Sharif Digital Repository

The inclusion of carbon nanotubes (CNTs) into metallic systems has been the main focus of recent literature. The aim behind this approach has been the development of a new property or improvement of an inferior one in CNT-dispersed metal matrix nanocomposites. Although it has opened up new possibilities for promising engineering applications, some practical challenges have restricted the full exploitation of CNTs’ unique characteristics. Non-uniform dispersion of CNTs in the metallic matrix, poor interfacial adhesion at the CNT/metal interface, the unfavorable chemical reaction of CNTs with the matrix, and low compactability are the most significant challenges, requiring more examination.... 

Metallic or ceramic micro/nanoporous materials have attracted particular attention due to some interesting structural and functional properties. There exist a variety of methods for producing porous materials by which optimized features can be reached. Spark plasma sintering (SPS) is one of these new-emerging approaches. This technique is often combined with conventional technologies and produce a variety of porous structures with tailorable microstructure and physicomechanical properties. This review addresses SPS and obtainable porous materials with nanoscale and microscale microstructural features. The processing methods, microstructural phenomena, and physicomechanical properties of... 

Copper slag (CS) is an industrial by-product, which is commonly disposed in engineered landfills. Prior studies have successfully incorporated CS as an aggregate phase in cementitious materials. However, the alkali-activated material (AAM) incorporating CS has been scarcely studied. Specifically, the elevated temperature behavior of AAM with CS has not been investigated previously. The present paper aims to study the effects of elevated temperature treatment on the mass loss and residual strength of alkali-activated slag mortars incorporating 0–100% (by volume) of CS with an incremental step of 20% instead of natural sand. The mass loss, compressive and flexural strengths, and microstructure... 

As a refractory ceramic, the thermal instability of aluminium titanate (AT or Al2TiO5) has been in the crosshairs of research works in recent years. The studies have indicated that different parameters such as atmosphere, grain size, additives, oxygen pressure, and synthesis method can bilaterally affect the thermal decomposition of AT ceramic and resultant physicomechanical properties. In the present study, the AT nanostructure was synthesized by a citrate sol-gel method and influence of nanostructuring nature on its thermal instability and reaction pathway was explored in some details. It was shown that the reduction of grain size down to 30 nm can destabilize AT, so that the reaction... 

ABSTRACTs: The need for fully dense material with well-engineered microstructures has led to the promising emergence of innovative sintering technologies among which the Spark Plasma Sintering (SPS) is one of the most favorite. Unlike the conventional sintering processes, SPS takes advantage of a current flow passing through the sintering die and metallic powders by which fast densification with minimal grain growth and enhanced physicomechanical properties can be obtained. Albeit there is a growing interest in the exploitation of SPS in producing sufficiently consolidated metallic parts, no analytical review has been released over the effects of SPS parameters on the densification behavior,... 

The influence of electron beam (EB) irradiation and organoclay (OC) loading on the properties of low-density polyethylene (LDPE)/ethylene-vinyl acetate (EVA) blends was investigated. The samples were subjected to the EB irradiation with the dose values of 50 and 250kGy. X-ray diffraction (XRD), gel content, mechanical, thermal, and electrical properties were utilized to analyze the characteristics of the LDPE/EVA blends with and without OC at different irradiation dosages. Gel content analysis showed that the OC promotes considerably the insoluble part so that the LDPE/EVA blends filled with OC become fully crosslinked at 250kGy; possibly through the formation of further crosslinks between... 

In this work, novel chitosan/bacterial cellulose (CS/BC) nanofibrous composites reinforced with graphene oxide (GO) nanosheets are introduced. As cell attachment and permeability of nanofibrous membranes highly depend on their fiber diameter, the working window for successful electrospinning to attain sound nanofibrous composites with a minimum fiber diameter was determined by using the response surface methodology. It is shown that the addition of GO nanosheets to CS/BC significantly reduces the average size of the polymeric fibers. Their mechanical properties are also influenced and can be tailored by the concentration of GO. Fourier transform infrared spectroscopy reveals hydrogen bonding... 

Recently, a wide variety of research works have focused on carbon nanotube (CNT)-ceramic matrix nanocomposites. In many cases, these novel materials are produced through conventional powder metallurgy methods including hot pressing, conventional sintering, and hot isostatic pressing. However, spark plasma sintering (SPS) as a novel and efficient consolidation technique is exploited for the full densification of high-temperature ceramic systems. In these binary nanocomposites, CNTs are added to ceramic matrices to noticeably modify their inferior properties and SPS is employed to produce fully dense compacts. In this review, a broad overview of these systems is provided and the potential... 

There are many engineering applications in which composite materials are required to satisfy two or more criteria regarding physical and mechanical properties. In this article, Al-matrix nanocomposites reinforced with different volume fractions of SiC nanoparticles (~ 50 nm; up to 6%) were processed by powder metallurgy (P/M) routes through mechanical milling and hot consolidation techniques. Microstructural studies showed that nano-metric Al2O3 particles with a size of ~ 20 nm and volume fraction of ~ 2% were formed and distributed in the metal matrix, owing to the surface oxides breaking. Microstructural analysis also revealed that the size of cellular structure and the density of... 

The growing industrial needs for the development of strong load-bearing materials by powder metallurgy and casting technologies has led to recent progress in the synthesis of in situ hybrid aluminium matrix composites (AMCs). Unlike their conventional counterparts, this class of engineering materials and their physicomechanical properties are sparsely investigated with no satisfactorily systematic approach and are not reviewed up to now. This is why providing an overview summarizing the formation mechanisms of in situ phases and mechanical properties of hybrid AMCs can systematically guide the research path in this field. The present review strives to categorize hybrid AMCs based on their... 

Bacterial cellulose (BC) is an extracellular natural polymer produced by many microorganisms and its properties could be tailored via specific fabrication methods and culture conditions. There is a growing interest in BC derived materials due to the main features of BC such as porous fibrous structure, high crystallinity, impressive physico-mechanical properties, and high water content. However, pristine BC lacks some features, limiting its practical use in varied applications. Thus, fabrication of BC composites has been attempted to overcome these constraints. This review article overviews most recent advance in the development of BC composites and their potential in biomedicine including... 

Effect of organoclay (OC) on the performance of styrene-butadiene rubber (SBR)/phenolic resin (PH) blend prepared by two-roll mill was investigated. The influence of OC content ranging between 2.5 and 30 phr on the performance of SBR/PH was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), interfacial energy analysis, tensile, dynamic mechanical, swelling, cure rheometry and thermogravimetric analysis (TGA). It was found that the OC is mainly localized in the SBR phase of SBR/PH blend through the kinetically favored mechanism relevant to rubber chains. The results also demonstrated the positive role of PH on the dispersion of OC. Both PH and OC showed... 

In order to regenerate bone defects, bioactive hierarchically scaffolds play a key role due to their multilevel porous structure, high surface area, enhanced nutrient transport and diffusion. In this study, novel hierarchically porous silk fibroin (SF) and silk fibroin-bioactive glass (SF-BG) composite were fabricated with controlled architecture and interconnected structure, by combining indirect three-dimensional (3D) inkjet printing and freeze-drying methods. Further, the effect of 45S5 Bioactive glass particles of different sizes (<100 nm and 6 μm) on mechanical strength and cell behavior was investigated. The results demonstrated that the hierarchical structure in this scaffold was... 

Abstract: In recent years, temporary skin grafts (TSG) based on natural biopolymers modified with carbon nanostructures have received considerable attention for wound healing. Developments are required to improve physico-mechanical properties of these materials to match to natural skins. Additionally, in-deep pre-clinical examinations are necessary to ensure biological performance and toxicity effect in vivo. In the present work, we show superior acute-wound healing effect of graphene oxide nanosheets embedded in ultrafine biopolymer fibers (60 nm) on adult male rats. Nano-fibrous chitosan-based skin grafts crosslinked by Genepin with physico-mechanical properties close to natural skins were...