On the compactness of the oxide layer induced by utilizing a porosification agent

Abstract

It is imperative to control the pore density and distribution of pores produced inevitably on the surface of the oxide layer produced by plasma electrolysis (PE) process since these factors could affect the final electrochemical performance of these layers. Up to this study, utilizing a porosification agent in order to optimize the compactness of the oxide layer grown on Al alloy via PE has been rarely reported. Here, a simple novel strategy was proposed in the present work to control these defects by triggering the incorporation of V2O5 through utilizing a high concentration of phosphate ions which was reported extensively as a porosification agent during PE process. For this aim, Al-Mg-Si alloy samples were treated by PE under AC conditions at a current density of 75 mA/cm2 for 5 min from V2O5-based electrolytes with 0, 6 and 18 g/L of Na3PO4. It was found that the oxide layer made from electrolyte with 18 g/L Na3PO4 was less porous and smoother than the counterparts with 0 and 6 g/L Na3PO4. This result was attributed to the development of uniform fine plasma sparks at the high concentration of Na3PO4 responsible for facilitating the incorporation of V2O5 particles into the oxide layer which resulted eventually in the formation of a conformal black coating. Accordingly, the electrochemical response of the oxide layer with 18 g/L Na3PO4 was superior to that with 6 g/L Na3PO4. This study would potentially pave a way to obtain a fully compact oxide layer with controllable surface properties in optical and aerospace applications.