مجله علوم و مهندسی خوردگی
سال سوم شماره 1 (پیاپی 7، بهار 1392)

In this study, the corrosion behavior of carbon steel API 5L Gr.B and injection rate of WS 86- 1 inhibitor was investigated in Piping System of Nowrooz Offshore Complexes. For this purpose, after immersion of samples at open circuit potential for 30 min, Tafel polarization and Electrochemical Impedance Spectroscopy (EIS) measurements were done. Tafel polarization curves showed that the minimum values for corrosion current density achieve at 40 ppm concentration of inhibitor. EIS results expressed that maximum values for polarization resistance achieve at 40 ppm concentration of inhibitor and demonstrated an agreement with the Tafel polarization results. Also, EIS results showed that the best electrical equivalent circuit presents two time constants. The first high frequencies time constant can be correlated with the charge transfer process and it is composed by the charge transfer resistance (R1) in parallel with the double layer constant phase element (Q1). While, the second low frequencies time constant can be related with the surface adsorption and it is composed by the adsorbed surface film resistance (R2) in parallel with the adsorbed surface film constant phase element (Q2).

The aim of this paper is to investigate the influences of different number layers of sol-gel derived YSZ coating on the electrochemical behavior of zircaloy-4 in 1 N H2SO4 solution. The coating formation process was investigated by thermal analysis (TG-DTA), elemental composition was studied by EDX, chemical composition was obtained by XRD, and surface morphology was studied by SEM. The corrosion behavior was investigated using Tafel and EIS tests. EDX results confirmed the presence of about 8 wt. % Yttria in the coating. XRD results showed the crystallization occurs at about 400 ̊C. According to SEM images, the best surface quality corresponds to 3 layers coating. The electrochemical results also confirmed the micro structural studies and the best corrosion protection performance were obtained for 3 layered coating.

Nanostructured titanium oxide coating due to the optical properties, resistance to oxidation, corrosion, and erosion has become highly regarded. There are different ways for applying nanostructure coating such as CVD, PVD, sol - gel and so on. Among of these methods, the sol - gel method was used more application, due to the ease of having such benefits as efficiency, homogeneity and uniformity of the chemical composition of the coating. So, in this paper, the intermediate coating, adhesive and porous nanostructured titanium oxide, as maintenance reserves cerium inhibitor, applied by sol - gel method on aluminum 2024, after that a layer of homogeneous, uniform and compact titanium oxide applied on the middle layer, then the structural properties, morphology and coating composition were investigated by XRD, FESEM and AFM and corrosion properties of the coatings in 3, 5% NaCl solution was measured by electrochemical techniques such as polarization and impedance measured. The results showed homogeneity, uniformity and free crack coating and also improving the corrosion resistance of Al 2024 from 36 to 2449 (KΩcm2), about 68 times. These effects can be due to self-healing mechanism of nano cerium inhibitors by releasing and producing cerium hydroxide and finally prevent cracks propagation.

In this study, nickel phosphorus coating was prepared by electrodeposition method on 304 stainless steel substrate. Microstructure and chemical composition of coating were investigated by SEM and EDS analysis. In order to identify the phases and calculating the nickel grain size, XRD and TEM analysis were used. Corrosion behavior of coating was studied by Tafel polarization experiments. Main effects and interaction between temperature, agitation and type of corrosive bath in two levels on corrosion current of Ni-13wt.%P coating was also investigated by using experimental designs such as Factorial method. The results demonstrated that the types of corrosive bath and temperature have the most and the least effect on corrosion current, respectively. In addition, the interaction between two parameters, namely the type of corrosive bath and agitation and also the interaction between three parameters have maximum and minimum effect on corrosion current, respectively. Investigation of contour plots and surface responses showed that an optimum state was obtained when three parameters were at low level and also, the maximum corrosion current of coating determined when the parameters were at high level.

In this study, experiments were conducted to evaluate the effect of limestone powder and iron particle on the properties of concrete. Therefore, the concrete specimen with replacement of 5% limestone powder and 2% iron particle, the concrete with 4% limestone powder and 3% iron particle were compared with the concrete specimen without replacement. In fact, limestone powder and iron particle are filler and they are replacement of sand in concrete and they decrease water and chloride penetration of concrete and therefore, decrease corrosion and increase mechanical properties of concrete. In present paper, water and chloride penetration, compressive strength of concrete and also, reinforcement potential, changing weight and optical microscopic images of reinforcement in concrete specimens were evaluated in various conditions and different ages of concrete. The results show water and chloride penetration and also, reinforcement potential, percent of changing weight of reinforcement in concrete specimens decrease and compressive strength of concrete increases in the concrete with 4% limestone powder and 3% iron particle with respect to the concrete with replacement of 5% limestone powder and 2% iron particle and concrete without replacement at various ages.

Dissimilar joints between austenitic stainless steels and low alloy and carbon steels have many usages in various industries and also have economic aspects. Loss of mechanical properties can be influenced by existence of hydrogen in corrosive enviroments. The effects of hydrogen on joints between carbon steel (A516) and stainless steel (AISI347) are compared and discussed in this research. For this reason samples made up from low-alloy steel prepared, then cladded with stainless steel 321 and Er347 by process of Gas Tungsten arc welding (GTAW). Then cladded samples putted under hydrogen cathodic charging. Ultrasonic tests, metallography, hardness measurment, bending and microscopic analysis (EDS) have used in order to compare these mechanical properties with uncharged samples. Result of these experiments shows that both materials, showed corrosion resistance against corrosive areas, but samples have broken from their interface while using force and penetrating hydrogen into it. In other hand it was seen separation in the interface of A516-Gr70 and AISI 321. Totally results show that AISI 347 clad shows better resistance than covered C-Steel with AIS 321.

In this study, the increasing oxidation resistance of Mo-Si-B alloys via intermetallic compounds was investigated. For this purpose, the Mo-Si-B bulk samples were fabricated by using mechanical alloying of 33Mo-57Si-10B and 30Mo-47Si-23B (at. %) powder compounds and subsequent sintering under Ar atmosphere at 1200 􀔨 for 3 h. The sintered samples were subjected to oxidation test in 1000 􀔨. Microstructure properties, phase composition of sintered samples and phase composition of oxide surfaces were investigated using scanning electron microscopy, X-ray diffraction and Energy dispersive spectroscopy. The results showed that more oxidation resistance in the 33Mo 57Si-10B alloy was acquired in comparison with 30Mo-47Si-23B alloy. However, this alloy had more pores. The presence of Mo5SiB2 compound in the microstructure of 33Mo-57Si-10B alloy caused formation of borosilicate protective scale. While, Composite microstructure composed of intermetallic compounds/Mo in 30Mo-47Si-23B alloy did not cause formation of oxidation resistance scale. Weight of this alloy was continuously decreased with 0.7mg/cm2h slope to oxidation test end.