基于SAXS方法的核石墨微孔结构的温度影响

X射线小角散射(Small Angle X-ray Scattering,SAXS)是研究纳米尺度微观结构的重要手段。本文利用同步辐射SAXS技术测量了25oC、100oC、200oC、300oC和400oC时,IG-110和NBG-18核石墨在纳米尺度范围内孔隙的数量分布及其分形特征的变化。实验结果表明,IG-110和NBG-18核石墨的微观结构中存在微小尺寸上的不均匀区域,且核石墨孔隙的固气结构具有明锐的界面。但随着温度的升高,固气界面的变化并没有呈现出明显的规律性。此外,在纳米尺度上,IG-110和NBG-18核石墨的孔隙数量随温度呈现增加的趋势,且IG-110核石墨孔隙数量的增加幅度大于NBG-18核石墨,其平均孔隙尺寸的减小幅度大于NBG-18核石墨。在核石墨的微孔结构内,其固气界面的分形维数随温度升高逐渐减小,且NBG-18核石墨分形维数的变化幅度小于IG-110核石墨。这表明核石墨的分形结构随温度的升高逐渐光滑。

Effect of temperature on the microporous structure of nuclear graphite studied by SAXS

Background:The distribution of nanoscale pore is of great significance to irradiation damage behavior of nuclear graphite under intense radiation. Small angle X-ray scattering (SAXS) is an important method used to study the number distribution and its fractal characteristics of pore in nanoscale.Purpose: This study aims at the changes in number distribution and its fractal characteristics of nanoscale pore in nuclear graphite.Methods:Two typical nuclear graphite, i.e., IG-110 and NBG-18 were sampled and tested at synchrotron radiation SAXS beamline station at temperatures of 25 oC, 100 oC, 200 oC, 300 oC and 400 oC, respectively.Results: The results showed that there was a non-uniform area in the microstructure of nuclear graphite, and the solid-gas structure of the nuclear graphite pore had a sharp interface, but the change of solid-gas interface does not show obvious regularity with the increase of temperature. In addition, the number of nanoscale pore in IG-110 nuclear graphite increases with the temperature, and is more obvious than that of NBG-18. The fractal dimension of the solid-gas interface decreases with the temperature increasing, indicating that the fractal structure of the graphite become smoother with the increasing of temperature. And the change of IG-110 is more obvious than that of NBG-18.Conclusion: The temperature has a significant impact on the pore number distribution and its fractal characteristics.