Amar Prasad Yadav

Electrochemical impedance study on galvanized steel corrosion under cyclic wet–dry conditions––influence of time of wetness

Abstract Electrochemical impedance technique has been applied to study the corrosion behavior of galvanized steel under wet–dry cyclic conditions with various drying periods. The wet–dry cycles were carried out for the period of 336 h by exposure to alternate conditions of 1 h immersion in a 0.5 M NaCl solution and drying for various time periods (11, 7 and 3 h) at 298 K and 60% RH. During the wet–dry cycles, the polarization resistance, Rp, and solution resistance, Rs, were continuously monitored. The instantaneous corrosion rate of the coating was estimated from the obtained Rp−1 and time of wetness was determined from the Rs values. The corrosion potential, Ecorr, was also measured only during the immersion period of each wet–dry cycle. In all cases, the corrosion was accelerated by the wet–dry cycles in the early stage, and started to decrease at a certain cycle and finally became similar to that at the initial cycle. The underlying steel corrosion commenced after the corrosion rate started to decrease. The shorter drying period in each cycle led to higher amount of corrosion of the coating because the surface was under wet conditions for longer periods. On the other hand, time to red rust appearance due to occurrence of the underlying steel corrosion became shorter as the drying period increased, although the total amount of corrosion was smaller. The corrosion mechanism of substrate steel under various drying conditions has been discussed, the galvanic coupling effect being taken into account.

Degradation mechanism of galvanized steel in wet–dry cyclic environment containing chloride ions

Abstract The wet–dry cyclic test of a galvanized steel (GI) and pure zinc (ZN), which simulates marine atmospheric environment, has been conducted to clarify the degradation mechanism of galvanized steel. The samples were exposed to alternate conditions of 1 h-immersion in a 0.05 M NaCl solution and 7 h-drying at 25 °C and 60%RH, and the corrosion was monitored for 10 days (30 cycles) using a two-electrode type probe. Simultaneously, the corrosion potential was measured every three cycles only during the immersed conditions. The reciprocal of polarization resistance R p −1 was taken as an index of the corrosion rate. Several sample plates of GI and ZN were exposed, together with the monitoring probes. They were removed from the test chamber at the end of 1st, 3rd, 9th, 18th, and 30th cycles of exposure and were analyzed for the corrosion products with XRD and laser Raman spectroscopy. Further, their cross sections were analyzed with FESEM–EDS. The FESEM photographs and elemental analysis of cross sections confirmed that the R p −1 value commences to decrease when the corrosion front reaches Zn–Fe alloy layers (boundary layers of zinc coating and steel substrate) due to localized nature of attack. A schematic model of degradation mechanism and the role of galvanic protection have been discussed.

Channel-Flow Double-Electrode Study on the Dissolution and Deposition Potentials of Platinum under Potential Cycles

A channel-flow double-electrode system has been employed to determine the potential regions of Pt dissolution and redeposition during a cyclic voltammetry (CV) measurement in 0.5 M H 2 SO 4 solution at 25°C. The double-electrode system consists of a Pt plate as a working electrode (WE) placed upstream and a Au plate as a collector electrode (CE) placed downstream with a separation gap of 0.1 mm. Pt ions dissolved at the WE during CV have been detected at the CE by employing an appropriate reduction potential and have been analyzed by using an electron probe microanalyzer (EPMA). The EPMA results show that the deposition of Pt from hydrated Pt ions occurs below 0.60 V vs the standard hydrogen electrode. When CV is carried out between 0.0 and 1.4 or 1.6 V, dissolution of Pt occurs during both the anodic and cathodic scans of the CV. When CV is carried out between 0.0 V and an upper potential limit of 1.2 V, the dissolution of Pt could be observed only in the anodic scan. The dissolution mechanism of Pt during CV is proposed.

EQCM Study on Dissolution of Ruthenium in Sulfuric Acid

This study reports on the nanolevel dissolution and polarization behavior of electrodeposited Ru in 0.5 mol L -1 H 2 SO 4 solution with the help of an electrochemical quartz crystal microbalance (EQCM) and inductively coupled plasma-mass spectrometry (ICP-MS) analysis. Results of the cyclic voltammetry showed that during anodic polarization a mass gain at Ru electrode was observed from -0.1 V due to water adsorption and the significant mass gain due to Ru oxide formation was observed from 0.5 V; the start of these processes depended on the potential. ICP-MS analysis of the solution after potential cycling of the Ru electrode showed that only a slight amount of the dissolution occurred when the potential was less than 0.5 V, but the amount of dissolution significantly increased from 0.5 V onward. The potential cycle accelerated the dissolution of Ru. A simple immersion test revealed that the potential of Ru increased until 0.8 V from -0.1 V during the immersion. This shows that the on-off cycle of a polymer electrolyte fuel cell (PEFC) can induce the potential cycle; this will lead to accelerate the dissolution of Ru in the anode catalyst of the PEFC.

Dissolution Behavior of Pt Alloy Catalysts in Sulfuric Acid Solution

Introduction Polymer electrolyte membrane fuel cell (PEMFC) is expected as an alternative power source because of high energy conversion efficiency and clean energy. Platinum is used as the cathode catalyst of PEMFC due to its high catalytic ability. However, platinum is expensive and the resource is limited. Recently, platinum alloy catalysts have been proposed to reduce the amount of platinum in the catalyst of PEMFC [1]. In use of alloy catalysts, however, the degradation due to corrosion becomes problem. The object in this study is to investigate dissolution behavior of alloy catalysts in sulfuric acid solution.