Uso do sal inorgânico persulfato de amônio e do ácido FRY na identificação de adulterações em chassis de automóveis no instituto de criminalística de Timon/MA

Abstract

Tampering with vehicle identification number (NIV) or chassis number is quite common in the world of crime, even after police retrieve stolen and / or stolen vehicles, returning the property to the owner only happens after the tampered vehicle passes by a Technical Expert to find the original NIV and thus identify the legitimate owner. Today, the chemical reagent FRY is the most used for revealing the original chassis number in the Brazilian Forensic Institutes, however this acid is very strong as well as exudes acid gases and is difficult to discard. Based on this, another reagent (ammonium persulfate), a salt, that was as good as the FRY in the revelation of the chassis number was investigated, and is easy to dispose of. However, this research was developed with the objective of investigating the chemical composition of the chassis steel, the residual stresses in the field of engraved characters and the chemical attack of both reagents. At first, a steel plate engraving a 17-character (17-character) chassis number was taken from a Renault-type vehicle and cut into nine samples, eight samples with two characters and one with one character was discarded. The eight samples were sanded and polished on the surface of the chassis number engraving with alumina 3 μm. The chemical composition of the steel was analyzed by Scanning Electron Microscopy (SEM) through Dispersive Energy Spectroscopy (EDS). The samples were then divided into two groups of four, the samples of one group being attacked by FRY acid and the samples of the other group attacked with ammonium persulfate. The attack of both reagents was by swabbing with cotton and the time to attack until development was measured for each reagent. The SEM analysis revealed the chemical composition of the steel, because the carbon content is important to decide the type of reagent to be used, the place where the reagents attack with the highest reaction speed is where there are residual tensions. The macrographic result showed that the revelation of the characters in the samples with the use of the ammonium persulfate was as good as the one obtained with the FRY, however, the revelation with the ammonium persulfate proved to be more effective, since the samples attacked with FRY oxidized fast and impaired future tests, whereas Persulfate produced long-lasting results and does not detract from future examinations.