Heloísa P. Dias

Documentoscopy by atomic force microscopy (AFM) coupled with Raman microspectroscopy: applications in banknote and driver license analyses

Document examination to determine document authenticity is an important field in forensic science. Methods of counterfeiting have become sophisticated, so the development of informative and effective tools for questioned document examination becomes necessary and challenging. Atomic force microscopy (AFM) and Raman microspectroscopy have been shown to be advantageous, allowing the comparison of inks, the sequencing of crossing lines, and providing physicochemical information about the nature of the paper and of the ink deposition mechanism. Herein, AFM and Raman techniques are explored for the analysis of both authentic and counterfeit Brazilian driver licenses, and national and international banknotes. For AFM results, parameters, such as roughness and topographic profiles of the chalcographic region of banknotes and Brazilian driver licenses, are sufficient to visually discriminate between authentic and counterfeit documents. However, statistical analysis using the Students t-test showed that the asymmetry (SSK) values obtained from series numbers and micro-letter regions identified the counterfeiting. Compared to the topographic profile obtained for homemade banknotes produced by different printers (inkjet and LaserJet), the AFM technique indicated that the paper used to counterfeit the Brazilian driver license and the real banknote was an “office” type with inkjet printing. For Raman spectroscopy results, bands of phthalocyanine, and diarylide (diazo) pigments, and carbon black were identified in authentic documents, whereas for counterfeit documents, only a high fluorescence was observed. The obtained data were reproducible via the video spectral comparison (VSC) technique, typically used by forensic police laboratories.

Study of the Corrosive Behavior of the AISI 1020 Steel in Acid Crude Oil by Microscopic Techniques (LM, AFM and SEM/EDX) and Raman Spectroscopy

Microscopic techniques were combined to study the influence of corrosion rate on the morphologic behavior of AISI 1020 steel specimens submitted to thermal degradation of a typical acid crude oil (total acid number (TAN) = 2.1390 mg KOH g and total sulfur (S) = 0.7778 wt.%). The techniques used were light microscopy (LM), scanning electron microscopy/energy dispersive spectroscopy (SEM/EDX), atomic force microscopy (AFM) as well as Raman spectroscopy. Assays were performed in six different degradation time (t = 6, 12, 24, 36, 48 and 72 h) at 320 °C. After the exposure of the specimens to petroleum, a reduction above 37% in the TAN after t = 72 h was observed, with a maximum corrosion rate during the first periods of degradation (t = 6 and 12 h). Correlating the TAN and corrosion rate data with the microscopic data, the images of LM, AFM, and SEM/EDX showed that after 6 h of exposure to petroleum, a passivation film was formed on the surface of the steel. This film consisted of two layers, an external one, formed of FeS, and an internal one, composed of iron oxides and oxyhydroxides. However, after 48 h of thermal degradation, this morphology was altered to a single layer of FeS coating the steel surface.

Study of the Naphthenic Corrosion of AISI 316 and AISI 1020 Steels by Light, Scanning Electron and Atomic Force Microscopies (LM, SEM and AFM)

Corrosion processes were evaluated for AISI 316 and AISI 1020 steels by scanning electron microscopy (SEM), atomic force microscopy (AFM) and light microscopy. Coupons were immersed in four crude oil samples with different total acid numbers (TANs) for 48 days at room temperature. The steels were also exposed to three blends (B1-B3), produced by quaternary mixtures of the oils, with lower TANs than their respective original oils. SEM micrographs showed pitting-type corrosion in most cases. AFM imaging showed drastic changes in the peak-to-peak values, topographic profiles and phase images of the AISI 1020 coupons exposed to all oils and blend B3 as compared to the unexposed steel. Defects were produced on the surface of almost all the samples exposed to naphthenic corrosion. Exposure to the oil blends reduced the extent of the naphthenic corrosion on the coupons, especially blends B1 and B2. The oil mixtures (blends) reduced corrosion.

Identification of Polyphenols: Sequence for Teaching High School Chemistry

This study describes an alternative method to identify polyphenols and its application on the organic chemistry learning process, making it more meaningful for students. The developed method uses low cost available materials, such as ferrous sulfate, hydrogen peroxide and cashew juice, yielding a greenish color when tannin is present. Thereafter, the method was included in a didactic sequence and applied to a class of second year high school students of Serra city, Espírito Santo State, Brazil, in the year of 2012. This study was classified as a qualitative investigation with a descriptive character, the technical procedures can characterize it as a research action. Two classes were involved: one theoretical and one practical. At the end of the practical class a questionnaire was applied for evaluation of the didactic sequence. The conclusion was that the work can be used in chemical experimentation as a pedagogical practice to make the process of teaching easier and enjoyable. It is worthy to highlight that this practice, when performed with alternative materials and low cost, becomes even more interesting since it can also be applied in schools that do not have easy access to chemicals.

Identificação de Polifenóis: Sequência Pedagógica para o Ensino Médio

No presente trabalho, aplicou-se um metodo alternativo de identificacao de polifenois dentro de uma sequencia didatica para o ensino de quimica, visando torna-lo mais significativo para os estudantes. O metodo foi desenvolvido empregando-se materiais de facil acesso e custo reduzido, como o suco de caju, rico em polifenois, sulfato ferroso e agua oxigenada, e foi baseado na capacidade de complexacao de metais com polifenois, em destaque os taninos, produzindo coloracao esverdeada. A partir do metodo, uma sequencia didatica foi elaborada e aplicada a uma turma do segundo ano do ensino medio de um colegio particular do municipio de Serra-ES, no ano de 2012. O estudo foi classificado como uma investigacao qualitativa de carater descritivo, cujos procedimentos tecnicos caracterizam uma pesquisa-acao. Para seu desenvolvimento, foram ministradas duas aulas, uma teorica e outra experimental. Ao final da aula experimental, aplicou-se um questionario de avaliacao da sequencia didatica empregada. Concluiu-se que e possivel utilizar a experimentacao em quimica como pratica pedagogica a fim de tornar o processo de ensino e aprendizagem mais interessante para os alunos e professores. Faz-se necessario ressaltar ainda que esta pratica, quando realizada com materiais alternativos e de baixo custo, torna-se mais viavel, pois possibilita a sua realizacao em escolas que nao tem acesso facil a reagentes quimicos. DOI: 10.5935/1984-6835.20140032