Intermetallic β-Al5FeSi phase and coarse Mg2Si particles have negative effects on extrudability and workability of 6xxx Al alloy billets. To achieve extruded products with a high surface quality ...as-cast billets are therefore heat-treated before extrusion. During heat treatment the undesired intermetallic particles, i.e., β-AlFeSi platelets, are transformed to a rounded α-Al(FeMn)Si intermetallic phase. This transformation was studied in-situ by TEM for 6005 and 6082 Al alloys. It was observed that the Mg2Si particles precipitate in the Al matrix at about 250 °C; this precipitation also occurred at the edge and faces of beta intermetallic particles, and the Mg2Si particles were the preferred sites for α-Al(FeMn)Si particle nucleation. The transformation proceeded faster and at lower temperatures, 350–450 °C, than what has been reported earlier for homogenization studies of bulk samples and industrial billets. This could be associated with the thin characteristic of used samples in TEM giving contribution from fast surface diffusion, but it was also concluded that the phase boundary layer diffusion was important for the understanding of how the transformations proceed.
Two types of phase transformation of β-AlFeSi platelets to a rounded α-Al(FeMn)Si intermetallic phase during homogenization in 6005 and 6082 Al alloys. Display omitted
•The in-situ phase transformations during homogenization were studied by TEM for Al alloys.•The Mg2Si precipitations were the preferred sites for α-Al(FeMn)Si particle nucleation.•After nucleation, the α-Al(FeMn)Si particles grow and coarsen via two different modes on the expense of the β−phase.•An explanation of the possible mechanisms taking place during transformation from β- to α-phase is presented.
Refractory metal high entropy alloy HfNbTaTiZr with ultrafine grained structure and grain size of ≈80 nm was processed by high pressure torsion. The development of microstructure, lattice defects and ...mechanical properties with increasing strain was examined. Grain refinement of HfNbTaTiZr alloy deformed up to the equivalent strain e ≈ 50 resulted in a significant enhancement of strength while keeping sufficient ductility. However, further straining e > 100 led to a decrease of strength and the loss of ductility due to the decomposition of solid solution facilitated by vacancies introduced by severe plastic deformation.
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•High entropy alloy HfNbTaTiZr was nanostructured by high pressure torsion.•Grain size of 80 nm was achieved by deformation to the equivalent strain e = 5.•Structure refinement resulted in remarkable enhancement of strength of the alloy.•Ductility remains sufficient for good workability.•Further deformation to very high strains resulted in loss of strength.
In as-cast 6xxx aluminium billets β-Al5FeSi intermetallic phase and coarse Mg2Si particles have negative effects on subsequent processes such as extrusion. To achieve extruded products with a high ...surface quality the billets are heat-treated by a so-called homogenization before extrusion. During the heat treatment undesired intermetallic particles, i.e. β-AlFeSi platelets, are transformed to rounded α-Al(FeMn)Si intermetallic particles. The transformations occurring during homogenization have up until now only been studied by interrupted experiments giving some insight into the process, but a complete picture of how these phase transformations are coupled to the geometrical changes has not evolved. In the present study transformations in 6060 and 6063 alloys have been observed in-situ by TEM, and several nucleation and growth modes have been identified. Boundary layer diffusion was found to be important for the understanding of how the transformations proceed, and also diffusion on the free surface contributed to higher transformation rates compared to industrial processes due to thin characteristics of TEM samples. Together with an earlier study of 6005 and 6082 alloys the homogenization process for all important industrial 6xxx alloys is now characterised in detail by in-situ monitoring.
•The in-situ phase transformations during homogenization were studied by TEM for Al alloys.•Several nucleation and growth modes have been identified, but normally α-particles nucleate on a number of places along a β-needle and grow during simultaneous dissolution of the needle.•Boundary layer diffusion as well as the Gibbs-Thomson effect was found to be important for the understanding of the transformations kinetics.•Together with an earlier study of 6005 and 6082 alloys the homogenization process for all important industrial 6xxx alloys is now characterised in detail by in-situ monitoring.
In this contribution, we report a novel, mild, and energy efficient approach for the preparation of covalent organic frameworks (COFs) at ambient conditions. For the first time, powerful plasmonic ...chemistry was applied for the synthesis of carbon triazine framework (CTF-1) on copper nanoparticles (CuNPs) as an alternative to common synthetic procedures, which are restricted by harsh experimental conditions and low throughput. Plasmonic CuNPs were functionalized by 4-cyanophenyl groups, which were further used as anchoring groups for surface-assisted growth of CTF-1 under the illumination at wavelength corresponding to plasmon absorption band of CuNPs. Prepared CuNPs@CTF-1 structure exhibit core-shell nature and outstanding sensing properties for CO2 in water. In the next step, the copper core was dissolved, and resulting CTF-1 powder with high surface area was isolated. Generally, our pioneering work demonstrates the power of plasmonic chemistry for unpretentious COF synthesis performed in mild and cheap manner without any special apparatus and harsh conditions, as well as for the preparation of applied sensing material.
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•An advanced route for preparation of CTF-1 via plasmon assisted condensation on the CuNPs surface is demonstrated.•Prepared CuNPs@CTF-1 are stable in water and can be applied as a selective colorimetric sensor for CO2 detection.•The copper core dissolving results in the formation of porous CTF-1 powder with high surface area and pore volume.•The catalytic route for plasmon-assisted CTF-1 synthesis is easy-to-perform, fast, and energy-saving.
The severe plastic deformation method known as constrained groove pressing was used to produce ultrafine-grained microstructure in recrystallized aluminium (99.99%) at room temperature. The impact of ...repeated groove pressing, upon microstructure refinement was investigated by transmission electron microscopy of thin foils. Changes in mechanical properties measured by tensile and by hardness tests were related to microstructure development. The formation of banded subgrain microstructure with dislocation cells, and appearance of polygonal subgrains was a common feature observed in deformed plate subjected to the first pass. The substantial impact of strain upon strength increase was observed after the first pressings. The yield stress and ultimate tensile strength reached a maximum after four passes. A loss of ductility was observed in all processed plates. Hardness values measured in different areas of the deformed plates indicated heterogeneous strain distribution even after large degrees of straining.
The action of fuel cells with proton-exchanged membranes (PEMs) requires the implementation of the hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (ORR) on the opposite sides of ...the PEMs. Recently, based on several models of electrochemical reactions a significant decrease in the thermodynamic activation barrier of both reactions under plasmon assistance was reported. In this work, we propose the design of a PEM fuel cell with a plasmon-active catalytic surface providing plasmonic triggering and enhancement of fuel cell efficiency. In particular, we deposited bimetallic (Au@Pt) nanostructures on the PEM surface and integrated them into the fuel cell design. Plasmon excitation occurs on the Au nanostructures under light illumination at the corresponding NIR wavelength, while the Pt shell is responsible for the introduction of catalytic sites. Light illumination results in a significant enhancement of the electric current produced by the fuel cell. In particular, the electric current increased several times. Control experiments indicated that the observed enhancement takes place only when the light wavelength is in compliance with the plasmon absorption band and the contribution from thermal effects is negligible. The present approach for the introduction of plasmon assistance into the design of advanced fuel cells makes them suitable for increasing the fuel cell efficiency under sunlight.
The design and implementation of an advanced active fuel cell on the basis of plasmon-assisted chemical redox transformations is proposed.
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•Novel method to fabricate heterogeneous Ag/C:H:N:O particles is developed.•The method utilizes in-flight inoculation of plasma polymer particles by silver.•Produced particles have ...strawberry-like structure as witnessed by SEM and TEM.
The study focuses on the synthesis of two-component heterogeneous nanoparticles with plasma polymer core decorated with silver. It is shown that such strawberry-like particles may be easily produced by the strategy that involves the in-flight deposition of silver onto plasma polymer particles produced by gas aggregation source.
Ni@Ti core-shell nanoparticles were prepared by a vacuum based method using the gas aggregation source (GAS) of nanoparticles. Ni nanoparticles fabricated in the GAS were afterwards coated by a Ti ...shell. The Ti shell was deposited by means of magnetron sputtering. The Ni nanoparticles were decelerated in the vicinity of the magnetron to the Ar drift velocity in the second deposition chamber. X-ray photoelectron spectroscopy and energy dispersive x-ray spectroscopy analysis of the nanoparticles showed the core-shell structure. It was shown that the thickness of the shell can be easily tuned by the process parameters with a maximum achieved thickness of the Ti shell ~2.5 nm. The core-shell structure was confirmed by the STEM analysis of the particles.
The influence of cold rolling on thermal and mechanical properties together with microstructure observation of cast AlZnMgCu(ScZr) alloys has been investigated. Differential scanning calorimetry ...measurements and microhardness were compared to microstructure that was observed by microscopy (scanning electron and transmission), electron backscatter and X-ray diffractions. Microstructure observation of all studied alloys proved eutectic phase at (sub)grain boundaries. The eutectic phase at grain boundary in the AlZnMgCuScZr has a disordered quasicrystalline structure (known as the
T
phase or Mg
32
(Al,Cu,Zn)
49
). In the AlZnMgCu alloy, the eutectic phase consists of two phases—predominant MgZn
2
phase and minor quasicrystalline
T
phase. During casting and subsequent cooling, multilayer primary Al
3
(Sc,Zr) particles also precipitated in the alloy with Sc,Zr addition. Solute clusters and/or Guinier–Preston zones were dissolved during the annealing up to ~ 170 °C in the alloys. The highest hardening is caused by particle formation of metastable
η
′ and stable
η
phase in AlZnMgCu system observed at ~ 200 °C. Precipitation of the secondary Al
3
(Sc,Zr) particles is probably the reason of hardening after annealing above 300 °C in the Sc,Zr-containing alloys. Melting of eutectic phases was observed in DSC curves at temperatures ~ 481 and ~ 493 °C in the studied alloys. Activation energies of the Guinier–Preston zones dissolution and/or solute clusters were calculated using Kissinger and Starink method as
Q
A
≈ 100 kJ mol
−1
and the formation of the particles of Al–Zn–Mg–Cu system as
Q
B
≈ 150 kJ mol
−1
. No significant effect on the calculation of activation energy values of thermal processes was observed in deformed alloys. Sc,Zr addition in the alloys stabilizes grains, and there is no recrystallization in the AlZnMgCuScZr alloy at temperature 450 °C/10 h.
Electronic properties of α-UH3 stabilized by Zr Tkach, I; Paukov, M; Drozdenko, D ...
Physical review. B, Condensed matter and materials physics,
03/2015, Letnik:
91, Številka:
11
Journal Article
Recenzirano
Pure hydride of the α-UH
3
type without any β-UH
3
admixture was prepared by high-pressure hydrogenation of
bcc
U stabilized by Zr. Such material, characterized by a general formula (UH
3
)
1-
x
Zr
x
..., is stable in air at ambient and elevated temperatures. H release is observed between 400-450 °C similar to β-UH
3
. Its stability allowed to measure magnetic properties, specific heat, and electrical resistivity in a wide temperature range. Despite rather different crystal structure and inter-U spacing, the electronic properties are almost identical to β-UH
3
. Its ferromagnetic ground state with Curie temperature
T
C
≈ 180 K (weakly and non-monotonously dependent on Zr concentration) and U moments of 1.0 μ
B
indicate why mixtures of α- and β-UH
3
exhibited only one transition. Magnetic ordering leads to a large spontaneous magnetostriction
ω
s
= 3.2
*
10
-3
, which can be explained by the increase of the spin moment between the paramagnetic (Disordered Local Moment) and the ferromagnetic state. The role of orbital moments in magnetism is indicated by fully relativistic electronic structure calculations.
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