فصلنامه علوم و مهندسی سطح ایران
پیاپی 57 (پاییز 1402)

In the petrochemical industry and in the cracking process, during the reactions that lead to the production of such products as ethylene and propylene, unfavorable reactions are also formed, which cause the formation of coke in the furnace coils. Appropriate coating of the steel can increase the resistance to hot corrosion and high temperature oxidation, largely prevent coke deposition and result in longer life of the reactors. In this research, in order to increase the anti-coking ratio and improve the resistance to oxidation and carburization of HP-micro alloyed steel, aluminide diffusion coatings were investigated. First, the chemical composition of the substrate was determined by optical spectroscopy and, then, the aluminizing process was employed to create a diffusion coating. The coating operation was carried out at 1000 degrees C and a holding time of 5 hours. The results of the X-ray diffraction test on the aluminized sample indicated the presence of NiAl phase on the surface. In order to evaluate the resistance to coke deposition, the coking test was performed to determine the anti-coking ratio. The results showed that the aluminized specimens significantly prevented the formation of filamentary coke due to the presence of the protective oxide layer, while in the untreated steel, the initial filaments formed by the reaction of hydrocarbon and the active elements of the substrate in large amounts over the surface.

In this research, the new high entropy alloy of Al0.5CoCrFeNiNb0.5-Si0.1 was synthesized by mechanical alloying process. Then, the synthesized powder was deposited on Inconel 718 through direct laser deposition process. The effect of process parameters of laser cladding, such as laser power, powder feeding rate and scanning speed was investigated with 24 experiments for forming the optimized single-track claddings. X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) equipped with Energy Dispersive Spectroscopy (EDS) were used to characterize the synthesized powders. Also, Optical Microscopy (OM) was used for investigation of geometry features and dilution of single-track clads. The XRD patterns of powder demonstrated that a singlephase solid solution (BCC) was formed after 30 hours of milling. SEM micrographs indicated the formation of solid solution after 30 hours. Also, the EDS results confirmed the compatibility of the chemical composition of the desired alloy with synthesized sample. OM images and geometrical calculations demonstrated that increasing the laser power and reducing the scanning speed led to increasing the width of single-track clad. The thickness or the height of single-track clads also was increased by reducing the scanning speed and increasing the feeding rate. Moreover, it was investigated that the laser power had the most effect on the penetration depth and dilution. The optimal conditions for direct laser deposition of synthesized powder on Inconel 718 was laser power of 500 W, feeding rate of 100 mg/s and laser scanning speed of 4 mm/s.

In this article, nickel-boron-reduced graphene oxide (Ni-B-rGO) coatings with concentrations of 0, 6.0, 20.5, and 40 mg of reduced graphene oxide (rGO) were deposited on AISI 4140 steel. Following the electrodeposition process, the samples were nitrogen-plasma treated in an atmosphere containing 25% nitrogen and 75% hydrogen for 120 minutes at a temperature of 400 °C, and their structure and wear behavior were examined. The structural properties of the coatings were investigated using X-ray diffraction tests, scanning electron microscopy and hardness tests. Additionally, the coefficient of friction and wear resistance of the samples were studied using a pin-on-disk tester. The results indicate that increasing the rGO concentration changes the coating structure from an amorphous to a semi-crystalline state, and the addition of rGO increases the hardness and enhances the wear resistance of the coating. Adding rGO up to a concentration of 20.5 mg/L improves the wear resistance and reduces the coefficient of friction. Moreover, the plasma nitrogen treatment leads to the crystallization of the coatings due to the formation of Ni2B, Ni3B, and h-BN phases. Furthermore, a two-hour plasma nitrogen treatment increased the coating hardness from 863 Vickers to 1490 Vickers. The wear resistance of the coatings increased after the plasma nitrogen treatment, resulting in a decrease in the specific wear rate from 0.75 × 10-9 kg/Nm (untreated sample) to 0.24 × 10-9 kg/Nm.

In this research, pure Ni, Ni-Cu and Ni-Cu-Fe coatings were produced as electrocatalyst material using electrodeposition method for hydrogen evolution reaction (HER). Scanning electron microscope and X-ray diffraction were used to examine the morphology and structure of the deposited coatings, respectively. The electrocatalytic behavior of the produced coatings in 1M KOH solution was investigated by cyclic voltammetry, linear scanning voltammetry and electrochemical impedance tests. The results showed that the surface morphology changed from pyramidal and cauliflower state in pure Ni and Ni-Cu coatings respectively to micro/nano-cone state in Ni-Cu-Fe coating, respectively. The presence of Fe improved the electrocatalytic behavior by changing the electronic structure and changing the morphology of the coating surface. The best electrocatalytic behavior was obtained in the Ni-Cu-Fe coating, requires overpotential of 195 mV at a current density of 10 mA/Cm2 for the hydrogen production reaction. The Tafel slope of this coating was measured 69.4 mV.dec-1 . Also, the highest electrochemically active surface was related to this coating. This research introduces a practical and effective method to produce an electrocatalyst material with appropriate behavior.

Polyethylene terephthalate (PET) polymer, a member of the polyester polymer family, is used for the manufacture of medical implants, especially in the manufacture of artificial vessels, due to its high mechanical and chemical stability. Basically, the current research has been carried out in order to modify the surface of this polymer with the aim of producing PET with optimal surface characteristics to increase compatibility and performance in medical applications. These modifications include adjusting the contact angle, changes in the surface chemical composition, improving the hydrophilic and hydrophobic properties of the surface, and changes in the surface morphology. The aim of this research is to improve the surface properties of PET in such a way as to improve its performance and efficiency in the production of artificial vessels and other medical applications. The variables investigated in this research include treatment time, sulfur dioxide gas concentration, plasma intensity and polymer surface properties. During this research, polymer film samples were placed inside the plasma device with a vacuum bag and were exposed to SO2 plasma. The functionalization of the polymer surface with the presence of molecules or chemical groups including sulfur and oxygen was investigated by spectroscopy (FTIR) and the results of infrared spectroscopy in the sample treated by SO2 gas plasma showed the presence of peaks of symmetrical bonds of SO2 in SO3 or SO4 in the sample. approved. 3D AFM images and contact angle test confirmed the morphological changes and wettability of the polymer surface. Using the plasma method with SO2 gas is a suitable method to modify the surface of polyethylene terephthalate and strengthens the application of this polymer in the field of biomedicine.

By applying the appropriate parameters in the PACVD process, It is possible to influence and improve the performance of lowalloy steels against surface factors. In this study, low-alloy steel substrate, 34CrNiMo6 is used in order to create microstructural changes and improve its surface properties, the coating process by method PACVD Contains vapors of TiCl4, CH4 and N2 in order to apply Ti, C, N along with adding Fe to the composition of the coatings by this process. Investigations of microstructure and chemical composition by X-ray diffraction, Field emission scanning electron microscopy and energy dispersive spectroscopy (EDS) have been characterized.to check the electrochemical properties of the samples, a 3.5% wt NaCl solution was used, and potential dynamic polarization and impedance spectroscopy (EIS) tests were performed on the samples. The results of the research show that by applying more CH4 gas, the sputter rate of Fe increased and its amount was increased at the surface of the coatings, and the surface of the coatings has been improved. Also, it can be seen that the formation of C3N4 phase and the amount of nitrogen on the surface of the coatings are considered to be the determining factors of the corrosion resistance of the coatings.