File:Короткое замыкание 2 (short circuit).jpg

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 266 micro-photos zoomed more than x800, 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. The basis of an alloy is made of copper in the form of small underdeveloped dendrites on which borders sites of a eutectic (Cu-Cu2O) are distributed. A light basis of a eutectic is copper, evenly distributed dark points on a light basis are copper oxide (I). Average value of the space taken by an eutectic is 42,37%; the content of oxygen calculated on a formula from State Standard 13938.13-93 makes 0,17%. There are numerous different pore sizes. The alloy is 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.