The electrochemical behavior of nickel, Inconel600, Incoloy800 and 316 stainless steel in different concentrations of HNO3 solutions was investigated using the cyclic voltammetry technique. . All the curves in the anodic cyclic voltammetry are characterized by an anodic dissolution peak (A) followed by a passive region (B), before oxygen evolution. On the other hand incoloy800and 316 stainless steel show an additional dissolution peak (C) and trans passive region followed by oxygen evolution. In the cathodic branch of the CVS there is one cathodic peak in the case of Ni. Inconel600 and Incoloy800.On the other hand, there is an unexpected peak in case of 316 stainless steel.This peak appeared on the anodic branch.All the anodic and cathodic peaks are interpreted. The passivation of Ni was explained based on the formation of NiO. In the alloys the passive layer was mainly composed of Ni+2, Fe+3and Cr+3 in Inconel600, Incoloy800, and Mo+6 in case of 316 stainless steel. The role of Cr+3 and Mo+6ions in the reinforcement of the passive film is explained.

The oxidation of isosorbide (S) by chromic acid (CrVI) has been studied in aqueous perchlorate solution at a constant ionic strength of 3.0 mol dm-3 and temperature of 25 C. The course of the reaction was followed spectrophotometrically. The reaction exhibited first-order dependence on [CrVI], less than unit order with respect to [S], and fractional-second-order dependence with respect to [H?]. Variation of the ionic strength or dielectric constant of the medium had no significant effects on the oxidation rate. Addition of MnII inhibited the oxidation rate. The oxidation product of isosorbide was identified as the corresponding monoketone derivative, namely (1S,4S,5R)- 4-hydroxy-2,6-dioxabicyclo[3.3.0] octan-8-one. A mechanism for the oxidation is proposed, and the corresponding rate-law expression has been deduced. The activation parameters associated with the second-order rate constant are presented and discussed

The effect of increasing the concentration of chloride ions as pitting corrosion agent on the potentiodynamic anodic polarization curves of nickel(Ni), Inconel 600, Incoloy 800 and 316 Stainless steel (SS) in 0.1M HNO3 solution at a scan rate 1.0 mV sec-1 was studied. The pitting corrosion potential varied with the logarithmic of the molar concentrations of chloride ions in case of Ni and Inconel 600 according to S-shaped curve. This behavior was explained according to re-passivation, propagation and continued propagation of the pits formed. In case of Incoloy 800 and 316SS a broken lines were observed according to re-passivation and propagation of the pits formed. It is found that,316SS is more resistance to pitting attack due to the presence of Mo in their chemical structure. The effect of the increasing concentration of some inorganic anions such as the sodium salts of chromate, tungstate, molybdate, phosphate dibasic and carbonate to inhibit the pitting corrosion was investigated. The values of the pitting corrosion potential were shifted to more positive values indicating the inhibiting action of these anions toward the pitting corrosion.

Kinetics of chromium(VI) oxidation of fluorene (Fl) and its halogenated derivatives, namely, 2,7-dichlorofluorene (Fl-Cl), 2,7-dibromofluorene (Fl-Br) and 2,7-diiodofluorene (Fl-I), in perchlorate solutions was investigated at a constant ionic strength of 2.0 mol dm3 and at 25 oC. The progress of the reactions was followed spectrophotometrically. The reactions showed a first order dependence on [Cr(VI)] and fractionalfirst order dependences with respect to hydrogen ion and fluorene derivatives concentrations. Under comparable experimental conditions, the order of the oxidation rates of the fluorene derivatives was: Fl > Fl-I > Fl-Br > Fl-Cl. The mechanism of the oxidation reactions was suggested and the rate-law expression was derived. Values of the rate constants of the slow step along with the equilibrium constants were calculated.

Oxidation kinetics of fluorene (Fl) and its halogenated derivatives, namely, 2,7-dichlorofluorene (Fl-Cl), 2,7-dibromofluorene (Fl-Br) and 2,7-diiodofluorene (Fl-I), by permanganate ion in both perchloric and sulfuric acid media have been investigated using conventional spectrophotometric technique. In both acidic media, the reactions manifested first order kineticsin [permanganate] and less than unit order each in [reductants] and [acid]. Increasing ionic strength had no effect on the oxidation rates. Oxidation rates of fluorenes in perchloric acid were higher than those in sulfuric acid and the order of the oxidation rates was: Fl > Fl-I > Fl-Br > Fl-Cl. Final oxidation products were identified by GC/MS and FT-IR analyses in all cases as 9H-fluorenone derivatives. Reaction constants as well as activation parameters of the second order rate constants were also evaluated

Kinetics of hexacyanoferrate (III) (HCF) oxidation of fluorene (Fl) in organic alkaline medium has been studied by spectrophotometric technique at a constant ionic strength of 0.15 mol dm-3 and at a temperature of 25°C. The reaction showed a first order kinetics with respect to [HCF] and fractional-first order dependences on both [Fl] and [OH- ]. The oxidation rate was increased with the increase in the ionic strength of the reaction medium. The oxidation mechanism was suggested which involves formation of a 1:1 intermediate complex between fluorene and HCF species in a pre-equilibrium step. The final oxidation product of fluorene was identified by spectroscopic and chemical tools as 9H-fluorenone. The appropriate rate law expression was deduced and the reaction constants involved in the mechanism were evaluated. The activation parameters of the rate constant of the slow step along with the thermodynamic quantities of the equilibrium constants were evaluated and discussed.

The electrochemical behavior of nickel, Inconel 600, Incoloy 800 and 316 stainless steel electrodes in different concentration of NaOH solution was investigated using the cyclic voltammetry technique (CV). All the curves in the anodic branch of the CV are characterized by anodic dissolution peak (A), passive region (B), anodic dissolution peak (C) before oxygen evolution. In the case of the cathodic branch of CV there is one reduction peak (D) in case of Ni electrode but there are two reduction peaks (D and E) in case of the three alloys used. All these peaks are explicated. The effect of chloride ion as a pitting agent on the cyclic voltammetry and the potentiodynamic anodic polarization of Ni ,Inconel 600, Incoloy 800 and 316 SS electrodes in NaOH solution was investigated. As the concentrations of the chloride ions increase the change of the amount of the anodic charge Δqa increases and the values of the pitting corrosion potential are shifted to the more negative direction indicating the breakdown of passivity and the imitation of the pitting corrosion. At one and the same Cl- ion concentration, the resistance to the pitting attack decreases in the following order: 316SS > Inconel 600 > Incoloy 800> 316 SS. This order depends on the chemical composition of these alloys.

The inhibiting power of three synthesized amino acids based-surfactant molecules, namely, sodium N-dodecyl asparagines (AS), sodium N-dodecylhistidine (HS) and sodium N-dodecyltryptophan (TS) on the dissolution of carbon steel was inspected in 0.5 M NaCl and 05 M NaOH solutions at 25 °C. The methods employed in this work were weight-loss (WL), potentiodynamic polarization (PP) and electrochemical impedance spectroscopy (EIS). The chemical structures of the synthesized surfactants were confirmed by FT-IR and 1 HNMR. The inhibition efficiencies were found to increase as the surfactants concentrations increase, while decreasing with increasing the concentration of the corrosive media (NaCl & NaOH) and temperature. Results obtained from the different techniques revealed that the inhibition efficiency of the compound TS was higher than those of both AS and HS. The inhibition efficiencies of the synthesized surfactants were declined in terms of strong adsorption of surfactants on the surface of carbon steel and forming a protective film and such adsorption was found to obey Langmuir isotherm. Both thermodynamic and kinetic parameters were evaluated which support the mechanism of physical adsorption of the inhibitors. The tested surfactants were found to act as mixed-type inhibitors with anodic predominance. The surface morphology of the carbon steel surface was examined by scanning electron microscopy (SEM). The inhibitory mechanism of carbon steel corrosion was suggested. Results obtained from all employed methods are consistent with each other

Three amino acids based-surfactants, namely, sodium N-dodecyl asparagines (AS), sodium N-dodecyl histidine (HS) and sodium N-dodecyl tryptophan (TS) were synthesized and were investigated as corrosion inhibitors for mild steel (ST-37-2) in 0.5 M HCl at 25 oC. The methods employed in this work were weight-loss (WL), potentiodynamic polarization (PP) and electrochemical impedance spectroscopy (EIS). The useful surface active properties of the synthesized surfactants were also evaluated. The inhibition efficiencies were found to increase with the inhibitor concentration, while decrease with increasing the concentration of hydrochloric acid and temperature. Results obtained from the different techniques revealed that the inhibition efficiency increases in the following sequence: AS < HS < TS. The high inhibition efficiencies of the synthesized surfactants were declined in terms of strong adsorption of the surfactant molecules on mild steel surface and forming a protective film separating the steel surface from the corrosive acid medium. The adsorption operation was found to obey Langmuir isotherm. Thermodynamic and kinetic parameters were evaluated by adsorption theory and kinetic equations which support the mechanism of physical adsorption of the inhibitors. The polarization measurements showed that the tested surfactant molecules act as mixed-type inhibitors with anodic predominance. The mechanism of inhibition of mild steel corrosion was also suggested. Results obtained from all employed methods are consistent with each others.

The inhibition of corrosion of mild steel in HCl in the presence of vanillin (van) coexisting with some amino acids, i.e., valine (val), cysteine (cys), methylcysteine hydrochloride (m-cys) and methionine (meth) are compared. The possible synergistic inhibition of the corrosion by these amino acids using vanillin are also examined. It has been found that the inhibition efficiency of the studied amino acids in HCl is arranged as follows; meth < m-cys < cys < val. In the presence of vanillin, the inhibition efficiencies are arranged as follows; m-cys < val < meth < cys. This arrangement of the inhibition efficiency is explained based on the possible synergistic adsorption of the studied amino acids with the pre-adsorbed chloride ions.