CW CO2 -Laser-Induced Formation of Fulgurite on Lime-Pozzolan Mortar

Abstract

A glassy material similar to fulgurites (fusion of the soil which has been struck by lightning) was prepared by continuous wave (CW) CO2 laser (λ = 10.6 μm) ablation of lime–pozzolan mortar at medium-vacuum conditions and atmospheric pressure. In all the irradiated samples, the determined surface temperature is higher than the melting temperature of mortar (1556 K), so the surface is melted and converted into an amorphous glassy when cooled. The samples were studied combining laser-induced breakdown spectroscopy (LIBS) and Raman spectroscopy. The emission induced by the CW CO2 laser is mainly due to electronic relaxation of Na, K, Si, Si+, Ca, O, N, and CaOH species along with an intense continuum due to blackbody emission. The emission induced on both natural and produced fulgurite is mostly due to electronic relaxation of Ca, Ca+, Si, Si+, Si2+, Si3+, H, Na, K, Mg, N, O, CaOH, and OH species with different relative intensities in some of them. Raman spectra show that the glassy formed material is similar to natural fulgurites, with the main difference arising from portlandite formed over the surface of the lime–pozzolan mortar. As the laser power increases, less density SiO2 glass is formed with more Q4 and Q1 units present.