Modification of as-cast Al-Mg/B4C composite by addition of Zr

Zirconium was used in Al-Mg/B4C composite to improve compocasting efficiency by increasing particle incorporation. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) results revealed that by addition of zirconium a reaction layer containing Zr, Al, B and C is formed on the interface of B4C-matrix. X-ray diffraction (XRD) analysis of extracted particles unveiled that the ZrB2 phase is the main constituent of this layer. Formation of ZrB2 is an exothermic reaction which can rise temperature locally around particles and agglomerates. Rising temperature around agglomerates in conjunction with turbulent flow of melt facilitates agglomerates wetting and dissolving into molten aluminum. As the result, final product contains more uniformly distributed B4C particles. Besides enhancing compocasting efficiency, addition of Zr and formation of reaction layer by improving particle matrix bonding quality, led to increase in ultimate tensile strength and elongation of the composite around 8% and 30%, respectively. SEM observations of the fracture surfaces confirmed that a proper bonding presents at the interface of particles and matrix in presence of Zr.Peer ReviewedPostprint (author's final draft

Dynamic deformation response of Al-Mg and Al-Mg/B4C composite at elevated temperatures

The dynamic deformations at high temperatures of Al-3 wt%Mg alloy and Al-3 wt%Mg/B4C composites with different volume fractions and particle sizes were studied using a dilatometer deformation instrument and a split Hopkinson pressure bar operating at strain rates of 10–1000 1/s. A comprehensive analytical procedure was developed to correct the effects of adiabatic heating, friction at interface of the specimen and bars, and strain rate variation, on flow stress curves. Then based on corrected data, a physical based constitutive equation was developed for modeling and prediction of flow stress. It was observed that composites in comparison with single phase alloy, after initial straining, showed lower hardening rate which is unexpected. EBSD micrographs and finite element analysis were used to investigate microstructural evolution and deformation condition around particles. It was concluded that particle fracture during deformation which is more expectable in larger particles, and also higher adiabatic heating in composite and not recrystallization related phenomena, are the main reasons for softening of stress flow curves at large deformation.Peer ReviewedPostprint (author's final draft

Microstructural investigation of Al-Mg/B4C composite deformed at elevated temperature

The microstructure evolution of Al-3wt.%Mg reinforced with 10¿vol% B4C during isothermal compression at temperatures ranging 300–500¿°C at strain rates of 0.001–10 s-1 was investigated by electron backscatter diffraction (EBSD). According to the results, at strain rates lower than 0.01 s-1 and temperatures higher than 400¿°C, the grain size distribution in the microstructure is uniform, dynamic recovery is the predominant softening mechanism and continues recrystallization through lattice rotation is responsible for grain refinement. However, during deformation at higher strain rates or lower temperatures, deformation zones appeared in special locations around particles where microstructure is formed by recovered and hardened grains, and particle stimulating nucleation leaded to partially discontinues dynamic recrystallization which in turns promoted finer average grain and sub-grain size than those in single phase Al-Mg alloy. Moreover, it was found that the variation of grain and sub-grain size with deformation parameters (Zener-Holloman parameter (Z)) can be described by a power law type equation rather than by an initially expected exponential expression.Peer ReviewedPostprint (author's final draft

Mutagenic effects of nanosilverconsumer products: A new approach to physicochemical properties

Serious concerns have been expressed about potential health risks of Nano silver containing consumer products (AgNPs) therefore regulatory health risk assessment on such nanoparticles has become mandatory for the safe use of AgNPsinbiomedicalproducts with special concerns to the mutagenic potentials. In this study, we examined the inhibitory and mutagenicity effects of AgNPs in three different sizes of three colloidal AgNPs by Minimal Inhibitory concentration (MIC), Minimal Bactericidal Concentration (MBC) and Bacterial Reverse Mutation Assay (Ames test).All samples were characterized by transmission electron microscopy (TEM), X-Ray Diffraction (XRD) and Dynamic Light Scattering (DLS). DLS analysis showed lack of large agglomeration of the AgNPs and TEM results showed the spherical AgNPswith the average sizes of 15, 19.6, 21.8 nms. Furthermore the XRD analysis showed the crystalline samples with a face centered cubic structure of pure silver.AmestestresultsonColloidal silver nanoparticles showed lack of any mutation in TA100, TA98, YG1029S. typhymuriumstrains. In addition colloidal silver nanoparticles reduced the mutation ratesin all three strains in a concentration dependent manner.This finding creates a new issue in the possible antimutagenic effects of colloidal AgNPsas a new pharmaceutical productwhich should be consideredinfuture studiesby focusing onthephysicochemical properties of AgNPs. © 2015 by School of Pharmacy Shaheed Beheshti University of Medical Sciences and Health Services

Accumulative roll bonding of aluminum/stainless steel sheets

An Al/Stainless Steel/Al lamellar composite was produced by roll bonding of the starting sheets at 400 °C. Afterward, the roll bonded sheet was cut in half and the accumulative roll bonding (ARB) process at room temperature was applied seven times. As a result, the central steel layer fractured and distributed in the Al matrix among different layers introduced by the repetition of roll bonding process. The tensile results showed that the roll bonded sheet has much higher strength and strength to weight ratio compared with the initial aluminum sheet as a result of the presence of continuous steel core. However, poor ductility properties were observed during tensile test, which were ascribed to the increasing deformation resistance and localized thinning of the central stainless steel sheet during the roll bonding process. The ARBed sample exhibited lower strength compared with the roll bonded sheet due to the breakup of stainless steel layer into many small segments. Anyway, an ultrafine grained microstructure with average grain size of 400 nm in the aluminum matrix and 71% strain-induced martensite in the steel segments were detected by the electron backscattered diffraction (EBSD) technique, which were found to be responsible for the enhancement of mechanical properties compared with the initial aluminum sheet.Peer ReviewedPostprint (published version

Texture development during hot deformation of an Al/Mg alloy reinforced with ceramic particles

Al-3Mg alloy reinforced with B4C particles in volume fractions of 5, 10 and 15% were subjected to hot deformation to investigate the impact of presence of ceramic particles and deformation condition on final texture. Single-heat hot compression test was performed at temperatures of 300–500¿°C with strain rates of 10-3 to 10 s-1. The electron backscatter diffraction method was applied to evaluate the final texture and microstructures. It was observed that the {110} fiber formed during deformation was intensified by increasing the Zenner-Holloman parameter, while deformation at lower Z makes {100} fiber pervasive throughout the matrix. Developing {100} fiber in such condition leads to continual softening of flow stress. Presence of particles by promoting particle stimulating nucleation mechanism at high Z and restricting grains rotation at low Z led to lower final texture intensity.Peer ReviewedPostprint (author's final draft

Acute and subchronic dermal toxicity of nanosilver in guinea pig

Silver has been used as an antimicrobial agent for a long time in different forms, but silver nanoparticles (nanosilver) have recently been recognized as potent antimicrobial agents. Although nanosilver is finding diverse medical applications such as silver-based dressings and silver-coated medical devices, its dermal and systemic toxicity via dermal use has not yet been identified. In this study, we analyzed the potential toxicity of colloidal nanosilver in acute and subchronic guinea pigs. Before toxicity assessments, the size of colloidal nanosilver was recorded in sizes <100 nm by X-ray diffraction and transmission electron microscopy. For toxicological assessments, male guinea pigs weighing 350 to 400 g were exposed to two different concentrations of nanosilver (1000 and 10,000 μg/mL) in an acute study and three concentrations of nanosilver (100, 1000, and 10,000 μg/mL) in a subchronic study. Toxic responses were assessed by clinical and histopathologic parameters. In all experimental animals the sites of exposure were scored for any type of dermal toxicity and compared with negative control and positive control groups. In autopsy studies during the acute test, no significant changes in organ weight or major macroscopic changes were detected, but dose-dependent histopathologic abnormalities were seen in skin, liver, and spleen of all test groups. In addition, experimental animals subjected to subchronic tests showed greater tissue abnormalities than the subjects of acute tests. It seems that colloidal nanosilver has the potential to provide target organ toxicities in a dose- and time-dependent manner

Biological and Non-biological Methods for Silver Nanoparticles Synthesis

The synthesis of metallic nanoparticles is an active area of academic and, more significantly, applied research in nanotechnology. Several methods (chemical, physical or biological) have been introduced for the synthesis of these materials. In chemical reduction methods, for example, the reducing agent is a chemical solution, whereas in biological ones, the collection of enzymes especially nitrate reductase plays this role. This study is an attempt to present an overview of silver nanoparticles (Ag NPs) preparation by various methods including biological and non-biological. Focusing on the advantages and disadvantages of each method, the paper aims to discuss some fundamental issues about biological and non-biological methods for silver nanoparticles synthesis

How does organizational learning contribute to corporate social responsibility and innovation performance? The dynamic capability view

Purpose: Innovative organizations are increasingly facing challenges in a dynamic market to address corporate social responsibility (CSR) issues; however, research on how organizational learning (OL) contributes to organizations’ social responsibility and innovation remains sparse. This study aims to bridge the gap in previous research and examines how OL and dynamic capabilities (DCs) act as drivers of CSR performance (CSRP) and innovation performance. Design/methodology/approach: This study is survey-based and uses time-lagged, multisource data from 151 pharmaceutical industry-related companies in Iran. Structural equation modeling was applied to test the validity of the measurement model and hierarchical regression was used to test the key hypotheses. Findings: DCs mediate the relationship between OL and CSRP. Moreover, CSRP significantly mediates the relationship between OL and innovation. Originality/value: Drawing on the perspective of DCs, this research is among the first to offer new insights in a new context on what antecedent conditions lead to the successful implementation of organizational CSRP and how CSRP would, in turn, lead to subsequent innovation performance improvement