The Al–La alloy was made from alumi

The Al–La alloy was made from aluminium (99.99% purity) and lanthanum (99.99% purity) with 12.6 wt.% lanthanum content (eutectic composition). They were melted in a recrystallized alumina crucible using a Radyne induction vacuum furnace under argon atmo- sphere as described by Jua´rez [14], and Hughes [23]. Cylindrical samples of the alloy approximately 3 mm in diameter and 5 mm long were made by directional solidification at rates of 0.1, 1.03 and 3.02 mm/s.For the EIS measurements, the samples were used as working electrode in a conventional three-electrode electrochemical cell with a saturated calomel electrode (SCE) and a graphite bar as the reference and auxiliary electrodes, respectively. The tests were carried out with a frequency response analyser Schlumberger model SI 1255 connected to a potentiostat/galvanostat EG&G model 273 A over a frequency range of 100 kHz down to 10—4 Hz using a 10 mV amplitude sinusoidal voltage. Results obtained in a previous work [15] indicated that the Al–12.6%La alloy showed a sudden anodic cur- rent rise during potentiodynamic polarization in dis- tilled water. The current rise took place at a different potential value for each solidification rate, 650, 100 and 100 mV vs SCE for the specimens solidified at 0.1,1.03 and 3.02 mm/s, respectively. This potential value (the potential of sudden current rise Escr) was used to establish the electrode potential level at which the EIS and SRET measurements were conducted in the main part of the present work.The EIS and SRET measurements were carried out in distilled water with a pH = 6 using samples under ano- dic polarization at 50 mV below and 100 mV above the Escr.