Julieta Daniela Chelaru

The main purpose of this work is to improve the corrosion resistance of steel substrates using the characterization of new composite zinc electrodeposits containing graphene oxides and reduced graphene oxide. The zinc-graphene based composite deposits were obtained by electrodeposition of an acidic electrolyte (pH = 5) at a current density of 20 mA/cm2. Anionic surfactant (i.e., sodium dodecyl sulfate) was used to obtain uniform and compact coating morphology. Also, the investigated deposits had in their structure the graphene oxides produced by graphite exfoliation and the results concerning corrosion behavior of the zinc electrodeposits (Zn/S235 and Zn-graphene/S235) were compared using the same experimental conditions. Microstructural characterization was carried out by SEM‐EDS, whereas corrosion resistance was evaluated by EIS and polarization curves.

Corrosion tests were carried out in order to find the best inhibitor for the protection of steel pipelines used in H3PO4 and fertilizers industry. The corrosion inhibition efficiency of five commercial inhibitors was investigated on mild steel by using electrochemical methods (EIS and polarization curves) in a 7M H3PO4 solution (pH 0.5). The efficiency of best corrosion inhibitors was tested at different concentrations.

The aim of this study is to investigate the corrosion behavior of low carbon steel (S235) used in petrochemical industry. The corrosion process was analyzed in simulated wastewater at different values of pH and at different temperatures and also in real wastewater from the exploitation of crude oil from Transylvania, Romania. Two commercial corrosion inhibitors (Nalco 73413 (Nalco Products, USA,) and Galoryl IC20 (ArrMazz Chemicals SAS, USA) were tested at different concentrations. The corrosion behavior was investigated by electrochemical impedance spectroscopy and potentiodynamic polarization measurements. Adsorption of these inhibitors was found to obey Langmuir adsorption isotherm.

The corrosion inhibition efficiency of three commercial inhibitors on low carbon steel was investigated by electrochemical methods (EIS and polarization curves). The efficiency of corrosion inhibitors was tested at different concentrations. Corrosion tests were carried out in a solution simulating a saline wastewater from petroleum industry (pH = 3) in order to find the best inhibitor for the protection of steel pipelines.

The study presents the preliminary research on the possibility to use the calcium sulphate waste (CSW) as replacing of sand in the cement mortar. The waste was chemically and mineralogical characterized. Four compositions of mortar without and with 7.5 %, 18.78 % and 37.50 % waste were prepared. The X-ray powder diffraction evidenced the main mineral compounds in mortar as hydration products of calcium silicates (CSH) with a low index of crystallinity and different oxide ratio CaO:SiO2:H2O, quartz, calcite, anhidrite and gypsum. Optical microscopy reveals that the samples contains aggregates as quartz, muscovite and rocks, especially of metamorphic origin (quartzite, micaschists, and quartzitic schists) embedded in a fine matrix resulted by hydration reactions of cement compounds or reactions of waste components with other compounds from system. The corrosion properties of mortar, at different CSW concentrations, on rebar, were investigated by polarization measurements and electrochemical impedance spectroscopy. The results revealed that at 7.5 % addition of waste anticorrosion properties are improved. As expected, the mechanical resistances (compressive and flexural strenght) decrease with increasing of waste in mortar composition.