Austenitic stainless steel is mostly used at high temperatures. It is known that during heating of the austenitic stainless steel with increasing temperature and time of annealing a microstructure is changed i.e. there is the precipitation of carbides followed by precipitation of secondary phases as a sigma phase. The presence of the delta ferrite in austenitic stainless steel enhances the formation of the sigma phase. This study represents the influence of delta ferrite on the sigma phase formation and the effect of the sigma phase on general corrosion. Corrosion tests were conducted in the corrosion cell according to Standard ASTM G5, on instrument potentiostat/galvanostat, Princeton Applied Research, model 263A-2, with the software PowerCORR® (Standard, ASTM G5-94). Examinations were carried out in 1% HCl and 10% FeCl3 solutions. The Tafel extrapolation method was used for the investigation of general corrosion. The results of corrosion testing indicated that the intensity of the general corrosion increases with the increase of the delta ferrite and sigma phase contents.
In this paper, the influence of hydrochloric acid and the addition of oxidizing agents on the rate of general corrosion of brass was investigated. For comparison, the corrosion rate of copper and zinc in hydrochloric acid and in hydrochloric acid with oxidizing agent was also tested. The Taffel extrapolation method was used to examine the general corrosion of brass, copper and zinc. The Taffel extrapolation method involves scanning potential of the working electrode of ±250 mV in relation to its open-circuit otential (EOCP), at a speed of 0.5 mVs-1. Investigation of corrosion was conducted in a corrosion cell according to the ASTM G5 (ASTM G5-94) standard, on a potentiostat/galvanostat instrument, Princeton Applied Research, model 263A-2, with PowerCORR® software, which is part of the Power Suite softwere package. The tests were performed at room temperature, 20±1°C. The results show that the corrosion rate of brass is higher in hydrochloric acid with oxidizing agent than the corrosion rate of brass in hydrochloric acid. Examining the effect of hydrochloric acid and the addition of oxidizing agent on the rate of general corrosion of brass, it was found that the corrosion of brass has caused the zinc contained in it. Corrosion of zinc is highest in 0.1 M HCl + 0.1 M H2O2 compared to corrosion of brass and copper in 0.1 M HCl + 0.1 M H2O2, where corrosion of copper is lowest in 0.1 M HCl + 0.1 M H2O2.
<p>The paper presents an examination of the possibility of applying raspberry fruit extract (Rubus idaeus L.) as a green inhibitor of general corrosion of copper in 3% NaCl. Raspberry fruits (Rubus idaeus L.) sort Polka was collected from the Starposle near Kakanj, Bosnia and Herzegovina. Raspberry fruit extracts in ethanol were obtained by the Soxhlet extraction and the ultrasonic method. By UV/VIS spectrophotometry analysis, a significant content of polyphenols was found in the raspberry fruit extracts. Due to the great importance of gallic acid, the concentration of gallic acid was also determined using liquid chromatography. Corrosion testing of copper by the DC techniques was performed on a measuring device consisting of an electrochemical cell and a potentiostat/galvanostat, and electrochemical impedance spectroscopy measurements were performed using a potentiostat/galvanostat. Results obtained by the DC technique (by the method of Tafel extrapolation) prove that the corrosion rate decreases in the presence of the raspberry fruit extract. Tests performed by the method of electrochemical impedance spectroscopy prove that the tested extracts slow down the kinetics of the corrosion process, which is visible through the increase in resistance. The results of the conducted tests prove that in an aggressive medium, such as a 3% NaCl solution, Polka raspberry fruit extract can be used as an inhibitor of copper&rsquo;s corrosion.</p>
Mechanical properties and corrosion resistance of metals are closely related to the microstructure characteristics of the material. The paper compares the results of these two sets of properties after investigating samples of base ductile iron and heat-treated samples of the base austempered ductile iron (ADI). The basic material is perlite ferritic iron alloyed with copper and nickel. To test the corrosion rate of the base material (ductile iron) and the heat-treated samples (ADI), electrochemical techniques of potentiostatic polarization were used (the technique of Tafel curves extrapolation and the potentiodynamic polarization technique).
Gallic acid is a phenolic acid widely spread in various plants, where it is present either in free form or as part of tannins, called gallotannins. It shows several positive effects on human health. It has different biological effects: antibacterial, antiviral, and anti-inflammatory. Many scientists are showing great interest in gallic acid precisely because of its antitumor effect. The content of gallic acid was determined in (Rubus idaeus L.) Polka raspberry by applying reverse-phase high-resolution liquid chromatography on reverse phases on Shimadzu Prominence Modular HPLC with UV/Vis detector, mobile phase degasser, pump, autosampler, and column oven. The analysis was performed in ethanolic extracts of Polka raspberry flower obtained by the Soxhlet extraction and the ultrasonic methods. Raspberry flowers (Rubus idaeus L.) Polka varieties were collected from two different localities in Bosnia and Herzegovina, namely: Starposle near Kakanj and Moševac near Maglaj. Gallic acid was determined in all analyzed samples of Polka raspberry. The highest gallic acid content was determined in the extract of Polka raspberry flower from the Maglaj-Moševac site, using the ultrasonic method (0.1789%), and the smallest in the Polka raspberry flower from the Kakanj Starposle site, using Soxhlet extraction (0.0995%). The proportion of gallic acid was higher in the extract of Polka raspberry flower from the Maglaj-Moševac site, which suggests that these flowers of Polka variety are recommended as better natural sources of this phenolic acid and that ultrasonic extraction has proven to be a more efficient method for extraction of gallic acid in ethanolic extracts, which is the goal of research.
Plant extracts contain a large number of organic compounds, and one of the large groups of compounds present are phenolic compounds. Researchers have shown that a certain number of these compounds can be used as effective metal corrosion inhibitors. Plant extracts of raspberries (leaves, flowers, and fruit) were obtained by ultrasonic extraction using 96% ethanol as a solvent. The UV/Vis spectrophotometric method was used to determine the content of total phenols in plant extracts. Phenolic acids and flavonoids in plant extracts were separated and quantified using the HPLC method. Tafel extrapolation was used for electrochemical characteristics. The corrosion characteristics and behavior of bronze in 3% NaCl solution, with and without the presence of plant extracts were investigated. The content of total phenols in leaves was found to be 107.14±3.63 mg/g in flowers 148.99±9.02 mg/g and in fruits was 8.75±0.61 mg/g. Leaf extract in a concentration of 0.04828 g/L according to the Tafel extrapolation method provides the best protection for bronze in a 3% NaCl solution. The same concentration in the case of flower and fruit extracts proved to be the most favorable.
The paper describes the mechanical properties and the corrosion behaviour of three Al?Si alloys in 0.5 M NaCl solution. The alloys have exhibited similar values of hardness, but the highest tensile strength and the lowest elongation have shown the specimens of alloy with 11.38 % of silicon. Higher content of both copper and magnesium has contributed to better tensile strength and lower elongation of as-cast hypoeutectic alloys. The harmful effects of iron on mechanical properties of all alloys have been reduced to some extent by nickel and cobalt addition. The differences in the values of the open circuit potential of the examined alloys were insignificant. The thickness of the protective oxide layer has increased over time, and the layer has become very compact. Slight differences in the values of the corrosion potential of the alloys were determined, whereas the lowest value of the corrosion current was indicated for the hypereutectic alloy. The presence of intermetallic phases in the alloys has shown that the oxide film was not consistent. The severe pits have not been found at the surface of the corroded samples. Based on the obtained results, the examined alloys may be used for the manufacturing of the internal combustion engine parts.