Sharif Digital Repository

Polycarbonate (PC) is known as one of the engineering plastics with remarkable mechanical properties, but the application of this polymer is limited due to its high notch sensitivity. Blending polycarbonate with other polymers such as acrylonitrile butadiene styrene (ABS) is a method to resolve this disadvantage. PC/ABS blends are commonly used in automotive industry, electrical and electronic devices. As PC and ABS are not completely miscible, a variety of compatibilizers are used to achieve a suitable microstructure and high engineering properties. Considering crucial applications of PC/ABS blends, different flame retardants are also used to reduce the flammability. These flame retardants... 

Recently, Polypropylene has been extensively used in a variety of applications in the polymer industry, but its quite low stiffness and toughness limit this polyolefin’s application in the engineering functions; thus, the market of polymer blend and composite manufacturing has grown noticeably in the last few years. In the current project, short Flax fibers are used in order to reinforce the PP matrix. Firstly, Flax fibers were washed with the gentle and harsh condition during the alkalization process, then the optimized alkalization condition was determined through comparison of results from X-ray Diffraction (XRD ), Attenuated Total Reflectance FTIR (ATR-FTIR) and microscopic surface... 

Nowadays, the development of different polymer blend nanocomposites is of great importance for achieving electrical and antistatic properties for various applications such as auto parts and the packaging industry. Immiscible polymer blends with conductive nanoparticles such as carbon nanotube, graphene, etc. can reach the conductivity threshold with low amounts of nanoparticles and produce desired electrical properties. In the present study, we have attempted to develop a polystyrene(PS)/ethylene-octene copolymer(EOC)/carbon nanotube(CNT) blend nanocomposite with suitable electrical conductivity. The compounding was performed by melt mixing at two weight percent of 80/20 and 50/50 (PS/EOC)... 

As contrast enhancement agent, two different structures of superparamagnetic nanoparticles were synthesized. Iron oxide nanoparticles were prepared through an alkaline coprecipitation method of Iron (II) and (III) ions. PEG-6000 was used as biocapping material and its effect on particle size, colloidal stability and cytotoxicity was evaluated. On the other hand, novel core/shell structures were produced by NaBH4 reduction process of iron (III) in an aqueous media following by further oxidation by two different methods using (CH3)3NO oxygen transferring agent and exposure to oxygen flow. In both cases, structural examinations were conducted via X-ray diffraction, electron microscopy and... 

The microstructure, morphology and quality of the perovskite organic-inorganic layer as an absorber layer in perovskite solar cells has a significant role on the efficiency and energy conversion of the device. Different solvent engineering methods have been employed to prepare the perovskite layer with the desired properties and thier reproducibility have been studied. Herein, we applied a two-step solution approach by solvent engineering method, using solvents such as isopropyl alcohol, acetone and thier mixture, for preparation of lead iodide films. Moreover, their metallurgical and photovoltaic properties were investigated. The impact of solvent engineering, using solvents such as... 

Surface tension is the most important interfacial parameter of a liquid. This quantity plays a key role in many processes such as extraction, distillation, absorption and chemical reactions. Various methods are proposed for measuring this quantity among which, the laser based methods are the most accurate ones. Unlike most of the mechanical methods, laser based methods remotely measure the surface tension. The aim of the current thesis is to measure the surface tension using laser beam, more specifically using homodyne detection system. This method implemented in both reflected and transmitted modes. In each of the mentioned methods, first the laser beam was incident to the liquid-air... 

Today, base lead piezoelectrics are the center of attention due to their very good electrical properties, and low cost of production. Among these ceramics are PZT which is a combination of Pb(ZrxTi1-x)O3 and PCN which is a combination of Pb(CoxNb1-x)O3. PZT is a normal piezoelectric whose dielectric properties would be improved if relaxor is added. PCN is ferroelectric with perovskite structure and curie temperature -27℃ which is known as a relaxor with high constant dielectric properties. In this research, adding PCN to PZT was done by sol-gel seeding method. Calcination at a temperature of 900℃ was causing the creation of single-phase perovskite powder. After that, conventional sintering... 

The aim of this study is to investigate the effect of Copper oxide on the microstructure, properties, and grain growth kinetic in Tin oxide- Based varistors. Copper oxide was mixed in Tin oxide with different concentration, including 0, 0.1, 0.25, 0.5, and 1 mol% and the samples were sintered at 1250, 1300, and 1350 oC. Then, phase and microstructural characterization was investigated and consequently, electrical properties were evaluated. According to results, Copper Oxide with forming the liquid phase through the sintering process, accelerated grain growth. It was found that, by increasing concentration of CuO, mean grain size was increased from 2.6 µm in 1250 oC and 5 hours to 17.1 µm... 

In this research, the surface of multi-walled carbon nanotubes (CNTs), as template, were coated by Lead zirconate titanate (PZT) with composition of Pb(Zr0.52Ti0.48)O3 via sol-gel process. The final product is called PZT-CNT hybrid material. For functionalizing of CNTs, benzyl alcohol was used. Simultaneous thermal analysis (STA) proved that the as-derived amorphous material crystallized at 520 ˚C. Scanning Electron Microscope (SEM) images verified the deposition of a uniform coating of PZT on the surface of CNTs and proved that the functionalizing treatment was done successfully. X-ray diffraction (XRD) showed that the crystal structure of the hybrid was tetragonal perovskite.... 

Ultrasound waves have been one of the passions of researchers of different fields for many years. In recent decades the potential of ultrasound waves for trapping and manipulating micro-particles has been noted by many researchers. “Acoustic Tweezers” is the name given to this application of ultrasonic devices. The advantages of this device over its optical counterpart, named “Optical Tweezers”, are its low price, ease of use, biocompatibility and its capability of being used in opaque media. In acoustic tweezers, particles can be trapped either by making standing acoustic waves, or by making highly focused narrow beams and trapping the particles in potential wells. In this research... 

Lipid bilayers are one of nature’s solutions to confine and compartmentalize molecules and microorganisms. Usually, the thickness of the membrane is very small compared to the length scale at which it is studied. Therefore it is convenient to represent it with a 2-dimensional surface that has a stretch, shear, and curvature energy. Triangulated surfaces are the most popular discretization method to study the mechanical behavior of vesicles and fluid membranes since their elastic and bending moduli can be rigorously defined. Fluid membranes pose a particular challenge because they do not have a shear modulus. The dynamic triangulation algorithm is the state-of-the-art method developed to... 

Composites are made to obtain several mechanical and physical properties selectively. But joining and manufacturing of complex shapes restricts their usages. Transient liquid phase (TLP) bonding is a novel method for joining of these materials without any defects that occur in other welding methods, such as melting or solid state methods. In this research, temperture gradiant TLP bonding of AA6061/SiC/15p using gallium as interlayer was performed. To obtain the optimum conditions, joining was performed at 260, 310, 360 and 410 ˚C, and pressure of 5 and 10 Mpa with holding time of 5 and 10 minutes, the joined samples then solutionized at 530˚C for 70 minutes. Optical and scanning electron... 

The goal of this project is production of composite laminated sheetswith bimodal microstructure using ARB process. It is planned to produce a laminated sheet having bimodal grain size distribution in microstructure to increase the formability while maintaining the strength. Two different aluminum alloys including AA 1050 and AA5083 were ARB processed up to 9 cycles, Then the ARB samples were annealed under controlled temperatures and times. Due to structural differences like stacking fault energy,stored cold work energy and solute atoms concentration, annealing ofThese two alloys lead to different recrystallized grain sizes. In order to evaluate the recovery and recrystallization behavior of... 

Last generation of solar cells which are organo-metal halide perovskite solar cells (PSCs) with power conversion efficiency over 20% are increasingly comparable to the silicon types, these PSCs are poorly stable under working environment. Carbon-based PSCs with lower cost and more stability seem a better choice for commercialization in future. In these PSCs TiO2 and NiO are working as electron and hole transporting materials, respectively. In addition, ZrO2 film between two mentioned layers works as a buffer layer to prevent direct contact. In this thesis, the initial powder, necessary for fabricating the buffer layer is synthesized at the first place. Then, since the printing method is a... 

In recent years, due to greater attention scientific communities to environment and environmental friendly material, use of natural fibers as reinforcing the polymers has increased significantly. High specific strength, low density, cheap, stiffness and recycled by nature, are including promotional items using natural fibers as reinforcing in the polymer composites. In This study has tried in the first place an appropriate method for producing polypropylene composites reinforced with short jute fibers should be presented and then the physical and mechanical properties of composites will be investigated. Used MAPP and Silane for compatibility took improved between natural jute fibers as a... 

Because of low friction coefficient, Copper-Graphite and Copper-Babbitt composites can be used as brushes and bearing materials instead of materials containing lead which cause environmental problems. So far, many methods such as powder metallurgy and centrifugal casting have been used to fabricate Copper-Graphite composites. The most important problem of these methods is agglomeration of Graphite particles. Simultaneous stirring of samples during fabrication process which is one of the features of friction stir processing (FSP), can solve the problem. Recently, FSP has been used for fabricating surface composite for the purpose of producing hard and wear resistance layers on ductile... 

In this study, friction stir lap welding of Al-5083 alloy sheets with 3 mm thickness to St-12 steel sheets with 1 mm thickness (joint without intermediate layer) and to Al-1100 clad St-12 sheets (joint with the Al-1100 intermediate layer) was investigated. The cladding process was done by rolling. For each type of joints, the bonding mechanism, optimum process parameters to reach the joints with the highest fracture loads and also the microstructure evolutions at the joint region were studied. Furthermore, for the joints without intermediate layer, the effects of the Al-5083 annealing treatment before welding and the post-weld heat treatment of the joints on the fracture loads were explored....