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Various electrochemical techniques were used to study the corrosion behaviour of the CNT-reinforced NiAl alloys under NaCl and Na2SO4 environments. The potentiodynamic polarization curves revealed activation Tafel behaviour when the NiAl alloy specimens were immersed in NaCl solution while passivation followed by slight development of transpassivation resulted under Na2SO4 environment. The reinforcement of pure NiAl alloy with up to 1.0 wt.% CNT increased the corrosion rate from 0.10 to 0.63 mm/yr under NaCl environment, while under Na2SO4 environment, the corrosion rate increased from 0.04 to 0.12 mm/yr. The observed increase in corrosion rate with an increase in CNT reinforcement (under both NaCl and Na2SO4 environments) suggested that the reinforcement of NiAl alloys with CNT reduced the corrosion resistance of NiAl. The X-ray diffraction analysis revealed that the corrosion products consisted of oxides including Al2O3 under NaCl environment, while scanning electron microscope analysis showed a porous passive layer on the surface of the alloy specimens immersed in Na2SO4 solution. [ABSTRACT FROM AUTHOR]

The behavior of steel coupons buried in soil under cathodic protection (CP) was studied during wet/dry cycles using electrochemical impedance spectroscopy and voltammetry. The coupons were left at open circuit potential for 7 days before applying CP for 51 days at potentials of −0.8 and −1.0 V versus Cu/CuSO4 on coupons 1 and 2, respectively. Wet/dry cycling was achieved by first saturating the soil with an electrolyte inside a sealed electrochemical cell and by allowing the soil to dry by opening the top lid of the cell for various periods in the experiment. Surface analysis was performed after the experiments by X‐ray diffraction and Raman spectroscopy. The soil electrolyte resistance Rs depended mainly on the variations of soil moisture for coupon 1 but was strongly affected by the effects induced by CP for coupon 2. Residual corrosion rates of 17–18 and 7–10 µm/year for coupons 1 and 2, respectively, were estimated via voltammetry. The kinetic parameters vary with the polarization level so that the data obtained with a coupon polarized at a given potential cannot be used to predict the residual corrosion rate of a coupon polarized at another potential. [ABSTRACT FROM AUTHOR]