Porosity analysis of superfine-grain graphite IG-110 and ultrafine-grain graphite T220

Abstract

Gas-escape pores in nuclear graphite IG-110 and T220 were characterized by using optical microscopy. It is proved that reliable size distribution of pores can be derived by processing optical images of graphite. The results were compared with those obtained from mercury porosimetry test and X-ray tomography. Optical microscopy showed that the majority of IG-110's (T220's) porosity is contributed by pores with sizes around 13 (3) µm, which was confirmed by X-ray tomography for IG-110. But, mercury porosimetry test indicated that pores with sizes around 2.3 (0.9) µm contribute the majority of IG-110's (T220's) porosity. The difference between mercury porosimetry and the other two techniques suggests that the graphite pores are connected by relatively thinner channels.

A statistical analysis of pores and microcracks in nuclear graphite

“…Furthermore, it is reported that the number of tiny pores could be easily altered by changing the grayscale threshold value. 2 Therefore, the number of tiny pores (cracks) shown in Figure 6A could be misleading. Fortunately, these tiny pores are reported to have a limited contribution to porosity.…”

“…Fortunately, these tiny pores are reported to have a limited contribution to porosity. 2 The porosity's distribution on pore (crack) area (A) is shown in represent the pore sizes. In the analysis of 3-D pore structures reconstructed from X-ray tomography, the diameter of inscribed sphere of one pore was defined as the pore size and was used to produce the porosity's distribution on pore size.…”

“…A technique combining optical microscopy and digital image processing has also been adopted to analyze pore structures of various graphite grades. 1,2,4 It has been demonstrated that X-ray tomography and optical micrograph processing give consistent pore-size distributions for IG-110 graphite. 2 Microcracks in graphite conventionally were observed via transmission electron microscope (TEM).…”

“…1,2,4 It has been demonstrated that X-ray tomography and optical micrograph processing give consistent pore-size distributions for IG-110 graphite. 2 Microcracks in graphite conventionally were observed via transmission electron microscope (TEM). It is very difficult to achieve a statistical analysis of microcracks based on TEM characterization because of its very limited field of view.…”

“…nuclear graphite. Direct observation and statistical analysis of graphite gas-escape pores have been achieved for pristine graphite, [1][2][3] oxidized graphite, 4,5 and irradiated graphite. 6 X-ray tomography has been used to compare pore structures of several graphite grades 3 and to investigate porosity changes induced by oxidation.…”