| 1. |
- Cordoba Gallego, Jose Manuel, et al.
(författare)
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New production of TiCxN1−x-based cermets by one step mechanically induced self-sustaining reaction : Powder synthesis and pressureless sintering
- 2008
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Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 28:10, s. 2085-2098
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Tidskriftsartikel (refereegranskat)abstract
- TiCxN1−x-based powdered cermets were synthesized by a one step mechanically induced self-sustaining reaction (MSR) process from mixtures of elemental powders, and subsequently sintered by a pressureless method. The composition and microstructure of the ceramic and binder phases before and after the sintering process were studied by X-ray diffraction, scanning and transmission electron microscopy, and electron diffraction. The powdered cermets showed excellent binder dispersion and a nanometer character for the ceramic and binder particles. The TiCxN1−x stoichiometry was consistently richer in carbon than expected from the raw powder composition. An important amount of titanium was present in the binder after MSR synthesis, and intermetallic Ti-Ni or Ti-Co phases were obtained in some cases. After sintering, the binder phase was always constituted by intermetallic compounds. The morphology of the ceramic phase in the final bodies was dependent on the C/N ratio of TiCxN1−x and its growth primarily occurred through a coalescence process. The presence of titanium in the binder reduced hard particle solubility in the melted binder and its grain growth.
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| 2. |
- Cordoba Gallego, Jose Manuel, 2000-, et al.
(författare)
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Nitriding study of titanium silicide intermetallics obtained by mechanical alloying
- 2008
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Ingår i: Intermetallics (Barking). - : Elsevier BV. - 0966-9795 .- 1879-0216. ; 16:8, s. 948-954
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Tidskriftsartikel (refereegranskat)abstract
- Titanium and silicon powder blends were ball-milled under an inert atmosphere and subsequently annealed in a nitrogen atmosphere. Ti62.5Si37.5, Ti55.6Si44.4, and Ti50Si50 mixtures suffered a mechanically induced self-propagating reaction during milling. The products of the combustion were Ti5Si3 for the Ti62.5Si37.5 mixture and a combination of intermetallic phases for the Ti55.6Si44.4 and Ti50Si50 mixtures. The Ti33.3Si66.7 blend did not show an MSR process, but prolonged milling allowed the formation of a mixture of stable C54-TiSi2 and metastable C49-TiSi2 by a diffusion reaction. The nitriding study showed a different behaviour for C54-TiSi2 and Ti5Si3. C54-TiSi2 nitriding took place in a two-step process: the first corresponded to the formation of TiN and Si and the second to the silicon nitriding leading to the formation of a- and b-Si3N4. However, silicon and titanium nitriding primarily occurred simultaneously during the annealing of Ti5Si3, and the final product was a mixture of TiN and a-Si3N4.
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| 3. |
- Cordoba Gallego, Jose Manuel, et al.
(författare)
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Morphology influence of the oxidation kinetics of carbon nanofibers
- 2009
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Ingår i: CORROSION SCIENCE. - : Elsevier BV. - 0010-938X. ; 51:4, s. 926-930
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports the stability and oxidation rate of five types of carbon nanofiber (CNF) with distinctly different orientation of their graphite sheets based on conversion to CO2 when heated in the presence of oxygen. A non-isothermal technique was used to determine the oxidation kinetic parameters including the activation energy (E-a) Graphite shows a similar activation energy (E-a = 158 kJ/mol(-1)) to CNF with longitudinal alignment (E-a = 156kJ/mol(-1)). CNF type herringbone (E-a = 126kJ/mol(-1)) and platelet (E-a = 145 kJ/mol(-1)) show the lowest oxidation resistance which improved dramatically after a heat treatment at 3023 K of the herringbone (E-a = 216 kJ/mol(-1)) and platelet (E-a = 174 kJ/mol(-1)) structures.
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| 4. |
- Amini, Shahram, et al.
(författare)
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On the Stability of Mg Nanograins to Coarsening after Repeated Melting
- 2009
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Ingår i: NANO LETTERS. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 9:8, s. 3082-3086
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Tidskriftsartikel (refereegranskat)abstract
- Herein we report on the extraordinary thermal stability of similar to 35 nm Mg-nanograins that constitute the matrix of a Ti2AlC-Mg composite that has previously been shown to have excellent mechanical properties. The microstructure is so stable that heating the composite three times to 700 degrees C, which is 50 degrees C over the melting point of Mg, not only resulted in the repeated melting of the Mg, but surprisingly and within the resolution of our differential scanning calorimeter, did not lead to any coarsening. The reduction in the Mg melting point due to the nanograins was similar to 50 degrees C. X-ray diffraction and neutron spectroscopy results suggest that thin, amorphous, and/or poorly crystallized rutile, anatase, and/or magnesia layers separate the Mg nanograins and prevent them from coarsening. Clearly that layer is thin enough, and thus mechanically robust enough, to survive the melting and solidification stresses encountered during cycling. Annealing in hydrogen at 250 degrees C for 20 h, also did not seem to alter the grain size significantly.
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