Portugaliae
Electrochimica Acta

The present article considers an experimental study of tribo-corrosion behavior of electroless Ni–P coatings in alkaline environment sliding against alumina. The study of wear and friction behaviour is carried out using different load and sliding speed with the help of a pin-on-disk tribometer. The wear rate increases with decrease in sliding speed and increase in the applied load. The friction coefficient initially decreases with increase in the applied load and then remains at nearly steady level at higher applied load. Also, it is found that the friction coefficient is lower at higher sliding speed. The friction coefficient does not change with the sliding duration after the initial transient running-in time. The coating is characterized using scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis and X-ray diffraction (XRD) analysis. The wear mechanism is also studied and has been found to be mostly abrasive in nature.

The inhibitive effect of aqueous extract of leaves of Polyalthia longifolia on the corrosion of mild steel was studied using the gravimetric (weight loss) method at the temperatures 303 and 318 K. The results show that the aqueous extract of Polyalthia longifolia leaves inhibited the corrosion of mild steel in dilute H2SO4 solution. It was found that the inhibition efficiency increased with inhibitor concentration and decreased with rise in temperature. Values of the activation energy of the inhibited corrosion reaction range between 45.40 kJ/mol and 62.22 kJ/mol. This is much higher than the 25.74 kJ/mol obtained for the blank. The adsorption of the extract was spontaneous and occurs according to Flory-Huggins adsorption isotherm. The corrosion inhibition of Polyalthia longifolia leaves extract was attributed to the adsorption of phytochemical molecules present in the extract onto the surface of the mild steel. Physical adsorption mechanism has been proposed for the adsorption of the inhibitor.

An ion selective membrane sensor from dioctyl phthalate as a plasticizer in a polymeric matrix of polyvinyl chloride (PVC) and β-cyclodextrin as an ionophore was constructed and evaluated according to IUPAC recommendations. Linear Nernstian response of DPPH• within the concentration ranges of 10−6 to 10−2 mol L−1 was obtained with average recovery 99.87±0.617. Nernstian slope of 58.5 mV/decade with excellent selectivity over the pH range of 3-8 was observed. The suggested method was standardized using butylated hydroxyl anisole (BHA). The 50% radical scavenging activity (IC50) determined by the proposed sensor correlated well with that of the common spectrophotometric method based on scavenging of 2,2-diphenyl-1-picrylhydrazyl (DPPH•). An algorithm implemented in Microsoft Visual Basic® 6.0 was used for calculating (IC50) values which are 7.38 μg/mL ± 0.35, 89.98 μg/ mL ± 0.45 and 1.45 mg/ mL ± 1.50 for BHA, Paracetamol and Dipyridamole, respectively. The proposed sensor represents a simple and reproducible tool for measuring DPPH• scavenging activity of Paracetamol and Dipyridamole in bulk powder, pharmaceutical formulations and simulated intestinal fluid (SIF) without sophisticated separation techniques.

The inhibition effect of 2- amino, 5- ethyl- 1, 3, 4 thiadiazole (TTD) compound on the corrosion of type 304 stainless steel in 3 M H2SO4 test solution was investigated using potentiodynamic polarization, weight loss techniques and open circuit potential measurements. Results showed TTD to be very effective with an average inhibition efficiency of 98% from weight loss analysis and 87% from polarization test. Data from open circuit potential measurement are well within passivation potentials at specific concentrations of TTD. Scanning electron microscopy showed the effect of the inhibiting compound on the surface topography of the steel, while X - ray diffractometry determined the phase compounds formed on the surface due to inhibitor adhesion. Adsorption of the compound was determined to obey the Langmuir isotherm model. Thermodynamic calculations showed the inhibition process occurred through chemisorption mechanism and results from statistical analysis revealed the overwhelming influence of inhibitor concentration over exposure time on the inhibition performance of the compound.

Poly para aminophenol (PpAP)/Al2O3 composite was prepared by in situ chemical polymerization of para aminophenol using ammonium persulphate as an oxidizing agent in an aqueous medium containing anionic surfactants like DBSA (dodecyl benzene sulphonic acid) and SDS (sodium dodecyl sulphate) at 0 ˚C. The synthesized composites were characterized by UV–VIS-NIR spectroscopy, FTIR, XRD and TGA. The inhibiting effect of synthesized composites on the corrosion of mild steel in 1 M HCl solution has been investigated by different techniques like potentiodynamic polarization and electrochemical impedance spectroscopy methods for four different concentrations ranging from 50 to 300 mg/L. The results indicated that the corrosion inhibition efficiency increased on increasing composites concentration till 200 mg/L and decreased on further increasing concentration. It has been found that PpAP/Al2O3-DBSA has got higher corrosion protection efficiency than that of PpAP/ Al2O3-SDS. Polarization studies reveal that composites act as a mixed type corrosion inhibitor and adsorption follows Langmuir adsorption isotherm.