3D crystalline transition metal carbides (TMCs) and nitrides (TMNs) are known as metallic ceramics because they combine the high hardness, melting point and chemical stability of ceramics with high metallic conductivity. Since the mid-20th century, they have been used as cutting tools, wear-resistant and high-temperature materials, and active materials for energy storage and conversion. By the discovery of 2D carbides and nitrides, MXenes, the family of TMCs and TMNs has grown exponentially in terms of chemical diversity, structures, and applications beyond the traditional 3D crystalline phases. Despite the large number of MXene studies, MXenes have barely been studied as ultra-high temperature 2D additives in metal and ceramic composites. The lack of such studies is primarily due to the oxidation and instability of MXenes at room temperature. However, any one-nanometer-size TMC grain is prone to oxidation at ambient conditions. This is why TMCs are always sintered in adequate high-temperature processes with low-oxygen content. Very recently, we showed that by high-temperature annealing of Ti3C2Tx MXene under inert atmosphere, MXene flakes transform to lamellar 3D crystalline ordered carbon vacancy TiCy and superstructure Ti2C up to 1000 C and disordered carbon vacancy TiCy above 1000C. Inspired by one of Dr. Yury Gogotsi's research expertise, this presentation will focus on the evolution of TMCs from bulk 3D crystalline phases to 2D carbide MXenes. We will also present the potential of MXenes to form novel 3D crystalline TMCs and the use of MXenes as the precursor and additive materials to potentially transform the ultra-high temperature ceramics.

From 3D carbide crystals to 2D MXenes and vice versa

ACS Fall 2021

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