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To prevent fire incidents, investigating fire traces and identifying the cause of the fire is a primary task in fire forensic evidence identification. Analysis of microscopic characteristics of copper conductors after a fire is an effective method for this purpose. This study simulated the temperature, time, and atmospheric conditions of a fire environment, generating fires caused by overcurrent faults, to investigate surface morphology, cross-sectional grain shape, and size of copper conductors after a fire. As the temperature increased and duration extended, oxidation degree of the copper conductor deepened, and grains continuously grew, exhibiting an axial shape. At 400 ℃, the grain size was 7~11 μm. At 600 ℃, it increased to 8~14 μm. At 800 ℃, it reached 13~17 μm. During the grain growth process, a large number of twins appeared due to low stacking fault energy. Average grain size of copper conductors was directly proportional to both annealing temperature and time, with temperature having a more significant impact. Linear fitting results showed that activation energy for grain boundary migration during grain growth was 0.68 kJ/mol. Under actual overcurrent fault conditions, the failure copper conductor formed molten beads and dendrites at the fracture site, indicating that an excessive current in the circuit caused the conductor to overheat, ultimately leading to fracture, with abnormal grain growth occurring near fracture zone.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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