From structural ceramics to 2D materials with multi-applications: A review on the development from MAX phases to MXenes

MAX phases (Ti3SiC2, Ti3AlC2, V2AlC, Ti4AlN3, etc.) are layered ternary carbides/nitrides, which are generally processed and researched as structure ceramics. Selectively removing A layer from MAX phases, MXenes (Ti3C2, V2C, Mo2C, etc.) with two-dimensional (2D) structure can be prepared. The MXenes are electrically conductive and hydrophilic, which are promising as functional materials in many areas. This article reviews the milestones and the latest progress in the research of MAX phases and MXenes, from the perspective of ceramic science. Especially, this article focuses on the conversion from MAX phases to MXenes. First, we summarize the microstructure, preparation, properties, and applications of MAX phases. Among the various properties, the crack healing properties of MAX phase are highlighted. Thereafter, the critical issues on MXene research, including the preparation process, microstructure, MXene composites, and application of MXenes, are reviewed. Among the various applications, this review focuses on two selected applications: energy storage and electromagnetic interference shielding. Moreover, new research directions and future trends on MAX phases and MXenes are also discussed.

Synthesis and Characterization of a Nearly Single Bulk Ti2AlN MAX Phase Obtained from Ti/AlN Powder Mixture through Spark Plasma Sintering

MAX phases are an advanced class of ceramics based on ternary carbides or nitrides that combine some of the ceramic and metallic properties, which make them potential candidate materials for many engineering applications under severe conditions. The present work reports the successful synthesis of nearly single bulk Ti2AlN MAX phase (>98% purity) through solid-state reaction and from a Ti and AlN powder mixture in a molar ratio of 2:1 as starting materials. The mixture of Ti and AlN powders was subjected to reactive spark plasma sintering (SPS) under 30 MPa at 1200 °C and 1300 °C for 10 min in a vacuum atmosphere. It was found that the massive formation of Al2O3 particles at the grain boundaries during sintering inhibits the development of the Ti2AlN MAX phase in the outer zone of the samples. The effect of sintering temperature on the microstructure and mechanical properties of the Ti2AlN MAX phase was investigated and discussed.

Crystal Chemistry of Ternary Rare Earth Transition Metal Carbides: Studies of the Tb-Fe-C System at 800°C

The isothermal section of the phase diagram of Tb–Fe–C system at 800 °C was studied in the full concentration range using powder X-ray phase and structure analyses, and energy-dispersive X-ray spectroscopy. Six ternary compounds Tb1.88Fe14C, Tb13Fe10C13, TbFeC2, Tb15Fe8C25, Tb5.64Fe2C9, Tb2FeC4 and a limited solid solubility of carbon in the crystal structure of the binary parent compound Tb2Fe17Cх (0≤ х ≤0.8) have been found to exist at 800 °C. The crystal structures of two new ternary carbides have been determined by means of powder X-ray diffraction: Tb15Fe8C25 with structure type Er15Fe8C25, space group P321, a = 11.9706(3) Å, c = 5.1733(2) Å, RB(I) = 0.07, RP = 0.06, RPw = 0.08, and Tb13Fe10C13 with structure type Gd13Fe10C13, space group P3121, a = 9.1800(9) Å, c = 23.703(5) Å, RB(I) = 0.04, RP = 0.16. Both compounds are representatives of the carbometalate class of complex carbides. Tb15Fe8C25 displays an itinerant ferro-or ferrimagnetic ordering of the Fe 3d-moments below TM ≈ 50 K while Tb 4f-moments remain essentially paramagnetic at least down to about 10 K.

Mechanical Properties of Carbon Nanotubes Reinforced AZ91 Composites by Enhanced Interfacial Bonding

The aim of this study is to enhance the interfacial bonding strength of carbon nanotubes (CNTs)/AZ91 composites by heat treatment (HT). Ternary carbides (Al2MgC2) were in situ formed and uniformly dispersed between CNTs and AZ91 matrix by 823K heat treatment of CNTs/AZ91 composites for 12 h. In situ synthesized Al2MgC2 can strengthen the interfacial bonding of CNTs/AZ91 composites, and guarantee an effective load transfer between matrix and CNTs. The HT-CNTs/AZ91 composites showed outstanding mechanical properties due to the excellent interface enhancing effect of Al2MgC2. Compared with pure AZ91 alloy, HT-CNTs/AZ91 composites exhibit improved ultimate tensile strength and 0.2% yield strength by 7% and 22% respectively.

Enhancement of the Pitting Corrosion Resistance of AISI 316LVM Steel with Ta-Hf-C/Au Bilayers for Biomedical Applications

Tantalum carbide (TaC), hafnium carbide (HfC), and Ta-Hf-C mixed coatings with and without a gold (Au) interlayer were deposited on 316LVM steel substrates by the magnetron cosputtering technique in order to improve the corrosion resistance of steel substrates in a simulated biological fluid. To study the effect of the gold interlayer on pitting corrosion, the different systems were placed in contact with Ringer’s solution at pH 7.4 and a temperature of 37°C. The electrochemical properties of the coatings were determined using polarization curves. Subsequently, the surface morphologies were observed using scanning electron microscopy (SEM) in order to analyze the corrosion processes on the different surfaces. The gold interlayer was found to significantly improve the electrochemical properties of the system, showing a decrease in the pitting corrosion and deterioration rate, while it is expected that the binary and ternary carbides provide mechanical stability to the bilayers protecting the gold.