Effects of sub-/super-critical CO_(2)on the fracture-related mechanical characteristics of bituminous coal

Injecting carbon dioxide CO_(2)into a coal seam is an important way to improve coalbed methane recovery and to store geological carbon.The fracture mechanical characteristics of bituminous coal determine the propagation and evolution of cracks,which directly affect CO_(2)storage in coal seams and the efficiency of resource recovery.This study applied CO_(2)adsorption and three-point bending fracture experiments using bituminous coal samples in a gaseous state(4 MPa),subcritical state(6 MPa),and supercritical state(8 and 12 MPa)to investigate the influence of CO_(2)state and anisotropy on the fracture-related mechanical response of bituminous coal.The results show that the change in mechanical properties caused by CO_(2)adsorption is CO_(2)state-dependent.The supercritical CO_(2)adsorption at 8 MPa causes the largest decrease in the mode-I fracture toughness(KIC),which is 63.6%lower than the toughness before CO_(2)adsorption.The instability characteristics of bituminous coal show the transformation trend of“sudden-gradual-sudden fracture”.With or without CO_(2)adsorption,the order of the KIC associated with three types of bituminous coal specimens is crack-divider type>crack-arrester type>crack-short transverse type.Phenomenologically,the fracture toughness of bituminous coal is positively correlated with its specific surface area and total pore volume;the toughness is negatively correlated with its average pore size.

Mode splitting revealed by Fano interference

An optical whispering gallery mode(WGM) resonator supports degenerate counter-propagating modes and the degeneracy is lifted as mode splitting due to Rayleigh scattering. However, quantitative analysis becomes difficult if the resonance experiences weak scattering. Here we develop a spectroscopical method to identify an arbitrary small scatterer using the Fano interference-induced spectral response modification. Scattering information can be revealed by fitting the responses as a function of the field’s phase and intensity. In addition, we show that this modified response helps achieve an ultra-low detection limit for the mode-splitting-based nanoparticle detection method. This approach may be promising in the characterization of high-Q-factor devices, novel sensing methods, and quantum coupling system investigation.