ABSTRACT:The behavior of a polybutadiene-carbon black composite entering into contact with organic solvents and gasoline was investigated. The composite used has a conductivity of 3.0 { 0.1 V 01 cm 01 . However, if it comes into contact with organic solvents (gasoline, for instance) the matrix absorbs them and consequently swells. This swelling causes the separation of the carbon particles and the concomitant diminution of the composite conductivity. During the tests performed, the resistivity of the composite grows exponentially with the exposure time to solvents. Typically, the material samples show a reduction of approximately 30% of its initial conductivity after only 1.5 min of exposure to solvents. Also, it was observed that the rate at which the conductivity decreases is related to the chemical nature of the solvent used in the test. To model the drop on composite conductivity induced by solvent swelling we use an effective media percolation approach. This approach was adapted to the needs of our experiments by modifying the definition of one of its main parameters (the critical volume of the low-conductivity fraction). The experimental data were successfully described by this model. Finally, the test performed shows that this composite is a very promising material that can be employed, for example, in various security and control devices to warning of accidental organic solvent or hydrocarbon leaks in pipelines or containers of chemical industries and refineries.

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AlCrN/TiSi, AlCrN/TiCrSiN and AlCrN/AlCrN + CrN coatings were deposited on Inconel 718 alloy by physical vapour deposition (PVD). The corrosion behaviour of uncoated and coated specimens was evaluated using electrochemical impedance spectroscopy (EIS) at open circuit potential in a 3.5 wt.% NaCl and 2 wt.% H2SO4 solutions. The EIS data acquired were curve fitted and analysed by equivalent circuit models to calculate the pore resistance, the charge transfer resistance and the capacitance. The Nyquist diagrams of all systems showed one part of the semicircle which could relate that reaction is a one step process, except for the AlCrN/TiCrSiN and AlCrN/AlCrN + CrN coatings in H2SO4 solution, for which two semicircles related to active corrosion in substrate alloy were found. However, from the Bode plots, it was possible to identify two the time constants for all systems exposed to NaCl and H2SO4 solutions. According to electrochemical results, the corrosion resistance of the AlCrN/TiSiN coating was better in the NaCl solution, whereas the AlCrN/AlCrN + CrN coating show better performance in the Sulphuric Acid solutions.

AC impedance measurements have been applied for over twenty years in electrochemistry and physics to investigate the electrical properties of conductive materials and their interfaces using an external electrical impulse (VOLTAGE, V or CURRENT, I) as driving force. Furthermore, its application has recently appeared to be destined in the Biotechnology field as an effective tool for rapid microbiologic diagnosis of living organism in situ. However, there is no doubt that the electrochemical impedance spectroscopy (EIS) is still one of the most useful techniques around the world for metal corrosion control and its monitoring. Corrosion has long been recognized as one of the most expensive stumbling blocks that concern many industries and government agencies, because it is a steel destructive phenomenon that occurs due to the chemical interaction with aqueous environments and takes place at the interface between metal and electrolyte producing an electrical charge transfer or ion diffusion process. Consequently, it is experimentally possible to determine through the EIS technique the mechanism and control that kinectics of corrosion reactions encounter. First, EIS data is collected through a potentiostat/galvanostat apparatus. After, it is fitted to a mathematical model (i.e. an equivalent electrical circuit, EEC) for its interpretation and analysis, fundamentally seeking a meaningful physical interpretation. Finally, this review reports some basic aspects of the corrosion mechanism applied to steels through the experimental EIS response using Nyquist or Bode plots. Examples are given for different applied electrochemical impedance cases in which steel is under study intentionally exposed to a corrosive aqueous solution by applying a sinusoidal potential at various test conditions.

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