Sharif Digital Repository

Corrosion of mild steel in aqueous solutions containing carbon dioxide was modelled under condition that protective iron carbonate films formed on the steel surface. In this model, the film form on the steel surface due to precipitation of iron carbonate from saturated solution. The precipitation of iron carbonate produces a porous layer on the steel surface, reducing the diffusion of species toward the steel surface. If the precipitation rate is high, the porosity decreases and the mass transport becomes slower. Therefore, formation of protective layers on the steel surface reduces the corrosion rate. In this case, the corrosion processes are controlled with diffusion of species. The model... 

Two kinds of carbon coated and uncoated 316L stainless steel are studied to use as bipolar plates in fuel cells. The results show that the conductive amorphous carbon film has a low corrosion rate in simulated PEMFC environment. Rather long term potentiostatic tests and SEM investigations indicate that carbon thin films can be a good candidate to use as bipolar plate  

The effects of Pd addition to Fe (Pd/Fe = 0, 2.5/7.5, 5/5, 7.5/2.5 and 1) and growth temperatures (920 and 970 °C) on density, diameter and growth mode of carbon nanotubes (CNTs) have been studied. SEM observations and TG analyses confirmed that the CNT yields depend on Pd/Fe ratios as (7.5/2.5) > (5/5) > Pd > (2.5/7.5) > Fe at both growth temperatures. TEM data showed that addition of Pd results in tip growth mode. From Raman spectroscopy data, the order of samples' structural quality (I G /I D ratio) are Fe > Pd/Fe (2.5/7.5) > (5/5) > (7.5/2.5) > Pd and the I G /I D ratios increase by decreasing the growth temperature. Films with higher concentration of Fe (Pd/Fe = 0, 2.5/7.5) contain some... 

Polymeric like carbon (PLC) films are grown by a capacitance coupled RF-PECVD on the grounded electrode at room temperature from liquid gas (40% propane and 60% butane) in two regimes with nitrogen and without nitrogen gas. Films are characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), Fourier transform infrared (FTIR) absorption and Raman spectroscopy. The result of FTIR analyses indicates that more than 90% of hydrogen atoms are bonded to carbon with sp 3 hybridization. The abundance of CH 3 is more than that of CH 2 and this one is more than that of CH for carbon with sp 3 hybridization in these films. The C 1s line of the XPS spectra is deconvoluted to... 

In this study the effect of deposition temperature and thickness on the physical properties of carbon films deposited by magnetron sputtering PVD was investigated. The results of Raman spectra and grazing incidence XRD (GIXRD) patterns show that the graphitization increases by increasing the deposition temperature. There is a change in deposition mechanism at 400 °C from amorphous carbon deposition to nano-structured graphite deposition. Also by increasing substrate temperature the electrical resistance of carbon films reduces significantly up to 300 °C and then remains largely constant. High intrinsic compressive stress in low temperature deposited carbon films causes cracks and... 

Two types of unfunctionalized and functionalized multi-wall carbon nanotubes (MWCNTs) were prepared to be applied in fabrication of MWCNT-ZnO nanocomposite thin films with various MWCNT contents. X-ray photoelectron spectroscopy indicated formation of functional groups on surface of the functionalized MWCNTs in the MWCNT-ZnO nanocomposite. Formation of the effective carbonaceous bonds between the ZnO and the MWCNTs was also investigated through photoinactivation of Escherichia coli bacteria on surface of the both unfunctionalized and functionalized MWCNT-ZnO nanocomposites. The functionalized MWCNT-ZnO nanocomposites showed significantly stronger photoinactivation of the bacteria than the... 

In the present work, graphene oxide (GO) and reduced graphene oxide (RGO) were incorporated at low-density polyethylene (LDPE)/ethylene vinyl acetate (EVA) copolymer blend using solution casting method. Monolayer GO with 1-nm thickness and good transparency was synthesized using the well-known Hummers's method. Fourier transform infrared and X-ray photoelectron spectroscopy data exhibited efficient reduction of GO with almost high C/O ratio of RGO. Scanning electron microscopy showed the well distribution of GO and RGO within LDPE/EVA polymer matrix. The integrating effects of GO and RGO on mechanical and gas permeability of prepared films were examined. Young's modulus of nanocomposites are... 

In this study a hot filament chemical vapour deposition (HFCVD) technique was used to prepare Fe-Cr films on Si substrate as catalysts for thermal CVD (TCVD) growing of carbon nanotubes (CNTs) from liquid petroleum gas (LPG) at 800 °C. To characterize the catalysts or CNTs, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy were used. The XPS spectra obtained at different stages of Ar+ sputtering revealed that in the depth of catalyst layers, the relative Fe-Cr concentrations are higher than the top-surface. SEM images of samples after TCVD indicate a significant CNT growing at the backside of catalyst... 

Multi-Walled Carbon nanotube (MWCNTs) films were obtained by Thermal Chemical Vapor Deposition method and coated by palladium sputtering process. Raman spectroscopy was used to study alteration in quality of the carbon nanotubes after the sputtering process. Fourier Transform Infra Red (FTIR) spectroscopy showed that hydrogenation process can reduce the C{double bond, long}O to C-O and also produce O-H bond. Furthermore, the electrical resistance measurement for Pd/MWNTs films was performed in a chamber with 1% hydrogen gas in a constant dry air flow. Hydrogen sensing behavior of the films was investigated at 50 °C. Pd/MWCNTs films presented an irreversible gas response to hydrogen in the... 

During the last decade, fabrication of high-quality graphene films by chemical vapor deposition (CVD) for nanoelectronics and optoelectronic applications has attracted increasing attention. However, processing of large-area monolayer and defect-free graphene films is still challenging. In this work, we have studied the effect of processing conditions on the self-limited growth of graphene monolayers on copper foils during low pressure CVD both experimentally and theoretically based on thermokinetics and kinetics of Langmuir adsorption. The effect of copper pre-treatment, growth time, and carbon potential of the atmosphere (indicated by the methane-to-hydrogen gas ratio, r) on the quality of... 

The WO3/multiwalled carbon nanotubes (MWNTs) hybrid films were fabricated by spin-coating on an alumina substrate. The structure, morphology, chemical composition and quality of the as-prepared WO3 nanoparticles, functionalized MWNTs and WO3/MWNTs hybrid films were studied by SEM, TEM, XRD, XPS, DLS and Raman spectroscopy methods. Results show that WO3 nanoparticles were nucleated on oxygenated functionalized MWNTs in hybrid suspension. After coating and annealing the films at 350 °C, the hybrid WO3/MWNTs films present rather linear gas sensitivity as a function of hydrogen concentrations at 300 °C. Results are discussed based on surface increase as well as development of two types of... 

We prepared Cu nanoparticles in a-C:H thin films by co-deposition of RF-sputtering and RF-PECVD methods at room temperature. By increasing Cu content in these films a nonmetalmetal (NM) transition is observed. This transition is explainable by the power law of percolation theory. The critical metal content is obtained 56% and the critical exponent is obtained 1.6, which is larger than the exponent for 2 dimension systems and smaller than the one for 3 dimension systems. The electrical conductivity of dielectric samples was explained by tunneling. Activation tunneling energy that was obtained from temperature dependence of electrical resistivity correlates with near infrared absorption peak... 

Multi-walled carbon nanotubes (MWCNTs) were immobilised with cobalt nanoparticles and analyzed by transmission electron microscopy. This modification procedure substantially improved colloidal dispersion of the immobilised MWCNTs in water and organic solvents, yielding uniform and stable thin films for modification of the glassy carbon electrode surface. The modified electrode showed an efficient catalytic role for the electrochemical oxidation of thioridazine (TR), leading to remarkable decrease in its oxidation overpotential of approximately 100 mV and enhancement of the kinetics of the electrode reaction, which can be confirmed by increasing in the peak current and sharpness of the peak.... 

We prepared copper-carbon nanocomposite films by co-deposition of RF-Sputtering and RF-PECVD methods at room temperature. These films contain different copper concentration and different size of copper nanoparticles. The copper content of these films was obtained from Rutherford Back Scattering (RBS) analyze. We studied electrical resistivity of samples versus copper content. A metal-nonmetal transition was observed by decreasing of copper content in these films. The electrical conductivity of dielectric and metallic samples was explained by tunneling and percolation models respectively. In the percolation threshold conduction results from two mechanisms: percolation and tunneling. In the...