The electrochemical behaviour of gallium amalgams. Their influence on the aluminium alloys activation. Part II

D.O. FLAMINI; S.B. SAIDMAN; J.B. BESSONE

Rio de Janeiro

Congreso; 2nd Mercosur Congress on Chemical Engineering, 4th Mercosur Congress on Process System Engineering; 2005

ENPROMER

In order to explain the extremely activation effect produced by Ga on pure Al and Al-4%Zn alloys, the electrochemistry of Ga and Ga-Al amalgam was studied. Different amounts of Al powder were added to liquid Ga, to produce Ga amalgams with 1 and 5 wt% of Al. Measurements were performed in 0.5 M NaCl, pH 2.5 at 25 ºC. Cathodic cleaning at ?2 VSCE during 10 min was applied previous to potentiodinamic, potentiostatic and galvanostatic studies. Different i-E responses were found depending on whether the interface was solid or liquid. Results indicate that a depolarised Al dissolution takes place under the liquid system, although at higher anodic polarization an anodic current density is attained controlled by the atomic Al diffusion within the amalgam. The activation mechanism changed from an amalgam depassivating control (in liquid state), to a chloride adsorption activation mechanism (in solid state). Galvanic reduction of Ga3+ species is enhanced by the presence of Zn in the Al-Zn alloy. Thus, a critical surface concentration of Ga needed to wet and to facilitate the formation of Ga-Al amalgam is assured.SCE during 10 min was applied previous to potentiodinamic, potentiostatic and galvanostatic studies. Different i-E responses were found depending on whether the interface was solid or liquid. Results indicate that a depolarised Al dissolution takes place under the liquid system, although at higher anodic polarization an anodic current density is attained controlled by the atomic Al diffusion within the amalgam. The activation mechanism changed from an amalgam depassivating control (in liquid state), to a chloride adsorption activation mechanism (in solid state). Galvanic reduction of Ga3+ species is enhanced by the presence of Zn in the Al-Zn alloy. Thus, a critical surface concentration of Ga needed to wet and to facilitate the formation of Ga-Al amalgam is assured.3+ species is enhanced by the presence of Zn in the Al-Zn alloy. Thus, a critical surface concentration of Ga needed to wet and to facilitate the formation of Ga-Al amalgam is assured.