Zrinka Šokčević

Corrosion Protection of AISI 316L Stainless Steel with the Sol-Gel Yttria Stabilized ZrO2 Films: Effects of Sintering Temperature and Doping

Nanostructured sol–gel zirconia (ZrO2) films containing 3, 5 and 7 mol % Y2O3 of one and three layers were prepared on stainless steel X2CrNiMo17-12-2 (AISI 316L) surface by the dip coating method. Yttria stabilized zirconia (YSZ) deposited films were sintered at 400 and 600 °C. For the preparation of sol zirconium(IV) butoxide was used as precursor, i-propyl alcohol as a solvent with addition of nitric acid as a catalyst, acetylacetone as chelating agent and water for hydrolysis. Thickness of sol-gel YSZ films deposited on stainless steel was determined by glow- discharge optical emission spectrometry (GD- OES). It was found that thickness of deposited films is barely affected by yttria content while increases by increasing the number of layers and temperature of sintering. The crystal structure of films was determined by X- ray diffraction. The corrosion resistances of uncoated and coated specimens were studied by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization in simulated marine environment (3.5 wt. % NaCl aqueous solution) at room temperature. The influence of yttria stabilized zirconia (YSZ) layers number and temperature of sintering on the corrosion protection was examined as well. Sol-gel derived YSZ films are capable of appreciable improvement in corrosion resistance of stainless steel in the investigated corrosive medium.

Woody biomass fly ash as a low-cost sorbent for the removal of ionic dye from aqueous solution: Isotherm, kinetic modelling and thermodynamics

The main goal of this work was to investigate a possible application of woody biomass fly ash (WBFA) as a low-cost sorbent for the removal of ionic, toxic and carcinogenic diazo dye (Congo red) from aqueous solutions. Biomass fly ash is a by-product generated during mixed wood biomass combustion in the 1 MW electric power facility in Udbina, Croatia. Batch sorption experiments were carried out to evaluate the influence of experimental parameters, such as initial dye concentration contact time and temperature on the sorption process. The experimental data were analyzed using different isotherm and kinetic models. The best fit was achieved by the Langmuir isotherm equation (R2 > 0.9904). Results of the kinetic studies showed that the CR dye sorption onto the WBFA was best described by the pseudo- second order kinetic model. The Weber-Morris intraparticle diffusion model indicated that the intraparticle diffusion is not the rate- limiting step, while the Boyd model suggested that the film diffusion might be rate-limiting. The calculated thermodynamic parameters (ΔG°, ΔH° and ΔS°) showed that the sorption of CR is feasible, spontaneous and endothermic. Experimental results confirmed that the WBFA had the potential to be utilized as a low-cost sorbent material for the removal of Congo red dye from aqueous media.