Study On The Influence Of Microwave Irradiation On Some Physical And Mechanical Properties Of Common Minerals

In the process of tunneling,hard rock often causes great wear to TBM roadheader tools and reduces the efficiency of tunneling.In order to improve the excavation efficiency,microwave is used to irradiate the excavated rock before excavation,which can make the rock damage and weaken to a certain extent,and can greatly improve the excavation efficiency of TBM.In the process of microwave weakening rock,different minerals have different microwave absorption degree,which leads to different weakening effects.Therore,it is necessary to study the weakening law of minerals under microwave irradiation.In this paper,the change rule of physical and mechanical characteristics of common monomer minerals in rock under microwave radiation is preliminarily explored,the influence rule of different kinds of minerals under microwave irradiation is studied,and the compressive strength,wear-resistant characteristics and quality loss of minerals after microwave irradiation are tested and analyzed.The paper also uses numerical simulation to study the change of electric field caused by the size and location of mineral sample in microwave oven,analyzes the temperature rise,stress characteristics and development law of plastic zone of the sample,preliminarily determines the position of mineral in the microwave oven cavity and the size of mineral in the test;through indoor test.The microwave irradiation test was carried out,the point load test and the mineral wear resistance test were carried out in comparison with the minerals after irradiation,and the surface and fracture observation and quality loss analysis were carried out for the minerals after irradiation.The main research results are as follows:(1)Using COMSOL to establish the numerical analysis model,the influence of sample size and placement position in the microwave oven cavity on the microwave irradiation effect was studied.The results show that the penetration ability of microwave to the strong absorbing minerals is reduced,and the whole mineral specimen with side length of 5?15mm will be destroyed under the condition of small thermal stress.When the side length of mineral specimen increases to 20mm or more,a weak electric field band with extremely weak microwave effect will appear in the mineral interior,and the electric field distribution in the mineral specimen with side length of 40 or 50mm is the most uneven.Microwave heating is non-uniform heating,with the increase of mineral size,the non-uniformity is more obvious.The electric field intensity at the mineral boundary and corner is the largest.The minerals in the symmetry axis of the cavity are the most evenly affected by the electric field.Considering comprehensively,the mineral specimen with side length of 20?30mm is placed in the center of the cavity,which is an ideal test scheme.(2)Six kinds of main rock forming minerals were selected to carry out the microwave irradiation test with constant power of 1kW and specified temperature(200?,400?,600?).The surface observation and micro fracture observation of the irradiated minerals were carried out,and the fracture characteristics of the minerals after point load test under different schemes were analyzed.The results show that with the increase of temperature,the internal structure of mineral breaks and thermochemical reactions of elements occur,which are the main reasons for the change of mechanical properties of mineral.(3)Through the point load test,the point load test value is converted into uniaxial compressive strength.It is found that the strength of pyroxene,K-feldspar and mica schist increases first and then decreases,while that of quartz,calcite and albite decreases monotonously with the increase of temperature.(4)Through the wear resistance test and mass loss test,the analysis shows that the wear resistance of K-feldspar,albite,calcite and mica schist decreases with the increase of irradiation temperature,which is closely related to the structural stability of minerals and the structural damage caused by temperature.From the analysis of mineral quality loss,it is concluded that the main factors leading to the loss of mineral quality are the internal water evaporation and the thermal decomposition of oxides with the increase of temperature.