MAX Phases as Nanolaminate Materials: Chemical Composition, Microstructure, Synthesis, Properties, and Applications

Abstract

Ceramics is one of the oldest materials prepared and used by human beings. Ancient ancestors started to make pottery by forming and burning clay since the earliest civilizations. Ancient people started to fabricate burnt claywares since %6500 B.C., and clayware as a commercial product was available by %4000 B.C. [1] In modern society, as one of the largest branches in material family, ceramics have been developed and used in almost every fields of human beings' lives. In some senses, ceramics and metals possess complementary properties; generally, ceramics show the advantages of high strength, high hardness, high chemical stability, high wear resistance, whereas ceramics typically show intrinsic brittleness and poor plasticity due to their covalent and/or ionic chemical bonding; metals have good plasticity, high toughness, and high thermal and electronic conductivity; however, they typically show lower chemical stability and lower hardness than ceramics. It would be marvelous for a material to combine the properties of ceramics and metals. MAX phases are the materials that meet the challenge.MAX phases are a family of nanolaminate ternary nitrides and carbides, which were first discovered by Nowotny and his colleagues in Vienna. [2] In the beginning, MAX phases have a general formula of M nþ1 AX n (n ¼ 1-3), where M is a transition metal, A is an element from group A, and X is either carbon or nitrogen. The n value could be 1, 2, or 3, and the phases are named as 211, 312, and 413 MAX phases, respectively. These MAX phases show a hexagonal crystal structure (P63/mmc), consisting of M 6 X octahedra separated by A atomic layers. [3] M─X bonds in M 6 X octahedra are strong covalent bonds, whereas the M─A bonds between M 6 X and A atomic layer are much weaker, especially in shear. This unique bonding structure is analogous to graphite, and it is the special bonding structure that endows MAX phases properties of both ceramics and metals. On the one hand, MAX phases are stiff, lightweight, chemically stable, and oxidation resistant, which are the features of ceramics; on the other hand, they exhibit good electric and thermal conductivity as well as excellent machinability and damage tolerance, which are the features of metals.Unfortunately, MAX phases had not attracted enough attention in both academia and industry until 1996 when Barsoum et al. [4] synthesized and characterized Ti 3 SiC 2 . Ever since then, material researchers become more interested in this material. [5] In the past two decades, many MAX phases have been synthesized and tested to show highly unusual properties, [6] which will be discussed with detail in the following sections. The intensive extent of the researches on MAX phases can be demonstrated by the published papers (Figure 1). A remarkable jump can be observed between 1998 and 1999, and after that, the number of published papers increases steadily, reaching as high as 980 papers in 2019 (Figure 1a). From another aspect, the citation of the milestone paper published by Barsoum [4] also signific...

High‐Entropy Carbonitride MAX Phases and Their Derivative MXenes

“…MAX phases are a class of layered transition metal carbides, nitrides, and carbonitrides in a chemical formula of M n+1 AX n (M is an early transition metal element, A represents an element mainly from groups 13–16, X is C and/or N, n = 1–4). [ 1–4 ] Typically, MAX phases possess a unique hexagonal crystalline structure with a space group of P 6 3 / mmc , in which strong covalent bonded M n+1 X n atomic layers are interleaved by A layers via weak metallic bonds, enabling MAX phases with good oxidation resistance, high electrical and thermal conductivities, holding great potential in the fields of mechanics, electrics, and protective coatings. [ 2,5–8 ] In a recent decade, MAX phases have been widely utilized to synthesize their derivative 2D MXenes (M n+1 X n T x , T is the surface functional group) by selective extraction of A layers.…”

Surface Functionalized MXenes for Wastewater Treatment—A Comprehensive Review

“…[118] A high surface area is an important characteristic for various fields such as catalysis. [130] In another study, layered structures of Ti 3 C 2 T x MXene were prepared and modified with amino groups and then further treated with a borate affinity sorbent, 4-formylphenylboronic acid (4-FPBA), to produce Fe 3 O 4 @Ti 3 C 2 -BA. BET analysis revealed that this nanocomposite possessed a high specific surface area of 33.77 m 2 g −1 (Table 1).…”

Metal (Mo, W, Ti) Carbide Catalysts: Synthesis and Application as Alternative Catalysts for Dry Reforming of Hydrocarbons—A Review

“…A special family of transition metal carbides is constituted by multilayer metal carbides with a 2D nanosheet structure similar to that of graphene, belonging to the group of compounds called MXenes. The term MXenes denotes carbides and nitrides of transition metals, with the general formula M n+1 X n T x , where n = 1, 2, 3, or 4, M refers to the transition metal (M = Sc, Ti, V, Cr, Mn, Y, Zr, Nb, Mo, Hf, Ta, and W [23,161]), and X refers to the p-block element (silicon, aluminum, gallium), while T describes the type of terminal groups (-O, -OH, -F, -Cl) in the amount of x per selected unit. They are obtained by selectively removing component A from the ternary MAX matrix.…”