Ceramic oxide coating formed on beryllium by micro-arc oxidation

Beryllium was oxidized at a current density of 10 mA cm−2 in a 0.5 M Na2CO3 (pH = 11.2) electrolyte to understand the micro-arc oxidation (MAO) process. Different oxidation stages were investigated by analysing the voltage-time responses and coating morphology. 'Electric breakdown' accompanied by sparks travelling across the metal/electrolyte interface occurs when the voltage rises above a certain point (∼202 V), leading to the formation of an off-white 'ceramic-like' BeO coating. The MAO coating consists of two layers-an inner barrier layer and an outer porous layer-and shows improved corrosion resistance and insulation properties. XPS and XRD indicate that the coating has a chemical composition of BeO and is crystalline. Further, corrosion resistance and insulation properties of the coating were estimated by EIS analysis.