Growth of Oxide and Nitride Layers on Titanium Foil and Their Electrochemical Properties.

The surface of titanium foil can be modified by heating in the air, in a N flow, and in an NH flow. Upon heating in the air, the elemental Ti gradually transforms to TiO at 550 °C and to rutile TiO at above 700 °C. Treatment in a N flow leads similarly to TiO at 600 °C and TiO at 700 °C, although the overall reaction is slower. Meanwhile, nitridation in the N flow is minimal, even at 900 °C. Heat treatment in an NH flow produces nitride phases through the ammonolysis of the hexagonal Ti. With an ammonolysis at 900 °C, trigonal TiN and cubic TiN form together while, at higher temperatures, TiN is dominant. The TiN layer can also be obtained via the ammonolysis of the TiO coating, that is, by the sequential treatments of Ti in the air and then in an NH flow. The titanium nitride layers have particulate microstructures and varying degrees of porosity, depending on the ammonolysis temperature and time. The TiO-derived TiN has a significantly higher capacitance than TiN derived directly from Ti. The optimally prepared TiN specimen exhibits an areal specific capacitance of 66.2 F/cm at 0.034 mA/cm.