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- Alling, Björn, 1980-, et al.
(författare)
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Comparison of thermodynamic properties of cubic Cr 1-x Al x N and Ti 1-x Al x N from first-principles calculations
- 2007
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 102:044314
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Tidskriftsartikel (refereegranskat)abstract
- In order to investigate the stability of the cubic phase of Cr1−xAlxN at high AlN content, first principles calculations of magnetic properties, lattice parameters, electronic structure, and mixing enthalpies of the system were performed. The mixing enthalpy was calculated on a fine concentration mesh to make possible the accurate determination of its second concentration derivative. The results are compared to calculations performed for the related compound Ti1−xAlxN and with experiments. The mixing enthalpy is discussed in the context of isostructural spinodal decomposition. It is shown that the magnetism is the key to understand the difference between the Cr- and Ti-containing systems. Cr1−xAlxN turns out to be more stable against spinodal decomposition than Ti1−xAlxN, especially for AlN-rich samples which are of interest in cutting tools applications.
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- Alling, Björn, et al.
(författare)
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Electronic origin of the isostructural decomposition in cubic M1-xAlxN (M=Ti, Cr, Sc, Hf) : A first-principles study
- 2008
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Ingår i: Surface and Coatings Technology. - : Elsevier BV. - 0257-8972. ; 203:5-7, s. 883-886
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Tidskriftsartikel (refereegranskat)abstract
- We have used first-principles calculations to investigate the mixing enthalpies, lattice parameters and electronic density of states of the ternary nitride systems Ti1-xAlxN, Cr1-xAlxN, Sc1-xAlxN and Hf1-xAlxN in the cubic B1 structure where the transition metals and aluminium form a solid solution on the metal sublattice. We discuss the electronic origins of the possible isostructural decomposition in these materials relevant for hard coatings applications. We find that in the systems Ti1-xAlxN and Hf1-xAlxN the electronic structure effects strongly influences the phase stability as d-states are localised at the Fermi level in AlN-rich samples. This leads to a strongly asymmetric contribution to the mixing enthalpy, an effect not present in Cr1-xAlxN and Sc1-xAlxN. The lattice mismatch is large in Sc1-xAlxN and Hf1-xAlxN, giving a symmetric contribution to the mixing enthalpies in those systems.
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- Alling, Björn, 1980-, et al.
(författare)
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First-principles study of the effect of nitrogen vacancies on the decomposition pattern in cubic Ti1-xAlxN1-y
- 2008
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 92, s. 071903-1-071903-3
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Tidskriftsartikel (refereegranskat)abstract
- The effect of nitrogen substoichiometry on the isostructural phase stabilities of the cubic Ti1−xAlxN1−y system has been investigated using first-principles calculations. The preferred isostructural decomposition pattern in these metastable solid solutions was predicted from the total energy calculations on a dense concentration grid. Close to the stoichiometric Ti1−xAlxN1 limit, N vacancies increase the tendency for phase separation as N sticks to Al while the vacancies prefers Ti neighbors. For nitrogen depleated conditions, N sticks to Ti forming TiN (0<<1) while Al tends to form nitrogen-free fcc-Al or Al–Ti alloys.
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- Alling, Björn, 1980-, et al.
(författare)
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Mixing and decomposition thermodynamics of c-Ti1-xAlxN from first-principles calculations
- 2007
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:045123
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Tidskriftsartikel (refereegranskat)abstract
- Wedescribe an efficient first-principles method that can be used tocalculate mixing enthalpies of transition metal nitrides with B1 structureand substitutional disorder at the metal sublattice. The technique isbased on the density functional theory. The independent sublattice modelis suggested for the treatment of disorder-induced local lattice relaxationeffects. It supplements the description of the substitutional disorder withinthe coherent potential approximation. We demonstrate the excellent accuracy ofthe method by comparison with calculations performed by means ofthe projector augumented wave method on supercells constructed as specialquasirandom structures. At the same time, the efficiency of thetechnique allows for total energy calculations on a very finemesh of concentrations which enables a reliable calculation of thesecond concentration derivative of the alloy total energy. This isa first step towards first-principles predictions of concentrations and temperatureintervals where the alloy decomposition proceeds via the spinodal mechanism.We thus calculate electronic structure, lattice parameter, and mixing enthalpiesof the quasibinary alloy c-Ti1−xAlxN. The lattice parameter follows Vegard'slaw at low fractions of AlN but deviates increasingly withincreasing Al content. We show that the asymmetry of themixing enthalpy and its second concentration derivative is associated withsubstantial variations of the electronic structure with alloy composition. Thephase diagram is constructed within the mean-field approximation.
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- Jeihanipour, A., et al.
(författare)
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Antimicrobial properties of fungal chitosan
- 2007
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Ingår i: Research Journal of Biological Sciences. - : Medwell Journals. - 1815-8846 .- 1993-6087. ; 2:3, s. 239-
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Tidskriftsartikel (refereegranskat)abstract
- Cell wall of zygomycetes fungus is an alternative source for chitosan production. In this study chitosan was extracted from cell wall of filamentous fungus Rhizopus oryzae and its antimicrobial properties was studied against three typical human pathogenic microorganisms, Escherichia coli, Klebsiella pneumoniae and Staphylococcus aureus. The viability of these bacteria reduced by more than 60%, when 200 ppm of the fungal chitosan was present in the solution. However, the Minimum Bactericidal Concentration (MBC) of the fungal chitosan was 300, 500 and 700 ppm for S. aureus, E. coli and K. pneumoniae, respectively. The antimicrobial activity of fungal chitosan was lower than that of crustacean shells chitosan, which had MBC of less than 100 ppm for the above mentioned bacteria. Furthermore, fungal chitosan similar to crustacean shells chitosan exhibited better inhibitory effects against gram-positive compared to gram-negative bacteria. The possible mechanism for antimicrobial activity of fungal chitosan could be the disruption of the outer membrane of cells but not preventing the nutrients from entering into the cell.
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