| Synchrotron radiation,as a high-intensity and high-collimation X-ray source,is a powerful probe in studying material structure.Small angle X-ray scattering(SAXS)method using synchrotron radiation as X-ray source can in situ characterize the geometrical structure of materials at nanoscale,including the shape,size and volume fraction of scatterers(such as pores or particles).Coal is an important energy and chemical raw material.Carbonization of coal under the condition of insulating air can produce char,coke,tar and gas,which is one of the main ways of comprehensive utilization of coal.Coal,char and coke are typical porous materials,which are suitable for study by small angle X-ray scattering with synchrotron radiation.However,the in situ SAXS study of coal carbonization process has not been seen in literatures.Based on the 1W2A small angle X-ray scattering station of Beijing Synchrotron Radiation Facility(BSRF),this dissertation studies the pore structure changes of coal in the process of carbonization,and explores the structural evolution characteristics and mechanism of coal carbonization based on the changes of fractal dimension,porosity,specific surface area and pore size distribution.The main contents are as follows:(1)The absolute scattering intensity of SAXS includes quantitative information related to the mass and density of matter,such as molecular weight of biological macromolecules,volume fraction of scatterers(such as pores or particles).Based on the SAXS station at BSRF,this dissertation studies the method of calibrating absolute scattering intensity by using standard samples of glass carbon and water,derives calibration formulas,formulates calibration steps,compares the advantages and disadvantages between glass carbon and water as standard samples,and overcomes the problem of tedious operation and poor repeatability by attenuating incident light with silicon or aluminum foils to calibrate the absolute intensity of the SAXS instrument at the 1W2A station of Beijing Synchrotron Radiation Facility(BSRF).This calibration method developed in this dissertation does not need to measure the incident light intensity,nor need to limit whether the incident light intensity is constant or not.It is easy to operate,simple to calculate and reliable in results.This calibration method has been successfully applied to calculate the molecular weight of protein and the change of porosity in the carbonization process of anthracite,and has been used by SAXS users at the 1W2A station of BSRF.(2)High temperature carbonization of coal is one of the main ways to improve comprehensive utilization of coal.Synchrotron radiation SAXS can be used for in-situ measurement of the changes of pore structure during carbonization of coal.The author of this dissertation developed a high temperature(1200?)furnace for in-situ SAXS measurements on coal carbonization.The device essentially consists of a heating body and a controller,which can heat coal to 1200? under the condition of isolating air,and the heating rate and holding time can be controlled by program.The furnace is compact in structure and convenient in use.The furnace has been applied to some user's experiments at the SAXS station on 1W2A beamline of BSRF.(3)Carbonization is one of the main methods for comprehensive utilization of bituminous coal.Bituminous coal and its solid products from carbonization,namely char and coke,have complex pore structure,which can be characterized by fractal.This work performed a study on the fractal structure of the solid products prepared from the bituminous coal of Shuiyu mine in Shanxi Province,China,at different carbonization temperatures(25?-1000?)by synchrotron radiation SAXS.The results show that the bituminous coal appears surface fractal structure in the whole carbonization process.The variation of fractal dimension with carbonization temperature illustrates the different stages of the carbonization process.(4)Lignite is coal with the lowest degree of coalification.Its utilization can be improved by carbonization.Pore structure is the main part of the physical structure of coal,char and coke.In this work,we performed an in-situ SAXS study on ultra-high temperature carbonization(1200?)of lignite taken from the Wulantuga mine in Inner Mongolia Autonomous Region,China.The variation of pore structure including pore size distribution,porosity and specific surface area of lignite illustrates the different stages of the carbonization process.There are characteristic pores with radius of approximate 4.6 nm in the lignite which change distinctly in ratio but only slightly in size during carbonization.(5)The changes of porosity and graphite-like microcrystalline geometric parameters of a bituminous coal during a medium-temperature carbonization(700?)process were studied in situ using a synchrotron radiation SAXS/WAXS method.The results also show that the carbonization has several distinct stages. |
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