Titanium Anodizing

Abstract

In a galvanic or voltaic electrochemical cell, the spontaneous reaction occurs and electrons flow from the anode (oxidation) to the cathode (reduction). In an electrolytic cell, a non-spontaneous reaction occurs using energy supplied by an external source. Electrons are forced from the external circuit at cathode to produce the reduction. The cathode is the negative electrode and is the black connection on the power supply. Electrons are drawn into the external circuit at the anode to produce the oxidation. The anode is the positive electrode and is the red connection on the power supply. Some metals form an oxide coating on the surface the metal as the metal is electrolytically oxidized. Since this oxidation takes place at the anode, the process is called anodizing. Aluminum metal is commonly anodized. 2 Al (s) + 3 H 2 O (l) → Al 2 O 3 (s) + 6 H +1 (aq) + 6 e -The layer of aluminum oxide bonds tightly to the metal and can be used to bond different dyes to the surface. Many types of sports equipment and furniture have a durable colored surface of dyed anodized aluminum. Titanium metal can be oxidized (anodized) by the following reaction. Ti (s) + 2 H 2 O (l) → TiO 2 (s) + 4 H +1 (aq) + 4 e -The oxide coating on the titanium, however, acts as a diffraction grating and separates white light into its colors so that no dyeing is necessary. The color of the surface depends on the thickness of the oxide layer on the surface, which is control by the voltage used during the anodizing process. A typical electrolytic cell is used. A stainless steel cathode is used in the cell. Water is reduced at the cathode.