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The electron spin resonance spectra of CH3 and CD3 adsorbed on a silica gel surface at 77 OK are characterized by a marked dependence of the line width on nuclear spin quantum number. This dependence can be interpreted in terms of the tumbling of the radicals on the surface, anisotropies in the hyperfine and g tensors giving rise to a relaxation mechanism dependent on M I . A quantitative comparison of the spectra with the theory of this relaxation mechanism developed by McConnell, Kivelson, and Freed and Fraenkel enables the tumbling frequencies, 2.0 x 107 s-1 and 1.3 x 107 s-1 for CH3 and CD3 respectively, to be determined.Canadian Journal of Chemistry, 46, 207 (1968) IntroductionThe electron spin resonance detection of methyl radicals adsorbed on various surfaces has been reported in recent years (1-4). Like V02+, for example (5), these spectra are often characterized by a marked dependence of the line width on the nuclear spin quantum number MI. Although Kazanskii et al. (1) suggested that this dependence was due to a combination of spin-orbit relaxation and incomplete averaging of the anisotropic hyperfine interaction, this idea was not developed quantitatively.McConnell (6) first proposed a mechanism which could explain this phenomenon. He showed that the tumbling of a system with anisotropies in the hyperfine interaction and g tensors provided a relaxation mechanism dependent on MI. Refinements and extensions to McConnell's theory have been made by Kivelson (7) and more recently by Wilson and Kivelson (8). Freed and Fraenkel (9) have given a more general theory capable of treating systems with sets of equivalent nuclei. In this case the lines can consist of several degenerate components with possibly different widths.In the present work we apply this theory to the electron spin resonance (e.s.r.) spectrum of methyl radicals adsorbed on a silica gel surface and quantitatively interpret the dependence of line width on M,.

The behavior of individual positive and negative electrodes of the sintered‐plate nickel‐cadmium battery system in the presence of foreign ions in KOH solutions has been examined. Carbonate choke: The variation of electrochemical capacity as a function of carbonate contamination of the electrolyte, temperature, and current density was measured for both positive and negative electrodes. The effect of carbonate on the negative cadmium electrode is much greater than on the positive. The general mechanism and the role of intermediate complexes are discussed. Nitrate shuttle: Self‐discharge occurs in cells containing nitrate, as a result of reduction of NO3− to NO2− at the cadmium electrode with subsequent reoxidation to NO3− at the nickel hydroxide electrode. Cations on the positive: Addition of Li+, Ag+ Sb+3, Al+3, and As+3 to the electrolyte had effects on capacity and on charge‐retention of well‐formed nickel hydroxide positive electrodes. Lithium promoted the highest average oxidation, particularly at high temperatures (55°C). Arsenic was the best inhibitor of loss of charge. Possible mechanisms are discussed.

A kinetic study and a~ialysis has been n~acle of the effects of ionic strength. acid activity, temperature, and salt type on the dissolution of magnesium in acidic salt sol~~tions. This is an exanlple of the simplest type of corrosion involving hydrogen evolution. The results are interpreted in terms of the effects of the various factors on the structure of a surface film which must be nlagnesil~rn oxide and/or hydroxide even in acidic solutions. The importance of internal dissolutions in the film a t high concentrations of attacking reagent, for this a~~d other cases, is shown. Owing to co~nplex formation, under certain conclitions a n odd case of "chemical control" of the dissolution rate in this sirnplest case bccomcs evide~it. Corrosion pote~ltial measurements aid in the interpretation. INTRODUCTIONAccording to King and co-workers (12), who support a modification of the diffusion-layer theory originally due to Noyes and Whitney (IS), and Nernst (17), the experinlental support for probable diffusion control of the rate of dissolution of metals in acidic aqueous solutions rests on the following facts. For convenience these are reproduced in part from the recent paper by Roald and Beck (19).1. Different solids dissolve a t nearly the same rate in the same reagent under the same conditions.2. Increased stirring increases the rate. That the rate of dissolution in many cases is a linear function of linear velocity, except a t very low linear velocity, has been demonstrated for some cases by the data of Icing et al. 3. The rate of dissolution has been found for many cases t o be nearly inversely proportional to the viscosity of the solution for a number of solutions.4. The rates of dissolution in acid solutions seen1 to follow the diffusion coefficients of the acid through the solution, perhaps even more closely than they follow the acid strength.5. Temperature coefficients have been found by many i~lvestigators to be of the order usually associated with a co~ltrolling step which is some physical transport process. Temperature coefficients are usually of the order of 3000 t o 5000 cal./mole. I t should be noted that these criteria-do not eliminate all but diffusion control. These criteria could apply equally well to ally type of Inass transfer step which is part of the dissolution process. T h a t the rates follow roughly the diffusion coefficients of the acid through the solution indicates t h a t the control of the process is related in some manner to the physical structure of the solutions. However, the rate of dissolution might well be controlled by any physical step whose rate, in turn, is depencle~lt upon the changing structul-e of the surface film. Each of the criteria listed above refers indirectly to the effects produced by changes in the properties of this surface layer. For instance, King and Cathcart (11) measured ( a ) the diffusion coefficient of the acid, and (b) the rates of dissolution of niagnesium in a series of solutions. 'l'he diffusion coefficients of the acids in the bulk solution wer...

Centre de recherches pour la difense, Ottawa, Canada Repu le 31 aoct 19703Les mCtaphosphates fondus et dkshydrates ne rkagissent pas avec le platine et le quartz A 650 "C; il a donc Ct C possible d'etudier en detail les processus chimiques et Clectrochimiques d'abord avec des electrodes de platine puis ensuite avec des Clectrodes de nickel. Des Ctudes ont aussi Ct C faites avec les mttaux suivants: Fe, Cu, Ca, Ag.Le degagement anodique d'oxyghe sur le platine a partir du mCtaphosphate de sodium fondu laisse voir un hystCrCsis dans la courbe V/I et un comportement Tafel (dq/d log i = 2.3RTlDnF) d'une exactitude surprenante impliquant que la dtcharge lente d'un Clectron dCtermine la vitesse de reaction sur un domaine Ctendu de vitesses. Le processus cathodique est complexe et le dCpbt contient du sodium 616-mentaire dans le platine.Le phosphure de nickel NilZPS prCdomine comme produit d'autocorrosion sur le Ni. Ce produit est rCduit activement s'il est couplC electrochimiquement avec le Ca, et de la mCme fapon est activement oxyde par 0,. L'Clectrolyse pousske introduit du nickel supplementaire a I'anode ou du phosphore a la cathode et modifie la structure cristalline du produit.Les rCsultats de I'analyse thermique diffkrentielle (ATD), de I'analyse par spectroscopie r.m.n.-phosphore et de la solubilitC du sel rCsiduel dans I'eau dCmontrent que la structure trimCrique du sel fondu est modifiCe par I'tlectrolyse. L'anolyte diff6re du catholyte. Le sel fondu ClectrolysC prCsente une conduction ionique et Clectronique a 650 "C mais les facteurs de transport Clectronique semblent Ctre dCtermints par un processus d'injection a la cathode. Interest in the possible use of molten metaphosphates as electrolyte and as reactant in electrochemical cells has been examined from the points of view of both electrochemical synthesis and sources of electrical energy. Both are shown to be possible.The anodic evolution of 0, from carefully dried molten NaP0, on Pt shows hysteresis in the V/I curve, and also shows Tafel behavior (dq/d log i = 2.3RTlDnF) with surprising exactness, which implicates one-electron slow discharge as rate-determining over a considerable range of rate of reaction. The cathodic process is complex, but includes deposition of Na into the Pt if the melt is dry.On Ni the phosphide NiIzP, predominates as the autocorrosion product. This material is actively reduced if electrochemically coupled with Ca, and can be electrochemically oxidized by 02. Forced electrolysis inserts extra nickel into a phosphide anode, or phosphorus into a phosphide cathode, and modifies its crystal structure. The trimeric structure of the melt is modified by electrolysis, as shown by DTA tracings, by phosphorus-n.m.r. spectra, by changes of color and of solubility of the products in water. Anolyte product differs from catholyte product. The electrolyzed melt can leak charge both electronically and electrolytically at 650 "C, but electronic transport is tenuous and seems to be determined by an injection process at the cathode. Reactions and ...