Characterization of Carbide Particles in S-65 Beryllium by Scanning Kelvin Probe Force Microscopy

Abstract

Scanning Kelvin probe force microscopy has been employed to examine the behavior of second phase carbide particles in beryllium at different relative humidity levels and after exposure to deionized water. Carbides are believed to have a role in the localized corrosion of beryllium as a result of their hydrolysis when exposed at the metal surface. The presence of beryllium carbide was confirmed by means of Auger electron spectroscopy and the particles were further characterized by scanning electron microscopy, energy/wavelength dispersive X-ray spectroscopy and scanning Kelvin probe force microscopy. The particles were found to have a more noble Volta potential than the beryllium matrix and a decrease in the Volta potential difference between the second phase particles and the matrix was observed as the humidity was increased. A thick beryllium oxide/hydroxide layer then formed on the particles following exposure to water significantly reducing their potential.

Toward Improving Ambient Volta Potential Measurements with SKPFM for Corrosion Studies

“…For ambient air SKPFM, the results show that the PFQNE-AL and SCM-PIT probes exhibit relative precision for a large population of data, with lower standard deviations (246 mV and 106 mV, re spectively) combined with low skewness values of +0.18 and +0. 47. The 25Pt300B probe also shows a relatively symmetric distribution (skewness of −0.29), but produces a much larger range of VPD values (standard deviation >700 mV, Figure 2d).…”

“…Due to the residual effects of electron beam irradiation and carbon pyrolysis, all SEM/EDS mapping was performed after SKPFM measurements. 36,47,80…”

“…3 Electrolyte factors, such as pH and ion concentration, play a major role in the kinetics, which are not addressed when observing fundamental electronic properties of the material in ambient conditions. SKPFM has therefore been utilized for predicting (in ambient or inert conditions) microgalvanic couples as localized corrosion initiation sites for a variety of pristine complex metallic systems, 23,26,[28][29][30][31]36,[44][45][46][47][48][49][50][51] ex situ measurements of such systems following periods of exposure to corrosive environments, 20,[52][53][54][55] and in situ measurements of VPD changes under non-ambient conditions. 22,23,25,[56][57][58][59][60][61] While much of the previously reported work has focused on distinguishing relative nobility within individual SKPFM maps, comparisons to other work are not direct.…”

Improving the Relative Calculations of Volta Potential Differences Acquired from Scanning Kelvin Probe Force Microscopy (SKPFM) from Comparing an Inert Material to First-Principle Calculations

“…Broadly, it has been shown that there is a direct correlation between materials' VPD values and their open circuit potentials (16)(17)(18). SKPFM has thus been able to provide a theoretical mapping of local phase nobility for complex metallic systems (19)(20)(21)(22)(23), as well as ex situ measurements following periods of exposure to corrosive mediums (24)(25). A notable lack of reproducibility of Volta potential differences has been discussed for different alloy series (15,19), and though much of previously reported work has been able to distinguish phase nobility for individual maps, subsequent mapping and other work are not discretely comparable (19).…”