Nikolay G. Razumov; Anatoly A. Popovich; Andrey V. Samokhin; Aleksei V. Grigoriev
Abstract
Spherical Nb-Si powder alloy is a perspective material to manufacture products for the aerospace industry by additive technologies. Nb-16Si (at.%) powder alloy was prepared by mechanical alloying from pure elemental powders using planetary ball mill Fritsch Pulverisette 4. Spheroidization was carried ...
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Spherical Nb-Si powder alloy is a perspective material to manufacture products for the aerospace industry by additive technologies. Nb-16Si (at.%) powder alloy was prepared by mechanical alloying from pure elemental powders using planetary ball mill Fritsch Pulverisette 4. Spheroidization was carried out on plasma generator based on thermal plasma arc generator with vortex discharge stabilization. Experimental results show that plasma spheroidizing of Nb-16Si powders obtained by mechanical alloying is possible. It is shown that after the spheroidization the particle surface is rough which indicates the cast structure of the material. Three phases having different optical contrast are revealed on microsections: Nb5Si3, Nb3Si and Nbss, which is confirmed by X-ray diffraction. It is shown that the main peaks in the X-ray graph after MA correspond to a solid solution of niobium with a cubic lattice and the parameter a = 0.333 nm, as well as niobium silicide Nb5Si3 with a hexagonal lattice (P63/m) a = 0.7536 nm and c = 0.5249 nm. After spheroidization the hexagonal lattice of niobium silicide Nb5Si3 is transformed into a tetragonal lattice (I4/m) with the parameter a = 0.6557 nm and c = 1.186 nm. The other phase components remain unchanged.
Satyabrata Mohapatra
Abstract
We report on the gettering behavior of Au at end-of-range (EOR) defects in float-zone grown Si(111), implanted with 1.5 MeV Au 2+ ions at room temperature. The effects of implantation dose and annealing temperature on the thermal evolution of gettering behavior of EOR defects have been investigated using ...
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We report on the gettering behavior of Au at end-of-range (EOR) defects in float-zone grown Si(111), implanted with 1.5 MeV Au 2+ ions at room temperature. The effects of implantation dose and annealing temperature on the thermal evolution of gettering behavior of EOR defects have been investigated using Rutherford backscattering spectrometry, while the microstructural evolution of Au implanted Si(111) has been studied using cross-sectional transmission electron microscopy combined with high resolution transmission electron microscopy. The gettering efficiency of EOR defects, comprising of dislocation loops, has been found to increase with increase in implantation dose up to 1.2 x 10 15 ions cm -2 , beyond which it was found to saturate at about 5 x 10 14 atoms cm -2 for annealing at 850 o C. We have observed that the gettering efficiency of the EOR defects for Au increased with increase in annealing temperature and reached 9 x 10 14 atoms cm -2 for annealing at 950 o C. The observed enhanced gettering efficiency of EOR defects is very promising for gettering applications in Si devices.
Mehdi D. Esrafili; Parisa Nematollahi
Abstract
In this letter, the mechanisms of the oxygen reduction reaction (ORR) on Si- and Al-doped graphene have been investigated to understand the effect of doped graphene on the ORR and predict details of ORR pathways. Density functional theory (DFT) calculations were used to achieve the true mechanism pathways ...
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In this letter, the mechanisms of the oxygen reduction reaction (ORR) on Si- and Al-doped graphene have been investigated to understand the effect of doped graphene on the ORR and predict details of ORR pathways. Density functional theory (DFT) calculations were used to achieve the true mechanism pathways of ORR on the surfaces. Also, free energy diagrams for the ORR were constructed to provide the stability of possible intermediates in the electrochemical reaction pathways. At first stage, the adsorption of O2 molecule on both surfaces was studied with two possible configurations: atop (most stable) and bridge with the Eads of -60.6 and -72.4 kcal/mol, while for bridge site they were about -48.9 and -60.4 kcal/mol, respectively. Then, the most stable configuration (atop) was selected and the pathways formed after the adsorption of four atomic hydrogen to O2 molecule for both surfaces. These mechanisms were similar in both Si- and Al- doped graphene but there was a little difference in the obtained intermediates formed in each surface. In each pathway, the O2 dissociation reaction was neglected because it was unlikely to occur due to the high activation energy (> 45 kcal/mol). The results of this study show an easy and economic way to obtain Si- and Al-doped graphene as a non-metal catalyst for ORR at the cathode electrode in fuel cells.