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| 2. |
- Alexandrova, L, et al.
(författare)
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The influence of mixed cationic-anionic surfactants on the three-phase contact parameters in silica-solution systems
- 2011
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Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 373, s. 145-151
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Tidskriftsartikel (refereegranskat)abstract
- The formation of thin wetting films on silica surface from aqueous solution of (a) tetradecyltrimetilammonium bromide (C14TAB) and (b) surfactant mixture of the cationic C14TAB with the anionic sodium alkyl- (straight chain C12-, C14- and C16-) sulfonates, was studied using the microscopic thin wetting film method developed by Platikanov. Film lifetimes, three-phase contact (TPC) expansion rates, receding contact angles and surface tension were measured. It was found that the mixed surfactants caused lower contact angles, lower rates of the thin aqueous film rupture and longer film lifetimes, as compared to the pure C14TAB. This behavior was explained by the strong initial adsorption of interfacial complexes from the mixed surfactant system at the air/solution interface, followed by adsorption at the silica interface. The formation of the interfacial complexes at the air/solution interface was proved by means of the surface tension data. It was also shown, that the chain length compatibility between the anionic and cationic surfactants controls the strength of the interfacial complex and causes synergistic lowering in the surface tension. The film rupture mechanism was explained by the heterocoagulation mechanism between the positively charged air/solution interface and the solution/silica interface, which remained negatively charged.
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| 3. |
- Halim, Joseph, et al.
(författare)
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Synthesis and Characterization of 2D Molybdenum Carbide (MXene)
- 2016
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Ingår i: Advanced Functional Materials. - : WILEY-V C H VERLAG GMBH. - 1616-301X .- 1616-3028. ; 26:18, s. 3118-3127
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Tidskriftsartikel (refereegranskat)abstract
- Large scale synthesis and delamination of 2D Mo2CTx (where T is a surface termination group) has been achieved by selectively etching gallium from the recently discovered nanolaminated, ternary transition metal carbide Mo2Ga2C. Different synthesis and delamination routes result in different flake morphologies. The resistivity of free-standing Mo2CTx films increases by an order of magnitude as the temperature is reduced from 300 to 10 K, suggesting semiconductor-like behavior of this MXene, in contrast to Ti3C2Tx which exhibits metallic behavior. At 10 K, the magnetoresistance is positive. Additionally, changes in electronic transport are observed upon annealing of the films. When 2 mu m thick films are tested as electrodes in supercapacitors, capacitances as high as 700 F cm(-3) in a 1 M sulfuric acid electrolyte and high capacity retention for at least 10,000 cycles at 10 A g(-1) are obtained. Free-standing Mo2CTx films, with approximate to 8 wt% carbon nanotubes, perform well when tested as an electrode material for Li-ions, especially at high rates. At 20 and 131 C cycling rates, stable reversible capacities of 250 and 76 mAh g(-1), respectively, are achieved for over 1000 cycles.
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| 4. |
- Kota, Sankalp, et al.
(författare)
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Magnetic properties of Cr2AlB2, Cr3AlB4, and CrB powders
- 2018
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Ingår i: Journal of Alloys and Compounds. - : ELSEVIER SCIENCE SA. - 0925-8388 .- 1873-4669. ; 767, s. 474-482
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Tidskriftsartikel (refereegranskat)abstract
- The MAB phases are ternary, atomically laminated compounds that crystallize with orthorhombic structures and consist of transition metal (M) boride sublattices interleaved with single or double layers of Al. To date, the magnetic properties of ferromagnetic Fe(2)AIB(2) have been well-studied experimentally, but those of most end member MAB phases with other transition metals remain poorly understood. Herein, predominantly single-phase Cr(3)AIB(4) and Cr(2)AIB(2) powders, with minor amounts of CrB impurities, were synthesized by heating mixtures of chromium monoboride (CrB), aluminum (Al), and boron or CrB and Al under flowing Ar. These reactants were found to substantially suppress the formation of undesired phases in the Cr-Al-B system. The magnetic properties of Cr(3)AIB(4), Cr(2)AIB(2) and CrB powders were characterized. All compounds exhibit paramagnetic behavior down to 4 K, with susceptibilities that are quite weakly temperature dependent at higher temperatures and a Curie-Weiss-like component prominent at low temperatures. Magnetization isotherms of the three compounds, showed approximately linear behavior above 5 kOe and no saturation of the magnetic moment up to 40 kOe, which is consistent with paramagnetism. The magnitude of the magnetic moments showed little variation with composition, on a per Cr atom basis. While the exact nature of the Curie-Weiss component is not entirely clear, we tentatively attribute it to dilute extrinsic impurities. (C) 2018 Elsevier B.V. All rights reserved.
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| 5. |
- Kota, Sankalp, et al.
(författare)
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Synthesis and Characterization of an Alumina Forming Nanolaminated Boride: MoAlB
- 2016
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Ingår i: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 6:26475
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Tidskriftsartikel (refereegranskat)abstract
- The MAlB phases are nanolaminated, ternary transition metal borides that consist of a transition metal boride sublattice interleaved by monolayers or bilayers of pure aluminum. However, their synthesis and properties remain largely unexplored. Herein, we synthesized dense, predominantly single-phase samples of one such compound, MoAlB, using a reactive hot pressing method. High-resolution scanning transmission electron microscopy confirmed the presence of two Al layers in between a Mo-B sublattice. Unique among the transition metal borides, MoAlB forms a dense, mostly amorphous, alumina scale when heated in air. Like other alumina formers, the oxidation kinetics follow a cubic time-dependence. At room temperature, its resistivity is low (0.36-0.49 mu Omega m) and - like a metal - drops linearly with decreasing temperatures. It is also a good thermal conductor (35 Wm(-1)K(-1) at 26 degrees C). In the 25-1300 degrees C temperature range, its thermal expansion coefficient is 9.5 x 10(-6) K-1. Preliminary results suggest the compound is stable to at least 1400 degrees C in inert atmospheres. Moderately low Vickers hardness values of 10.6 +/- 0.3 GPa, compared to other transition metal borides, and ultimate compressive strengths up to 1940 +/- 103 MPa were measured at room temperature. These results are encouraging and warrant further study of this compound for potential use at high temperatures.
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