ABSTRACT
In aqueous solutions or in other oxidative media free of complexing agents, the surface of Titanium (Ti) reacts readily with its environment to form oxide films of varying composition and stability depending on the pH and the nature of the electrolyte. A number of complexes of both zirconium and hafnium have been prepared, and stability constant measurements have been reported in some cases. To compound the difficulties facing the experimentalist, zirconium and hafnium readily form a surface layer of oxide, so that passivity in solution may be significant. All in all, the dearth of reliable experimental results for the standard potential comes as no surprise. The aqueous solution chemistry of zirconium and hafnium presents formidable barriers to the experimental determination of standard electrode potentials. The values calculated from available thermochemical data are valid only within the limits of the assumptions made as to the species present in aqueous solution.
