Laser powder bed fusion (LPBF) additive manufacturing technology is sensitive to variations in powder particle morphology and size distribution. However, the absence of a clear link between the ...powder characteristics and the LPBF performances complicates the development, selection and quality control of LPBF powder feedstock. In this work, three Ti-6Al-4 V powder lots produced by two different techniques, namely, plasma atomization and gas atomization, were selected and characterized. Following the micro-computed tomography analysis of the powder particles’ morphology, size and density, the flowability of these powder lots was concurrently evaluated using Hall and Gustavsson flowmeters and an FT4 powder rheometer. Using established rheology-based criteria, a figure of merit was proposed to quantify the overall powder suitability for the LPBF process. Next, the same three powder lots were used to 3D-print and post-process a series of testing specimens with different layer thicknesses and build orientations, in order to establish a correlation between the powder characteristics and the geometric and mechanical properties of a final product. This study demonstrates that the use of highly spherical powders with a limited amount of fine particles promotes their flowability and yields LPBF components with improved mechanical and geometric characteristics.
Bimetallic nanoparticles of noble metals are of high interest in imaging, biomedical devices, including nanomedicine, and heterogeneous catalysis. Synthesis, properties, characterization, biological ...properties, and practical applicability of nanoparticles on the basis of platinum group metals and the coin metals Ag and Au are discussed, also in comparison with the corresponding monometallic nanoparticles. In addition to the parameters that are required to characterize monometallic nanoparticles (mainly size, size distribution, shape, crystallographic nature, surface functionalization, charge), further information is required for a full characterization of bimetallic nanoparticles. This concerns the overall elemental composition of a bimetallic nanoparticle population (ratio of the two metals) and the internal distribution of the elements in individual nanoparticles (e.g., the presence of homogeneous alloys, core–shell systems, and possible intermediate stages). It is also important to ensure that all particles are identical in terms of elemental composition, that is, that the homogeneity of the particle population is given. Macroscopic properties like light absorption, antibacterial effects, and catalytic activity depend on these properties. The currently available methods for a full characterization of bimetallic nanoparticles are discussed, and future developments in this field are outlined.
Bimetallic nanoparticles offer many possibilities beyond their constituents, that is, the pure metals. For instance, their imaging properties can be fine‐tuned, the antibacterial effects of silver can be changed by blending it with a second metal, and the performance in heterogeneous catalysis including electrocatalysis can be enhanced. The current concepts on synthesis and characterization are outlined.
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•Bio-inspired encapsulation of Iron oxide nanoparticles for cancer therapy is presented.•State-of-the-art synthetic routes and various surface architectures with biopolymers.•Advances ...on, biocompatibility, and functionalization of FeNPs for drug delivery.
Cancer cells are typified by proliferating mass of cells that grow faster than other smaller cell tissues within the body. Efforts to combat this effect through chemotherapy, radiotherapy, immunotherapy and surgery are still challenging. Magnetic Iron oxide nanoparticles (FeO-NPs) encapsulated with biopolymers as a local drug delivery system with the control via an external magnetic field has been widely used as a drug delivery system in cancer therapy, minimizing the side effects and lack of pathological site-specific action common to the conventional approaches. For the FeO-NPs to function optimally in actualizing the applications as mentioned earlier, it requires that the FeO-NPs have high magnetization values, narrow particle size distribution and a special surface encapsulation. Biopolymers used for surface functionalization offer several advantages in biomedical applications, owing to their defined primary structures, nontoxicity, biocompatibility and biodegradability. The functionalized FeO-NPs offer various possibilities, which include targeting ligands, proteins, antibodies and covalent attachment of drugs using an external magnetic field for cancer therapeutic purposes. This work discusses recent advances in the development of FeO-NPs from fabrication to applications and the state-of-the-arts synthetic routes. The work gives special attention to the biopolymer surface functionalization of FeO-NPs now and future perspective of drug delivery in oncologic disease therapy chiefly cancer cells.
Abstract
The strong metal-support interaction (SMSI) has long been studied in heterogonous catalysis on account of its importance in stabilizing active metals and tuning catalytic performance. As a ...dynamic process taking place at the metal-support interface, the SMSI is closely related to the metal surface properties which are usually affected by the size of metal nanoparticles (NPs). In this work we report the discovery of a size effect on classical SMSI in Au/TiO
2
catalyst where larger Au particles are more prone to be encapsulated than smaller ones. A thermodynamic equilibrium model was established to describe this phenomenon. According to this finding, the catalytic performance of Au/TiO
2
catalyst with uneven size distribution can be improved by selectively encapsulating the large Au NPs in a hydrogenation reaction. This work not only brings in-depth understanding of the SMSI phenomenon and its formation mechanism, but also provides an alternative approach to refine catalyst performance.
•The influence of an alternating magnetic field on the CaCO3 fouling is studied.•The fouling induction period can be prolonged by the alternating magnetic field.•The growth of CaCO3 is inhibited and ...smaller size calcite crystals are formed.•An evaluation index is introduced to define the fouling inhibition effect.•The fouling inhibition characteristics presented a multi-extremum feature.
Experiments were performed to investigate the influence of an alternating magnetic field with different magnetic induction intensities on the calcium carbonate (CaCO3) fouling of a heat transfer surface. Experimental results indicated that the alternating magnetic field could effectively inhibit the fouling deposition on the heat transfer surface by prolonging the fouling induction period and slowing down the growth rate of CaCO3 fouling. Moreover, the fouling inhibition characteristics of the alternating magnetic field presented a multi-extremum feature. The fouling inhibition effectiveness depended on the selection of operating parameters in the alternating magnetic field. The most significant period was 300 Gs in this work, during which the fouling inhibition rate was 91.57%. Meanwhile, the fouling induction period increased by 132.3% and the growth rate decreased by 38.8% compared with the blank test. According to the scanning electron microscopy and particle size distribution, the morphology of CaCO3 particles exhibited changes with the alternating magnetic field. The smaller crystal size and terrace-ledge-kink growth were two reasons that impeded CaCO3 fouling from adhering easily on the heat transfer surface. This work can provide a sound theoretical guidance for future alternating magnetic field system design and application in fouling inhibition.
The accumulation of soiling on photovoltaic (PV) modules affects PV systems worldwide. Soiling consists of mineral dust, soot particles, aerosols, pollen, fungi and/or other contaminants that deposit ...on the surface of PV modules. Soiling absorbs, scatters, and reflects a fraction of the incoming sunlight, reducing the intensity that reaches the active part of the solar cell. Here, we report on the comparison of naturally accumulated soiling on coupons of PV glass soiled at seven locations worldwide. The spectral hemispherical transmittance was measured. It was found that natural soiling disproportionately impacts the blue and ultraviolet (UV) portions of the spectrum compared to the visible and infrared (IR). Also, the general shape of the transmittance spectra was similar at all the studied sites and could adequately be described by a modified form of the Ångström turbidity equation. In addition, the distribution of particles sizes was found to follow the IEST-STD-CC 1246E cleanliness standard. The fractional coverage of the glass surface by particles could be determined directly or indirectly and, as expected, has a linear correlation with the transmittance. It thus becomes feasible to estimate the optical consequences of the soiling of PV modules from the particle size distribution and the cleanliness value.
•The result of various range of Pt particle size was compared with the constant size.•PDF was used to randomly distribute Pt particles of different sizes to get a real CL.•Numerical result for ...non-uniform Pt particles is consistent with experimental result.
Platinum (Pt) nanoparticles are used as an electrocatalyst in polymer electrolyte membrane (PEM) fuel cells. Visualization data of PEM fuel cell catalysts have shown that the size of Pt particles in the catalyst layer (CL) varies locally from several nanometers to tens of nanometers, owing to the agglomeration and degradation of Pt particles. Although many computational-fluid-dynamics-based PEM fuel cell modeling and simulation studies have been conducted, the majority of them have used the average value of the size of Pt particles owing to the complexity involved in considering the nonuniformity of the Pt particle size in the CL. In this study, we present a new approach to fuel cell CL modeling in PEM fuel cell simulations; the approach involves the consideration of various Pt particle size distributions. In the approach, a probability density function is used to randomly distribute Pt particles with different sizes in a computational domain under the assumption that the Pt particle size distribution follows a normal distribution curve. A sufficient number of grids, typically more than several million grid points, are used to obtain a Pt particle size distribution similar to that in a real CL. The new approach was applied to a comprehensive multiscale PEM fuel cell model and full three-dimensional fuel cell simulations were performed for different CL designs, Pt catalyst degradation levels, and operating conditions. Numerical simulation results clearly showed the significant effect of a nonuniform Pt particle size distribution on multidimensional contours of species concentration, temperature, and current density as well as the overall cell performance.
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A new model for the yield stress in superalloys accounting for unimodal and multimodal γ′ size distributions is presented. A critique of the classic models on γ′ shearing is presented ...and important features not previously considered are incorporated in our model. This is extended to account for multimodal particle size distribution effects by weighting the individual particle contribution to the total strength. This analysis is focused on powder metallurgy alloys. The yield stress and particle strengthening are predicted for eight superalloys containing wide variations in initial microstructure, composition and at temperatures up to 700°C. We demonstrate through a theoretical approach that the strength of alloys with multimodal γ′ is lower than those with unimodal γ′ radius in the vicinity of 10–30nm. For the first time, a parameter-free physics-based model is able to predict the yield stress in superalloys with complex microstructures, including unimodal and multimodal γ′ size. This has been possible by removing limitations inherent to the classical models. Such approach also enables critical evaluation of the relevant factors contributing to the yield strength of polycrystalline superalloys.
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•Street sweeping may reduce OPs and nano/microparticle loads to stormwater (75).•Street sweeping washwater conc. of aliphatics and PAHs were extremely high (77).•Nanoparticles in the ...range 1–300 nm were present in street sweeping washwater (77).•OPs quantified in washwater are attached to small particles or truly dissolved (82).•Washwater collected by street sweeping needs treatment before disposal (73).
Road areas are pollution hotspots where many metals, organic pollutants (OPs) and nano/microparticles accumulate before being transported to receiving waters. Particles on roads originate from e.g. road, tyre and vehicle wear, winter road maintenance, soil erosion, and deposition. Street sweeping has the potential to be an effective and affordable practice to reduce the occurrence of road dust, and thereby the subsequent spreading of pollutants, but there is currently little knowledge regarding its effectiveness. In this paper we investigate the potential of street sweeping to reduce the amounts of OPs and nano/microparticles reaching stormwater, in a case study sampling road dust and washwater from a street sweeping machine, road dust before and after sweeping, and stormwater. The compound groups generally found in the highest concentrations in all matrices were aliphatics C5–C35 > phthalates > aromatics C8–C35 > PAH-16. The concentrations of aliphatics C16–C35 and PAHs in washwater were extremely high at ≤ 53,000 µg/L and ≤ 120 µg/L, respectively, and the highest concentrations were found after a 3-month winter break in sweeping. In general, fewer aliphatic and aromatic petroleum hydrocarbons and PAHs were detected in road dust samples than in washwater. The relative composition of the specific PAH-16 suggests tyre wear, vehicle exhausts, brake linings, motor oils and road surface wear as possible sources. The study indicates that many of the hydrophobic compounds quantified in washwater are attached to small particles or truly dissolved. The washwater contains a wide range of small particles, including nanoparticles in sizes from just below 1 nm up to 300 nm, with nanoparticles in the size range 25–300 nm present in the highest concentrations. The results also indicated agglomeration of nanoparticles in the washwater. The street sweeping collected a large amount of fine particles and associated pollutants, leading to the conclusion that washwater from street sweeping needs to be treated before disposal.
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