Papers by Keyword: SKP

Abstract: The influences of Nb₂O₅ on the phase, microstructure and hydrochloric acid corrosion behaviors of Nb₂O₅-Al₂O₃ ceramics sintered with 2.45 GHz microwave energy were investigated. The results showed that Nb2O5 reacted completely with Al₂O₃ to form AlNbO₄ and densified the pure Al₂O₃ at a lower sintering temperature and in a short sintering time. Nb₂O₅-Al₂O₃ ceramic samples were corroded in diverse concentration hydrochloric acid for different time. Weight loss rate of Nb₂O₅-Al₂O₃ ceramic rose dramatically when the corrosion time was not longer than 4 h, and it increased slowly beyond 24 h. After Nb₂O₅-Al₂O₃ ceramic samples were corroded for 1 h, pitting corrosion was observed by scanning electric microscope, which was consistent with the analysis results of the scanning Kelvin Probe.

Abstract: Scanning Kelvin Probe (SKP) potentiometry is used to systematically investigate the effect of surface abrasion and subsequent heat-treatment on the open-circuit potential in humid air of the AA6016 surface. SKP is also used to follow the kinetics of filiform corrosion and to determine characteristic potentials associated with the electrolyte-filled filiform head and dry filiform tail. It is shown that simply abrading with 180 grit SiC produces a surface potential up to 0.5V lower than the bulk. When the abraded sample is overcoated with a 30 micron layer of PVB (polyvinyl butyral) and exposed to HCl a fast, superficial filiform corrosion (FFC) is observed in which metal loss is limited to the thickness of the surface layer. Filiform head OCP values are similar to that of the surface layer, whereas filiform tail OCP values are similar to the bulk. A mechanism is proposed in which the ultra-fine grain structure of the surface layer produces an anodic activation and the potential difference between the surface layer and the bulk provides and increased thermodynamic driving force for corrosion. For post-abrasion heat treatment temperatures up to 350°C the fast filiform process is followed by a slower, deeper form of FFC.