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.... 

Abstract In this study, aluminium titanate (AT) particles and nanofibers were synthesized through citrate sol gel and sol gel-assisted electrospinning methods in both nanostructured powder and nanofiber forms. The results of X-ray diffraction analysis, field-emission scanning electron microscopy and differential thermal analysis showed that the synthetic products benefit a nanostructured nature with a grain size less than 70 nm. The optimal values for time and temperature at which a roughly pure AT is attained were determined as 2 h and 900 C, respectively. It was found that the sol gel precursor bears an amorphous structure till 700 C and begins to be crystallized to alumina, anatase and AT... 

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... 

To enhance physicomechanical properties and bioactivity of fibrous membranes for wound dressing and tissue engineering applications, novel composite scaffolds consisting of fibrous mats and thermosensitive hydrogel particles were prepared by concurrent electrospinning and electrospraying technique. The composite scaffolds were composed of keratin/bacterial cellulose fibers (150 ± 43 nm) which are hybridized with hydrogel particles (500 nm to 2 μm) based on nonionic triblock copolymers conjugated with Tragacanth gum (TG). FTIR and H-NMR studies indicated ester reactions between carboxylated copolymers and TG through carbodiimide crosslinker chemistry. The hydrogel particles were uniformly... 

Al-Zn-Mg-Cu alloys (7xxx series Al alloys) are extensively used for their superior mechanical and corrosion performance. These properties are microstructure-sensitive and highly dependent on the formation, growth and coarsening of precipitates. To date, a wide variety of ageing procedures have been developed to tailor the evolved microstructures so as to yield a good combination of mechanical capacity and corrosion resistance of 7xxx series Al alloys. Among these methods, isothermal ageing, multi-stage ageing, non-isothermal ageing, retrogression and re-ageing (RRA), and stress ageing (i.e. creep ageing) are the most significant. In the present review, all of these approaches are... 

Aluminum-Al3Ti reinforced MMCs were produced with a large amount (up to ~30 vol%) of Al3Ti phase via mechanical alloying, hot extrusion and heat treatment (as a supplementary process) of the Al–Ti elemental powder mixture, respectively. Samples in each stage were studied precise and comprehensive by field emission electron microscope, energy dispersive spectroscopy, X-ray diffraction, differential scanning calorimetry, densitometry, macro and micssro hardness, nanoindentation and tensile tests. The results indicated that after 4-h vibratory milling, the aluminum crystallite size reached 63 nm and Al3Ti phase formed in powder mixture. After hot extrusion, the volume percentage of Al3Ti... 

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... 

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... 

In this research, the possibility that nanostructured aluminium titanate (tialite) powder can be used as a chemical source for producing Al2O3 and Al3Ti precipitates in aluminium matrix composites has been investigated. Optical microscopy, FE-SEM, XRD, DSC and TGA examinations were used to characterize the synthesized specimens. The results showed that a porous structure and inferior mechanical properties were obtained in as-sintered samples. The further thermomechanical treatments i.e. cyclic rolling and hot extrusion improved the mechanical properties and led to a dense microstructure with a homogeneous distribution of Al2O3 and... 

The present work focuses on the preparation of V2C MXene from Al-V2O5-C mixture heated in a microwave and etched under HF-based process. In the first stage of process, microwave heating caused the formation of an uncommon periodic pattern of V2AlC-Al2O3 MAX phase. In the second stage of process the aggressive leaching (temperature of 80 °C for 96 h) was performed in HF to remove the interlayer aluminum and Al2O3 particles as impurities. The leaching was not completed at room temperature even after 24 h. XRD and FESEM analyses confirmed the successful formation of V2C MXene and its distorted layer, respectively. HRTEM, XPS and Raman analyses also confirmed a perfect structure of V2C MXene. It... 

The technological and industrial needs for development of fully dense nanocomposites have led to significant advances in spark plasma sintering (SPS) technique and its enhanced forms. This technique has opened up a new prospect over carbon nanotube (CNT)-metal matrix nanocomposites (MMNCs) with superior physical or mechanical characteristics. To date, a large number of authentic papers have been published over this ongoing field, but have not been comprehensively reviewed. The pertinent research works cover some significant aspects of CNT-MMNCs requiring a concise review on (i) the potential phase transformations of pure CNTs and microstructure evolution; (ii) the novel approaches for... 

The thermal decomposition of Aluminum Titanate in exposure to pure Aluminum was examined both in powder and in bulk form. Optical microscopy, FE-SEM, XRD, DSC and TGA examinations were conducted to take the possible chemical reactions between Aluminum Titanate and Al into consideration. It was found that as Aluminum Titanate particles are exposed to Al matrix, the thermal stability of Aluminum Titanate is degraded and its decomposition temperature is reduced from 850°C to 550°C. Also, the chemical reactions between Aluminum Titanate and Al start along the interfaces, and the reaction products, i.e. Al3Ti, Al2O3, TiO2 and O2 gas are left there. A mechanism was suggested to describe the... 

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 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,... 

In this study, aluminum titanate (Al2TiO5)-based nanostructure with the outstanding photocatalytic performance was prepared via the simple citrate sol-gel method. The effects of thee operational variables such as pH, temperature, catalyst dosage, and initial dye concentration on the photodegradation efficiency of methylene blue (MB) were explored in some details. The results showed that compared to TiO2, AT benefits a superior photocatalytic activity due to its narrow band gap (2.88 eV) and low recombination rate of charge carriers. Increasing the wastewater temperature from 25 to 60 °C can improve the degradation percent from 22.15 to 52%. Based on the thermokinetic calculations, the... 

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...