On the formation of Al2O3 nanofibers during self-propagating high-temperature synthesis of TiO2–Al–C system in various environments

Abstract

The present study deals with the formation of Al2O3 fibers during self-propagating high-temperature synthesis of the TiO2–Al–C system triggered in argon, oxygen, nitrogen and air environments. Results showed TiC and Al2O3 were the primary products obtained in the argon and oxygen atmospheres. However, the dissolution of nitrogen in the structure of TiC resulted in the formation of Ti(C, N) after synthesis in nitrogen and air environments. Al2O3 fibers just were extensively attained in an air atmosphere with a low partial pressure of oxygen. Long nanofibers were primarily formed at the surface of the compact, while short fibers were developed at the inner part; especially adjacent to the internal pores. The formation mechanism of Al2O3 fibers was proposed as (a) the formation of Al2O gas through reaction of Al with O2 in the environment having low oxygen partial pressure like air; (b) further reaction of Al2O vapor with O2 and the development of Al2O3; and (c) precipitation of Al2O3 in the form of fibers by vapor-solid mechanism.