Journal of Ultrafine Grained and Nanostructured Materials
Volume:52 Issue: 2, Dec 2019

In this paper, 2wt.% Fe doped TiO2 nanopowder was prepared by a combination of sol-gel and mechanical alloying methods. The mechanical alloying of Fe powder with Ti(OH)4 gel produced from the sol-gel method was used to produce Fe doped TiO2 nanopowder. The synthesized samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and diffuse reflectance spectroscopy (DRS). The photocatalytic behavior of nanopowder was examined by the degradation of methylene blue (MB) under visible light irradiation. XRD result showed that the phase structure was a combination of anatase and rutile phases and the anatase percentage was considerably increased to 72.3 % by Fe doping. The FESEM results demonstrated that the average particle size of TiO2 was decreased to 45 nm by Fe doping through ball milling. DRS results indicated the band gap of photocatalyst has shifted from 2.95 to 2.60 eV by Fe doping through ball milling. Photodegradation of MB was evaluated and the degradation rate was reached to 47% after 240 min under visible light irradiation. The photocatalytic performance of TiO2 nanoparticles improved by doping Fe through mechanical milling. Degradation reaction conformed by the first-order reaction kinetic model. The recycled Fe doped TiO2 nano-photocatalyst showed only a slight decrease of 7% in degradation rate after the third cycle.

An AM30 magnesium alloy was processed through ECAP method at 200 °C. Optical and transmission electron microscopy as well as electron back scattered diffraction (EBSD) technique were employed to characterize the deformed microstructure. A partially recrystallized microstructure including ultrafine/nano structures was obtained. The area fraction of 49% was measured for the recrystallized regions, where grains of 95 nm to 1 micron were detected. X-ray diffraction pole figure measurements were conducted to assess the final texture. The processed material exhibited moderate randomized texture including three basal pole peaks denoting the effect of dynamic recrystallization on deformation texture. TEM analysis confirmed the contribution of nano twinning during deformation of AM30 alloy. EBSD characterization implied that extension twin may contribute to the nucleation of new grains and thereby to be related to texture evolution. The apparent crossing pattern of intersected extension twins provided fine domains with high angle grain boundaries, which act as DRX nuclei. The formation of intersection boundaries also plays a critical role in pileup of dislocations and provide a local high stored-energy for dynamic recrystallization nucleation site. The aforementioned recrystallization mechanisms generally adopt orientations which are different from those produced by conventional recrystallization mechanisms, and thus it offers a route to manipulate the texture.

Silicon nanoparticles are the focus of attention thanks to their potentialities in advanced applications such as new batteries, photovoltaic cells and so on. The need to porous silicon is thus rising and will follow the same trend. In this work, highly porous nanostructured silicon is synthesized via Self-propagating high-temperature synthesis (SHS) route. Microstructural and phase analyses show that the employed technique is capable of producing a three-dimensional porous silicon which can act as a skeleton for embedding lithium ions and therefore, resisting large volume expansions arising during lithiation phase. Considering the fact that the wave front experiences high temperatures (above 1900°C) which can result in nanoparticles’ sintering, and in order to improve the porosity level, ammonium nitrate is used as a neutral additive at Mg/SiO2/NH4NO3 (2.4:1:0.1) molar ratio. The influence of nitrate addition on the final microstructure is studied through comparing salt-added samples with bare ones. Results show that ammonium nitrate can hinder the agglomeration of silicon nanoparticles during the progress of combustion wave thus affecting the specific surface area significantly (138.3 m2 g-1 as compared to for the 43.8 m2 g-1 for the reference sample which lacks NH4NO3). On the other hand, it was found that the added salt does not affect the product purity as examined through X-ray diffraction analysis.

In this study, the effect of slip casting parameters on the ultrafine microstructure and the density of pore-free YAG ceramic was evaluated. A stable, high concentrated aqueous YAG slurry using Dolapix-CE64 as a dispersant was prepared. The effect of dispersant concentration as well as the solid load on the stability and rheological behavior of the slurry was also studied. The optimal dispersant content for suspension was 1.5%wt which led to the slurry with minimum viscosity and near Newtonian behavior. The results show that increasing the solid load of the YAG slurry causes higher viscosity and alters the rheological behavior of slurry to slight shear thinning. By increasing the solid load of slurry up to a specific amount, 75%wt, relative green density of the slip cast sample was increased to about 65%, but further increase in solid loading reduced the green density. The density and the microstructure of the sintered body in the air and vacuum atmospheres bear a direct relationship to the green density of the slip cast body. Although, relatively the pore-free ultrafine YAG ceramic was obtained using vacuum sintering of the slip cast green body of 65% relative green density, the presence of nitrogen molecules in the air atmosphere inhibited full densification of YAG ceramic.

In this study, mechanical alloying was done by a high-energy planetary ball milling technique. A mixture of NiO and MoO3 and graphite powders were used as initial materials. After milling of powder mixture with 40 wt.% additional graphite, a temperature of 400, 550 and 1000 °C for 1 h was considered for the heat treatment of powder mixture. Also, powder mixtures containing 60, 80 and 100 wt.% additional graphite was heat-treated at 1000 °C for 1 h. The results of the thermodynamic analysis showed that full reduction of molybdenum-nickel oxide at ambient temperature during milling does not occur and thermal activation is required for complete reduction of mixed metal oxide. Investigation of hydrogen release through the electrochemical test in 1 M electrolyte solution of KOH at 28 °C showed that the reduced sample containing 60 wt.% additional graphite with ~187 mV additional potential in current density of ~10 mAcm-2, has the most activity in the release of hydrogen. This sample showed the lowest Rct of 17 ohm which means the good electrochemical characteristics of Ni-Mo alloy due to the good electrical conduction pathways and high access for the electrolyte solution with the high electrochemically active surface area.

A mixture of 10 wt% CuO-10 wt% Fe2O3 supported on cordierite were prepared by wet impregnation. The as-prepared solids doped with Li2O (0.75-3 mol %) were calcined at 500-900 ºC. The crystalline phase, morphology, and surface area were investigated by XRD, HR-TEM and N2-adsoprtion-desorption. Moreover, their photocatalytic activities of samples calcined at 700°C on the degradation of phenol were evaluated under UV-irradiation. The catalytic activity of different solids toward H2O2 decomposition was studied. Nano-materials were used to adsorb dyes as Remazole-Red and Congo-Red from aqueous solution. The sorption process was in good agreement of pseudo-second order equation and the Langmuir equation through their adsorption kinetics and isotherms, respectively. The CuO-Fe2O3/ cordierite doped with 0.75% Li2O at 700 ºC adsorbent was found to possess the highest removal efficiency of Remazole-Red and/or Congo-Red dyes and potentially lowering capital and operational costs for practical applications. The highest removal efficiency of the anionic dyes over 0.75% Li2O at 700 ºC can be discussed by observing the appearance of new active phases as CuO, CuFe2O4 and LiCuO, decreasing the crystallite size of these active phases. 0.75 mol% Li2O has the greatest activity in H2O2 decomposition reached 700 %. This result may be related to the lowest particle size and the highest surface area of this sample, which also produced a large number of electrons donating active sites for H2O2 decomposition

Recently, high-performance lightweight materials with outstanding mechanical properties have opened up their way to some sophisticated industrial applications. As one of these systems, aluminum matrix composites/nanocomposites (AMCs) offer an outstanding combination of relative density, hardness, wear resistance, and mechanical strength. Until now, several additive manufacturing methods have been developed for fabrication of 3D metallic components among them, selective laser melting (SLM), electron beam melting (EBM), laser metal deposition (LMD), Wire+Arc additive manufacturing (WAAM), and ultrasonic additive manufacturing (UAM) are of prime significance. Unlike other methods, in ultrasonic additive manufacturing, the ultrasonic waves are used instead of applying the sintering process. This technique is well-known for its ability to produce 3D components by repeating the alternative welding and machining procedures at low temperatures. This is why it can overcome the technological issues arisen from the high-temperature sintering. The present review strives to provide an inclusive introduction to the principles of ultrasonic additive manufacturing method and recent advances in ultrasonic additive manufacturing of aluminum matrix composites/nanocomposites. Also, the challenges of this new emerging technique, i.e. its dependence to the applied weld power, is addressed in the paper. The authors attempt to give some perspectives to the researchers for further investigations in this new-emerging field.

A novel nano-initiator containing kojic acid moiety, [5-(benzyloxy)-4-oxo-4H-pyran-2-yl)methyl-2-bromo-2-methylpropanoate was synthesized by the reaction of 5-(benzyloxy)-2-(hydroxymethyl)-4H-pyran-4-one with 2-bromoisobutyryl bromide in triethylamine and used as initiator in the atom transfer radical polymerization (ATRP) of styrene and methyl methacrylate in the presence of Cu(0)/CuCl2and N,N,Nʹ,N″,N″-pentamethyl diethylenetriamnie (PMDETA). The characteristics of resulting polymers were verified by proton nuclear magnetic resonance spectroscopy (1H NMR), thermogravimetric analysis (TGA), and gel permeation chromatography (GPC). 1H NMR spectra were recorded in deuterated chloroform (CDCl3) with a Fourier transform (FT)-nuclear magnetic (NMR) spectrometer. To investigate the living nature of polymerization, the obtained polymers were subjected to further chain extension reaction. The chain extension of polystyrene (PS) and poly(methyl methacrylate) (PMMA) macroinitiators demonstrated that the chain ends of the obtained PS-Br and PMMA-Br were enable for further functionalization. After chain extension, the GPC curves shifted to high molecular weight. The values of number average molecular weight (Mn) of PS and PMMA increased from 37853 to 40808 g/mol and from 107640 to 156310 g/mol, respectively. These results demonstrated that the chain extension reaction was successful and exhibited the living features of the chain end. To the best of our knowledge, the synthesis of ATRP initiator containing kojic acid moiety has not been reported. Herein, we report the synthesis and characterization of an ATRP initiator containing kojic acid moiety, and its application for the polymerzation of styrene and methyl methacrylate.

The dependency of uniform corrosion of structural steel on the average grain size (D) should be quantified for design purposes. In the present work, a spectrum of grain sizes was obtained by simple heat treatment routes in st37 structural steel. It was revealed that the corrosion current density (icorr) increased by grain refinement, which was related to the increased density of grain boundaries. The data on the plots of hardness and icorr versus 1/√D were successfully fitted by a straight line and an exponential function, respectively. Therefore, the mechanical response was rationalized by a Hall-Petch type relationship with a slope of 237.8 MPa/µm0.5. Moreover, the obtained simple relationship between icorr and 1/√D can be used for prediction of the dependency of uniform corrosion on the average grain size.

Excellent mechanical properties and fatigue performance of Al/Al2O3 metal-based nanocomposites caused to introduce this material as a good candidate for various applications. In this regard, the preparation and characterization of this composite can be considered as a hot issue for research. The study was carried out in several steps including: (i) preparation of Al/Al2O3 metal-based nanocomposites at various Al2O3 content as reinforcement (4, 6 and 8 wt.%) using wet attrition milling; (ii) hot forward extrusion process of prepared samples; (iii) determination of mechanical properties of prepared composite by tensile test; (iv) usage of rotating-bending fatigue test for determination of the fatigue performance of prepared composite and (v) analysis of the fracture surfaces of fatigue tests specimens to determine the mechanism/s of failure based on scanning electron microscope analysis. The results showed that the presence of Al2O3 nanoparticles up to 6 wt.% enhanced the fatigue strength of Al/Al2O3 nanocomposites while the higher amount of reinforcement has a detrimental effect on the fatigue strength. Also, the statistical nature of fatigue data confirmed the higher coherency as well as homogeneity of prepared composites by 6 wt.% of reinforcement. The EDX spectrum confirmed the presence of Al2O3 at the origin of crack. As a consequence, the most probable mechanisms for crack initiation through the cyclic loading can be considered as the fracture and/or detachment of reinforcement particles.

Effects of different amounts of lead (Pb) and tin (Sn) on microstructure and tensile properties of the AZ91 alloy were studied. The results presented that the microstructure of AZ91 alloy is consisted the α-Mg phase and semi-continuous network of β-Mg17Al12 intermetallics. For the as-cast AZ91 alloy, the average grain siz and the β phase volume fraction were 96.2 µm and of 25.3%, respectively. By adding 1 wt.% Pb and 0.5 wt.% Sn, the lowest grain size and volume fraction values obtained. Exceeding Pb and Sn additions have been led to the increasing of the grain size. Furthermore, Sn additions formed the Mg2Sn intermetallic, while Pb additions didn’t form any obvious intermetallics. The Ultimate Tensile Strength (UTS) and tensile elongation (%El) values of the cast AZ91 alloy were 129 MPa and 2.7%, respectively. The optimum amounts of UTS and %El values were achieved by adding 1 wt.% Pb and 0.5 wt.% Sn, respectively. More Pb and Sn additions deteriorated the tensile properties. The fracture surface observations showed that fracture mode in the cast AZ91 alloy was cleavage. Moreover, 1 wt,% Pb and 0.5 wt.% Sn additions altered the fracture mode to more quasi-cleavage fracture.