Issue 50

L. He et alii, Frattura ed Integrità Strutturale, 50 (2019) 649-657; DOI: 10.3221/IGF-ESIS.50.55 655 into a major crack. In the light area, owing to the relatively high presence of quartz and feldspar, the quartz phase transition at 573 °C and the thermal expansion between different minerals would cause micro-cracks. On the other hand, when most of the minerals in the dark area reached the melting point, the magma would overflow out of these major cracks, which could even push away the adjacent light area (Figs. 4d and 4f). With temperature continuously increasing, a big cavity is formed in the specimen bulk, owing to the melting and flow of minerals, which also accelerates structural disintegration. Figure 8 : Schematic of the failure process of schistosity structural granite under microwave radiation. C ONCLUSIONS he effects of microwave radiation-induced high temperature on schistosity structural granite were investigated. Specimens were heated to different temperatures (300, 400, 500, 600, 700, and 800 °C) and kept for 15 minutes. Cracking at the cubic edge and local melting at 500 °C were owing to the thermal stress and biotite enrichment, respectively. Above 600 °C, most of the macro-cracks in the dark area were parallel to the schistosity trend, owing to the weak connection in the direction perpendicular to the schistosity plane. The diffraction peak intensity of biotite decreased and even disappeared with increasing temperature, owing to the melting in the biotite-rich area. The average peak stress of the specimens significantly declined from 122.41 MPa (25 °C) to 45.49 MPa (800 °C), and the strength was almost completely lost at 700 °C and above. It was concluded that microwave radiation can effectively destroy rocks by generating high temperatures. The granite samples were destroyed owing to the confluence of multiple factors, such as differences in the thermal expansion properties of minerals, loss of water, phase transformation of quartz, and hot melting. In addition, the schistosity structure of rock significantly affected the cracking pattern. A CKNOWLEDGEMENTS his work was supported by the National Natural Science Foundation of China (21677118). The authors would like to thank Lanjie Hou of Southwest University of Science and Technology for the help in rock mineralogical analysis. R EFERENCES [1] Scott, G., Bradshaw, S.M., Eksteen, J.J. (2008). The effect of microwave pretreatment on the liberation of a copper carbonatite ore after milling, Int. J. Miner. Process., 85(4), pp. 121–128. T T