Sharif Digital Repository

In this research, first thin films with nanostructures of titanium nanotube arrays (TNAs) synthesized by anodization under different applied voltage (20- 60 V) and different reaction times (120 and 200 min). The electrolyte solution for synthesizing the samples contained 90% ethylene glycol (EG), 10% DI water, 0.1 M NHR4RF and a little HR3RPOR4R to reach the pH to 5.6. The synthesized samples crystallized under annealing treatment at 500 °C (with heating rate of 9.5 °CminP -1 P). The scanning electron microscopy (SEM) analysis was indicate that the length and the inner diameter of the nanotubes have increased from 1.6 μm and 67 nm (for 30 V anodization and for 2h) to 4.2 μm and 125 nm (for... 

The main purpose of this theses is to synthesize graphene by chemical vapor deposition (CVD) of a hydrocarbon gas such as methane on the nickel foam substrate and then to characterize this kind of graphene. Graphene is a single layer of carbon atoms, discovered in 2004, which has led mankind to new eras in all fields by its extraordinary features such as extra high electron mobility, high thermal conductivity, excellent mechanical strength, optical transparence and extra high specific surface. The advantage of this method compared to other methods is that the graphene generated has a better structural quality. Graphene foam firstly, because of the continuity of the foam structure, has better... 

Hydrophobic and superhydrophobic surfaces find many applications in different fields of science. The aerospace industry is one such field that can take the advantage of superhydrophobicity for anti-icing coatings. In order to make hydrophobic and superhydrophobic surfaces on hydrophilic materials, two-step process is usually need, at first, making a rough surface and then modifying it with hydrophobic coatings with low surface free energy. In this research, we have used glancing angle deposition (GLAD) RF sputtering technique to fabricate Teflon coated tungsten on glass substrate for obtaining hydrophobic surface. GLAD approach is a method to grow structures such as nanorods and zigzag... 

One of the major challenges in Additive Manufacturing is the creation of residual stresses due to the high temperature gradient in the solidification zone. This will cause problems such as cracks in the structure, metallurgical defects as well as deformation and dimensional accuracy reduction in the finished product. The purpose of this study is to perform mathematical modeling and computer simulation of the selective laser melting process (SLM) to predict these stresses as well as identify the effective parameters on this phenomenon. The conditions were adjusted in this model with the actual coefficients of the device. Additionally, the powder used in this project is Ti6Al4V material. By... 

Lead-containing solder alloys in particular Sn-37Pb is the most common alloy used in electronics industry, this alloy has the good mechanical properties and excellent wetting properties and low prices. Recently, increasing environmental and health concerns over the toxicity of lead combined with strict legislation to ban the use of lead-based solders have provided an inevitable driving force for the development of lead-free solder alloys. A group of these lead-free solders are nanocomposite solders that because of having the reinforcement nano particles exhibit lots of unique properties, such as good mechanical and thermal properties. The aim of this research produce a new tin base... 

More than 70 weight percentage of using parts in diverse industries (such as military, civil, automobile productions and etc.) are produceed by the casting processes. For each one of the casting procceses, mold cavity is requisite for arrived molten metal in the mold cavity to get eventuated as a solidified part. Based on mold ilk, if the mold is permanent, the cast part must be capable to be remoeved from the the mold inside. For the non-permanent mold (asssuming multi-piece and non-monolithic), if the model requires to be removed from the mold inside after molding and before casting, only model (no cast part) has to be moldable (why for removing the solidified cast part from the... 

Physical and mechanical properties of cast alloys is partly a function of the morphology and volume fraction of phases from freezing. The microstructure of the eutectic solidification is function of physical properties (especially mobility and surface tension) and the volume fraction of phases involved in the evolution. The prediction of solidification microstructures will be very helpful for improving the mechanical properties of casting alloys and designing of new families of alloys. The theoretical study of the formation of eutectic microstructures is very difficult and almost impossible in general cases and empirical studies are expensive. The purpose of this study is to predict the... 

In this thesis, by deliberately embedding “emplacements” in the system to locally break the inversion and the time reversal symmetries, the manifold of all possible microstructures is navigated in pursuit of the one that can give rise to maximal magnetoelectric effect mediated by elastic energy of piezoelectric-piezomagnetic phases via their interface --- needless to mention the low intensity of such an effect in single-phase multiferroics. The configuration with the maximal coupling is sought within the context of phase-field modeling. In order to numerically track the conserved dissipative dynamics of the interface (namely, the Cahn-Hilliard equation) --- that is nonlocal by the nature of... 

bulk metallic glass Unlike metal materials that have a crystalline structure, amorphous glass is an amorphous material with an irregular atomic structure that simultaneously has the same physical properties as metals. Due to the absence of crystal defects such as dislocation and grain boundaries, these materials show unique mechanical properties such as high strength and elastic strain, abrasion resistance and proper corrosion. However, their plastic deformation is heterogeneous, concentrated, and accompanied by sudden failure. Unlike metals, these materials do not have a long-range crystalline order, and their atomic structure includes short-range and mid-range order. The short-range order...