Anodic dissolution of zirconium in Bun4NBr-containing n-butanol solutions was investigated using cyclic voltammetry, linear sweep voltammetry and potentiostatic current–time transient and scanning electron microscopy (SEM). Zirconium did not exhibit active dissolution due to passivation in the potential region of 0.2 to 1.2 V vs. SCE. The zirconium dissolution in passive state was under mass transfer control. Pitting corrosion took place as a result of passivity breakdown by Br− anions and the typical steady-state pitting potential was between 1.55–1.60 V vs. SCE in n-butanol solutions containing 0.08 M Bun4NBr. SEM images confirmed the occurrence and the intensification of pits with an increase of potential. Increasing Bun4NBr concentration accelerated the pit nucleation and growth. The reaction order leading to pit nucleation process was 1.0 with respect to bromide anions. The dissolution of zirconium in n-butanol solution produced Zr(OC4H9)4.
Anodic dissolution behavior of zirconium in Bu n 4 NBr-contaning isopropanol solution was investigated using cyclic voltammetry, linear sweep voltammetry and chronoamperometry, complemented with a scanning electron microscope (SEM). The voltammograms did not exhibit active dissolution until the breakdown of passive layer induced by aggressive bromide anions. SEM images confirmed the existence of pits on zirconium surface. The depth and breadth of pits were intensified with increasing potential. The pitting potential shifted negatively as either temperature or Bu n 4 NBr concentration was increased, while it increased with increasing scan rate. The corrosion current density increased with increasing temperature. The apparent activation energy of anodic dissolution of zirconium was 21.88 kJ/mol. The chronoamperometry revealed that increasing Bu n 4 NBr concentration shortened the incubation time for passivity breakdown and accelerated the pit nucleation and growth. The experimental results were helpful to obtain the optimum conditions for electrosynthesis of zirconium isopropoxide.
To understand the role of water on zirconium passivation in n-butanol solutions containing Bun4NBr, composition and corrosion properties of the passive film were studied using cyclic voltammetry, X-ray photoelectron and electrochemical impedance spectroscopy. Zirconium undergoes spontaneous passivation followed by pitting corrosion as a result of passivity breakdown by the aggressive attack of bromide anions. The passive film consists mainly of ZrO2, ZrO2·2H2O and a small amount of zirconium butoxide. The pitting potential shifts positively and pitting corrosion is seriously inhibited with the addition of a small amount of water. Water improves the pitting corrosion resistance of the passive film by changing the thickness and the relative ratio of OH−/O2−. The result is helpful to electrosynthesize zirconium butoxide with high energy efficiency.
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