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Symposium CE
Progress in Nano-laminated Ternary Carbides, Nitrides and Borides (MAX/MAB) Phases and Derivatives Thereof (MXenes)

ABSTRACTS

CE-1:IL01  Chemically Ordered Laminate Borides and their Two-dimensional Derivatives from Chemical Exfoliation
J. ROSEN, Materials Design, Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping, Sweden

Exploratory theoretical predictions in uncharted structural and compositional space are integral to materials discoveries. A more recent addition to the family of MAB phases is new types of chemically ordered quaternary borides, i-MAB (M´4/3M´´2/3AlB2) and o-MAB (M´4M´´SiB2), in which the M-atoms are in-plane and out-of-plane chemically ordered, respectively. Both types of phases can be chemically exfoliated into 2D sheets, and selectively prepared in multilayer form, as delaminated single-layer sheets in colloidal suspension, or as additive-free filtered films. For example, Ti4MoSiB2 o-MAB can be used to derive 2D TiOxCly of high yield. (Mo2/3Y1/3)2AlB2 and (Mo2/3Sc1/3)2AlB2 i-MAB can be used for realization of so called boridene in the form of single-layer 2D sheets with ordered metal vacancies, Mo4/3B2-xTz (Tz = -F, -O, -OH). The present talk will summarise the results to date of 2D materials synthesis from laminated borides, the mechanisms behind the realization of these 2D materials, and evaluation of selected properties.


CE-1:IL02  New Solid Solution MAX Phases
B. Tunca, K. Van Loo, J. Vleugels, KU Leuven, Department of Materials Engineering, Heverlee, Belgium; K. Lambrinou, SCK CEN, Mol, Belgium & University of Huddersfield, School of Computing and Engineering, Huddersfield, UK

The number of MAX phase compounds is increasing quickly, especially the number of new out-of-plane ordered (o-MAX) as well as in-plane ordered (i-MAX) MAX phases rises on a monthly basis. This presentation will address the current evolution towards (M,M’)n+1(A,A’)Cn MAX phases solid solutions, with elemental substitution on the M and/or A sites. Amongst the studied new solid solution MAX phases are reactive hot pressed or spark plasma sintered (Zr,Ti)2(Al,Sn)C, (Zr,Nb)2(Al,Sn)C, (Ta1-x,Hfx)4AlC3, (Ta1-x,Nbx)4AlC3, (Ta0.75,Hf0.25)4(Al0.5,Sn0.5)C3, (Ta0.75,Nb0.25)4(Al0.5,Sn0.5)C3 and Zr2(Al1-x,Bi2x/3,Pbx/3)C. The addition of Sn as A-site alloying element allowed to enhance the phase purity of the solid solution (M,M’)2AlC and (M,M’)4AlC3 phases, which is explained in terms of a change in the prismatic and octahedral distortion of the MAX phase crystal lattice. The general observation is that large M-atoms combine better with large A-atoms, whereas small M-atoms combine better with small A-atoms. The M and A atomic radii match can be used as a practical guideline for the synthesis of new MAX phase solid solutions with appealing properties. In general, the concept of a double solid solution was found advantageous in terms of ease of MAX phase synthesis and MAX phase purity.


CE-1:L04  Investigation of Two-dimensional Boridene from First Principles and Experiments 
P. HELMER1, J. HALIM1, J. Zhou1, R. MOHAN2, B. WICKMAN2, J. Björk1, J. Rosen1, 1Materials Design Division, Department of Physics, Chemistry and Biology, IFM, Linköping University, Linköping, Sweden; 2Chemical physics, Department of Physics, Chalmers University of Technology, Gothenburg, Sweden

Research interest in the family of 2D MXenes has expanded rapidly since their discovery in 2011. Chemically etched from the 3D laminated carbides and nitrides called MAX phases, they show a wide range of properties. With inspiration from MAX phases and MXenes, efforts has been directed towards laminated structures outside the MAX family, in hope of discovering new families of 2D materials. MAB phases are similar to MAX phases but contain B instead of C or N, and recently a novel 2D metal boride, given the name boridene, was indeed derived from a quarternary MAB phase. Atoms or functional groups are absorbed on the surface of the 2D sheets in the etching process. These are called terminations, and they play a large role for the materials properties. Therefore we have used first principles calculations, guided by detailed XPS analysis, to investigate possible terminations (O, OH, and F) on the boridene. Several different structures were found dynamically stable, and the electronic properties for these indicate metallic and semiconducting characteristics, depending on choice of terminations. We have also performed characterization of selected properties, and show that the boridene has high catalytic performance for the hydrogen evolution reaction, with an onset potential of 0.15 V.


CE-1:IL05  Theoretical and Experimental Exploration for Expanding the Elemental Space of Chemically Ordered and Disordered MAX and MAB Phases
M. DAHLQVIST, J. Rosen, Materials Design Division, Department of Physics, Chemistry, and Biology (IFM), Linköping University, Linköping, Sweden

The exploration of MAX and MAB phases can be accelerated by theoretical structural design on the atomic level combined with combinatorial experimental synthesis. This was recently demonstrated for a range of MAX and MAB phase alloys, (i) with out-of-plane chemical order (1-3) and (ii) with in-plane chemical order (4-6). We use predictive phase stability calculations to explore quaternary MAX and MAB phases upon alloying between two transition metals, M´ and M´´, from Group 3 to 9. Important to note is that for the materials investigated, focus is both chemical ordering of M´ and M´´, and their disordered counterpart. This is key for making reliable predictions since this information is not known a priori. We confirm all experimentally known phases to date, and suggest a range of stable ordered and disordered hypothetical combinations. We also suggest rules for when preference for chemical order or disorder are expected. In extension, we suggest a matching set of novel 2D counterparts, from selective etching of the A-element. The here demonstrated structural design on the atomic level expands the property tuning potential of functional ceramics.


CE-1:L07  Theoretical Stability Predictions of Orthorhombic and Hexagonal Ternary MAB Phases
A. CARLSSON, J. Rosén, M. Dahlqvist, Materials Design Division, Department of Physics, Chemistry, and Biology (IFM), Linköping University, Linköping, Sweden

In the quest for finding novel thermodynamically stable, layered, MAB phases promising for synthesis, we herein explore the phase stability of ternary MAB phases by considering both orthorhombic and hexagonal crystal symmetries for various compositions (MAB, M2AB2, M3AB4, M4AB4, M4AB6) where M = Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co and A = Al, Ga, In. The thermodynamic stability of seven previously synthesized MAB phases are confirmed, three additional phases are predicted to be stable, and, in addition, 23 phases are found to be close to stable. Furthermore, the crystal symmetry preference for forming orthorhombic or hexagonal crystal structures is investigated where the considered Al-based MAB phases tend to favorize orthorhombic structures whereas Ga- and In-based phases prefer hexagonal structures. The theoretically predicted stable MAB phases along with the structural preference is intended to both guide experimental efforts and to give an insight on the structural properties for different structural symmetries of MAB phases.


CE-1:L08  Chemical Exfoliability of MAX Phases in Hydrogen Fluoride Studied from First Principles
J. Björk, J. Halim, J. Zhou, J. Rosen, Materials Design Division, Department of Physics, Chemistry and Biology (IFM), Linköping University, Sweden

The factors controlling the top-down manufacturing of MXenes by selectively etching the A elements from parent MAX phases are still under debate. Particularly, it is of great interest to understand why it is possible to etch the A element from some MAX phases to create MXenes, while for others it is not. Here we have computationally studied the etching of more than 20 MAX phases in HF. We consider both the complete exfoliation process from MAX to MXene, as well as comparing the competing processes during the initial steps of the etching. The results are compared to MAX phases successfully converted to MXenes experimentally, as well as to those that have been unsuccessful, including previously unpublished experimental data. The results show that for all MAX phases for which the free energy differences for the initial removal of an A element and an M element are negative and positive, respectively, are experimentally exfoliable. Furthermore, we provide a detailed understanding of why the Mo2Ga2C is exfoliable while Mo2GaC is not. Our results offer unprecedented understanding for the synthesis of MXenes under acid conditions, which we also anticipate being of vital importance for the computational exploration of new families of 2D materials synthesizable by chemical exfoliation.

 
CE-2:IL01  Quat Derived Nanomaterials or QDNs
M.W. BARSOUM, Department of Materials Science and Engineering, Drexel University, Philadelphia, PA, USA

One- (1D) and two-dimensional (2D) materials offer advantages that their 3D counterparts do not. To produce such materials in bulk there are  two  conventional approaches: bottom-up and top-down.  MXenes are an excellent example of the latter. The main drawback of this approach is high cost in first making the layered solid and then the many steps needed to etch and delaminate them. The bottom-up approach is in principle much more scalable. There are several bottom-up approaches, the one of interest here is the sol-gel approach common in the processing of ceramic powders, especially oxides of Ti and Si. The man disadvantages of this approach are the need to rely on the solubility of the precursor salt or compound in water and the need for a calcination and/or hydrothermal step that is usually needed to crystallize the products made at lower temperatures. In trying to etch the MAX phases without HF, we stumbled on a very powerful method to make 1D and 2D materials. The general idea is to dissolve inexpensive, non-water soluble, precursors in quaternary ammonium cation salts, or quats, at temperatures < 100 °C under ambient pressures for a few days. The aim of this talk is to describe the resulting materials and some of their properties in two systems: Ti and Mn. In the former, we converted 10 binary and ternary titanium carbides, nitrides, borides, phosphides, and silicides into anatase-based, 1D sub-nano filaments ≈ 6x10 Å in cross-section that self-assemble into 2D flakes by immersing them in a tetramethylammonium hydroxide, TMAH, solution at temperatures in the 50 to 85 °C range. The 2D flakes are quite well-ordered in the stacking direction. In some cases, the conversion is 100 % precluding the need for centrifuges, filters, etc. We currently routinely make 100 g batches in a lab setting. In some cases, we also make mesoscopic powders. Electrodes made from some of filtered films performed well in lithium-ion and lithium-sulphur systems. These materials also biocompatible and reduce the viability of cancer cells thus showing potential in biomedical applications. In the Mn-case, five water-insoluble Mn-bearing precursors, viz. Mn3O4, Mn2O3, MnB, Mn5SiB2, and Mn2AlB2, were converted to birnessite 2D MnO2 flakes, that are remarkably crystalline. Here again, the precursor powders are immersed in 25 wt. % TMAH aqueous solutions at 50 °C to 80 °C, for 4 to 2 days, respectively. The 2D sheets demonstrate reversible O2 electrocatalysis with activities comparable to those of a commercial Pt/C catalyst. Synthesizing 1D and 2D materials in bulk, at near ambient conditions, starting with non-layered precursors (e.g., TiC, Mn3O4) could usher a new age where 1D and 2D materials can be mass produced inexpensively using earth abundant elements and a green process.


CE-2:IL02  Synthesis of MAX Phases with Unique Shapes and Morphologies
C.S. Birkel, J.P. Siebert, Arizona State University, Tempe, AZ, USA; N. Kubitza, Technische Universität Darmstadt, Darmstadt, Germany

MAX phases are typically prepared by high-temperature – sometimes also high-pressure – solid-state synthesis techniques. The metal, binary carbide or intermetallic powders that are used as starting materials limit their processability and the target materials typically form as layered crystals in the tens of micrometer size regime. In contrast we have developed a wet chemical-based synthesis route that starts with an aqueous gel containing atomically mixed metal precursors that are coordinated by citric acid. Upon heating this gel transforms into anisotropic and needle-like particles of MAX phase Cr2GaC that are highly crystalline. We have further extended this approach to prepare MAX phase microwires, (hollow) microspheres and thick films. We study the structure, morphology and transport properties of these new shapes of MAX phases. Ultimately, this can pave the way to additional functionalities and potential areas of application for these types of materials.


CE-2:L04  Near Ambient Conditions, Bottom-up Synthesis of Metal Oxides 2D flakes, their Properties, and Potential Applications
H. BADR, M. Barsoum, Department of Material Science and Engineering, Drexel University, Philadelphia, PA, USA

Two-dimensional (2D) materials, which possess nanometer thickness and infinite planner dimensions, thrive on the rich variety of features that are distinctive from their bulk counterparts. The conventional method for the bulk synthesis of 2D materials has predominantly been through etching of layered solids. Herein and for the first time, we convert – at near ambient conditions – a dozen of different precursors into 2D flakes. In that, the precursor is simply heated up in a polyethylene bottle with common, cheap salts for a few days. The structure, composition, oxidation state, and morphology of the prepared sheets are resolved by density functional theory, X-ray diffraction, X-ray photoelectron, electron energy loss, Raman, X-ray absorption near edge structure spectroscopies, atomic force microscope, scanning, transmission and high-resolution transmission electron microscopies and selected area diffraction. The resulting flakes of different intercalants enabled the fabrication of electrodes that performed well in Li-ion and Li-S battery. They were also tested in cancer therapy and found to reduce the viability of cancer cells. Synthesizing 2D materials in bulk at near ambient conditions is paradigm shifting and will open new and exciting avenues of research/applications.


CE-2:L05  Pulsed Laser Deposition as a New Tool for the Epitaxial Growth of MAX Phase Thin Films
H. Pazniak1, M. Stevens1, A. Jemiola1, M. Felek1, M. Farle1, 2, U. Wiedwald1, 1Faculty of Physics and Center for Nanointegration Duisburg-Essen, University of Duisburg-Essen, Germany; 2Kirensky Institute of Physics, Federal Research Center KSC SB RAS, Krasnoyarsk, Russia

Much attention has been put on the epitaxial growth of MAX phase thin films [1]. Besides magnetron sputtering, pulsed laser deposition (PLD) is a powerful tool to grow epitaxial films. PLD allows the stabilization of metastable phases and gives rise to a good mixture due to the high energy impact of incoming atoms (up to 100 eV). Moreover, the stoichiometry of the films can be precisely adjusted using elemental targets, and it is only limited by the amount of material deposited per laser pulse (~0.01 monolayer). In this work, we present the first successful preparation of the Cr2AlC MAX phase on MgO(111) and Al2O3(0001) substrates by PLD at 600°C with film thicknesses of 10-50 nm [2]. The KrF Laser (248 nm) hits the 3 elemental targets at an energy density of 13 J cm-2. Structural and morphological investigations reveal a columnar growth mode with Cr2AlC(0001) || MgO (111) and Cr2AlC [11-20] || MgO[10-1]. Cr2AlC serves as parent compound for Fe doping up to 4 at-% [3].
Funding by the DFG within CRC/TRR 270, project B02 (Project-ID 405553726) is gratefully acknowledged.
[1] A. S. Ingason et al., J. Phys.: Condens. Matter 28, 43 (2016). [2] M. Stevens et al., Materials Research Letters 9, 343-349 (2021). [3] H. Pazniak et al., ACS Applied Nano Materials, in revision.



CE-2:L07  Synthesis in Hydride Cycle of Ti-Al-C based MAX-Phases from mixtures of Titanium Carbohydrides and Aluminum powders
G.N. MURADYAN1, S.K. Dolukhanyan, A.G. Aleksanyan, O.P. Ter-Galstyan, N.L. Mnatsakanyan, K.V. Asatryan, S.S.Mardanyan, A.B. Nalbandyan Institute of Chemical Physics of Armenian National Academy of Sciences (IChPhNAS RA), Yerevan, Armenia

At IChPh of NAS RA, new, highly efficient “hydride cycle” (HC) method has been developed for synthesis ofrefractory metal alloys. The gist of the method is the use of transition metal hydrides as starting materials. In the present work, for the first time HC was used in the synthesis of Ti2AlC and Ti3AlC2 MAX-phases. Two reactions were studied: TiC0.45÷0.55H0.22÷1.17+0.5Al→ Ti2AlC+Н2↑ and TiC0.67H0.31÷0.39+0.33Al→Ti3AlC2. Preliminarily, HCP TiC0.45H1.07÷1.17 and FCC TiC0.67H0.31÷0.39 titanium carbohydrides were synthesized in combustion mode (SHS). The influences of the titanium carbohydride/aluminum ratio, grain sizes of titanium carbohydrides (micro and nano sizes), pressure of charge compaction, dehydrogenation/sintering modes (heating temperature and rate) on the characteristics of the HC-synthesized phases were studied. For certification of the obtained phases, the chemical, differential thermal, X-ray phase, SEM analyses were used. The XRD and DTA analyses of the intermediate and final products permitted to follow the path of the MAX-phases formation: MAX-phases in HC formed in solid phase reaction, by diffusion mechanism, in one technological stage. A number advantages of HC method relative to the traditional ones in the synthesis of the MAX-phases were demonstrated.


CE-2:L08  Extrusion-based AM of MAX Phases Ti3SiC2 and Cr2AlC Feedstocks
E. Tabares1, A. Jimenez-Morales1, M. Kitzmantel2, E. Neubauer2, S.A. Tsipas1, 1Departamento de Ciencia e Ingenieria de Materiales e Ingenieria Quimica, IAAB, Universidad Carlos lll de Madrid, Leganes, Spain; 2RHP-Technology GmbH, Forschungs- und Technologiezentrum, Seibersdorf, Austria

The versatility in component design and production of Additive Manufacturing (AM) combined with the unique properties of MAX phases, makes AM a great method to produce MAX phase samples. Extrusion-based AM techniques use feedstocks in granulated or pellet form as raw materials and deposit them layer by layer, through extrusion of the material. This processing technique stands as an interesting alternative for feedstocks that cannot be produced in filaments, avoiding the complex step of filament production, or for materials that are not suited for powder-based techniques or wire deposition. In this work, the suitability of different Ti3SiC2 and Cr2AlC MAX phase sustainable feedstocks was studied, and printed samples were examined, to analyse the influence of the process on the internal microstructure. For each feedstock and geometry, the printing parameters were optimised and adjusted for good quality samples. In addition, debinding was achieved through a two-step process (solvent and thermal debinding), in order to ease the elimination of the polymeric binder. Finally, sintering of the samples was optimised through pressureless sintering, studying the influence of different thermal cycles and sintering atmospheres.


CE-2:L09  Optimized Spark Plasma Sintering of Bulk (Cr1-xMnx)2AlC MAX-phase
K. SOBOLEV, M. Gorschenkov, M. Dorokhin, V. Rodionova, Immanuel Kant Baltic Federal University, Kaliningrad, Russia; National University of Science and Technology MISiS, Moscow, Russia; Lobachevsky Nizhny Novgorod State University, Nizhny Novgorod, Russia

MAX-phases have recently attached the great interest due to the unique combination of ceramic and metallic properties. The search for the magnetic MAX-phases is also an ongoing goal as they may be applied in the plethora of fields, including spintronics, etc. One of the promising compositions is (Cr1-xMnx)2AlC. Recently the synthesis approach to produce highly-doped phase-pure (Cr1-xMnx)2AlC MAX-phase powders was proposed. However, attempts to further compress Mn-containing powders into bulk suffer from the growth of secondary phases. In this work we studied the high-temperature kinetics of (Cr1-xMnx)2AlC MAX-phase powder samples using DSC, XRD and TEM-EDX analysis. We observed the shift of DSC peaks, referring to the MAX-phase temperature decomposition, towards lower temperatures with the increase of Mn content in the structure. The decomposition is accompanied by the growth of the secondary phase grains on the surface of the MAX-phase particles. Knowing this, we optimized the spark plasma sintering (SPS) technique, previously applicable for the parental Cr2AlC MAX-phase, to successfully compress (Cr1-xMnx)2AlC MAX-phase ceramics into bulk in the whole range of Mn concentrations. The obtained results are of the significant value for the further application-oriented researches.


CE-3:IL01  Avoiding the Formation of Carbides in Cr2AlC MAX Phases under Oxidizing Environments
C. AZINA1, J. GONZALEZ-JULIAN2, P. Eklund3, J.M. Schneider1,  1Materials Chemistry, RWTH Aachen, Germany; 2Forschungszentrum Jülich, IEK-1, Germany; 3Energy Materials Unit, Thin film Physics Division, IFM, Linköping University, Sweden

Phase stability is likely to be one of the most important specifications which determine the lifetime of materials operating in extreme environments. In the case of MAX phases, the weakly bonded A-elements diffuse along the basal planes when a thermal load is applied or when in presence of oxidizing environments. That is the case of Cr2AlC, the loss of Al causes the decomposition of the MAX phase into the binary carbide, Cr7C3. In this work, the possibility of continuously supplying Al to a Cr2AlC coating is investigated, in order to avoid the formation of the carbide layer. To this end, Cr2AlC substrates with different microstructures were produced using Spark Plasma Sintering (SPS) from either elemental powders, or Cr2AlC powders obtained by solid state reaction and molten salt shielded synthesis (MS3). Using different starting powders allowed consolidating bulk samples of different grain sizes and phase purities. The substrates were subsequently coated with Cr2AlC coatings which were sputter-deposited from a powder metallurgical composite target. The thermal stability and oxidation behavior of the MAX/MAX assemblies were investigated both in- and ex-situ in order to assess the feasibility of supplying Al to Cr2AlC during oxidation at high temperatures.


CE-3:IL02  Breakaway Oxidation of Ti2AlC MAX Phase
J. GONZALEZ-JULIAN, S. Badie, O. Guillon, R. Vaßen, Institute of Energy and Climate Research, Forschungszentrum Jülich, Jülich, Germany

Aluminum-based MAX phases are well known by their unique combination of properties, such as lightweight, high elastic modulus, outstanding oxidation and corrosion resistance, good damage tolerance, easily machinability, excellent creep resistance, and high thermal and electrical conductivities. In particular, Ti2AlC is one of the compositions that most attention has attracted due to the excellent oxidation and corrosion resistance up to temperatures around 1300 °C.
The oxidation response up to temperatures around 1300 °C is excellent due to the formation of an external and protective alumina layer. However, under some environmental conditions and sample preparation, high amount of TiO2 is formed on the surface, which is a non-protective material. As a consequence, Ti2AlC is continuously oxidized since a homogenous and dense alumina scale is not formed anymore. In this work, we will study the different parameters that are critical to avoid the formation of TiO2, leading to run the samples at 1200 °C under thermal shock conditions for more than 1000 h.


CE-3:IL03  Alumina Forming MAX phases: Current Status and Future Perspectives
M. RADOVIC, Department of Materials Science & Engineering, Texas A&M University, College Station, TX, USA

Out of more than 165+ MAX phases sharing the same nanolayered crystal structure and chemical formula Mn+1AXn (where n = 1, 2 or 3, M is an early transition metal, A is an A-group element, and X is either C or N) those having Al on the A sublattice – most notably Ti2AlC and C2AlC – can form protective, self-healing and adherent alumina protective oxide scale in oxidizing environments at elevated temperatures. Apart from their excellent oxidation resistance, the fact that they are also elastically stiff, readily machinable, damage tolerant, resistant to thermal shocks, and some of them creep and fatigue resistant, makes them appealing for structural application at high temperatures. In this lecture, our current understanding of what makes some of the alumina forming MAX phases exceptionally oxidation resistant will be reviewed in more details. Oxidation mechanisms and kinetics observed in different alumina forming MAX phases will be discussed, including effect of impurities, secondary phases and grain size on the oxidation mechanism and morphology of the protective oxide layers. In addition, recent results on the oxidation breakaway studies carried out using for Ti2AlC and C2AlC wedge-shaped samples will be presented and discussed.


CE-3:L04  Elementary Deformation Mechanisms in Single-crystals of MAX Phases Analyzed by Complementary Experimental Approaches
S. Parent, C. Tromas, A. Joulain, H. Bahsoun, Pprime Institute, CNRS, University of Poitiers, ISAE-ENSMA, France; G. Renou, SIMAP, Grenoble, France

It is well known that at room temperature, plastic deformation in MAX phases is governed by dislocations movement. In most cases, the dislocations are a-type and glide in the basal plane. They may interact to form pairs of low angle-boundaries (kink band). Strong local crystal rotation that may be associated with delamination are also observed. Nevertheless, the elementary mechanisms are not fully understood yet. We present here a study of elementary deformation mechanisms of single-crystalline Cr2AlC. Spherical nanoindentation testing is used to initiate plasticity in single crystals in a chosen crystallographic orientation. The deformation microstructure is analysed by combining observations at the surface by Atomic Force Microscopy and in the volume by Transmission Electron Microscopy performed on thin foils prepared by Focussed Ion Beam in cross section through the indents. Crystallographic orientations of the highly misoriented domains below the indents are determined by Automated Crystal Orientation Mapping in the TEM. The analysis provide evidence of original deformation microstructures in MAX phases, including deformation twinning as well as unexpected dislocations configuration


CE-3:L05  Intrinsic Deformation and Failure Response of Single Crystal MAX Phases
Zhiqiang Zhan, H. Rathod, M. Radovic, A. Srivastava, Department of Materials Science & Engineering, Texas A&M University, College Station, TX, USA

A family of ternary carbides and nitrides, referred to as MAX phases, possess unique set of properties. These are light, stiff, thermodynamically stable and refractory, like ceramics, but damage-tolerant, pseudo-ductile at high temperatures and readily machinable like metals. Prior works have shown that polycrystalline MAX phases exhibit a range of deformation and failure mechanisms, such as crystallographic slip, ripplocation, twist, delamination and kinking. Here, we aim to correlate the single crystal level mechanical response of MAX phases to the overall mechanical response of the polycrystalline aggregate. To this end, micropillars are extracted from grains of know orientations using FIB milling and are subsequently deformed under compression using a flat-punch nanoindenter. The mciropillar experiments are complemented with novel in-situ SEM indentation experiments on single crystals of MAX phases. Our results shed new lights on the activation of various competing deformation and failure mechanisms in MAX phases at the single crystal level.


CE-3:IL06  High-temperature Oxidation of Alumino-forming MAX Phases: Relationship between Powder Metallurgy Processing Routes, Microstructural Characteristics and Oxidation Resistance
V. GAUTHIER-BRUNET1, E. Drouelle1,2, B. Levraut1, A. ZUBER1, J. Cormier1, P. Villechaise1, P. Chartier1, S. Dubois1, P. Sallot2, 1Institut Pprime, CNRS - Université de Poitiers - ENSMA, UPR CNRS 3346, Futuroscope Chasseneuil, France; 2Safran CRT, Magny-les-Hameaux Cedex, France

Alumina scale-forming materials are used to operate at high temperature in oxidizing atmospheres due to their high chemical stability. Selective oxidation of aluminum results in the formation of a protective oxide scale, acting as a barrier reducing further oxidation of the material. Attention has been granted in the past two decades to MAX phases containing Al as A-element, showing their ability to form a protective α-Al2O3 scale at high temperatures. In this study, fine and coarse-grained -Tin+1AlCn (n=1 and 2) and Cr2AlC- samples were respectively synthesized using Spark Plasma Sintering and Hot Isostatic Pressing techniques. The operating parameters were varied to modify microstructural characteristics. The effects of porosity, grain size, nature of secondary phases onto the oxidation resistance in air of Tin+1AlCn and Cr2AlC phases were investigated from 800 to 1400 ° C. Surface roughness effect was also studied after short-time oxidation tests. The effect of both the oxidation conditions and the MAX phases microstructural characteristics were examined via the observation of the oxide layers, the analysis of the oxidation products and the study of the oxidation kinetics. The oxidation behavior of Tin+1AlCn MAX phases was finally compared to the one of Cr2AlC.


CE-3:L09  Cr2AlC Crystal Structure Evolution Prediction during Oxidation 
A. ZUBER1, G. Frapper2, V. Brunet1, S. Dubois1, 1Institut PPRIME, Chasseneuil du Poitou, France; 2IC2MP, Poitiers cedex, France

MAX phases are nanolamellar nitrides and carbides consisting of a combination of M6X octaedrons and A plans. During oxidation of the MAX phase Cr2AlC, the outward diffusion of aluminum in the basal plane allows formation of an alumina scale at the surface. According to other MAX phases’behaviour, the nanolamellar structure of the Cr2AlC structure depleted of its aluminum is supposed to remain stable with half of it. This statement wasn’t verified experimentally, while the observed evolution of the depleted Cr2AlC consist in the formation of chromium carbide Cr7C3. The Cr7C3 structure is likely to be based on the nanolamellar structure of the former Cr2AlC and we believe that the evolution of the structure during the oxidation process can be studied by calculation of the thermodynamically stable structure of the Cr2AlxCy compounds. For this purpose, we propose to use the evolutionnary algorithm USPEX and ab initio code VASP. For each composition in the ternary system Cr-Al-C, a consistent number of structures will first be randomly generated by USPEX and optimized by succesive VASP calculations. After optimization of all the generation’s structures for a given composition, the most stable are determined and used as a basis for the next generation with new randomly generated ones.


CE-3:L10  Analysis of 2D Ti3C2Tz MXene Oxidation and its Influence on Biological Response in Vitro
A.M. JastrzEbska1, A. Rozmysłowska-Wojciechowska, A. Szuplewska, Warsaw University of Technology, Faculty of Materials Science and Engineering, Warsaw, Poland

Despite intensive research on the application of MXenes in medicine, the knowledge concerning their mechanisms of bio-action is still not fully clear. In recent years, we have been analyzing the most explored MXene and the influence of its surface chemistry on various interactions with biological matter. Current results point to the conclusion that surface oxidation of 2D Ti3C2Tx MXene into TixOy oxides is responsible for the observed bio-action. As material's surface is responsible for its first impression on a mammalian cell in vitro, such an event must have a tremendous impact on further cell behavior. Therefore, by carefully studying the 2D Ti3C2Tz MXene etching and delamination pathway and allowing for oxidation, we were able to elucidate its underlying mechanisms of biological action. Our findings give evidence that the synthesis, processing, and oxidative instability of 2D Ti3C2Tz MXene are responsible for the specific biological response in vitro. This knowledge is an essential tool for materials design and should be rationally used to develop future biotechnological applications of MXenes and related materials.


CE-4:IL02  Electrically Conductive Alumina-MXene Nanocomposite
M. SOKOL, Tel Aviv University, Ramat Aviv, Israel

MXenes are widely acknowledged as a promising 2D material reinforcement in advanced composites due to their in-plane mechanical strength, high young’s modulus, electrical conductivity, and high-temperature phase stability. Combining MXenes into a polymer, metal, or ceramic matrix can have a substantial influence on the respective physical and mechanical properties. As it is extremely convenient to incorporate MXenes into polymers, much research work has already been done on MXene/polymer. In addition, MXenes can also be incorporated into metals and ceramics. There are some challenges in trying to produce ceramic matrix composites, CMCs, among them are achieving dense samples with proper distribution of the MXene, retaining the 2D structure of MXene, and chemical reactions at elevated temperatures. Co-sintering of two or more different powders is one of the straightforward ways to fabricate CMCs. However, during sintering at elevated temperatures, it is difficult to prevent the reaction of MXene with the surrounding ceramic matrix. Using advanced sintering methods such as spark plasma sintering (SPS) and, more so, high-pressure SPS (HPSPS) allow consolidating powders at relatively low temperatures. Accordingly, making it possible to control the process, prevent unwanted chemical reactions, and fabricate MXene-based CMCs with little or no degradation of the 2D-structured MXene. Herein, we report on the fabrication of fully dense conductive alumina-MXene nanocomposites using HPSPS.


CE-4:IL03  Physical Vapour Deposition of MoAlB Thin Films and Direct MoBene Formation
S. Evertz1, P. Pöllmann1, D.M. Holzapfel1, E. Mayer1, R. Sahu1, 2, D. Bogdanovski1, J.-O. Achenbach1, C. Scheu2, 3, J.M. Schneider1, 2, 1Materials Chemistry, RWTH Aachen University, Aachen, Germany; 2Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf, Germany; 3Materials Analytics, RWTH Aachen University, Aachen, Germany

The nanolaminated ternary boride MoAlB exhibits a promising high-temperature oxidation resistance due to the formation of a dense alumina scale. While bulk synthesis of MoAlB requires temperatures higher than 1000 °C with up to 40% of excess Al in the feedstock, here we report the temperature range for the formation of single phase, orthorhombic MoAlB synthesized by magnetron sputtering from a stoichiometric target is 450 – 650 °C. Lower synthesis temperatures yield the formation of amorphous films, while at 700 °C, impurity phases form in addition to orthorhombic MoAlB. Amorphous MoAlB films were observed by in-situ X-ray diffraction to crystallize between 545 and 575 °C. Hence, we infer that the formation of orthorhombic MoAlB thin films is surface diffusion mediated below 545 °C. As bulk diffusion is activated between 545 and 575 °C the synthesis of fully dense MoAlB films with a maximum hardness of 15 ± 2 GPa and a Young’s modulus of 379 ± 30 GPa at 600 °C is surface and bulk diffusion mediated. The potential of MoAlB thin films depostited by magnetron sputtering for the direct formation of 2D MoBene is appraised.


CE-4:L04  MXenes in Polymers and Nonpolar Solvents – Effects of Surface Modification on Stability and Dispersion
M. CAREY, M.W. Barsoum, Department of Materials Science and Engineering, Drexel University, Philadelphia, PA, USA

The family of 2D, graphene-like transition metal carbides and nitrides known as MXenes have been the center of a large body of research since their discovery in 2011, being explored in a wide variety of research fields. Typically, MXenes are hydrophilic and are utilized as colloidal suspensions in water or polar organic solvents. However, this severely limits the use of MXenes in systems where nonpolar solvents are preferred or even required. MXene based nanocomposites synthesized by in-situ polymerization reactions or by solution based processing are therefore extremely limited and restricted to small scales. In our work, we have explored the surface modification of MXenes, namely through amino acid and quaternary ammonium ion functionalization, resulting in hydrophobic MXene which can be readily dispersed in nonpolar solvents such as hexane, cyclohexane, toluene, p-xylene or decahydronaphthalene, remaining stable and oxidation free for long periods of time. Additionally, we have demonstrated that this modification allows for the incorporation into various polymer hosts such as nylon-6, epoxy resins and polyethylene. In both nylon-6 and epoxy nanocomposites with less than 2 vol. % Ti3C2Tz, the barrier properties were significantly enhanced, with a ~95% reduction in permeability.


CE-4:IL05  Design of Functional Composites by Using MAX and MAB Phases
s. GUPTA, University of North Dakota, Grand Forks, ND, USA

MAX and MAB phases have emerged as strong contenders for structural applications. These solids have important attributes like low-moderate hardness, refractoriness, compressive strength, and triboactive behavior. The philosophy of this work is to design functional composites by using particles of MAX or MAB phases. Recently, I had classified these composites as 3-0 composites where metals, polymers, or ceramics form the 3D structure, and MAX/MAB particles are embedded in them. In the presentation, I will review the manufacturing processes for fabricating MAX and MAB particulates. Thereafter, I will summarize the microstructure, mechanical, and triboactive behavior of these solids.


CE-5:IL01  Contribution of Single Crystal Measurements to the Understanding of MAX Phase Electronic Properties
T. OUISSE, D. Pinek, M. Barbier, Y. Kim, Université Grenoble-Alpes, CNRS, LMGP, Grenoble, France; T. Ito, M. Ikemoto, Nagoya University Synchrotron radiation Research Center (NUSR), Nagoya University, Nagoya, Japan; K. Furuta, Graduate School of Engineering, Nagoya University, Nagoya, Japan; M. Nakatake, Aichi Synchrotron Radiation Center, Seto, Japan; K. Yaji, S. Shin, Institute for Solid State Physics, University of Tokyo, Chiba, Japan; C. Opagiste, Université Grenoble-Alpes, Inst. NEEL, Grenoble, France; F. Wilhelm, A. Rogalev, European Synchrotron Radiation Facility (ESRF), Grenoble cedex, France

The availability of single crystals is key for a better understanding of any electronic or other physical property of MAX phases. We shall present a collection of results issued from single crystal experiments mainly conducted on large scale instruments, using techniques such as ARPES on conventional MAX phases [1-3], or ARPES, XANES and XMCD on magnetic i-MAX phases [4]. We will show how these results, when combined with theory and ab initio calculations, do not only shed light on some specific aspects, but also allow one to draw general and unifying considerations about the physics of MAX phases.
[1] T. Ito et al., Phys. Rev. B 96, 195168 (2017). [2] D. Pinek et al., Phys. Rev. B 98, 035120 (2018). [3] D. Pinek et al., Phys. Rev. B 100, 075144 (2019). [4] Q. Tao et al., Phys. Rev. Mat. 2, 114401 (2018)


CE-5:L03  Growth and Characterization of Epitaxial (Cr1-xMnx)2GaC MAX Phase Thin Films by Pulsed Laser Deposition
H. PAZNIAK1, M. Farle1, 2, U. Wiedwald1, 1Faculty of Physics and Center for Nanointegration (CENIDE), University of Duisburg-Essen, Duisburg, Germany; 2Kirensky Institute of Physics, Federal Research Center KSC SB RAS, Krasnoyarsk, Russia

Due to their nanolaminated structure, tunable chemistry, and high oxidation resistance, MAX phases (where M is an early transition metal, A is a late or post-transition metal, and X is carbon or nitrogen) are interesting materials for a vast variety of applications. The partial substitution of M atoms is one of the ways to tailor their properties to specific applications. In this study, we grow (Cr1-xMnx)2GaC MAX phase films to fine-tune their magnetic response by systematic stoichiometry variations for x = 0.5-1. High-quality epitaxial (Cr1-xMnx)2GaC MAX phase films with 50 nm and 100 nm thickness are synthesized by pulsed laser deposition on MgO (111) substrate by using a Cr, Mn1-yGay and C targets. The combination of structural and morphological characterization (XRD, pole figures, SEM, EDX) reveals a strong competition between the (Cr1-xMnx)2GaC MAX phase and the (Cr1-xMnx)3GaC antiperovskite phase. We suppress the formation of the antiperovskite phase for growth temperatures set to 540-550°C. Vibrating sample magnetometry measurements of the (Cr0.25Mn0.75)2GaC MAX phase shows long-range magnetic order above 300 K. Funding by the Deutsche Forschungs¬gemeinschaft (DFG) within CRC/TRR 270, project B02 (Project-ID 405553726) is gratefully acknowledged.


CE-5:L04  The Magnetic Structure of Rare Earth i-MAX Phases Explored by Neutron Diffraction and Muon Spin Rotation
D. Potashnikov, IAEC, Tel-Aviv, Israel; O. Rivin, A. Pesach, E.N. Caspi, NRCN, Beer-Sheva, Israel; Q. Tao, J. Rosén, Linköping University, Sweden; D. Sheptyakov, Z. Salman, PSI, Switzerland; C. Ritter, ILL, France; H.A. Evans, NIST, USA; P. Bonfá, University of Parma, Italy; T. Ouisse, M. Barbier, University Grenoble-Alps, France; A. Keren, Technion, Israel

The recently discovered [Q. Tao et al. Chem. Mater. 2019] in-plane ordered MAX phases (henceforth i-MAX) with the chemical formula (Mo2/3RE1/3)2AlC where RE is a lanthanide, have opened the possibility to manufacture magnetically ordered 2D derivatives [Q. Tao et al., Nat. Comm. 2017]. In this work, we have set to explore the magnetic ground state of 5 members of this family with RE=Nd, Tb, Ho Er, and Gd by means of combined neutron powder diffraction (NPD), and muon spin rotation (µSR) measurements. Since Gd is a strong neutron absorber, direct observation of its magnetic structure with NPD was unpractical. To overcome this limitation, we have combined NPD, and µSR information extracted from the other i-MAX compounds with µSR measurements on the Gd i-MAX, magnetic symmetry analysis and density functional theory based muon site determination. The magnetic structure of the Gd i-MAX is found to be a simple antiferromagnet with a magnetic moment of ~6.5 µB. Temperature dependence of its magnetic moment is well described by a calculation of a nearly two-dimensional layered antiferromagnet, thus showing that magnetism is likely to survive when exfoliated into a 2D sheet.


CE-5:L05  Non-collinear Antiferromagnetic Structure of the Mn2GaC Thin Film (MAX Phase) -evidenced by 55Mn NMR
M. WOJCIK1, E. JEdryka1, J. DEY1, R. KALVIG1, U. Wiedwald2, R. Salikhov2, M. Farle2, J. Rosen3, 1Institute of Physics, Polish Academy of Sciences, Warsaw, Poland; 2Faculty of Physics and Center for Nanointegration (CENIDE), University of Duisburg-Essen, Duisburg, Germany; 3Thin Film Physics, Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping, Sweden

Mn2GaC ternary compound, a member of the rich family of the so-called MAX phase materials, presents an atomically laminated structure stacked along the hexagonal c-axis, where the Mn-C-Mn stacks are interleaved with the atomic layers of gallium. It is magnetically ordered with the critical temperature of the order-disorder transition of 507 K. At around 214 K this compound undergoes a first order phase transition, and the magnetic structure below the transition point has been a subject of controversial reports. The experiments of unpolarized neutron reflectometry indicated the features of a collinear antiferromagnetic order with periodicity of two unit cells, in consistence with the AFM[0001]A4 structure proposed from the theoretical calculations [1]. On the other hand, a nonzero magnetic remanence suggests the long range ferromagnetic correlations [2]. In this work we used Nuclear Magnetic Resonance (NMR) technique to shed some light on the low temperature magnetic structure. We present the results of 55Mn NMR experiment carried out on a 100 nm film sample grown on the MgO (111) substrate with the hexagonal axis perpendicular to the film plane. The experiments have been performed at 4.2K in zero field and in presence of the external field up to 1T applied in the film plane. The data indicate a non-collinear antiferromagnetic structure, in consistence with the latest Monte Carlo simulations using a Heisenberg Hamiltonian [3].
1. Ingason, A. S., Palsson, G. K., Dahlqvist, M., Rosen, J., Phys. Rev. B 94, 024416 (2016). 2. Novoselova, I.P., Petruhins, A.,Wiedwald, U., Ingason, A.S., Hase, Th., Magnus, F., Kapaklis, V., Palisaitis, J., Spasova M., Farle, M., Rosen, J., Salikhov, R., Scientific Reports 8, 2637 (2018). 3. Martin Dahlqvist and Johanna Rosen, Scientific Reports 10, 11384 (2020). This work has been supported in part by a grant from the National Science Center, Poland (UMO-2019/35/B/ST3/03676)


CE-5:IL06  Electronic Structure of Some Selected MAX Phases
TAKAHIRO ITO, Nagoya University Synchrotron radiation Research center (NUSR), Nagoya University, Nagoya, Japan; K. Furuta, Graduate School of Engineering, Nagoya University, Nagoya, Japan; D. Pinek, Y.-S. Kim, M. Barbier, T. Ouisse, Université Grenoble-Alpes, CNRS, LMGP, Grenoble, France; M. Nakatake, Aichi Synchrotron Radiation Center, Seto, Japan; S. Ideta, K. Tanaka, Institute for Molecular Science, Okazaki, Japan; P. Le Févre, F. Bertran, Synchrotron-SOLEIL, L’Orme des Merisiers, Saint-Aubin, France

Direct investigation of the electronic structure is the most fundamental way to understand the origin of electronic properties of materials. Angle-resolved photoemission spectroscopy (ARPES) is a powerful experimental technique for investigating the energy band structure, momentum distribution and Fermi surface at the bulk/surface of materials. Yet, there are only few examples of ARPES studies of MAX phases and related compounds, due to a lack of single crystalline samples. So far we have reported ARPES measurements of the electronic structures of Cr2AlC [1] and V2AlC [2], which are fully consistent with density functional theory (DFT) calculations. In this talk, we will present new ARPES results on Ti3SiC2 [3] and Mo4Ce4Al7C3 [4]. For Ti3SiC2, we have identified a complex three-pointed star shaped Fermi surface caused by the band inversions near K points and found that its definitive three dimensionality is effective for the thermoelectric power properties. For Mo4Ce4Al7C3, we have investigated the itinerant Ce 4f character at the Fermi surface as expected for a Kondo system.
[1] T. Ito et al., Phys.Rev.B 96, 195168 (2017). [2] D. Pinek et al., Phys.Rev.B 98, 035120 (2018). [3] D. Pinek et al., Phys.Rev.B 102, 075111 (2020).[4] M. Berbier et al., Phys.Rev.B 102, 155121 (2020).


CE-5:IL07  Magnetism in MAX and MAB Phases
E.N. CASPI, Nuclear Research Centre - Negev, Beer-Sheva, Israel

Since the last progress session on MAX/MAB phases undertaken in CIMTEC 2018, considerable amount of work has been done to explore and understand the magnetic properties in these important nano-laminated materials. Progress was made both in introducing new samples as candidates for interesting magnetic properties and in using additional local probes for studying their magnetism. In CIMTEC 2018, I demonstrated how important it is to use local probes to understand the microscopic magnetic behavior of individual crystallographic sites in the material. It leads to a better understanding of the nature of the magnetic state, and to a unique link between measurement and studied phase, impurities notwithstanding. Here, I will give an overview on the progress made in this field during the last three years, focusing on research led by the NRCN neutron scattering group in collaboration with the Drexel and Linköping groups. I will review how understanding magnetism in MAX phases expanded with the use of the NMR, and µSR methods, and with the introduction (by Linköping) of the REMAX samples, a rich and sophisticated sub-class of MAX phase materials. I will also show, how crucial neutron scattering is for “fine-tuning” the magnetocaloric effect of MAB phase solid solutions provided by Drexel.


CE-5:L08  Quantitative MXene Spectroscopy in TEM using ab initio Simulations
T. Bilyk1, H.-W. Hsiao2, R. Yuan2, M. Bugnet3, M.-L. David1, S. Célérier4, J.-M. Zuo2, J. Pacaud1, V. Mauchamp1, 1Pprime Institute –UPR 3346–CNRS, Poitiers University, ISAE-ENSMA, Department of Physics and Mechanics of Materials, Futuroscope-Chasseneuil, France; 2Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, USA; 3Université de Lyon, INSA Lyon, UCBL Lyon 1, MATEIS–UMR 5510 CNRS, Villeurbanne, France; 4Institut de Chimie des Milieux et Matériaux de Poitiers (IC2MP), CNRS, Poitiers University, Poitiers, France

MXene multilayers properties depend on their architecture (i.e., number of layers, interlayer distance), their functionalization and structural defects. Now that in situ or operando transmission electron microscopy has become a reliable platform to probe materials dynamics and properties, reaching an exact description of the structural parameters of the MXene multilayers under study in TEM is important. Here, we consider Ti3C2Tx as a benchmark material and show that valence electron energy-loss spectroscopy (VEELS) in TEM allows to directly quantify the absolute number of layers in Ti3C2Tx stacks for thicknesses below ∼ 10 nm. This can be done using the large change between the surface and bulk modes intensity ratios in the VEEL spectrum, as predicted by DFT simulations, and confirmed experimentally. DFT also shows that the bulk plasmon shift gives access to interlayer distance modifications in a given stack with sub-angström sensitivity. Further, the edges corresponding to the excitation of core electrons provide information on a very local scale. Using the carbon K-edge as a marker, we show that DFT simulations allow to interpret the changes in spectra collected from different samples in terms of perturbations of the Ti3C2Tx layers surface, or structural disorder.


CE-5:L09  Energy Resolved Contributions of the Functionalization Groups on the Valence Band Spectra of the T3C2Tx MXene
F. BRETTE1, 2, H. Pazniak1, R. Larciprete3, A. Liedl4, P. Lacovig5, D. Lizzit5, E. Tosi5, F. Boucher2, V. Mauchamp1, 1Institut Pprime, Poitiers, France; 2Institut des Matériaux Jean Rouxel (IMN), Nantes, France; 3CNR-Institut for Complex Systems (ISC), Italy; 4INFN-LNF, Italy; 5Elettra-Sincrotrone Trieste, Italy

The surfaces functionalization terminal groups like -F, -OH, =O, -Cl plays a major role on MXene’s electronic properties. Understanding the precise contribution of these surface groups to the electronic structure of Mxenes is then a key point to optimize their properties. In this context, valence band X-ray photoelectron spectroscopy (VBXPS) is a very interesting tool, still rarely used in the MXene community. Herein, we report the interpretation from state-of-the-art first principles DFT calculations of synchrotron high resolution VBXPS spectra acquired at 100 and 650 eV photon energies on well oriented spin-coated T3C2Tx thin films. In order to study the role of the etching agents on the MXene electronic properties, samples obtained from powders synthesized using the two most common etching agents, i.e. HF or LiF/HCl are compared. Based on the very good agreement between experiments and simulations, and taking advantage of the energy dependence of the atomic x-ray cross sections, we show that modifying the etching conditions operates in well-defined characteristic energy domains of the MXene valence band. In addition, although both halogens, -F and -Cl groups are shown to have very different contributions. We will also emphasize the importance of considering the energy dependence of the valence band spectra in the simulation.


CE-6:IL04  MXene Chemistry: Fundamentals and Applications
V.N. MOCHALIN, Department of Chemistry and Department of Materials Science & Engineering, Missouri University of Science & Technology, MO, USA

We will discuss our recent progress in understanding fundamental chemistry of 2D transition metal carbides/nitrides (MXenes), in particular, their reactions with water. The use of the MXene reactivity for development of applications will also be illustrated.
1. S. Huang, V. N. Mochalin, ACS Nano, 14(8), 10251–10257 (2020); 2. S. Huang, V. N. Mochalin, Inorganic Chemistry, 58(3) 1958-1966 (2020); 3. S. Chertopalov, V. N. Mochalin, ACS Nano, 12(6), 6109-6116 (2018); 4. Y. Li, S. Huang, C. Wei, C. Wu, V. N. Mochalin, Nature Communications, 10, 3014 (2019); 5. Y. Dong, S. Chertopalov, K. Maleski, B. Anasori, L. Hu, S. Bhattacharya, A. M. Rao, Y. Gogotsi, V. N. Mochalin, R. Podila, Advanced Materials, 30(10), 1705714 (2018)


CE-6:L06  Electrochemical Investigation on Anti-corrosion Behavior of Functionalized 2D Mxene Reinforced Powder Coating Nanocomposites
Z. NAZARLOU, U. Aydemir, Department of Chemistry, Koç University, Sariyer, Istanbul, Turkey; M.S.S. Dorraji, Department of Chemistry, University of Zanjan, Zanjan, Iran

Corrosion protection by polymer coating technology has attracted great attention because of its high efficiency and low cost. These coatings have limitations regarding their long-term corrosion resistance. Polymeric powder coating is a solvent-free, cost-efficient, and eco-friendly process that seems very assuring in replacing harmful liquid paints. The traditional inhibitors used in polymeric coatings include heavy-metal particles like chromium and lead that are highly toxic to the environment and human health. Mxenes as new generation of two-dimensional (2D) nanomaterials have shown outstanding potential for many applications such as anticorrosive polymer coatings due to their layered structure and performance characteristics. In this study, Silane functionalized Zn-MAX and Mxene nanosheets were prepared by replacing and etching aluminum atoms layer of Ti3AlC2 precursor along with layering technique. The resultant nanosheets have been homogeneously dispersed into an extruded polymeric matrix to design a smart barrier enhancer of powder coating and improve the anti-corrosion performance of VOC-free powder paint. The potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) measurements confirmed less corrosion rate than neat powder paint.


CE-7:L01  MXene for Electrochemical Water Desalination
M. Torkamanzadeh, L. Wang, Y. Zhang, INM - Leibniz Institute for New Materials, Saarbrücken, Germany; Saarland University, Saarbrücken, Germany; V. Presser, INM - Leibniz Institute for New Materials, Saarbrücken, Germany. Saarland University, Saarbrücken, Germany. Saarene - Saarland Center for Energy Materials and Sustainability, Saarbrücken, Germany

Capacitive deionization (CDI) is a promising water purification technology that promises energy-efficient desalination of brackish or selective ion separation. A key focus of CDI research is the choice of electrode materials, which dictates the desalination capacity, efficiency, or selectivity. For example, nanolamellar materials such as transition metal carbides (MXene) have been introduced as promising CDI electrodes. MXenes, unlike nanoporous carbon materials, immobilize ions via ion insertion into sub-nanometer interlayer spacing. This study highlights the capability of Ti3C2 MXene as an emerging ion intercalation material for desalination of seawater-level saline media [1]. We have applied Ti3C2 (MXene) and activated carbon as electrodes for stable desalination of brackish water (20 mM NaCl) and seawater (600 mM NaCl) salinity levels for 100 cycles, where capacities of up to 12 mg/g (i.e., mg NaCl removed per g of electrode material) and charge efficiencies over 80% were achieved. This work has shown that with proper control of cell voltage, mass balancing of the electrodes, and capitalizing from the negative surface terminations of MXene, one can minimize the notorious co-ion desorption phenomenon.
[1] Torkamanzadeh et al. ACS applied materials & interfaces 12(23), 2020


CE-7:IL02  Highly Conductive MXene for Electronics: From Fundamental to Applications
SHUN SAKAIDA, F. Naruse, T. Torita. Murata Manufacturing Co., Ltd., Shiga, Japan

With growing interest in two-dimensional (2-D) materials club and their outstanding properties, considerable attention has been paid to a family of 2-D transition metal carbides MXene. Herein we summarize our recent works on electrically conductive MXene, especially for Ti3C2Tx in thin-film state, from fundamental properties to industrial applications including electromagnetic shielding performance in the gigahertz range. Our scale-up production system provides high quality crystalline MXene flakes to exhibit remarkable electrical conductivity as high as 18000 S/cm @5 μm thickness. Several techniques were successfully used to monitor the stability of MXene dispersion and the fabricated films. X-ray crystallographic studies indicated that the interlayer spacing change by water intake has a significant effect on the conductivity, and therefore further investigation to prevent degradation are highly required for applications under humid condition at high temperature. We also demonstrate that MXene film with prominent electrical conductivity can effectively interfere electromagnetic wave propagation in the frequencies up to 10 GHz.


CE-7:IL03  Pre-Intercalated Multi-layer MXenes as Outstanding Electrodes for Electrochemical Energy Storage
Kun Liang, K. Prenger, M. Naguib, Department of Physics and Engineering Physics, Tulane University, New Orleans, Louisiana, USA

Two-dimensional transition metal carbides and nitrides “MXenes”, discovered in 2011, have already shown an enormous potential in the field of electrochemical energy storage, due to their excellent capabilities to host ions and protons in addition to their high electrical conductivity. For example, free-standing films of delaminated two-dimensional titanium carbide MXenes exhibit excellent gravimetric and volumetric capacitance at high rates in aqueous electrolytes specially in aqueous sulfuric acid electrolyte. One of the challenges for utilizing these electrodes for large-scale applications is scaling up their areal capacitance since the thickness of these free-standing films is usually in the few microns range. Here we will discuss the effect of pre-intercalation in multi-layer MXene to achieve comparable gravimetric capacitance to that of delaminated MXenes but with significantly higher areal capacitance. We will also report on utilizing intercalated multi-layer MXene as electrodes for organic and room-temperature ionic liquid electrolytes supercapacitors with outstanding s energy and power densities of 256 Wh/kg and 46000 W/kg, respectively.


CE-7:IL05  Tuning the MXene Surface Chemistry with the Etching Agent. Application in Electrocatalysis
M. Benchakar, L. Loupias, C. Canaff, S. Morisset, C. Morais, A. Habrioux, S. Célérier, IC2MP, Poitiers, France; T. Bilyk, J. Pacaud, P. Chartier, V. Mauchamp, Pprime, Poitiers, France

MXenes are among the newest and largest family of 2D materials with already demonstrated applications in diverse fields. Beyond the possibility to tune the MXene compositions and related properties by changing the MAX phase precursor, the etching process is also a key step since it leads to the surface functionalization of the MXene sheets with different T terminal groups (F, OH or O) which also deeply alter the MXenes properties. Although crucial for many applications, controlling the MXenes surface is still in its infancy because of the limited number of etching processes and the need to establish characterization protocols allowing the accurate determination of the generated surface properties. The aim of this presentation is to highlight the role of different etching agents (HF, LiF/HCl and FeF3/HCl) on the control of the surface chemistry of Ti3C2 MXenes. A complete set of characterizations (XRD, SEM, EDX, XPS, Raman, TEM/EELS) is proposed to determine their surface properties and particular attention is paid on their activities towards hydrogen and oxygen evolution reaction (HER and OER). The ultimate goal is to show how the etching agent can be selected to tune the MXenes surface chemistry and obtain the most suitable material for the targeted application.

 

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