Journal of Ultrafine Grained and Nanostructured Materials
Volume:54 Issue: 2, Dec 2021

One of the main challenges in processing of metal matrix nanocomposites through the powder metallurgy method is achieving a dense compact with minimum internal porosity. Pores act as stress risers and deteriorate the mechanical properties of nano-materials. In the present investigation, powder mixtures of commercially pure Al (CP-Al) and 5252 Al alloy reinforced with nanometric SiC particles (0-7 wt.%) were produced by in situ powder metallurgy (IPM) method. These powders were consolidated through cold compaction, sintering and hot extrusion processes and subjected to density measurements, microstructural studies and thermal analysis. Microstructural studies showed that SiC nanoparticles formed a continuous network around the CP-Al powders, restricting effective densification during the cold compaction stage. This network was also shown to prevent metal-to-metal contact during sintering, especially at higher SiC contents. Therefore, a remarkable decrease in the sintered relative density was observed with increasing SiC contents in the CP-Al/SiC compacts. However, in the 5252 Al/SiC composite powders, the SiC nanoparticles embedded within the alloy matrix during the IPM process. As a result, a more homogeneous SiC particle distribution was attained. This led to enhanced cold densification and improved sinterability compared with those of CP-Al/SiC powder mixture. Besides, the presence of Mg in the 5252 alloy matrix was effective in reducing the oxide film covering the Al particles. The differential scanning calorimetry (DSC) revealed the formation of liquid phase during the sintering of 5252 Al/SiC powder compacts. As a result, mass transfer promoted through the liquid phase sintering enhancing densification. However, improved densification was obtained after hot extrusion of the nano-SiC reinforced composites. Results showed that the pressure required for extrusion increased with increasing SiC content. This was attributed to the enhanced redundant work induced by SiC particles.

The relatively small specific capacitance along with poor electrochemical activity and weak electrical conductivity of TiO2 has resulted in several studies on the methods of modifying TiO2. In this study, a different mechanism for improving the electrochemical properties of TiO2 nanotubes is employed. Nitrogen doping of TiO2 nanotube arrays fabricated using two-step anodization was used to narrow the bandgap of TNTs as a non-metal doping technique. To better demonstrate the impact of the nitrogen content on enhancing the electrochemical activity, TNTs were immersed in 0.5, 1, 2, 4, and 8 molars of ammonia solution. Electrochemical reductive doping was implemented on TNT and N-TNT. The phase structure and surface morphologies of the as-prepared TiO2 nanotubes were identified by X-ray diffraction (XRD), field scanning electron microscope (FSEM) and Fourier transformed infrared spectroscopy (FT-IR) measurements. The electrochemical response of the TiO2 NTAs following nitrogen and electrochemical doping was evaluated using cyclic voltammetry (CV), galvanostatic charge-discharge tests, and electrochemical impedance spectroscopy (EIS). The electrochemical measurements of the modified samples confirmed that a noticeable improvement was achieved in the electrochemical behavior and that the areal capacitance of R-N-TNT was roughly 400 orders of magnitude greater than that of TNT with long-term stability (93% of its initial capacitance after 500 cycles).

Activation energies and other kinetic parameters of primary crystallization of Al86Cu6Co2Y6 (at.%) amorphous alloy describing the mechanism was determined. Melt spinning on a child copper wheel was used to prepare the Al86Cu6Co2Y6 (at. %) amorphous ribbons. The ribbons at as-spun and annealed conditions were studied by optical microscopy (OM), differential scanning calorimetry (DSC), X-ray diffraction and field emission scanning electron microscopy (FESEM). The kinetic parameters of the crystallization process were determined by Kissinger and Moynihan methods at non-isothermal condition. Crystallization mechanism was studied using the Johnson–Mehl–Avrami equation. According to the average value of Avrami exponent (2.0650.16), the primary crystallization process is conducted by 3D diffusional growth with decreasing rate. The α-Al nanoparticles below 50 nm in size distributed evenly in the glassy matrix and intermetallic phases (Al3Y, AlCu3 and Al11Y3) were formed during the first and second stages of crystallization, respectively.

Plasma electrolytic oxidation (PEO) procedure has been considered as a proper method to increase the corrosion resistance of Mg alloys. In this study, the effect of current density and duty cycle as the operating parameters on the corrosion behavior of coatings at a constant frequency was studied. Also, hydroxyapatite nanoparticles were added to the electrolyte to improve the biological activity of the final coating. The top and cross-section view of the coatings was studied using scanning electron microscopy (SEM) to explore the microstructure changes by the operating parameters. The corrosion performance of coatings was evaluated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) assays in simulated body fluid (SBF), respectively. The appropriate current density selection of 300 mA/dm2 and a duty cycle of 50 % confirmed the high corrosion resistance of obtained coating because of the morphology of the coating. At the optimum parameters, the results of the in vitro immersion test showed that the coating containing hydroxyapatite has higher biological activity, and also it could protect the coating for a longer period of time.

Level set method (LSM) is a mathematical approach for obtaining structures with specified characterization by moving the interface boundaries between material domain and void domain. This paper used LSM for topology optimization (TO) of a statically loaded structures and also auxetic meta-materials. It is shown that different groups of auxetic structures as very useful materials in many areas, such as the piezoresistive sensor field could be obtained by using level set method. Different groups of auxetic structures obtained by LSM are re-entrant, chiral and some novel auxetic structures that have not been reported before were designed by changing initial design and volume fraction. The scale of production of auxetic structures is in the range of 0.1nm to 10 m and these structures are used in the field of piezoresistive sensors by coating them with ultrafine particles such as nanocarbons. Furthermore, our study revealed that the performance of the code retains the number and direction of symmetries of initial design for final structure. So, auxetic structures with desired symmetries could be designed by using the same symmetries for initial designs.

Nanostructured ZnO thin films with two different dopants namely Pb and Co were prepared by a sol–gel method. The thin films have been prepared from zinc acetate, monoethanolamine and iso-propanol and then they were deposited on glass substrate by using a dip coating method. The structural, morphological, photocatalytic activity and optical absorbance of thin films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet-visible spectrophotometer and degradation of methylene blue dye (MB). The all thin films exhibited a polycrystalline hexagonal wurtzite structure that revealed by XRD. Due to doping, the average grain size of ZnO thin film increased. All films showed a wrinkle morphology. Photocatalytic activity of thin films was evaluated in aqueous solutions of Methylene Blue (MB) under UV-light illumination. The results indicated that the photocatalytic activity of ZnO thin films increased by Pb doping, conversely Co doping reduced the photocatalytic activity in comparison with the pure ZnO films. Hence speed of degradation of methylene blue by Pb doped ZnO is higher than that of pure and Co doped ZnO.

In this study, gene expression programming (GEP) was used as a new method for the formulation of the size of Ag nanoparticles (AgNPs) as functions of the AgNO3-to-opium syrup (OS) ratio, pH, temperature (T), agitation speed (AS) and feed rate (Fr) of reducing agent in green synthesis. The models differ from each other concerning their genes number, chromosomes, interconnected function, and head size. A total of 63 samples were selected at different practical parameter products to generate databases for the new particle size formulations, testing, and training sets. The training and testing sets included 47 and 16 randomly selected mixtures for the proposed models. The best GEP model is found, and this final model can predict the size of AgNPs with an R squared of 0.828, a root means square error (RMSE) of 5.894, a root-relative squared error (RRSE) of 0.44. All results in the models indicated an applicable performance for predicting the minimum particle size of the AgNPs and found it reliable. The predicted model showed that all of the input parameters affect the resulting particle size. GEP modeling results denoted that the selected GEP successfully predicts the behavior of the size of nanoparticles as functions of operating variables.

Poly(vinylidene fluoride), PVDF, has been studied extensively because of its outstanding piezoelectric properties. PVDF shows five crystalline polymorphs known as α, β, γ, δ, and ε phases. Among them, the β phase exhibits piezoelectric properties, but the α phase is thermodynamically more stable. The incorporation of additives into PVDF can promote β phase formation. In this study, PVDF-nano SiC composites with different SiC contents were fabricated through hot compression molding and the effects of SiC on the crystal structure, crystallinity and piezoelectric properties of PVDF were studied. The microstructure of the composite samples was investigated by SEM. The prepared samples were perfectly dense with a density more than 97% of the theoretical density. The amount of β phase was determined by FTIR analysis and the crystallinity of the PVDF was deduced from DSC analysis. Finally the piezoelectric properties of the samples were measured by a piezotester. The results showed that by increasing SiC content up to 1 wt%, the amount of β phase, crystallinity and sensitivity of the samples increased and then decreased afterwards.

Cardiovascular diseases (CVDs) are known as killer diseases and to overcome these diseases, novel approaches are needed. Although many approaches were able to control this disease, they still had high risks for the patients. One of the best ways to control CVDs is to use targeted Nanosystems, with the help of Nanotechnology and Biology Sciences. Despite current therapeutic strategies to reduce risk, patients still experience the consequences of CVD. Improve visualization of early atherosclerotic lesions to decrease residual CVD risk is one of its goals. Nanomaterials used as Nanocarriers are mainly Polymeric based, Magnetic, Metalic, Silica based and Liposomes. In addition, some drugs can be loaded to these Nanocarries. In this review, we focused on nanocarriers to manage Atherosclerosis, which is the most prevalent type of CVD. We divided these nanocarriers into five main groups: Polymeric nanocarriers, Magnetic nanocarriers, Metalic nanocarriers, Liposomes and Silica-based nanocarriers.

The investigations on the synthesis and various applications of the bismuth telluride (Bi2Te3) nanoparticle have gained great attention in the present era due to its wide range of applications. Continued efforts are made by researchers to develop devices based on nanostructured materials. In this review paper, different methods for the synthesis of nanostructured Bi2Te3 are presented. Dependence of properties based on the synthesis methods is reviewed as well. Both physical and chemical methods are applied to get different forms of nano compounds. The merits and demerits of both methods are also explained in this review. Briefly, the different synthesis methods of bismuth telluride nanoparticles and its unique properties are critically discussed in this overview.

In this paper, we model and investigate the electrostatic pull-in instability of a perforated cantilever nanoswitch subjected to van der Waals and Casimir forces. The nanocantilever is a beam structure perforated with a periodic square holes network, which has been considered as an electrode material for this new structure. Closed-form solutions for the critical pull-in parameters are derived from the standard deformation beam equation, in which an equivalent bending stiffness is considered due to presence of square holes network. The electrostatic and dispersion forces are included by modifying the standard deformation beam equation, while the small scale effect is introduced by using the Eringen’s nonlocal elasticity theory. Pull-in parameters analysis of the perforated nanoswitch indicated that both pull-in voltage and pull-in deflection are affected by the gap ratio as well as the hole size ratio and the number of holes along the section of perforated nanocantilever beam. Therefore, these results are compared with literature results where new remarks are deduced and presented with detailed discussion for a proper design and investigation of M/NEMS nanoswitches.

In this study, by combining crystal plasticity notions developed by Taylor and the mathematical expression of Hill’s yield criterion for anisotropic materials, a model is introduced to describe the flow behavior of grains in a grain aggregate. In this model, Hill’s yield criterion coefficients are calculated in terms of Taylor factors for different straining conditions for each grain. The convexity of the proposed model is proved by sign determination of the eigenvalues of the associated Hessian matrix. It is found that the experimental load-displacement curves of specimens showing the size effect are enveloped by the bounds obtained from simulations using the proposed model, which to some extent verifies the applicability of the developed model. Using the developed model, the microforging of miniature rods consisting of 50 and 200 grains in their cross-section are simulated. In agreement with the literature, the results showed that due to the difference in the mechanical behavior of grains, the distribution of strain abruptly changes from one grain to another. Moreover, it is shown that as the number of grains in the cross-section of the specimen increases, the plastic equivalent strain tends toward that predicted by the classical plasticity theories, proving the applicability of the proposed model. Finally, the results suggest that the successful production of microparts by forming processes requires raw materials in microforming to be the products of the severe plastic deformation techniques, where the microstructure is scaled down to the nanometer.