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► Carbon plays a dual role in perovskite/carbon composites for the ORR. ► It improves the conductivity of the layer and the utilization of the perovskite surface. ► Simultaneously, it ...plays an active role in the ORR by catalyzing the O2 reduction to H2O2. ► Perovskites catalyze the ORR and the H2O2 reduction and/or decomposition.
Perovskite oxides are promising materials for the ORR in alkaline media. However, catalytic layers prepared from perovskite powders suffer from high Ohmic losses and low catalyst utilization. An addition of carbon to the catalytic layers greatly improves the performance of the electrodes in the ORR. In this work composite thin film electrodes comprised of a perovskite oxide (either LaCoO3 or La0.8Sr0.2MnO3) and pyrolytic carbon of the Sibunit family were investigated in aqueous 1M NaOH electrolyte using cyclic voltammetry and rotating disc electrode (RDE) method with the objective to unveil the influence of carbon on the catalyst utilization and on the ORR electrocatalysis. By systematically varying the oxide to carbon ratio we arrive to the conclusion on the dual role of carbon in composite electrodes. On the one hand, it is required to improve the electrical contact between perovskite particles and the current collector, and to ensure maximum utilization of the perovskite surface. On the other hand, carbon plays an active role in the ORR by catalyzing the O2 reduction to H2O2. Composite electrodes catalyze the 4e− ORR in contrast to carbon which is only capable of catalyzing the 2e− reduction. For LaCoO3 composite electrodes, carbon is responsible for the catalysis of the first steps of the ORR, the role of LaCoO3 being largely limited to the hydrogen peroxide decomposition and/or reduction. For La0.8Sr0.2MnO3 composite electrodes, along with the catalysis of the chemical decomposition and/or reduction of H2O2 produced on carbon, the perovskite also significantly contributes to the first steps of the ORR. The results of this work suggest that the ORR on the carbon and the oxide components of composite cathodes must be considered as coupled reactions whose contributions cannot be always separated, and that neglecting the contribution of carbon to the ORR electrocatalysis may lead to erroneous values of the catalytic activity of perovskite materials.
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•Structure of the AlSi10MgCu(Zr, Ce) alloy in different thermal states.•Mechanical properties of the AlSi10MgCu(Zr, Ce) alloy in different thermal states.•Comparison of mechanical ...properties between Al-Si-Mg-(Cu) alloys was conducted.
The article presents investigation of structure and mechanical properties of an advanced aluminum alloy Al-10Si-0.9Cu-0.7 Mg-0.3Zr-0.3Ce, produced by selective laser melting. By means of SEM, TEM and EDX-analysis some aspects of the alloy microstructure in as-built and thermal treated states are discussed. The alloy has high level of strength (UTS > 390 MPa, YS > 330 MPa) in T6-state, providing good elongation (El. > 6%). In annealed state the alloy also provides good combination of mechanical properties (UTS > 350 MPa, YS > 240 MPa, El. > 9%).
This paper provides a review of the dates used to define major hydrologic changes in the Caspian Sea during the Late Pleistocene that includes the Early Khvalynian and Hyrcanian highstands and the ...Atelian lowstand, and it discusses their driving mechanisms. Dates obtained by 14C (that are the most numerous), by OSL and by U/Th for samples that are well identified in the literature through their geographic location and their laboratory number, are considered. Samples derive from sediments both in the current Caspian Sea coast and in its Middle and Northern basins. Most of dates concern the Early Khvalynian highstand while less abundant ones correspond to the Hyrcanian highstand and Atelian lowstand that preceded the Early Khvalynian. The review of these Late Pleistocene dates provides an overall revision of the hydrologic changes that the Caspian Sea experienced. Accordingly, the Early Khvalynian highstand presents two major phases. The first Early Khvalynian phase (hv1-1) took place between 36.0 and 22.0 cal kyr, and water level reached ca 0 m a.s.l. Its second phase (hv1-2) is characterised by the deposition of the so-called Chocolate Clays especially in the Northern Peri-Caspian and took place between ca 22.0 and 12.5 cal kyr BP with a water level rise until at least 40 m a.s.l. between ca 17 and 13 cal kyr BP. Before the Early Khvalynian highstand, the Caspian water level underwent a lowstand between at least 70.0 and 36.0 kyr, i.e. the Atelian lowstand, which was interrupted by the Hyrcanian highstand. During the late stage of the Atelian lowstand, between 43.5 and 42.9 and 36.0 cal kyr BP, the water level decreased between more than −60 m a.s.l. and less than - 90 m a.s.l. at 42.0 cal kyr BP. The importance of the water level drop in the early stage of the Atelian regression between ca 70 and 55.2 kyr could not be estimated but according to seismic profiles, it was much less pronounced than later. The dates for the Hyrcanian highstand range from 55.2 (or even before) to 43.5–42.9 cal kyr BP and the water level reached at least 0 m a.s.l. in its late phase. Through this synthesis, the origins of water inflows into the Caspian Sea could be suggested for the upper part of the Early Khvalynian transgression: it matches with a very large inflow of meltwater from the southern front of the Scandinavian Ice Sheet; the fluvio-glacial waters from the ice cap discharging to the Caspian Sea via the Volga River. Concerning the Hyrcanian transgression, meltwater inputs from the glaciers of western High Asia can be proposed, the fluvio-glacial waters being transported into the Caspian Sea by the Syr Darya and Amu Darya (via the Aral Sea or bypassing it).
•Synthesis of Early Khvalynian, Atelian and Hyrcanian chronology, Caspian Sea basin.•Caspian Sea water level change and palaeogeography between 70 and 12 cal kyr BP.•Motors of Caspian water level change; Eurasian Ice Sheet, West High Asia, meltwater.•Largest database established for Late Pleistocene Caspian Sea; 14C, OSL, U/Th.
Magnetic Flux Leakage (MFL) method is widely used in non-destructive testing of ferromagnetic specimens such as steel pipes, ropes and rails. Inspection velocity is a critical factor in online rail ...track evaluation due to specific inspection conditions. As the speed increases the distribution of magnetic induction inside rail becomes inhomogeneous primarily under the influence of eddy currents. This complicates MFL signals interpretation and reduces the ability to detect deep subsurface defects in the rail head. In this paper we explore the speed limitations of the traditional MFL rail inspection and contemplate the ways to overcome the said limitations. To investigate the dependence of flux leakage data on inspection velocity two different methods were applied. The first one is 3D computer simulation of interaction between the fixed rail and the moving magnetizing system. The second method is the set of field measurements in which an experimental setup consisted of electromagnets and sensors moved along rail with artificially made defects. The results of both methods indicate to detect defects located in the center of the rail head at speeds over 80 km/h the distance between magnetizing system poles should exceed conventional 3 m or some alternatives should be employed such as MFL remote field analysis.
A special magnetodynamic effect arising from high-speed testing of conductive objects by magnetic flux leakage method was studied. At a significant speed of motion of the magnetizing system relative ...to the test object, under the influence of eddy currents, the region of the maximum level of magnetization shifts in the direction opposite to the direction of motion. As a result, a magnetization zone forms behind the back pole of the magnetizing system—a tail field. The structure of the tail field and the possibilities of using the results of its leakage to obtain defect data were investigated. The rail was taken as a test object, since it is precisely when inspecting the railway track that the testing speeds are high and the magnetodynamic effects play an important role. The results of a three-dimensional computer simulation indicate the presence of two oppositely directed magnetic fluxes behind the back pole of the magnetizing system, one of which propagates in the bulk of the metal, and the other on its surface. The resulting distribution of the magnetic field behind the back pole can be used to differentiate signals from surface and internal flaws.
The ability of the Magnetic Flux Leakage (MFL) method to detect flaws in railway rails in two different ways has been studied. First, a three-dimensional computer simulation of the leakage of ...magnetic flux around a transverse crack in the rail head was carried out to determine the relationship between the main characteristics (size and depth) of the defect and the magnetic sensor signal. Second, signals were analyzed from more than 600 actually confirmed defects of the rail track, enabling statistically determined conclusions on the detectability of various types of flaws by magnetic and ultrasonic methods. It has been established that the MFL method detects rail head defects with the critical size at a depth of up to 20 mm under the upper rail edge. In general, the revealed defects constitute more than 90% of hazardous damage to rail head; this confirms the high efficiency of the MFL method in comparison with acoustic methods, which are also traditionally used in rail non-destructive testing.
The article investigates the possibility of detecting defects in the form of transverse cracks in rail foot under continuous in-service inspection of rails. The MFL method is chosen as an alternative ...to ultrasonic testing. Computer modeling was carried out, based on the results of which a working model of the system for magnetizing and recording of monitoring signals was developed and constructed. Experimental studies on detection of crack models in rail foot were carried out in laboratory conditions. The studies confirmed the results of computer modeling and proved the possibility of detecting such crack models. The minimum sizes of detectable crack models in the zone of rail fastening and between them have been estimated.
The efficiency of a flaw detector magnetizing system using wheels as magnetic poles was studied. To obtain information on the emerging magnetic field distributions, three-dimensional computer ...simulation and research on an experimental model were carried out. The rail was used as a test object. It is shown that with the same magnetomotive force of the electromagnet, the wheel magnetizing system provides a higher magnetization of the test object compared to the traditionally used U-shaped magnetizing system.
The authors consider the use of a Cr
3+
:BeAl
2
O
4
laser operating in the mode of free generation as a source of radiation for the optical pumping of vapors of rubidium alkali metal. The use of ...dispersive elements in the composition of the laser resonator allows smooth tuning of the radiation and generation at wavelengths corresponding to lines D
1
and D
2
of isotopes
85
Rb and
87
Rb. The optical pumping of rubidium isotopes using laser radiation with wavelengths of 795 and 780 nm, respectively, is performed experimentally. The fluorescence of the isotopes is demonstrated. The use of tunable wavelength laser generation in the spin-exchange optical pumping of noble gases is discussed.
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