Electrochemical Behaviour of Cobalt in NaOH Solutions

1994 ◽  
Vol 59 (11) ◽  
pp. 2383-2389 ◽  
Author(s):  
Sayed S. Abd El Rehim ◽  
Ahmed A. El Basosi ◽  
Salah M. El Zein ◽  
Magda M. Osman
Keyword(s):  
Cyclic Voltammetry ◽  
Passive Film ◽  
Polarization Curve ◽  
Anodic Polarization ◽  
Electrochemical Behaviour ◽  
Anodic Polarization Curve ◽  
Potential Region ◽  
Voltammetric Techniques ◽  
Scan Rate ◽  
Reverse Scan

The electrochemical behaviour of cobalt in 0.001 - 1 M NaOH was investigated by voltammetric techniques coupled with ESCA examination. The anodic polarization curve exhibits a well defined peak which corresponds to the formation of Co(OH)2 or CoO. Further peaks in the transpassive potential region correspond to the electrooxidation of Co(II) species to Co3O4 and CoOOH, respectively. The heights of the anodic peaks increase with the increase of NaOH concentration, temperature and scan rate. In cyclic voltammetry, the reverse scan consistently shows three cathodic peaks which are ascribed to the reduction of CoOOH, Co3O4 and CoO oxides, respectively. ESCA examination confirmed the presence of these oxides in the passive film.

scholarly journals Electrode processes during electrodeposition, electropolishing and oxidation of niobium

2021 ◽  
Vol 12 (2-2021) ◽  
pp. 192-196
Author(s):  
M. A. Okunev ◽  
◽  
S. A. Kuznetsov ◽  
Keyword(s):  
Cyclic Voltammetry ◽  
Formation Mechanism ◽  
Polarization Curve ◽  
Anodic Polarization ◽  
Film Formation ◽  
Anodic Polarization Curve ◽  
Niobium Pentoxide ◽  
Potential Range ◽  
Electrode Processes ◽  
Film Formation Mechanism

The electrode processes occurring during the electrodeposition, electropolishing and oxidation of niobium are considered. The discharge of Nb(IV) complexes during Nb electrodeposition was studied by cyclic voltammetry. The anodic polarization curve on niobium in a mixture of acids H2SO4:HF (9:1) was obtained by chronopotentiometry method, the potential range at which the highest quality and speed of electropolishing is achieved was found. The film formation mechanism of niobium pentoxide Nb2O5 on niobium was studied by cyclic voltammetry.

Effect of Nitrite Ions on Polarization Behavior of Steel Immersed in Simulated Concrete Pore Environments

2013 ◽  
Vol 368-370 ◽  
pp. 919-924
Author(s):  
Zhong Lu Cao ◽  
Makoto Hibino ◽  
Hiroki Goda
Keyword(s):  
Polarization Curve ◽  
Current Density ◽  
Linear Polarization ◽  
Anodic Polarization ◽  
Cathodic Polarization ◽  
Corrosion Current ◽  
Anodic Polarization Curve ◽  
Polarization Curves ◽  
Passive State ◽  
Nitrite Concentration

The influence of nitrite concentration on the linear polarization curves of steel, Tafel slope and Stern-Geary constant B have been investigated in three different pH environments simulating the highly alkaline environment, carbonated environment and neutral environment that really existed on the surface of steel in concrete. The results indicate that when the steel is in passive state, the presence of nitrite has little influence on anodic/cathodic polarization curves and Stern-Geary constant B; but when the steel is corroded, the presence of nitrite not only reduces the current density of anodic polarization curve but also decreases the value of Stern-Geary constant B. If this influence is not considered in practical corrosion measurement, the corrosion current will be overestimated.

scholarly journals Electrochemical characterization of the passive films formed on niobium surfaces in H2SO4 solutions

2006 ◽  
Vol 71 (2) ◽  
pp. 177-187 ◽  
Author(s):  
Irena Arsova ◽  
Abdurauf Prusi ◽  
Toma Grcev ◽  
Ljubomir Arsov
Keyword(s):  
Cyclic Voltammetry ◽  
Passive Film ◽  
Chemical Structure ◽  
Open Circuit ◽  
Passive Films ◽  
Anodic Films ◽  
Potential Region ◽  
Passive Transition ◽  
Cyclic Voltammetry Data

The electrochemical formation and characteristics of passive films on niobium surfaces in aqueous H2SO4 solutions were studied using open circuit potential and cyclic voltammetry. In the potential region between -1.0 and 1.2 V(NHE), the cyclic voltammetry data showed that the active/passive transition involves slow metal dissolution followed by the formation of semiconducting passive oxide films. The possible electrochemical reactions and the change of the oxidation steps of some niobium oxides occurring in the passive film during the polarization are proposed. A strong influence of the natural air-formed oxide film on the chemical composition of the passive film was shown. This influence makes chemical structure of thin passive films more complicated than that of thick anodic films. It is shown that the passive films consists of more or less stable oxides, such as NbO, NbO2 and Nb2O5. The Raman spectra revealed that the thin passive films were amorphous, while the films formed at higher voltages consist, primarily, of well-crystallized Nb2O5.

scholarly journals Effects of Bicarbonate Ion and Silica on Anodic Polarization Curve of Carbon Steel

2004 ◽  
Vol 53 (9) ◽  
pp. 434-439 ◽  
Author(s):  
Masayuki Itagaki ◽  
Yoshinobu Yamada ◽  
Kunihiro Watanabe ◽  
Takahiro Nukaga ◽  
Fumio Umemura
Keyword(s):  
Carbon Steel ◽  
Polarization Curve ◽  
Anodic Polarization ◽  
Anodic Polarization Curve

Effects of Foreign Metals on Corrosion of Titanium In Boiling 2M Hydrochloric Acid

CORROSION ◽  
1959 ◽  
Vol 15 (11) ◽  
pp. 26-30 ◽  
Author(s):  
ROGER BUCK ◽  
BILLY W. SLOOPE ◽  
HENRY LEIDHEISER
Keyword(s):  
Hydrochloric Acid ◽  
Corrosion Rate ◽  
Polarization Curve ◽  
Nickel Alloys ◽  
Anodic Polarization ◽  
Saturated Calomel Electrode ◽  
Anodic Polarization Curve ◽  
Cobalt Nickel ◽  
Metallic Cations ◽  
Made In

Abstract The rate of corrosion of titanium was determined in boiling 2M HC1 when contacted to aluminum, cadmium, tin, zirconium, lead, bismuth, mercury, silver, copper, antimony, vanadium, 70:30, 50:50 and 30:70 copper-nickel alloys, iron, palladium, cobalt, nickel, gold, rhodium, platinum and iridium. Less extensive corrosion measurements of the same type were also made in 0.6 and 2M H2SO4. The potentials of the couple and of the two members of the couple were determined in boiling 2M HC1 for 20 of the systems studied. A plot of the corrosion rate vs the couple potential yielded a polarization curve which was similar to the anodic polarization curve for titanium with an impressed voltage. The curve exhibited a maximum in corrosion rate at a couple potential of —0.49-volt vs the saturated calomel electrode. The potential of titanium in boiling 2 M HC1 was also determined as a function of concentration of the following metallic cations in the acid: copper, silver, antimony, nickel, gold, palladium, rhodium, platinum and iridium. The influence of the cations on the corrosion rate was explained in relation to the polarization curve. 6.3.15

Electrochemical behaviour of silver in aqueous chromate solutions

1998 ◽  
Vol 76 (8) ◽  
pp. 1156-1161 ◽  
Author(s):  
Sayed S Abd El Rehim ◽  
Magdy AM Ibrahim ◽  
Hamdy H Hassan ◽  
Mohammed A Amin
Keyword(s):  
Cyclic Voltammetry ◽  
Electrochemical Behaviour ◽  
Anode Surface ◽  
Cyclic Voltammograms ◽  
Oxidation Peak ◽  
Surface Layers ◽  
Compact Layer ◽  
X Ray ◽  
Solid Films ◽  
Scan Rate

The electrochemical behaviour of silver was studied under cyclic voltammetry and chronoamperometry conditions in aqueous K2CrO4 solutions. The forward cyclic voltammograms exhibited one oxidation peak, A1, due to the formation of Ag2CrO4. The height of the anodic peak, A1, increases with increasing chromate concentration, temperature, and scan rate. The solid films formed on the anode surface have been examined by X-ray diffractometry. The reverse voltammograms exhibited two reduction peaks, C1 and C2, indicating the formation of two distinct surface layers of Ag2CrO4, an inner compact layer reduced in peak C1 and an outer powdery layer reduced in peak C2.Key words: silver electrode, cyclic voltammetry, K2CrO4 solutions.

Sulfates in the Passive Iron Layer

CORROSION ◽  
1964 ◽  
Vol 20 (9) ◽  
pp. 275t-281t ◽  
Author(s):  
O. L. RIGGS
Keyword(s):  
Steady State ◽  
Polarization Curve ◽  
Anodic Polarization ◽  
Saturated Calomel Electrode ◽  
Anodic Polarization Curve ◽  
Iron Layer ◽  
Chemical Compositions ◽  
X Ray Diffraction ◽  
Polarization Data ◽  
X Ray

Abstract Anodic polarization data were obtained on iron in 20 N H2SO4 at 25 C (77 F). Along the polarization curve, the potential was held constant at 20 mv increments and the current was recorded at the end of 60 minutes. Minimum currents, the average of four experiments, were noted at 260, 520, 810, 1060, 1320 and 1600 mv noble potential with reference to the saturated calomel electrode (S.C.E.). The various chemical compositions were identified with reproducible X-ray diffraction data. A technique involving an ethyl alcohol rinse permitted the X-ray study of the passive surface. The passive iron layer was identified as FeSO4.H2O, Fe2(SO4)3 H2O,FeSO4.4H2O and as FeSO4.7H2O at 260, 520, 810 and 1320 mv noble to S.C.E., respectively. The structures were reported to be responsible for the steady-state minimum currents. The X-ray diffraction values of the specimens held at 1060 and 1600 mv (S.C.E.) were not identified. The anodic polarization curve was discussed in terms of specific electrochemical events.

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