Papers by Author: M. Daud

Abstract: This paper presents the cathodic protection of steel embedded concrete of aluminum based alloy in brackish mud. In this experiment, aluminum based alloys containing 5% zinc, 2% magnesium, and 0.5-2% stannum were fabricated. These elements were added because they produce heat treatable alloys, improved anti friction characteristics, fluidibility, and contain highest strengthening effect on aluminum alloys. These alloys were tested as sacrificial cathodic protection for the standard steel embedded concrete exposed to sea water and brackish mud. Surface morphology of the samples after subjected to corrosion was investigated through scanning electron microscopy (SEM) and anode capacity test (efficiency test). The results revealed that sample with the composition of 95.6% of aluminum, 3.83% of zinc, and 0.19% of stannum showed the best performance hence it was selected for cathodic protection in brackish mud.

Abstract: In this paper, a study on the electrochemical behaviour and electrical properties of Al-Zn and Al-Zn-Sn alloys in tropical seawater using open circuit potential (OCP) measurement and electrochemical impedance spectroscopy (EIS) are reported. The results from both the OCP and EIS tests show that surface activation was observed in the Al-Zn alloy with the addition of 1.34 wt.% Sn which can be manifested by the shift of OCP values towards more electronegative direction. The EIS spectra of Al-Zn alloy exhibits a semicircle loop, while the EIS spectra for the Al-Zn-Sn alloy exhibits a semicircle with a semicircle inductive loop. The change in EIS spectra for Al-Zn-Sn alloy is correlated to the increase of surface activation resulting in a less stable passive layer. Equivalent circuits models were proposed to fit the impedance spectra and the corresponding electrical parameters with optimum values were deduced. The modulus impedance in the low frequency region or polarization resistance, R_pol obtained for the Al-Zn-Sn alloy, R_pol = 2.76 kΩ cm²) is slightly decreased compared to the corresponding value of the Al-Zn alloy, R_pol = 3.97 kΩ cm²), indicating a considerable reduction in the protective capability of the oxide layer on the Al-Zn-Sn alloy. It appears that the heterogeneous oxide film and pores formed on the Al-Zn-Sn alloy play a key role in reducing total resistance to the flow of electron at the alloy-electrolyte interface.

Abstract: Electrochemical behaviour of cast Al-Zn alloys in natural chloride solution were investigated by potentiodynamic measurements and electrochemical impedance spectroscopy (EIS). Results from open circuit potential (OCP) measurement against immersion time showed a stable free corrosion process was achieved after 15 kiloseconds and alloys with more Sn contents had shifted OCP value towards more negative direction. Potentiodynamic polarisation curves showed that the corrosion potential (Ecorr) of aluminium alloys with Sn addition were much active compared to alloy without Sn. The anodic curves were characterized by no sign of passive current due active dissolution on the surface of the Al-Zn-Sn alloy. SEM images show that the presence of Sn in Al-Zn alloys produces better and uniform dissolution morphology. EIS results confirm that the presence of Sn is beneficial in improving anodic dissolution of Al-Zn alloys by reducing resistance to polarization (Rp). The presence of 0.1%wt. Sn in Al-Zn alloy has been found to be useful in activating electrochemical reaction at alloy-solution interface based on inductive loop in EIS diagram.