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Crystal Chemistry and Specific Crystal Structures
Published in David W. Richerson, William E. Lee, Modern Ceramic Engineering, 2018
David W. Richerson, William E. Lee
MAX phases are a family of mostly hexagonal ternary carbides and nitrides with the general formula Mn+1AXn with n being an integer, M being an early transition metal, A being a group 13–16 element and X being C and/or N. More than half of known MAX phases were first synthesized in the 1960s by Nowotny et al.8 They were little studied for more than two decades until Barsoum and El-Raghy reported in 1996 the remarkable mechanical properties of Ti3SiC2 (see Barsoum and El-Raghy9), and further demonstrated these properties were shared by the other MAX phases. Due to their structure consisting of the stacking of n “ceramic” layer(s) of MX interleaved by an A “metallic” plane (Figure 5.22 from Zapata-Solvas et al.10), MAX phases are characterized by a combination of both ceramic and metallic behavior. Like most metals and alloys, they possess high thermal shock resistance, have a good machinability, and high thermal and electrical conductivities, while like most ceramics, they have high decomposition or melting temperature and high elastic stiffness. This combination of properties has led to extensive research into MAX phases with potential structural applications in the energy, aerospace, and other sectors. Furthermore, MAX phases are also of interest as precursors for MXenes (Mn+1Xn 2-D nanosheets) which have properties analogous to graphene.
Electroerosion resistant composite materials and coatings of electrical contacts
Published in Denis A. Romonov, Stanislav V. Moskovskii, Viktor E. Gromov, Surface Structure Modification nd Hardening of Al-Si Alloys, 2020
Denis A. Romonov, Stanislav V. Moskovskii, Viktor E. Gromov
MAX phases with the formula Mn + 1AXn (where M is a transition metal; A is an element of group IIIA or IVA; X is C and/or N; n = 1–3) are a group of layered ternary compounds with a high modulus of elasticity, as well as good thermal and electrical conductivity, combining the properties of both metals and ceramics [5]. As typical MAX phases, Ti3AlC2 [6] and Ti3SiC2 [7] efficiently strengthen copper-based electrical contact materials. Professor M.M. Liu et al. [8] fabricated Ag/Ti3AlC2 composites by hot pressing and found that they are potentially suitable for materials of sliding electrical contacts and can be used with high efficiency because they showed good mechanical and electrical properties. In [9], the authors prepared Ag/10 wt.% Ti3AlC2 is an electric contact material by powder metallurgy and its resistance to arc erosion was studied, which turned out to be comparable to the commercial Ag/CdO contacts used in contactors. As a rule, the grain size of the matrix phase and the size of the filler are of great importance for the mechanical and electrical properties of the composite.
Advanced 2D Materials for Energy Applications
Published in Ram K. Gupta, 2D Nanomaterials, 2022
Immanuel Paulraj, Chia-Jyi Liu
Since the isolation of one atom thick, 2D crystal graphene from graphite in 2004, numerous 2D materials have been discovered including TMD monolayers, 2D hexagonal boron nitrides (2D-hBN), and MXenes. The 2D materials MXenes consist of few-atoms-thick layers of metal carbides (MCs), nitrides, or carbonitrides. MXenes are composed of Mn+1Xn stacked sheets, which are held together by van der Waals interactions and/or hydrogen bonds. MXenes are used in a wide range of applications because of their unique and rich properties such as metallic conductivity, tunable surfaces, excellent mechanical strength, transparency, high transmittance, and acting as a host for intercalation. MXenes have three structures and are inherited from the parent MAX phases: M2X, M3X2, and M4X3. In 2011, Naguib et al. [3] developed a method to produce 2D nanosheets composed of a few Ti3C2 layers and conical scrolls by selectively etching out “A” elements (Al) from a MAX phase (Ti3AlC2) at room temperature in hydrofluoric acid. The MAX phases have a hexagonal layered structure with the general formula of Mn+1AXn, (MAX) where A is an element from group 13 or 14 of the periodic table. Since the surfaces of MXene sheets are often terminated by a functional group such as O, F, OH, or Cl, they are represented by a general formula Mn+1XnTx, where n = 1 to 4, M is an early transition metal, X either carbon and/or nitrogen and T a functional group. MXene-based PCMs have recently attracted attention due to their good thermal performance. MXene-based PCM composite films are easy to make and have high electrical conductivity; they are also stable in water, strong and stiff.
Effect of hydrochloric acid and hydrofluoric acid treatment on the morphology, structure and gamma permeability of 2D MXene Ti3C2Tx electrodes
Published in Canadian Metallurgical Quarterly, 2022
Mesut Ramazan Ekici, Emre Tabar, Ahmet Atasoy, Emrah Bulut, Gamze Hoşgör
Primarily two-dimensional (2-D) materials have attracted tremendous attention because of their fast ion diffusion properties. It makes them essential host materials for metal-ion batteries [1]. Recently, a new class of 2-D early transition metals, so-called Mxenes with structures similar to graphene, have been synthesised by removing intermediate elements from MAX phases using hydrofluoric acid (HF) at room temperature [2,3]. Here, the MAX phases are triple-layered carbides or nitrides, commonly known by the general formula Mn+1AXn (n = 1, 2, 3), where M refers to an early transition metal, A is the group A elements, and X is carbon or nitrogen [3]. The general formula for the synthesised Mxenes also reads Mn+1XnTx (n = 1, 2, 3), where M and X are again transition metals and carbon or nitrogen, respectively, and Tx defines surface groups [2,4].
Ion sputtering for preparation of thin MAX and MXene phases
Published in Radiation Effects and Defects in Solids, 2020
J. Vacík, P. Horák, S. Bakardjieva, V. Bejsovec, G. Ceccio, A. Cannavo, A. Torrisi, V. Lavrentiev, R. Klie
Currently, increasing attention is paid to the development of new thin-film composites with attractive properties and high functionality (7). Such composites are also MAX and MXene phases (with the stoichiometric nomenclature Mn+1AXn and Mn+1Xn, respectively, where n = 1, 2, 3, M is an early-transition d metal, A is an element from the IIIA or IVA groups of the periodic chart, and X is carbon or nitrogen) (8). The properties of the MAX and MXene systems are based on combination of the best attributes of the metals and ceramics. For example, MAX phases are resistant to radiation, thermal shock or corrosion and exhibit high electrical conductivity. MXenes show, e.g. a rare combination of very good electronic conductivity and hydrophilicity. These unusual properties make these novel ceramic materials particularly suitable for applications in extreme environment or high-tech systems: e.g. MAX phases in nuclear engineering, metallurgy, mining or space technology; MXenes in thin electronic devices, thin optical conductive coatings, thin battery energy storage, or as nanocomposite fillers in functional polymers (9).
Radiation-induced phase separation in nanostructured Hf-In-C ternary thin films under irradiation with 200 keV Ar+ ion beam
Published in Radiation Effects and Defects in Solids, 2022
Jiri Vacik, Antonino Cannavò, Snejana Bakardjieva, Jaroslav Kupcik, Vasily Lavrentiev, Giovanni Ceccio, Pavel Horak, Jiri Nemecek, Alessio Verna, Matteo Parmeggiani, Lucia Calcagno, Robert Klie, Jan Duchoň
A class of solids, namely ternary carbides or nitrides called MAX-phases, has attracted increasing attention due to their unique chemical, physical, electrical, and mechanical properties, which are halfway between metals and ceramics (1, 2). The formal stoichiometry formula is Mn+1AXn, in which M is an early transition metal (i.e. Sc, Ti, Mo, Hf), A is an A-group element (i.e. Al, Si, In, Sn), X is either C and/or N, and parameter n = 1, 2, 3. The main advantage stands in the 3D nanolayered hexagonal phase, (D6h4, P63/mmc), where the M–X bonds have a mix of ionic, metallic and covalent contributions, while M-A bonds are purely metallic. The possibilities of using the unusual combination of metallic and ceramic properties of the MAX phases have led to their rapid worldwide applications in many research and technological fields (3). Unlike other 3D layered materials, such as graphite and transition metal dichalcogenides (4), which are weaker due to Van der Waals interactions, MAX phases represent composites with a unique combination of properties, e.g. good electrical and thermal conductivity high-temperature stability, resistance to oxidation, radiation tolerance and high resistance to shear or other mechanical stress (2, 5–8). Due to these properties, MAX phases can find applications in extreme environments, e.g. as construction materials for heating elements (nozzles and heat exchangers), rotating bearings of electrical contacts, or as protective coating materials against corrosion and radiation damage in nuclear engineering.