Effects of ultrasound on both electrolytic and electroless nickel depositions
The effects of ultrasound on both electrolytic and electroless nickel depositions were investigated by polarization and a.c. impedance methods. The ultrasound accelerated the charge transfer process at the metal-electrolyte interface in the electrodeposition and the mass transport process in the electroless deposition. In the electrodeposition with Watts bath, the crystal orientations of deposited film largely changed in the presence of ultrasound. The imposition of ultrasound gave rise to decreasing cathodic overpotential and increasing exchange current density, and these effects depended upon the ultrasonic frequency. The values of exchange current density estimated from a.c. impedance were dependent upon the measured electrode potentials. In the electroless deposition with citrate bath, the deposition rates increased in the presence of ultrasound. There were two kinds of Ni(2+)-citrate complex which were reduced at -0.7 V and -1.1 V. The electroless deposition process was controlled by the Ni(2+)-citrate complex that was reduced at -0.7 V. This reduction rate was diffusion controlled and largely increased in the presence of ultrasound. The effects of ultrasonic frequency on both electrodeposition and electroless deposition increased in order of no irradiation < 100 kHz < 28 kHz < or = 45 kHz.
Kobayashi
K
Department of Materials Chemistry, Yokohama National University, Japan. kat-koba@cms.ynu.ac.jp
Chiba
A
Minami
N