Approximate rate formulation of non-elastic bifurcation problem for thin-walled structures

Simplified set of equations is derived for solution of a non-elastic bifurcation problem in thin-walled structures. The rate formulation is preferable, and based on the classical Hill's approach. It is shown that for a particular case of small strain the problem can be reduced to a more simple eigenvalue problem. As an example, the approach proposed has been applied to a circular stationary disk subjected to thermal expansion. The material of the disk is assumed to be elastic–perfectly plastic obeying the von Mises yield criterion with its associated flow rule. The influence of the width ratio on the bifurcation behavior has been discussed.     

Stable and inexpensive electrodes for the hydrogen evolution reaction

The HER activities of Raney–Ni electrodes obtained by partial leaching of Al in a Ni–Al–Fe alloy doped with Mo, Cr or Pd were studied in 28% KOH. PTFE bonded Gas Diffusion Electrodes (GDEs) were prepared by the rolling method before sintering at 300 °C under N₂. Ni in alkaline electrolyte has a lower intrinsic HER activity than Pt in acid. However, the spongy and highly porous character of Raney–Ni greatly enhances HER resulting in a cheap material with outstanding catalytic performance. The polarization behavior of GDEs consisting mainly of Raney–Ni catalysts with optional addition of co-catalyst or conductivity enhancing powders, such as carbonyl iron, carbonyl nickel, copper and molybdenum oxide are studied as a function of temperature and time in order to determine activities, behavior in the high current density regime, and long term stability in view of potential exploitation in industrial electrolysis. Cr and Pd-doped Raney–Ni initially achieve outstanding performances with unusually low “Tafel slopes”. After weeks long cathodic treatments, these GDEs eventually attain inferior but stable activities due to an apparently irreversible aging of Raney–Ni. The aging of Mo-doped Raney–Ni is less conspicuous, and relevant performances are sometimes improved by additives. A clear picture is emerging of the mechanisms controlling polarization and aging behavior of Raney–Ni GDEs. From this picture, suggestions are put forward on how to improve stability and performances of full electrode assemblies and make them suitable for use in advanced alkaline electrolyzers.     

Possible use of unsoldered ribbing in the turn of a heat exchanger made of tubes ribbed with wire

Translated from Khimicheskoe i Neftyanoe Mashinostroenie, No. 1, pp. 46–48, January–February, 1996.     

Pulsed difference frequency generation regime in dual-wavelength vertical-external-cavity surface-emitting laser

The parameters of middle-IR radiation (λ ∼ 17 μm) generated as a result of the intracavity nonlinear optical interaction in a semiconductor dual-wavelength vertical-external-cavity surface emitting laser operating in a pulsed regime have been numerically analyzed. The dependence of the peak output radiation power on the length of the nonlinear crystal has been studied for various values of the loss factor.     

Oxygen evolution in alkali with gas diffusion electrodes

Progresses in the area of the oxygen evolution reaction (OER) are now occurring at a much faster rate relative to few years ago. For this reason, it has been deemed appropriate to present a critical review of the major and most recent contributions towards a fundamental understanding of what determines the OER electrocatalytic properties of a material. Furthermore, the technologies used to produce practical OER electrodes with top activities are assessed and the current benchmarks of performance are identified. Furthermore, results pertaining to our work on Raney–Ni gas diffusion anodes, which have been optimized in thickness and composition, are presented. An addition of 10 wt.% of a Co₃O₄ micrometric powder as co-catalyst (with Raney Ni–Fe) was found to enhance the polarization behavior and performance. The electrode so obtained achieves activities comparable with those of the best electrodes reported in the literature.     

Application of Mises yield criterion to rotating solid disk problem

Continuous stress–displacement solution to thin rotating solid disk problem is obtained for elastic–perfectly plastic material. The solution follows the classical approach based on equation of motion, Hooke’s law, yield criterion, and conditions of continuity of stresses and/or displacement at the elastic/plastic boundary. It is shown that both the displacement field derived from the flow rule associated with Mises yield criterion and the stress distributions are continuous at the elastic/plastic boundary in contrast with the discontinuous solution based on Tresca yield criterion and its associated flow rule.