Spatiotemporal and emission characteristics of laser-induced plasmas from aluminum-zirconium composite powders

Abstract

Laser-induced plasmas and reactions therein depend on the ablated target's chemical composition and morphology. Recently, we have characterized plasma properties such as spatiotemporal morphology, electron density, species temperature within the plasma, ionization degree, etc. for pure Al under variations in morphology. Here, we utilize a bi-metal powder system to study similar characteristics as a function of powder chemistry. Micron-sized ball milled Al/Zr composites of three chemistries (3Al:2Zr, Al:Zr, and Al:3Zr) are compared to similarly-sized pure Al, pure Zr, and a mixture of Al + Zr powder. We find that the introduction of increasing concentrations of Zr has several interesting effects on the plasma compared to pure Al, including a dramatic increase in the electron density (to ~3–5 × 1020 cm−3), and the earlier onset of ZrO emission bands which have a higher disassociation energy and are thermodynamically preferred over AlO at high temperatures. Differences in plume morphology, the spatial distribution of molecular species, and the emission intensities of ZrO, Zr I and Al I were observed for Al + Zr and ball-milled Al:Zr samples, indicating the influence of microstructure on the chemical reactions. We measured plasma temperatures using the Saha-Boltzmann plot method; the composites demonstrate higher temperatures than pure Zr, Al + Zr mixtures, and pure Al. We observe only minor differences in temperature as a function of increasing Zr-content within the composites. This work continues to build on our understanding of the relationships between plasma properties and microsecond-timescale chemical reactions of reactive materials.