Spectroscopic Characterization of Acidity of Titanium (6% AI-4%, V) Surfaces

Abstract

Acid-base characteristics of titania powders and of Ti 6–4 metal coupons after pretreatment by the Turco 5578 and phosphate-fluoride processes have been studied. Color changes of indicators spread from solution on the metal surface were detected using diffuse reflectance visible spectroscopy (DRVS). The Turco etched Ti 6–4 surface was found to be basic while the phosphate-fluoride etched Ti 6–4 surface was acidic. Effects due to the experimental conditions of time, solvent, and temperature were also examined. ESCA (electron spectroscopy for chemical analysis) was done to determine if shifts in binding energy were observed for the acid and base forms of the indicators on the Ti 6–4 surfaces. Different binding energies were detected for the oxygen photopeaks of bromthymol blue on Turco and phosphate-fluoride etched Ti 6–4 surfaces. More stearic acid was adsorbed from cyclohexane solutions on the Turco etched Ti 6–4 surface than on the phosphate-fluoride surface as detected by specular reflectance infra-red spectroscopy (SRIRS). A model for the Ti 6–4 surface was deduced based on the results above.