The possibility of determining the concentration of heavy metal ions, i.e., Cu2+ ions in an aqueous solution of CuSO4 ∙ 5H2O, was tested by electrochemical means. For this purpose, polarisation ...curves were recorded on a Pt electrode in solutions of known (0.1, 0.5, 1.0, 2.5, 5.0, 7.5, 10.0, 50.0, and 100.0 mM) and unknown concentrations of Cu2+ ions with the reading of the limiting diffusion current. Polarisation measurements were performed in the potential range from open circuit potential to −3.0 V with different potential scan rates (1, 5, 10, 20, and 50 mV s–1). By cathodic deposition on the Pt surface, a reddish-brown copper coating was deposited, the thickness of which increased as the concentration of Cu2+ ions in the solution increased. Furthermore, the limiting diffusion current id increased linearly with the increase in Cu2+ ion concentration, c. The id = f(c) plot was constructed and the unknown concentrations of Cu2+ ions in three randomly prepared CuSO4 ∙ 5H2O solutions were determined. Heavy metal ions from polluted waters (Cu2+ ions) can be successfully removed by electrochemical means, and their concentration determined.
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.
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 study investigates the changes at the electrodes and in the solution during crystal violet dye removal by electrocoagulation at different current densities (0.016, 0.024, and 0.032 A cm –2 ) and ...initial pH values (3.2, 5.5, and 7.0). The electrocoagulation process, which lasted 50 min, revealed changes in pH, temperature, electrical conductivity, and concentration of the crystal violet dye in the solution. The results demonstrate complete removal of crystal violet dye at the highest current density (achieved after 40 min) and an initial pH of 5.5 (complete removal after 30 min). During the electrocoagulation process, both the anodic and cathodic electrode materials were consumed. The consumption of electrode material increased with higher current density and solution pH, the influence of current density being more pronounced. Examination of the electrode surfaces under a light microscope revealed that the anodes dissolved uniformly and locally during the electrocoagulation process, while the cathodes mostly underwent uniform corrosion.
Promatrane su promjene na elektrodama i u otopini tijekom uklanjanja kristalno ljubičaste ( crystal violet ) boje elektrokoagulacijom, izvedene pri različitim početnim gustoćama struje (0,016, 0,024 i 0,032 A cm –2 ) i početnim pH (3,2, 5,5 i 7,0). Tijekom procesa elektrokoagulacije, koji je trajao 50 min, uočene su promjene pH, temperature, električne vodljivosti i koncentracije kristalno ljubičaste boje u otopini. Dobiveni rezultati istaknuli su ukupno uklanjanje kristalno ljubičaste boje pri najvećoj gustoći struje (potpuno uklanjanje nakon 40 min) i pri početnom pH od 5,5 (potpuno uklanjanje nakon 30 min). Materijal anodne i katodne elektrode troši se tijekom procesa elektrokoagulacije. Potrošnja elektrodnog materijala raste s porastom gustoće struje i pH otopine, pri čemu je utjecaj gustoće struje sve izraženiji. Izgled površina elektroda (snimljen svjetlosnim mikroskopom) pokazuje da se anode otapaju ravnomjerrno i lokalno tijekom procesa elektrokoagulacije, dok su katode uglavnom podložne ravnomjernoj koroziji.
The electrochemical behavior of commercially pure titanium (CP Ti) and Ti-6Al-4V (Grade 5) alloy in phosphate buffered saline solution (PBS, pH = 7.4) at 37 °C (i.e., in simulated physiological ...solution in the human body) was examined using open circuit potential measurements, linear and potentiodynamic polarization and electrochemical impedance spectroscopy methods. After the impedance measurements and after potentiodynamic polarization measurements, the surface of the samples was investigated by scanning electron microscopy, while the elemental composition of oxide film on the surface of each sample was determined by EDS analysis. The electrochemical and corrosion behavior of CP Ti and Ti-6Al-4V alloys is due to forming a two-layer model of surface oxide film, consisting of a thin barrier-type inner layer and a porous outer layer. The inner barrier layer mainly prevents corrosion of CP Ti and Ti-6Al-4V alloy, whose thickness and resistance increase sharply in the first few days of exposure to PBS solution. With longer exposure times to the PBS solution, the structure of the barrier layer subsequently settles, and its resistance increases further. Compared to Ti-6Al-4V alloy, CP Ti shows greater corrosion stability.
The corrosion behaviour of Cu-Al-Ni alloy in 0.5 mol dm–3 H2SO4 solution was investigated by electrochemical methods including open circuit potential measurement, electrochemical impedance ...spectroscopy measurements, linear and potentiodynamic polarization. Measurements were performed in 0.5 mol dm–3 H2SO4 at temperatures 20 and 40 °C. After polarization testing, corroded electrode surfaces were ultrasonically cleaned in deionized water and examined by light and scanning electron microscopy, while the elemental composition at individual points of the alloy surface was determined by EDS analysis. The results of the investigations revealed the occurrence of intergranular corrosion on the Cu-Al-Ni surface, which became more pronounced with increasing temperature.
Korozijsko ponašanje Cu-Al-Ni legure u 0,5 mol dm–3 H2SO4 otopini ispitivano je elektrokemijskim metodama kao što su mjerenje potencijala otvorenog strujnog kruga, mjerenje metodom elektrokemijske impedancijske spektroskopije, linearne i potenciodinamičke polarizacije. Mjerenja su provedena u 0,5 mol dm–3 H2SO4 pri temperaturama od 20 i 40 °C. Nakon polarizacijskih mjerenja korodirane površine elektroda ultrazvučno su očišćene u deioniziranoj vodi i ispitane svjetlosnim i pretražnim elektronskim mikroskopom, dok je elementarni sastav na pojedinim točkama na površini određen EDS analizom. Rezultati ispitivanja pokazali su da dolazi do interkristalne korozije na površini Cu-Al-Ni legure, čiji intenzitet raste s povećanjem temperature elektrolita.
The main goal of this paper is to determine the machining conditions that simultaneously meet the conditions of clean production and producing a product with the best surface roughness and corrosion ...resistance. Based on experimental results, the influence of feed rate, cooling and lubrication techniques (cutting fluid, minimum quantity of lubrication and cooling with compressed cold air) on surface roughness and corrosion resistance during face milling, were analyzed. Observed workpiece materials comprise technically important steel, such as S275JR, 42CrMo4 and AISI 304. Electrochemical measurements (potentiodynamic and linear polarisation measurements) and measurements of surface roughness have shown that the feed rate of 0.04 mm/tooth and the application of a minimum quantity of lubrication in the machining of stainless-steel specimens are the parameters providing the required surface integrity (surface roughness Ra = 0.68 μm, polarisation resistance Rp = 53.228 kΩ cm2 and corrosion currency 0.37 μA/cm2) and ecological acceptability. Finally, the physical changes on the workpiece surface under different machining conditions are described in detail.
•Milling of S275JR, 42CrMo4 and AISI304 was conducted in MQL, CCA and dry conditions.•Influence of surface quality and coolants on corrosion resistance were examined.•The results indicate that use of MQL can be a good strategy for cleaner production.•Small feed rate and use of MQL result in maximum workpiece corrosion resistance.
The effect of temperature (from 288 to 308 K) and concentration of sulfide ions (up to 40 ppm) on the corrosion behavior of AISI 304L and AISI 316L stainless steels in seawater was studied with ...measurements of open-circuit potential, linear and potentiodynamic polarization, and electrochemical impedance spectroscopy. An increase in temperature and pollutant concentration negatively affects the corrosion stability of stainless steels at the open circuit (the resistance, compactness, and thickness of the surface layer decrease and the corrosion current increases), in the passive region (the passivation current increases, the depassivation potential decreases, and the passive potential region narrows), and in the transpassive potential region (the rate of metal dissolution increases). The occurrence of pitting corrosion on the surface of the samples was confirmed with optical microscopy and a non-contact 3D profilometer. A few large pits (depth 80–100 μm and width 100 μm) were formed on the surface of AISI 304L steel, while several smaller pits (depth 40–50 μm and width 50 μm) were formed on the surface of AISI 316L steel. With increasing temperature and sulfide ion concentration, the width, depth, and density of the pits increased on both steel samples. In the studied temperature and concentration range of sulfide ions, the AISI 316L steels exhibited higher corrosion resistance. Overall, the influence of sulfide ions on steel corrosion was more pronounced than the influence of temperature.
Anodic and spontaneous corrosion of different types of stainless steel (AISI 304L, AISI 316L and 2205 DSS) in phosphate-buffered saline solution (PBS, pH = 7.4) at 37 °C (i.e., in simulated ...physiological solution in the human body) were examined using open circuit potential measurements, linear and cyclic polarization, and electrochemical impedance spectroscopy methods. After the anodic and spontaneous corrosion, the surface of the tested samples was investigated by light and scanning electron microscopy (SEM) with EDS analysis. It has been established that the tendency of the examined steel materials towards local corrosion decreases in the order: AISI 304L < AISI 316L < 2205 DSS. Namely, the possibility of repassivation and the resistance to local corrosion increases in the same order. The corrosion resistance of steel samples at open circuit potential is a consequence of forming a natural oxide film with a bi-layer structure and consists of an inner barrier and an outer porous film. The inner barrier film has a small thickness and extremely high resistance, while the outer porous film is much thicker but also has significantly lower resistance. The inner barrier layer mainly prevents corrosion of examined steel samples in order: AISI 304L < AISI 316L < 2205 DSS. Light microscopy and SEM/EDS analysis after pitting and spontaneous corrosion showed damage on the AISI 304L and AISI 316L surface, while the surface of 2205 DSS was almost undamaged by corrosion.
In this research, a solid-state recycling process of aluminum was performed. It consisted of aluminum EN AW 6082 alloy machining chip cold precompaction and hot extrusion followed by a combination of ...equal channel angular pressing (ECAP) and heat treatment. The main aim of this paper is to determine the fatigue and corrosion behavior of the recycled specimens. In order to determine the recycled specimen fracture mode after fatigue testing, fractography analysis was performed. The corrosion behavior of all specimens was investigated in 0.5 M NaCl solution using open circuit potential measurements, polarization and electrochemical impedance spectroscopy (EIS) methods. It was found that the corrosion resistance of the tested specimens is similar for reference and as-extruded recycled specimens, while it is increased for those which were additionally processed with equal channel angular pressing and heat treatment. Namely, the corrosion current decreased in the same order, while the polarization resistance increased. Impedance measurements have shown that the subsequent plastic deformation and heat treatment of recycled specimens facilitated passivation of tested materials and improved surface film properties, which is confirmed with scanning electron microscopy and energy-dispersive x-ray spectroscopy. Fatigue life was similar for recycled and reference specimens for the selected stress levels. However, fractography showed that multiple cracks appeared inside the recycled specimens which caused different crack propagation mechanisms compared with reference specimens.
The corrosion properties of an EN AC AlSi9Cu3(Fe) alloy (reference sample (RS)) and samples produced by recycling chips of RS by direct hot extrusion (DHES) and subsequent thixoforming (TFS) were ...tested in 0.5 M NaCl solution. The plastic deformation changes the microstructure of RS, and brittle, coarse Si particles and intermetallic compounds (IMCs) were effectively broken into ultrafine-grained particles and redistributed homogeneously into the α-Al matrix in DHES. TFS exhibits a globular structure, and polyhedral clusters rich in Si and IMCs were observed along the grain boundary. Electrochemical measurements combined with surface characterisation show that the microstructure significantly influences the tested samples’ corrosive properties. It was confirmed that corrosion resistance increased in the following order: RS < TFS < DHES. Similarly, the corrosion potential becomes nobler, the corrosion current decreases, the passive area increases, and the oxide layer becomes more stable (higher resistance and thickness). Also, the percentage of the surface affected by corrosion and the volume of pits reduce. The effect of microstructure is particularly pronounced in the level of the corrosion current and the volume of pits formed. The corrosion current of DHES and TFS decreases by 4–5 times, while the pit volume of DHES and TFS decreases by several orders of magnitude compared to RS. The corrosion stability of DHES and TFS in relation to RS is a consequence of the comminution of the Si particles and the IMC. The refined and homogeneous microstructure contributes positively to forming a stable oxide film on DHES and TFS and increases their corrosion resistance in an aggressive environment. The applied recycling method represents an innovative and sustainable process for the recycling of semisolid materials, with lower energy consumption and less greenhouse gas emissions compared to conventional recycling. The fact that the products obtained through recycling have a significantly higher corrosion resistance further increases the economic and environmental impact of the process.
PDF
