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

CG:KL  Expanding the Structural and Elemental Space of MAX Phases and MXenes
J. ROSEN, Linköping University, Department of Physics, Chemistry and Biology (IFM), Linköping, Sweden

The exploration of new MAX phases and MXenes is an active area of materials discovery. A more recent addition to field is a new type of atomic laminated phases, coined i-MAX, in which the M-atoms in (M12/3M21/3)2AlC are in-plane chemically ordered. The first phase discovered was (Mo2/3Sc1/3)2AlC, and it has been shown that this was a first example of a large, more than 30 to date, set of thermodynamically stable phases, typically obtained from an interplay between theoretical predictions and experimental verification. Using the i-MAX phases for MXene synthesis allows a new route for tailoring the MXene structure and composition: By employing different etching protocols, it is possible to I) remove only the Al atoms, and obtain a MXene with in-plane elemental order, or II) remove Al and one of the M-elements, and obtain a MXene with ordered vacancies. The i-MAX phases realize 3D and 2D materials with elements beyond those traditionally associated with MAX phases and MXenes, and expand the range of attainable properties. This has implications for the tuning potential of these materials in applications for, e.g., energy storage and catalysis, as well as for new diverse magnetic MAX phase phenomena.


Session CG-1 - Bulk and Thin Film Transport Properties of the MAX/MAB/MXenes

CG-1:IL01  Transport Properties in MAX Single Crystals and MXenes
T. OUISSE¹, D. PINEK¹, M.W. BARSOUM², T. ITO³, ¹Université Grenoble-Alpes, CNRS, LMGP, Grenoble, France; ²Department of Materials Science and Engineering, Drexel University, Philadelphia, PA, USA; ³Synchrotron Radiation Research Center, Nagoya University, Nagoya, Japan

Herein we critically assess the magnetotransport properties of the MAX phases and their 2D derivatives, MXenes. We will show that for most phases, taking into account the specific shape of the MAX Fermi Surfaces can allow one to describe the weak field magnetotransport properties reasonably well, including the apparent carrier compensation observed in all phases. Much less is known about MXene. We will review the transport properties published so far. We will detail the mechanisms of transport already evidenced in such 2D metallic materials, arguing that many of them are still affected by morphological disorder.


CG-1:IL02  Mn2GaC Thin Films: Magnetic MAX Phase from Theory and Experiment 
A.S. INGASON^{1, 2}, M. DAHLQVIST¹, A. MOCKUTE¹, A. PETRUHINS¹, G.K. PALSSON^{3, 4}, J. ROSEN¹, ¹Thin Film Physics, Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping, Sweden; ²Grein Research, Reykjavik, Iceland; ³Dept. of Physics and Astronomy, Uppsala University, Uppsala, Sweden; ⁴Institut Laue-Langevin, Grenoble, France

In 2013 the first two papers were published dealing with measurements of magnetism in MAX phases by alloying an existing Cr-based MAX phase with Mn. Further studies into magnetic properties and how the inherently laminated structure and chemistry plays a part have since been made. However, uncertainty regarding exact amounts of Mn in samples and detailed information of its distribution in the structure further complicates interpretation of magnetic data from such alloy materials. Most progress in the study of magnetism in this interesting class of materials has therefore been made through the discovery and measurements of Mn2GaC, with a single M element, predicted through theoretical calculations and synthesised as an epitaxial thin film. This talk will focus on this material and how the interplay between theory and experiments has gradually exposed the intricate interplay between both magnetic and nuclear structural changes with temperature and applied magnetic field, most recently through neutron reflectivity measurements.


CG-1:IL03  Ab-initio Calculations of the Thermoelectric Properties of MXenes
U. SCHWINGENSCHLOGL, Physical Science and Engineering Division (PSE), King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia

The presentation gives an overview of ab-initio calculations addressing the thermoelectric performance of MXenes. Specific examples include a comparison of Ti2CO2, Zr2CO2, and Hf2CO2 in order to evaluate the role of the metal atom. The lattice thermal conductivity is demonstrated to grow along the series Ti-Zr-Hf in the temperature range 300-700 K, resulting in the highest figure of merit in the case of Ti2CO2. Flat conduction bands promote the thermopower in the case of n-doping. Functionalization effects are studied for Sc2C, which is semiconducting for various functional groups, including O, F, and OH. The lowest lattice thermal conductivity is found for OH functionalization. Despite a relatively low thermopower, Sc2C(OH)2 therefore and due to a high electrical conductivity can be interesting for intermediate-temperature thermoelectric applications. We also discuss results on heterostructures built of MXenes and transition metal dichalcogenide monolayers. Low frequency optical phonons are found to occur as a consequence of the van der Waals bonding. They contribute significantly to the thermal transport and compensate for reduced contributions of the acoustic phonons (strong scattering), such that the thermal conductivities become similar to those of the constituent MXenes.

 
Session CG-2 -  New MAX/MAB/MXenes

CG-2:IL01  Prediction and Synthesis of New MAX Phases with in- and out of Plane Chemical Ordering
M. DAHLQVIST, JUN LU, R. MESHKIAN, QUANZHENG TAO, L. HULTMAN, J. ROSEN, Department of Physics, Chemistry, and Biology (IFM), Linköping University, Linköping, Sweden

The enigma of MAX phases and their hybrids prevails. The exploration of the taxonomy of these can be accelerated by theoretical structural design on the atomic level combined with combinatorial experimental synthesis. This was recently demonstrated for the MAX phase alloys (i) o-MAX with out-of-plane chemical order Mo2ScAlC2 (1), and (ii) i-MAX with in-plane chemical order (Mo2/3Sc1/3)2AlC (2). Here, we use predictive phase stability calculations to probe transition metal (M), from groups 3 to 6 and period 4 to 5, alloying in i-MAX phases for metal size, electronegativity, and electron configuration. Subsequent materials synthesis of predicted stable i-MAX phases (V2/3Zr1/3)2AlC and (Mo2/3Y1/3)2AlC (3) indicates a potentially large family of thermodynamically stable phases, with Kagomé-like and in-plane chemical ordering, and with incorporation of elements previously not known for MAX phases, including Y. In extension, we suggest a matching set of novel MXenes, from selective etching of the A-element. The here demonstrated structural design on both 3D and 2D atomic levels expands the property tuning potential of functional ceramics.
1. R. Meshkian et al., Acta Mater., 2017, 125, 476-480. 2. Q. Tao et al., Nat. Commun., 2017, 8, 14949. 3. M. Dahlqvist et al., Sci. Adv., 2017, 3.


CG-2:IL02  Novel Zr-based MAX Phase Solid Solutions
J. VLEUGELS¹, T. LAPAUW^{1, 2}, B. TUNCA^{1, 2}, K. VAN LOO¹, K. LAMBRINOU², ¹KU Leuven, Department of Materials Engineering, Heverlee, Belgium; ²SCK•CEN, Mol, Belgium

The high interest in Zr-based MAX phase systems is driven by the small thermal and fast neutron cross-section of Zr for advanced nuclear system applications. Although Zr2AlC and Zr3AlC2 MAX phases have been recently experimentally synthesized, the synthesis of phase pure MAX phase compounds in the Zr-Al-C system is extremely challenging and has not been realized yet. In an approach to synthesise phase pure Zr-Al-C based MAX phase ceramics, the addition of judiciously selected alloying elements on the MAX phase content was assessed. (Zr0.9,M0.1)2AlC and Zr2(Al0.9,A0.1)C solid solutions were synthesized by reactive hot-pressing, with M an early transition metal and A an element of group 13 or 14 of the periodic table. A first screening of the M and A elements was performed based on the phase assembly deduced from X-ray diffraction (XRD) analysis. Subsequently, the most promising solid solutions with the highest MAX phase content were investigated in more detail. The crystal structure was refined and the influence of the alloying elements on the crystallographic parameters was analysed. From the engineering point of view, the stiffness, flexural strength and fracture toughness of the high MAX phase content ceramics were measured.

CG-2:IL03  Magnetic MAX-phases: The Ultimate Material Class for Innovations in Spin-based Technologies ?
M. FARLE, R. SALIKHOV, U. WIEDWALD, Faculty of Physics, University of Duisburg-Essen, Duisburg, Germany

Magnetic MAX phases have become an exponentially growing field of fundamental research due to their tunable complex magnetic behavior and possible applications in magnetic wear resistant coatings for magnetic storage media, magneto-calorics and spin transport applications (see for example [1-4]) . Due to their laminar structure decomposition into quasi 2D layers appears feasible and might turn this material into a magnetic 2D material (“MXene” [5]) which can compete with the currently investigated Graphene and Chalcogenide derivatives. In this talk, an overview of current achievements and understanding of the fundamental properties of selected magnetic MAX phases as well as a critical discussion on the perspectives and future challenges [6, 7] to make this class of materials applicable in spin based technologies is given.
Work performed in close collaboration with the group of J. Rosen (Linköping Univ.)
1. Salikhov, R., et al., J. Appl. Physi., 2017. 121: 163904. 2. Tao, Q., et al., APL Materials, 2016. 4: p. 086109. 3. Salikhov, R. et al., Mat. Res. Lett., 2015, 3, 156-160 4. Dahlqvist, M., et al., Phys. Rev B 84, (2011) 5. Anasori, B.et al.; Nat. Rev. Mat., 2017. 2: 16098 6. Lai, C.-C., et al., Mat. Res. Lett. (June 2017) 7. Dahlqvist, M. et al, Sci. Adv. 3 (2017) e170064


CG-2:IL04  Novel MXene Materials and their Properties
JIE ZHOU, MIAN LI, XIAOJING BAI, XIANHU ZHA, SHIYU DU, QING HUANG, Ningbo Institute of Industrial Technology, CAS, Ningbo, China

MXenes, as a new family of two-dimensional (2D) materials have attracted increasing attentions in recent years since their discovery in 2011. Approximate twenty MXenes have been synthesized up to date, which include Ti3C2Tz, Ti2CTz, Ta4C3Tz etc. In general, MXenes are synthesized by etching corresponding Al-containing MAX phases (M denotes an early transitional metal, A is group13 or 14 elements of the periodic table, X is C and/or N). However, it’s still a challenge to synthesis the Al-containing MAX phases for transitional metals zirconium and Hafnium, which restricts the preparations of the Zr- or Hf-based MXenes. Recently, we chose new layered compound M3Al3C5 (M=Zr and Hf) instead of the MAX phase in fabricating of corresponding MXenes. The weak bonded Al3C3 units in M3Al3C5 were etched out, and we firstly obtained the Zr\Hf-based MXenes. In this presentation, the strategy to find more MXenes will be discussed as well as their functional exploration.


CG-2:L05  Compatibility of Zr2AlC, (Zr,Ti)2AlC and (Zr,Ti)3AlC2 MAX Phases with Lead-Bismuth Eutectic (LBE)
B. TUNCA^{1, 2}, T. LAPAUW^{1, 2}, K.G. PRADEEP³, J. SCHNEIDER³, R. DELVILLE¹, J. HADERMANN⁴, J. VLEUGELS², K. LAMBRINOU¹, ¹Belgian Nuclear Research Centre, SCK•CEN, Mol, Belgium; ²Dept. of Materials Engineering, KU Leuven, Heverlee, Belgium; ³Materials Chemistry, RWTH Aachen University, Aachen, Germany; ⁴Dept. of Physics, University of Antwerp, Antwerp, Belgium

Nano-laminated ternary carbides in the MAX phase ‘family’ are considered potential means of liquid metal corrosion protection for stainless steel fuel cladding materials intended for use in Gen-IV lead-fast reactors (LFRs). In this respect, MAX phases are envisaged as coating materials and their limited interaction with the primary coolant is a key requirement: for the MYRRHA reactor system, the primary coolant is the liquid lead-bismuth eutectic (LBE), which is corrosive to nuclear grade stainless steels. This work reports on the compatibility of select Zr-based MAX phases, i.e., Zr2AlC, (Zr,Ti)2AlC and (Zr,Ti)3AlC2, with oxygen-poor ([O]<10-8 mass%) static liquid LBE after an exposure of 1000 h at 500 °C. Zr-based MAX phases are appealing for fuel cladding applications, due to the low neutron cross-section of Zr. This work deployed scanning/transmission electron microscopy, energy dispersive X-ray spectrometry and atom probe tomography to investigate the LBE/MAX phase interaction down to the nanoscale. It was found that Pb/Bi atoms diffuse, primarily along the MAX phase basal planes, forming Zr2(Al/Pb/Bi)C and (Zr,Ti)n+1(Al/Pb/Bi)Cn (n=1 & 2) solid solutions, due to the substitution of Al by Pb/Bi in the crystal lattice. Locally, the solid solutions exhibited long-range ordering.


CG-2:L06  New MAX Phases and MXenes for Energy Relevant Applications
M.H. TRAN, C.S. BIRKEL, Technische Universität Darmstadt, Darmstadt, Germany

We use non-conventional methods, microwave heating and spark plasma sintering, to prepare new MAX phases. Target materials are mainly Ti-, V- and Cr-based compounds as well as their Mn (and Fe) doped analogs. We are particularly interested in their structural and magnetic properties. Furthermore, these MAX phases are exfoliated to obtain the corresponding two-dimensional MXenes. Here, we focus on their surface structure and investigate them in the context of their catalytic and electrochemical behavior. We pursue a scale bridging approach in order to fully understand the new materials on different lenghts scales by using local as well as bulk diffraction and imaging techniques.


Session CG-3 - Mechanical Properties and Oxidation of MAX/MAB/MXenes

CG-3:IL01  Ripplocations: A Universal Mechanism in the Deformation of Layered Solids
M.W. BARSOUM, Drexel University, Philadelphia, PA, USA

Layered solids – defined herein as solids in which the deformation, at least initially, is confined to two dimensions - are ubiquitous in Nature and span more than 14 orders of magnitude in scale; from sub-nanometer graphene layers, to laminated composites at the meter scale, to geologic formations at the 100 km range. Not surprisingly, the deformation of these very different solids was assumed to be different. Herein, using a combination of molecular dynamic calculations on graphite at 10 K and a simple instrumented indentation experiment on various layered solids – spanning the gamut from plastic playing cards to thin steel and Al sheets to mica single crystals - we show, that in all cases, confined buckling - that results in the formation of ripplocations - is the operative deformation mechanism. We therefore make the case that understanding ripplocation nucleation and propagation is fundamental in understanding the deformation of any layered solid, over 14 orders of magnitude.


CG-3:IL02  Self-healing Properties of MAX-phases: Thermodynamic Predictions and Reality
S. VAN DER ZWAAG, W.G. SLOOF, Delft University of Technology, Delft, The Netherlands

MAX phase materials have interesting mechanical, physical and chemical properties as a result of their layered microstructure. Some of the MAX phases have the ability to recover their mechanical strength as a result of oxidative filling of the cracks when the material is exposed to high temperatures. We present a scheme to predict which of the known MAX phase materials will show this behaviour. Furthermore, we present in-situ tomographic and fracture mechanical tests on a number of Self Healing MAX phases which demonstrate the local crack closure and the recovery of the mechanical properties, Finally, we present some of our first results on self healing MAB phase materials.


CG-3:IL03  Oxidation, Thermal Stability, and Mechanical Deformation of the Alumina-forming Nanolaminated Boride: MoAlB
S. KOTA, A. LY, O. ELKASSABANY, A. HUON, S.J. MAY, M.W. BARSOUM, Department of Materials Science & Engineering, Drexel University, Philadelphia, PA, USA; E. ZAPATA-SOLVAS, W.E. LEE, Centre for Nuclear Engineering & Department of Materials, Imperial College London, UK; YEXIAO CHEN, D. LOPEZ, M. RADOVIC, Department of Materials Science & Engineering, Texas A&M University, College Station, TX, USA; JUN LU, L. HULTMAN, Linköping University, Department of Physics (IFM), Linköping, Sweden; B. GARDIOLA, O. DEZELLUS, Université Claude Bernard LYON1, Laboratoire des Multimatériaux et Interfaces, UMR CNRS 5615, Villeurbanne, France

Two decades of research on the atomically-layered, ternary transition metal carbides and nitrides, known as the MAX phases, show them to have the unusual combination of metal- and ceramic-like properties. The alumina-forming ones – e.g. Ti2AlC – are being considered for high-temperature applications. These phases inspired us to synthesize and characterize other layered solids, such as the atomically laminated, ternary transition metal borides (MAB phases). This work concerns MoAlB, which is composed of a Mo-B sublattice interleaved with double Al layers. MoAlB forms slow-growing alumina scales when heated in air to temperatures up to 1350 °C, making it the first highly oxidation resistant transition metal boride. More recently, we showed that MoAlB incongruently melts at ≈ 1435 °C, but maintains high, and roughly temperature independent thermal conductivity (>25 W/m/K) and high Young’s moduli (319 GPa at 1200 °C) up to the melting point. Together, these properties bode well for its application at high temperatures in air. Herein, the oxidation kinetics, transient oxide formation, and structural evolution of the oxide scales from 1100-1400 °C are reviewed. In addition, the phase decomposition, thermodynamic parameters, and high-temperature mechanical deformation are discussed.


CG-3:IL04  MAX Phase High-temperature Plasticity: Nanoindentation and Transmission Electron Microscopy Analysis of Dislocations Elementary Mechanisms
W. SYLVAIN, A. JOULAIN, C. TROMAS, L. THILLY, Pprime Institute, CNRS, University of Poitiers, ISAE-ENSMA, France; S. SCHROEDERS, C. ZEHNDER, S. KORTE, C. IMM- RWTH Aachen University, Germany; G. RENOU, SIMAP,  Grenoble, France

It is well known that at room temperature, plastic deformation in MAX phases is governed by basal slip of dislocations. At high temperature, in the ductile regime, out of the basal plane dislocations have been reported [Guitton et al. Sciences Reports, 2015, Zhang at al. , J. Am. Cer. Soc. 2015]. However the origin of the brittle to ductile transition is still questioned. We present here a study of elementary deformation mechanisms of Ti2AlN. We focus our study on the transition from basal slip to cross slip into prismatic and pyramidal planes. In order to avoid intergranular effects, nanoindentation testing, at room temperature and elevated temperature, is used to initiate plasticity in individual grains. The deformation mechanisms involved during these tests are investigated by two methods. The first one consists in studying by Atomic Force Microscopy (AFM) the slip lines on the surface due to the emergence and propagation of the dislocations. In a second approach, the dislocation configurations are characterized by transmission electron microscopy in thin foils prepared by Focussed Ion Beam in cross section through the indents. Crystallographic orientations of the subgrains below the indents are determined by Automated Crystal Orientation Mapping in the TEM.


CG-3:IL05  Ablation and Thermal Shock Behaviours of MAX Phases
SHIBO LI, Center of Materials Science and Engineering, School of Mechanical and Electronic Control Engineering, Beijing Jiaotong University, Beijing, China

For high-temperature applications especially in hypersonic vehicles, rockets and nozzles, most bulk monolithic ultra high-temperature ceramics (UHTCs) are significantly limited due to their poor oxidation, thermal shock, and ablation resistance as well as poor damage tolerance. Some Al-containing MAX phases may be useful in high-temperature applications due to their combination of good oxidation resistance, nonsusceptibility to thermal shock, damage tolerance, high thermal conductivity and crack healing capability. The excellent oxidation resistance is ascribed to the formation of a dense and adherent α-Al2O3 layer on the surface which prevents further oxidation. The nonsusceptibility to thermal shock is due to the healing of thermal shock induced cracks with the formation of solid reaction products during quenching. To evaluate the ablation properties of MAX phases, two Ti2AlC and Cr2AlC phases were chosen to study their ablation behaviors under the oxyacetylene torch test. In addition, the abnormal thermal shock behavior of the MAX phases was mainly demonstrated during quenching in water. It is not clear that the unique thermal shock behavior remains valid during quenching in other quenching media. Thermal shock behaviors of Cr2AlC in water, oil and molten salt were studied by quenching test. The influences of quenching media and quenching temperatures on the mechanical property have been investigated. The microstructures of the ablated and quenched MAX samples were characterized. The relative mechanisms have been discussed.


CG-3:IL06  Mechanical Behavior and Strengthening of Alumina forming MAX Phases
M. RADOVIC¹, R. BENITEZ², HULI GAO², YEXAIO CHEN¹, WEN HAO KAN³, G. PROUST³, P. NAIK PARRIKAR⁴, ARUN SHUKLA⁴, ¹Department of Material Science and Engineering, Texas A&M University, College Station, TX, USA; ²Department of Mechanical Engineering, Texas A&M University, College Station, TX, USA; ³School of Civil Engineering, The University of Sydney, NSW, Australia; ⁴Department of Mechanical, Industrial and Systems Engineering, University of Rhode Island, Kingston, RI, USA

Out of more than 70 different MAX phases known today, some of those containing Al on A site are considered excellent candidates for high temperature applications mostly because of their good oxidation resistance due to the formation of spallation-resistant and self-healing protective Al2O3 layer on surfaces exposed to air and/or water vapor. Herein we report on mechanical behavior of Ti2AlC and Ti3AlC2 in compression in quasi-static and dynamic loading conditions. Effects of grain size and secondary phases (mostly TiAlx) on micro-yielding, stress-strain hysteresis and plasticity were examined in 25 °C – 1100 °C temperature range. A Hall-Petch type relationships between grain size and all micro-yielding stresses or ultimate compressive strength can be observed in both quasi-static and dynamic conditions only below brittle-to-plastic transition temperature. Above that temperature, a negative Hall-Petch effect was observed. In addition, microstructural changes after loading at different temperatures were studied using EBSD, and related to the observed macroscopic behavior. Possibilities for further improvements in mechanical properties by grain size refinement, solid solution strengthening and reinforcement with alumina fibers are also discussed in more details.


CG-3:L08  Relationship between Microstructure and Oxidation Resistance of Ti3AlC2 MAX Phase
V. GAUTHIER-BRUNET¹, E. DROUELLE^{1, 2}, J. CORMIER¹, P. VILLECHAISE¹, S. DUBOIS¹, P. SALLOT², ¹Institut Pprime, CNRS, Université de Poitiers, ENSMA, UPR CNRS 3346, Futuroscope Chasseneuil, France; ²Safran CRT, Magny-les-Hameaux Cedex, France

For several decades, the lightening of structures has become a major issue for the transport industries. In this context, Ti3AlC2 MAX phase deserves to be considered. Although few studies have investigated the high-temperature mechanical properties of these materials, many studies have shown the ability of MAX phases containing aluminum to form a protective α-alumina layer at high temperatures, despite the low aluminum content of these materials compared to TiAl alloys. In this study, Ti3AlC2 samples were produced using powder metallurgy route by performing spark plasma sintering onto home-made Ti3AlC2 powder. The selected operating parameters (purity of the Ti3AlC2 powder; temperature, pressure and holding time of the densification step) were varied in order to modify the microstructural characteristics (porosity, grain size, nature and content of secondary phases) of the Ti3AlC2 end-product. The oxidation resistance of Ti3AlC2 samples was then investigated in air, under isothermal conditions, in the temperature range 800-1000 ° C. The effect of both the oxidation conditions (temperature, oxidation time) and the microstructural characteristics of the Ti3AlC2 samples were studied via the observation of the morphology of the oxide layers and the study of the oxidation kinetics.


CG-3:L09  Corrosion Behaviour of MAX Phases in Molten Solar Salt and Liquid Heavy Metal
K. VAN LOO¹, T. LAPAUW^{1, 2}, P. SZAKÁLOS³, K. LAMBRINOU², J. VLEUGELS¹, ¹KU Leuven, Department of Materials Engineering, Heverlee, Belgium; ²SCK•CEN, Mol, Belgium; ³KTH, Surface and Corrosion Science, Stockholm, Sweden

Molten salt and heavy liquid metals are envisaged to be used as heat transfer fluids in concentrated solar applications. The currently used structural materials like stainless steel and Ni-based alloys however are subject to severe corrosion in these extreme environments. In this context, the corrosion resistance of several MAX phase ceramics was tested in molten solar salt (a mixture of 40 wt% KNO3 and 60 wt% NaNO3) for an exposure time of 1000 hrs at 600°C and in liquid lead for 2016 hrs at 750°C. The oxygen content in the molten solar salt was estimated to be 10-5 wt%, whereas the atomic oxygen content in liquid lead was controlled at 10-6 wt%. Nb-based MAX phases severely corroded in molten solar salt already after one week, showing a clear Nb-oxide layer. Ti2AlC gradually degraded with the formation of a non-protective TiO2 layer. Cr2AlC remained completely stable. Exposure to liquid lead resulted in complete oxidation of Zr-based MAX phases. Other MAX phases suffered from progressive degradation, like Nb4AlC3 and its derivatives, implying 10-6 wt% [O] was a too high O-level to avoid oxidation. The materials with a higher stoichiometric amount of Al were more stable. Ti2AlC and Cr2AlC formed a protective alumina layer, being the best candidates for solar applications.


CG-3:L10  Experimental and Theoretical Investigations on MAX/Intermetallic Two-phase Materials
G. HUG¹, K. PIVEN¹, A. JANKOWIAK², C. LU^{1, 3}, JIE ZHANG³, ¹LEM ONERA-CNRS, Chatillon, France; ²DMAS ONERA, Châtillon France; ³Harbin Institute of Technology, Harbin, China

MAX phase materials are evaluated to improve performances of turbo machines thanks to their as high temperature behavior and their corrosion/oxidation resistance. Different applications can be envisaged in the form of bulk materials or protective coatings, which requires specific tuning of properties in each particular case. In this study, we report on the influence of selected doping elements to improve strength and oxidation resistance in a two-phased materials consisting of Ti2AlC ceramics and intermetallic compounds produced by Spark Plasma Sintering (SPS) or Hot Uniaxial Pressing. The influence of the composition and structure of the starting powders and of doping elements like Si, W, Nb, on the microstructure, mechanical properties and oxidation resistance of the sample are studied. We present Density Functional Theory results to study the thermodynamic stability of the materials. The distributions of the dopants in the MAX of Intermetallic phases are also determined by DFT and experimental characterization.


CG-3:L11  Environmental Resistance of Cr2AlC MAX Phase under Realistic Conditions
J. GONZALEZ-JULIAN, T. GO, D. MACK, O. GUILLON, R. VAßEN, Forschungszentrum Jülich, Institute of Energy and Climate Research (IEK-1), Juelich, Germany

Cr2AlC is one of the most promising MAX phases for high temperature application (> 1000 °C) due to its excellent oxidation and corrosion resistances, as well as other features such as readily machinability and high thermal and electrical conductivities. However, to transfer Cr2AlC – and in general MAX phases - to real final applications, realistic tests at high temperature under aggressive environments are absolutely required. In this work, dense Cr2AlC materials were tested under environmental realistic conditions for the first time using a burner rig. The severe thermal cycling conditions were based on 500 cycles at 1200 °C, with an accumulative time of more than 58 h. In addition, dense Cr2AlC were coated with Thermal Barrier Coatings (TBCs) and tested under thermal cycling conditions at temperatures between 1100 and 1300 °C for 500 h. The samples survived perfectly under these conditions due to the formation of an outer protective α-Al2O3 layer, which presents a strong adhesion with the Cr2AlC substrate. A complete characterization of both approaches (burner rig and coatings with TBCs) will be shown. The results are rather promising and confirm the potential of the MAX phases to operate under long term applications of high temperature and oxidizing environments.


CG-3:L12  Tensile Creep Properties of Ti3AlC2
S. DUBOIS¹, E. DROUELLE^{1, 2}, J. CORMIER¹, V. GAUTHIER-BRUNET¹, P. VILLECHAISE¹, P. SALLOT², ¹Institut Pprime, CNRS - Université de Poitiers - ENSMA, UPR CNRS 3346, Futuroscope Chasseneuil, France; ²Safran CRT, Magny-les-Hameaux Cedex, France

In an aim to reduce fuel consumption, aeronautic companies select new materials to be investigated. Among them, MAX phases deserve to be considered. Indeed, the first mechanical tests performed indicate their good specific properties at high temperatures for half the density of superalloys. In this study, tensile creep tests have been performed on Ti3AlC2 samples in the 800-1000°C temperature range for stresses up to 210 MPa. Despite a brittle behavior at room temperature, Ti3AlC2 exhibits a brittle-to-ductile transition at 750°C; 20% strain can be reached at 1000°C. SEM observations on cross sections enabled to identify cavitation as the main damage mechanism at 900 and 1000°C, eventually assisted by oxidation. TEM observations were performed on a specimen crept at 900°C up to 7.5% strain. Three different types of characteristic microstructures were identified and can be associated to intra-granular deformation: highly dense dislocation networks, stacking faults and eventually numerous new defects similar to basal slip bands in metals. These latter defects, the most representative of the creep microstructure, confer to Ti3AlC2 its ability to plastically deform during creep. Further tests were performed to assess the contribution of each microstructure on the first steps of specimen deformation and to evaluate the influence of oxidation on creep mechanisms.


Session CG-4 -  MAX/MAB and MXene Composites and their Properties

CG-4:IL01  On the Processing and Characterization of MRM (MAX and MAB Reinforced Metals) Composites
S. GUPTA, M. FUKA, F. ALANAZI, S. GHOSH, M. DEY, University of North Dakota, Grand Forks, ND, USA

MAX Phases are novel ternary carbides and nitrides. MAB phases (ternary borides) are a new addition to this family of ternary solids which further diversify the properties of these exciting materials. Recently, we found that it is possible to enhance the properties of metals by adding these phases as particulate additives. We refer to this new class of composites as MRMs. In the presentation, we will focus on some of the recent research on Al-MRM, Ag-MRM, Bi-MRM, and Ni-MRM. We have investigated the microstructure of these composites by using SEM analysis. In general, the addition of Ti3SiC2 particulates in the matrix improved the compressive yield strength of these composites, but it also decreased their ductility. Ti3SiC2 particulates also had a beneficial effect on the tribological behavior. It was also documented that the tribological behavior of these composites is governed by the formation of tribofilms. We will present a detailed analysis of these tribofilms.


CG-4:L02  Influence of Secondary Phases on Mechanical Properties of MAX Phases               
K. KOZAK, G. ANTOU, T. CHOTARD, Université de Limoges, SPCTS, UMR 7315, Limoges, France; J. LIS, L. CHLUBNY, AGH UST, Cracow, Poland

In this study, room temperature mechanical properties of two ternary carbides (Ti3SiC2 and Ti2AlC) were investigated under cyclic bending test with in situ acoustic emission monitoring (AE). Different phase compositions of materials used in this work gave the opportunity to investigate the influence of secondary phases on properties of MAX phase materials and to establish microstructure/properties relation. AE results combined with post-mortem SEM observations permitted to associate acoustic emission response with observed microstructural changes resulting from imposed mechanical stresses. Deformation mechanisms such as delaminations of layers in MAX phases grains or damage occurrence in secondary intermetallic phases (microcracking) were identified with their specific acoustic signatures.


CG-4:L03  Magnetic Ordering Investigation in Mn2AlB2 using Neutron Diffraction              
D. POTASHNIKOV, IAEC, Tel-Aviv, Israel; O. RIVIN, A. PESACH, E.N. CASPI, NRCN, Beer-Sheva, Israel; A. HOSER, HZB, Berlin, Germany; S. KOTA, M.W. BARSOUM, Drexel University, Philadelphia, PA, USA

The ternary Mn2AlB2 belongs to the (TB2)nTAl ceramics (T = Cr, Fe, Mn) which exhibit promising bulk properties [M. Ade and H. Hillebrecht, Inorganic Chem. 2015] and their magnetic state was predicted to include the magneto-caloric effect (MCE) [L. Ke. et al, Phys. Rev. B, 2017]. In the present work, the magnetic state of Mn2Al11B2 is investigated using a DC SQUID magnetization and neutron diffraction. The two-fold increase in magnetization, found at ~60 and ~2 K, is shown to be accompanied by both a rapid change in lattice parameters and an increase of the neutron count of the crystallographic reflections. Below 2 K, a ferromagnetic structure, oriented within the orthorhombic a-c plane is found. This finding solves previous controversy surrounding the magnetic ground state of this compound and will contribute to the future design of magnetic properties in these materials.

 
Session CG-5 -  Electronic Properties, ab initio Calculations and Structural Characterization

CG-5:IL01  MXene Surface Functionalization Characterized on the Nanometer Scale using EELS in the TEM
V. MAUCHAMP, D. MAGNE, C. GARNERO, T. BILYK, P. CHARTIER, T. CABIOC’H, J. PACAUD; Institut Pprime - CNRS, Poitiers University, ISAE/ENSMA S. CELERIER, IC2MP, Poitiers University, France

In a very similar way to graphene, the surface functionalization of MXenes is among the key parameters to deeply alter their properties. In order to fully take advantage of this possibility, the characterization of MXenes' functionalization is of fundamental interest and, in this context, Electron Energy Loss Spectroscopy (EELS) in a TEM is particularly relevant: (i) it allows probing the electronic structure of MXene sheets on the nanometer scale with chemical selectivity, (ii) it gives a direct correlation between local order (probed on the order of 1 nm) and electronic properties, and (iii) state of the art DFT calculations provide a quantitative understanding of the experimental data. In this presentation, the benefits of combining EELS with DFT simulations will be illustrated on Tin+1CnTx MXenes (T being -OH, -F, and/or -O). The localization of the T groups on the MXene sheets is identified and their role on the MXenes' optical properties evidenced. In addition, based on the characterization of the surface chemistries resulting from different synthesis processes, the possibility to modify the O/F ratio, the electronic density of states or insert transition metal cations between the MXene sheets will be evidenced together with significant consequences in terms of reactivity.


CG-5:IL02  Understanding the Magnetic Properties of Nano-laminated Ternary Carbides, Nitrides and Borides: the Role of Neutron Scattering               
E.N. CASPI, O. RIVIN, A. PESACH, NRCN, Beer-Sheva, Israel; H. SHAKED, BGU University, Beer-Sheva, Israel; A. HOSER, HZB, Berlin, Germany; R. GREGORII, MLZ, Garching, Germany; Q. TAO, J. ROSEN, Linköping University, Linköping, Sweden; S. KOTA, M.W. BARSOUM, Drexel University, Philadelphia, PA, USA

Interest in nano-laminated ternary carbides, nitrides, and borides (MAX/MAB phases) have increased significantly in recent years due to their vast applicative potential. One of the most sought for attributes in these layered materials is spontaneous long-range magnetism, yet to be fully added to their arsenal of physical properties. Moreover, since MXenes are the 2D derivatives of MAX phases, a magnetic MAX could be the precursor for long range ordered 2D magnetic material. Many theoretical work has been done in the last few years predicting long range magnetic MAX and MAB phases in several compounds. However, experimental proof of such materials in their bulk form is limited to observations of macroscopic magnetic response, and no understanding could be drawn from these measurements on the microscopic magnetic behavior of individual crystallographic sites. Such understanding is important to answer some fundamental questions related to the origin of magnetism in these materials, such as whether the MAX phases magnetic response originates from localized moments or itinerant magnetism. Neutron diffraction (ND) can uniquely identify the existence of long range magnetism in a crystallographic site of a particular phase, and estimate its value. In this work the advantages of ND in solving the origin of magnetic behavior in MAX/MAB phases will be discussed, demonstrated for (Cr_0.96Mn_0.04)₂GeC, and mentioned for Mn₂Al¹¹B₂.


CG-5:IL04  Band Structure and Fermi Surfaces of MAX Phases investigated by Angle Resolved Photoemission Spectroscopy (ARPES)
TAKAHIRO ITO, Nagoya University Synchrotron Radiation Research Center (NUSR), Nagoya University, Nagoya, Japan; T. FUJITA, Graduate School of Engineering, Nagoya University, Nagoya, Japan; D. PINEK, 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

MAX phase compounds have recently attracted much attention due to their possible application to the production of a new class of two-dimensional systems called MXenes. On the other hand, the bulk electronic structure of MAX phases has been studied mostly through ab initio, density functional theory (DFT) calculations, mainly due to a lack of single crystalline samples. We have for the first time performed angle-resolved photoemission spectroscopy (ARPES) on single crystals of several MAX phase compounds in order to directly investigate the bulk electronic structure of these systems. For instance, in the case of Cr2AlC, we evidence hole bands centered around the Μ points and electron bands centered around the G point in reciprocal space. Electron and hole bands exhibit an open, tubular structure along the c-axis, confirming the quasi-two-dimensional (2D) character of this highly anisotropic, nano-lamellar compound. The overall electronic structure and orbital characters show good agreements with DFT calculations. However, we find significant differences between the effective mass values extracted from ARPES and those computed by DFT, and kink dispersive features. The results could indicate that a strong-renormalization effect or electron-phonon coupling play a role in Cr2AlC.  


CG-5:IL05  Atomically Resolved Electron Microscopy of MXenes
P.O.A. PERSSON, Linköping University, Linköping, Sweden

Since the discovery of graphene the research area of two-dimensional (2D) materials have attracted vast attention as a consequence of the exceptional properties that arise from their reduced dimensionality. Among these materials we find the MXenes, a rapidly expanding family of 2D transition metal carbides/nitrides that after etching of the parent MAX phases and subsequent surface functionalization are generally described by Mn+1XnTx, where T denotes the surface terminations. MXenes and other 2D materials are best observed by electron microscopy that enables atomically resolved determination of both the structure and the chemistry, much thanks to a rapid development in optics and detectors. With new properties, electron microscopes are rapidly transforming into micro-scale laboratories enabling a large variety of in situ experiments to be performed during direct observation. Combining this with the rich chemistry of MXenes and the possibility of surface engineering through functionalization , offers extensive research efforts to electron microscopists. This presentation will highlight current examples of structural and chemical investigations together with associated in situ investigations from a range of contemporary MXenes.


CG-5:L07  Theoretical Study on the Intrinsic Point Defect Sinks in MAX Phases under Irradiation
JIEMIN WANG, J.Y. WANG, High-performance Ceramic Division, Shenyang National Laboratory for Materials Science, Institute of Metal Research, CAS, Shenyang, China

Nano-laminated MAX phases are promising nuclear materials due to the good stability under corrosion attack and radiation damage. The A atomic layer is supposed to be the key factor and provides intrinsic point defect sinks for the good irradiation resistance. To understand the effects of A atomic layer on the point defects generation and accommodation processes under irradiation, low energy atom recoil events in Ti3AC2 (A=Si, Al) and rock-salt ZrC are studied by using the ab initio molecular dynamics (AIMD) modeling. The threshold displaced energies (Ed) are calculated and the related defect generation and accommodation processes are analyzed. Our results show that the intercalation of A atomic layer in Ti3AC2 can lower the Eds of defect atoms in rock-salt structure, and the generated point defects are easily trapped near the A atomic layer. The present work provides insight into the irradiation resistance of MAX phases by illustrating the key role of intrinsic point defect sinks in the crystal structure.


CG-5:L08  Vacancy-ordered Mo1.33C MXene from first principles and x-ray photoelectron spectroscopy
H. LIND, J. HALIM, S.I. SIMAK, J. ROSEN, Department of Physics, Chemistry, and Biology, Linköping University, Linköping, Sweden

MXenes are composed of transition-metal carbides/nitrides of the general formula Mn+1XnTx, where T represents surface terminations, typically O, OH and/or F. Recently, a new type of MXene was discovered, Mo1.33CTx, with in-plane ordered vacancies and electronic properties superior to those of traditional MXenes without vacancies[1,2]. We present first principle calculations based on density functional theory of Mo2CT2 and Mo1.33CT2, where T is O, F, OH or a mixture thereof. Results are presented on structural changes upon vacancy formation, preferred termination and termination site, and resulting dynamical stability and electronic properties. It is shown that while Mo2C is typically O terminated, mixed terminations with a high F content are suggested for Mo1.33CTx, which is consistent with data from X-ray photoelectron spectroscopy. The latter gives the highest metallicity out of all the configurations investigated. In addition, the results indicate a strong tuning potential of the bandgap through choice of terminations, with an electronic structure changing between insulating to metallic depending on termination(s) and their configuration.
[1] Q. Tao et al., Nat. Commun. 8, 14949 (2017). [2] H. Lind, et al., Phys. Rev. Materials 1, 044002 (2017).


Session CG-6 - Synthesis and Fabrication of MAX/MAB/MXenes

CG-6:IL01  2D Atomic Sandwiches of Ordered Double-transition Metal Carbides (MXenes)
B. ANASORI, Y. GOGOTSI, A.J. Drexel Nanomaterials Institute and Department of Materials Science & Engineering, Drexel University, Philadelphia, PA, USA

Ordered double-transition metal MXenes, such as Mo2TiC2 and Mo2Ti2C3, are a subfamily of MXenes, in which one or two layers of a transition metal (e.g., Ti) are sandwiched between the layers of another transition metal (e.g., Mo) in a 2D carbide structure. Tailoring of atomic ordering, where one atomic plane in a MXene can be replaced by another type of transition metal, gives unique control over materials properties at the atomic level for these ~1-nm thick 2D materials. For example, in Mo2TiC2, we can replace the inner Ti atomic sheet with V to form Mo2VC2, or replace the outer Mo atomic planes with Cr and form Cr2TiC2, which can further modify the electronic, magnetic, electrochemical and optical properties of MXenes. In this talk, we discuss the phase stability and ordering to non-ordering arrangements of these structures, as well as the resulting properties of these 2D MXene sandwiches.


CG-6:IL02  MAX Phase Thin Film Synthesis by Annealing Techniques               
T. CABIOCH, D. MAGNE, V. MAUCHAMP, J. NICOLAI, M.F. BEAUFORT, Département de Physique et Mécanique des Matériaux, Institut P', University of Poitiers-CNRS-ENSMA, Chasseneuil-Futuroscope, France

MAX phase thin film synthesis is generally achieved by using PVD techniques. It allows for growing high quality thin films but its industrial scale transfer is difficult to achieve (use of high temperature, very narrow set of experimental parameters,..). Therefore, new approaches based on thermal annealing of thin films deposited at room temperature were recently developed. In this contribution, three different ways of obtaining MAX phase thin films by thermal annealing are described. The most simple method consists in synthesizing, at room temperature, amorphous or nanocrystallized thin films with the appropriate stoichiomety and then to anneal the samples. In a second approach, multilayers (MX/MA or M/AX or MX/A)are deposited at room temperature and annealed to allow for interdiffusion processes between the layers that lead to the MAX phase formation. For the last method, interdiffusion processes between the substrate and a thin film deposited at room temperature control the MAX phase thin film formation during a thermal annealing. Several examples of MAX phase thin films recently synthesized by these three indirect approaches will be discussed.


CG-6:IL03  MXene Electrochemical Etching and Morphology Alteration               
WANMEI SUN, SMIT SHAH, TOUSEEF HABIB, M. RADOVIC, M.J. GREEN, A. McFERRIN, Dept. of Chemical Engineering, Dept. of Materials Science & Engineering, Texas A&M University, College Station, TX, USA

We successfully demonstrate the electrochemical etching of Al fromporous Ti2AlC electrodes in dilute hydrochloric acid to form a layer of Ti2CTx MXene on Ti2AlC. This is the first report of etching of the A layer fromtheMAX phase in a fluoride-free solution. In addition, these MXenes possess only –Cl terminal groups, as well as the common ones, such as –O and –OH. However, electrochemical etching can also result in subsequent over-etching of parent MAX phases to carbide-derived carbon (CDC). We propose a core–shell model to explain electrochemical etching of Ti2AlC to Ti2CTx and CDC. The proposed model suggests that a careful balance in etching parameters is needed to produce MXenes while avoiding overetching. Our electrochemical approach expands the possible range of both etching techniques and resulting MXene compositions. We also demonstrate that colloidal MXene nanosheets encapsulated within spray-dried droplets can be scrolled, bent, and folded into 3D crumpled structures by capillary forces during drying. This morphological change was observed to be reversible upon rehydration.


CG-6:L04  Self-propagating High-temperature Synthesis and Properties of the MAX Phases in Ti-Al-C System              
A. PAZNIAK, D. KUZNETSOV, NUST "MISiS", Moscow, Russia, P. BAZHIN, A. STOLIN, ISMAN, Chernogolovka, Russia

The MAX phases in the Ti–Al–C ternary system such as Ti2AlC and Ti3AlC2 were synthesized by Self-propagating High-temperature Synthesis (extrusion and compression) at various technological parameters and molar ratios of the initial components (titanium, alumina and carbon black). The phase composition and lattice parameters of fabricated materials have been investigated by X-ray diffraction as well as their structure and morphology were examined by scanning electron microscopy. The results show that some impurities present in samples, almost TiC and TiAl intermetallides, the amount of which depends on the molar ratio of the initial components. Under the load of 3 N, the Vickers hardness and Young's modulus of Ti2AlC and Ti3AlC2 is measured to be 5.87-7.08 GPa and 130.0-215.0 GPa, respectively, in dependence of fabrication method and component ratio. Stress-strain behavior of the synthesized MAX phases depending on the manufacturing method (extrusion and compression) has also been discussed.


CG-6:L05  Synthesis of MAX Phases by Molten Salt Shielded Synthesis Process in Air              
A. DASH, O. GUILLON, R. VAßEN, J. GONZALEZ-JULIAN, IEK-1, Forschungszentrum Jülich GmbH, Jülich, Germany

High temperature processing of oxidation prone materials had never been easy and is always accompanied with oxidation. Synthesis of MAX phases has been done by reactive hot pressing, spark plasma sintering or vacuum sintering, in such routes we obtain a dense body of MAX phase and not powder and moreover the process is carried out in vacuum or inert gas atmosphere which renders the process expensive and limits the use of MAX phases at an industrial scale. In this work a process has been developed which enables the synthesis of MAX phases in air in the form of powder using a new process based on molten salt shielded synthesis with an acronym of MSSS.The process involves the consolidation of precursor powders mixed with Potassium Bromide (KBr). The already consolidated sample is further encapsulated with KBr to protect from oxidation during heating. Synthesis of Ti3SiC2 in a molten salt medium facilitates the diffusion of species thereby reducing the synthesis temperature, further the high solubility of KBr in water eliminates the grinding/milling step required to obtain MAX phase powder, mere dissolution in water yields powder with a particle size of 40 µm. The synthesis of any MAX phase (Ti3SiC2, Ti2AlN, Ti4AlN3, Ti3AlC2, Ti2AlC) is possible with high purity and in powder form.

 
Session CG-8 - Energy Storage

CG-8:IL01  High-capacitance Mechanism for Ti3C2Tx MXene by in Situ Electrochemical Raman Spectroscopy Investigation
XIAOHUI WANG, Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, China

MXenes represent an emerging family of conductive two-dimensional materials. Their representative, Ti3C2Tx, has been recognized as an outstanding member in the field of electrochemical energy storage. However, an in-depth understanding of fundamental processes responsible for the superior capacitance of Ti3C2Tx MXene in acidic electrolytes is lacking. Here, to understand the mechanism of capacitance in Ti3C2Tx MXene, we studied electrochemically the charge/discharge processes of Ti3C2Tx electrodes in three aqueous sulfate electrolytes containing different cations, coupled with in situ Raman spectroscopy. It is demonstrated that hydronium in the H2SO4 electrolyte bonds with the terminal O in the negative electrode upon discharging while debonding occurs upon charging. Correspondingly, the reversible bonding/debonding changes the valence state of Ti element in the MXene, giving rise to the pseudocapacitance in the acidic electrolyte. In stark contrast, only electric double layer capacitance is recognized in the other electrolytes of (NH4)2SO4 or MgSO4. Both surface functional group-involved bonding/debonding-induced pseudocapacitance, and ion exchange-featured charge storage, simultaneously contribute to the superior capacitance of Ti3C2Tx MXene in acidic electrolyte.


CG-8:IL02  MXenes as Hosting Materials for Ions and Molecules               
M. NAGUIB, Department of Physics and Engineering Physics, Tulane University, New Orleans, LA, USA

MXenes are large family of two-dimensional transition metal carbides and nitrides of Mn+1XnTz composition; where M is an early transition metal (e.g. Ti, V, Mo, Nb) and X is either carbon or nitrogen, “Tz” stands for a mixture of surface terminations (e.g. O, OH, F), and n can be 1, 2, or 3. So far, about two dozens of MXenes have been produced experimentally (e.g. Ti3C2, V2C, Mo2C, Ti3CN, and Nb4C3). In addition, ab initio calculations predicted many others to be stable. MXenes combine the metallic conductivity of transition metal carbide/nitrides with the hydrophilic nature of their terminated surfaces. MXenes can be intercalated by a wide range of intercalants from mono- and multi-valent ions to organic and inorganic molecules. Since their discovery, intercalation has been of a critical importance for MXenes processing and applications including electrochemical energy storage, water purification and sensing. However, very little has been known for the nature of intercalant and the bonding between MXenes surface and the intercalant. In this presentation, the recent fundamental findings and understanding for the complexity of intercalations in MXenes, will be discussed. In addition, the performance of MXenes as electrode materials hosting ions for batteries will be presented.


CG-8:IL03  Microwave-assisted Synthesis of MXene-based Hybrids for Energy Storage in Supercapacitor and LIB              
W. ZHENG, ZHENG MING SUN, Jiangsu Key Laboratory of Advanced Metallic Materials, School of Materials Science and Engineering, Southeast University, Nanjing, P.R. China

MXenes have received great attention in energy storage area such as supercapacitors, LIBs, fuel cells etc. for their novel electrical conductivity and abundant tailorable surface chemistries. However, similar to other 2-D materials MXenes suffered from restacking and collapse during discharge-charge cycles. Herein, we report a facile method via microwave irradiation to introduce second phase into MXene as spacers. The resulted hybrids exhibit enhanced electrochemical performance in supercapacitor and LIBs. With this method, we have synthesized SnO2@Ti3C2 hybrid and applied it to electrode material, a specific capacitance of 125.63 F g-1 at 1 A g-1 with high cycle stability was achieved, which is almost two times as high as that of pristine Ti3C2. Similarly, we have synthesized CNTs@Ti3C2 hybrid which delivers a reversible capacity of 430 mA h g-1 at 1 A g-1 and 175 mA h g-1 at 10 A g-1, which is much higher than that of pristine Ti3C2 and commercial graphite at high rates. The findings in this work may open new exciting opportunities to developing electrode materials with high specific capacity for energy conversion and storage.


CG-8:L04  A Fast Route to Synthesize CNTs@Ti3C2 Hybrid Structures               
WEI ZHENG¹, P.G. ZHANG¹, W.B. TIAN¹, J. CHEN¹, Y.M. ZHANG², Z.M. SUN¹, ¹Jiangsu Key Laboratory of Advanced Metallic Materials, School of Materials Science and Engineering, Southeast University, Nanjing, P.R. China; ²Jiangsu Key Laboratory of Construction Materials, School of Materials Science and Engineering, Southeast University, Nanjing, P.R. China

We report herein a fast and scalable approach to synthesize carbon nanotubes-Ti3C2 (CNTs@Ti3C2) hybrid structures via microwave irradiation under ambient condition. The effect of three arcing materials, CNT, graphite (C) and carbon fiber (Cf), on the growth of CNTs on Ti3C2 were investigated. The resulting CNTs@Ti3C2 nanostructures were tested as anodes in LIBs and they all exhibited better electrochemical performance than pristine Ti3C2. Remarkably, CNTs@Ti3C2-Cf delivers a reversible capacity of 430 mA h g-1 at 1 A g-1 and 175 mA h g-1 at 10 A g-1, which is much higher than that of commercial graphite at high rates. The mechanisms for the microwave irradiation process as well as for the improvement in electrical performance will be discussed. The findings in this work may open new exciting opportunities to developing electrode materials with high specific capacity for energy conversion and storage.


CG-8:L05  Core-shell SnO2@C Decorated 3D d-Ti3C2 Xerogel Framework as the Anode for High-performance Lithium-ion Battery               
HENG ZHANG, P.G. ZHANG, W. ZHENG, J. CHEN, W.B. TIAN, Z.M. SUN, Jiangsu Key Laboratory of Advanced Metallic Materials, School of Materials Science and Engineering, Southeast University, Nanjing, P.R. China; Y.M. ZHANG, Jiangsu Key Laboratory of Construction Materials, Southeast University, Nanjing, P.R. China

Recently, new two-dimensional (2D) transition-metal carbides and carbonitrides, MXenes, were exploited and employed as the active substance of the electrode with prominent performance. Herein, a three dimensional (3D) SnO2@C/d-Ti3C2 (S-TCS) network frame architecture was fabricated by employing sol-gel method to anchor the core-shell SnO2@C onto the d-Ti3C2 xerogel framework. Such core-shell SnO2@C decorated 3D d-Ti3C2 xerogel framework exhibited an excellent Li-ions storage performance as the anode of lithium ion batteries (LIBs). Typically, 3D S-TCS delivered reversible specific capacity of 520 and 492 mA h g-1 at the current density of 1.0 and 2.0 A g-1, respectively, after 1000 times charge-discharge cycles. The enhanced electrochemical performance is attributed to the synergetic effect of the SnO2 pulverization suppression by coated carbon and the conductive pathway established by 3D MXene framework.


CG-8:L06  Binder-free Ti3C2 MXene-carbon Nanotube Supercapacitor Electrode Produced by Electrophoretic Deposition                
LI YANG¹, P. ZHANG¹, W. ZHENG¹, W.B. TIAN¹, J. CHEN¹, Y.M. ZHANG², Z.M. SUN¹, ¹Jiangsu Key Laboratory of Advanced Metallic Materials, School of Materials Science and Engineering, Southeast University, Nanjing, P.R. China; ²Jiangsu Key Laboratory of Construction Materials, School of Materials Science and Engineering, Southeast University, Nanjing, P.R. China

Binder-free Ti3C2 MXene-carbon nanotubes (Ti3C2-CNTs) composite films were successfully deposited onto graphite substrate by electrophoretic deposition (EPD) and subsequently used as an electrode for supercapacitor. The as-prepared Ti3C2-CNTs electrode exhibited enhanced specific capacitance, approximately 1.5 times and 2.5 times higher than that of pure Ti3C2 and CNTs, respectively. Furthermore, Ti3C2-CNTs electrode showed excellent cycling stability after 1000 cycles. Introducing CNTs into MXene builds a robust structure and prevents MXene from restacking, leading to an enhancement in electrochemical performance. These results suggest that Ti3C2-CNTs films prepared by EPD, a simple, economical and eco-friendly method, has the potential as electrode materials for high-performance energy storage devices.

 
Session CG-9 - Applications of the MAX/MAB and MXene Phases

CG-9:L03  Applications 2D Carbides, Nitrides and Carbonitrides (MXenes)              
Y. GOGOTSI, B. ANASORI, A.J. Drexel Nanomaterials Institute, and Department of Materials Science & Engineering, Drexel University, Philadelphia, PA, USA

2D materials are receiving much attention due to their unusual electronic, mechanical and optical properties. They can also serve as convenient building blocks for a variety of layered structures, membranes and composites [1]. Transition metal carbides, carbonitrides and nitrides (MXenes) are among the latest additions to the 2D world [2,3]. Ti3C2Tx was the first MXene reported in 2011 [2] and since then, about 30 different MXene compositions have been synthesized and dozens more predicted to exist and studied in silico [2]. MXenes’ versatile chemistry renders their properties tunable for a large variety of applications, such as energy generation and storage, transparent conducting coatings, electromagnetic shielding, plasmonics, SERS, reinforcement for composites, water purification, chemical, photo- and electro-catalysis; bio, chemical and gas sensors, lubricants, etc. [2] This presentation will provide an overview of the most recent and exciting applications of MXenes.
1 B. Mendoza-Sánchez, Y. Gogotsi, Adv. Mat., 28, 6104, 2016 2 M. Naguib, et al., Two-Dimensional Nanocrystals Produced by Exfoliation of Ti3AlC2, Adv. Mat., 23, 4248, 2011 3 B. Anasori, M. R. Lukatskaya, Y. Gogotsi, 2D metal carbides and nitrides (MXenes) for energy storage, Nature Rev. Mat., 2, 16098, 2017


CG-9:L04  Irradiation Tolerance of Zr2AlC MAX Phase               
H. QARRA, K. KNOWLES, University of Cambridge, Cambridge, UK

Zr−Al−C variations of the MAX phase family are potentially promising materials for components in future nuclear reactor systems. The capability of these materials will be limited by their behaviour under hostile reactor conditions, high irradiation damage and high temperatures. It is therefore encouraging that, in general, MAX phases have been shown to be remarkably resistant to damage when irradiated at high doses at high temperatures. However, no prior studies on the effects of irradiation on Zr MAX phases have been reported. In this study material containing the MAX phase Zr2AlC with 35 wt% ZrC as a secondary phase has been successfully synthesised. This material was then irradiated with swift Au ions. The irradiation was undertaken at temperatures from room temperature to 600 C. The damage acquired was estimated to be in the range 1­–3.5 dpa. These irradiated materials have then been characterised by transmission electron microscopy, scanning electron microscopy, nano-indentation hardness tests and X-ray diffraction techniques. Initial results suggest that both Zr2AlC and ZrC show little internal damage at these doses, but that there is a temperature-dependent microcracking phenomenon on the bulk material independent of the irradiation dose.


CG-9:IL05  On the Feasibility of Nano-laminated Carbides as ATF Coatings in LWRs              
JIE ZHANG, YIMING LEI, LINA CHEN, JINGYANG WANG, Shenyang National Laboratory for Materials Science, Institute of Metal Research, CAS, Shenyang, China

Due to the unique combination of good thermal conductivity, machinability, high temperature stability, and irradiation tolerance, MAX phases are considered as potential advanced nuclear materials for various applications, including light water reactors (LWRs) and future generation (Gen IV) fission reactors. In the present talk, we focus on the application of MAX phases as protective coatings on zircaloy cladding tubes for the accident tolerant fuel systems (ATF) in LWRs. Firstly, the high temperature steam oxidation behaviors of typical MAX phases under simulated LOCA scenario were investigated. Integrated carbides coatings with optimal irradiation resistance, steam oxidation resistance as well as CTE match were designed and then synthesized by PVD method with temperature friendly to Zircaloy cladding. With the systematic investigation of the mechanical and chemical compatibility between integrated coating and substrate as well as the HT steam oxidation tests, feasibility of nano-laminated carbides in accident-tolerant fuel/clad system were evaluated.


CG-9:IL06  MAX Phase Materials for Gen-IV Lead-fast Nuclear Reactors (LFRs)               
K. LAMBRINOU¹, T. LAPAUW^{1, 2}, B. TUNCA^{1, 2}, J. VLEUGELS², ¹Belgian Nuclear Research Centre, SCK•CEN, Mol, Belgium; ²Department of Materials Engineering, KU Leuven, Heverlee, Belgium

One of the principal challenges in the development of Gen-IV lead-cooled fast reactors (LFRs) is the inherent corrosiveness of heavy liquid metal coolants to both structural and cladding steels intended for use in such nuclear systems. The primary coolant of the MYRRHA irradiation facility, currently under development at SCK•CEN, Belgium, is the liquid lead-bismuth eutectic (LBE), which limits the safe long-term use of nuclear grade stainless steels below 400°C. The safe and efficient operation of MYRRHA at higher temperatures demands the development of corrosion-resistant materials for key applications, such as the geometrically complex pump impeller component. This work presents the challenges in developing MAX phase materials tailored to the needs of the pump impeller targeted application, i.e., immunity to corrosion, erosion & liquid metal embrittlement (LME), damage tolerance, machinability, and radiation tolerance. The performance of the candidate MAX phase materials has been assessed (a) in low-oxygen ([O]<10-8 mass%) static and fast-flowing LBE in terms of resistance to liquid metal corrosion and erosion, respectively, (b) in low-oxygen static LBE in terms of susceptibility to LME under mechanical load and (c) under in-situ ion irradiation in terms of radiation tolerance.


CG-9:L07  Effect of Temperature and Atmosphere on Sn Whisker Growth on Ti2SnC              
YUSHUANG LIU¹, P. ZHANG¹, W.B. TIAN¹, Y.M. ZHANG², Z.M. SUN¹, ¹Jiangsu Key Laboratory of Advanced Metallic Materials, School of Materials Science and Engineering, Southeast University, Nanjing, P.R. China; ²Jiangsu Key Laboratory of Construction Materials, School of Materials Science and Engineering, Southeast University, Nanjing, P.R. China

Spontaneous Sn whisker growth has resisted interpretation for 70+ years. Effect of temperature and atmosphere on Sn whisker growth on Ti2SnC is studied in this work. One set of ball-milled and then pressed Ti2SnC-Sn powder compacts were heated at various temperatures in air, while another set were heated in argon with the same temperature profile. The samples heated in air have higher number density of Sn outgrowth than these heated in argon. In air, the number density increased with the increase of incubation temperature, while, in argon, the 160 °C incubation led to the highest number density and 210 °C led to thicker and longer Sn whiskers. Sn polyhedrons and prisms formed on the samples heated in argon. A catalysis-based mechanism is developed to interpret the growth behavior of the Sn whiskers, in which cleavage planes of Ti2SnC grains introduced by ball milling play the role of nucleation sites. Lower nucleation energy and higher diffusion rate of Sn under elevated temperatures facilitate the nucleation and growth of the Sn whiskers. This work will not only help to secure the application of MAX phases, but also may shed new lights on understanding the general Sn whisker growth.