BENEFICIAL EFFECT OF CU CONTENT AND AUSTEMPERING PARAMETERS ON THE HARDNESS AND CORROSION PROPERTIES OF AUSTEMPERED DUCTILE IRON (ADI)

The effect of copper content (0.031 wt.% Cu, 0.32 wt.% Cu, 0.51 wt.% Cu and 0.91 wt.% Cu) on the hardness and corrosion properties of ADI was investigated. Samples austenitization were carried out at 850°C for 60 min followed by its austempering at temperatures from 250°C to 420°C for different time (30 to 60 min) in 50% (KNO3 + NaNO3) salt bath. It was concluded that hardness rises with copper content but decreases with higher austempering temperatures and times. The corrosion properties of the samples with minimum and maximum Cu content were investigated by electrochemical methods in 0.5 M NaCl solution. Samples with a higher copper content have shown higher values of polarization resistance (Rp) and lower values of corrosion current (icorr). After polarization measurements, corroded surfaces were analyzed with SEM/EDS analysis

INHIBITION OF ALUMINIUM ALLOY CORROSION IN CHLORIDE SOLUTION BY CAFFEINE ISOLATED FROM BLACK TEA

Caffeine (1,3,7-trimethylxanthine) was isolated from black tea and characterised using different physical methods. The corrosion inhibition performance of the caffeine isolate (in concentration from 110-5 to 110-3 mol/dm3) on aluminium alloy corrosion in neutral 0.5 mol/dm3 NaCl solution was investigated using potentiodynamic and linear polarization measurements at 20 C. Corrosion potential, corrosion current and polarization resistance were determined and surface coverage of inhibitor molecules and inhibition efficiency were calculated. The obtained results show that caffeine effectively inhibited the corrosion reaction in the chloride solution with an inhibition efficiency of up to 76%. Furthermore, caffeine was found to function essentially as a mixed type with a higher influence on cathodic reaction. The adsorption behaviour of investigated inhibitor can be described by the Freundlich adsorption isotherm. The adsorption free energy closes to -10 kJ/mol indicates physical adsorption of the caffeine on the aluminium alloy surface in NaCl solution

Corrosion investigations of Al-Si casting alloys in 0.6 M NaCl solution

This paper presents results of the corrosion investigations of specimens made from finished parts for the automotive industry, produced by high-pressure die casting and gravity die casting process of six Al-Si alloys (40000 series). Open circuit potential and potentiodynamic polarization measurements have been performed using a potentiostat with three-electrode set-up in 0.6 M NaCl naturally aerated solution. Microstructural characterization before and after electrochemical investigations has been carried out with optical microscope to establish the connection between microstructure and corrosion parameters of investigated alloys and to analyze and record surface changes of each sample due to electrochemical corrosion. All alloys show good corrosion resistance, which manifests with low values of corrosion rates, calculated from the corrosion current densities obtained from potentiodynamic polarization measurements. Differences in electrochemical behavior appear due to the distinctions in their chemical composition and microstructure. The type of casting process does not affect electrochemical behavior of Al-Si alloys

Primjene različitih metala kao elektrodnog materijala u obradi kompostne procjedne vode

In this paper, different metallic materials (alloys of Fe, Al, and Zn) were investigated as sacrificial anodes during electrocoagulation (EC) for the treatment of compost leachate. Taguchi’s L9 orthogonal array design was applied to investigate the four controllable factors (different metallic material, initial pH value, stirring speed, and contact time) on decrease of chemical oxygen demand (COD) and electrodes mass loss. COD decrease reached values in the range of 75.72–92.97 %. The Taguchi optimisation results showed that the most effective factor for decrease of COD is the duration of the experiment, while the electrode material was for electrodes mass loss. The zinc electrode showed the lowest potential for use in the EC process for treatment of compost leachate, while the Al and Fe electrodes could be used in an acid or slightly acidic environment. The following decreasing order of energy consumption was recorded: Zn > Al > Fe. The measured values of metal electrode mass loss exceeded the theoretical values calculated using Faraday’s law in EC experiments with Al electrodes, while in experiments with Fe and Zn electrodes, those differences were insignificant.U ovom radu različiti metalni materijali (legure Fe, Al, Zn) ispitivali su se kao žrtvene anode tijekom elektrokoagulacije (EK) za obradu kompostne procjedne vode. Taguchijev L9 ortogonalni niz primijenjen je za ispitivanje četiriju kontroliranih čimbenika (različiti metalni materijali, početne pH vrijednosti, brzine vrtnje miješala i vremena kontakta) na uklanjanje organske tvari izražene preko kemijske potrošnje kisika (KPK) i gubitak mase elektroda. Učinkovitost uklanjanja organske tvari izražene preko KPK-a dosegla je vrijednosti u rasponu od 75,72 do 92,97 %. Rezultati optimizacije Taguchi pokazali su da je najučinkovitiji čimbenik za uklanjanje organske tvari, izražene preko vrijednosti KPK-a, trajanje eksperimenta, dok je gubitak mase elektroda za materijal elektrode. Cinkova elektroda pokazala je najmanji potencijal za uporabu u EK procesu za pročišćavanje kompostne procjedne vode, dok se Al i Fe elektroda mogu upotrebljavati u kiselom ili blago kiselom području. Zabilježen je sljedeći opadajući redoslijed potrošnje energije: Zn > Al > Fe. Izmjerene vrijednosti gubitka mase metalne elektrode premašuju teorijske vrijednosti izračunate Faradayevim zakonom u EK eksperimentima s Al elektrodama, dok su u eksperimentima s Fe i Zn elektrodama te razlike manje

The influence of chloride ion concentration on the corrosion behavior of the CuAlNi alloy

The influence of different chloride ion concentration (0.1 %, 0.5 %, 0.9 % and 1.5 % NaCl solution) on the electrochemical behaviour of the cast CuAlNi alloy was examined with electrochemical techniques (open circuit potential measurements, linear and potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS)). After polarization measurements, electrode surfaces were examined with an optical microscope and the SEM/EDS analysis. Polarization measurements revealed that an increase in chloride ion concentration leads to an increase of the corrosion current density values and a decrease of the polarization resistance values, which indicated a higher corrosion attack on the alloy. The examination of alloy surfaces with an optical microscope and the SEM/EDS analysis has shown that there is no indication of pitting corrosion in the 0.1% NaCl solution, but pits were clearly visible on the samples which were examined in the higher chloride concentration solutions. The EDS analysis has shown the existence of copper oxide on the electrode surface and a presence of a small percentage of aluminium in the form of aluminium oxide

Electrochemical and corrosion behaviour of copper shape memory alloy in NaCl solution

This paper presents a review of electrochemical and corrosion investigations on behaviour of CuAlNi and CuAlMn alloys in NaCl solutions, which were carried out within the framework of the project IP-2014-09-3405“ Design of microstructure and functional properties of copper-based shape memory alloys”, supported by the Croatian Science Foundation. The influence of alloys heat treatment on their corrosion behaviour was investigated, as well as the influence of chloride concentration, pH values and electrolyte temperatures. Cu-shape memory alloys were produced by continuous vertical casting and melt spinning method. Investigations were conducted by electrochemical methods such as open circuit current measurement method, electrochemical impedance spectroscopy method, linear and potentiodynamic polarization. Corroded specimens characterization was obtained by optical and scanning electron microscope. Analysis of the corrosion product composition was carried out by EDS method

Investigation of Effects of Inhibitor on Corrosion of Carbon Steel in Water with Biocide

U ovom radu istražen je utjecaj komercijalnog inhibitora (Chemtec FI30) na proces korozije ugljičnog čelika P235 u različitim vodenim otopinama; demineraliziranoj i/ili vodovodnoj vodi uz dodatak komercijalnog biocida (Chemtec BI01). Istraživanja su provedena gravimetrijskom metodom i elektrokemijskim metodama, dok je površina ispitivanog materijala analizirana pomoću optičkog mikroskopa. Analize pokazuju da inhibitor smanjuje brzinu korozije ugljičnog čelika u ispitivanim otopinama, ima visoku djelotvornost te da se može svrstati u anodne inhibitore. Također, uočeno je da inhibitor smanjuje opću i jamičastu koroziju ugljičnog čelika u korozivnim vodenim otopinama. Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna.The effect of a commercial inhibitor (Chemtec FI30) on the corrosion of P235 carbon steel in water (demineralised and/or tap water) with the addition of a commercial biocide (Chemtec BI01) was studied in the present work. This study was carried out by weight loss and electrochemical methods, while specimen’s surface was examined using optical microscope. Results obtained from gravimetric measurement revealed that P235 carbon steel corroded in aqueous solution, i.e., in a solution of demineralised and tap water (50 : 50) and a biocide (Fig. 1), and in tap water with a biocide (Fig. 5). By analysing the surface of carbon steel with an optical microscope, general and pitting corrosion was observed, which was more pronounced in tap water with biocide (Figs. 2 and 6). The addition of a commercial inhibitor significantly reduced the occurrence of corrosion damage on the surface of carbon steel (Figs. 3, 4, 7, and 8) and decreased the rate of carbon steel corrosion in all aqueous solutions (Table 1). Electrochemical investigations performed by open circuit potential measurement, linear polarisation and potentiodynamic polarisation measurement showed that the inhibitor Chemtec FI03 shifted the potential to more positive values (Figs. 9 and 10), increased polarisation resistance (Table 3), decreased the rate of carbon steel corrosion, and had high efficiency in all tested solutions (Table 4). The results obtained showed that this commercial inhibitor could be used as an effective inhibitor for the corrosion of carbon steel in aqueous media. This work is licensed under a Creative Commons Attribution 4.0 International License