| China is one of the few countries in the world that has both crystalline and cryptocrystalline graphie.With the advent of the carbon age,the development and utilization of graphite resources has gradually received attention from countries around the world.Coal-based graphite,a kind of cryptocrystalline graphite,is the product of coal which experienced from high metamorphic stage to the graphitization stage.However,there are few studies on the graphitization of coal and it is not unclear on the research of the characterization of coal-based graphie,influcing factors of graphitization and the graphitization mechanism of coal.Thus,it is essential to study the the characteristics of coal-based graphite and the graphitization of coal,which has important value for the rational development and efficient utilization of coal-based graphite.In this paper,based on the theoretical knowlodege of coalifield geology,mieneraloy,material science,coal petrology and structural geology,and on the analysis of macro specimens description,optical microcroscopy,scanning electron microscopy(SEM),X-ray diffraction(XRD),laser Raman spectroscropy(Raman)and high-resolution transmission electron microscopy(HRTEM),meta-anthracite and coal-based graphite with different metamorphic degree from Lutang mines,Hunan Province,southwestern Fujian Procince and Chongyi mine,Jiangxi Province were studied.From the point of the characteristics of the graphtization of coal,the structural characteristics of coal-based graphite at macro-micro-nano scales were revealed,and the graphitization of coal and the controlling factors were anlaysed.Furthermore,the differentiated graphitization of coal was studied.Based on the research of the tectonic-thermal geological background,regional tectonic setting and coal-bearing zones in China,the coal-based graphite minetallogenic zones were divided in China.Moreover,the correlation between the coal-based graphite and tectonic-magmatic activities were discussed,and the mineralization models of coal-based graphite were presented.Finally,the mechanism of tectonic stress during the graphitization of coal was revealed.(1)China was squeezed by multiple plates in history,which has multi-period,highly intense tectonic-magmatic activities.Based on the regional tectonic pattern and coal-bearing belts in China,combined with the tectonic-thermal conditions for the mineralization of coal-based graphite,the coal-based graphite metallogenic zones and belts were divided,including four metallogenic domains and nine metallogenic belts.The first-level metallogenic domains present a pattern of One-vertical and Three-horizonal.The one-vertical domain was the NNE spreading cirfic pacific coal-based graphite domain along the east of the Greater Khingan moutains-Taihang mountain-Xuefeng mountain.The three-horizonal daoman was Nanling coal-based graphite domain,Qinling-Dabie coal-based graphite domain and Yinshan-Yanshan coal-based graphite domain,which was controlled by the three EW spreading tectonic-magmatic belts.(2)Based on the microscopy analysis,XRD,Raman spectroscopy and HRTEM,the characteristics of coal-based graphite was revealed at different scales.The research results show that there are three kinds of microscomponents in coal-baed graphite,namely,coal macerals,pyrolytic carbons and newly formed graphit-like particles.Granular particles,silk-like graphite and flakes graphite are three sub-graphite particles.With the increase of graphitization degree,the crystallization degree of aromatic macro molecules gradually increase,and a broad 002 peak transitions to an asymmetric peak,and finally to a high and sharp peak.In the Raman spectra,D1,D2,D3 and D4 bands gradually subside until disappear.Wheareas,the G band increase and become higher and sharper,and the intensity of the S1 band in the second-region also increases and shows an asymmetric band,which represents the formation of three-dimensional ordered structure.At the nanoscale,the curved,disordered and non-oriented aromatic layers gradually become uniformly aligned with the increase of the graphitization degree.The local moleculaer oretation domains LMOs are firstly formed,which conneted each other as the decrease of carbon curvatures.The carbon layers are nearly flat,forming long-range ordered structures in ordered graphite.(3)Based on the characteristics of the graphitization of coal,the chemical composition paraters were used as the basic index and the structural parameters were used as accurate index to classify the type of coal-based graphite with different graphitization degree.The coal-based graphite was classified into graphitized anthracite(III),semi-coal-based graphite(II2 and II1)and coal-based graphite(I).The results show that samples from Lutang mines are coal-based graphite(I)in majority,samples from the southwestern Fujian Province are manily semi-coal-based graphite(II)and coal-based graphite(I)and graphitized anthracite(III)are next.Whereas,samples from Chongyi mine are mainly graphtized anthracite(III).(4)The controlling factors on coal-based graphite were clarified and can be divided into internal and external factors.The internal factors are mainly different coal macerals and minerals in coal.Since the difference of chemical composition and structural characteristics of macro molecules,the macerals response differently to temperatures and pressures which show different graphtization behavior.Moreover,clay minerals also have catalytic effect during graphitization.The external factors are mainly temperature and tectonic stress.Temperature provides the required activiation energy for the graphitization of coal.Due to the limitation of temperature,tectonic stress plays a key role in graphitization.(5)Differentiated graphitization was revealed during the graphitization of coal.At micro scale,it shows the different graphitzation of coal macerlas.The exinite is firstly graphitized,followed by the vitrinite and the inertinite is the last graphitized.The border of fractures and pores is graphitized firstly.Moreover,different deformation can induce the differentiated graphitization of coal.The ductile deformed samples are seems graphitized with higher graphitization degree than brittle deformed samples.At macro scale,since the effect of multiple factors such as tectonic-magmatic activities,the distribution of coal-based graphite are discontinuous,namely samples at the same distance from the intrusion show different graphitization degree,while samples at different distance from the intrusion seem develop similar graphitization degree.(6)The graphitization of coal,graphitization degree and distribution of coal-based graphite are intensely related with the tectonic-magmatic thermal activities.The graphitization degree in Lutang mining areas,Hunan Province,gradually increases from west to east,and from south to north,along with the degree of structural deformation and magmatic thermal metamorphism.In southwestern Fujian Province,the central coal-bearing zone is strongly influenced by tectonic-thermal activities,occurrencing graphitized anthracite(III)– coal-based graphite(I).And the western coal-bearing belt has weak tectonic-thermal activities which mainly occurences meta-anthracite – graphitized anthracite(III).While the eastern coal-bearin belt occurences semi-coal-based graphite(II)and coal-based graphite(I).(7)Based on the tectonic-thermal conditions for the graphitization of coal,the minerallogenic models of coal-based graphite were proposed,namely,enclosed metallogenic model,semi-enclosed metallogenic model and open metallogeni model.The enclosed metallogenic model mainly forms high-temperature and high-pressure environment,which occrrences coal-based graphite in major,such as the eastern subregion in Lutang mining areas and the central coal-bearin belt in southwestern Fujian Province.The semi-enclosed metallogenic model forms sub-high temperature and sub-high pressure environment,which predominantly occurrences semi-coal-based graphite(II)in the central zone and subregion in Lutang mining areas and the eastern coal-bearing belt in southwestern Fujian Province.And the open metallogenic model forms low-temperature and pressure which occurrences meta-anthracite and graphitized anthracite(III)in western coal-bearting belt in southwestern Fujian Province.(8)Tectonic deformation not only causes the coal seams to be deformed macroscopically and microscopically,but induces the ordering of disordered structure.Drawing on the lessons of the dynamic recrystallization memanism of minerals,the mechanism of tectonic stress in the graphitization of coal is proposed,namely,stress-induced graphitization.In the ductle deformation environment,due to the heterogeneous distribution of stress and stress concentration,which could lead the local BSUs(basic structural units)to align along the same direction,forming local oriented domains(LMOs).With the adjustment and migration of structural defects and the expansion of LMOs in a whole,the graphitization degree of sample is gradually enhanced. |
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