Determination of the property evolution in rock after laser irradiation by nanoindentation and nuclear magnetic resonance

Abstract

Laser technology, as a novel approach to rock breaking, holds great promise for accessing resources in deep, hard rock layers. Therefore, it is crucial to conduct microscopic testing and analysis of rocks following laser irradiation. In this study, the changes in minerals and elements of the rocks after laser irradiation are clarified using X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). Additionally, the primary temperature range for rock weight loss is determined through thermogravimetric analysis (TGA). The rocks' microscopic features after irradiation are observed using a scanning electron microscope (SEM) and nuclear magnetic resonance (NMR), while the micromechanical properties of the rocks after irradiation are analyzed using nanoindentation techniques. New components such as Ca(OH)2 and CaO are generated in the laser irradiation zone. There is a decrease in the mass percentage of carbon (C), from 10.10 % without laser irradiation to 9.70 % with irradiation, and a decrease in the mass percentage of oxygen (O), from 46.38 % without irradiation to 43.99 % with irradiation. The percentage of large and medium-sized pores is evenly distributed, accounting for more than 50 % of the total after laser irradiation. The small pores occupy 18.85 % and 18.08 % within the size range of 0.0025–0.01 μm and 0.01–0.025 μm, respectively, accounting for a combined total percentage of slightly over 35 %. In the nanoindentation test, the laser irradiation area exhibits more significant deformation, with an average maximum indentation depth increase of 139.4 % compared to non-irradiated areas. The average microscopic modulus of elasticity of the rocks decreases from 36.69 GPa without laser irradiation to 10.06 GPa with laser irradiation, representing a reduction of 72.58 %. Moreover, the average hardness of the rocks decreases from 1.67 GPa without laser irradiation to 0.47 GPa with laser irradiation, indicating a decrease of 71.86 %. This study provides valuable foundational data for potential engineering applications.