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.

Two-dimensional (2D) MoB MBene has attracted much attention due to its fascinating properties and functional applications. So far work on synthesis of 2D MoB nanosheets through acid or alkaline etching of MoAlB has not been very successful. It has been proposed that 2D MoB MBene may be fabricated by chemical etching of a Mo₂AlB₂ precursor, but further investigations were not performed possibly due to the difficult preparation of the metastable Mo₂AlB₂ compound at high temperatures by solid state reactions. Here, we report on the successful synthesis of the Mo₂AlB₂ compound and 2D MoB nanosheets by deintercalation of Al from MoAlB through a ZnCl₂ molten salt etching approach at relatively low temperatures. The influences of etching temperature, etching time, and starting mixtures on the formation of desirable phases have been investigated. A pure Mo₂AlB₂ compound was synthesized at temperatures below 600℃, while 2D MoB MBene nanosheets were obtained at 700℃ through the molten salt etching of MoAlB. In addition, the present work further confirms that the MoB MBene can be prepared by etching of the as-synthesized Mo₂AlB₂ precursor in a LiF-HCl solution. Our work demonstrates that the molten salt etching is an effective method to prepare 2D MoB MBene.

Ti₃C₂T_x MXene, a new 2D nanosheet material, is expected to be an attractive reinforcement of metal matrix composites because its surfaces are terminated with Ti and/or functional groups of –OH, –O, and –F which improve its wettability with metals. Thus, new Ti₃C₂T_x/Al composites with strong interfaces and novel properties are desired. To prepare such composites, the chemical stability of Ti₃C₂T_x with Al at high temperatures should be investigated. This work first reports on the chemical stability of Ti₃C₂T_x MXene with Al in the temperature range 500–700 °C. Ti₃C₂T_x is thermally stable with Al at temperatures below 700 °C, but it reacts with Al to form Al₃Ti and TiC at temperatures above 700 °C. The chemical stability and microstructure of the Ti₃C₂T_x/Al samples were investigated by differential scanning calorimeter, X-ray diffraction analysis, scanning electron microscopy, and transmission electron microscopy.