فصلنامه مواد پیشرفته و پوشش های نوین
پیاپی 26 (پاییز 1397)

The solid electrolyte interphase (SEI) is a passivating film that is formed on the anode surface by electrolyte decomposition in a lithium ion battery. The proper understanding of the SEI formation process on the graphite anodes can create a wider view to overcome the challenges associated with these anodes, which lead to better cyclic performance. In this research, cyclic voltammetry, electrochemical impedance spectroscopy and cyclic charge/ discharge tests were used for graphite anode coin cell to obtain a perfect understanding of SEI formation process on the surface of graphite anode. The results of cyclic voltammetry test indicate that the large part of SEI layer is formed in the first cycle and the SEI will be stable by continued voltammetric cycles. The electrochemical impedance studies show that the charge transfer resistance (Rct) of graphite anode decreases from 122 Ω to 62.5 Ω after electrochemical cycles, which indicates the facility of the charge transfer process after the formation of the SEI layer. The results of cyclic charge/ discharge test also represent that the irreversible capacity of first cycle is consumed to form the SEI, and the reversibility has been sustained after the subsequent charge / discharge cycles.

In this study, a nanobiosensor was fabricated for ethanol gas detection, and its electrochemical response to various concentrations of this gas was studied. In the first phase, in order to fabricate this nanobiosensor, the Graphene-Oxide/Polyaniline (GO/PANI) nano-composite was synthesized. Chemical composition, morphology and the structure of the nano-composites was studied by Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), High-resolution transmission electron microscopy (HR-TEM) and X-ray diffraction (XRD). The results show that the synthesis of graphene oxide is done correctly and the polyaniline particles are well bonded on the surface of the graphene oxide sheets as physically and chemically. Owning to the formation of the correct graphene-oxide/polyaniline nano-composite the analyzes indicate that the formation of polyaniline polymer chains on the surface of graphene oxide has led to the deformation of graphene sheets, which are normally flattened and uniformed sheets into the form of non-flattened and non-uniformed sheets. In the second phase, the formed nano-composite was placed on silver coated electrodes and then, by placing the nanoparticles of tin oxide, the nanobiosensors were sensitive toward the ethanol gas. Through the amperometric experiments, responsiveness and sensitivity and selectivity of the nanobiosensors to each of ethanol, carbon dioxide, methane and ammonia gases were measured and the results showed that the sensitivity of nanobiosensor fabricated to detection of the ethanol gas is acceptable. The results of the electrochemical tests showed that the nanobiosensors also have responded slightly to ammonia and methane.

In this work, the influence of oxygen vacancy defects, crystallite shape and size on oxygen diffusion in SrTiO3 nanocubes and nanowires has been studied by molecular dynamics simulation method. The SrTiO3 nanocubes with different sizes and nanowires with different lengths and axial direction of [001], were considered for this purpose. The oxygen vacancies ranging from 0 to 5% were created by random deletion of oxygen atoms from perfect SrTiO3 structure. All of the simulations have been performed at 1000K and atmospheric pressure by using Buckingham + columbic potential. The diffusion process of oxygen atoms was investigated by analyzing the mean square displacement curves. The achieved oxygen diffusion coefficients have a good agreement with experimental reports. In addition the results show that diffusion constant of oxygen atoms in individual nanocubes are increased by decreasing the size of nanocubes. The results also show that in individual SrTiO3 nanowires, the oxygen diffusion process is increased by increasing the length of the nanowires.

In this research, we tried to prepare the aqueous suspension of zirconia nanoparticles at different pH and investigate their rheological behaviors. The solids content was 40% by weight and the suspensions were prepared without additives. In this study, the pH value was varied from 3 to 8, and the rheological behavior (shear stress in terms of shear rate and viscosity in terms of shear rate) was investigated; also, the theoretical viscosity was calculated using existing relationships, and compared with experimental viscosity. Based on theoretical relationships, high viscosity values were predicted for nano zirconia suspensions, while in reality the prepared zirconia suspensions showed less viscosity and more ideal behavior. The results also indicated that the addition of Dolapix CE64 dispersant was lead to the Newtonian like behavior. The calculated rheological coefficients also proved that at pH=4 and using Dolapix, better conditions could be obtained for rheological and deflocculation and increased suspension stability.

We synthesized various types of barium and strontium hexaferrite nanoparticles using barium chloride and strontium nitrate salts by co-precipitation method in microwave. The solvent was either water, ethylene glycol or mixture of them with three different natural surfactants. XRD and SEM analysis were performed to evaluate the morphological characters of the products. The mean diameter of barium and strontium hexaferrite particles in all products was less than 100 nm, indicating successful formation of nanoparticles. The purity of nanoparticles was documented by FT-IR spectrometry. SEM analysis shows that the nanostructures of products would change with respect to type of solvents and surfactants. So it is possible to change the size and structure of nanoparticles for various purposes with manipulation of primary parameters. In the second phase various proportions of barium chloride and strontium nitrate were used for production of nanoproducts. All the products had pure nanoparticles of barium and strontium hexaferrite which again was confirmed by XRD analysis. VSM analysis was performed to study the ferromagnetic characteristics of the products. Hysteresis curves disclosed that all the products have ferromagnetic properties. Strontium hexaferrite nanoparticles are hard ferromagnetics and barium hexaferrite nanoparticles are soft ferromagnetics and nanocomposite barium/strontium hexaferrite nanoparticles have the intermediate ferromagnetic properties.

Using aliphatic polyamides in electrospinning is very interesting due to their unique properties such as processability. But these polymers have some disadvantages of low dimensional stability and poor thermal stability that limited their use. To solve this problem, various methods such as polymer blending have been suggested. In this research, for the first time, a newly synthesized poly (amide-imide) (PAI) polymer was added to polyamide 66 (PA66) and nanofibers fabricated from PA66/PAI blend with different amounts of PAI polymer. Morphology, dynamical-mechanical properties and thermal stability of nanofibers were analyzed by SEM, DMTA, and TGA, respectively. SEM images revealed that the PA66/PAI nanofibers with uniform structure and without beads were prepared even for nanofibers containing 50% PAI. Moreover, with increasing PAI polymer content in PA66/PAI solution, the average nanofiber diameter increased from 319±66 nm for neat PA66 to 522±65 nm for nanofibers containing 50% PAI polymer. DMA results showed that the storage modulus of PA66/PAI nanofibers in both glassy and rubbery regions were higher than that of neat PA66 nanofibers. At 60 °C, the storage modulus values for neat PA66 nanofibers and PA66/PAI containing 50% PAI were 16.85 MPa and 70 MPa, respectively, showing about four times increase. Furthermore, by incorporating PAI polymer into PA66 matrix, glass transition temperature was moved to higher temperatures. TGA data indicated that with increasing the content of PAI polymer, thermal stability of PA66/PAI nanofibers improved significantly; 65 °C increase in Tmax was obtained for nanofibers containing 50% PAI as compared to neat PA66 nanofibers.

Creating of resistant and anti-corrosion coatings in nano dimensions are widely used in various industries. The quality of the coating is related to the collision of the nano droplet on the surface and then spreading on it. In many cases, the oblique surface is in the front of the spray nozzle, and then the nano droplet collides obliquely with a surface. Due to expensive and time consuming of the experiments and simulations, model determination for illustrating the effects of the factors on the nano-droplet spreading is very important. In this research, the multivariate regression model is being proposed for predicting the nano-droplet spreading data. The nano-droplet spreading has been depended to the speed and impact angle on the surface and that for this reason five models have been considered. The results for comparing the provided models show that the proposed non-linear regression has the most efficient and lowest error and has a high fit with optimal output. Also, the residual analysis of the proposed model accepts the normality assumption. Moreover, the correlation between the speed and nano-droplet spreading is 0.95 which is at a very high level.