I. A. Ammar

Anodic oxide film on antimony: II. Parameters of film growth and dissolution kinetics in neutral and alkaline media

Summary Growth of the anodic oxide film on Sb has been studied in Na2SO4, NaCl, K2CO3, Na3PO4 and NaOH solutions. Anodization gives linear potential/time relations (up to 50–60 V) in both sulphate and chloride solutions, particularly at relatively high cds. In alkaline solutions, however, active dissolution occurs before oxide growth. The latter is characterized by two regions in the anodic charging curve. The mechanism of dissolution is discussed on the basis of the experimental Tafel slope (23–27 mV). The results indicate that the formation of HSbO2 (soluble meta-antimonious acid or passivating surface oxide SbO·OH) is rate-determining. Oxide growth follows the exponential law in all solutions. The parameters of film formation are recorded. The results are explained on the basis of (i) oxide contamination by anions and (ii) partial dissolution of the anode film. Dielectric breakdown by sparking occurs in sulphate solutions only, at 95–96 V.

Behaviour of bismuth as valve metal in phosphate, borate, benzoate, and tartrate solutions

Summary Anodization of Bi has been studied in 0.05 M solutions of H3PO4, NaH2PO4, Na2HPO4, Na3PO4, ammonium borate, benzoate, and tartrate at 30°C using the galvanostatic technique. In all phosphate solutions, borate, and benzoate, the anodic reaction is mainly the growth of anode film to potentials above 100 V. Both anodic dissolution and film growth occur in tartrate solutions. The ionic conduction within the oxide phase follows the high field approximation for all results. The kinetic parameters for anodic oxidation are recorded, and their dependence on the nature of electrolyte is discussed. Evidence is provided in support of the Verwey model. The effect of electrolyte concentration on the oxide formation rate has been investigated. The results show that film growth is influenced by both the pH of solution and the degree of contamination by anions. Dielectric breakdown commences at 120–130 V (NHS) for all electrolytes, and is associated with oscillations, gas evolution, and finally sparking.

A review on the electrochemistry of tin

Abstract The recent literature on the electrochemistry of tin has been reviewed since 1970. In order to avoid unnecessary length, only papers which contain significant contributions are included. The review has been written in a bibliographical manner, and papers are arranged chronologically in each section. In this manner, the reader can follow the developments in each section as new techniques and new ideas are introduced, and can easily draw conclusions regarding the agreement and contradictions between the results of various authors. Furthermore, he has the liberty of formulating plans for future research, without being biased by the reviewers personal opinions. The contents of this review have been classified into twelve sections: 1. (1) Anodic dissolution of Sn and tinplate. 2. (2) Corrosion of Sn and tinplate. 3. (3) Passivity and anodic passivation of Sn, tin alloys, and tinplate. 4. (4) Cathodic passivation in dichromate. 5. (5) Electrodeposition (electroplating) of Sn and Sn alloys. 6. (6) Electrochemical properties of electroplated Sn alloys. 7. (7) Semi-conducting properties of SnO 2 . 8. (8) Some industrial aspects of tinplate. 9. (9) Cathodic processes. 10. (10) Electron transfer studies between soluble Sn species. 11. (11) Photo-effects. 12. (12) Miscellaneous studies. Each section written as concisely as possible, and 190 references are included.

Kinetics of the ferro—ferricyanide electron transfer reaction on anodically formed tin oxide

Abstract The kinetics of electron transfer reaction across a layer of tin oxide formed on tin electrodes were measured in borate buffer pH = 8. The effect of concentration of the redox system, Fe(CN)3−6/Fe(CN)4−6, on the rate of the process and also the effect of oxide thickness were measured by cathodic and anodic polarization curves. A reaction order of 0.7 with respect to the redox system was found. An exponential dependence of the exchange c.d, i0, on film thickness was interpreted on the basis of direct tunnelling through the oxide. Thick films formed at potentials within the O2-evolution range showed increase of i0 as function of film thickness.

Cathodic hydrogen evolution on tungsten significance of the dual tafel slopes

Summary Cathodic polarization has been measured on W in acid (HCl, H 2 SO 4 , H 3 PO 4 ), neutral (KCl, Na 2 SO 4 , KNO 3 ) and alkaline (NaOH, Na 3 PO 4 , Na 2 CO 3 ) solutions in the current density range 5×10 −9 −10 −2 A cm −2 at 30°C. Two Tafel slopes have been observed on W metal and on anodized surfaces in all solutions. The effects of: (i) temperature (30–60°C) in 0.05 M H 2 SO 4 , (ii) excess neutral salts (KCl, Na 2 SO 4 ) at constant acid concentration (0.1 M HCl, 0.05 M H 2 SO 4 ), (iii) acid concentration (0.0005–0.05 M H 2 SO 4 ) in solutions saturated with salts, and (iv) alkali concentration (0.1–10 M NaOH), have been studied. Of the various possibilities considered for interpretation of the dual Tafel slopes, it appears that the dual barrier model for electrochemical reduction processes on thin oxide films is the most probable explanation.