The 2101, 2205 and 2507 are duplex stainless steels. They have two phases: austenite and ferrite. The metallurgical characterization was performed by means of Scanning Electron Microscopy (SEM) with EDX and X-ray diffractometry (XRD). The corrosion behaviour was evaluated by potentiodynamic tests. The corrosion tests were conducted with the aid of potentiostat. The SEM and XRD revealed phases of austenite and ferrite without any intermetallic phase. The elemental analysis of the phases showed that the elements partitioned more into the phases that they promoted. The corrosion resistance of 2507 was higher than 2205 and 2101 as it may be seen on the polarization curves. Comparing the two media, the following relation to their corrosion resistance: 2507 > 2205 > 2101 was established.

Effect of ceramic powder coating on low carbon steel samples was presented. Electrostatic deposition method was used to produce ceramic coatings on low carbon steels. The coatings were fabricated over a range of temperatures (100˚C-400˚C). Detailed investigation on the corrosion behaviour, the hardness property and electrode potential of the fabricated and uncoated samples are reported. The ceramic materials used are locally available in Ondo-State Nigeria. The coating temperatures affect the rate of corrosion, the hardness property and the electrical resistivity of the coated steel sample. The sample coated at 300˚C with ceramic powder Y showed the best corrosion resistance in 0.5 M NaCl solution. The highest resistivity occurred in the sample coated at 300˚C with ceramic powder Z. All the samples coated with ceramic powder Y had better corrosion resistance in 0.5 M NaCl than the one coated by sample Z.

The 2205 duplex stainless steel and 316 austenitic stainless steels were studied in 1 M sulphuric acid and 1% NaCl solution. The microstructures of the specimens were investigated with scanning electron microscopy with energy dispersive X-ray analysis. X-ray Diffraction analysis was used for phase analysis. The electrochemical behaviour was evaluated using potentiodynamic method. The results show that the critical current density is higher for 316 austenitic stainless steels than 2205. The passive range was longer for 316 than 2205 at all the temperatures understudy. 2205 was found to have better corrosion resistance than 316.

Purpose This paper aims to investigate the stability of passive oxide film formed on the surface of 316L stainless steel in 3.5 Wt.% NaCl in the presence of two environmentally non-toxic inhibitors, i.e. leaf extracts of Musa spp. (MS) and Jatropha curcas (JC). Design/methodology/approach Current transients and potentiodynamic polarization curves were used to explain the stability of the passive film on Current transients and potentiodynamic polarization curves were used to explain the stability of the passive film on 316L stainless steel at both ambient temperature (25 °C) and 70 °C. For the potentiostatic tests, the coupons underwent cathodic stripping to remove the native oxide on their surfaces at −850 mV for 600 s, and a potential of 50 mV was imposed to observe the repassivation for 200 s. For the potentiodynamic tests, the pitting potential measured at 100 μA/cm2, corrosion potential and cathodic current density were obtained for analysis. Findings The current transients perfectly fitted into the exponential decay curve; i = is + ipeak exp(−t/τ), where the decay constant, τ measures the repassivating speed and extent to which the newly formed film heals and stabilizes. The current transients showed that MS and JC help in the repassivating process, especially at 300 ppm and 200 ppm, respectively, both at the lower temperature. The potentiodynamic curves mostly correlated with the current transients except for the hybrid inhibitor. The inhibitors increased the pitting potentials at concentrations that are correlated to their scanning electron micrograph images. Research limitations/implications Because they are cheap and environmentally friendly, plant extracts that are proven corrosion inhibitors could be used to aid the formation of passive film on passive alloys in not-so-aggressive environments. Practical implications Both MS and JC improve the film stability mostly at intermediate concentrations of 200 and 300 ppm, respectively, at ambient temperature and 70° C. Social implications Using leaf extracts of plants as green inhibitors is considered an environmentally friendly engineering solution. Originality/value The leaf extracts are a convenient resource of green inhibitors because their plants are readily available or could be easily naturalized, the processing technique to obtain the extracts is very cheap and the inhibitors are environmentally friendly. In addition, cathodic stripping exposes a relatively larger surface area than that obtained using the most common forms of depassivation; hence, the efficiency of the inhibitor in aiding the formation of the new oxide film to cover the bare surface would be better measured. There is very lean research data on the combined use of green inhibitors and cathodic stripping to study repassivating kinetics of passive alloys.

The research investigated the effect of silver nanoparticles on the corrosion behaviour of Mild steel and 316 Austenitic stainless steel in 0.5M H2SO4 using the potentiodynamic polarization method. The nanoparticles were synthesized from the sweet potato (Ipomoea batatas) plant extracts using Silver Nitrate (AgNO3) and were characterized using Atomic Adsorption Spectroscopy, Fourier Transform Infrared Spectroscopy and the Ultraviolet Visible Spectroscopy Technique. The AAS results showed that the plant extract is eco-friendly as it does not contain heavy metals. The FTIR results showed the different functional groups present in the extracts obtained from the different parts of the plant to be Alcohol O-H, Nitrile C≡N, Alkyne C≡C, Alkene C=C and Benzene Ring C=C. The UV-Vis results showed the presence of phenolic compound which aided inhibition. The results from the potentiodynamic polarization showed that the nanoparticle obtained from the leaf has the highest corrosion inhibition efficiency and the corrosion inhibition efficiency increases as the concentration of inhibitors increases.