The effect of zinc bath temperature on the morphology, texture and corrosion behaviour of industrially produced hot-dip galvanized coatings

The purpose of this work is to identify the influence of zinc bath temperature on the morphology, texture and corrosion behavior of hot-dip galvanized coatings. Hot-dip galvanized samples were prepared at temperature in the range of 450-480 °C in steps of 10 °C, which is the conventional galvanizing temperature range in the galvanizing industries. The morphology of coatings was examined with optical microscopy and scanning electron microscopy (SEM). The composition of the coating layers was determined using energy dispersive spectroscopy (EDS) analysis. The texture of the coatings was evaluated using X-ray diffraction. Corrosion behavior was performed using salt spray cabinet test and Tafel extrapolation test. From the experimental results, it was found that increasing the zinc bath temperature affects the morphology of the galvanized coatings provoking the appearance of cracks in the coating structure. These cracks prevent formation of a compact structure. In addition, it was concluded that (00.2) basal plane texture component was weakened by increasing the zinc bath temperature and, conversely, appearance of (10.1) prism component, (20.1) high angle pyramidal component and low angle component prevailed. Besides, coatings with strong (00.2) texture component and weaker (20.1) components have better corrosion resistance than the coatings with weak (00.2) and strong (20.1) texture components. Furthermore, corrosion resistance of the galvanized coatings was decreased by increasing the zinc bath temperature.  http://dx.doi.org/10.5937/metmateng1401041

Erosive and Abrasive Wear Resistance of Polyurethane Liners

Material removal caused by the impact and sliding of a stream of particles is a typical wear mode in the oil and gas industry. Protective coatings can be employed to increase the service life of equipment that is exposed to harsh erosive and abrasive environments. Among all the types of protective coatings and liners, polyurethane elastomers have received great attention owing to their excellent wear resistance and comparatively low cost that would allow for large-scale applications. The excellent wear resistance of polyurethane elastomers is a result of their high resilience and propensity to elastic deformation that enables the absorption of impact energy of erodant particles with minimal damage. The relation between the wear resistance of polyurethane and its mechanical properties has been the subject of previous studies. This chapter reviews the research that has been conducted to study the wear resistance of polyurethane elastomers. Testing apparatuses employed, material characterization techniques, evaluations of material removal mechanisms, and parameters with the strongest effect on wear resistance of polyurethane elastomers are herein explored. A review of finite element modelling approaches for in-depth study of the wear phenomenon of polyurethane elastomers is also presented in this chapter

Investigation of a Jacobian-free Newton-Krylov solution to multiphase flows

The current study is focused on investigating a Jacobian-Free Newton-Krylov (JFNK) method to obtain a fully-implicit solution for two phase flows. In the JFNK formulation, the Jacobian matrix is not directly determined potentially leading to major computational savings compared to a simple Newton's solver. Prior to the implementation of JFNK to solve two-phase flow problem, it is utilized to solve the governing equations corresponding to single phase flow. The objectives of the present study are (i) Application of the JFNK method to two-fluid models, (ii) Investigation of the advantages and disadvantages of the method compared to commonly used explicit methods, and (iii) Comparison of the numerical predictions with those obtained by the current version of the Network thermalhydraulics code, CATHENA. The background information required is presented and the numerical setup for each test case is discussed in detail. Three well-known benchmarks are considered, the 1D dam break problem, the water faucet and the oscillating manometer. For single phase flow simulations, the Shallow Water Wave Equations is selected to model the motion of the fluid and a backward Euler scheme is utilized for the temporal discretization along with a central-upwind Godonuv scheme for the spatial discretization. For the two-phase simulations, an isentropic (four equation) two fluid model is chosen. Time discretization is performed by a backward Euler scheme and the AUSM+ scheme is applied to the convective fluxes. The source terms are discretized using a central differencing scheme. For comparison, one explicit and two implicit formulations, one with Newton's solver with the Jacobian matrix and one with JFNK, are implemented for each set of governing equations. A detailed grid and model parameter sensitivity analysis is performed to identify the advantages and disadvantages of JFNK for each case. For all three benchmarks, the JFNK predictions are in good agreement with the analytical solutions and explicit profiles. Further, stable results can be achieved using high CFL (Courant–Friedrichs–Lewy ) numbers up to 100 with a suitable choice of JFNK parameters. The computational time is significantly reduced by JFNK compared to the calculations requiring the determination of the Jacobian matrix. This reduction is in the order of 80%

Simulation of Soot Formation in Turbulent Diffusion Flames Using Conditional Source-term Estimation

Conditional Source-term Estimation (CSE) is a turbulent combustion model which uses the conditional averages of scalars for calculating the mean reaction source term in the species transport equation. CSE has been shown to be a very efficient and accurate method for simulating turbulent flames without being limited to certain conditions and regimes. In this study, for the first time, CSE is used for the simulation of soot formation in turbulent diffusion flames. The objective of the present research is to develop a CSE code for simulating soot formation in turbulent diffusion flames. The modeling of soot formation is investigated for two turbulent flames, at atmospheric and 3 atm pressure conditions. A semi-empirical soot formulation that accounts for soot inception, coagulation, surface growth, and oxidation processes is coupled with the CSE turbulent combustion model using Reynolds Averaged Navier Stokes equations. Detailed chemistry is included and an optically thin radiation model is considered. Good agreement with the experiments is found for turbulent mixing and temperature fields in both flames, with some discrepancies believed to be due to the turbulence model. The predicted soot volume fraction values match the experimental data well at 1 atm with some under prediction in the range of experimental uncertainty. At higher pressure, the predicted level of soot increases, as expected. At 3 atm, underpredictions can be noticed in the predicted soot volume fraction. In the current work, the CSE framework is extended to include the effect of radiation in the chemistry tables and to have better predictions for species mass fractions and reaction rates. This is applied to the turbulent methane-air flame at 3 atm pressure and significant improvements are observed for the temperature and soot predictions. A detailed soot model that takes into account the soot aerosol dynamics, the Quadrature based Method of Moments (QMOM) is added to the CSE code as an advanced model after promising results were observed from the semi-empirical soot model. The CSE-QMOM method is applied to an ethylene turbulent flame. The results show very good predictions of soot volume fraction. Finally, a Poly cyclic Aromatic Hydrocarbon (PAH) based model is implemented into the CSE-soot framework. PAH based inception models are known to provide more accurate predictions compared to the conventional acetylene based models. The CSE-soot model is capable of providing good predictions for soot volume fraction. Possible sources of discrepancies and limitations of the model are discussed and future improvements are explained

Incorporation mechanism of colloidal TiO2 nanoparticles and their effect on properties of coatings grown on 7075 Al alloy from silicate-based solution using plasma electrolytic oxidation

Plasma electrolytic oxidation (PEO) was applied using a pulsed unipolar waveform to produce Al2O3-TiO2 composite coatings from sol electrolytic solutions containing colloidal TiO2 nanoparticles. The sol solutions were produced by dissolving 1, 3, and 5 g/L of potassium titanyl oxalate (PTO) in a silicate solution. Scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction, and Raman spectroscopy were applied to characterizing the coatings. Corrosion behavior of the coatings was investigated using polarization and impedance techniques. The results indicated that TiO2 enters the coating through all types of micro-discharging and is doped into the alumina phase. The higher level of TiO2 incorporation results in the decrease of surface micro-pores, while the lower incorporation shows a reverse effect. It was revealed that the higher TiO2 content makes a more compact outer layer and increases the inner layer thickness of the coating. Electrochemical measurements revealed that the coating obtained from the solution containing 3 g/L PTO exhibits higher corrosion performance than that obtained in the absence of PTO. The coating produced in the absence of PTO consists of gamma-Al2O3, delta-Al2O3 and amorphous phases, while alpha-Al2O3 is promoted by the presence of PTO

Silicate and Hydroxide Concentration Influencing the Properties of Composite Al2 O3-TiO2 PEO Coatings on AA7075 Alloy

This work evaluates the effect of sodium meta-silicate pentahydrate (SMS) and potassium hydroxide concentrations on properties of Al2O3-TiO2 coatings produced through plasma electrolytic oxidation in a solution containing 3 g L−1 potassium titanyl oxalate, (PTO), using a unipolar waveform with constant current density. The surface and cross-section characteristics of PEO coatings including morphology, elemental distribution, and phase composition were evaluated using FESEM, EDS, and XRD techniques. Voltage-time response indicated the concentration of SMS and KOH had a significant effect on the duration of each stage of the PEO process. More cracks and pores were formed at the higher concentrated solutions that resulted in the incorporation of solution components especially Si into the coating inner parts. Ti is distributed throughout the coatings, but it had a dominant distribution in the Si-rich areas. The coating prepared in the electrolyte containing no silicate consisted of non-stoichiometric γ-Al2O3 and/or amorphous Al2O3 phase. Adding silicate into the coating electrolyte resulted in the appearance of α-Al2O3 besides the dominant phase of γ-Al2O3. The corrosion behaviour of the coatings was investigated using the EIS technique. It was found that the coating prepared in the presence of 3 g L−1 SMS and 2 g L−1 KOH, possessed the highest barrier resistance (~10 MΩ cm2), owing to a more compact outer layer, thicker inner layer along with appropriate dielectric property because this layer lacks the Si element. It was discovered that the incorporation of Ti4+ and especially Si4+ in the coating makes the dielectric loss in the coating

Down Regulation of Osteocalcin Gene in Chickens Treated with Cadmium

Background: Cadmium is one of the heavy metals with harmful effects on different body organs and systems. The aim of this study was to investigate the harmful effects of cadmium, as a heavy metal, on the histological structure of bone and the expression of osteocalcin gene. Methods: Forty chickens were obtained, anesthetized and their femurs were surgically removed. The real time polymerase chain reaction (PCR) was used to study the osteocalcin gene expression. Results: The osteocalcin gene expression rate were: 1.000± 0.1; 0.86± 0.01; 0.63± 0.09, and 0.41± 0.06 in the controls, experiment I, experiment II and experiment III groups, respectively (P < 0.05). Also, the nuclear pyknosis in osteocytes and decreased bone formation were observed in the histology slides of the chicken bones. Conclusions: We conclude that cadmium adversely affected the chicken bones as evident by the decreased osteocalcin gene expression and the adverse effects on the bone histology. We recommend that plans be developed to prevent the outbreak of cadmium and other heavy metals in animal and human environment

MicroRNA-mediated regulation of Nrf2 signaling pathway: Implications in disease therapy and protection against oxidative stress

MicroRNAs (miRs) are small non-coding pieces of RNA that are involved in a variety of physiologic processes such as apoptosis, cell proliferation, cell differentiation, cell cycle and cell survival. These multifunctional nucleotides are also capable of preventing oxidative damages by modulating antioxidant defense systems in a variety of milieu, such as in diabetes. Although the exact molecular mechanisms by which miRs modulate the antioxidant defense elements are unclear, some evidence suggests that they may exert these effects via nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway. This intracellular mechanism is crucial in the maintenance of the physiologic redox balance by regulating the expression and activity of various cellular antioxidative defense elements and thereby plays a pivotal role in the development of oxidative stress. Any impairment in the Nrf2 signaling pathway may result in oxidative damage-dependent complications such as various diabetic complications, neurological disorders and cancer. In the current review, we discuss the modulatory effects of miRs on the Nrf2 signaling pathway, which can potentially be novel therapeutic targets