| 1. |
- Persson, Ingemar, et al.
(författare)
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2D Transition Metal Carbides (MXenes) for Carbon Capture
- 2019
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Ingår i: Advanced Materials. - : WILEY-V C H VERLAG GMBH. - 0935-9648 .- 1521-4095. ; 31:2
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Tidskriftsartikel (refereegranskat)abstract
- Global warming caused by burning of fossil fuels is indisputably one of mankinds greatest challenges in the 21st century. To reduce the ever-increasing CO2 emissions released into the atmosphere, dry solid adsorbents with large surface-to-volume ratio such as carbonaceous materials, zeolites, and metal-organic frameworks have emerged as promising material candidates for capturing CO2. However, challenges remain because of limited CO2/N-2 selectivity and long-term stability. The effective adsorption of CO2 gas (approximate to 12 mol kg(-1)) on individual sheets of 2D transition metal carbides (referred to as MXenes) is reported here. It is shown that exposure to N-2 gas results in no adsorption, consistent with first-principles calculations. The adsorption efficiency combined with the CO2/N-2 selectivity, together with a chemical and thermal stability, identifies the archetype Ti3C2 MXene as a new material for carbon capture (CC) applications.
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| 2. |
- Persson, Ingemar, et al.
(författare)
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On the organization and thermal behavior of functional groups on Ti3C2 MXene surfaces in vacuum
- 2018
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Ingår i: Current Opinion in Chemical Engineering. - : Institute of Physics Publishing (IOPP). - 2211-3398. ; 5:1
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Tidskriftsartikel (refereegranskat)abstract
- The two-dimensional (2D) MXene Ti(3)C(2)Tx is functionalized by surface groups (T-x) that determine its surface properties for, e.g. electrochemical applications. The coordination and thermal properties of these surface groups has, to date, not been investigated at the atomic level, despite strong variations in the MXene properties that are predicted from different coordinations and from the identity of the functional groups. To alleviate this deficiency, and to characterize the functionalized surfaces of single MXene sheets, the present investigation combines atomically resolved in situ heating in a scanning transmission electron microscope (STEM) and STEM simulations with temperature-programmed x-ray photoelectron spectroscopy (TP-XPS) in the room temperature to 750 degrees C range. Using these techniques, we follow the surface group coordination at the atomic level. It is concluded that the F and O atoms compete for the DFT-predicted thermodynamically preferred site and that at room temperature that site is mostly occupied by F. At higher temperatures, F desorbs and is replaced by O. Depending on the O/F ratio, the surface bare MXene is exposed as F desorbs, which enables a route for tailored surface functionalization.
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| 3. |
- Mockuté, Aurelija, et al.
(författare)
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Age hardening in (Ti1-xAlx)B2+Delta thin films
- 2017
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Ingår i: Scripta Materialia. - : Elsevier BV. - 1359-6462 .- 1872-8456. ; 127, s. 122-126
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of (Ti0.71Al0.29)B2+1.08 have been deposited by magnetron sputtering. Post-deposition annealing at 1000 degrees C for 1 h results in increased hardness and elastic modulus, from 32 to 37 GPa and from 436 to 461 GPa, respectively. In both as-deposited and annealed states the films adhere well to the substrate, indicating no considerable internal stress. The initial high hardness is attributed to a columnar microstructure consisting of crystalline (Ti,Al)B-2 columns separated by an amorphous B matrix. The observed age hardening corresponds to phase separation within the (Ti,Al)B-2 columns including the formation of Ti-deficient crystallites within the grain interior upon annealing.
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| 4. |
- Mockuté, Aurelija, et al.
(författare)
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Synthesis and characterization of (Ti1-xAlx)B2+Delta thin films from combinatorial magnetron sputtering
- 2019
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Ingår i: Thin Solid Films. - : ELSEVIER SCIENCE SA. - 0040-6090 .- 1879-2731. ; 669, s. 181-187
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Tidskriftsartikel (refereegranskat)abstract
- (Ti1-xAlx)B2+Delta films with a lateral composition gradient of x = [0.30-0.66] and Delta = [0.07-1.22] were deposited on an Al2O3 wafer by dual magnetron sputtering at 400 degrees C from sintered TiB2 and AlB2 targets. Composition analysis indicates that higher Ti:Al ratios favor overstoichiometry in B and a reduced incorporation of O. Transmission electron microscopy reveals distinctly different microstructures of Ti- and Al-rich compositions, with formation of characteristic conical growth features for the latter along with a lower degree of crystallinity and significantly less tissue phase from B segregation at the grain boundaries. For Al-rich films, phase separation into Ti- and Al-rich diboride nanometer-size domains is observed and interpreted as surface-initiated spinodal decomposition. The hardness of the films ranges from 14 to 28 GPa, where the higher values were obtained for the Ti-rich regions of the metal boride.
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| 5. |
- Nedfors, Nils, et al.
(författare)
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Influence of pulse frequency and bias on microstructure and mechanical properties of TiB2 coatings deposited by high power impulse magnetron sputtering
- 2016
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Ingår i: Surface & Coatings Technology. - : ELSEVIER SCIENCE SA. - 0257-8972 .- 1879-3347. ; 304, s. 203-210
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Tidskriftsartikel (refereegranskat)abstract
- The high plasma density and large fraction of ionized species created in a high power impulse magnetron sputtering (HiPIMS) discharge add new measures to control the sputtering process. We have studied the sputtering of TiB2 coatings by HiPIMS from a compound target in an industrial system. How the degree of ionized species effects coating microstructure and mechanical properties has been investigated by varying the pulse frequency between 200 Hz and 1000 Hz while keeping the average power constant at 2 kW. The coatings have a B/Ti atomic ratio amp;gt;= 2.5 and a microstructure exhibiting 001 textured nanocolumnar grains with an amorphous B tissue phase in grain boundaries. Lower frequencies provide higher degree of ionization, which does, however, increase the compressive residual stress in the coatings. This results in harder coatings and the highest hardness of 49 GPa is measured for the coating deposited at 200 Hz (-3.8 GPa residual stress). A change in texture from random orientation to 001 texture is achieved when going from regular dc sputtering to HiPIMS at a floating bias. Superhard (H = 43 GPa) TiB2 coatings with a relatively low compressive stress of about -1 GPa can be deposited by HiPIMS at 1000 Hz using floating bias. (C) 2016 Elsevier B.V. All rights reserved.
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| 6. |
- Näslund, Lars-Åke, et al.
(författare)
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X-ray Photoelectron Spectroscopy of Ti3AlC2, Ti3C2Tz, and TiC Provides Evidence for the Electrostatic Interaction between Laminated Layers in MAX-Phase Materials
- 2020
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Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 124:50, s. 27732-27742
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Tidskriftsartikel (refereegranskat)abstract
- The inherently nanolaminated Ti3AlC2 is one of the most studied MAX-phase materials. MAX-phases consists of two-dimensional Mn+1Xn-layers (e.g., T3C2-layers) with strong internal covalent bonds separated by weakly interacting A-layers (e.g., Al-layers), where the repetitive stacking of the Mn+1Xn-layers and the A-layers suggests being the foundation for the unusual but attractive material properties of the MAX-phases. Although being an important parameter, the nature of the bonding between the Mn+1Xn-layers and the A-layers has not yet been established in detail. The X-ray photoelectron spectroscopy data presented in this paper suggest that the weak interaction between the Ti3C2-layers and the Al-layers in Ti3AlC2 is through electrostatic attraction facilitated by a charge redistribution of the delocalized electrons from the Ti3C2-layers to the Al-layers. This charge redistribution is of the same size and direction as between Ti atoms and Al atoms in TiAl alloy. This finding opens up a pathway to predict and improve MAX-phase materials properties through A-layer alloying, as well as to predict new and practically feasible MXene compounds.
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