Effect of strong dielectric substances on the damage characteristics of rocks exposed to microwave radiation: Insight from experiments and mechanisms

Abstract

It has been demonstrated that microwave pretreatment can weaken rocks, reduce tool wear, and improve mechanical rock breaking efficiency. The dielectric properties of rock minerals are a major factor affecting the ability of rocks to absorb microwaves, so it is important to conduct experimental research on rock modification to improve the microwave absorption capacity of rocks. The concept of “microwave-assisted absorbing reagents” has been proposed to increase the microwave absorption capacity of rocks. Sandstone specimens are first pretreated with strong dielectric substances before being exposed to microwave radiation to increase their microwave absorption capacity, then they are exposed to microwave fields and finally conducted to uniaxial compression tests. Enhancement in microwave absorption capacity of sandstone specimens is showed by P-wave velocity, nuclear magnetic resonance, and mechanical tests before and after microwave treatment. The results showed that barium titanate suspension and water are both effective microwave-assisted absorbing agents. The specimens treated with barium titanate suspension exhibited better microwave absorption capacity; in 5 kW microwave power irradiation, its p-wave velocity falls by 14.04%, porosity rises by 25.43%, and uniaxial compressive strength falls by 24.98%. Additionally, the failure form of sandstone specimens changes from brittle to plastic once it has fully absorbed microwave energy.

Analysis of Pore Characterization and Energy Evolution of Granite by Microwave Radiation

“…Accordingly, the porosity fractal dimension can be obtained by taking the logarithm of the NMR technique porosity distribution curve and fitting a linear regression to Equation (11) with a slope of the regression curve of (3 − D), see Figure 10, and the results are shown in Table 2.…”

“…where 𝑇 , is the maximum relaxation time. Taking the logarithm on both sides of Equation ( 10) yields lg𝑆 = 3 − 𝐷 lg𝑇 + 𝐷 − 3 lg𝑇 , (11) Accordingly, the porosity fractal dimension can be obtained by taking the logarithm of the NMR technique porosity distribution curve and fitting a linear regression to Equation (11) with a slope of the regression curve of 3 − 𝐷 , see Figure 10, and the results are shown in Table 2. shows an approximate exponential function decreasing law with the increase in power, while there is no correlation shown between 𝐷 and power, so the microwave has more influence on the microporosity of granite than the macroporosity, and it is necessary to take the condition of microporosity into account in the actual microwave-assisted rock-breaking project.…”

“…Most scholars include additives in order to improve the effect of microwave radiation [9,10]. Gao, F et al [11] studied the degree of microwave absorption in barium-titanate-suspension-immersed rocks and water-saturated rocks and found that the wave-treated P-wave velocity, porosity, and strength appeared to cause more serious damage, and at the same time, the barium titanate suspension rocks absorbed microwaves better than water-saturated rocks. To carry out multi-faceted research, studies have compared traditional heating and microwave heating [12], unilateral and bilateral heating [13], cyclic microwave irradiation [14], and so on.…”