Eric Schindelholz

Wetting phenomena and time of wetness in atmospheric corrosion: a review

Abstract The concept of time of wetness (TOW) is extensively used in the atmospheric corrosion disciplines for such purposes as corrosion prognostics and environmental corrosivity classification. Time of wetness can generally be defined as the amount of time a metal surface remains wet during atmospheric exposure. Although the basic concept and importance of TOW in governing atmospheric corrosion is generally agreed upon, what is meant by “wet” has generally remained ambiguous and its practical determination has been widely varied throughout its history. The objective of this review is to demystify TOW in terms of definition and measurement and identify issues that inhibit this parameter from providing deeper insight into the effect wetness duration has on atmospheric corrosion. Specifically, this paper summarizes the current state of TOW determination methods along with the parallel concept leaf wetness used in environmental science. Furthermore, wetting and drying phenomena associated with atmospheric corrosion and thought to control TOW are overviewed. From this framework, current issues and limitations of TOW are identified and avenues for further improvement suggested.

Application of Inkjet Printing for Depositing Salt Prior to Atmospheric Corrosion Testing

This study examined the feasibility of using an unmodified office inkjet printer for the precise deposition of soluble salt particles on planar metal samples for atmospheric testing. The density of the salt loading achieved in printing solid swaths ranged from 10 to 180 μg cm ―2 using aqueous 1 and 4 M NaCl solutions with 95% confidence intervals ≤2 μg per print. Printing these solutions on a steel coupon produced particles with a multimodal size distribution and mean Feret diameters ≤11 μm. An application of the method for studying the effect of loading density on the atmospheric corrosion of steel is described.

Hygroscopic Particle Behavior Studied by Interdigitated Array Microelectrode Impedance Sensors

The hygroscopic behavior of soluble salts bears importance in many research fields including atmospheric sciences, corrosion, porous building materials, and pharmaceuticals. Several methods have been used to study deliquescence (solid to liquid) and efflorescence (liquid to solid) phase transitions of these salts. In this study, we measured the deliquescence and efflorescence RH values of single salt microparticles deposited on an interdigitated microelectrode sensor via electrical impedance. The salts examined were NaCl, LiCl, NaBr, KCl, and MgCl2. Measured values were in agreement with in situ optical microscopic observations and, with the exception of MgCl2, literature values. In the case of MgCl2, deliquescence occurred at 33% RH and 12-15% RH, with the latter range being previously unreported. The depressed deliquescence RH was hypothesized to be a result of the formation of a metastable MgCl2 hydrate. Incomplete efflorescence of MgCl2 was also observed after exposure to <1.5% RH for up to 22 h due to formation of solid shells which trapped fluid. The phenomena elucidated by these results provide an explanation for the anomalous water retention and uptake behavior of MgCl2 below 33% RH reported elsewhere in the literature. The results presented in this study validate the use of this method as an alternative or complementary method for study of bulk-phase transitions of substrate-deposited particles across a broad RH range. These findings also demonstrate the utility of this method for detection of fluid trapping which cannot be directly ascertained by gravimetric and line-of-sight techniques commonly used in the study of hygroscopic particles.

Corrosion Properties of Powder Bed Fusion Additively Manufactured 17-4 PH Stainless Steel

The corrosion susceptibility of a laser powder bed fusion (LPBF) additively manufactured alloy, UNS S17400 (17-4 PH), was explored compared to conventional wrought material. Microstructural charact...