Activity of SiC Particles in Al-Based Metal Matrix Composites Revealed by SECM

Abstract

Scanning electrochemical microscopy ͑SECM͒ is used to image variations in electrochemical activity over the surface of an aluminum-based metal matrix composite ͑MMC͒ in contact with buffered or unbuffered neutral solutions. The composite consists of an Al-13.5% Si-9% Mg alloy matrix and reinforcing silicon carbide particles (SiC p ). Feedback-mode SECM imaging using ferrocenemethanol as a redox mediator in 0.1 M NaCl solution and in buffer solution ͑pH 6.8͒ revealed that the SiC particles are electrochemically active. The data suggest that the electronic conductivity at these sites is higher than that of the Al 2 O 3 film covering the alloy matrix surface. The reduction of dissolved oxygen on the silicon carbide particles was investigated by in situ SECM images of samples and current vs. tip-substrate distance curves. The results with samples of SiC p /Al composites immersed in distilled water alone or in either 0.1 M NaCl or boric acid/borax buffer containing ferrocenemethanol as mediator demonstrate that the silicon carbide particles are conductive and act as local cathodes for the reduction of oxygen.

Preparation of Tip-Protected Poly(oxyphenylene) Coated Carbon-Fiber Ultramicroelectrodes

“…This corrosion occurred during the SECM imaging experiment while immersed in the boric acid-borax buffer and highlights susceptibility of this surface to corrosion. These results are all in agreement with the previous study [34].…”

“…Unfortunately, these materials are susceptible to corrosion, likely due to galvanic coupling between the aluminum matrix and the semiconducting SiC particles [48 -51]. In our report, we demonstrate that SiC particles in Al/SiC p composite samples are conductive and act as local cathodes for the oxygen reduction in water as well as in NaCl and borate solutions [34]. Figure 11A shows an optical micrograph of an Al/SiC p composite.…”

“…Storing the electrode in a sealed, dust-free container permitted their use up to one year after initial construction. Aluminum/silicon carbide particle (Al/SiC p ) electrodes were prepared and polished as mentioned previously [34]. Before each SECM experiment, this electrode and the Au/ Kel-F substrate were polished with 0.3 mm alumina slurry on cloth then rinsed and sonication in deionized water.…”

“…In a previous paper, we used SECM to examine the electrochemical properties of an aluminum/silicon carbide (Al/SiC p ) metal matrix composite (MMC) [34]. These composites are often employed as structural materials because of their low density and enhanced mechanical properties compared to conventional aluminum alloys [47].…”

Silane-incorporated epoxy coatings on aluminum alloy (AA2024). Part 1: Improved corrosion performance

“…The SECM is an effective ''in situ'' method for the investigation of coated or uncoated metals [51][52][53][54][55][56]. Here, SECM feedback mode is employed to monitor the swelling of epoxy coating by measuring the tip-substrate distance which is derived from the decreased feedback current with the assistance of approach curve [57,58].…”