| 1. |
- Bakhit, Babak, et al.
(författare)
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Improving the high-temperature oxidation resistance of TiB2 thin films by alloying with Al
- 2020
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Ingår i: Acta Materialia. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1359-6454 .- 1873-2453. ; 196, s. 677-689
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Tidskriftsartikel (refereegranskat)abstract
- Refractory transition-metal diborides (TMB2) are candidates for extreme environments due to melting points above 3000 degrees C, excellent hardness, good chemical stability, and thermal and electrical conductivity. However, they typically suffer from rapid high-temperature oxidation. Here, we study the effect of Al addition on the oxidation properties of sputter-deposited TiB2-rich Ti1-xAlxBy thin films and demonstrate that alloying the films with Al significantly increases the oxidation resistance with a slight decrease in hardness. TiB2.4 layers are deposited by dc magnetron sputtering (DCMS) from a TiB2 target, while Ti1-xAlxBy alloy films are grown by hybrid high-power impulse and dc magnetron co-sputtering (Al-HiPIMS/TiB2-DCMS). All as-deposited films exhibit columnar structure. The column boundaries of TiB2.4 are B-rich, while Ti0.68Al0.32B1.35 alloys have Ti-rich columns surrounded by a Ti(1-x)Al(x)By tissue phase which is predominantly Al rich. Air-annealing TiB2.4 at temperatures above 500 degrees C leads to the formation of oxide scales that do not contain B and mostly consist of a rutile-TiO2 (s) phase. The resulting oxidation products are highly porous due to the evaporation of B2O3 (g) phase as well as the coarsening of TiO2 crystallites. This poor oxidation resistance is significantly improved by alloying with Al. While air-annealing at 800 degrees C for 0.5 h results in the formation of an similar to 1900-nm oxide scale on TiB2.4, the thickness of the scale formed on the Ti0.68Al0.32B1.35 alloys is similar to 470 nm. The enhanced oxidation resistance is attributed to the formation of a dense, protective Al-containing oxide scale that considerably decreases the oxygen diffusion rate by suppressing the oxide-crystallites coarsening. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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| 2. |
- Dahlqvist, Martin, et al.
(författare)
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Out-Of-Plane Ordered Laminate Borides and Their 2D Ti-Based Derivative from Chemical Exfoliation
- 2021
-
Ingår i: Advanced Materials. - : Wiley-VCH Verlagsgesellschaft. - 0935-9648 .- 1521-4095. ; 33:38
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Tidskriftsartikel (refereegranskat)abstract
- Exploratory theoretical predictions in uncharted structural and compositional space are integral to materials discoveries. Inspired by M5SiB2 (T2) phases, the finding of a family of laminated quaternary metal borides, M M-4 SiB2, with out-of-plane chemical order is reported here. 11 chemically ordered phases as well as 40 solid solutions, introducing four elements previously not observed in these borides are predicted. The predictions are experimentally verified for Ti4MoSiB2, establishing Ti as part of the T2 boride compositional space. Chemical exfoliation of Ti4MoSiB2 and select removal of Si and MoB2 sub-layers is validated by derivation of a 2D material, TiOxCly, of high yield and in the form of delaminated sheets. These sheets have an experimentally determined direct band gap of approximate to 4.1 eV, and display characteristics suitable for supercapacitor applications. The results take the concept of chemical exfoliation beyond currently available 2D materials, and expands the envelope of 3D and 2D candidates, and their applications.
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| 3. |
- Dorri, Megan, et al.
(författare)
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Synthesis and characterization of CrB 2 thin films grown by DC magnetron sputtering
- 2021
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Ingår i: Scripta Materialia. - : Pergamon-Elsevier Science Ltd. - 1359-6462 .- 1872-8456. ; 200
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Tidskriftsartikel (refereegranskat)abstract
- CrB x thin films with 1.90 < x < 2.08 have been deposited by direct-current magnetron sputtering (DCMS) from a stoichiometric CrB 2 target at 5 and 20 mTorr (0.67 and 2.67 Pa) Ar pressure onto sapphire (0 0 01) substrates. All films, irrespective of deposition conditions, exhibit a (0 0 01) texture. Attesting to the achievement of close-to-stoichiometric composition, epitaxial film growth is observed at 900 ?C, while film growth at 500 ?C yields (0001) fiber texture. Film composition does not depend on substrate temperature but exhibits slightly reduced B content with increasing pressure for samples deposited at 900 ?C. Excess B in the overstoichiometric epitaxial CrB 2.08 films segregates to form B-rich inclusions. Understoichiometry in CrB 1.90 films is accommodated by Cr-rich stacking faults on { 1 1? 00 } prismatic planes. ? 2021 The Author(s). Published by Elsevier Ltd on behalf of Acta Materialia Inc. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ )
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| 4. |
- Halim, Joseph, et al.
(författare)
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Experimental and Theoretical Investigations of Out-of-Plane Ordered Nanolaminate Transition Metal Borides: M4CrSiB2 (M = Mo, W, Nb)
- 2023
-
Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 62:14, s. 5341-5347
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Tidskriftsartikel (refereegranskat)abstract
- We report the synthesis of three out-of-plane chemically ordered quaternary transition metal borides (o-MAB phases) of the chemical formula M4CrSiB2 (M = Mo, W, Nb). The addition of these phases to the recently discovered o-MAB phase Ti4MoSiB2 shows that this is indeed a new family of chemically ordered atomic laminates. Furthermore, our results expand the attainable chemistry of the traditional M5SiB2 MAB phases to also include Cr. The crystal structure and chemical ordering of the produced materials were investigated using high-resolution scanning transmission electron microscopy and X-ray diffraction by applying Rietveld refinement. Additionally, calculations based on density functional theory were performed to investigate the Cr preference for occupying the minority 4c Wyckoff site, thereby inducing chemical order.
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| 5. |
- Halim, Joseph, 1985-, et al.
(författare)
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Synthesis of Two-Dimensional Nb1.33C (MXene) with Randomly Distributed Vacancies by Etching of the Quaternary Solid Solution (Nb2/3Sc1/3)2AlC MAX Phase
- 2018
-
Ingår i: ACS Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; 1:6, s. 2455-2460
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Tidskriftsartikel (refereegranskat)abstract
- Introducing point defects in two-dimensional (2D) materials can alter or enhance their properties. Here, we demonstrate how etching a laminated (Nb2/3Sc1/3)2AlC MAX phase (solid solution) of both the Sc and Al atoms results in a 2D Nb1.33C material (MXene) with a large number of vacancies and vacancy clusters. This method is applicable to any quaternary, or higher, MAX phase, wherein one of the transition metals is more reactive than the other and could be of vital importance in applications such as catalysis and energy storage. We also report, for the first time, on the existence of solid solution (Nb2/3Sc1/3)3AlC2 and (Nb2/3Sc1/3)4AlC3 phases.
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| 6. |
- Hellgren, Niklas, et al.
(författare)
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High-power impulse magnetron sputter deposition of TiBx thin films : Effects of pressure and growth temperature
- 2019
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Ingår i: Vacuum. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0042-207X .- 1879-2715. ; 169
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Tidskriftsartikel (refereegranskat)abstract
- Titanium boride, TiBx thin films are grown in pure Ar discharges by high-power impulse magnetron sputtering (HiPIMS) from a compound TiB2 target Film compositions are determined by time-of-flight elastic recoil detection analysis and Rutherford backscattering spectrometry as a function of deposition temperature (T-s = 25-900 degrees C) and Ar pressure (p(Ar) = 0.67-2.67 Pa, 5-20 mTorr). For reference, films are also grown by direct current magnetron sputtering (dcMS) under similar conditions. The HiPIMS waveform, average target power P-T, and resulting film compositions are strongly dependent not only on P-Ar, but also on T-s. At high pressures the effect of varying T-s on P-T is minimal, while at lower P-Ar the effect of T-s is more pronounced, due to substrate-temperature-induced gas rarefaction. Films grown by HiPIMS at 0.67 Pa are understoichiometric, with B/Ti = 1.4-1.5, while at 2.67 Pa, B/Ti decreases from 2.4 to 1.4 as T-s increases from 25 to 900 degrees C. dcMS-deposited films are overstoichiometric (B/Ti similar or equal to 3) when grown at low pressures, and near-stoichiometric (B/Ti similar or equal to r 1.9-2.2) for higher P-Ar. All experimental results are explained by differences in the ionization potentials of sputtered Ti and B atoms, together with P-Ar- and T-s-dependent gas-phase scattering.
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| 7. |
- Meshkian, Rahele, et al.
(författare)
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Theoretical Analysis, Synthesis, and Characterization of 2D W1.33C (MXene) with Ordered Vacancies
- 2019
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Ingår i: ACS APPLIED NANO MATERIALS. - : AMER CHEMICAL SOC. - 2574-0970. ; 2:10, s. 6209-6219
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Tidskriftsartikel (refereegranskat)abstract
- Synthesis of delaminated 2D W1.33C (MXene) has been performed by selectively etching Al as well as Sc/Y from the recently discovered nanolaminated i-MAX phases (W2/3Sc1/3)(2)AlC and (W2/3Y1/3)(2)AlC. Both quaternary phases produce MXenes with similar flake morphology and with a skeletal structure due to formation of ordered vacancies. The measured O, OH, and F terminations, however, differ in amount as well as in relative ratios, depending on parent material, evident from X-ray photoelectron spectroscopy. These findings are correlated to theoretical simulations based on first-principles, investigating the W1.33C, and the effect of termination configurations on structure, formation energy, stability, and electronic structure. The theoretical results indicate a favored F-rich surface composition, though with a system going from insulating/semiconducting to metallic for different termination configurations, suggesting a high tuning potential of these materials. Additionally, free-standing W1.33C films of 2-4 mu m thickness and with up to 10 wt % polymer (PEDOT:PSS) were tested as electrodes in supercapacitors, showing capacitances up to 600 F cm(-3) in 1 M H2SO4 and high capacitance retention for at least 10000 cycles at 10 A g(-1). This is highly promising results compared to other W-based materials to date.
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| 8. |
- Meshkian, Rahele, et al.
(författare)
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W-Based Atomic Laminates and Their 2D Derivative W1.33C MXene with Vacancy Ordering
- 2018
-
Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 30:21
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Tidskriftsartikel (refereegranskat)abstract
- Structural design on the atomic level can provide novel chemistries of hybrid MAX phases and their MXenes. Herein, density functional theory is used to predict phase stability of quaternary i-MAX phases with in-plane chemical order and a general chemistry (W 2/3 M 2 1/3 ) 2 AC, where M 2 = Sc, Y (W), and A = Al, Si, Ga, Ge, In, and Sn. Of over 18 compositions probed, only two—with a monoclinic C2/c structure—are predicted to be stable: (W 2/3 Sc 1/3 ) 2 AlC and (W 2/3 Y 1/3 ) 2 AlC and indeed found to exist. Selectively etching the Al and Sc/Y atoms from these 3D laminates results in W 1.33 C-based MXene sheets with ordered metal divacancies. Using electrochemical experiments, this MXene is shown to be a new, promising catalyst for the hydrogen evolution reaction. The addition of yet one more element, W, to the stable of M elements known to form MAX phases, and the synthesis of a pure W-based MXene establishes that the etching of i-MAX phases is a fruitful path for creating new MXene chemistries that has hitherto been not possible, a fact that perforce increases the potential of tuning MXene properties for myriad applications.
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| 9. |
- Nygård, K., et al.
(författare)
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ForMAX – a beamline for multiscale and multimodal structural characterization of hierarchical materials
- 2024
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Ingår i: Journal of Synchrotron Radiation. - : International Union of Crystallography (IUCr). - 0909-0495 .- 1600-5775. ; 31:Pt 2, s. 363-377
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Tidskriftsartikel (refereegranskat)abstract
- The ForMAX beamline at the MAX IV Laboratory provides multiscale and multimodal structural characterization of hierarchical materials in the nanometre to millimetre range by combining small- and wide-angle X-ray scattering with full-field microtomography. The modular design of the beamline is optimized for easy switching between different experimental modalities. The beamline has a special focus on the development of novel fibrous materials from forest resources, but it is also well suited for studies within, for example, food science and biomedical research.
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| 10. |
- Nyholm, Per-Georg, 1958, et al.
(författare)
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The use of a genetic algorithm search for molecular mechanics (MM3)-based conformational analysis of oligosaccharides.
- 2005
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Ingår i: Carbohydrate Research. - : Elsevier BV. - 0008-6215 .- 1873-426X. ; 340:5, s. 1059-1064
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Tidskriftsartikel (refereegranskat)abstract
- We have implemented a system called glygal that can perform conformational searches on oligosaccharides using several different genetic algorithm (GA) search methods. The searches are performed in the torsion angle conformational space, considering both the primary glycosidic linkages as well as the pendant groups (C-5–C-6 and hydroxyl groups) where energy calculations are performed using the MM3(96) force field. The system includes a graphical user interface for setting calculation parameters and incorporates a 3D molecular viewer. The system was tested using dozens of structures and we present two case studies for two previously investigated O-specific oligosaccharides of the Shigella dysenteriae type 2 and 4. The results obtained using glygal show a significant reduction in the number of structures that need to be sampled in order to find the best conformation, as compared to filtered systematic search.
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| 11. |
- Palisaitis, Justinas, et al.
(författare)
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Where is the unpaired transition metal in substoichiometric diboride line compounds?
- 2021
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Ingår i: Acta Materialia. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1359-6454 .- 1873-2453. ; 204
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Tidskriftsartikel (refereegranskat)abstract
- The atomic structure and local composition of high quality epitaxial substoichiometric titanium diboride (TiB1.9) thin film, deposited by unbalanced magnetron sputtering, were studied using analytical high-resolution scanning transmission electron microscopy, density functional theory, and image simulations. The unpaired Ti is pinpointed to inclusion of Ti-based stacking faults within a few atomic layers, which terminates the {1 (1) over bar 00} prismatic planes of the crystal structure and attributed to the absence of B between Ti planes that locally relaxes the structure. This mechanism allows the line compound to accommodate off-stoichiometry and remain a line compound between defects. The planar defects are embedded in otherwise stoichiometric TiB2 and are delineated by insertion of dislocations. An accompanied decrease in Ti-Ti bond lengths along and across the faults is observed. (c) 2020ActaMaterialiaInc. PublishedbyElsevierLtd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)
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| 12. |
- Rosen, Jimmy
(författare)
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Prediction of 3D structures of oligosaccharides. Methodological development and studies on saccharide antigens of interest for vaccine design
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents 3D structure predictions of five immunologically active surfacepolysaccharides of pathogens, which are of interest as targets for development of glycoconjugatevaccines. Furthermore it describes two methods which have been used for theconformational predictionsThe Shigella dysenteriae type 2 Oantigenwas predicted to form a compact helicalstructure with three repeating pentasaccharide units per turn. Favoured conformations werealso predicted for the Shigella dysenteriae type 4 and Escherichia coli O159 Oantigens,which have been reported to be crossreactivewith antibodies. We propose a commonepitope at the branch region of the repeating units. The conformation of the Burkholderiacepacia exopolysaccharidewas also predicted and was shown to form an extended fibre,with the three branches of the repeating unit packing tightly against the main chain.Furthermore, the 3D structure of a Schistosoma mansoni cercarial surface polysaccharidethat has been reported to be immunologically reactive, was predicted. The fucosyl brancheswrap tightly around the main chain, reducing the molecule's flexibility.The polysaccharides studied are of interest for development of glycoconjugatevaccines,and the results suggest that oligosaccharide 3D structure prediction can be an importanttool for rational vaccine design. These rapid predictions provide detailed information aboutpotential epitopes and the basis of immunological crossreactivityas well as conformationsof the polymer.Methods used for the conformation predictions were filtered systematic search and geneticalgorithm search. The filtered systematic search method thoroughly explores theconformational space below a set filter cutoffenergy. It can be used for structures up totetrasaccharide size with reasonable computational requirements. It is guaranteed to findthe global minimum energy conformation and the results can be used to generate adiabaticenergy maps, clearly describing the conformational restrictions and flexibility of theoligosaccharide. The genetic algorithm search is a very fast conformational search method.It scales well and is suitable for large oligosaccharides approximately up to the size ofdecasaccharides. It finds most local energy minima in the conformational space quickly, butis not guaranteed to find the global minimum conformation.
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| 13. |
- Rosen, Jimmy, et al.
(författare)
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The conformations of the O-specific polysaccharides of Shigella dysenteriae type 4 and Escherichia coli O159 studied with molecular mechanics (MM3) filtered systematic search.
- 2004
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Ingår i: Carbohydrate Research. - : Elsevier BV. - 0008-6215. ; 339:5, s. 961-966
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Tidskriftsartikel (refereegranskat)abstract
- The branched O-antigens of Escherichia coli O159 and Shigella dysenteriae type 4 are structurally related and are known to show cross-reactivity with antibodies. In the present study, conformational analyses were performed on these two O-antigens using molecular mechanics MM3(96) with filtered systematic search. The results show very strong steric restrictions for the trisaccharide at the branch point of the E. coli O159 antigen, especially for the β-d-GlcNAc-(1 → 3)-β-d-GlcNAc linkage of the main chain. For the type 4 O-antigen the calculations show essentially a single conformation with respect to the α-d-GlcNAc-(1 → 3)-α-d-GlcNAc linkage of the main chain and three different favoured conformations for the fucose branch. Consecutive repeating units of the S. dysenteriae type 4 and E. coli O159 O-antigens form linear extended chains with significant flexibility between the branches. Comparative calculations carried out with the SWEET server indicate that our method of filtered systematic search is a superior method in the case of branched, constrained oligosaccharides. Based on the results of the MM3 calculations, we propose that the common epitope explaining the cross-reactivity comprises the fucose branch, the downstream GlcNAc and part of the uronic acid.
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| 14. |
- Siebert, Hans-Christian, et al.
(författare)
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alpha 2,3/alpha 2,6-sialylation of N-glycans: non-synonymous signals with marked developmental regulation in bovine reproductive tracts
- 2006
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Ingår i: Biochimie. - : Elsevier BV. - 0300-9084. ; 88:5, s. 399-410
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Tidskriftsartikel (refereegranskat)abstract
- The glycan part endows cellular glycoconjugates with significant potential for biological recognition. N-Glycan branches often end with α2,3/α2,6-sialylation, posing the question whether and how placement of the sialic acid at 3´- or 6´-acceptor positions of galactose has cell biological relevance. As attractive model to study developmental regulation we monitored the expression of α2,3/α2,6-sialylated determinants in fetal and adult bovine testes and ovaries by lectin histochemistry. Distinct expression patterns were detected in both organ types. Oocyte staining, as a prominent example, was restricted to the presence of α2,6-sialylated glycans. Treatment with sialidase abolished binding and thus excluded sulfate esters as lectin targets. We added computer simulations to rationalize the observed evidence for non-random expression of the two closely related sialylgalactose isomers. Extensive molecular mechanics and molecular dynamics calculations reveal that the seemingly minor shift of the glycosidic bond from the α2,3 position to the α2,6 configuration causes significant shape and flexibility changes. They give each disaccharide its own characteristic meaning as signal in the sugar code.
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| 15. |
- Strino, Francesco, 1980, et al.
(författare)
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Conformation of the exopolysaccharide of Burkholderia cepacia predicted with molecular mechanics (MM3) using genetic algorithm search.
- 2005
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Ingår i: Carbohydrate Research. - : Elsevier BV. - 0008-6215 .- 1873-426X. ; 340:5, s. 1019-1024
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Tidskriftsartikel (refereegranskat)abstract
- We present a computational conformational analysis of the exopolysaccharide of Burkholderia cepacia, which is believed to play a role in colonization and persistence of B. cepacia in the lungs of cystic fibrosis patients. The repeating unit of the exopolysaccharide is a heptasaccharide with three branches, which cause significant steric restraints. Conformational searches using glygal, an in-house developed software using genetic algorithm search methods, were performed on fragments as well as on the complete repeating unit with wrap-over residues. The force field used for the calculations was MM3(96). The search showed four favored conformations for an isolated repeating unit. However, for a sequence of several repeating units, the calculations indicate a single, well-defined linear conformation.
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| 16. |
- Thörnberg, Jimmy, et al.
(författare)
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Improved oxidation properties from a reduced B content in sputter-deposited TiBx thin films
- 2021
-
Ingår i: Surface & Coatings Technology. - : Elsevier Science SA. - 0257-8972 .- 1879-3347. ; 420
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Tidskriftsartikel (refereegranskat)abstract
- Transition-metal diboride thin films, which have high melting points, excellent hardness, and good chemical and thermal conductivity, severely suffer from rapid oxidation in air. Here, we explore the influence of varying B content and resulting nanostructure change on the oxidation properties of TiBx thin films, with x = 1.43, 2.20, and 2.70. Results show that all as-deposited layers have columnar structure. The column boundaries of asdeposited TiB2.20 and TiB2.20 films grown by direct current magnetron sputtering (DCMS) are B-rich, while the as-deposited TiB1.43 films grown by high-power impulse magnetron sputtering (HiPIMS) show no apparent grain boundary phases and contain Ti-rich planar defects. The oxidation rate of TiBL43 air-annealed at 400 degrees C up to 48 h is significantly lower than that of TiB2.20 and TiB2.20 films. The oxidation rate of TiB1.43, TiB2.20, and TiB2.20 films was measured at 2.9 +/- 1.5, 7.1 +/- 1.0, and 20.0 +/- 5.0 nm/h, respectively, with no spallation of even as thick oxide scales as 0.5 mu m in any of the films. The improved oxidation resistance can be explained by the absence of B-rich tissue phase at the column boundaries of understoichiometric TiBx films, a phase that interlaces the nanocolumnar TiB2 structures in the corresponding overstoichiometric films. An easy oxidation pathway is thus eliminated.
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| 17. |
- Thörnberg, Jimmy, et al.
(författare)
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Microstructure and materials properties of understoichiometric TiBx thin films grown by HiPIMS
- 2020
-
Ingår i: Surface & Coatings Technology. - : ELSEVIER SCIENCE SA. - 0257-8972 .- 1879-3347. ; 404
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Tidskriftsartikel (refereegranskat)abstract
- TiBx thin films with a B content of 1.43 <= x <= 2.70 were synthesized using high-power impulse magnetron sputtering (HiPIMS) and direct-current magnetron sputtering (DCMS). HiPIMS allows compositions ranging from understoichiometric to overstoichiometric dense TiBx thin films with a B/Ti ratio between 1.43 and 2.06, while DCMS yields overstoichiometric TiBx films with a B/Ti ratio ranging from 2.20 to 2.70. Excess B in overstoichiometric TiBx thin films from DCMS results in a hardness up to 37.7 +/- 0.8 GPa, attributed to the formation of an amorphous B-rich tissue phase interlacing stoichiometric TiB2 columnar structures. We furthermore show that understoichiometric TiB1.43 thin films synthesized by HiPIMS, where the deficiency of B is found to be accommodated by Ti-rich planar defects, exhibit a superior hardness of 43.9 +/- 0.9 GPa. The apparent fracture toughness and thermal conductivity of understoichiometric TiB1.43 HiPIMS films are 4.2 +/- 0.1 MPa root m and 2.46 +/- 0.22 W/(m.K), respectively, as compared to corresponding values for overstoichiometric TiB2.70 DCMS film samples of 3.1 +/- 0.1 MPa root m and 4.52 +/- 0.45 W/(mK). This work increases the fundamental understanding of understoichiometric TiBx thin films and their materials properties, and shows that understoichiometric films have properties matching or going beyond those with excess B.
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| 18. |
- Thörnberg, Jimmy, et al.
(författare)
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Oxidation resistance and mechanical properties of sputter-deposited Ti0.9Al0.1B2-y thin films
- 2022
-
Ingår i: Surface & Coatings Technology. - : Elsevier Science SA. - 0257-8972 .- 1879-3347. ; 442
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Tidskriftsartikel (refereegranskat)abstract
- Direct-current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering (HiPIMS) were used to deposit understoichiometric Ti(1-x)Al(x)B(2-y )diboride coatings by sputtering from a segmented TiB2-AlB2 target using Ar and Kr as sputtering gas. For films with a fixed Al/(Ti + Al) ratio of x = 0.1 (Ti0.9Al0.1B2-y), the B content was varied with y & ISIN; (0.1, 0.6 and 0.7). For films with a fixed y = 0.7 (Ti1-xAlxB1.3), the Al content was varied with x & ISIN; (0.1, 0.4 and 0.7). Evaluation of the mechanical properties of the Ti1-xAlxB1.3 samples showed a reduction in both hardness and elastic modulus with increasing Al concentration, while the Ti0.9Al0.1B2-y samples showed a hardness increase with decreasing B content. Thus, Ti0.9Al0.1B1.3 films exhibited a superior hardness of 46.2 +/- 1.1 GPa and an elastic modulus of 523 & PLUSMN; 7 GPa, compared to the values for Ti0.9Al0.1B1.4 and Ti0.9Al0.1B1.9, showing a hardness of 44 +/- 1 GPa and 36 +/- 1 GPa, and an elastic modulus of 569 +/- 7 GPa and 493 +/- 6 GPa, respectively. The oxidation behavior of the mechanically most promising Ti0.9Al0.1B2-y sample series was investigated through air-annealing at 600 C for durations from 1 h to 10 h. All films formed a mixed non-conformal Al2O3-TiO2 oxide scale which acts as an inward and outward diffusion barrier, significantly reducing the oxidation rate compared to TiBz films, which form an oxide scale consisting of porous TiO2. The thinnest oxide scale after 10 h was found in the B-deficient samples, Ti0.9Al0.1B1.3 and Ti0.9Al0.1B1.4, at ~200 nm, which is significantly below that for Ti0.9Al0.1B1.9 at 320 nm. The enhanced oxidation resistance of highly understoichiometric films is due to the elimination of the B-rich tissue phase that is present at the grain boundaries for higher B content, where the latter has been shown to enhance the rate of oxidation in borides.
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| 19. |
- Thörnberg, Jimmy, 1987-
(författare)
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Synthesis and Characterization of Transition Metal Diborides
- 2021
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is devoted towards physical vapor deposition (PVD) of thin films of transition-metal (TM) diborides, focused on the material system TiBx, Ti1-xAlxB2-y and CrBx. The metal diborides are a large family of compounds with both metallic and ceramic properties, due to its bonding nature being a mix of covalent and ionic bonds. Their characteristics include, e.g., good mechanical, electrical and thermal properties, while an improved oxidation and corrosion resistance are currently sought after. Furthermore, while the ideal composition of these diborides is TMB2, i.e. with a B to metal ratio of 2, the stoichiometry in the PVD deposited films typically diverges from this ratio. TiBx is often reported to be overstoichiometric, with x well above 2. One of the most known and commonly used member of the TM diboride family is TiBx, primarily used in hard-coating applications such as tools for machining Al. However, the material displays a fracture toughness and oxidation resistance that ideally needs to be improved.The films presented in this thesis were deposited by high power impulse magnetron sputtering (HiPIMS) and direct current magnetron sputtering (DCMS). Using both methods facilitates an improved control of both microstructure and composition, and hence the materials properties. With HiPIMS, understoichiometric TiBx films were grown and it was shown that these films can match and even exceed the overstoichiometric counterpart, deposited with DCMS, in terms of mechanical properties. The hardness and fracture toughness for TiB1.43 films were measured at 43.9±0.9 GPa and 4.2±0.1 MPa√m, compared to TiB2.70 films at 37.7±0.8 GPa and 3.1±0.1 MPa√m. Furthermore, the understoichiometric films significantly improve the oxidation resistance. Air annealing of TiB1.43, TiB2.20, and TiB2.70 films at 400 °C showed an average oxidation rate of 2.9±1.5, 7.1±1.0, and 20.0±5.0 nm/h, respectively, explained by the microstructural difference between over- and understoichiometric material. In TiBx films where x > 2, there is a B-rich tissue phase in the grain boundaries which is suggested to enhance oxidation. The hydroscopic nature of B2O3 causes more rapid oxidation and evaporation thus providing an easy oxidation pathway in B-rich regions. However, understoichiometric films where x < 2 do not show any significant boundary phases. Instead, the B deficiency is presented as planar defects with Ti-rich stacking faults. Hence the absence of the B-rich tissue phase has strongly contributed to increasing the oxidation resistance.Oxidation resistance and mechanical properties were also investigated for understoichiometric Ti1-xAlxB2-y coatings with varying Ti:Al and B:M ratios, obtained from both HiPIMS and DCMS depositions. Al alloying of the TM diboride TiBx significantly enhances the oxidation resistance. However, incorporating too much Al is at the expense of the excellent hardness seen in the pure TiBx, going from 46.2±1.1 GPa to 22.6±1.1 GPa for Ti0.9Al0.1B1.3 and Ti0.3Al0.7B1.3, respectively. Hence, a reduction in the Al content is needed to retain the mechanical properties. The boundary phase in this material consists of a Ti1-xAlxB2-y tissue phase, rich in either Al or B depending on the x and y values. An improved oxidation resistance in Ti1-xAlxB2-y was seen with reduced Al and B content, proposed to be due to absence of tissue phase in the grain boundaries, in line with the observations for TiBx. The oxide scale thickness of Ti0.9Al0.1B1.3 and Ti0.9Al0.1B1.9 after air annealing at 600 °C for 10 h was measured to be 205 nm and 320 nm, respectively. Moreover, the trends indicate a reduced oxidation rate as the oxide scale grows thicker.A systematical study of DCMS deposited CrBx coatings, 1.90 ≤ x 2.08, was also performed, motivated by CrBx being a material of interest for providing potential corrosion resistance. All films, irrespectable of the deposition conditions, exhibited (001) texture, with epitaxial growth observed when increasing temperature from 500 °C to 900 °C. Higher density (5.2 g/cm3) and smoother surfaces was seen in films grown at lower pressure, 5 mTorr (0.67 Pa), compared to higher pressure, 20 mTorr (2.67 Pa), and was explained by less gas scattering leading to more energetic particles impinging on the surface. CrBx film composition show no apparent dependence on substrate temperature, and has a slight dependence on deposition pressure for the samples deposited at 900 °C, with reduced B content for increasing pressure. Overstoichiometric CrB2.08 films showed the presence of large B-rich inclusions, and B deficiency in CrB1.90 films presented as planar defects with Cr-rich stacking faults, similar to understoichiometric TiBx.The thorough investigations of all the systems in this thesis are aimed towards improving the understanding of the correlation between the thin film synthesis process and the resulting composition and microstructure, which in turn dictates the properties of thin films. A particular emphasis is put on control of composition.
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| 20. |
- Thörnberg, Jimmy, et al.
(författare)
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Synthesis of (V2/3Sc1/3)(2)AlC i-MAX phase and V2-xC MXene scrolls
- 2019
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Ingår i: Nanoscale. - : ROYAL SOC CHEMISTRY. - 2040-3364 .- 2040-3372. ; 11:31, s. 14720-14726
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Tidskriftsartikel (refereegranskat)abstract
- We report the synthesis and characterization of a new laminated i-MAX phase, (V2/3Sc1/3)(2)AlC, with in-plane chemical ordering between the M-elements. We also present evidence for the solid solution (V2-xScx)(2)AlC, where x amp;lt;= 0.05. Chemical etching of the Al and Sc results in a two-dimensional (2D) MXene counterpart: V2-xC from the latter phase. Furthermore, etching with HF yields single-sheet MXene of flat morphology, while LiF + HCl gives MXene scrolls. We also show a 4x reduction in etching time for (V2-xScx)(2)AlC compared to V2AlC, suggesting that traces of Sc changes the phase stability, and make the material more susceptible to etching. The results show a path for improved control of MXene synthesis and morphology, which may be applicable also for other MAX/MXene systems.
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| 21. |
- von der Lieth, Claus-Wilhelm, et al.
(författare)
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EUROCarbDB : an open-access platform for glycoinformatics
- 2011
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Ingår i: Glycobiology. - : Oxford University Press (OUP). - 0959-6658 .- 1460-2423. ; 21:4, s. 493-502
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Tidskriftsartikel (refereegranskat)abstract
- The EUROCarbDB project is a design study for a technical framework, which provides sophisticated, freely accessible, open-source informatics tools and databases to support glycobiology and glycomic research. EUROCarbDB is a relational database containing glycan structures, their biological context and, when available, primary and interpreted analytical data from high-performance liquid chromatography, mass spectrometry and nuclear magnetic resonance experiments. Database content can be accessed via a web-based user interface. The database is complemented by a suite of glycoinformatics tools, specifically designed to assist the elucidation and submission of glycan structure and experimental data when used in conjunction with contemporary carbohydrate research workflows. All software tools and source code are licensed under the terms of the Lesser General Public License, and publicly contributed structures and data are freely accessible. The public test version of the web interface to the EUROCarbDB can be found at http://www.ebi.ac.uk/eurocarb.
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