摘要:

Methods are suggested for calculating kinetic parameters of moderately rapid redox reactions from current–potential curves obtained with (a) rotating electrodes or stationary electrodes in stirred solutions, (b) dropping mercury electrodes. Experimental results for the V2+/V3+reaction at a dropping mercury electrode are presented and compared with a-c. impedance measurements on the same system. It is found that there is a good agreement between the kinetic parameters obtained by the two methods when the current–potential curves are interpreted with the aid of Koutecky's theory of diffusion to a dropping mercury electrode.

ISSN:0008-4042    

DOI:10.1139/v59-031

出版商:NRC Research Press    

年代:1959

数据来源: NRC

摘要:

The polarographic behavior of the hexaaquochromium(III) and dichlorotetraaquochromium(III) ions was observed in the absence of maxima suppressors, and in the presence of various concentrations of perchloric acid, hydrochloric acid, and neutral salt. The polarographic waves obtained for each Cr(III) species in the different media were analyzed by plotting the function log[i/(id−i)] vs.E; the plots generally consist of two straight lines intersecting at about the half-wave potential and can best be explained by assuming two different concurrent mechanisms for the electron transfer process: the direct transfer of an electron to the Cr(III) ion from the electrode at the mercury–solution interface, and the transfer of an electron to Cr(III) from a Cr(II) ion produced at that interface. Only for the dichlorotetraaquochromium(III) ion in 12 MHCl does the direct transfer process appear to be dominant. Polarography of Cr(III) in the latter medium before and after reaction with the medium shows no change incorresponding to the shift observed in the ultraviolet spectra; this is accounted for by the "catalytic" degradation, i.e., the loss of chloride of the higher chloro complexes due to the rapid anion transfer mechanism for the electron transfer process between halo Cr(III) and Cr(II) ions.

ISSN:0008-4042    

DOI:10.1139/v59-032

出版商:NRC Research Press    

年代:1959

数据来源: NRC

摘要:

not available

ISSN:0008-4042    

DOI:10.1139/v59-033

出版商:NRC Research Press    

年代:1959

数据来源: NRC

摘要:

not available

ISSN:0008-4042    

DOI:10.1139/v59-034

出版商:NRC Research Press    

年代:1959

数据来源: NRC

摘要:

A study was made of the anodic passivation of iron in solutions of 0.1 Msodium sulphate at a pH of 3.0. A mass balance of iron equivalent to coulombs required for passivation and iron found in solution after passivation showed that approximately 0.002 coulomb/cm2is involved in the passive layer. À Flade arrest does not appear in decay traces of anodic potential unless a potential of at least 1.2 v (EH) is achieved on charging the electrode, indicating incomplete coverage by the passive layer below 1.2 v. Partial cathodic reduction followed by anodic reformation of the passive layer at the Flade arrest showed that the first charging current involved in reformation is highly efficient even when as much as 70% of the Flade arrest is reduced. These results support the view that only a fraction of the passive layer is represented by coulombs involved in the Flade arrest and that after partial reduction the remainder of the passive layer disintegrates spontaneously. Addition of chelating agents to the electrolyte has an adverse effect on passivation by chelation of ferrous ion.

ISSN:0008-4042    

DOI:10.1139/v59-035

出版商:NRC Research Press    

年代:1959

数据来源: NRC

摘要:

Various models are considered for the growth of anodic oxide films (metal ions mobile). In general, a transition is expected, as the thickness of the film is increased, from control by the metal/oxide interface (Cabrera and Mott) with very thin films to control by the movement of ions through the body of the film (Verwey), with the concentration of mobile ions taking up the value (p, say) which gives electroneutrality. The field strength only varies with thickness in the transition region of thickness. Dewald's theory is the special case ofpzero, which gives a field increasing continuously to infinite thickness. The high field production of Frenkel defects (with the vacant cation sites immobile and the interstitial ions mobile) as postulated by Bean, Fisher, and Vermilyea, and a slight mobility of oxygen ions are two processes which would allowpto vary with the field strength, and which would, therefore, give rise to "overshoot" in the transients in the field strength which occur when the applied current is suddenly changed. However, if the field strength is sufficiently great to produce Frenkel defects it would be expected to be sufficiently great to cause the vacancies to be mobile. This case is considered. Finally, it is noted that in an amorphous oxide it is difficult to maintain a distinction between lattice and interstitial ions, and, in fact, a range of site energies and jump distances would be expected. Some of the observed features (including "overshoot", and Tafel slope anomalies) of the kinetics for tantalum may, therefore, be due simply to the fact that the oxide is amorphous.

ISSN:0008-4042    

DOI:10.1139/v59-036

出版商:NRC Research Press    

年代:1959

数据来源: NRC

摘要:

A unified mechanism for the formation of passive films on iron in aqueous solutions is presented. The effects of water, oxygen, and oxidizing and non-oxidizing ions are considered. The γ-Fe2O3film is formed first by the oxidation of water-formed magnetite and further thickening of the film takes place by the oxidation of diffusing Fe++ion at the water surface of the oxide film. The main force leading to diffusion is the field set up by the adsorbed negative ion and the positive Fe++ions at the surface of the metal. Some of the properties of the protective γ-Fe2O3film and factors leading to its destruction are discussed.

ISSN:0008-4042    

DOI:10.1139/v59-037

出版商:NRC Research Press    

年代:1959

数据来源: NRC

摘要:

The nickel – nickel oxide electrode forms the positive plate in the charged nickel–cadmium battery. After "charging" the electrode to a chemical state represented by the non-structural formula NiOx, wherexcan vary from about 1.4 to 1.8 depending on the current density and temperature, loss of oxygen and a fall of potential on open circuit occurs. In the present work this "self-discharge" effect has been examined by study of (i) the rate of decay of e.m.f. on open circuit, (ii) rate of oxygen evolution on open circuit, (iii) the electrochemical capacity of the electrode, and (iv) the build-up or charging curves for the electrode. The decay behavior has been studied in aqueous KOH solutions from 0.0015 to 15 M. Tafel slopes are obtained from the plots of e.m.f. vs. log (time of decay), and abrupt changes occur at certain electrode potentials which indicate changes of rate-determining mechanism in the self-discharge process. The slopes observed are interpreted in terms of a new scheme of consecutive reactions for anodic oxygen evolution by deducing, by means of the Christiansen method, the relevant Tafel slopes. It is shown that the scheme proposed uniquely accounts for the experimental behavior and that the change of mechanism observed in the self-discharge can only be explained if two consecutive and not alternative processes are involved. The dependence of the rates of self-discharge upon OH−ion and water activity is deduced and the significance of these results is discussed.

ISSN:0008-4042    

DOI:10.1139/v59-038

出版商:NRC Research Press    

年代:1959

数据来源: NRC

摘要:

not available

ISSN:0008-4042    

DOI:10.1139/v59-039

出版商:NRC Research Press    

年代:1959

数据来源: NRC

摘要:

Direct measurement of the surface concentration Г of methylene blue, adsorbed from a phosphate buffer solution onto an ideally polarized mercury electrode, has produced a Lang-muir-type isotherm. The maximum value of Г, Гm, was found to be dependent on the potential applied (E). Surface tension measurements showed that the rate-controlling process is not diffusion, but, presumably, the exchange of methylene blue cation (MB+) with phosphate ions. A model for this process has been proposed. This allowed the calculation of the rate constant of adsorption (ka) from the surface tension values as a function of time (ka~ 5 × 10−5 cm/sec;dka/dE~ 30 × 10−5). There is some evidence for the occurrence of a consecutive process, most likely the combination of adsorbed MB+to dime

ISSN:0008-4042    

DOI:10.1139/v59-040

出版商:NRC Research Press    

年代:1959

数据来源: NRC