Characterizing thermal damage of diorite treated by an open-ended microwave antenna. (January 2022)

• Record Type: Journal Article
• Authors: Ma, Zhongjun; Zheng, Yanlong; Li, Jianchun; Zhao, Xiaobao; Zhao, Qinhua; He, Julong; Fu, Huanyu
• Is Part Of: International journal of rock mechanics and mining sciences. Volume 149(2022)
• Publication Date: 2022-01
• Subjects: Microwave heating and fracturing -- Dielectric-loaded converging waveguide antenna -- P-wave velocity -- Thermal damage zone; Rock mechanics -- Periodicals; Soil mechanics -- Periodicals; Mining engineering -- Periodicals; Roches, Mécanique des -- Périodiques; Sols, Mécanique des -- Périodiques; Technique minière -- Périodiques; 624.151305
• DOI: 10.1016/j.ijrmms.2021.104996
• Languages: English
• ISSNs: 1365-1609

Abstract

Abstract: The thermal damage induced by microwave treatment in rocks has not been well explored, especially when using the dielectric-loaded converging waveguide antennas (DLCWAs). In this paper, the effects of microwave power level, heating time and working distance on the temperature increase, ultrasonic wave velocity reduction, and more importantly, the fracturing characteristics and the damage zone, are comprehensively investigated using a 6 kW microwave source and a customized DLCWA. A novel method is also proposed to adjust the P-wave velocity ( V p ) reduction across the thickness of the specimens and to determine the equivalent damage zone. The results show that the temperature and high temperature area, crack number, length and density, and the V p reduction rate as well as the damage zone all increase as either the power level or the heating time increases and decrease as the working distance increases. The damage zone can be divided into the crushed zone, fracture zone and discrete fragment zone based on the crack characteristics and the crack generation mechanisms. The method proposed is demonstrated to be reliable in predicting the damage zone induced by microwave heating. Highlights: Used a dielectric loaded converging waveguide antenna to fracture a biotite diorite. Investigated the effects of microwave power level, heating time and working distance on thermal fracturing. Proposed a novel method to estimate the P-wave velocity distribution across the total thickness. Determined the equivalent thermal damage zone based on the spatial P-wave velocity reduction.