13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- in our experiment is Na2OCaO6SiO2, in which Na2O and CaO are about 15% and 16%. Our DES is not sensitive to the elements with smaller atomic number such as H, C, O and Na, so the energy spectrums of these elements cannot be displayed in Figs. 5(b)-5(c). Comparing the Fig.5(b) with Fig.5(c), the content of element of Si is highest than the ones of others, which has not large difference in quantity of different position. It is difficult to correlate it to electrification of facture. 0.25 0.30 0.35 0.40 0.45 0.50 0.55 3mm*15mm 3mm*20mm 4mm*15mm Surface charge density (C/m2) 4mm*20mm Fig. 4 Surface charge density of broken surface for different cross section Fig. 5 SEM observation result for fractography of broken glass slab (a), in which I is a black spot and II is a white spot. (b) DES of I in (a), and (d) DES of II in (a). It is worthy to point that, when we scanned the broken surface by SEM, we found an interesting phenomenon that is there are many white spots distributed in the broken surface and the number of white spots decrease with the distance away from the nick increasing shown as in Fig.6(a). A white spot is about 10m in size (see Fig. 6(b)). And when we continually bombard the white spot by electrons, the white spot will disappear after several seconds. That means that the white spot is comprised by the elements with smaller atomic number. The scanned specimen has Element Line Atomic% Al Ka 1.16 Si Ka 70.35 K Ka 4.05 Ca Ka 23.93 Fe Ka 0.52 Element Line Atomic% Al Ka 2.09 Si Ka 70.64 K Ka 3.26 Ca Ka 23.51 Fe Ka 0.50 (b) (c) I II (a)
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