ADVANCED MATERIALS AND NOVEL COATINGS
Year:2019 | Volume:7 | Issue:27 |Papers Count:7

In the present study, an organic dye based on benzoxanthene-3, 4-carboxilic anhydride was synthesized to be used in dye-sensitized solar cell. In order to do that, acenaphthene was utilized as the main reagent and a series of consecutive reactions were conducted to yield the mentioned benxoxanthene-3, 4-carboxilic anhydride, including bromination, nitration, oxidation, reduction, phenolation and cyclization. In order to purify the intermediates and the final dye, recrystallization was done and followed by column chromatography and the materials were analyzed by Fourier Transform Infrared Spectroscopy, Nuclear Magnetic Resonance Spectroscopy, UV-Vis Spectrophotometery and Mass Spectroscopy. Finally, the synthesized dye was used as a sensitizer in a dye-sensitized solar cell. Photovoltaic parameters of the fabricated dye-sensitized solar cell were investigated by solar simulator and were compared to the cell fabricated by the dye N719 as a reference. Results show that the ratio of the power conversion efficiency of the cell based on the benzoxanthene-3, 4-carboxilic anhydride to the corresponding value of the cell based on N719 was approximately 34%.

Conductive polymer coatings due to their ease of synthesis and chemical and electrical properties are the focus of attention. In this research, polyaniline coating formed on commercial titanium substrate with current density of 10, 20, 30 and 40 m A /cm2 by electropolymerisation. The morphology and surface structural were analyzed by scanning electron microscopy (SEM). For investigation of chemical bonds, samples were studied by Fourier transformation infrared spectroscopy analysis (FTIR). The corrosion resistance was evaluated by potentiodynamic polarization and electrochemical impedance. SEM results showed the formation of polyaniline coating with Cauliflower structure. The average grain size of coating was about 1 micron. The results showed that a uniform polyaniline coating was formed on the surface of titanium substrate. The FTIR results confirmed the formation of polyaniline coating on the titanium substrate. Applying a polyaniline coating with current density of 30 mA /cm2 reduced corrosion current density up to 217 times in sodium in 3. 5% chloride solution.

HH grade heat resistant steels are widely used in various industries due to their high temperature strength, excellent oxidation and corrosion resistance. The major degradation of these steels is due to oxidation at high temperatures. The use of diffusion barrier coating can increase the life of these steels. One of the preferred coatings is NiAl, an intermetallic compound with high oxidation resistance. In this research, the effect of Cr2O3 and TiO2 additives on the high temperature oxidation resistance of high velocity oxygen fuel (HVOF) sprayed NiAl coating was studied. At First, the NiAl powder mechanical alloying synthesis conditions were determined using Ni and Al powders. Then, each of the Cr2O3 and TiO2 powders were separately added to the NiAl mixture 5% by weight. The powder sprayed on the surface of HH steel by HVOF method. samples, SEM scanning electron microscope, hardness test, high temperature oxidation test, and thickness test were used to investigate and evaluate the quality of coated. The results showed that the composite coated steel had less porosity and had a thicker and harder surface than NiAl coating. Thermal shock resistance of samples with composite coating is much higher than that of the NiAl coating, and the maximum oxidation resistance at 1200 ° C belongs to the NiAl-TiO2 coating sample.

In the present study, nickel-boron-carbon nanotubes coatings were deposited in AISI 4140 steel substrate by varying carbon nanotubes concentration, and then the structure and wear behavior of the coatings were taken into investigation. The structure of the coatings was studied through XRD, SEM, and microhardness tests. Additionally, the wear behavior of the samples was evaluated using pin on disk method, and the worn surface of the samples was studied by SEM and EDS analysis. Results indicated that by increasing carbon nanotubes concentration the crystallographic structure of the coatings changes from amorphous to semi-crystalline. Moreover, SEM images of the samples and microhardness results indicated that increasing carbon nanotubes concentration increases surface microhardness and lead to higher coating thickness. Increasing carbon nanotubes concentration up to 0. 6 gr/lit increased the wear resistance, and decreased the coefficient friction. However, increasing carbon nanotubes concentration up to 1 gr/lit increased the wear rate of the coating which was due to agglomeration of carbon nanotubes.

Plastisols are the liquid suspension compositions containing polyvinyl chloride resin (PVC), plasticizers and extenders, with various applications such as automobile coatings as seam sealers, which converts to the flexible material using heat. Rheological and mechanical properties of these compositions are related to the type of reinforcing materials. Reinforcing materials like nano silica has been used for improvement of different properties of these compositions. In this research, using Taguchi method and optimized model calculated from experimental design, effect of PVC type, particle size of calcium carbonate, type of plasticizer and silica particle size on mechanical and rheological properties like viscosity, strength, hardness and morphology were investigated. Particle size was evaluated using scanning electron microscopy and the results were analyzed. Based on variance analysis, it was found that for reaching to the optimum process conditions and highest strength of plastisol coatings, K-value for PVC resin must be about 70, mesh size of calcium carbonate about 1000, type of plasticizer was dibutyl phthalate (DBP) and nano silica particle size was about 200 nm.

In order to study thermal barrier coatings reliability and durability understanding their failure mechanisms is crucial. These coatings are used in high temperature and extreme heat gradients working conditions. In this paper an overview of failure mechanisms of air plasma spray thermal barrier coatings under various thermal and mechanical loading has been carried out. Since the costs of experimental tests with real working conditions of these coatings are very high and there are many limitations for these methods in terms of their performance conditions, these methods cannot provide the actual conditions for TBC to reflect well. Hence, the finite element methods play an important role in study of these issues and it is expected for these methods to be able to determine the TBC failure patterns under real conditions. In this paper the applicability of new finite element methods to simulate the failure mechanisms of thermal barrier coatings under thermal and mechanical loads has been discussed. Some of these methods are virtual crack closure technique, extended finite element method and cohesive zone model. Meanwhile, a comparison between these finite element methods in terms of advantages and limitations have been made.

The focus of this study is on the effect of citrate as chelating agent on the formation of morphology of hydroxyapatite particles synthesized by hydrothermal method. The powder samples were characterized by various techniques. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy confirmed the formation of crystalline powder and purity in the synthesized hydroxyapatite. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies revealed the importance of Ca/citrate ratio in regulating the particle morphology. In the presence of citrate under hydrothermal process, a two-dimensional monetite phase evolved into three-dimentional hydroxyapatite microspheres with an average diameter of 4-6 µ m. The results also indicate that the surface morphology of microspheres can be engineered from nanosheets to nanorods by regulating chelating agent concentration. The BET specific surface analysis showed an increase in the surface area with the increase in the citrate ion concentration. The observed specific surface area of microplates was 30 m2/g in absence of citrate, which increased to100 m2/g for microspheres. The BJH pore size distribution was in the range of 8-20 nm.