Noureddine Azzouz

Study of Rust Effect on the Corrosion Behavior of Reinforcement Steel Using Impedance Spectroscopy

Most studies on corrosion of steel reinforcement in concrete are conducted on steel samples with polished surface (free of all oxides) in order to reproduce the same experimental conditions. However, before embedding in concrete, the steel bars are often covered with natural oxides (rust), which are formed during exposure to the atmosphere. The presence of this rust may affect the electrochemical behavior of steel rebar in concrete. In order to understand the effect of rust on the corrosion behavior of reinforcement steel, potentiodynamic and electrochemical impedance spectroscopy (EIS) tests were carried out in a simulated concrete pore solution using steel samples with two different surface conditions: polished and rusted samples. The obtained results have shown that the presence of rust on the steel bar has a negative effect on its corrosion behavior, with or without the presence of chlorides. This detrimental effect can be explained by the fact that the rust provokes a decrease of the electrolyte resistance at the metal-concrete interface and reduces the repassivating ability. In addition, the rust layer acts as a barrier against the hydroxyl ion diffusion, which prevents the realkalinization phenomenon.

Inhibitive Effect of Molybdate Ions on the Electrochemical Behavior of Steel Rebar in Simulated Concrete Pore Solution

Several compounds tested as corrosion inhibitors have proven to possess good effectiveness in protection of steel rebar in concrete. However, most of them are considered as pollutant compounds, which limits their use. The aim of this work is to investigate the inhibitive effect of sodium molybdate, which is considered as a nonpollutant compound, against pitting corrosion of steel rebar in simulated concrete pore solution. Corrosion behaviors of steel in different solutions were studied by means of corrosion potential, potentiodynamic polarization, and electrochemical impedance spectroscopy. The results indicate that the addition of sodium molybdate to the chlorinated solution decreases significantly the corrosion rate of steel. Due to its passivating character, the sodium molybdate inhibitor promotes the formation of a stable passive layer on the surface of steel, acting as a physical barrier against chloride ions, on one hand, and consolidating the passivation mechanism of steel, on the other. The optimal inhibition rate is given by the concentration of molybdate ions, corresponding to a [MoO42−]/[Cl−] that is equal to 0.5.

Development and validation of a new sensor for methomyl detection

A new highly sensitive and selective voltammetric method for the determination of methomyl insecticide is reported. After alkaline hydrolysis of methomyl to its oxime, the ability of this insecticide to inhibit the electrocatalytic oxidation of its hydrolysis product at a copper oxide modified carbon paste electrode (Cu-CPE) was studied. The base signal was obtained by the electrocatalytic oxidation of a fix concentration of methomyl oxime (MO) at the studied modified electrode. All electrochemical measurements for optimization and evaluation of the developed sensor were performed using square wave voltammetry and cyclic voltammetry techniques. Under the optimized conditions, an excellent sensitivity and selectivity to methomyl in terms of inhibition percentage was obtained at Cu-CPE (50% CuO) with a low detection limit of about 0.02 μM and wide linear range from 0.086 to 16 μM. The new method was successfully used to determine methomyl concentration in ground water indicating that the developed method can be used for the monitoring of this pesticide.

Adsorptive removal of cadmium (II) using P. oceanica biomass: effect of NaCl concentration on equilibrium and kinetic parameters

Abstract In this study, biosorption of cadmium (II) from saline solutions by Posidonia oceanica (L.), a marine biomass, was studied as a function of pH, initial cadmium (II) and NaCl concentrations in a batch system. The sorbent exhibited the maximal cadmium (II) uptake at pH 6 in the absence and in the presence of increasing concentration of NaCl. Equilibrium uptake increased with the cadmium (II) concentration up to 250 mg/L and diminished considerably in the presence of increasing concentrations of salt up to 50 g/L. At 100 mg/L, initial cadmium (II) concentration, P. oceanica biosorbed 15.69 mg/g of cadmium (II) without salt medium. When NaCl concentration was raised to 50 g/L, this value dropped to 6.87 mg/g of cadmium (II) at the same conditions resulting in 56.21% decrease in biosorption capacity. The equilibrium sorption data were analysed by using Freundlich, Langmuir and Redlich–peterson models. Langmuir was the most suitable adsorption model for describing the biosorption equilibrium data of ca...

Infrared Spectroscopic Study of the Thermo-Oxidative Aging of Polyethylene Containing Pro-Oxidant

Synthetic polymers are not normally biodegradable until they are degraded into low molecular mass species that can be assimilated by microorganisms. This means that biodegradation must be preceded by an abiotic degradation that produces monomeric and oligomeric products. It has been shown that carboxylic acids, alcohols, ketones, etc... can be utilized by microorganisms as nutrients to produce cell biomass. Polyethylene is resistant to oxidation and biodegradation because of the presence of antioxidants and stabilizers. However, it can be made oxo-biodegradable by the use of prooxidant additives. The most active prooxidants are those based on transition metal particulary Fe, Co and Mn. This study is an attempt to investigate the effect of prooxidant additives on the thermo-oxidation of polyethylene. Three differentes mulch films of polyethylene, two films with prooxidant additives consisting of salt based on cobalt and iron and the third film whitout prooxidant, were subjected to thermo-oxidative degradation which was conducted in an air oven at 70°C that normally occur during composting conditions, for extended time periods. Based on Fourier transform infrared spectroscopy the chemical and structural changes induced by this exposure were followed by monitoring the changes in carbonyl index and cristallinity. The results reveal an increase in the carbonyl groups with aging time more important for the polyehylene films containing a combination of Fe and Co additives than these obtained by the films with only one transition metal additive (Co) while the LDPE without additives represents no increase in carbonyl groups. The results show also a small variation of cristallinity for the two differents polyethylene films with pro-oxidant. This indicates that the transition metal prooxidant plays an important role in the degradation of PE films and accelerates the degradation of PE.

Regeneration of Peel of Peas (Pisum sativum) After Zinc Adsorption

The dissemination of heavy metals such as zinc in the environment caused a contamination of groundwater and rivers. In order to curb this phenomenon, it becomes essential to develop a method to remove these toxic materials. Among these techniques, we have adsorption on biosorbents; these materials are efficient, inexpensive, and abundant.