribution of fine-dispersed particles (2.5–10.0 µm) that are hazardous to health. The impact of temperature and humidity conditions is reduced in power. The temperature and humidity regime, atmospheric pressure, cloudiness with frequent fog affect the ultrafine dust spectrum in the slightly polluted island area of the city. The above factors contribute to the enhancement of the nanoparticle nucleation process. Self-purification of the air surface layer from dust particles in both polluted and slightly polluted areas of Vladivostok is associated with the southerly winds. The monsoon maritime climate defines the air purifying in the region. The temperature and humidity regime actively affects the dust disperse composition in both sampling sites. In the island area of the city it determines the content of particles up to 10 µm; in the continental area – fractions of 0.1–50.0 µm.

Selective flotation separation of scheelite from calcite using hexamethylenediamine tetramethylene phosphonic acid as a novel depressant

Scheelite, a strategic calcium-bearing mineral, usually coexists with calcite. Froth flotation is the most commonly used method of separating scheelite from calcite, but it is difficult to selectively separate them because of their similar Ca active sites. Sodium silicate with a high dosage and low selectivity is usually used as calcite depressant, which leads to the loss of scheelite and formation of stable colloidal dispersions of fine particles in the tailings slurry, making tailings treatment difficult. Therefore, this work developed a novel depressant, hexamethylenediamine tetramethylene phosphonic acid (HDTMP or H6L), which is a hexabasic acid. The flotation results of single mineral and binary mixed minerals showed that HDTMP at a concentration of 2 × 10−5 mol/L could selectively depress calcite with 4 × 10−5 mol/L NaOL at pH 10.0. Adsorption capacity, Ca2+ concentrate, and contact angle measurements showed that HDTMP was adsorbed more on calcite. Zeta potential measurement and solution chemistry calculations indicated that HL5− anion was the main active species of HDTMP at pH 10.0. Density functional theory (DFT) calculations further revealed that HDTMP had stronger interaction with calcite through chemically bonding with Ca sites and hydrogen bonds (P-O⋯Hwater and P-O H⋯Ocalcite) formed by the phosphate groups in HDTMP and H/O atoms on calcite surfaces. Therefore, HDTMP presents substantial potential for practical applications as a novel calcite depressant in scheelite flotation.

Investigation on deformation behaviors and dynamic recrystallization mechanism of spray formed Al–Zn–Mg–Cu alloy under hot compression

The thermal deformation behavior of spray formed Al–Zn–Mg–Cu alloy was investigated by the isothermal hot compression tests at the strain rates of 0.001–10 s−1 with the temperature range of 350–450 °C. An Arrhenius constitutive equation was established by the corrected strain-stress curves, and then the processing map was constructed based on the 3D instability map and 3D power dissipation map. The influence of strain rate and temperature on both flow stress and dynamic softening has been unveiled. The results show that dynamic recovery (DRV) is the primary softening mechanism and dynamic recrystallization (DRX) is substantively retarded due to the fine dispersed particles uniformly distributed in the spray formed alloy. Continuous dynamic recrystallization (CDRX) is the primary DRX mechanism at a low temperature or high strain rate. DRX grain was observed at the grain boundaries, especially at the triple junctions. The appropriate thermal deformation condition is recommended at the temperature range from 430 °C to 450 °C and strain rates from 0.003 s−1 to 0.1 s−1.

Chitosan in the treatment of mine spoil rainwater - An approach to protect the aquatic biota

The mining industry suppresses vegetation, exposing large soil areas in its ordinary operation. Water pollution and turbidity are caused by the carrying of solids, mainly colloidal particles, to the watercourses due to the effect of rainfall events. Therefore, the discharge of those effluents will lead to failure with watercourse quality parameters. Thus, there is a need to treat drainages (rainwaters) from the mining industry. However, using common coagulants and flocculants can result in acute or chronic ecotoxicity for aquatic biota. In this scenario, this research aimed to evaluate using a natural coagulant, the biopolymer Chitosan, to remove turbidity from mining industry spoiled water through bio-coagulation. The ecotoxicity of the natural coagulant was compared to the commonly used coagulants. For this purpose, we used synthetic rainwater (SRW) from the dispersion of fine (colloidal) particles in natural waters. Materials (water and soil) were collected in the mining area's sumps (sedimentation basins). The turbidity of the produced SRW ranged from between 500 and 4000 NTU. Jar Tests using Chitosan (CTS), polyaluminum chloride (PAC®12), and Superfloc®N100 variable doses were carried out to compare the effects of the coagulating/flocculating agents on the SRW turbidity reduction. The obtained results demonstrated the efficiency of CHS on turbidity reduction. The results were encouraging for low turbidity samples (<1000 NTU), making it possible to meet the limit parameters recommended by the Brazilian legislation. In addition, it was possible to conclude both CHS and the effluents treated with this coagulant have lower toxicity to aquatic biota than the combination of PAC®12 and Superfloc®N100.

Abstract 10 — Enhancing Dissolution Efficiency of Ketoprofen, A Rheumatoid Arthritis Pain Management Drug, through Solid Dispersion Formulation

Background Ketoprofen (KPN) is commonly prescribed drug to alleviate pain related with rheumatoid arthritis (RA). However, KETO belongs to the BCS class-II category, characterized by poor water solubility, resulting in less dissolution capability leading to limited systemic absorption. Purpose of this study was to increase aqueous solubility as well as rate of dissolution of KPN using solid-dispersion technique. Methods Two different hydrophilic carriers, D-mannitol and polyvinylpyrrolidone K30 (PVP K30) and, were utilized, in varying ratios with the drug, to formulate solid dispersions. Kneading and solvent evaporation techniques were employed for preparing KPN solid dispersions with PVP K30, while kneading and melting methods were utilized for solid dispersions containing D-mannitol. The liquid state of the formulations was characterized through phase-solubility studies, while Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FTIR) spectroscopy, Differential Scanning Calorimetry (DSC) and X-ray diffraction (XRD) analysis were performed to examine the solid state. Results Both carriers demonstrated a favorable impact on the aqueous solubility of KPN. Solid state examination of D-mannitol solid dispersions revealed that KPN existed as fine particles, while it was entrapped within the polymer matrix in solid dispersions with PVP K30. Compared to poor rate of dissolution of pure drug KPN, the drug dispersions in both carriers showed a significantly improved dissolution rate. Improvement of dissolution rate can be ascribed to enhanced wetting behavior and dispersion of fine particles along with reduced crystalline fraction and an increase in the amorphous nature of KPN. Conclusion PVP K30 solid dispersions of KPN exhibited a noteworthy enhancement in the dissolution efficacy of KPN. Moreover, physical mixtures of KPN exhibited better dissolution profiles with D-mannitol and PVP K30 in comparison to pure KPN.

Partitioning temperature-dependent microstructures and mechanical properties of precipitation-hardened medium-Mn steel

This study reports the partitioning temperature-dependent microstructures and mechanical properties of precipitation-hardened medium Mn steel processed by room-temperature quenching and partitioning. The hot-rolled Fe–7Mn-0.3C–3Ni-1.5Si–1Al–1Cu-0.3V (wt.%) steel was processed by austenitization, water quenching to room-temperature, and partitioning treatment at 200, 300, 400, and 500 °C for 600 s. The samples before and after the partitioning process at temperatures below 400 °C show a microstructure consisting of lath martensite and retained austenite, whereas the sample partitioned at 500 °C shows a notably high fraction of retained austenite, owing to the formation of austenite grains during the partitioning process. The C partitioning during the partitioning process led to higher C contents in the samples processed by austenitization, quenching, and partitioning than in the sample processed by austenitization and quenching. The co-precipitation of VC precipitates and dispersed fine particles could exhibit a precipitation-strengthening effect. The sample partitioned at 200 °C shows an excellent strength-ductility combination, i.e., a yield strength of 740.9 MPa, an ultimate tensile strength of 1623.6 MPa, and a total elongation of 23.8%. Film-like retained austenite stabilized by carbon partitioning could exhibit high mechanical stability, leading to a gradual transformation induced plasticity (TRIP) effect and superior mechanical properties. In contrast, the samples partitioned at temperatures above 400 °C show poor ductility with brittle fracture, which could be related to the formation of martensite/retained austenite (M/A) constituents.

Weakening of mechanical parameters of ion-absorbed rare-earth ores subjected to leaching

Ion-adsorbed rare-earth ores are mined using in-situ leaching, and their mechanical properties significantly affect the efficient and safe recovery of rare earth elements. However, the mechanism of the change in the mechanical properties of the ore body due to the physicochemical processes caused by leaching remains unclear. To explore the strength evolution characteristics of the ore body during the leaching process, unconsolidated undrained triaxial tests were conducted to confirm how the stress–strain curve and shear strength of rare-earth samples change during leaching. Magnetic resonance imaging and T2 spectral characterizations were obtained by using nuclear magnetic resonance technology to measure the interior pore structure of samples during leaching. A scanning electron microscope equipped with an energy dispersive spectrometer was used to investigate the morphology evolution and the composition changes of the internal micro-area of the samples, to demonstrate the correlation between the microstructural change and the macroscopic mechanical properties. The results show that when a 2% ammonium sulfate solution is employed for mineral leaching, the effective leaching duration is 0–3 h. During this time, ion exchange occurs along the direction of solution seepage, resulting in the dispersion and migration of fine particles from the top to the bottom of the sample, which further triggers a change in the sample's pore structure and pore size. In addition, the local loss of fine particles resulted in a reduced bond strength between minerals, forming an unstable soil structure with a loose upper part and a dense lower part, which is macroscopically expressed as a declining shear strength parameter of the rare-earth sample.Graphical abstract

Parametric Optimization of Powder-Mixed EDM of AA2014/Si3N4/Mg/Cenosphere Hybrid Composites Using Fuzzy Logic: Analysis of Mechanical, Machining, Microstructural, and Morphological Characterizations

This research focuses on a comprehensive exploration of the experimental and mechanical aspects of the electrical discharge machining (EDM) process, specifically targeting the machining characteristics of AA2014/Si3N4/Mg/cenosphere hybrid composites. The aim is to optimize the process parameters for enhanced machining performance through a combination of testing, optimization, and modelling methodologies. The study examines the effects of key EDM variables—peak current, pulse on time, and pulse off time—on critical output responses: surface roughness (Ra), electrode wear rate (EWR), and material removal rate (MRR). Leveraging an L9 Taguchi orthogonal array experimental design, the impact of controllable factors on these responses is analysed. An integrated approach utilizing MATLAB’s logic toolbox and Mamdani’s technique is employed to model the EDM process, and a multiple-response performance index is calculated using fuzzy logic theory, enabling multiobjective optimizations. Furthermore, a mechanical behaviour evaluation of AA2014/Si3N4/Mg/cenosphere hybrid composites is performed through mechanical testing, with a comparison between experimental machining results and predicted values. Scanning electron microscopy (SEM) images reveal the presence of filler reinforcements within the base alloy, displaying an improved microstructure and uniform reinforcement dispersion. An X-ray diffraction (XRD) analysis confirms the major elemental constituents—aluminium, silicon, and magnesium—in the hybrid composites. A microstructural analysis of the hybrid metal matrix composites (MMCs) prepared for EDM showcases closely packed reinforcement structures, circular ash-coloured spots indicating silicon and nitrates, and a fine dispersion of cenosphere reinforcement particles. The study’s outcomes demonstrate a promising application potential for these hybrid composites in various fields.

Chemically dealloyed Mg–Cu alloy lamina as an interlayer for reinforcing a C/C composite – TC4 alloy vacuum brazed joint

Here, a novel brazing interlayer of bicontinuous nanoporous copper (NP–Cu) lamina was produced by chemically dealloying a magnesium-copper (Mg–Cu) binary alloy and applied for brazing a C/C composite and TC4 alloy along with AgCuTi alloy brazing filler. SEM, EDS, XRD, XPS, TEM and SAED were used to characterize the differences in microstructure and phase distribution of the samples and compare with samples without an interlayer. Mechanical testing in the form of shear tests were conducted to evaluate the change in shear strength caused by the interlayer. The large specific area, uniform nano scale porosity and ligaments of the NP-Cu lamina interlayer induced the transformation of Ti–Cu compounds from their bulk agglomerates to dispersed fine particles and formed eutectic phases, which contributed to relieving the residual stress and enhancing the plasticity of the joint seam. This led to a shear strength increase of 185% as compared to samples without an interlayer.

Investigating the effects of particle spatial evolutions on the vibration-induced compaction deformation of gap-graded mixtures via DEM models

The vibration-induced compaction deformation of gap-graded mixtures is caused by changes in particle spatial distributions. This study utilizes the discrete element method (DEM) to obtain spatial distribution information and verifies the accuracy of DEM models through physical tests. Spatial autocorrelation analysis and neighbor matching tests quantify spatial distributions in terms of particle aggregation. The correlations between mixture deformation and particle spatial distribution are investigated, with discussions on the influences of size ratio (SR) and fine content (FC). Results show a strong correlation between deformation and particle motions in mixtures with SR = 3, while the correlation becomes complex for mixtures with SR ≥ 4.45. Weakened aggregation facilitates pore-filling by fine particles and promotes deformation in mixtures with FC = 10%. Mixtures with 20% ≤ FC ≤ 30% exhibit the smallest deformation due to opposing particle motions and effective pore-filling by dispersed fine particles. Mixtures with FC > 40% experience deformation related to the aggregation state of coarse particles, despite being primarily composed of fine particles. This study sheds light on the vibration-induced deformation mechanism of mixtures through a mesoscopic perspective of particle spatial distributions.

Understanding and control of Zener pinning via phase field and ensemble learning

Zener pinning refers to the dispersion of fine particles which influences grain size distribution via movement of grain boundaries in a polycrystalline material. Grain size distribution in polycrystals has a significant impact on their properties including physical, chemical, mechanical, and optical to name a few. We explore the use of Phase-field modeling and machine-learning techniques to understand and improve the control of grain size distribution via Zener pinning in polycrystalline materials. We develop a machine learning model that determines the relative importance of various parameters to exercise microstructure control via Zener pinning. Our workflow combines high-throughput phase-field simulations and machine learning to address the computational bottlenecks associated with large-scale simulations as well as identify features necessary for microstructure control in polycrystals. A random forest (RF) regression model was developed to predict grain sizes based on five Phase-field model parameters, achieving an average prediction error of 0.72 nm for the training data and 1.44 nm for the test data. The importance of the input parameters is analyzed using the SHapley Additive exPlanations (SHAP) approach which reveals that diffusivity, volume fraction, and particle diameter are the most important parameters in determining the final grain size. These findings will allow us to select the best second-phase particles, optimize grain size distributions and thus design microstructures with the desired properties. The developed method is a highly versatile and generalizable approach that can be used to assess the combined effects of individual features in the presence of multiple variables.

Study on laminar structure and process on high strength brazed aluminum alloy for heat exchangers

A high-strength brazable 4343/3003/6A02/3003 aluminum alloy laminar composite and its brazing-aging treatment process were studied for the lightweight of heat exchangers. The high strength which average maximum tensile strength of the composite reaches 298 MPa, and yield strength is up to 263 MPa after brazing-aging treatment, comes from the precipitation strengthening of nanoscale fine dispersed Mg2Si particles generated by the heat-treatable 6A02 layer, while the brazeability is ascribed to the effectively hindrance for the diffusion of Mg elements into the brazing layer and surface by 3003 barrier layer with a thickness ratio of 8%. Both air-quenching and water-quenching after brazing at 600°С for 10 min can simultaneously achieve the brazing joint and full solution treatment, while the maximum mechanical properties of the composite are obtained after aging at 200°С for 2 h. Brazing with air-quenching and aging process is friendly to industrial production, and meets the expected mechanical properties for lightweight of heat exchangers. The laminar structure design with different functional components provides a new strategy for brazed lightweight materials.

Assessment of PM2.5 particulate air pollution near highways

Introduction. The purpose of this study is to investigate air pollution with respect to PM2.5 particulate matter hazardous to the health of the urban population, generated by the movement of motor vehicles. The development of existing and construction of new transport networks in large cities leads to the fact that the problem of air pollution by PM2.5 particles becomes extremely urgent.&#x0D; &#x0D; Materials and methods. The ENVI-met calculations were based on the data provided by the meteorological station. The following methods were applied: system analysis, numerical modelling method — finite difference method, processing of numerical results.&#x0D; &#x0D; Results. A calculation model of Moscow district territory was developed in ENVI-met programme in order to determine PM2.5 dispersion patterns along the road network of the selected district. The calculation was carried out for a 24-hour time period. The schemes of fine particles dispersion on the territory of the building at a height of 1.5 and 10 m are obtained. Their evaluation shows that the highest concentration of PM2.5 is observed along the most frequent wind direction near roads. The width of the roadway and, accordingly, the number of cars passing per hour plays a paramount role in the formation of PM2.5.&#x0D; &#x0D; Conclusions. The greatest negative impact of fine dust occurs in residential buildings located along highways. It is most rational to increase the density of landscaping in areas with a high concentration of PM2.5 along the main roads and on the roofs of existing low-rise buildings and medium-rise buildings.

Removal of Congo Red from Wastewater Using ZnO/MgO Nanocomposites as Adsorbents: Equilibrium Isotherm Analyses, Kinetics and Thermodynamic Studies

One step polyacrylamide gel method was used to synthesize the ZnO/MgO adsorbents and the adsorption behavior with Congo red (CR) from wastewater was extensively investigated. Various advanced techniques were applied to confirm the ZnO/MgO adsorbents consist of Zn, C, Mg and O elements and do not contain any other impurity elements. With the increase of MgO content, the morphology of ZnO/MgO adsorbent changes from the agglomeration of large particles to evenly dispersed fine particles and then to icicle structure. Results demonstrated that the adsorption process of ZnO/MgO adsorbents was significantly affected by the change in initial dye solution pH, initial adsorbent dosage, contact time and reaction temperature. The optimum pH, adsorbent dosage, contact time and reaction temperature is 9.81, 2 g /L, 65 min and 293 K, respectively. The maximum adsorption capacity of ZnO/MgO (nZnO:nMgO = 8:2) adsorbents (295.138 mg/g) for the adsorption of CR dye was approximately double that of previous reports (125 mg/g). The adsorption equilibrium data are well fitted by the Freundlich and Langmuir isotherm models. Thermodynamic studies indicate that the adsorption process of ZnO/MgO adsorbents is an exothermic process. Based on the experimental and theoretical analysis, the adsorption mechanism for the ZnO/MgO adsorbents consisted of hydrogen bonding, n-π interaction and electrostatic interaction. The present work pioneers the potential application of ZnO/MgO adsorbents for the adsorption of CR dye and further provides experimental evidence for the synthesis of other adsorbents.

Enhanced plasticity due to melt pool flow induced uniform dispersion of reinforcing particles in additively manufactured metallic composites

Additive manufacturing has gained increasing interest to fabricate metal matrix composites. Particle agglomeration remains a critical challenge and can severely compromise the mechanical properties, in particular tensile ductility. Here we investigated and utilized laser powder-bed-fusion (L-PBF) to uniformly disperse particles in metal matrices, taking advantages of particle flow dynamics during melting and remelting. We demonstrate our approach in a TiB2 reinforced aluminum system and produce a high dispersion of fine TiB2 particles (with sizes down to tens of nanometers) in a single print. Both micron- (1-5 μm) and nano-sized (40 nm) TiB2 particles are found to be uniformly dispersed in composites, with a volume fraction of up to 25%. High-fidelity computer modeling indicates that although particles flow with Marangoni vortexes, the melt pool overlapping and subsequent re-melting/re-solidification play an important role for the successful dispersion. The propelling effect of vapor depression and particle filling via the Marangoni vortex flow are the two main mechanisms that lead to the uniform dispersion. A geometric criterion for hatch spacing is derived and verified by experiments for the successful uniform dispersion of reinforcing particles. Compared to composites with nonuniform particle dispersion, L-PBF aluminum 2024 composites show ∼30% higher tensile strength and ∼16% higher Young's modulus, together with a marked improvement of tensile ductility (up to three times higher). The uniform dispersion of reinforcing particles is also achieved in copper materials and thus demonstrates the versatility of our approach to other metals and alloys.

Interfacial microstructure and strength of magnetic pulse welded A5052 aluminum alloy/SPCC steel lap joint

A5052 aluminum alloy and SPCC steel plates were welded using magnetic pulse welding, and interfacial microstructure and strength of the lap joint were examined. The A5052 aluminum alloy and the SPCC steel plates were used for a flyer plate and a parent plate, respectively. Charging energy stored in capacitor and gap between the A5052 aluminum alloy and the SPCC steel plates were changed. Microstructure was examined by using an optical microscope, a scanning electron microscope and a scanning transmission electron microscope. Tensile-shear test was used for evaluating the strength of the joint. The magnetic pulse welding of A5052 aluminum alloy and SPCC steel was achieved at the charging energy above 6.0 kJ and at the gap between the plates above 1.0 mm. The range of charging energy in which the strong welding is accomplished was different at each gap and the range increased with decreasing the gap. The lap joint was not fractured at the welding interface by the tensile-shear test whereas the fracture occurred at a part of the aluminum base metal. The welding interface exhibited characteristic wavy morphology. An intermediate layer was produced along the wavy interface. Scanning transmission electron microscope observation revealed that the intermediate layer is composed of fine Al-Mg grains and dispersed dendritic Al-Fe intermetallic compound particles.