Pulsed laser nitriding of uranium

Abstract

Pulsed laser nitriding offers several advantages such as high nitrogen concentration, low matrix temperature, fast treatment, simple vacuum chamber and precise position control compare to ion implantation, which is favorable for radioactive material passivation. In this work, uranium metal was nitrided using an excimer laser for the first time. The nitrided layers are characterized by X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy. The nitride layer is composed mainly of UN and U2N3 and depends on nitriding process. The amount of nitride increases with energy density and pressure. The irradiated area has a wavy structure which increases the roughness, while scratches and asperities caused by sand paper polishing were eliminated. Scan speed has a profound influence on the nitride layer, at low speed U2N3 is more likely to form and the nitride layer tends to crack. XPS analysis shows that nitrogen has diffused into interior, while oxygen is only present on the surface. Ambient and humid–hot corrosion tests show the nitrided sample has good anticorrosion property.