Rinsing effect of alkaline electrolyzed water on nickel surfaces

Abstract

The improvement in the surface cleanliness of electroplated nickel by rinsing in alkaline electrolyzed water (AEW) was determined. When the nickel plated sample was rinsed with the AEW, it was found that the amount of residual sulfate ion on the surface of a sample decreased approximately by half compared to one rinsed only with de-ionized pure water. Because nanosize hydrogen bubbles are present in the AEW, and the zeta-potential has a negative value, we then surmised that the mechanism of rinsing was as follows: The sulfate ions are selectively absorbed on the nanosize colloidal hydrogen bubbles, or substituted for anions absorbed on the hydrogen bubbles. The sulfate ions absorbed on the nickel surface then become detached. The detached sulfate ions are absorbed on the surface of the hydrogen bubbles, and negatively charge the hydrogen bubbles. It can be considered that any detached sulfate ions do not re-adhere due to the electrical repulsion force of the negatively charged nickel surface. Thus the sample is efficiently rinsed.

Behavior of hydrogen nanobubbles in alkaline electrolyzed water and its rinse effect for sulfate ion remained on nickel-plated surface

“…For removal of ionic impurities including sulfate ions, various techniques are used during cleaning after plating: repeated cleaning with pure water, ultrasonic cleaning, or the like. In a previous article, we reported that cleaning with pure water after a nickel-plated specimen was once immersed into AEW (hereinafter, rinsing) was able to decrease the amount of sulfate ions remaining on the nickel-plated surface [5]. Results of this study verified our idea that the rinse effects of AEW are attributable to hydrogen bubbles generated in AEW, particularly nanosize hydrogen bubbles (hereinafter, hydrogen nanobubbles).…”

“…Experiments were performed according to the following steps to verify that AEW rinses away sulfate ions [5]:…”

“…Consequently, hydrogen bubbles of micrometer and nanometer size were observed. Hydrogen bubbles mutually join over time to become large bubbles; they then flow outside the liquid and disappear in about 1 h [5]. Although the stability of hydrogen bubbles depends on electrolytic conditions and the electrolyte type, fine hydrogen bubbles reportedly disappear in about 1-6 h [10].…”

“…The rinse effect by AEW can also be considered as attributable to actions by hydrogen bubbles similarly to the mechanism for particulate removal. Previously, the authors demonstrated that AEW is an aqueous solution having negative zeta-potential including nanosize and micrometer-size hydrogen bubbles [5]. Therefore, hydrogen generated from electrolysis is present in AEW as negatively charged colloidal bubbles.…”