Study On Temperature Rising And Weakening Effect Of Minerals And Rocks Under Microwave Irradiation

Mechanical excavation is widely applied in rock breakage for it's advantages of slight damage of surrounding rock,high automaticity,and high operating efficiency However,it will still come across the drawbacks of severe tool wear,slow excavation progress,and high cost when facing hard rocks.Recent researches have proved that microwave irradiation can effectively weaken the rock structure.Thus a new method of microwave assisted rock breaking was put forward(Declining the rock strength and abrasion with microwave irradiation in advance,and improving the excavation efficiency as well as reducing the tool wear),which has a promising application prospect.This paper takes igneous rocks as research object.Ten common rock-forming minerals and ten igneous rocks are treated under 500W microwave irradiation for 3min,and their responses to microwave are distinguished by heating rates.In addition,the influence of crystal form and element on heating rate of minerals,mineral proportion and structure on that of rocks are studied.On the other hand,the changing law of physical and mechanical properties of five igneous rocks is analyzed to reveal the principle and factors of rock weakening.The following conclusions are obtained(1)Different minerals have various responses to microwave.Hypersthene is classified as strong-absorbing minerals,hedenbergite and biotite as middle-absorbing minerals,and forsterite,diopside,hornblende,plagioclase,orthoclase,and quartz as weak-absorbing minerals.Ore minerals like hematite,magnetite and pyrite have much better response than common rock-forming minerals,and they are classified as very strong-absorbing minerals(2)With regard to Mineralogy,the heating rate is connected with mineral species(groups and subgroups)and element distribution(proportion of Fe).In terms of groups,pyroxene and biotite have good response to microwave,while feldspar,olivine,quartz,and hornblende don't;In terms of subgroups.Orthopyroxene has better response to monoclinic pyroxene;In terms of element distribution,minerals containing more Fe have higher heating rates in the same subgroups(3)The heating rate of rock is mainly influenced by the kind and proportion of strong-absorbing minerals contained.Among the ten igneous rocks studied in this paper,those contain more pyroxene and biotite have higher heating rate.On the whole,basic rocks have best temperature response,followed by intermediate rocks,and acid rocks the worst.(4)The prediction model of rock heating rate is influenced not only by the types and content of minerals,but also by proportionality and structural coe fficient.In the bi-gram model,the proportionality coefficient of hypersthene is greater than 1,and reduce to 1 as its content increases;The proportionality coefficient of plagioclase is less than 1,and increase to 1 as its content increases.The heating rate of rock powder is twice or 3 times that of rock blocks of the same mass,and the influence of rock structure is greater in basic rocks than in intermediate rocks,and acid rocks(5)The weakening effect of Adamellite 1#under 2kW turns out to be better as the duration increases(Strength declined 0.05%,20.7%and 41.7%for 2min,4min and 6min,respectively).After 2kW microwave irradiation for 4min,basic rocks have the best weakening effects(Diabase1#weakened 31.5%),followed by intermediate rocks(Adamellite1#and Adamellite2#weakened 20.7%and 16%,respectively),and acid rocks the worst(With little change in alkali-feldspar granite).Apart from mineral composition and the original strength of rock,some special constructions or component will also influence the weakening effects(The carbonate almond body and iron ore surrounding void in Diabase2#),which results in easier breakage of Diabase2#under the same test condition in spite of its higher strength than Diabase1#.