13th International Conference on Fracture June 16–21, 2013, Beijing, China -6- been neutralized when we scanned it, so we infer that when the specimen was broken, the positions occupied by the white spots are the charged ones, which absorbed the charged ions such as H+ when the broken surface put in the air. It means that the positions occupied by white spots are the charged positions when the specimen is broken. As mentioned above, the main charged positions are distributed near the prefabricated nick, therefore we can easily explain why the surface charge density is related to the thickness of glass slab but it is not linearly relationship. However, so far we cannot know the electrification mechanism of fracture. We cannot know what results in the broken part of glass charged and why the charges distribute near the nick when the glass slab is broken. Although some reports indicate that the existing Na+ ions make some of the [SiO4] three dimension network structures broken [20] and number of non-bridged oxygen significantly increases. Na+ ions occurred near the center of the non-bridged oxygen hole neutralize the net charges. When the glass is broken, the Na+ ions are free, therefore it may result in the broken glass charged. But the non-bridged oxygen should uniformly distribute in the glass, so if the inference mentioned is true, the charges also uniformly distribute in the broken surface and not near nick shown in Fig. 6(b). Unfortunately, we cannot know how to correlate the electrification mechanism with them and expect further studies. Fig. 6 SEM observation results of fratographies of broken surface of glass slab, in which many white spots distribute, (a) result magnified by 100 times and (b) result magnified by 500 times Acknowledgements This work is supported by the grants of National Natural Science Foundation of China (No.1121202, No.11072096 and No.11272139), and authors express their sincere appreciation to those supports. References [1] V. Frid. Calculation of electromagnetic radiation criterion for rockburst hazard forecast in coal mines. Pure Appl Geophys, 158 (2001) 931-944. [2] V. Frid. Electromagnetic radiation method water-infusion control in rockburst prone strata. J Appl Geophys, 43 (2000) 5-13. [3] S. P. Kanagy II, C. J. Mann, Electrical properties of eolian sand and silt. Earth Sci Rev, 36 (1994) 181-204. (a) (b)
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