Study on the effect of temperature and pressure on nickel-electroplating characteristics in supercritical CO 2

Abstract

In this work, it was investigated the effect of solubility in supercritical CO 2 on the nickel-electroplating characteristics. The plating characteristics could be controlled by electric resistance and dispersion in emulsion as well. CO 2 concentration had better be controlled at lower concentration than 50 CO 2 wt% to decrease electric resistance since supercritical CO 2 is non-polar material. Non-ionic surfactant with EO/PO block copolymer was more efficient than any other surfactant and the dispersion at 0.2 surfactant wt% was better than at any surfactant concentration and over-added surfactant concentration over 0.2 wt% brought to the decrease of dispersion properties. Electric resistance was constant at 20 Ω in ranging from pH 2.2 to pH 3.5 and increased slowly to 50 Ω at pH 4 and rapidly to 400 Ω at pH 5. Characteristics of nickel film has a close relation with solubility in supercritical CO 2 and solubility is dependent on pressure and temperature. Solubility at 16 MPa was higher than that any other at pressure and at constant pressure of 16 MPa, solubility in supercritical CO 2 increased with an increasing temperature from 31 to 45 °C and decreased over 45 °C.