| 1. |
- Berg, Sven, et al.
(författare)
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High pressure characterization and modelling of CaCO3 powder mix in the Bridgman anvil apparatus
- 2012
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Ingår i: High Pressure Research. - : Informa UK Limited. - 0895-7959 .- 1477-2299. ; 32:4, s. 490-508
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Tidskriftsartikel (refereegranskat)abstract
- For investigating high pressure sintering processes, numerical models can be used. This will demand material models which give realistic mechanical response throughout the whole parameter space of the actual process. As the pressures become higher, the material density approaches its full theoretical value and the elastic part of the material properties becomes increasingly important. In this investigation, Poisson's ratio was determined using ultrasonic pulse-echo measurements. A new elastic model and an improved plasticity model were implemented into a user-defined material subroutine in a finite element (FE) code. To experimentally investigate the load displacement response and pressure distribution in powder compacts during pressing, a pressure instrumented Bridgman anvil apparatus was used. Validation of the FE model was conducted against experimental data from pressing experiments using two different start densities. The results show that the simulation model is indeed capable of reproducing load–thickness curves and pressure profiles reasonable close to the experimental curves.
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| 2. |
- Konopkova, Zuzana, et al.
(författare)
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Thermal conductivity of hcp iron at high pressure and temperature
- 2011
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Ingår i: High Pressure Research. - : Informa UK Limited. - 0895-7959 .- 1477-2299. ; 31:1, s. 228-236
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Tidskriftsartikel (refereegranskat)abstract
- Results of steady-state heat transfer experiments on iron in laser-heated diamond anvil cell, combined with numerical simulation using finite-element method are reported. Thermal boundary conditions, dimensions of sample assemblage, heating-laser beam characteristics and relevant optical properties have been well defined in the course of experiments. The thermal conductivity of the polycrystalline hexagonal-iron foil has been determined up to pressure 70GPa and temperature 2000K. At these conditions, the conductivity value of 32 ± 7W/mK was found. Sources of errors arising from uncertainties in input parameters and applied experimental procedures are discussed. Considering results of earlier preferred-orientation studies in diamond anvil cell, an averaging effect of polycrystalline texture on the intrinsic anisotropy is assumed. The obtained conductivity is interpreted as an effective value, falling in between the upper and lower bounds on the average conductivity of a random aggregate of uniaxial crystals.
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| 3. |
- Moser, D., et al.
(författare)
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An in situ neutron diffraction measurement of the pressure-temperature evolution of a MgD2:TiD2 mixture
- 2010
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Ingår i: High Pressure Research. - : Informa UK Limited. - 0895-7959 .- 1477-2299. ; 30:4, s. 643-652
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Tidskriftsartikel (refereegranskat)abstract
- The hydrogen storage capacity of Mg-Ti-H films is approximately five times that of conventional metal hydride electrodes in NiMH-batteries. Mg and Ti are considered to be immiscible in the bulk and the ambient pressure phase diagram of Mg and Ti indicates that no binary stable bulk compounds are formed. However, in the presence of hydrogen, an Mg-Ti-H phase has been obtained by Kyoi et al. using a high pressure synthesis - where magnesium hydride is compacted with different TM-hydrides in an anvil cell at pressures of the order several GPa (4-8GPa) and at a temperature of 873K. In this work, we have proved the feasibility of in situ powder diffraction using the Paris-Edinburgh high pressure cell for the observation of structural changes on this system and we propose modifications to improve the output of the experiment.
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| 4. |
- Sundqvist, Bertil, et al.
(författare)
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Ionic conductivity in three crystalline phases of LiBH4 under pressure
- 2013
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Ingår i: High Pressure Research. - : Taylor & Francis. - 0895-7959 .- 1477-2299. ; 33:1, s. 141-151
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Tidskriftsartikel (refereegranskat)abstract
- The AC electrical conductivity of LiBH4 was investigated below 2GPa between 1Hz and 1.6MHz. The high-temperature phase has an ionic conductivity of up to 0.01Scm(1), while the low-temperature phases have conductivities two orders of magnitude lower. All phases show an Arrhenius behaviour with activation energies E-a between 0.5 and 0.7eV, in good agreement with earlier data except for phase III, which is found to have the highest activation energy of the phases studied. The high-temperature phase has a minimum in E-a near 1GPa, close to the triple point, correlated with a sudden change in activation volume. These features may indicate an isostructural phase transition. The conductivities of the ambient temperature phases increase temporarily by an order of magnitude after transitions between these phases, probably due to new diffusion channels via structural defects. The phase diagram agrees well with earlier results.
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| 5. |
- You, Shujie, et al.
(författare)
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Probing structural stability of double-walled carbon nanotubes at high non-hydrostatic pressure by Raman spectroscopy
- 2011
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Ingår i: High Pressure Research. - : Informa UK Limited. - 0895-7959 .- 1477-2299. ; 31:1, s. 186-190
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Tidskriftsartikel (refereegranskat)abstract
- Theoretical calculations predict that the collapse pressure for double-walled carbon nanotubes (DWCNTs) is proportional to 1/R3, where R is the effective or average radius of a DWCNT. In order to address the problem of CNT stability at high pressure and stress, we performed a resonance Raman study of DWCNTs dispersed in sodium cholate using 532 and 633 nm laser excitation. Raman spectra of the recovered samples show minor versus irreversible changes with increasing ID/IG ratio after exposure to high non-hydrostatic pressure of 23 and 35 GPa, respectively. The system exhibits nearly 70% pressure hysteresis in radial breathing vibrational mode signals recovery on pressure release which is twice that predicted by theory.
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