Electrochemical corrosion behavior of magnesium and titanium alloys in simulated body fluid

The electrochemical behavior of AZ91D and Ti–6Al–4V alloys was investigated in simulated body fluid (SBF) at 37 °C. The aim of the present study was to evaluate their corrosion performance through the analysis of corrosion resistance variation with time, using electrochemical impedance spectroscopy (EIS) tests and corrosion current density using potentiodynamic polarization measurements. Very low current density was obtained for Ti–6Al–4V alloy compared to that of AZ91D alloy, indicating a typical passive behavior for Ti alloy. EIS results exhibited high corrosion resistance indicating a highly stable film on titanium alloy compared to magnesium alloy in SBF.     

Influence of halides on the dissolution and passivation behavior of AZ91D magnesium alloy in aqueous solutions

The electrochemical behavior of AZ91D in various aqueous sodium halide solutions was investigated using open-circuit potential (E_oc), potentiodynamic polarization and ac impedance (EIS) techniques. Generally, the results reveal that during immersion a protective layer of a salt film is formed on the alloy surface whose passivation performance depends on the halide nature, its concentration and temperature. E_oc shifts positively with time until attaining a steady (E_st) value, which becomes less noble with increasing concentration or temperature of the test solution. At any given conditions, self-passivation was found to be favored in the order F⁻ > I⁻ > Br⁻ > Cl⁻. This sequence is consistent with that for surface film resistance (R_T) and its relative thickness (1/C_T). Nevertheless, in F⁻ medium each of the above parameters increases with [F⁻] up to a critical value of 0.3 M then decreases. Increasing concentration above 0.3 M induces large change in the microstructure of the outermost layer of the fluorinated extremely protective film and depassivation behavior predominates. In Br⁻ and I⁻ solutions, as well as the lower Cl⁻ concentrations (≤0.01 M), AZ91D exhibits pseudo-passive state over the polarization range from the corrosion potential (E_corr) to the knee point (E_pt) in the anodic scan, at which passivity breakdown occurs with rapid increase in the anodic current and hydrogen gas reaction. At Cl⁻ concentrations >0.01 M the negative difference effect (NDE) occurs under cathodic polarization where E_pt lies negative to E_corr. Addition of F⁻ to the Cl⁻ solution can induce large changes in the behavior of AZ91D. Equal concentration addition (1:1) produces the highest propensity of the surface to form passivating layer that can afford better protection.     

Electrochemical determination of niobium cathode as an efficient electrocatalyst for hydrogen generation in acidic media

Hydrogen gas (H₂) is notified as a renewable energy carrier. It is wanted to discover a low-cost electrocatalyst for the hydrogen evolution reaction (HER) to substitute the high-cost Pt in electrolysis cell. Niobium electrocatalyst nominated to substitute noble materials for electrocatalytic H₂ production and its electrochemical manner was estimated in H₂SO₄ acid of various concentrations utilizing a steady-state polarization and electrochemical impedance spectroscopy (EIS). The influences of acid concentration, cathodic potential and temperature on the H₂ creation were examined. The outcomes display that HER on Nb electrode proceeds by the Volmer-Heyrovsky mechanism. EIS tests, under open circuit and under cathodic polarization, were performed and the fitting has been done utilizing a suggested model for the electrode/electrolyte interface. Apparent activation energies (E_a) were estimated to be ca. 10.5 kJ mol^?1 for the HER on Nb. Thus, Nb is a good electrocatalyst for the cathodic H₂ manufacturing.     

Electrochemical behaviour of passive films on molybdenum-containing austenitic stainless steels in aqueous solutions

Passivation and its breakdown reactions have been studied on Mo-containing stainless steel specimens using different electrochemical techniques. Mo-containing stainless steel specimens were polarized in both naturally aerated NaCl and Na₂SO₄ solutions of different concentrations at 25 ± 0.2 °C between −1000 and 1500 mV versus saturated calomel electrode (SCE). The results of potentiodynamic polarization showed that i_corr and i_c increases with increasing either Cl⁻ or SO₄²⁻ concentration indicating the decrease in passivity of the formed film. EIS measurements under open circuit conditions confirmed that the passivity of the film decrease with increase in either Cl⁻ or SO₄²⁻ concentration.     

Comparative studies of some local oil seeds and seed cakes

A survey on the chemical constituents (protein, fat, carbohydrates, ash, fibre, calcium, phosphorus, iron) of 4 seeds and their cakes was done. These seeds are safflower seed (Carthamus tinctorius variety Giza 1), sunflower seeds (Helianthus annuus variety Giza 1), linseeds (Linum usitatissimum variety Giza 4) and imported rape seeds (Brassica napus Erglue). Caloric value of these seeds and seed cakes was calculated, PER, NPR and NPU were determined. No great variation was found with respect to the moisture content. The 4 seeds are rich in protein and fat. The ash content varies from (5.11 ± 0.26)% to (3.17 ± 0.13)%. The fiber content was low in both safflower and sunflower seeds and higher in both linseeds and rape seeds. The caloric values of the different seeds were very close. The seeds were found to be rich in phosphorus and low in calcium and contain considerable amounts of iron. The average PER values were 1.51, 1.61, 1.59, 1.84 and 2.50 for safflower seed cake, sunflower seed cake, linseed cake, rape seed cake and casein diet respectively. The average NPR was 3.11, 2.84, 2.84, 3.05 and 3.53 for safflower seed cake, sunflower seed cake, linseed cake, rape seed cake and casein respectively. The NPU values of the seed meals were 48.5, 49.3, 47.4 and 93.6 compared with 67.8 for casein. Using the different criteria (PER, NPR and NPU), it was clear that the protein quality of sunflower seed is very close to that of the linseed. Comparing the protein quality of safflower seed with those of both sunflower and linseed, NPU was in the same range, while PER was somewhat lower and NPR was higher than those of safflower and sunflower seed.     

Physical and magnetic properties of iron oxide nanoparticles with a different molar ratio of ferrous and ferric

The magnetite (Fe₃O₄) nanoparticles were synthesized with the same reaction conditions like co-precipitation method, molar ratio, and raw materials, but their magnetization values were not the same. This due to the change of some properties of ferrous oxide (Fs) nanoparticles when exposed it to the air. So this work suggested the core-shell design of magnetite nanoparticles (MA), this core-shell was prepared from ferric oxide (Fc) nanoparticles coated with sheets from ferrous oxides (Fs). The magnetic properties of iron oxide nanoparticles with different molar ratios of ferrous and ferric were studied via co-precipitation with NaOH. The crystallographic and phase structure of prepared iron oxides nanoparticles were investigated by employing Wide angle X-ray diffraction (WAXD), Particle size and zeta potential, Vibrating Sample Magnetometer (VSM), X-ray fluorescence (XRF), Fourier transforms infrared spectroscopy (FTIR) and High resolution transmission electron microscopy (HR-TEM). The changed magnetic moment of iron oxide nanoparticles was attributed to the presence of different a concentration of manganese atoms.     

Investigation on the corrosion and hydrogen evolution for AZ91D magnesium alloy in single and anion-containing oxalate solutions

Corrosion characterization of AZ91D alloy was studied in aqueous sodium oxalate solutions with various concentrations using different electrochemical techniques (open circuit potential, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV)). The corrosion rate and consequently the rate and extent of hydrogen evolution were found to increase significantly with increasing oxalate anion concentration and temperature or with decreasing the pH of solution. Increasing additions of various anions over the lower concentration range (0.001-1.0 mM) in the blank oxalate solution increases to a varying extent the corrosion rate of the alloy and hence increases the hydrogen evolution rate and decreases surface film stability in the following order Cl⁻ > SO₄²⁻ > F⁻. On the other hand, addition of phosphate anion exhibits a reverse trend, where the active corrosion rate decreases with increasing PO₄³⁻ anion concentration, implying that this anion acts as a passivator for AZ91D alloy. The obtained electrochemical results are further confirmed by scanning electron microscopy (SEM) analysis.     

Corrosion characterization of new tin-silver binary alloys in nitric acid solutions

Electrochemical techniques were used to characterize the corrosion behavior of four new binary alloys xSn-Ag (x = 26, 50, 70 and 96.5 wt%) alloys and their individual metal components in nitric acid solutions. The experimental data were collected by using open-circuit potential, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Over the concentration range studied (0.075-4.5 M), each of the two corrosion parameters (E_corr and i_corr) shows a regular dependency on both the alloy composition and the solution concentration. In general, for all studied samples, especially pure Ag and those with lower Sn contents (26 and 50 wt%), increasing the acid concentration increases i_corr, meanwhile causes a shift of the corresponding E_corr towards more positive values. This is probably due to the increase in the effect of cathodic depolarizer as the nitric acid concentration is increased. EIS results at the free corrosion potential confirmed well this behavior, where at concentrations ?1.5 M the thickness of the surface film increases while its resistance decreases with increasing tin wt%, indicating formation of less protective thicker film. However, at higher concentrations all samples exhibit identical behavior.     

Corrosion inhibition, hydrogen evolution and antibacterial properties of newly synthesized organic inhibitors on 316L stainless steel alloy in acid medium

Electrochemical corrosion behavior and hydrogen evolution reaction of 316L stainless steel has been investigated, in 0.5 M sulfuric acid solution containing four novel organic inhibitors as derivatives from one family, using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) measurements and surface examination via scanning electron microscope (SEM) technique. The effect of corrosion inhibitors on the hydrogen evolution reaction was related to the chemical composition, concentration and structure of the inhibitor. The inhibition efficiency, for active centers of the four used compounds, was found to increase in the order: -Cl < -Br < -CH₃ < -OCH₃. The corrosion rate and hydrogen evolution using the compound with methoxy group as a novel compound was found to increase with either increasing temperature or decreasing its concentration as observed by polarization technique and confirmed by EIS measurements. The compound with methoxy group (newly synthesized) has very good inhibition efficiency (IE) in 0.5 M sulfuric acid (98.3% for 1.0 mM concentration). EIS results were confirmed by surface examination. Also, antibacterial activity of these organic inhibitors was studied. The results showed that the highest inhibition efficiency was observed for the compound that posses the highest antibacterial activity.     

Supplementation of wheat flour with some local legumes

Egyptian bread made with broad bean flour, lentil flour, and wheat flour was scored for aroma, crust colour, crumb colour, texture, flavour and over-all acceptability by Egyptian judges. Protein quality of the bread was measured by a rat growth study. Analysis of variance for the data from the organoleptic evaluation was insignificant. The results indicate that broad bean flour could be added to wheat flour in making Egyptian Ballady bread up to 20% without affecting any of the tested characteristics. However, supplementation of wheat flour with more than 15% lentil flour might have some effect on flavour and hence on overall acceptability. The addition of 5, 10, 15 and 20% broad bean flour and lentil flour was accompained by an increase in the PER. It was clear that wheat flour supplemented with broad bean flour had a more pronounced effect on the PER at a 5 and 10% level of supplementation than that supplemented with lentil. The PER data were subjected to analysis of variance. At 1% level of significance the increase in PER for the 10, 15 and 20% broad bean breads was significant. Also the differences in the PERs between 5, 10 and 15% broad bean flour was significant. At 1% level of significance there was a significant difference in the PER values of bread made with 15 and 20% lentil flour. Incorporating broad bean flour into bread at a 20% level had a significant effect on the NPR at 1% and 5% level of significance. At 1% level of significance the only significant increase in NPR was noticed using the 20% level of lentil flour.