Material investigations on the thermal stability of solar salt and potential filler materials for molten salt storage

The thermal and chemical stability of solar salt during isothermal tests is assessed under manifold conditions. Solar salt stored at 560°C under synthetic air stabilizes readily after a few days with both nitrate and nitrite content remaining relatively stable over time. A nitrogen atmosphere enhances degradation due to a continuous reduction of nitrate to nitrite. In an open atmosphere CO2 formation is pronounced owing to the reaction of the molten nitrates with atmospheric CO2. The stability of some filler materials, as potential candidates to be used in thermocline storage concepts, was investigated in long term experiments up to 5.000h. Additional anionic traces in the melt as corrosion products from the filler due to the reaction of instable mineral species with nitrates/nitrites were identified. However, No impact on the the thermal properties of the salt could be determined. These properties remain to be unchanged over a time frame up to 5.000h which is confirmed by relatively stable nitrate/nitrit...