Efeitos dos nanocristais de celulose obtidos da fibra de sisal nas características de depósitos à base de Zn-Ni obtido por eletrodeposição

Abstract

Zn-Ni alloys have been used to decrease the corrosion rate of carbon steel substrates. These are used in applications such as bolt coatings, threaded parts, swift valves for gas pipelines, aircraft landing gear, brake system components and others. Zn-Ni coatings containing nanocrystals of cellulose (CNC) obtained from sisal fiber (Sif), were manufactured using the electroplating technique. Obtaining the nanocrystals involved bleaching raw sisal fiber and then acid hydrolysis to extract the nanocrystals. The effect of the concentrations of the CNC-Sif (0 % V/V, 2% V/V, 3% V/V, and 4% V/V) on the morphology and microstructure of the Zn-Ni coating was analyzed through Scanning Electron Microscopy (SEM), X-ray diffraction, and roughness measurements using confocal microscopy. The effect of the addition of CNC-Sif on the efficiency of galvanostatic deposition was analyzed. The corrosion rate through mass loss and electrochemical tests were also analyzed. The effect of adding CNC-SIF on coating microhardness investigated. The results show that the addition of nanocrystals alters the structure, the morphology, increases current efficiency and the corrosion resistance of the Zn-Ni coating and these effects are more significant with the addition of 2% V/V. At this concentration, the addition of CNC-Sif decreased the roughness from 0.39± 0.04 μm to 0.21± 0.03 μm, the crystallite dimension from 57.4± 0.2 nm to 48± 0.2 nm, and increased the texture coefficient corresponding to the (330) γ plane of 75% to 96%. This elevation of the texture coefficient favors the packing density of the coating. Regarding the deposition current efficiency, it was observed that the addition 2% V/V of CNC-Sif increases the deposition current efficiency of the Zn-Ni coating from 85% to 93%. Furthermore, it was found that this concentration decreases the corrosion rate from 0.146 ± 0.021 mm/year to 0.036 ± 0.017 mm/year and increases polarization resistance from 1083 ± 173 Ohm to 3485 ± 324 Ohm. Regarding the analyzed mechanical property, it was found that the addition of the nanocrystals increases the microhardness of the coating, in the presence of 2% V/V of the CNC-Sif, from 238 ± 12 HV to 336.3 ± 32 HV. The results obtained indicate that the addition of the CNC-Sif in the Zn-Ni coating is promising, because it reduces the energy consumed during the electrodeposition process in addition to increasing corrosion resistance of the Zn-Ni coating and the microhardness.