INCORPORATION OF MULTI-WALLED CARBON NANOTUBES INTO OXIDE LAYER FORMED ON AL ALLOY BY PLASMA ELECTROLYTIC OXIDATION

Abstract

Plasma electrolytic oxidation (PEO) is an electrochemical-based surface modification technique that produces oxide layers on valve metals. The PEO process is performed in an electrolyte solution, which offers the possibility of particles’ incorporation into the growing oxide layer. In this study, we employed a PEO technique on a commercial Al alloy in an aqueous suspension of carbon nanotubes (CNTs) to fabricate CNT-incorporated oxide layer. The voltage–time response was recorded during the process. The surface of the resulting oxide layer was characterized by means of a scanning electron microscope (SEM), an energy-dispersive X-ray spectrometer (EDS), and X-ray diffraction (XRD). It was found from the SEM observation that the CNTs were successfully incorporated into the oxide layer. The PEO with the addition of CNTs led to a delay in time to breakdown (50[Formula: see text][Formula: see text][Formula: see text]s) and a decrease in breakdown voltage (442[Formula: see text][Formula: see text][Formula: see text]V) in the voltage–time curve. The microstructural feature was clearly distinguishable between the oxide layers produced with and without CNTs: a pancake-like structure for PEO without CNTs, and a doughnut-like structure for PEO with CNTs. However, neither the results of the structure analysis nor the elemental analysis provides a clear indication of carbon, even though the presence of CNTs in the oxide layer is evident, suggesting that further optimization of CNT concentration is required.