Dip-immersion is simple and cost-effective method for the preparation of Ce-based conversion coatings (CeCCs), a promising alternative to the toxic chromate coatings, on the metal substrates. In this work CeCCs were prepared on Al-alloy AA6060 from aqueous solution of cerium chloride at room temperature. Effect of immersion time and post-treatment in phosphate solution on the microstructure and corrosion properties of the coatings was studied. The longer immersion time, the thicker but nonhomogeneous and cracked CeCCs. The post-treatment contributed to the sealing of cracks, as proven by an increase in corrosion resistance compared with as-deposited coatings. CeCCs prepared at longer deposition time and post-treated showed much better corrosion protection than those prepared at short deposition time. A detailed EIS study was undertaken to follow the evolution of corrosion behaviour of CeCCs with time of exposure to aggressive chloride environment (3.5 % NaCl). For the sake of comparison, the EIS properties of bare AA6060 were also investigated. A linear voltammetry was performed to complete the study. Results confirmed a formation of protective CeCCs on AA6060 surface. However, even CeCCs prepared at longer deposition time and post-treated provided a short term protection in aggressive environment, due to the small thickness. [Projekat Ministarstva nauke Republike Srbije, br. III 45019 i br. III 45012
The impact of the surface charge of alumina support on the adsorption of
Candida rugosa lipase has been investigated in terms of zeta potential of the
adsorption partners. Lipase adhered onto alumina with similar efficiency
under both repulsive and attractive electrostatic conditions, shifting the
zeta potential of the support towards that of the enzyme. The behavior was
explained by a heterogeneous distribution of the surface charge of the lipase
molecule. Special emphasis in this study was placed on the effect of
immobilization on enzyme kinetics and principal reasons for enzyme
immobilization: improvement in stability and potential for reuse. The enzyme
affinity was not altered by its adsorption onto alumina, while Vmax of the
lipase decreased. Thermostability of adsorbed lipase was improved.
Significant potential for reuse was found. [Projekat Ministarstva nauke
Republike Srbije, br. III 43004 i br. III 45012]
In the primary circuit of pressurized water reactors (PWR), the dynamic sealing system in reactor coolant pumps is ensured by mechanical seals whose ceramic parts are in contact with the cooling solution. During the stretch-out phase in reactor operation, characterized by low boric acid concentration, the leak-off flow has been observed to abnormally evolve in industrial plants. The deposition of hematite particles, originating from corrosion, on alumina seals of coolant pumps is suspected to be the cause. As better understanding of the adhesion mechanism is the key factor in the prevention of fouling and particle removal, an experimental study was carried out using a laboratory set-up. With model materials, hematite and sintered alumina, the adhesion rate and surface potentials of the interacting solids were measured under different chemical conditions (solution pH and composition) in analogy with the PWR ones. The obtained results were in good agreement with the DLVO (Derjaguin-Landau-Verwey- Overbeek) theory and used as such to interpret this industrial phenomenon
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