The influence of sodium fluoride on the dissolution kinetics of metallic titanium in citric acid solution using the rotating disc method

This study reports the effect of sodium fluoride on the dissolution kinetics of pure metallic titanium in a citric acid solution. The effects of sodium fluoride concentration, citric acid concentration, temperature, stirring speed, and disc surface area were examined. The dissolution rate of titanium increases strongly with increasing citric acid and sodium fluoride concentrations. Fluoride ions react with hydrogen ions to form hydrofluoric acid, which removes the passive layer of titanium dioxide. An increase in the concentration of NaF and acid causes the formation of a brown layer on the surface of titanium. X-ray diffraction and SEM-EDX analyses showed that the layer composition is mostly of titanium fluoride (TiF₃) and titanium fluoride oxide (TiOF₂). A mixed kinetic model with an activation energy of 26.4 kJ/mol can be used to explain the reaction kinetics.