(657c) Investigation of Reaction Mechanism In Ti/C System: Influence of High Energy Ball Milling

The influence of High Energy Ball Milling (HEBM) on the stoichiometric (1: 1 molar ratio) mixture of titanium and graphite powders milled at room temperature under argon atmosphere with ball to powder ration 40:1 at 650 rpm is discussed. Crystal structures and phases were characterized by X-ray diffractometry (XRD) and energy dispersive X-ray spectroscopy (EDS) analysis. Microstructure of the initial and as-milled samples was investigated by SEM and internal structures characterized by focused ion beam (FIB) techniques. Ignition characteristics and effective activation energy measurements were carried out by, the so-called, Electro Thermal Explosion (ETE) method [1]. Special attention was paid on the microstructure variations with respect to self-ignition temperatures and reaction kinetics for media obtained at different milling durations.

For example, analysis of the specific surface area (BET) showed that after 2 min of such milling the specific surface area of the reactive media significantly increases to ~100 m²/g, being only 3 m²/g for initial mixture. At this stage, XRD and SEM studies revealed complete amorphorization of the graphite powder. It was also shown that Ti/C laminated composite particles start to form as early as after 3 min of HEBM. This transformation leads to corresponding decrease of self-ignition temperatures from 1933 K (melting point of titanium) to 1800 K. The formation of TiC-phase nucleolus (~20 nm) was observed after 5 minutes of treatment. The self-ignition temperatures further decreases to ~1500 K for samples after 7.5 min of milling time. Finally, it was shown that the nano-scale (~500 nm) TiC powder is produced after 9.5 min of process time. Reaction mechanism in Ti and C system after such treatments is also proposed and discussed.

[1] A. S. Shteinberg, Y.-C. Lin, S. F. Son, A. S. Mukasyan. “Kinetics of High Temperature Reaction in Ni-Al System: Influence of Mechanical Activation” J. Phys. Chem. A, 2010, 114 (20), pp 6111–6116.