Sharif Digital Repository

Due to the negative effects of conventional plastics on the enviroment, especially in the packaging sector, extensive efforts have been put to replace these polymers with biodegradable polymers. Starch is one of the biodegradable polymers which has attracted a lot of attentions because of low cost and good processability. Native starch has the form of granule and can be processed to a continuous phase after gelatinization in the presence of a plasticizer. The resulting material is a biodegradable plastic-like material called thermoplastic starch (TPS) which is processed using conventional technologies, but suffers from low mechanical properties and high hydrophilicity. Addition of natural... 

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... 

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... 

Particulate ceramic reinforced aluminum matrix composites have high specific strength and stiffness; however, low fracture toughness and deformability have restricted their industrial applications. Among the methods introduced to overcome this shortcoming is fabricating the layered composites which contain alternative layers of aluminum (Al) and discontinuously reinforced aluminum (DRA). In this study, two different routes; i.e., "Powder extrusion - Casting - Rolling" and "Powder extrusion - Roll bonding" were employed to produce layered Al-DRA composites. After production of Al6061/SiCp composites via hot powder extrusion, mentioned processes were utilized to make DRA-Al-DRA laminate. In... 

In this research, friction and wear behaviors of 2024 Al and 2024 Al-20 vol.% SiC composite -prepared by powder metallurgy method- were investigated in the temperature range 20- 250°C. Dry sliding wear tests were conducted at a constant sliding velocity of 0.5 m/s, an applied load of 20 N, and a sliding distance of 2500m using a pin-on-disc apparatus. Some of the wear tests were carried out with artificially aged specimens in order to determine the aging effects. Worn surfaces and wear debris were also examined by using SEM, EDS and XRD techniques. All specimens showed a transition from mild to severe wear above a critical temperature. In the mild wear regime, the wear rate and the friction... 

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.... 

TLP diffusion bonding method refers to a method in which two metal pieces can be bonded by putting an interlayer between two pieces and heating to a temperature lower than base metal melting point. Theoretically, this process shows that the bonding line disappears completely at the end of the process and it is not possible to recognize it. However, these assumptions were not accomplished in practice. Therefore, various parameters such as material of interlayer, thickness of interlayer, temperature and time of bonding, temperature and time of homogenizing and applied pressure on metal pieces should be controlled to achieve the best shearing strength results. Aluminum based composites have... 

In the present research, transient liquid phase bonding of dissimilar st52 low carbon manganese steel to 304 stainless steel by pure Cu foil, in induction furnace and SIC furnace, was investigated. Samples were bonded in induction and SIC furnace at 1150 0C for different bonding times. Samples were then cut transversely and cross section of samples was examined by optical and scanning electron microscope. Complete isothermal solidification time was more than 9 hours and 90 minutes for SIC and induction furnace, respectively. Micro hardness and shear strength tests were done on samples bonded in optimum condition. Shear strength of none homogenized samples which had been bonded in SIC... 

The purpose of this study is fabrication and characterization of a mesoporous Perovskite solar cell using Barium Titanate as the mesoporous electron transfer layer. In this study, TiO2 nanoparticles and BaTiO3 oxide perovskites were prepared by sol-gel synthesis method and their pastes were applied to the conductive substrate by spin coating method and applied to electron transfer layer in perovskite solar cells. Then Perovskite solar cells were fabricated with different structures from the electron transfer layer.The results of X-ray diffraction analysis showed that pure Barium Titanate and Titanium dioxide nanoparticles were successfully synthesized with tetragonal and cubic crystal... 

Quince seed gum is a natural material that was used in Iranian traditional medicine for wound treatment. Alginate is a beneficial biomaterial that has been used in making commercial wound dressings for a long time. In this work, the preparation method and properties of films based on Alginate and Quince seed gum for drug delivery and wound healing have been investigated. According to the obtained results about crosslinking and plasticizing, the suitable condition of synthesis is 0.5% CaCl2 concentration, 2min soaking time, and 13% glycerol in crosslinking solution. In this crosslinking solution, a film with good mechanical properties (tensile strength: 13MPa, elongation: 27.3%, and Young’s... 

Many efforts have been put into increasing the efficiency of dye-sensitized solar cells that part of it has been devoted to structure and chemical composition of photoanode electrode. In this thesis, the effect of changes in the composition and its influence on light scattering ability in photoanode of dye sensitized solar cells was studied.First, the nanoparticles of titanium dioxide powder through solvothermal method as well as spherical particle and barium titanate powder by sol-gel method were synthesized. XRD and FE-SEM analyses indicated that synthesized powders are in good size and morphology regarding the intended chemical composition. Optical properties of TiO2 particles were... 

In this research, wear behaviors of 6061Al and 6061Al-20 vol% SiC composite -prepared by powder metallurgy method- were investigated in the temperature range 25- 200°C. Dry sliding wear tests were conducted at a constant sliding velocity of 0.34 m/s, an applied load of 20 N and 50N, and a sliding distance of 2450m using a pin-on-disc machine test. Some of the wear tests were carried out with artificially aged specimens in order to determine the aging effects on wear rate of composite. Worn surfaces and wear debris were also examined by using SEM and EDS techniques. Also for determining the effect of age hardening treatment on wear behavior of composite, specimens were solution treated at... 

In this project, Dissimilar Friction Stir Welding (FSW) between aluminum alloys (1100-H12 and 5083-O) and Magnesium alloy (AZ31B-O) with 3mm thickness were butt joined. Fusion welding of aluminum/magnesium alloys has failed because of forming much more intermetallic compounds. By using friction stir welded samples, effect of welding parameters such as tool travel speed, tool rotation rate, tool position respect to weld centerline, and sheet position respect to tool direction on mechanical (tensile strength, yield strength and elongation) and microstructural properties of the welds were investigated. After several tests, range of optimum parameters were obtained. In both 1100 and 5083 alloys,... 

Perovskite solar cells, with high efficiency operation, have been candidated as a cost-effective and environmentally friendly technology. Despite the great progress, there are some primarily issues remained regarding to the perovskite film and its fabrication methods. A very common perovskite cell structure is FTO/TiO2/CH3NH3PbI3/Spiro-OMeTAD/Au. Although, this structure has some advantages, lack of full surface coverage of perovskite film leads researchers to put much effort on finding other constructions. This surface inhomogeneity reduces the amount of light absorption and therefore efficiency. One way to produce a complete and uniform film is applying mixed-halide composition; such as... 

In line with advances in science and technology in the areas of robotics, artificial intelligence, computer and control, unmanned vehicles are being more utilized and focused. On the other hand, development and further advances of these vehicles is highly dependent on the level of their autonomy. Motion planning is one of the most important issues in this regard. Due to high levels of autonomy required for unmanned air vehicles (UAV), the subject of motion planning is of valuable interest in aerospace applications. The goal of the motion planning problem, that is the subject of this research, is to extract an optimal trajectory for the UAV from an initial location toward its target point... 

In the present investigation, the mechanical alloying (MA) technique was employed to produce nanocrystalline Al-Ti Powder mixtures. Elemental Al and Ti powders were mixed with different compositions (0, 5, 10, and 20 wt.% Ti) and then, milled in a vibratory mill up to 7 hr. The variations of powder morphology and particle size, apparent and tap densities, microstructure, grain size, lattice strain, and microhardness were studied with increasing the milling time. While dissolution of Ti in the Al matrix resulted to the formation of supersaturated Al-Ti solid solution in the samples containing 5 and 10 wt.% Ti, the specimen with 20 wt.% Ti, eventually, led to nanocomposite powder with... 

The aim of this research was to fabricate an in-situ Al-Al3Ti nanocomposite from pure microsized aluminum and titanium powders by mechanical alloying and hot extrusion without any usage of nanometric particles or applying secondary heat treatments. The focus of the present research was fabricating a nanocomposite material with high strength, modulus and hardness accompanied with high fracture toughness that could be comparable with aluminum alloys in terms of fracture toughness. Mechanical alloying and hot extrusion techniques were employed to produce in-situ fully dense Al-Ti composites. Platenary and high energy vibratiory mill was used to produce composites with different percent of... 

Providing more choices to customers for determining the cost of their required reliability levels is one of the most important targets of restructured power system. Centralized management of reliability in Vertically Integrated Utility (VIU) applying the same policies to different customers is replaced with decentralized management allowing customers to participate in reliability management based on their required reliability levels. In this thesis, impact of emergency demand response programs, interruptible load contract and wind farms on the long-term security constrained unit commitment has been studied. Random outages of generators and transmission lines, load forecast inaccuracies as...