O legado das bifenilas policloradas (PCBs)

Polychlorinated biphenyls (PCBs) are a class of 209 chemical compounds with the molecular formula C12H10-nCl n, where 1 <= n <= 10. They were commercially produced as complex mixtures for various uses, being employed principally as dielectric fluids in capacitors and transformers. They are not easily degraded due their chemical and physical stability and tend to bioaccumulate in the organisms. After the discovery of their xenobiotic activity, restrictions were imposed for their use, as well as for their discards. Nowadays the development of recovery processes for contaminated environment urges to be done due to the extension of reached areas.

Desempenho físico-químico de metais e estruturas de concreto de redes de distribuição de energia: estudo de caso na região de Manaus

The influence of natural aging furthered by atmospheric corrosion of parts of electric transformers and materials, as well as of concrete poles and cross arms containing corrosion inhibitors was evaluated in Manaus. Results for painted materials, it could showed that loss of specular gloss was more intensive in aliphatic polyurethane points than in acrylic polyurethane ones. No corrosion was observed for metal and concrete samples until 400 days of natural aging. Corrosion in steel reinforcement was noticed in some poles, arising from manufacturing faults, such as low cement content, water/cement ratio, thin concrete cover thickness, etc. The performance of corrosion inhibitors was assessed by many techniques after natural and accelerated aging in a 3.5% saline aqueous solution. The results show the need for better chemical component selection and its concentration in the concrete mixture.

Determinação de ascarel em óleo isolante de transformadores

The contamination level of silicon oil used as insulation liquid in high-voltage transformers by ascarel (PCBs) is above those permitted by the Brazilian law. Thus new techniques able to detect ascarel, with low operational costs, are very attractive. The present work proposes an analysis of the contamination levels of silicon oil using the following techniques: naphthalene anion radical reaction for ascarel dechlorination; and potentiometry with an ion-selective electrode for chloride ion determination. The data obtained with the proposed methodology agree well with those from the official methodology, (method IEC 61619).

Avaliação de diferentes métodos para a determinação de cobre em óleo mineral isolante por espectrometria de absorção atômica com forno de grafite

This aim of this work was to compare two methods for copper determination in insulating oils from power transformers by GFAAS. The first method was extraction induced by emulsion breaking, which determined the preconcentration of copper in an aqueous solution and exhibited a limit of quantification of 0.27 µg L-1. Also, a second method based on the direct introduction of samples into GFAAS in the form of detergent emulsions, prepared with Triton X-114 and HNO3, was investigated. In this case, the limit of quantification was 1.7 µg L-1. Seven samples of used oils were successfully analyzed by both methods.

AVALIAÇÃO DAS NORMAS DE ENSAIO APLICADAS NA QUANTIFICAÇÃO DE PCBs EM ÓLEO ISOLANTE

Polychlorinated biphenyls (PCBs) were widely used between 1940 and 1970 as an insulating fluid for transformers and capacitors. However, they are bioaccumulative and potentially carcinogenic and, according to the 2001 Stockholm Convention, must be eliminated by 2025. In Brazil, they have been gradually eliminated but contaminated equipment remains. The Brazilian official standard for PCBs content in oil analysis is the ABNT NBR 13882 and there is also the IEC 61619 International Standard, both based on GC-ECD quantification. This work identified the inefficiency of these analytical methods and highlights potential failures which generated discrepancies on quantification of these contaminants. It was observed that the IEC 61619 is superior to ABNT NBR 13882 in analytical criteria, but has problems with the inefficiency of the adsorbent material used in pretreatments for removal of oxidation products from oil where these adsorbents adsorbed some PCBs molecules, causing errors in quantification.