Potentiostatic control of ionic liquid surface film formation on ZE41 magnesium alloy

The generation of potentially corrosion-resistant films on light metal alloys of magnesium have been investigated. Magnesium alloy, ZE41 [Mg−Zn−Rare Earth (RE)-Zr, nominal composition 4 wt % Zn, 1.7 wt % RE (Ce), 0.6 wt % Zr, remaining balance, Mg], was exposed under potentiostatic control to the ionic liquid trihexyl(tetradecyl)phosphonium diphenylphosphate, denoted [P_6,6,6,14][DPP]. During exposure to this IL, a bias potential, shifted from open circuit, was applied to the ZE41 surface. Electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA) were used to monitor the evolution of film formation on the metal surface during exposure. The EIS data indicate that, of the four bias potentials examined, applying a potential of −200 mV versus OCP during the exposure period resulted in surface films of greatest resistance. Both EIS measurements and scanning electron microscopy (SEM) imaging indicate that these surfaces are substantially different to those formed without potential bias. Time of flight-secondary ion mass spectrometry (ToF-SIMS) elemental mapping of the films was utilized to ascertain the distribution of the ionic liquid cationic and anionic species relative to the microstructural surface features of ZE41 and indicated a more uniform distribution compared with the surface following exposure in the absence of a bias potential. Immersion of the treated ZE41 specimens in a chloride contaminated salt solution clearly indicated that the ionic liquid generated surface films offered significant protection against pitting corrosion, although the intermetallics were still insufficiently protected by the IL and hence favored intergranular corrosion processes.

Imparting sensitization resistance to an Al-5Mg alloy via Nd addition

Low-level Nd additions, up to 0.17 wt%, were added to Al-5Mg to explore the impact on the subsequent degree of sensitization. Following heat treatment at 150°C for 1 day and 7 days, nitric acid mass loss (NAMLT) tests revealed that additions of >0.11% Nd were effective at decreasing the amount of subsequent intergranular attack.

The influence of heat treatment on the corrosion behaviour of as-spun amorphous Al88Ni6La6 alloy in 0.01 M NaCl solution

The effect of the heat treatment on the corrosion behaviour of amorphous Al₈₈Ni₆La₆ made by melt-spun has been investigated by electrochemical measurements. Heat treatment was carried out at 523 K and 673 K for 4 min and 15 min respectively. The evolution of the crystallization process after annealing was identified by differential scanning calorimeter (DSC) as well as X-ray diffraction. The XRD patterns show that the structure of samples heat-treated at higher temperature changes towards a crystal state. The results obtained from the polarization curves reveal that all Al₈₈Ni₆La₆ alloys exhibit spontaneously passivated behaviour. Furthermore, it is noted that the partially crystallized alloy has the best corrosion resistance in comparison with as-spun amorphous and fully crystallized alloys, while the fully crystallized sample shows deterioration in the corrosion resistance.

Effect of crystallization on corrosion resistance of Cu52.5Ti30Zr11.5Ni6 bulk amorphous alloy

The effects of crystallization on the corrosion resistance of a  Cu52.5Ti30Zr11.5Ni6 bulk amorphous alloy in 1 mol/L HCl, and 6 mol/L NaOH solutions were studied. The amorphous alloy was identified by  differential thermal analysis(DSC) and by X-ray diffraction(XRD). The partially and fully crystallized alloys were prepared by controlling the annealing  temperatures at 738 and 873 K for 1 and 12 min, respectively, and the corrosion resistances of those annealed alloys were compared with that of the amorphous alloy by immersion test and potentiodynamic measurements in 1 mol/L HCl and 6 mol/L NaOH solutions. The results show that the  partially crystallized alloy exhibits high corrosion resistance, whereas full crystallization results in deteriorated corrosion resistance compared with that of the as-cast amorphous alloy.

Monitoring the corrosion of concrete reinforcement using control curves

Corrosion testing (half-cell and LPR) was carried out on a number reinforced concrete panels which had been taken from the fascia of a twenty five year old high rise building in Melbourne, Australia. Corrosion, predominantly as a result of carbonation of the concrete, was associated with a limited amount of cracking. A monitoring technique was established in which probe electrodes (reference and counter) were retro-fitted into the concrete. The probe electrode setup was identical for all panels tested. It was found that the corrosion behaviour of all panels tested closely fitted a family of results when the corrosion potential is plotted against the polarisation resistance (Rp). This enabled the development of a so-called 'control curve' relating the corrosion potential to the Rp for all of the panels under investigation. This relationship was also confirmed on laboratory samples, indicating that for a fixed geometry and experimental conditions a relationship between the potential and polarisation resistance of steel can be established for the steel-concrete system. Experimental results will be presented which indicate that for a given monitoring cell geometry, it may be possible to propose criteria for the point at which remediation measures should be considered. The establishment of such a control curve has enabled the development of a powerful monitoring tool for the assessment of a number of proposed corrosion remediation techniques. The actual effect of any corrosion remediation technique becomes clearly apparent via the type and magnitude of deviation of post remediation data from the original (preremediation) control curve.