Research on Force and Thermal Phenomena of Short Circuited Melted Mark in Electrical Fire
This paper mainly does a research on force and thermal phenomena of short circuited melted mark in electrical fire. The primary short circuited melted mark and secondary short circuited melted mark were prepared by the experiment, and were characterized by metallographic microscope, powder X-ray diffraction, scanning electron microscope and energy dispersive spectroscopy, the role of forces and heat in short circuited melted mark in electrical fire were demonstrated and investigated. It is found that they show a similar shape that the melted ball close to one side for anode melted marks, and their particles show the specific and uniform direction and the most particle size of anode melted marks are larger than the particle size of cathode melted marks, both below the copper wire grain size 64.2nm, similarly, it can be clearly seen that the ratio of O: Cu in deposit layer of all melted marks are below 0.5. Finally, these above special phenomena gave short circuited melted mark the primary statement from the theoretical point of view.
Study on discrimination between primary and secondary molten marks using carbonized residue
Abstract In most places where a fire started, electric molten marks that may be the cause of the fire are found. Various methods have been studied for identifying these electric molten marks to be either the cause of a fire (a primary molten mark (PMM)) or one caused by the flames of the fire (a secondary molten mark (SMM)). Little was studied, however, on their identification using the carbonized residue remaining in the molten marks. In this study, therefore, it was examined whether it was possible to discriminate between the PMMs and SMMs by analyzing the crystal structure of the carbon in the carbonized residue, which came from PVC insulation, remaining in the primary and the SMMs. As a result, it has been found that PMMs contain both graphitized carbon and amorphous carbon, whereas SMMs only contain amorphous carbon.
Experimental investigation of the geotechnical properties and microstructure of lime-stabilized saline soils under freeze-thaw cycling
Abstract The Song-Nen Plain in northeastern China holds one of the three largest expanses of soda saline-alkali soil in the world. Due to its disadvantageous geotechnical properties, the saline soil in this area is unable to meet the needs of construction projects. This study evaluates the stabilizing effect of adding lime to such soils. Specifically, it investigates how the physicochemical and mechanical properties and microstructure of soda saline-alkali soil are altered by lime and how these changes are affected by both freeze-thaw cycling and the duration of curing. The results reveal that adding lime to saline soil transforms clay particles into sand and silt particles and causes the pore size distribution (PSD) to become bimodal, with small-pore and macropore populations. An increase in lime content leads to an increase in the unconfined compressive strength (UCS) but a gradual decrease in both the cation exchange capacity (CEC) and plastic index. Freeze-thaw cycles break up coarse particles and aggregate finer particles, increasing the diameter of macropores and decreasing the USC; however, the effect on specimens with >9% lime is negligible. It is further shown that the geotechnical properties of the soil change immediately after the addition of lime, indicating that the cation exchange reaction takes place very quickly. Furthermore, the pozzolanic reaction leads to an increase in the percentage of sand-sized particles and a decrease in porosity after 28 days of curing. Overall, these results indicate that it is feasible to use lime to improve the engineering properties of soda saline-alkali soil in this area.