Abstract
<p>Ni-Al<sub>2</sub>O<sub>3</sub> composite coatings electrodeposited from Watt’s electrolyte include Al<sub>2</sub>O<sub>3</sub> nano-and submicron particles. The effect of particle size and concentration of the particles in the electrolyte were investigated on the morphology and incorporation value of particles into the deposits. The influence of alumina particles on the electrodeposition behavior of Ni was also studied by means of electrochemical impedance spectroscopy. The results achieved from the impedance measurements and the correlation with the layer characterization could help to better understand the codeposition mechanism derived from the impact of different particle characteristics including size and concentration on the nature of the double-layer. The increase in the concentration of particles from 1 to 20 g/l resulted in an increase of the double-layer capacity and decrease of the charge transfer resistance, while the addition of submicron particles had a higher influence on the characteristics of the double-layer compared to the nano particles. Although the alumina particles with submicron size could stimulate the incorporation of particles faster than those with nano size, the strengthening performance of the layers not only depended on the incorporation value of the particles, but also on the microstructure of the deposits.</p>
Highlights
Composite coating has been well developed for the last decades
The increase in the concentration of particles from 1 to 20 g/l resulted in an increase of the double-layer capacity and decrease of the charge transfer resistance, while the addition of submicron particles had a higher influence on the characteristics of the double-layer compared to the nano particles
The alumina particles with submicron size could stimulate the incorporation of particles faster than those with nano size, the strengthening performance of the layers depended on the incorporation value of the particles, and on the microstructure of the deposits
Summary
Composite coating has been well developed for the last decades. The simultaneous deposition of the non-metal inclusions and metal phases to form composite layers entails a significant improvement on several physical and mechanical properties of the coating. The final performance in the composite coatings is highly dependent on the characteristics of the particles used in the electrodeposition process including type, size and concentration (Zahavi 1982; Stankovic, 1996; Bakhit, 2013; Ehrhardt, 1985; Bazzard, 1972; Verelest,1991; Chen, 1971; Roos, 1978; Stojak, 1999; Stojack, 2001). Except for the effect of the particle size, the influence of the particle type cannot be neglected It seems that there are some characteristics between alumina alpha and gamma like different zeta-potential or magnetic properties, which can eventually change their codeposition behavior in different solutions (Chen, 1971; Roos, 1978; Stojak, 1999; Stojack, 2001)
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