Gas-phase driven nano-machined TiO2 ceramics

A simple, inexpensive gas phase reaction termed as “nanocarving process” converts TiO2 grains into arrays of single crystal nanofibers by selective and anisotropic etching. This process is conducted by exposing dense polycrystalline TiO2 to a H2/N2 environment at 700 °C. The dimensions of nanofibers are around 20 nm in diameter and 1 μm in length. The preferred crystallographic orientation for the nanocarving process is the <001> direction. Nanoparticles composed of Fe and Ni were observed on the surface of TiO2 that formed nanofiber tips. Sintering parameters before the nanocarving treatment play a critical role in the formation of nanofibers. As sintering temperature and time increased, the rate of nanofiber generation decreased. Moreover, it was observed that by varying the heat treatment conditions, it is possible to create other structures like nanowhiskers and nanofilaments. Nanowhiskers were formed by reoxidation of nanofiber-formed TiO2 over 600 °C. Nano-filaments were generated by heat treating sintered TiO2 in N2-carrying water vapor at 700 °C.