Comer weakness

The current distribution on a macroprofile is very important in technical metal electrodeposition. In electroplating, the current distribution determines the local variations in the thickness of the coating. In electrowinning and electrorefining of metals, a non-homogeneous current distribution can cause a short circuit with the counter electrode and the comer weakness effect in electroforming. This is very important in the three-dimensional electrodes, as well as in some storage batteries. In all the cited cases, a uniform current density distribution over the macroprofile is required. 

Comer weakness appears in deposits or electroforms at screened cathode parts, i.e., comers. The deposit is thinner in the comers of the cathode, and at these areas, in extreme cases, there is no deposition at all along the line of the comer bisector [16],... 

Fig. 3.19 (a) Simulation of a growth of the deposit from the model protrusion (h = 5 cm, / = 15 cm) calculated for a pure ohmic control employing Eqs. (3.57) and (3.58) and (b) schematic representation of microphotographs illustrating the comer weakness effect (Reprinted from Ref. [3] with permission from Springer and Ref. [7] with permission from the Serbian Chemical Society and adapted from [16])... 

A number of microphotographs of deposit cross sections illustrating the comer weakness effect can be found in the literature. They are schematically exemplified by Fig. 3.19b. It can be seen that the calculated deposit profile (Fig. 3.19a), with a crack appearing along the comer bisector, looks very similar to that typically obtained in a plating practice (Fig. 3.19b). 

Evenly distributed deposits, without comer weakness, may be obtained only by deposition under complete activation control at high Tafel slopes (Fig. 3.20a). In practice, this is usually achieved by employing appropriate surface active additives, as seen in Fig. 3.20b. 

In this way, not only the comer weakness effect is fully explained but also a new method of current density distribution evaluation in electrochemical cells is promoted. 

Popov KI, Stevanovic RM (2000) A new line division concept for the dettnminaticurrent distribution in electrochemical cell. Part I. Theoretical background of the comer weakness effect in electroforming. J Serb Chem Soc 65 905-914... 

Potassium chloride actually has the same stnicture as sodium chloride, but, because the atomic scattering factors of potassium and chlorine are almost equal, the reflections with the indices all odd are extremely weak, and could easily have been missed in the early experiments. The zincblende fonn of zinc sulphide, by contrast, has the same pattern of all odd and all even indices, but the pattern of intensities is different. This pattern is consistent with a model that again has zinc atoms at the comers and tlie face centres, but the sulphur positions are displaced by a quarter of tlie body diagonal from the zinc positions. 

Johnstone (2000) emphasises the importance of beginning with the macro and symbolic levels (Fig. 8.3) because both comers of the triangle are vistrahsable and can be made concrete with models (p. 12). The strb-micro level, by far the most difficult (Nelson, 2002), is described by the atomic theory of matter, in terms of particles such as electrorrs, atoms and molecules. It is commorrly referred to as the molecular level. Johnstone (2000) describes this level simirltaneorrsly as the strength and weakness of the subject of cherrristry it provides strength through the intellectual basis for chemical explanatiorrs, but it also presents a weakness when novice students try to learn and rmderstand it. 

H2 adsorption is weak on the anatase surfaces [8], No dissociative adsorption of H2 takes place over the smooth surfaces of Au at temperatures below 473 K [9,10]. On small Au particles, adsorption is possible at low temperature. Dissociative adsorption of H2 can be accelerated by the negatively charged molecular oxygen species at steps, edges, comers of Au particles [5]. 

D flows and time-dependent 2D flows, and mixes the fluid by continuously stretching different volumes of the fluid and folding them into one another. In a qualitative sense, the path taken by a given fluid element in the flow depends in a sensitive way on its encounters with a series of weak secondary flows or eddies, present even at low Re in the comers of channels, which transport the element across the flow [167],... 

The transition-metal monopnictides MPn with the MnP-type structure discussed above contain strong M-M and weak Pn-Pn bonds. Compounds richer in Pn can also be examined by XPS, such as the binary skutterudites MPn , (M = Co, Rh, Ir Pn = P, As, Sb), which contain strong Pn-Pn bonds but no M-M bonds [79,80], The cubic crystal structure consists of a network of comer-sharing M-centred octa-hedra, which are tilted to form nearly square Pnn rings creating large dodecahedral voids [81]. These voids can be filled with rare-earth atoms to form ternary variants REM Pnn (RE = rare earth M = Fe, Ru, Os Pn = P, As, Sb) (Fig. 26) [81,82], the antimonides being of interest as thermoelectric materials [83]. 

Fig. 22 (a) Model system able to perform six different logic functions depending on its structural parameters e and k. Current intensity passing through this system for e = k = 0 eV, v = 5 meV, and a and [1 going from 0 to 1 eV. The variation of the current respects the XOR truth table a strong current is obtained for = 0=1 and =1 = 0 and a weak one for = 0 = 0 and =1 = 1. Due to the stable plateaux at the comers of the map, this device naturally corrects small deviations in the inputs that lead to even smaller deviations in the output... 

Ions with large charges generally yield weak electrolytes, so the numbers of ions in solution are often smaller than predicted. For this reason, values of I calculated for salts represented by the bottom right-hand comer of Table 7.5 might be too high. 

In the Linnett, weak-field model of an octet, the spin-densities off opposite comers of the octet are of opposite signs, Fig. 32. This suggests that two, identical magnetic ions coordinated colinearly by an oxide ion might be coupled antiferromagnetically, Fig. 33, as, in fact, has been... 

Differences in Pt-H bond strength may result from several reasons. First, the metal clusters in a heterogeneous catalyst are small and therefore contain only small crystal surfaces and many edges and corners. The atoms on the corners and edges are coordinatively highly unsaturated and therefore will bond strongly to H atoms. So the strongest bonded H atoms may be the H atoms that are chemisorbed on the corners of the clusters. After saturation of the cluster with a monolayer of H, these comer-atoms will still be relatively unsaturated and can bond to yet another H atom. This H however will be bonded rather weakly. 

Pt-Pt coordination number N = 4-6) Pt particles have many edges, so there are significant amounts of both types of H. Thus it is likely that the so-called weakly adsorbed H corresponds to H adsorbed on the flat faces of the cluster, and that the strongly adsorbed H is chemisorbed near the edges and comers of the metal particles. 

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