Sharif Digital Repository

Gelcasting is a new ceramic forming technique getting worldwide attention. The process is based on casting of slurry; containing powder, water and water-soluble organic monomers. The premix solution was prepared using Acrylamide as a monomer and Methylene bisacrylamide as a crosslinker with AM:MBAM ratio of 25:1, and Poly Acrylic Acid Sodium as a dispersant (1 wt% based on ceramic powders weight). A series of Al2O3/ZrO2 ceramic nanocomposites with 15, 17.5 and 20 wt% content of ZrO2 and 40, 43, 45, 47, 50, 53 and 55 vol.% of solid loading were fabricated by gelcasting. After casting the mixture, the monomer was polymerized to form gel parts. Drying, burning out and sintering completed the... 

In the present work, nanocrystalline Al-4wt%Cu alloy reinforced with nanometric Al2O3 particles was synthesized by in-situ reactive milling of Al and CuO powder mixture and hot extrusion. The effect of nanometric Al2O3 particles on the aging behavior and mechanical properties of this alloy was investigated. During mechanical milling, copper oxide were reduced and dissolved in the aluminum lattice. consequently, Al(Cu) solid solution matrix was produced. Also, nanometric Al2O3 particles were also distributed in the matrix uniformly. The powder blend was then pressed in an Al can at 100 MPa pressure and subsequently extruded at 450 0C at the extrusion ratio of 16:1. The density of the... 

Polyethylene (PE) is used as an insulation material for wires and cables because of its excellent electrical properties. For such application, it can be exposed to the high energy irradiation such as gamma ray and electron beam (EB), making possible crosslinking of the PE. Most of the properties of PE are improved greatly after irradiation, but it was harden and split easily. Due to the flexibility of EVA, depending on the vinyl acetate content, it can improve the toughness of the LDPE significantly upon addition to this polymer. As a result, radiation induced LDPE/EVA blend has been a good candidate for the wire and cable insulation. Also, upon addition of a few amount of OC, different... 

Polyampholyte hydrogels are hydrophilic networks that contain both positively- and negatively-charged functional groups on their structure. Polysulfobetaines are the most important type of polyampholytes, which have been extensively studied. However, these hydrogels exhibited poor gel strength causing limitation of their applications. Consequently, much attention has been focused on the preparation of nanocomposite hydrogels with high gel strength and lower cost using organomodified clays. In this project, Novel polyampholytic superabsorbing nanocomposites based on the zwitterionic sulfobetaine monomer [3-(methacrylamido)propyl)]dimethyl(3-sulfopropyl) ammonium hydroxide (MPDSAH) were... 

Homo-polymer of Polypropylene is a commodity thermoplastic with good physical and mechanical properties along with fair recyclability and cost. However, its application is limited in some cases, especially in automotive industry, due to a lack of toughness. One of the approaches for PP toughening is the copolymerization of PP with some ethylene co-monomers. However, existence of elastomers in this kind of polymers causes a decrease in tensile properties. Besides, glass fibers improve tensile properties of homo-and co-PP and decrease toughness of co-polymers but result in an increase for homo-polymers. A rise in expenditure of energy due to increasing the processing temperature and... 

In this research, nano composite MgH2-TiCr1.2 Fe0.6 nano crystalline was synthesized by mechanical alloying and Vacuum arc re-melting (VAR). the effect of Milling conditions and adding nano crystalline TiCr1.2 Fe0.6 as a catalyst on the structure and hydrogen desorption properties of MgH2 were studied. MgH2 powder grain size after 4 hours milling gained to 15nm and strain network reached to 0.8%. Determined that the increasing of accumulated lattice strain because of mechanical milling combined with adding nano crystalline alloy TiCr1.2 Fe0.6 significantly improve the properties of MgH2 hydrogen desorption. After an hour mill working, high pressure phase of γ-MgH2 was appeared in... 

In this investigation, hydroxyapatite-carbon nanotube nano composite coatings were applied on the 316L stainless steel implants. After polishing with 1200 sand paper, stainless steel implants were coated via dip coating method. The specimens were heat treated at 350˚C after being coated with HAP and HAP-CNTs composite. In vitro test was done in simulated body fluid (SBF) in 1 to 4 weeks periods. XRD evaluation of powder obtained from sol-gel process, showed the presence of HAP and CNTs in the powders. Comparison of XRD results of HAP and HAP-CNTs powders showed the better crystalinity of composite hydroxyapatite. After in vitro tests, specimens were studied with atomic force microscope (AFM)... 

In this study, first nano structure powders of Fe3AL / Al2o3 by different percentages of reinforcement phases (10, 20 and 50 percent of volume) based on mechanical milling procedure was created. To do so, iron, Al and iron oxide (hematite) pure powder based on special weight percentages mixed with each other and milled in 20 to 100 hour periods based on two different weights of ball toward powder: 10 and 20. Morphological variations, particles sizes and powder densities, lattice strain and phase variations in different timing periods of mechanical milling process was studied by Scanning Electron Microscopy(SEM) , analyzing apparatus of particles sizes by laser , gaseous picnometer and X-ray... 

Blending can be used as one of the ways of producing materials with appropriate properties, which have many relative advantages in comparison with other methods like polymerization. Among the existing blends in the market and scientific areas, blends of polyurethane thermoplastic and polypropylene have been also studied because of its commercial importance and scientific interest. This blending can improve the mechanical properties, friction resistance, improvement of impact strength at low temperatures and improvement of plasticity properties. In this research, blends with different ratios of TPU/PP is produced by melt mixing, and for improving properties of blends, two kinds of nano fumed ... 

Polypropylene/clay nanocomposites are considered as a group of widely used nanocomposites in industrial applications due to their desired properties, yet reasonable cost. However, dissimmilar chemical nature of polypropylene and clay do not allow perfect dispersion of silicate layeres in the matrix and thus restricts full advantages of these composites.An earlier investigation in this group considered solving this shortcoming through incorporation of PA6 as an intermediate phase to enhance clay platelets dispersion. The current project follows this route via studing the influence of molecular weight of the PP matrix, compatibilzer and the mixing procedure of the compound. To investigate the... 

In this project, two multiscale modeling procedures have been implemented to study the mechanical behavior of SWCNT/polymer composites. First, a new three-phase molecular structural mechanics/ finite element (MSM/FE) multiscale model has been introduced which consists of three components, i.e. a carbon nanotube, an interphase layer and outer polymer matrix. The nanotube is modeled at the atomistic scale using MSM, whereas the interphase layer and polymer matrix are analyzed by the FE method. Using this model, we have investigated the macroscopic material properties of nanocomposite with and without considering the interphase and compared the results with molecular dynamics (MD) simulations.... 

In the preparation of nanocomposites, the multi-walled carbon nanotubes (MWCNTs) functionalized by hydroxyl groups were used. Subsequently, the polyethylene/multi-walled carbon nanotube (PE/MWCNTs) nanocomposites were prepared via in situ polymerization technique. In this study, effect of MWCNTs on the thermal degradation of these PE/MWCNT nanocomposites was investigated; the thermal degradations of pure PE and PE nanocomposites with different concentrations of nanotubes (0.5, 1.5, 3.5 wt %) have been studied by using thermal gravimetric analysis (TGA). Samples were heated to 700˚C at different heating rates (5, 10, 15, and 20˚C/min). TGA was used to investigate the effect of the MWCNTs on... 

Excellent mechanical properties and high aspect ratio of carbon nanotubes have been the reason for extensive research on nanocomposites reinforced by this nanostructure, and recently metal matrix type of these nanocomposites, due to their advantages, have received great attention. Moreover, nanoporous materials are another type of nanostructured materials which due to their very high porosity have special applications in hydrogen storage, separating molecules, purification and energy absorption. Because of completely neglecting the details of nanoscale structure and not paying attention to the length scale, classical continuum mechanics methods are not precise enough for evaluating different... 

Using materials with better mechanical properties is always advantageous. Many sectors, including automotive and aerospace industries, are always seeking new materials with better mechanical properties and lower weight. A lighter vehicle means lower emission and higher fuel efficiency. Thus, developing new methods to investigate novel materials is very important. One of these novel materials are Metal Matrix NanoComposites (MMNCs). MMNCs are fabricated using nano scale particles embedded in metallic matrix. High strength, stiffness, and hardness are the three most important mechanical properties of MMNCs. Introducing a suitable way of modeling these materials is important since it will... 

PVDF (polyvinylidene fluoride) magnetic nanocomposite films were prepared by solution casting using two types of nanomagnetic particles: (i) magnetic nanoparticles synthesized by using an alkaline solution of mixed ferrous/ferric salts along with oleic acid as a coating agent at 70˚C; (ii) Fe3O4 nanoparticles prepared by hydrolysis of aqueous solution of ferrous/ferric salts with potassium hydroxide at room temprature. Scanning electron microscopy (SEM) showed that the PVDF magnetic nanocomposite had a porous structure with Fe3O4 nanoparticles dispersed inside the porous polymer matrix. The presence of crystalline magnetite within the polymer matrix was confirmed by X-Ray diffraction method... 

Multiwall carbon nanotubes (MWCNTs) and carbon black (CB) reinforced polypropylene/polyamide6 (75/25) nanocomposites were prepared by melt compounding approach. Polypropylene grafted with maleic anhydride (PP-g-MA) was used as compatibilizer. Different amount of fillers were introduced into the polymer blends. The morphology, mechanical, rheological properties and crystallization behavior of the composites were investigated. Scanning electron microscopy was employed to study the microstructure. Differential scanning calorimetry (DSC) results showed that the addition of MWNT or CB to PP/PA6 blend resultes increase in crystallinity degree of PA6. The fillers were found to be located... 

Classical theory of elasticity, which is founded upon results of mechanical experiments on the large scale materials, has reasonable results in predicting mechanical properties. The basic idea in this theory is that stress at a point of the material is only a function of the local strain and it is independent of the nonlocal strains. Therefore, the size of the material does not play any role in analyzing mechanical behavior of materials using this theory. However, results from experiments and atomic simulations have shown that in nano scale materials, such as carbon nanotubes (CNTs) and their composites, mechanical properties are strongly dependent on the size parameters of these materials.... 

Poly (vinylidene Fluoride) (PVDF)/organoclay nanocomposite films were prepared via melt mixing, solution casting and Co-precipitation techniques. The effects of different kinds of nanoclay, sample preparation techniques and electron beam irradiation on PVDF/Nanoclay nanocomposite are reported in this research project. Differential scanning calorimetry was used to study thermal properties and crystallinity of the PVDF and its nanocomposites. The chemical and crystalline structure of the samples was analysed by Fourier transform infrared (FTIR) and X-ray diffraction (XRD) and the mechanical properties of the PVDF nanocomposite were characterized by stress strain test. The degree of... 

In this research UHMWPE/FUMED SILICA nanocomposites with different concentrations of nano fumed silica (0.5, 1.5, 2.5, 4.5 wt %) were prepared via in situ polymerization using a novel Bi-supported Ziegler-Natta catalytic systems. Magnesium etoxide and Fumed Silica functionalized by hydroxyl groups were used as supports of catalyst. TiCl4 accompanied by triethylaluminum constituted Ziegler-Natta catalytic system. Preparation of catalyst and polymerization were done in slurry phase under the argon atmosphere. Scanning Electron Microscopy (SEM) images also certified very good dispersion of fumed silica throughout PE matrix. Intrinsic viscosity measurements showed high molecular weight for... 

In recent years, carbon nanotubes have been the focus of considerable researches. Numerous investigators have reported remarkable physical and mechanical properties for this new form of carbon. In particular, the exceptional mechanical properties of carbon nanotubes, combined with their low density, offer scope for the development of nanotube reinforced composite materials. The potential for nanocomposites reinforced with carbon tubes having extraordinary specific stiffness and strength represent tremendous opportunity for application in this century and recently metal matrix type of these nanocomposites, due to their advantages, have received great attention. Classical theories of...