| 1. |
- Andersson, Matilda, et al.
(författare)
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Deposition and characterization of magnetron sputtered amorphous Cr-C films
- 2012
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Ingår i: Vacuum. - : Elsevier BV. - 0042-207X .- 1879-2715. ; 86:9, s. 1408-1416
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Tidskriftsartikel (refereegranskat)abstract
- Thin films in the Cr-C system with carbon content of 25-85 at.% have been deposited using non-reactive DC magnetron sputtering from elemental targets. Analyses with X-ray diffraction and transmission electron microscopy confirm that the films are completely amorphous. Also, annealing experiment show that the films had not crystallized at 500 degrees C. Furthermore, X-ray spectroscopy and Raman spectroscopy show that the films consist of two phases, an amorphous CrCx phase and an amorphous carbon (a-C) phase. The presence of two amorphous phases is also supported by the electrochemical analysis, which shows that oxidation of both chromium and carbon contributes to the total current in the passive region. The relative amounts of these amorphous phases influence the film properties. Typically, lower carbon content with less a-C phase leads to harder films with higher Young's modulus and lower resistivity. The results also show that both films have lower currents in the passive region compared to the uncoated 316L steel substrate. Finally, our results were compared with literature data from both reactively and non-reactively sputtered chromium carbide films. The comparison reveals that non-reactive sputtering tend to favour the formation of amorphous films and also influence e.g. the sp(2)/sp(3) ratio of the a-C phase.
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| 2. |
- Andersson, Matilda, et al.
(författare)
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Magnetron sputtering of Zr-Si-C thin films
- 2012
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 520:20, s. 6375-6381
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Tidskriftsartikel (refereegranskat)abstract
- The phase composition and chemical bonding of Zr-C and Zr-Si-C films deposited by magnetron sputtering has been studied. The results show that the binary Zr-C films at higher carbon contents form nanocrystallites of ZrC in an amorphous carbon matrix. The addition of Si induces a complete amorphization of the films above a critical concentration of about 15 at.%. X-ray diffraction and transmission electron microscopy confirm that the amorphous films contain no nanocrystallites and therefore can be described as truly amorphous carbides. The amorphous films are thermally stable but start to crystallize above 500 degrees C. Analysis of the chemical bonding with X-ray photoelectron spectroscopy suggests that the amorphous films exhibit a mixture of different chemical bonds such as Zr-C, Zr-Si and Si-C and that the electrical and mechanical properties are dependent on the distribution of these bonds. For higher carbon contents, strong Si-C bonds are formed in the amorphous Zr-Si-C films making them harder than the corresponding binary Zr-C films.
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| 3. |
- Dahbi, Mohammed, et al.
(författare)
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Combustion synthesis and electrochemical performance of Li2FeSiO4/C cathode material for lithium-ion batteries
- 2012
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 205, s. 456-462
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Tidskriftsartikel (refereegranskat)abstract
- A novel preparation technique was developed for synthesizing Li2FeSiO4/C nanoparticles through combustion of reaction mixtures containing silicon source. Li and Fe sources that operate as oxidizers and sucrose that act as a fuel. A systematic investigation of the synthesis parameters, such as the effect of the fuel content, on purity, morphology and electrochemical properties of the samples was performed. The samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), specific surface area (BET) and electrochemical measurements, respectively. Among the synthesized cathode materials, Li2FeSiO4 obtained with 1.5 mol of sucrose, showed the best electrochemical performance in terms of discharge capacity, cycling stability and rate capability. Discharge capacity of 130 mAh/g at C/20, 88 mAh/g at C/2 and 44 mAh/g at 2C were obtained with no capacity fading after 50 cycles.
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| 4. |
- Kadas, Krisztina, et al.
(författare)
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Structural properties of amorphous metal carbides : Theory and experiment
- 2012
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 60:12, s. 4720-4728
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Tidskriftsartikel (refereegranskat)abstract
- By means of theoretical modeling and experimental synthesis and characterization, we investigate the structural properties of amorphous Zr-Si-C. Two chemical compositions are selected: Zr0.31Si0.29C0.40 and Zr0.60Si0.33C0.07. Amorphous structures are generated in the theoretical part of our work by the stochastic quenching (SQ) method, and detailed comparison is made regarding the structure and density of the experimentally synthesized films. These films are analyzed experimentally using X-ray absorption spectroscopy, transmission electron microscopy and X-ray diffraction. Our results demonstrate a remarkable agreement between theory and experiment concerning bond distances and atomic coordination of this complex amorphous metal carbide. The demonstrated power of the SQ method opens up avenues for theoretical predictions of amorphous materials in general.
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| 5. |
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| 6. |
- Lewin, Erik, et al.
(författare)
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Synthesis, structure and properties of Ni-alloyed TiCx-based thin films
- 2010
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Ingår i: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 0959-9428 .- 1364-5501. ; 20:28, s. 5950-5960
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Tidskriftsartikel (refereegranskat)abstract
- By using non-reactive sputter deposition at low temperatures metastable solid solution phases in the Ti–Ni–C system were synthesized. Produced thin films were either single phase carbides or nanocomposite of nanocrystalline carbide and amorphous C. In the Ni-containing samples a supersaturated solid solution phase (Ti1−xNix)Cy was identified, and was present either as single phase or in a nanocomposite with amorphous C. By modification of the chemical stability of the carbide phase, the addition of Ni was found to strongly promote the formation of amorphous carbon phase in the coatings. Samples have been microstructurally analyzed using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Mechanical properties have been evaluated through nanoindentation and pin-on-disc measurements; electrical properties were determined by measurement of the resistivity and the contact resistance. Alloyed nanocomposite coatings were also found to exhibit enhanced tribological and electrical properties, with a decreased resistivity and friction. This makes these thin films very interesting for application in sliding electrical contacts. The mechanisms responsible for the reductions remain to be determined.
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| 7. |
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| 8. |
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| 9. |
- Urbonaite, Sigita, et al.
(författare)
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Effect of ethanol-assisted electrode fabrication on the performance of silicon anodes
- 2010
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 195:16, s. 5370-5373
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Tidskriftsartikel (refereegranskat)abstract
- The performance of high-silicon-content anodes was tested as a function of silicon particle-size (44 mu m, 1.8 mu m and 70-100 nm), surface pre-treatment and solvent chosen for anode preparation. Two simple procedures, leading to significant improvements in electrode performance are reported. First, pretreatment of nano-Si in ethanol which unexpectedly yields functionalised surfaces improving cycling stability. Second, the use of a 30:70 solution of ethanol and water to dissolve the CMC-binder for the electrode preparation boosts specific battery capacity. Ethanol pre-treatment of nano-Si also resulted in improved adhesion of the electrode to the current collector as well as in de-agglomeration of nano-Si powder. All these treatments improved capacity stability during cycling. Changes in surface chemistry of nano-Si before and after ethanol treatment have been analysed by XPS. A stable capacity of about 1630 mAh g(-1) was obtained after 25 cycles for an electrode containing 80% silicon using ethanol during electrode coating preparation.
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| 10. |
- Urbonaite, Sigita, et al.
(författare)
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Porosity development along the synthesis of carbon from metal carbides
- 2008
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 113:1-3, s. 14-21
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Tidskriftsartikel (refereegranskat)abstract
- Carbide derived carbons (CDCs) are materials containing a wide range of pore size, their properties and applications being a function of the pore structure. For this reason it is important to find the relationship between synthesis parameters, such as initial carbide and temperature, and resulting structure. In this work, CDCs were prepared from VC, TiC, WC, TaC, NbC, HfC and ZrC at different temperatures and they have been characterized by means of gas adsorption. Nitrogen at −196 °C and carbon dioxide at 0 °C adsorptions were used to obtain structural information such as apparent surface area (SBET), micropore volume (Vmicro) and pore size distribution (PSD). These studies show that these parameters vary strongly depending on synthesis temperature (700–1200 °C) and initial carbide. Since the size of micropores is near the range suggested as being ideal for methane (CH4) storage, the high-pressure methane adsorption at 25 °C was performed to check the possible use of CDCs as storage material. The CH4 adsorption capacity of CDCs can compete with other carbons on a gravimetric basis, though the volumetric one is far from desired due to their low packing density.
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| 11. |
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| 12. |
- Urbonaite, Sigita, 1974-
(författare)
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Synthesis and Characterisation of Carbide Derived Carbons
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Carbide derived carbons (CDCs) have been synthesised through chlorination of VC, TiC, WC, TaC, NbC, HfC and ZrC at different temperatures. The aim of the investigation was to systematically study changes of structural and adsorption properties depending on the synthesis conditions. CDCs were characterised using nitrogen and carbon dioxide adsorption, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and electron energy loss spectroscopy. The studies revealed the CDCs structures to range from amorphous to ordered, from microporous to mesoporous. It was found that structural ordering and porosity can be modified by: i) synthesis temperature, ii) precursor, iii) density and volume of precursor, iv) catalysts, v) incorporation of nitrogen in to carbide structure, and CDCs can be tuned up to the demanded quality. They also exhibited a high potential for methane storage.
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| 13. |
- Younesi, Reza, et al.
(författare)
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The Cathode Surface Composition of a Cycled Li–O2 Battery : A Photoelectron Spectroscopy Study
- 2012
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:39, s. 20673-20680
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Tidskriftsartikel (refereegranskat)abstract
- A layer of reaction products, dominantly built up of C and O in the form of ethers and lithium alkyl carbonates, is formed on the surface of the carbon cathode during discharge of a Li–O2 battery in an electrolyte of 1 M LiPF6 in PC. The results are based on a detailed surface analysis combining the use of in house X-ray photoelectron spectroscopy (XPS) and synchrotron based hard X-ray photoelectron spectroscopy (HAXPES). The Li–O2 batteries were investigated at uncycled state (stored), after the first discharge, after the first charge, and at the end of life (discharge state). The results showed little to no Li2O2 and/or Li2O among the discharge products. The surface layers on the cathode were dominantly removed during charging of the battery. At the end of battery life, no complete discharge product layer is formed. The cathodes showed a strong indication of binder decomposition during cycling of the Li–O2 cell. Overall, the results obtained in this investigation show that the whole cathode formulation as well as the electrolyte composition need a completely new approach for the realization of a recyclable Li–O2 battery.
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| 14. |
- Younesi, Reza, et al.
(författare)
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The Effect of Pore Size on the Performance of the Li-O2 Battery
- 2010
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Ingår i: ECS Transactions. - : The Electrochemical Society. - 1938-5862 .- 1938-6737. ; 25:35, s. 121-127
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Tidskriftsartikel (refereegranskat)abstract
- Lithium-airbatteries are complex electrochemical systems. This study deals with thecomposite cathode, where oxygen is reduced and different lithium-oxygen speciesare formed as reaction products. The amount of stored reactionproduct and thus the battery capacity is known to dependon surface area and pore-volume in the cathode. Here therole of pore size is studied for three different carbonsand their corresponding composite cathode films. Gas adsorption studies showthat film-forming Kynar polymer is blocking micropores and mesopores below~300 Å. This influences battery performance of the high surfacearea carbon, containing micropores only, where the capacity is shownto be negligible. The two other carbons, with wider pore-sizedistributions, show a battery capacity in the order of 1300-1500mAh/g carbon. This shows that it is vital to consideralso the pore size in the cathode film for agood battery performance.
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| 15. |
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| 16. |
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| 17. |
- Younesi, S Reza, et al.
(författare)
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Influence of the Cathode Porosity on the Discharge Performance of the Lithium-Oxygen Battery
- 2011
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 196:22, s. 9835-9838
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Tidskriftsartikel (refereegranskat)abstract
- By varying the ratio between the amount of carbon and Kynar binder in the cathode of a lithium-oxygen battery, it could be shown that an increasing amount of binder resulted in a decrease in the discharge capacity, mainly as a result of the decrease in the cathode porosity. It was shown that the Kynar binder blocked the majority of the pores with a width below 300 angstrom as determined by studying the pore volume and pore size distribution by nitrogen adsorption. Three carbonate based electrolytes (PC, PC:DEC (1:1), and EC:DEC (2:1) with 1 M LiPF(6)) were tested with the various cathode film compositions. Generally, the PC:DEC and EC:DEC based electrolytes provided higher capacities than PC. The results indicated that the air electrode composition and its effect on the porosity of the cathode, as well as electrolyte properties, are important when optimizing the discharge capacity.
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| 18. |
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