Discovery of Reversible Switching of Coloration of Passive Layers on Titanium

Abstract

Colored passive layers on Ti can be prepared by electrochemical means and their coloration can be switched reversibly between several colors by increasing or decreasing the AC voltage (VAC) in a stepwise manner. The coloration, which originates from iridescence, is directly related to the passive layer’s thickness (d) achieved at each VAC value. Two concurrently occurring processes, the passive layer growth and passive layer dissolution, control the passive layer thickness. At a given AC voltage, the passive layer reaches a steady-state thickness at which the growth rate (υgrowth) equals the dissolution rate (υdiss). An increase or decrease in VAC modifies the values of υgrowth and υdiss until a new steady-state thickness, and new coloration, is achieved.