Caffeine (1,3,7-trimethylxanthine) was isolated from black tea and characterized using different physical methods (determination of melting point, thin layer chromatography, FTIR spectroscopy and UV ...spectrophotometry). The corrosion inhibition performance of the caffeine isolate on copper corrosion in neutral 0.5 mol L-1 NaCl solution was investigated using potentiodynamic polarization and electrochemical impedance spectroscopy measurements. The obtained results show that caffeine effectively inhibited the corrosion reaction in the chloride solution with inhibition efficiency up to » 92 %. Furthermore, caffeine was found to function essentially as a cathodic inhibitor by adsorption on the copper surface according to the Langmuir adsorption isotherm. The adsorption free energy of » –37 kJ mol-1 indicates strong adsorption of the caffeine on the metal surface. Quantum chemical computations and molecular dynamics simulations were adapted to understudy the adsorption of a single caffeine molecule as well as a polymeric cluster of caffeine molecules on a model Cu surface at a molecular level and show good agreement with the experimental findings.
In this investigation the possibility of inhibiting corrosion of copper using ethanol extract of propolis in 0.5 mol dm-3 NaCl solution was investigated. The measurements were carried out in 200 cm3 ...of NaCl solution to which 4 ml of ethanol extract of propolis was added. Also, the protective effect of propolis coating, which was formed by applying the ethanol extract of propolis to the electrode surface, followed by air drying for 24 h, was investigated. Experiments were performed using electrochemical methods: open circuit potential measurements, linear and potentiodynamic polarization method and electrochemical impedance spectroscopy measurements (EIS). The results showed that the coating of propolis significantly shifted the value of the open circuit potential of Cu to more positive values, significantly increased the value of polarization resistance and as well led to a reduction in corrosion current density. On the other hand, addition of propolis in solution yielded minor changes in the value of the stable open circuit potential of copper, but increased the value of polarisation resistance and decreased the corrosion current density. After polarisation measurements, the electrode surface was examined by optical microscopy. Quantum chemical modelling of selected constituents of propolis was undertaken in order to ascertain their contributions to the corrosion inhibition performance.
► We examine corrosion behaviour of Cu–Al–Ni shape memory alloy. ► Adsorption of chloride ions leads to the decrease of
E
OCP and the breakdown of the protective surface oxide film. ► Polarization ...behaviour was determinated by the dissolution of copper to soluble cuprous chloride ion complex (CuCl
2
−). ► The microstructure consisted of grains with martensite plates. ► After corrosion testing occured of corrosion products at Cu–Al–Ni surface.
The corrosive behaviour of Cu–Al–Ni shape memory alloy in deaerated 0.5
M NaCl solution at 20
°C was studied by means of open circuit potential measurements, linear polarization, potentiodynamic polarization measurements, cyclic voltammetry and electrochemical impedance spectroscopy measurements. The electrode surface was examined by light microscope, SEM, XRD and EDX methods. The polarization measurements have shown that corrosive behaviour of Cu–Al–Ni alloy in NaCl solution was dominated by the Cu component. The results of impedance measurements at open circuit potential have shown that the overall impedance of the system increases with immersion time due to continuous growth of the passive film on the alloy surface. The XRD and EDX analysis showed the presence of copper, aluminium and nickel compounds, Cu-oxides and Cu-chlorides on alloy surface.
Headspace solid-phase micro-extraction (HS-SPME) and ultrasonic solvent extraction (USE) were used for red clover honey volatiles extraction. The extracts were analysed using gas chromatography and ...mass spectrometry (GC-MS). Lilac aldehyde isomers dominated in the headspace (individual range from 7.6 % to 21.4 %) followed by phenylacetaldehyde (10.1-31.2 %) and benzaldehyde (7.0-15.7 %). Higher aliphatic alcohols and hydrocarbons were the predominant constituents of the honey extracts. The honey and its extracts exhibited rather weak anti-radical activity (DPPH assay) and total antioxidant activity (FRAP assay). On the other hand, the honey’s inhibitive properties towards the corrosion of AA 2017A alloy in NaCl solution (potentiodynamic polarisation and potentiostatic pulse measurements) revealed the honey to be a very good anodic inhibitor (efficiency up to 76 %) while the honey extracts (USE) showed better inhibition efficacy.
Današnji trend u razvoju pomorstva i tehnologije općenito, a samim time i pritisci brodara, nagnali su proizvođače velikih brodskih dvotaktnih sporohodnih dizelskih motora da konstrukcijskim ...modifikacijama omoguće uporabu goriva sve lošije kvalitete. Takva goriva sadržavaju tvari koje u određenim uvjetima mogu postati vrlo korozivne. Danas se, generalno gledajući, za pogon trgovačkih brodova koristi sporohodnim dvotaktnim dizelskim motorima u rasponu snaga od 5,000 do 80,000 kW i to na goriva vrlo loše kvalitete. Izgaranje takvih goriva u cilindrima motora neminovno uzrokuje stvaranje elektrokemijske i kemijske korozije, te trenje i trošenje elemenata cilindara i ispušnih vodova. U ovom će se radu analizirati problem nastanka korozije i zaštita kojom se danas služi poradi sprečavanja korozijskog djelovanja u cilindrima velikih brodskih dvotaktnih sporohodnih dizelskih motora.
The effects of flow rate and temperature on the corrosion behaviour of the Al-2.5 Mg alloy in a 3% NaCl solution and the inhibiting efficiency of (+)-catechin on the corrosion of the same alloy have ...been examined. Measurements were carried out in a flow-through cell, at different flow rates (v1 = 0.0029 m s-1, v2= 0.0059 m s-1 and v3=0.0118 m s-1) and temperatures (20, 30, 40DGC). Electrochemical parameters for the Al-2.5 Mg alloy were determined by polarisation techniques and electrochemical impedance spectroscopy (EIS). Increased flow rate and temperature cause a stronger corrosion attack on the alloy. The addition of (+)-catechin inhibited corrosion at all temperatures and flow rates. The inhibitor efficiency decreased with increase in flow rate and temperature.
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