Stability experiments were made on plane Poiseuille flow generated in a long channel of a rectangular cross-section with a width-to-depth ratio of 27·4. By reducing the background turbulence down to a level of 0·05 %, we succeeded in maintaining the flow laminar at Reynolds numbers up to 8000, which is much larger than the critical Reynolds number of the linear theory, about 6000. The downstream development of the sinusoidal disturbance introduced by the vibrating ribbon technique was studied in detail at various frequencies in the range of Reynolds number from 3000 to 7500. This paper presents the experimental results and clarifies the linear stability, the nonlinear subcritical instability and the breakdown leading to the transition.

The electrochemical stabilities of several electrodes were investigated by cyclic voltammetry and chronoamperometry in a tetrahydrofuran solution containing phenylmagnesium chloride and aluminum chloride. The existence of chloride ions in the electrolyte caused pitting of affordable, non-noble metal electrodes at high potentials and crucially lowered their corrosion resistance. In contrast, Pt and glassy carbon electrodes exhibited high corrosion resistance. Since Pt is expensive and bulk glassy carbon is not flexible, these two materials are not suitable current collectors in commercial batteries. A considerable improvement in corrosion resistance was confirmed when glassy carbon coatings were formed on the affordable electrodes by plasma carburization, which can be one solution to this corrosion problem.

Synthesis of binary magnesium-transition metal oxides, MgM 2 O 4 (M: Cr, Mn, Fe, Co) and MgNiO 2 , was performed by calcination at relatively low temperatures of 500 and 750 C for 24 h through inverse coprecipitation of carbonate hydroxide precursors. The important roles of the precipitation agent, sodium carbonate, were clarified by considering equilibria in an aqueous solution. The structure parameters of the obtained binary magnesium-transition metal oxide powders, specifically the occupancy of atomic sites, were evaluated from synchrotron X-ray diffraction (XRD) profiles by Rietveld refinement in addition to the magnetic properties at room temperature. The present work provides general guidelines for lowcost and high-volume synthesis of complex oxides, which are easily decomposed at high temperatures.

No abstract

Chevrel compounds have been reexamined as potential positive electrodes for magnesium rechargeable batteries; their redox potential can be as high as about 2–3 V vs. Mg/Mg2+.