Time variations of the concentration profile of CuSO4 and of the velocity profile of laminar natural convective flow were measured near the electrode surface during the transient electrolysis after reversing the current. A symmetrical transient variation of natural convection was observed after anodic and cathodic current reversions. It was found that the concentration profile possesses an extreme value, and the inverted flow appears near the electrode surface. The effects of current density and vertical location on the natural convection were discussed. Based on the experimental results, the space-time structure of the transient natural convection was considered.Among numerous works (1-3) in the past on the natural convective flow along the surface of a plane vertical electrode installed in unstirred electrolyte, only a few works concerned the transient natural convection encountered in the unsteady electrolysis. This is in spite of its importance in the practical operation of unsteady electrolysis, such as periodic current reversal in copper refining, as well as in the study of the nature of transient natural convective flow itself.Tvarusko et al. (4, 5) studied the transient natural convection at the start of electrolysis by applying a technique of Mach-Zehnder interferometry and showed that both the concentration difference of CuSO4 between bulk electrolyte and cathode surface and the thickness of the cathodic diffusion layer increase in proportion to the square root of time elapsed from the start. However, they were not successful in photographing the concentration profile of CuSO4 in the diffusion layer which develops downstream. This is supposed to be due to the severe optical restriction in two-beam interferometry.Only after the application of a technique of holographic interferometry, it became possible to precisely measure the concentration profile in the diffusion layer near the electrode surface, and the transient cathodic diffusion layer (6, 7) was studied by applying this technique. In addition, the corresponding transient velocity profile was measured by recording the motion of colophonium particles suspended in the cathodic hydrodynamic boundary layer (7,8).Following these studies, it is intended in the present work to study the transient natural convection after the direction of eIectrolytic current is reversed. Time variations of the concentration profile of CuSO4 and of the velocity profile of natural convective flow are measured during the time period from reversing the current until the steady natural convection in reversed direction is established.
Segregation of reactive metals at the bonding interface has been observed in various ceramic and/or metal joints bonded with reactive metal-bearing braze alloys. When a d.c. of 20 mAcm -2 is applied to the ceramic/braze/ceramic system at a brazing temperature of, say, 1373 K, the electric field assists the segregation at the braze-ceramic interface on the cathode side and suppresses the segregation at the interface on the anode side. This may imply that reactive metal atoms in the braze can migrate as a cation. E.m.f. measurement on the ceramic (AIN or ZrB2)-metal foil systems with increasing temperature shows that a negative e.m.f, to the ceramic pole appears from about 900 K for AIN and from 500 K for ZrB 2, as does the thermally stimulated current in polymers. These temperatures coincide well with those where the electrical conductivity of AIN and ZrB 2, respectively, begins to increase with increasing temperature. Therefore, it is considered that the polarization of the ceramics may take place and assist the migration, and consequently segregation, of reactive metals in braze alloys to the braze-ceramic interface during brazing.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.