Abstract
Specimens were electrolyzed by AC with various current waveform (sine wave, square wave and saw-tooth wave) and frequencies (10∼kHz) in NH4OH-NH4F system bath and NaOH-H2O2 system bath at a current density of 2A/dm2 for 30min, at 20°C.
The use of a 10Hz square waveform resulted in a formation of a thicker film (5∼6μm) in both the NH4OH-NH4F and NaOH-H2O2 system baths. In the former case (NH4OH-NH4F system bath), film thickness decreased at frequencies above about 200Hz, reaching about 1∼2μm at frequencies above 1kHz. In the latter case (NaOH-H2O2 system bath), film thickness decreased according to increase of frequency, and it was about 0.5∼1μm in thickness at high frequency more than about 500Hz.
The films anodized in the NaOH-H2O2 system bath with square current waveform was much rougher than those fromed using with sine or saw-tooth waveforms and larger pores were observed by microscope.
Many large pores were observed in the coatings formed at high frequency and those formed in NaOH-H2O2 system bath had larger pores than those fromed in NH4OH-NH4F system bath.
