Precipitation kinetics of niobium carbide and copper in a low carbon,chromium-free steel

Co-precipitation of niobium carbide and BCC copper is being investigated as a basis for making a high strength, easily weldable, low carbon, chromium-free structural steel as an alternative to tempered martensite. Theoretical curves were calculated for the nucleation and growth rates of NbC and BCC Cu precipitates in ferrite as a function of temperature for various austenizing temperatures. Calculated nucleation and growth rates for NbC in ferrite were significantly influenced by austenizing temperature while Cu precipitation kinetics were not effected. Nucleation and growth rate curves for copper and the nucleation rate curve for NbC showed the typical inverse “C” type behavior. For all austenizing temperature, the BCC Cu nucleation rate was orders of magnitude faster than NbC. Aging treatments selected on the basis of the computed curves are in approximate agreement with them.     

Size-controlled synthesis of gold nanoparticles using a micro-mixing system

A new microfluidic reaction chip capable of mixing, transporting and controlling reactions has been developed for the size-tunable synthesis of gold nanoparticles. This chip allows for an accelerated and efficient approach for the synthesis of gold nanoparticles. The microfluidic reaction chip is made by computer-numerically controlled machining and PDMS casting processes, which integrate a micro-mixer, a normally closed valve and a micro-pump onto a single chip. The micro-mixer is capable of generating a vortex-type flow field, which achieves a mixing efficiency as high as 95% within 1 s. Successful synthesis of dispersed gold nanoparticles has been demonstrated within an 83% shorter period of time (13 min), as compared to traditional methods (around 2 h). By using different volumes of reagents, the dispersed gold nanoparticles are found to have average diameters of 19, 28, 37 and 58 nm. The optical absorption spectra indicate that these synthesized nanoparticles have different surface plasmon resonance peaks, which are 521, 525, 530 and 537 nm, respectively. The development of this microfluidic reaction system holds promise for the synthesis of functional nanoparticles for further biomedical applications.     

Sn–Ag–Cu nanosolders: Melting behavior and phase diagram prediction in the Sn-rich corner of the ternary system

Melting temperatures of Sn–Ag–Cu (SAC) alloys in the Sn-rich corner are of interest for lead-free soldering. At the same time, nanoparticle solders with depressed melting temperatures close to the Sn–Pb eutectic temperature have received increasing attention. Recently, the phase stability of nanoparticles has been the subject of plenty of theoretical and empirical investigations. In the present study, SAC nanoparticles of various sizes have been synthesized via chemical reduction and the size dependent melting point depression of these particles has been specified experimentally. The liquidus projection in the Sn-rich corner of the ternary SAC system has also been calculated as a function of particle size, based on the CALPHAD-approach. The calculated melting temperatures were compared with those obtained experimentally and with values reported in the literature, which revealed good agreement. The model also predicts that with decreasing particle size, the eutectic composition shifts towards the Sn-rich corner.     

Hollow-core polymeric nanoparticles for the enhancement of OLED outcoupling efficiency

This work presents the possibility of the hollow core nanoparticles to improve luminance in an organic light emitting diode device. The finite difference time domain simulation estimates the effect of the hollow core nanoparticles on the external quantum efficiency of the organic light emitting diode device. The efficiency depends on the size and the volume fraction of the hollow core nanoparticles in the polymer layer, together with the refractive index and the thickness of the polymer layer. It is shown that the hollow core nanoparticles dispersed in a polymer layer can enhance the external quantum efficiency by a factor of 2.5. This work also introduces a continuous production method of the hollow core nanoparticles by using the microfluidic self-assembly of amphiphilic polymers and the layer formation dispersed with them for the rigorous light scattering.     

Solidification structure of CaO–SiO2–MgO–Al2O3 (–CaF2) systems and computational phase equilibria: Crystallization of MgAl2O4 spinel

The solidification behaviour of the CaO–SiO₂–Al₂O₃–CaF₂–10% MgO system, which is similar to the inclusion compositions in the stainless steel and the crystallization of spinel have been investigated using XRD, SEM-EDS, and an image analyser. The solidification mode and the phase equilibria were computed by employing thermochemical software. The liquidus temperature of the oxides containing 5% CaF₂ increases with increasing alumina content from 10% to 30%, while the solidus temperature has little dependence on alumina content. The size of spinel crystals in the final microstructure increases on increasing the content of alumina, resulting from that the oxides spending more time at higher temperatures below the liquidus temperature, where crystal growth is generally faster than nucleation, during slow cooling. The liquidus temperature of the oxides containing 30% Al₂O₃ is scarcely varied, while the solidus temperature decreases by increasing the content of CaF₂ to 10%. The size of spinel crystals decreases as the content of CaF₂ increases, resulting from the fact that the oxides could spend more time at relatively lower temperatures, where nucleation is faster than growth, during the cooling process.     

Microdroplet formation of water and nanofluids in heat-induced microfluidic T-junction

This paper reports experimental investigations on the droplet formation and size manipulation of deionized water (DIW) and nanofluids in a microfluidic T-junction at different temperatures. Investigations of the effect of microchannel depths on the droplet formation process showed that the smaller the depth of the channel the larger the increase of droplet size with temperature. Sample nanofluids were prepared by dispersing 0.1 volume percentage of titanium dioxide (TiO₂) nanoparticles of 15 nm and 10 nm × 40 nm in DIW for their droplet formation experiments. The heater temperature also affects the droplet formation process. Present results demonstrate that nanofluids exhibit different characteristics in droplet formation with the temperature. Addition of spherical-shaped TiO₂ (15 nm) nanoparticles in DIW results in much smaller droplet size compared to the cylindrical-shaped TiO₂ (10 nm × 40 nm) nanoparticles. Besides changing the interfacial properties of based fluid, nanoparticles can influence the droplet formation of nanofluids by introducing interfacial slip at the interface. Other than nanofluid with cylindrical-shaped nanoparticles, the droplet size was found to increase with increasing temperature.     

Numerical efficiency of some exponential methods for an advection–diffusion equation

In this paper, we investigate several modified exponential finite-difference methods to approximate the solution of the one-dimensional viscous Burgers' equation. Burgers' equation admits solutions that are positive and bounded under appropriate conditions. Motivated by these facts, we propose nonsingular exponential methods that are capable of preserving some structural properties of the solutions of Burgers' equation. The fact that some of the techniques preserve structural properties of the solutions is thoroughly established in this work. Rigorous analyses of consistency, stability and numerical convergence of these schemes are presented for the first time in the literature, together with estimates of the numerical solutions. The methods are computationally improved for efficiency using the Padé approximation technique. As a result, the computational cost is substantially reduced in this way. Comparisons of the numerical approximations against the exact solutions of some initial-boundary-value problems for different Reynolds numbers show a good agreement between them.     

The oblique collision efficiency of nanoparticles at different angles in Brownian coagulation

The oblique collision efficiency of nanoparticles at different colliding angles in Brownian coagulation is investigated. A model of central oblique collision between two nanoparticles is presented to derive equations which are solved to get the collision efficiency by considering van der Waals force and elastic deformation force. Based on the calculated data of collision efficiency under different colliding angles and particle diameters, a new expression relating central oblique collision efficiency at different colliding angles to particle diameter is brought forward.     

Surface plasmon resonance of metal nanoparticles for interface characterization

This paper demonstrates three cases of simple analytical classical Maxwell-Garnett model to estimate the size and concentration of silver and gold nanoparticles and their interface. The examples show that the model can satisfactorily interpret the spectral properties of ISTC and, in particular, to determine the presence and thickness of the shell on the surface of metallic nanoparticles in colloidal solution, and their interface in porous glass and complex colloidal solutions. The results can be used to study the optical properties of heterogeneous systems with metal nanoparticles, including the evolution of biological systems in vivo and the type of interaction precious metal nanoparticles with biological objects. The text was submitted by the authors in English.     

Simulation of transport and extravasation of nanoparticles in tumors which exhibit enhanced permeability and retention effect

Determining the factors that influence the delivery of sub-micron particles to tumors and understanding the relative importance of each of these factors is fundamental to the optimization of the particle delivery process. In this paper, a model that combines random walk with the pressure driven movement of nanoparticles in a tumor vasculature is presented. Nanoparticle movement in a cylindrical tube with dimensions similar to the tumor's blood capillary with a single pore is simulated. Nanoparticle velocities are calculated as a pressure driven flow over imposed to Brownian motion. The number and percentage of nanoparticles leaving the blood vessel through a single pore is obtained as a function of pore size, nanoparticle size and concentration, interstitial pressure, and blood pressure. The model presented here is able to determine the importance of these controllable parameters and thus it can be used to understand the process and predict the best conditions for nanoparticle-based treatment. The results indicate that the nanoparticle delivery gradually increases with pore size and decreases with nanoparticle size for tumors with high interstitial fluid pressure (in this work we found this behavior for head and neck carcinoma and for metastatic melanoma with interstitial pressures of 18 mmHg and 19 mmHg, respectively). For tumors with lower interstitial fluid pressure (rectal carcinoma with 15.3 mmHg) however, delivery is observed to have little sensitivity to particle size for almost the entire nanoparticle size range. Though an increase in nanoparticle concentration increases the number of nanoparticles being delivered, the efficiency of the delivery (percentage of nanoparticles delivered) is found to remain closely unaffected.     

Laser synthesis of optical media with silver nanoparticles by nanosecond pulses at air

The present work is dedicated to further development of the laser synthesis method for metal nanoparticles formation at air conditions. On the base of complex investigation of processes taking place during laser erosion of metals by intensive nanosecond pulses the method of silver nanoparticles fluxes formation is proposed. By the implantation of silver nanoparticles into liquid media (water or solutions of a polymeric base) the transarent media with silver nanoparticles can be obtained (particularly water colloids and modified polimer films). For the aims of investigation of formed polymeric films the complex diagnostics method is used     

Temporal dynamics of site percolation in nanoparticle assemblies

Dynamics of the formation of self-assembled sub-monolayer networks of colloidal nanoparticles is studied in the two-dimensional lattice gas model by Monte Carlo simulation. The site-percolation threshold (pc) is studied for various temperatures and chemical potentials. Our numerical results show that pc is greatly reduced due to the evaporation-driving self-organization. The results are qualitatively consistent with our experimental observation.     

ZnO hierarchical nanostructures grown at room temperature and their C2H5OH sensor applications

Highly crystalline ZnO hierarchical nanostructures were prepared at room temperature through the alkaline hydrolysis of zinc salt by the forced mixing of two immiscible solutions: Zn-nitrate aqueous solution and oleic-acid-dissolved n-hexane solution. The oleic acid acted as a surfactant in the room-temperature formation of well-defined ZnO hierarchical nanostructures, which subsequently demonstrated a sensitive and selective detection of C₂H₅OH. The responses of these hierarchical nanostructures to 10-100 ppm C₂H₅OH ranged from 15.7 to 177.7, which were 7-9 times higher than those of the agglomerated nanoparticles.     

Discovery and prediction capabilities in metal-based nanomaterials: An overview of the application of machine learning techniques and some recent advances

The application of machine learning (ML) techniques to metal-based nanomaterials has contributed greatly to understanding the interaction of nanoparticles, properties prediction, and new materials discovery. However, the prediction accuracy and efficiency of distinctive ML algorithms differ with different metal-based nanomaterials problems. This, alongside the high dimensionality and nonlinearity of available datasets in metal-based nanomaterials problems, makes it imperative to review recent advances in the implementation of ML techniques for these kinds of problems. In addition to understanding the applicability of different ML algorithms to various kinds of metal-based nanomaterials problems, it is hoped that this work will help facilitate understanding and promote interest in this emerging and less explored area of materials informatics. The scope of this review covers the introduction of metal-based nanomaterials, several techniques used in generating datasets for training ML models, feature engineering techniques used in nanomaterials-machine learning applications, and commonly applied ML algorithms. Then, we present the recent advances in ML applications to metal-based nanomaterials, with emphasis on the procedure and efficiency of algorithms used for such applications. In the concluding section, we identify the most common and efficient algorithms for distinctive property predictions. The common problems encountered in ML applications for metal-based nanoinformatics were mentioned. Finally, we propose suitable solutions and future outlooks for various challenges in metal-based nanoinformatics research.     

Microwave assisted fast synthesis of various ZnO morphologies for selective detection of CO, CH4 and ethanol

ZnO nanocrystals with various morphologies were synthesized via a fast and facile microwave assisted method using zinc acetate as starting material, guanidinium and acetyl acetone as structure directing agents, and water as solvent. Reaction conditions, templates and pH of the reaction medium were adjusted in order to achieve nanorod, nanoparticle, and flower-like morphologies. As synthesized ZnO samples were characterized using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and nitrogen adsorption analysis (BET). Response and selectivity of the samples to CO, CH₄ and ethanol were measured in a flow system. It is shown that different morphologies of ZnO nanoparticles exhibit different responses and selectivities. Flower-like morphology is highly selective to CO, while nanorods and nanoparticles are selective to methane and ethanol, respectively. Moreover, in a wide range of temperatures, response of ZnO nanorods and nanoparticles towards CO is temperature independent.     

Boundary element methods for transient convective diffusion. Part I: General formulation and 1D implementation

A general formulation of higher-order boundary element methods (BEM) is presented for time-dependent convective diffusion problems in one- and multi-dimensions. Free-space time-dependent convective diffusion fundamental solutions originally proposed by Carslaw and Jaeger are used to obtain the boundary integral formulation. Linear, quadratic and quartic time interpolation functions are introduced in this paper for approximate representation of time-dependent boundary temperatures and normal fluxes. Closed form time integration of the kernels is mandatory to attain both accuracy and efficiency of the numerical approach. A complete set of time integrals for the one-dimensional formulation is presented here for the first time in the literature.     

Selectivity of flame-spray-made Nb/ZnO thick films towards NO2 gas

Unloaded ZnO and Nb/ZnO nanoparticles containing 0.25, 0.5 and 1 mol.% Nb were produced in a single step by flame-spray pyrolysis (FSP) technique. The nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The BET surface area (SSA_BET) of the nanoparticles was measured by nitrogen adsorption. FSP yielded small Nb particles attached to the surface of the supporting ZnO nanoparticles, indicating a high SSA_BET. The morphology and accurate size of the primary particles were further investigated by TEM. Nb/ZnO nanoparticles paste composed of ethyl cellulose and terpineol as binder and solvent respectively was coated on Al₂O₃ substrate interdigitated with gold electrodes to form thick films by spin coating technique. After the sensing tests, the morphology and the cross-section of sensing film were analyzed by SEM and EDS analyses. The influence on a low dynamic range of Nb concentration on NO₂ response (0.1-4 ppm) of thick film sensor elements was studied at the operating temperatures ranging from 250 to 350 °C in the presence of dry air. The optimum Nb concentration was found be 0.5 mol.% and 0.5 mol.% Nb exhibited an optimum NO₂ response of ∼1640 and a short response time (27 s) for NO₂ concentration of 4 ppm at 300 °C.     

Robust efficiency measures in a stochastic efficiency model

Two types of robust solutions of a class of efficiency models known as data envelopment analysis (DEA) are explored here. One is the minimax method and the other is related to the concept of a core in the theory of n-person games where the payoffs are random. Some potential applications of these robust solutions are also briefly discussed.     

Axisymmetric pressure boundary loading for finite deformation analysis using p-FEM

Follower loads, i.e. loads which depend on the boundary displacements by definition, frequently occur in finite deformation boundary-value problems. Restricting to axisymmetrical applications, we provide analytical and numerical solutions for a set of problems in compressible Neo-Hookean materials so to serve as benchmark problems for verifying the accuracy and efficiency of various FE methods for follower load applications. Thereafter, the weak formulation for the follower-load in 3-D domain is reduced to an axisymmetrical setting, and, subsequently, consistently linearized in the framework of p-FEMs, exploiting the blending function mapping techniques. The set of axisymmetric benchmark solutions is compared to numerical experiments, in which the results obtained by a p-FEM code are compared to these obtained by a state-of-the-art commercial h-FEM code and to the “exact” results. These demonstrate the efficiency and accuracy of p-FEMs when applied to problems in finite deformations with follower loads.     

Hydrothermal synthesis of hierarchical nanoparticle-decorated ZnO microdisks and the structure-enhanced acetylene sensing properties at high temperatures

Nanoparticle-decorated ZnO microdisks showing a hierarchical structure were successfully synthesized through a citric acid-assisted hydrothermal process. The ZnO microdisks had a hexagonal wurtzite structure with high crystallinity. Sensors based on these microdisks exhibited high response values, fast response-recovery, good selectivity and long-term stability to 1-4000 ppm acetylene at 420 °C. In addition, even 1 ppm acetylene can be detected with high response (S = 7.9). The hierarchical structure can facilitate to fix the ZnO nanoparticles leading to a less aggregated configuration, which is expected to contribute much to the excellent acetylene sensing properties at high temperatures.