Sharif Digital Repository

It is well known that the classical continuum theory does not consider size effect in predicting material’s behavior, however at the micro and nano scales, this effect is not negligible and the classical theory has deficiencies at these scales. To take into account the size effect, higher order continuum theories introduce new material constants into the formulation. One famous version of these theories is couple stress which is applied in this research. This theory considers size effect of inhomogeneity by employing Characteristic length of materials. Quasi-static couple stress and classical dynamic approaches do not include explicitly the size of the material unit cell in the formulation... 

TiO2 is one of the most frequently used photocatalyst materials. Porous TiO2 nanostructure has drawn much attention recently due to high decomposition rate of organic pollutants. In this thesis, TiO2 nanoparticles were synthesized via sol-gel method and were coated on cotton and jute fiber separately; besides, the impregnated fibers were heat treated to eliminate cellulose. Titanium tetraisopropoxide (TTIP) was used as a precursor and two solutions, acidic and alcoholic, were used as the primary solutions for synthesis. In acidic solution, the crystalline phase and size distribution of TiO2 nanoparticles were evaluated with changing pH.Then, the appropriate pH was chosen for coating. In... 

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... 

H2S is a toxic gas used in chemical laboratories and industries. H2S is also liberated in nature due to biological processes and also from mines and petroleum fields. At some threshold level, exposure to concentrations over 10 ppm can result in headaches, irritability, dizziness and in some case leads to death. So that introducing sensors which sense H2S at ppm level with the low response time is so essential. The present work emphasizes on H2S resistance-sensing properties of pure and Pd doped WO3 films prepared by Arc discharge method. XRD, SEM, EDAX and XPS were applied to analyze crystal structure, morphology and chemical composition of the films. The analyzes results showed that films... 

Hydrothermal supercritical method is one of the most suitable methods for metal oxide nano powder, ceramics and mineral catalyst synthesis. Metal oxides nanopowder in its pure or mixed form has wide potential application as chemical industrial catalyst, hot Superconductors, magnetic material, gas sensors and car catalyst convertors. One of the most important metal oxides aspects of application is uranium oxide as nuclear reactor fuel is used. In addition, UO2 is selective catalyst for converting methane to methanol process and Decomposition of organic Chlorine material. In Supercritical hydrothermal method done in high pressure reactor with critical to fluid, is new method for the... 

Considering that automobile weigth reduction in industry is important, improvement the strength of low carbon steel sheets is important. These sheets can be supported the service condition in lower thicknesses. Bulk nano-structured materials have been mostly attracted in materials science due to their unique physical and mechanical properties. Severe plastic deformation (SPD) is one of the most efficient methods to produce ultra fine grained or nano-structured materials. Materials produced by SPD are of great importance because of (1) non-porous structure, (2) great mechanical properties such as high strength and toughness and (3) proper dimension for mechanical and physical testing. ... 

Transparent conductive materials have been widely used in semiconductor technology. Among them all, Indium tin oxide (ITO) has been utilized as electrodes in liquid crystal displays, solar cells, heat reflecting films and gas sensors.In general, the desired properties of transparent conductive oxides are high conductance and transmission. However, due to the complexity of ITO molecular structure, the film properties strongly depend on the depositon parameters.In first part of this thesis, physical properties and electrical characteristic of ITO films, different deposition techniques, and effects of deposition parameters (substrate temperature, pressure, power, etc. ) on film properties are... 

In this research, molecular structural mechanics method is employed to calculate the Young’s modules of a two-layered carbon graphene sheet. For this purpose, covalent bonds are modeled using non-linear beam elements and van der Waals interactions are replaced by nonlinear truss elements. Morse potential and Lennard-Jones potential equations are used to simulate the covalent bonds and van der Waals interactions, respectively. For each atom, van der Waals forces are considered from all other atoms located in its cut-off radius. Young’s modulus, bending modules and Poisson’s ratio of single and two-layered graphene sheets were calculated and the results revealed that Young’s modulus decreases... 

Some widely used drugs such as paclitaxel (PTX) are poorly water soluble. The clinical use of PTX with solubilizer causes side effects. These problems limited its application in treatments. In this work has been studied the effect of β-CD-g-PG (HPCD) hybrid nanomaterials, conjugated PG branches onto β-CD core, on the water solubility of PTX. First HPCD has been synthesized. Then the inclusion complex of PTX with HPCD was prepared. The inclusion complex efficiency for PTX:HPCD complex in 1:25 mole ratio was 87%. Then solubility of PTX with HPCD in water has been determined, showing Ap type phase solubility diagram. Then stability constants were calculated. The first order and second order... 

Several SPD methods have been invented for processing rods and sheets, and their physical and mechanical properties have been investigated so far. The materials processed by these methods have not been industrialized thoroughly. Moreover, in previous investigations, few works have been carried out on tubular types of materials. Thus, in this study, aluminum tube goes through a tubular channel in order to achieve different values of strains. This method is named Tube Channel Pressing. The mechanical and microstructural investigations on aluminum tubes which have been processed up to 5 passes shows that ultimate strength increases 1.7 times and sub-grains size reaches to 360 nm. Applying final... 

Mechanical properties of commercial purity copper sheets are improved and grain size of material is refined into Nano scale after using a severe plastic deformation technique called constrained groove pressing (CGP). Since there are high levels of stored energy and non-equilibrium grain boundaries in nanostructure, annealing behavior and thermal stability of material should be investigated. Although there is not a clear distinction between annealing phenomena, it is essential to determine the intervals of annealing phenomena in order to control their sequences on mechanical properties and nanostructure. Also mechanisms of annealing phenomena should be determined to realize annealing behavior... 

As aluminum sheets are used in transportation and aerospace industries, an increase in strength of these materials is important since with increasing of strength to weight ratio, energy and materials are saved. Recently, there are a lot of interests in ultrafine grained materials obtained using severe plastic deformation (SPD). The strength of material is increased while the shape and dimensions of material are not changed during SPD processes. Due to some limitations of SPD techniques, the ultrafine grained materials cannot be still made large enough for industrial applications; also it is difficult to directly manufacture a complex structure with an ultrafine microstructure. Therefore,... 

In this work, hypereutectic Al-20Si-5Fe-2Ni powder was prepared by gas atomizing method. The alloy was fabricated by melting of commercially pure metals and re-melting at approximately 200 K above the liquidus temperature. The molten alloy was then atomized by nitrogen at a gas pressure of 0.8 MPa. The nozzle diameter was 3 mm. The aluminum alloy powders were milled under pure Argon atmosphere with a ball to powder ratio of 10:1 in a planetary ball for 12, 24, 36 and 48 hours. The gas-atomized and milled powders were then consolidated by cold sintering method. Microstructure and phase analysis were performed by SEM and XRD technique. Mechanical properties were evaluated by microhardness and... 

The goal of this thesis is to survey natural frequencis of nanostructures such as nanobeams and nanoplates using nonlocal theory of elasticity by finite element method. In nonlocal theory of elasticity,the constitutive relation appears as an integral form so that the stress of a point is a function of the strain of all points in the field such that by getting away from the assumed point, the effect of strains on the stress of that point decreases. In fact, the stress on a point is an average of stress in the field and the effect of stress of other points in determined by a function called the kernel function. In order to achieve natural frequencies and shape modes of a structure, we need to... 

Paclitaxel is using as a drug against breast and ovary cancers. Although paclitaxel has high biologic activity, it has very poor solubility in water the same as some other drugs. Since drugs should be solved in water to be absorbed by the body, for absorb enhancement, we should use carriers which includes both polar and non polar sites.
Beta-Cyclodextrin which has this feature is capable for producing inclusion complex in its hydrophobic pores with non polar materials. In this project, by adding polymeric polyglycerol branches on Beta-Cyclodextrin, a polymeric nanostructure has been developed to enhance water solubility in comparison with pure Beta-Cyclodextrin.
Study on producing... 

Nanocrystalline steel was developed by severe cold-rolling and subsequent annealing of HSLA steel with an original microstructure of lath martensite. Specimens are austenitized at 1000 ºC for 30 min followed by quenching in brine. The quenched specimens are cold rolled with 80% to 90 % reduction and then annealed at temperatures from 400 to 700ºC for 10 to 120 min.The specimens annealed at temperature 500oC for 60 min showed the multiphased ultrafine structure composed of equiaxed ultrafine ferrite grains with the mean grain size of 180 nm, nano-carbides distributed uniformly and blocks of tempered martensite. The produced nanostructured steel exhibited a yield stress and UTS, of 1280 MPa... 

Fluorapatite (FA) has been widely used on orthopedic and dentistry prosthesis due to its excellent bioactivity properties. Therefore, the aim of this work is to prepare and characterize copper doped nanostructured fluorapatite powder via mechanical alloying (MA) method using a high energy planetary ball mill.FA powder samples with the general chemical formula Cux.Ca(10-x).(PO4)6.F2 (where x is the ratio of substitution of Cu-2 by F−1) are successfully synthesized using the starting materials of calcium oxide (CaO), phosphorous pentoxide (P2O5), calcium fluoride (CaF2), and copper (II) oxide (CuO) powders under various milling times. In order to evaluate the antibacterial effect of copper,... 

The purpose of this project is to construct a gas sensor based on one-dimensional nanostructured electrodes of copper oxide. By creating of these nanostructures, can be reduced breakdown voltage of gases, including flammable, to a few hundred volts. The CuO nanowires were grown by thermal oxidation on copper substrate to form self-assembled. In this method, by heating the copper foil,Cu2O also was formed on substrate. Effects of surface tension of substrate and oxidation temperature on surface density and structure of the nanowires were studied. SEM images taken from the samples showed that the surface tensions increases the density of nanowires and increasing the oxidation temperature leads... 

NiTi is known as a most important material for manufacturing implants and other medical devises duo to its shape memory and super elasticity properties, high energy damping and high corrosion resistance.In this project the possibility of producing nano structured NiTi implant with high porosity was investigated. For reaching to nano scale mechanical alloying process was done on Ti and Ni powder as row materials. Mechanical alloying process and the possibility of reaching nano structure or amorphous phase was investigated. Space holder technic was used for reaching a porous structure. Sintering process was planned in a way to inhibit grain growth as much as possible. The samples sintered in... 

The aim of this research is preparation of tungsten trioxide nanoparticles film for hydrogen sulfide gas sensing. These nanoparticles were made by simple and inexpensive sol-gel method. To improve gas sensing properties, various precursors of copper and copper oxides were added to the sol. This solution was coated on alumina substrate by spin coating method. After annealing, sensing properties of samples were studied by measuring the electrical resistance. Best precursor and its molar percentage of copper to tungsten were selected (WO3-Cu2O (1%)). All tests for this sample were done in temperatures below 100 °C and gas concentration lower than 10 ppm. Sensitivity of WO3-Cu2O (1%) to 1 ppm...