ABSTRACT
Understanding and controlling the chemical processes between molten salts and alloys is vital for the safe operation of molten-salt nuclear reactors. Corrosion processes in molten salts are highly dependent on the redox potential of the solution that changes with the presence of fission and corrosion processes, and as such, reactor designers develop electrochemical methods to monitor the salt. However, electrochemical techniques rely on the deconvolution of broad peaks, a process that may be imprecise in the presence of multiple species that emerge during reactor operation. Here, we describe in situ measurements of the concentration and chemical state of corrosion products in molten FLiNaK (eutectic mixture of LiF-NaK-KF) by high-resolution X-ray absorption spectroscopy. We placed a NiCr foil in molten FLiNaK and found the presence of both Ni2+ ions and metallic Ni in the melt, which we attribute to the foil disintegration due to Cr dealloying.
ABSTRACT
The effects of ionizing radiation on materials often reduce to "bad news". Radiation damage usually leads to detrimental effects such as embrittlement, accelerated creep, phase instability, and radiation-altered corrosion. Here we report that proton irradiation decelerates intergranular corrosion of Ni-Cr alloys in molten fluoride salt at 650 °C. We demonstrate this by showing that the depth of intergranular voids resulting from Cr leaching into the salt is reduced by proton irradiation alone. Interstitial defects generated from irradiation enhance diffusion, more rapidly replenishing corrosion-injected vacancies with alloy constituents, thus playing the crucial role in decelerating corrosion. Our results show that irradiation can have a positive impact on materials performance, challenging our view that radiation damage usually results in negative effects.
ABSTRACT
OBJECTIVE: To develop a novel biodegradable collagen-chitosan-[poly(vinyl alcohol), PVA] composite artificial lacrimal canaliculus for treating tear overflowing (epiphora) caused by canalicular obstruction. METHODS: Homo-generously mixing solution composed of collagen, chitosan and PVA with different ratios was prepared. After several cycles of freezing/thawing process, the mixing solution was transferred into elastic hydrogel. Then the hydrogel was rinsed, punctured, dehydrated and trimmed, and three groups (T1, T2 and T3) of novel artificial lacrimal canaliculus were obtained. The appearance and diameter of all samples were observed under optical microscopy. The cross-section before and after drying as well as phase distribution of sample T2 was observed by SEM. The water absorption ratio and expanding ratio in PBS solution were calculated from three swelling behavior curves. The degradability of groups T1, T2 and T3 were preliminary analyzed by degradation experiment in vitro. RESULTS: The micro-tubes with 0.5-0.7 mm in inner diameter, 0.9-1.5 mm in outer diameter and more than 20 mm in length were fabricated successfully through physical crosslinking without addition of toxic cross-linker. SEM result showed that the sample had uniform phase distribution and smooth surface at dried state as well as interpenetrate network structure at hydrogel state. It was seen from the swelling behavior curves that groups T1, T2 and T3 swelled rapidly within 10-30 minutes, and formed elastic composite hydrogel pipes. In addition, the expanding ratio of inner and outer diameter of the tube was 20%-30% and 100%-120% with swelling, respectively. The equilibrium water content of the hydrogel pipes increased with increase of collagen composition. Three groups of samples were immersed in PBS solution contained 2 mg/mL lysozyme at 37 degrees C for 1 month, their nozzle cracked, their wall became thin and more transparent. And also, there was small floc deposited on the tube surface. The samples were degraded into mash after they were soaked in PBS solution at 70 degrees C for 2 days. CONCLUSION: The novel artificial lacrimal canaliculus with good mechanical property and high water absorption is in favor of operation, tear passing and anti-conglutination. It will be a potential candidate for treating the lacrimal passage occlusion.
