Luke Olson

Intergranular corrosion of high temperature alloys in molten fluoride salts

Abstract Six Ni and Fe–Ni based austenitic alloys were exposed to molten LiF–NaF–KF: 46.5–11.5–42mol% salt, commonly referred to as FLiNaK, at 850°C for 500 h. Corrosion was noted to occur predominantly from dealloying of Cr resulting in void formation, an effect that was particularly pronounced at the grain boundaries. Alloy weight-loss due to molten fluoride salt corrosion correlated with the initial Cr-content of the alloys up to a Cr content of about 20wt%, and was consistent with the Cr-concentrations measured in the salts after corrosion tests. However, in the nominally 20 wt% to 23 wt% Cr containing alloys, this weight-loss correlated linearly with the carbon content of the alloys, due to the formation of chromium carbide phases at the grain boundaries and its subsequent dissolution into the molten salt along the grain boundaries. The Cr-lean intermetallic precipitates found in the alloys were resistant to corrosion in the molten FLiNaK salt.

High temperature electrochemistry of molten fluoride salt for measurement of dissolved chromium

Abstract An in situ electrochemical probe, utilising anodic stripping voltammetry (ASV), has been developed to measure dissolved Cr concentration in the molten salt LiF–KF–NaF (46·5–11·5–42 mol.-%), commonly referred to as FLiNaK. Tests were performed in a glassy carbon crucible in an argon atmosphere glovebox at a molten salt temperature of 650°C. Cyclic voltammetry was performed to determine reversibility and mid peak potential. The Cr2+/Cr0 reaction occurred with a mid peak potential of −0·51 V versus a 10 mol.-% Ni2+/Ni0 reference electrode. The integrated current from the anodic waves at this potential were used for Cr cation quantification. The integrated current from the ASV measurements correlated linearly with Cr concentration, measured independently using neutron activation analysis, over a range of 30–950 ppm (1·2–38 mmol L−1). This study is significant for determining Cr concentrations in high temperature molten FLiNaK salts exposed to Cr containing structural materials.

Molten Salt Heat Transport Loop: Materials Corrosion and Heat Transfer Phenomena

An experimental system for corrosion testing of candidate materials in molten FLiNaK salt at 850 degree C has been designed and constructed. While molten FLiNaK salt was the focus of this study, the system can be utilized for evaluation of materials in other molten salts that may be of interest in the future. Using this system, the corrosion performance of a number of code-certified alloys of interest to NGNP as well as the efficacy of Ni-electroplating have been investigated. The mechanisums underlying corrosion processes have been elucidated using scanning electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy of the materials after the corrosion tests, as well as by the post-corrosion analysis of the salts using inductively coupled plasma (ICP) and neutron activation analysis (NAA) techniques.