Sharif Digital Repository

We present a novel hybrid electrode based on reduced graphene oxide/nickel/zinc oxide heterostructures. The sensor was fabricated by template-free hydrothermal growth of ZnO nanorod arrays on conductive glass substrates (FTO) followed by conformal electrodeposition of nickel nanoparticles with an average size of 18 nm. Then, in-situ reduction and electrophoretic deposition of graphene oxide (GO) nanosheets on the structured ZnO/Ni electrode was performed. The prepared three-dimensional nanostructure exhibited fast electrocatalytic response (<3 s) towards glucose oxidation due to the large surface area and high electro-activity. The prepared biosensor possessed a wide linear range over... 

Microstructural features, thermal stability and crystallization kinetics of various melt spun Al-based alloys containing transition metals (TM = Ni, Cu) and Ce-based rare earth metals (MM: Misch Metal) were investigated via X-ray diffractometry (XRD), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). It is shown that the extended topological instability of Egami-Waseda model (λ criterion) is a useful tool to predict the crystallization behavior of the prepared alloys. FCC-Al nanoparticles are formed during the initial crystallization process. Calculation of the apparent activation energy using the Kissinger method indicates that partial replacement of... 

The paper presents graphene-templated self-assembly of gold nanorods into long fibers with controllable optical properties. It is shown that the size of self-assembled nanostructures varies with time and is controlled by chemical reactions between amine groups of graphene and the functional groups of gold. The absorption peak of the nanostructures changes over time while the photoluminescence intensity is quenched. The self-assembled nanostructures with variable plasmon resonance effects are potentially usable for the fabrication of nanoscale devices for biomedical applications. © 2018 Elsevier B.V  

Abstract: The hot deformation behavior of coarse-grained (CG), ultrafine-grained (UFG), and oxide dispersion-strengthened (ODS) AA6063 is experimentally recognized though carrying out compression tests at different temperatures (300–450 °C) and strain rates (0.01–1 s−1). Microstructural studies conducted by TEM and EBSD indicate that dynamic softening mechanisms including dynamic recovery and dynamic recrystallization become operative in all the investigated materials depending on the regime of deformation. Moreover, the high temperature flow behavior is considerably influenced by the initial grain structure and the presence of reinforcement particles. The constitutive and artificial neural... 

The fabrication of complex-shaped parts out of Co-Cr-Mo alloy and 316L stainless steel by three-dimensional printing (3DP) is studied using two grades of each alloy with average particle size of 20 and 75 nm, respectively. To produce sound specimens, the proper 3DP processing parameters were determined. The sintering behavior of the powders is characterized by dilatometric analysis and by batch sintering in argon atmosphere at 1280°C for 2h. The 3DP process has successfully produced complex-shaped biomedical parts with total porosity of 12-25% and homogenous pore structure, which is suitable for tissue growth into the pores  

This paper presents the densification and microstructure of bilayer structures made from 316L and 17-4PH stainless steels powders during sintering. The requirements for such objects could be magnetic properties at one area of the part and non-magnetic properties at another area of the object. A pressureless solid state sintering method in conjunction with a powder layering technique was used. The sintering was carried out at temperatures ranging from 1100 to 1340 °C for 120 min in hydrogen and vacuum atmospheres. Non-isothermal sintering behavior was also examined by dilatometric analysis. It was found that the strain rate of 17-4PH stainless steel powder is higher than that of 316L during... 

Theranostic liposomes have recently found a broad range of applications in nanomedicine due to stability, the high solubility of biomacromolecules, bioavailability, efficacy, and low adverse effects. However, the limitations of liposomes concerning the short systemic circulation in the body, limited controllability of the release rate, and the inability of in vivo imaging remain challenging. Herein, the development of novel hybrid ultrasound-activated piezoelectric nanoparticles based on a hybrid liposome nanocarrier composed of poly(vinylidene fluoride‐trifluoroethylene), graphene quantum dots (GQDs), and Silibinin (a hydrophobic drug) is presented. The hybrid nanoparticles are an... 

Submerged friction-stir processing under cryogenic conditions was employed to fabricate ultrafine-grained nanocomposites with enhanced mechanical characteristics. Al-Mg alloy sheet with 3vol% TiO2 nanoparticles were processed under air (ambient temperature), a water-dry ice medium (~-25°C), and liquid nitrogen. It is shown that a homogenous distribution of reinforcement particles throughout the metal matrix is attained at a rotational speed of 1400rpm and a traverse velocity of 50mm/min after 4 passes. In situ formation of Al3Ti and MgO nanophases during multi-pass processing is shown by transmission electron microscopy. Under the cryogenic cooling condition, ultrafine grains and cellular... 

A fine-grained aluminum-matrix hybrid nanocomposite reinforced with TiO2, MgO and Al3Ti nanoparticles was prepared via reactive friction stir processing (FSP) of an Al-Mg sheet with pre-placed TiO2 particles (50nm; 3.1vol%). The microstructure of the hybrid nanocomposite comprises high-angle grain boundaries (~90%) with an average size of 2μm and hard inclusions with sizes in the range of 30-50nm. Evaluation of the hot deformation behavior of the nanocomposite by uniaxial tensile testing at different temperatures (300-450°C) and strain rates (0.001-0.1s-1) shows that the deformation apparent activation energy of the nanocomposite is 137kJmol-1 at ≤300°C. The values of the activation energy... 

The size mono-dispersity, saturation magnetization, and surface chemistry of magnetic nanoparticles (NPs) are recognized as critical factors for efficient biomedical applications. Here, we performed modified water-in-oil inverse nano-emulsion procedure for preparation of stable colloidal superparamagnetic iron oxide NPs (SPIONs) with high saturation magnetization. To achieve mono-dispersed SPIONs, optimization process was probed on several important factors including molar ratio of iron salts [Fe3+ and Fe2+], the  

While full densification of conventional WC-Co hardmetals is achieved via liquid phase sintering at temperatures >1400°C, many studies 3, 4, 5, 6, 7 and 8 have indicated rapid densification during solid-state sintering is concurrent with significant grain growth. The material cost of nanostructured cemented carbides presents another limitation in industrial usage of these materials. One way to circumvent the cost factor is to reduce the amount of ultrafine grained hardmetal used by combining it in composite parts with cheaper, but functionally graded, materials such as stainless  

The fabrication of strong photocatalysts applied to the degradation of organic pollutants is necessary in environmental applications. In a single-stage method, acetate precursor and poly vinyl pyrolydine are used to produce ZnO nanostructures with various morphologies in annealing temperatures ranging from 300 to 900 °C. The physical properties of the prepared nanostructures were characterized by SEM, TEM, XRD, BET, DRS, CHN analysis and PL spectroscopy. The SEM images exhibit a variety of the as-prepared hexagonal zinc oxides including wires, rods, particles and porous network of welded particles of ZnO nanoparticles. The results of the photocatalytic degradation of methylene blue as an... 

Recently, nanodiamonds have attracted interest in biomedical applications such as drug delivery, targeted cancer therapies, fabrication of tissue scaffolds, and biosensors. We incorporated diamond nanoparticles in alginate–bioactive glass films by electrophoretic process to prepare functional coatings for biomedical implants. Turbidity examination by time-resolved laser transmittance measurement revealed that a stable multi-component aqueous suspension of alginate, bioactive glass and diamond particles could be obtained at concentrations of 0.6, 1.3, and 0.65 g/l, respectively. Uniform films with ~ 5 μm thickness were deposited on 316 stainless steel foils by employing constant field... 

Gallium-67 labeled superparamagnetic iron oxide nanoparticles ([ 67Ga]-SPION were prepared and evaluated for their altered biodistribution in normal rats. Superparamagnetic iron oxide nanoparticles (SPION) with narrow size distribution were synthesized by a co-precipitation technique using ferrous salts at Fe3+/Fe2+ = 2 molar ratio followed by structure identification using XRD, TGA, DSC, VSM, HRSEM, TEM and FT-IR techniques (≈ 5 nm diameter). In order to trace SPION bio-distribution, the radiolabeled iron oxide nanoparticles were prepared using 67Ga with a high labeling efficiency (over 96%, RTLC method) and they also showed an excellent stability at room temperature for at least 4 d. The... 

Nanofibrous structures mimicking the native extracellular matrix have attracted considerable attention for biomedical applications. The present study aims to design and produce drug-eluting core-shell fibrous scaffolds for wound healing and skin tissue engineering. Aloe vera extracts were encapsulated inside polymer fibers containing chitosan, polycaprolactone, and keratin using the co-axial electrospinning technique. Electron microscopic studies show that continuous and uniform fibers with an average diameter of 209 ± 47 nm were successfully fabricated. The fibers have a core-shell structure with a shell thickness of about 90 nm, as confirmed by transmission electron microscopy. By... 

An ultrafine-grained Al6063/Al2 O3 (0.8vol.%, 25nm) nanocomposite was prepared via powder metallurgy route through reactive mechanical alloying and hot powder extrusion. Scanning electron microcopy, transmission electron microscopy, and back scattered electron diffraction analysis showed that the grain structure of the nanocomposite is trimodal and composed of nano-size grains (<0.1μm), ultrafine grains (0.1-1μm), and micron-size grains (>1μm) with random orientations. Evaluation of the mechanical properties of the nanocomposite based on the strengthening-mechanism models revealed that the yield strength of the ultrafine-grained nanocomposite is mainly controlled by the high-angle grain... 

To study the effect of size and shape of metallic nanoparticle on their Curie temperature, an analytical model is proposed. The core average coordination number (CAC) and surface average coordination number (SAC) of freestanding nanoparticles are considered in the model. Clusters of icosahedral (IC) and body centred cubic (BCC) structure without any vacancies and defects are modelled. A critical Curie temperature is introduced for metallic clusters with a diameter of 2-3 nm. This critical diameter is related to clusters which the ratio of surface atoms to total atoms is about 50%. The "shape effect" is shown to be important at sizes less than 20 nm. The obtained results are supported by... 

Single-walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs) were synthesized in aqueous solutions containing FeCl2, FeCl3, FeSO4 and Fe2(SO4) 3. The effects of iron charge and the counter ions on the formation of carbon nanotubes (CNTs) were investigated. Thermogravimetric (TG) analysis indicated that carbon multilayer structures including CNTs and multishell graphite particles were formed in deionized (DI) water without the iron precursor. SWCNTs were also synthesized in the presence of the iron ions. It was also found that the mole ratio of [Fe2+]/[Fe3+] in the solution has a significant influence on the purity of CNTs and the process yield. The highest yield was... 

Uniaxial compression test at different temperatures [573 K to 723 K (300 °C to 450 °C)] and strain rates (0.01 to 1 s−1) was employed to study the hot deformation behavior of an ultrafine-grained (UFG) Al6063 alloy prepared by the powder metallurgy route. The UFG alloy with an average grain size of ~0.3 µm was prepared by mechanical milling of a gas-atomized aluminum alloy powder for 20 hours followed by hot powder extrusion at 723 K (450 °C). To elaborate the effect of grain size, the aluminum alloy powder was extruded without mechanical milling to attain a coarse-grained (CG) structure with an average grain size of about 2.2 µm. By employing the dynamic materials model, processing maps for... 

Recent strategies to locally deliver antimicrobial agents to combat implant-associated infections—one of the most common complications in orthopedic surgery—are gaining interest. However, achieving a controlled release profile over a desired time frame remains a challenge. In this study, we present an innovative multifactorial approach to combat infections which comprises a multilayer chitosan/bioactive glass/vancomycin nanocomposite coating with an osteoblastic potential and a drug delivery capacity. The bioactive drug-eluting coating was prepared on the surface of titanium foils by a multistep electrophoretic deposition technique. The adopted deposition strategy allowed for a high...