Recent Progress in Alkali Nitrate/Nitrite Developments for Solar Thermal Power Applications

Abstract

The paper presents recent developments of alternative anhydrous alkali metal and alkaline earth nitrate and nitrite mixtures with low melting temperatures and high thermal stabilities for concentrating solar power (CSP) applications. First, known minimum melting temperatures of the relevant binary and ternary systems are reported. These systems have typical liquidus temperatures above 100 °C. The paper summarizes minimum melting temperatures of subsystems of the quinary reciprocal system Ca, K, Li, Na // NO2, NO3. Own measurements on the quaternary reciprocal system K, Li, Na // NO2, NO3 with a differential scanning calorimeter (DSC) and an optical melting point apparatus (MPA) are reported. Phase diagram details of this system with a minimum liquidus temperature of around 80 °C are presented. Finally, the thermal stability of nitrates, nitrites and minimum melting temperature mixtures are examined by thermogravimetry with coupled gas analysis (mass spectrometer).