Portnoia V.K.,Moscow State University |
Leonova A.V.,Moscow State University |
Bogdanovb V.I.,Vologda State Technical University |
Popovb V.A.,Vologda State Technical University |
And 2 more authors.
Physics of Metals and Metallography | Year: 2014
Mechanochemical synthesis (MS) of Ni70Al25Mo 5 (composition 1) and Ni75Al20Mo5 (composi- tion 2) mixtures, in which 5 at % Mo substitutes for the equal amount of Ni or Al, leads to the formation of Ni-based nanocrystalline (coherent domains are ∼7-12 nm in size) solid solutions; in this case, some amount of molybdenum remains free. A comparison of the lattice parameters of solid solutions, which were deter- mined experimentally, with the magnitudes determined theoretically using Vegard law and Bozollo-Ferrante simulation, which takes into account volume modules of elasticity of elements, showed an increase in inter- actions between atoms composed the solid solution and the formation of regions characterized by short-range order. The heating of mechanically synthesized three-component Ni(Al, Mo) solid solutions to 720°C in a calorimeter chamber forms the ordered γ phase (L12) at T ∼ 450°C. An analysis of the ratio of relative inten- sities of superlattice and fundamental reflections showed that, whatever the composition of initial mixture, Mo atoms always occupy positions in the Al sublattice. This arrangement of Mo atoms was confirmed by cal- culations of coefficients of concentrational variations of the lattice parameters. When molybdenum is added to Ni 3Al, Mo atoms, rather than Ni atoms, complete the Al sublattice. In this case, vacancies compensate for the lack of atoms in the Ni sublattice. © 2014 Pleiades Publishing, Ltd.
Manukhina E.B.,University of North Texas Health Science Center |
Manukhina E.B.,Institute of General Pathology and Pathophysiology |
Jasti D.,University of North Texas Health Science Center |
Vanin A.F.,Institute of Chemical Physics |
Fred Downey H.,University of North Texas Health Science Center
Experimental Biology and Medicine | Year: 2011
Although intermittent hypoxia is often associated with hypertension, experimental and clinical studies have demonstrated definite antihypertensive effects of some intermittent hypoxia conditioning (IHC) regimens. Mechanisms of this antihypertensive response are unknown. Endothelial dysfunction related to disturbed synthesis and/or reduced availability of nitric oxide (NO) has been linked to hypertension. Thus, experiments were conducted to determine if IHC can improve endothelium-dependent relaxation and formation of releasable vascular NO stores of young (4-8-week-old) spontaneously hypertensive rats (SHR). Rats were subjected to either IHC (9.5-10% O 2, 5-10 min, 5-8 times per day, 20 d) or to sham conditioning. Endothelium-dependent relaxation to acetylcholine was measured in norepinephrine-precontracted, isolated aortic rings, and the size of NO stores was evaluated by percent relaxation to N-acetylcysteine (NAC), which releases stored NO. The capacity of aortic rings for NO storage was evaluated by the relaxation to NAC after prior incubation with an NO donor. IHC significantly suppressed the development of hypertension in young SHR. Endothelial function decreased from 54.7±4.6% to 28.1±6.4% relaxation to acetylcholine after 20 d of sham IHC, whereas endothelial function was sustained (60.3±6.0% relaxation) in IHC rats. IHC also induced formation of available NO stores and enhanced the capacity of aortic rings to store NO. Therefore, the antihypertensive effect of IHC in young SHR is associated with prevention of endothelial dysfunction and with increased accumulation of NO stores in vascular walls. © 2011 by the Society for Experimental Biology and Medicine.
Rumyantsev B.V.,RAS Ioffe Physical - Technical Institute |
Klimenko V.Yu.,Institute of Chemical Physics
AIP Conference Proceedings | Year: 2012
The mechanism of penetration of the jet in silicon carbide had been investigated experimentally and numerically. In contrast to of metals, the penetration of shaped-charge jet into ceramics has an anomalous character and a smaller depth of penetration. The penetration into ceramics is accompanied by a radial interaction of a crater wall fragments with the jet elements and this leads to a partial melting and evaporation of the elements. Appearance of a "gas" phase enables dispersion of the elements, mixing with the wall fragments, formation of an internal absorption volume, and destabilization of further part of the jet. As a result a considerable part of the jet loses the ability by the penetration. © 2012 American Institute of Physics.
In a feat that could be described as taking the bull by the horns, researchers have exploited a process that normally destroys supported metal catalysts to make stable ones consisting of isolated platinum atoms on a solid support (Science 2016, DOI: 10.1126/science.aaf8800). The counterintuitive strategy may offer a practical way to maximize the use of platinum and other expensive noble metals by producing stable single-atom catalysts. Tiny particles of platinum can transform petrochemicals, clean up engine emissions, and catalyze other reactions. But when exposed to high temperatures and oxidizing conditions, the particles agglomerate, forming larger particles. Known as Ostwald ripening, the process reduces catalytic activity by burying the majority of the atoms in the growing particles’ interiors, where they can’t catalyze reactions. Rather than avoiding those conditions, a team led by University of New Mexico chemical engineer Abhaya K. Datye exploited them, sacrificing an alumina-supported platinum nanoparticle catalyst to make a catalyst consisting of isolated platinum atoms on ceria. Datye described the work last week in China at a conference on single-atom catalysis at the Dalian Institute of Chemical Physics. From earlier work, Datye and coworkers knew that hot oxidizing conditions turn platinum nanoparticle catalysts into larger, less active platinum clumps by converting the metal to PtO , which is volatile and desorbs from nanoparticle surfaces. Datye reasoned that this supply of mobile atoms could allow his team to produce single-atom catalysts. “The challenge is coming up with a way to trap those atoms individually,” he said. Datye and coworkers wondered if ceria might serve as this atom trap because other researchers had shown that small amounts of the oxide prevented nanoparticle sintering or fusing. They mixed an alumina-supported platinum-lanthanum catalyst with various forms of ceria and heated the mixtures to 800 °C in air for a week. After the treatment, X-ray diffraction and other methods showed the complete absence of platinum nanoparticles. Electron microscopy revealed that platinum had migrated from the alumina and become trapped as isolated atoms on ceria nanorods and octahdera along lattice features known as step edges. In the absence of ceria, the harsh treatment formed large platinum crystals on alumina. The team showed that the single-atom catalysts were effective at CO oxidation—a key reaction in engine-emissions cleanup—and that the platinum atoms remained isolated during the reaction. “I’m very impressed with this work,” said Northwestern University’s Peter C. Stair, a catalysis specialist who attended the conference. Coming up with a way to stabilize isolated, catalytically active metal atoms on solid supports has practical relevance for industrial catalysis, he added. “It points to strategies for making catalysts that remain stable for years.” Exactly how platinum is bound to the ceria surface remains an open question, Stair said. But that question applies equally well to most efforts to prepare single-atom catalysts. This article has been translated into Spanish by Divulgame.org and can be found here.
« Quanergy acquires Otus People Tracker software from Raytheon BBN for advanced autonomous driving and security LiDAR applications | Main | NOHMs raises $5M for commercializing non-flammable, ionic-liquid containing electrolytes for EV batteries » Researchers at Dalian Institute of Chemical Physics (China) have synthesized an advanced catalytic layer in the membrane electroide assembly (MEA) for proton exchange membrane fuel cells (PEMFCs) using vertically aligned polymer–polypyrrole (PPy) nanowire arrays as ordered catalyst supports. In a paper published in the Journal of Power Sources, they report that a single cell fitted with their MEA yields a maximum performance of 762.1 mW cm−2 with a low Pt loading (0.241 mg Pt cm−2, anode + cathode). The advanced catalyst layer indicates better mass transfer in high current density than that of commercial Pt/C-based electrode. The mass activity is 1.08-fold greater than that of US Department of Energy (DOE) 2017 target. Polymer electrolyte membrane fuel cells (PEMFCs) are one of the most promising alternative energy sources for stationary and transportation applications because of their high power density, quick start-up, zero or low emission, and low operating temperature. However, the cost of the PEMFCs must be reduced for wide adoption. Over the past decades, significant research has been devoted to decrease the cost of cell components without sacrificing their performance and durability and to decrease the amount of platinum (Pt). Many studies have focused on (1) the development of non-Pt-group metal catalysts and (2) the utilization of other metals (Pd, Fe, Co, Ni, and Cu) with Pt to form a core-shell structure or alloy, or the improvement of Pt utilization efficiency with an ordered electrode structure. Of these efforts, the development of advanced catalytic layer architecture is of importance to obtain an efficient membrane electrode assembly (MEA), which is the core part of PEMFCs and has significantly influenced the performance and durability of fuel cells. The team investigated PtPd alloy catalysts with various Pt loadings formed on PPy nanowire arrays in the anode or cathode (PtPd-PPy). The arrays were hot-pressed on both sides of a Nafion membrane to construct a membrane electrode assembly (without additional ionomer). The ordered thin catalyst layer (approximately 1.1 μm) was applied in a single cell as the anode and the cathode without additional Nafion ionomer. Since there is no additional ionomer on the catalyst layer of the proposed electrode, the water film acts as the proton-conducting pathway. They concluded that the high performance attained is due to the ordered electrode structure with a high Pt utilization and the improvement of the mass transport of the reactant and products in high current density. Broadly, the benefits of the approach are: However, cell performance needs further improvement through structure optimization. Our work provides a novel idea for the fabrication of a core-shell structure catalyst in the microscale and a new method to prepare a thin-film electrode. Furthermore, the approach developed in this work is of good scalability and is beneficial to the development of other fuel cells.