THERMAL-EXPANSION MODELS FOR POLYCRYSTALLINE SALT-CERAMICS

This paper describes a method for the estimation of the thermal expans ion in polycrystalline hybrid systems. These new materials have been d eveloped for use in high temperature thermal storage applications. A s imple crystallite model is compared with the complex model specified b y Hashin and Shapery. After describing and validating the models, the calculated expansions are compared with measurements on the following different hybrid systems: MgO/Na2SO4, Na2SO4-fraction 10-45% SiO2/Na2S O4, Na2SO4-fraction 20-50% The results show that all measurements are within the calculated second order boundaries. A good estimation is al so given by the simple crystallite model. The maximum deviation betwee n calculated values and measurements at 800 degrees C is less than 10% . This model can also be applied for SiO2 as a carrier component.