The subject of Metallography researches microstructures of different products made from metals and their alloys. The essence of metallographic research of the melted electricity cables consists in studying the microstructure of melted and adjoining to the melted particles of material for the purpose of definition those conditions in which they were formed. In other words, before the fire (and, perhaps, they were its reason) or during the fire (and, perhaps, turned out to be its consequence).

Here you can observe a panoramic image of the microstructure of an electricity copper cable which has been melted by an electric arch, investigated within a judicial fire expertise for the purpose of differentiation conditions of fire-dangerous operating mode of the power supply network. This image is synthesized from 467 micro-photos^[2] zoomed more than x1000, and made on metallographic microscope, an eyepiece camera and the special software. The reactant applied to etching consists of ferric chloride, hydrochloric acid and the distilled water in ratios: FeCl3 - 5g, HCl (1,19 g/cm3) - 30 ml, H2O – 100 ml. The studied microstructure has a sharp edge between the melted and not melted parts of an electricity cable that is a clear sign of short circuit.

Alloy has a complex microstructure which includes fine dendrites which take ~ 50% of the area of the analysis, and the large well developed dendrites (up to axes of the fourth order) which take 10% of the area of the analysis, and large colonies of a eutectic (Cu-Cu2O) take 40% of the area of the analysis. Light basis of an alloy is copper, dark points are copper oxide (I), the maximum content of oxygen is 0,39% (3,4% of Cu2O). There is a small porosity of different sizes. The alloy is a eutectic and hypoeutectic The microstructure of not melted part of an electricity cable was etched poorly, borders of grains aren't distinguishable. Numerous impregnations of oxide of copper (I) are observed over the all area of analysis.

The microstructure of the melted electric cable has typical signs of emergency operating of the power supply network – the short circuit was formed in conditions before the fire.

[2] The most interesting of the panorama microportions:

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