TiC Nanocrystal Formation from Carburization of Laser-Grown Ti/O/C Nanopowders for Nanostructured Ceramics

Abstract

Refractory carbide ceramics (TiC and ZrC) raise interest as promising materials for high-temperature applications such as structural materials for the future generation of nuclear reactors. In this context, nanostructured ceramics are expected to exhibit improved thermomechanical properties as well as better behavior under irradiation when compared to conventional materials. It is therefore necessary to synthesize carbide nanocrystals of such materials to elaborate the ceramics. We report here the formation study of TiC nanocrystals through the direct carburization of Ti/O/C nanopowders grown by laser pyrolysis. A spray of titanium tetraisopropoxide was laser pyrolyzed with ethylene as the sensitizer, leading to Ti/O/C nanopowders with various C contents controlled by the synthesis conditions. Annealing treatments performed on these nanopowders under an inert atmosphere without any C addition enabled the formation of TiC grains through the carburization of the oxide phase by free C incorporated during the synthesis. The powders were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The final TiC grain size was about 80 nm, and the grains were monocrystalline. The influence of the free C content on the grain growth during the annealing step, together with its effects on the densification of the ceramics after sintering by high-pressure flash sintering, was examined. A 93% densification was finally achieved.

Nanoparticle Size Effects on Phase Stability for Molybdenum and Tungsten Carbides

“…Transition-metal carbides (TMCs) are utilized for a wide range of applications including heterogeneous catalysis and fuel cells, − in part because of their diversity of crystal structures and phase compositions. However, this structural diversity results in complex crystallization pathways and metastable phases during crystallization, presenting challenges for the synthesis of TMCs with specific compositions and surfaces. − Common synthetic routes include temperature-programmed reaction at a variety of temperatures and with variable metal, carbon, and metal oxide precursors; − topotactic syntheses; , pyrolysis of ordered crystal structures; − and, more recently, solution-based synthesis routes . Several synthesis methods for TMCs display excellent particle size tunability and uniformity.…”

Application of the laser pyrolysis to the synthesis of SiC, TiC and ZrC pre-ceramics nanopowders

“…(1) has already been determined in a previous study by annealing Ti/O/C samples in [21]. The value was found to be as low as 1300 8C, which is lower than conventional carburization temperature of raw TiO 2 /C black mixtures (1700-2100 8C) and comparable to other synthesis techniques of TiC nanoparticles using advanced carboreduction processes [22,23].…”

“…This can be attributed to the presence of O impurities [26] (see Table 2) mainly coming from oxidization in air after annealing. This phenomenon can be avoided by keeping the sample under inert atmosphere or using a starting Ti/O/C mixture with more C to obtain a protective thin layer of C on the TiC nanograins surface after carburization [21]. The final TiC mean crystallite size is estimated to T XRD = (75.9 AE 5.3) nm from Fig.…”

Synthesis of nanosized zirconium carbide by laser pyrolysis route

“…When applied to Zr/O/C powders synthesis, this system could allow production rates as high as 50 g h −1 on a laboratory scale. Aiming at the carburization, the Zr/O/C nanocomposites were annealed in a graphite furnace under Ar atmosphere for several annealing temperatures (Ta) to remove oxygen and form ZrC, as already seen for Ti/O/C reduction toward TiC in a previous work [20].…”