Papers by Keyword: Passivity

Abstract: The corrosion behaviour of a high-alloy CrMnNi steel was investigated electrochemically in a 0.5 M sulphuric acid solution. The characteristic regions of the active, passive and transpassive state for the material were monitored by means of acoustic emissions. To this end, the steel was potentiostatically polarised and the acoustic emission signal was recorded on the specimen’s surface at a distance of 5 cm from the location of corrosion. Analysis of the acoustic emission signals revealed an increase in signal intensity due to hydrogen bubble formation when the material was cathodically polarised. Furthermore, for anodic polarisation, a continuous decline in the signal-time correlation occurred when the material was polarised in the active/passive state, whereas a sharp point of inflexion and drastic reduction in intensity was recognised when the material was polarised in the passive state. Moreover, a further increase in signal intensity was observed when the transpassive state was reached. The increase at transpassivity was related to the onset of oxygen bubble formation at the electrode.

Abstract: This paper presents an experimental study on corrosion of carbon steel as reinforcement bar in artificial solution of geopolymer paste by Open Circuit Potential (OCP). The OCP measurements have been used in reinforcement bar concrete studies for many years to determine the corrosion behavior of materials. OCP is the potential of the working electrode relative to the reference electrode when no current or potential is being applied to cell. The OCP of reinforcement bar was recorded with time and this experiment has been done for 30 days. A copper/copper sulfate (Cu/CuSO₄) reference electrode with a potential V-SHE of +0.318 V (at 25oC) was used in this study. The pH of geopolymer concrete was observed to be in the range of 11.5 to 12.5 depending on the formulations. Thus, in this study the artificial solutions of geopolymer paste that were used are pH 11, pH 12 and pH 13. It has been found that the potential values of three solutions were fluctuated from the beginning until day 30. The highest potential value was indicated by pH 13 whereas the maximum value is 0.542 V and minimum value is 0.205 V while pH 11 shows the lowest potential value with the maximum value 0.356 V and the minimum value-0.047 V. However, all the redox potential values for pH 11, pH 12 and pH 13 were located at passivity region, Fe₂O₃. The Fe₂O₃ is the stable phase in which this oxide acts as a protective film or passive layer in this region. It would be expected to provide some protection against corrosion. Keywords: corrosion, artificial solution, geopolymer paste, reinforcement bar, open circuit potential, passivity

Abstract: Austenitic stainless steels and cermets alloy has been used extensively in many sectors due to their highly resistance to corrosion attack and excel in mechanical properties. However, in corrosive media both materials are susceptible to corrosion attack especially in seawater and high temperature. Cermet alloys are a combination of ceramic and metal. Therefore, cermets exist in high corrosion resistance in aqueous media and the corrosion rate is complex to identify. This paper presents the corrosion mechanism of 316L and cermets alloy exposed to high concentration of sulphate in the salinity of seawater. The solution (media) was prepared according to the same composition as seawater including pH, salinity and dissolved oxygen. The corrosion mechanism were characterized to breakdown potential (E_b) of 316L which are the potential once reaches a sufficiently positive value and also known as pitting potential. This is the most point where localized corrosion susceptibility to evaluate and considered a potential, which could be an appropriate point according to any given combination of material/ambient/testing methods. The E_b value of 316L in high sulphate are higher compared to seawater in every temperature which elucidate that some anions accelerate corrosion attack whereas some anions such as sulphate behaves as inhibiting effect to 316L.

Abstract: Structural and chemical attributes of amorphous and nanocrystalline metals, which affect their corrosion behaviour are outlined. Effects of the fraction of intercrystalline regions, diffusivity, chemical homogeneity / heterogeneity and local ordering are indicated. These features can lead to higher or lower corrosion resistance as compared to coarse-grained counterparts, depending on the nature of tested metal and corrosive environment. Contributions of these factors are represented by two examples of passive behavior of nanocrystalline metals and amorphous Ni-P alloys.

Abstract: Based on the basic principles of anti-islanding detection, this paper puts forward an anti-islanding (AI) detection method which combined/q-axis voltage decoupling and positive feedback with Euler-Lagrange (EL) model .The proposed method is classified as an passive islanding detection method and it is based on the voltage change at the point of common coupling (PCC) that occurs in islanding .In the method, Add the d-axis decoupling voltage of PCC to the d-axis reference current of the EL model. A simulation study shows that the method is simple and feasible.

Abstract: A new stabilization control method for underactuated linear mechanical systems is presented in this paper. By proper setting the desired closed-loop system, the matching condition for controller design is reduced to one equation and an adjustable parameter (damping coefficient) is introduced to the controller. Stability of the closed-loop system is proved based on passivity. As an application example, stabilization control of 2-DOF Pendubot is studied. The system is linearized at its equilibrium point and the proposed controller design method is applied to the linearized system. The procedure of solving matching condition and design controller for the Pendubot is provided. The simulation results verify feasibility of the proposed method.

Abstract: The Euler-Lagrange (EL) model of the three-phase induction motor is set up based on the mathematical model of the three-phase induction motor in the two-phase static coordinate. The passivity and dissipativity of the three-phase induction motor are studied by EL model. Based on the passivity of induction motor, the passivity-based controller of system is designed with the method of damping injection under the conditions of the stator flux oriented.The system simulation model of the three-phase induction motor is established under MATLAB/Simulink environment. The Simulation results show that the passivity-based controller designed with the method of damping injection under the conditions of the stator flux orientedis feasible.

Abstract: Passivity-based tracking control of the underactuated linear mechanical systems is investigated in this paper. As our main contribution, the matching condition is decreased into two equations and an adjustable gain (damping gain) is introduced into the controller by setting the desired closed-loop system properly. Stability of the closed-loop system is proved based on passivity of the system. Furthermore, as examples, tracking control of 2-DOF Acrobot and 2-DOF Pendubot are studied. The systems are linearized at their equilibriums and the passivity-based controller design method is applied to the linearized systems. Matching conditions are solved and the design procedures of associate controllers for the two robots are provided. The simulation results show that the designed controllers can realize asymptotical tracking for the given desired trajectories.

Abstract: This paper focuses on the problem of non-fragile robust passive control for a class of nonlinear singular systems which contain structure uncertainties and time delay. A memorial state feedback controller is considered, and the controller is constructed such that closed-loop systems are generalized quadratically stable and passive with dissipation. The algorithm is given for obtaining the maximum dissipation, at the same time, the maximum guaranteed dissipation controller is proposed. Numerical example is presented to show the validity and applicability of the proposed method.

Abstract: Artificial aging behaviour of a 7017 Al-Zn-Mg alloy was studied by hardness measurement. The electrochemical behaviour of various alloy tempers, such as under-, peak-, and over-aged, have been evaluated by measuring variation of open circuit potential (OCP) with time and potentiodynamic polarization study in different environments. All the alloy tempers were tested in 3.5 wt. % NaCl solution at neutral (pH 7), at acidic (pH 1) and at alkaline (pH 12) conditions. It has been observed that the OCP values of the alloy tempers shifted toward noble direction with the increase of aging time in 3.5 wt. % NaCl solution. The polarization curves are more or less similar in shape exhibiting only active region in neutral (pH 7) and in acidic (pH 1) conditions, but an active-passive region at alkaline (pH 12) condition. The electrochemical parameters; E_corr, I_corr, passive potential range (E_p) and passive current (i_p), obtained from potentiodyanamic polarization curves for the alloy tempers in acid, neutral and alkaline solution; depend on the alloy tempers and the pH of the solution as well. Attempts have been made to explain the observed electrochemical behaviour of the alloy tempers, which is influenced by the microstructure, presence and distribution of second phase precipitates, accessed by DSC and XRD techniques.