Synthesis of M2AC (M = titanium, vanadium, chromium, niobium, zirconium, A = aluminum, tin, sulfur) (MAX) carbide phases and study of their physical behavior under extreme conditions

Shrinivas Raghavendra Kulkarni, Florida International University

Abstract

Materials known as Mn+1 AXn phases, where n is 1, 2, or 3, and M represents an early transition metal, A an A-group element, and X is either Carbon and/or Nitrogen [1], are fast becoming technologically important materials due to the interesting combination of unique properties. However, a lot of important information about the high temperature and high pressure behavior of many of these compounds is still missing, which needs to be determined systematically. In this dissertation the synthesis of M2 AC (M = Ti, V, Cr, Nb, Zr) and A = (Al, Sn, S) compounds by arc melting, vacuum sintering and piston cylinder synthesis is presented along with the synthesis of Zr 2 SC, which has been synthesized for first time in bulk form, by piston cylinder technique. The microstructural analysis by electron microscopy and phase analysis by x-ray diffraction is presented next. Finally, a critical analysis of the behavior of these compounds under the application of extreme pressure (as high as 50 GPa) and temperature ([approximate] 1000°C) is presented. The high pressure studies, up to 50 GPa, showed that these compounds were structurally intact and their bulk moduli ranged from 140 to 190 GPa. The high temperature studies in the inert atmosphere showed that the M 2 SnC compounds were unstable above 650°C and the expansion along the a-axis was higher than that along the c-axis, unlike the other phases. M2 SC compounds on the other hand showed negligible difference in the thermal expansion along the two axes. The oxidation study revealed that Ti2 AC (Al, S) compounds had highest resistance to oxidation while the M2 SnC compounds had the least. Furthermore, from the oxidation study of these compounds, which were short time oxidation experiments, it was found that all of these compounds oxidized to their respective binary oxides.

Recommended Citation

Shrinivas Raghavendra Kulkarni, "Synthesis of M2AC (M = titanium, vanadium, chromium, niobium, zirconium, A = aluminum, tin, sulfur) (MAX) carbide phases and study of their physical behavior under extreme conditions" (January 1, 2008). ETD Collection for Florida International University. Paper AAI3343271.
http://digitalcommons.fiu.edu/dissertations/AAI3343271