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It has been widely acknowledged that the presence of impurities in molten fluoride salt can alter the salt/material interactions. However, the effects of various impurities such as oxides, metal fluorides, reducing impurities, etc., on the behavior of nuclear-grade graphite in molten fluoride salts have not been reported. This study focuses on understanding the effects of various oxidizing and reducing impurities on the wetting and infiltration behavior of molten FLiNaK salt for nuclear-grade IG-110 graphite. Our results suggest that different impurities can cause different effects on nuclear graphite–molten salt interactions, with some impurities leading to significant degradation of the graphite. Our results demonstrate that certain impurities, such as Cr2O3 and CrF3, lead to a limited increase in wetting and infiltration of molten salt into nuclear graphite, while impurities such as Li2O lead to significantly increased wetting and infiltration throughout the cross section of the graphite specimen. Certain impurities, such as Li, can also lead to significant degradation of the graphite in the salt, with the extent of degradation increasing with the increase in the quantity of Li added. Our results also demonstrate that firing of IG-110 graphite at 900°C under a reducing atmosphere made the graphite surface resistant to wetting by molten FLiNaK salt, as compared to the nonfired sample. [ABSTRACT FROM AUTHOR]

Reliable performance of structural alloys is essential for the successful implementation of Generation-IV fluoride salt–cooled high-temperature reactors (FHRs). Most FHR designs are considering molten salt (2LiF-BeF2), or FLiBe, as a primary coolant or fuel carrier. The main corrosion mechanism for alloys exposed to molten fluoride salts is the selective dealloying of active alloying elements. Alloy composition has a significant effect on their high-temperature mechanical properties, but also affects their corrosion behavior. Although Hastelloy-N and its variants show good corrosion resistance compared to higher Cr-containing Ni- or Fe-based alloys, the mechanical properties of these alloys degrade quickly at temperatures above ~600°C. Twelve Ni-based or Fe-based alloys were selected due to their high temperature stability or their low Cr alloy composition and tested for their corrosion behavior in FLiBe. The results show that the mode and the extent of alloy degradation by selective dissolution mechanism corelates well with the overall alloy composition, and not just the concentration of active elements. It was found that there was good correlation between weight loss of the tested alloys and the ratio of major active elements (Cr, Mn) to that of the more noble alloying elements (Ni, Mo). [ABSTRACT FROM AUTHOR]

The subject of nanofriction having its origins in the late 19th century has slowly but surely started picking up lately. With rapid advancements in science and technology throughout the last century, understanding nanofriction has been gaining prominence. In this context, and in the current 21st century of nanotechnology, it is expected that nanofriction will play a predominant role, as we try moving forward to solve the most pressing medical and biological problems with the usage of nanobots. It is important to understand the challenges we have to encounter in order to solve these problems for the benefit of the human race. The availability of high speed computers and smart algorithms has made it possible to investigate the problems (as outlined above and many more) without compromising on the complexities involved. The focus of the present review is to bring together major theoretical/mathematical models and computational approaches to study friction at nanoscale. The role of adhesion in the estimation of force of friction at nanoscale has also been clearly outlined. A critical discussion on the significance of single and multiple asperity models towards estimating friction at nanoscale has also been provided. At the end, a short description on scanning probe microscopy in estimating nanofriction has been provided for the completeness of the review. [ABSTRACT FROM AUTHOR]