SUMMARY

As next-generation clean energy technologies like concentrated solar power (CSP) and molten salt reactors (MSR) operate at ever higher temperatures, using molten chloride salt as a heat transfer fluid can provide many benefits, including extended storage and low operating pressure. In this extreme environment, understanding the thermophysical properties and salt corrosion behavior of candidate alloys and aluminosilicate refractories for salt storage tanks, piping, etc. is essential. However, corrosion studies of the candidates are not easily comparable; for several alloys and many refractories, published corrosion data does not exist. Thermophysical data of these materials are more available, though not consistently in the temperature range of interest (600–800°C). The purpose of this project was to characterize the materials’ high-temperature thermophysical properties and, for a subset of candidates, their chloride salt corrosion behavior. Several Ni-based alloys and aluminosilicates were selected for testing and commercially sourced. The temperature-dependent thermal diffusivity and specific heat of these materials were determined via light flash analysis (LFA) and differential scanning calorimetry (DSC), respectively. These results were compared with manufacturer data where available. For the alloys, the specific heat and thermal diffusivity were linear as a function of temperature, but there was evidence of second-order phase changes in the DSC data. In situ XRD testing showed that the alloys’ crystal structure was expanding with temperature in a linear manner, though there were no new phases observed in the selected alloys. After the 100hr immersion testing, uniform corrosion was visible on many of the alloy surfaces and the corrosion attack depth increased with temperature, particularly in the alloys with significant iron content. XRF scans of the corroded alloys’ surfaces showed several compositional changes, including depletion of active metals and a corresponding enrichment in more noble elements. For the pre-oxidized alloys, no significant difference in performance was observed compared to the alloys; the developed oxide layer provided no measurable corrosion protection after 200hrs of salt corrosion. Corrosion of the refractories revealed no consistent trend in mass gain after 200hrs of salt immersion at three temperature points. This thesis work is significant because it provides a broad, high-temperature thermophysical characterization of candidate alloys and refractories for the next-generation solar and nuclear industries. Compared to the manufacturer data, the temperature-dependent runs from this thesis work provides a much finer dataset and elaborates on trends in the published archive. The results from the molten salt corrosion testing of the alloys and refractories contribute important new data for these same industries where understanding material corrosion resistance is critical for safe and economic performance.