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.
Calcium aluminate-based refractory ceramic was developed as an innovative refractory material, using garden snail (Helix aspersa) shells as a natural source of CaCO 3. A 1:1 molar ratio mixture of CaCO 3 from snail shells and commercial Al 2 O 3 powder was prepared by means of high-energy mechanical milling. The mixed powder was compacted in cylindrical samples (disks) and consolidated by sintering at 1450°C and 1500°C for 1h. The density and porosity were evaluated using the Archimedes principle, while the mechanical properties (hardness, fracture toughness, and shear modulus) were determined by indentation and ultrasonic methods, respectively. The thermal shock resistance was tested by heating samples to temperatures between 900 and 1400°C and subsequent quenching in water at room temperature. X-ray diffraction patterns of sintered samples indicate the formation of different calcium aluminate phases, such as CaAl 12 O 19 (krotite/monoclinic), CaAl 4 O 7 (grossite/monoclinic) and CaAl 2 O 4 (hibonite-5H/hexagonal). The fracture toughness and shear modulus values of materials sintered at 1450°C were higher (0.48 MPa•m 1/2 and 59 GPa, respectively) than those of materials sintered at 1500°C (0.43 MPa•m 1/2 and 55 GPa, respectively). Also changes in the bulk density, hardness and thermal shock resistance values were observed in materials sintered at 1450°C and 1500°C.
Here we continue [J. Chem. Phys. 76, 5404 (1982)] a quantum mechanical study of the fundamental causes for the different coordination properties of the Mg2+ and Ca2+ ions. We look into the effects of nonadditivity in the second hydration shell, mainly in relation to structure. We also compare our predictions with recent experimental evidence.
Pharmaceutical effluents are a serious environmental issue, which require to be treated by a suitable technique; thus, the electrochemical process is actively considered as a viable method for the treatment.
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