Evaluation of durability of alumina, silicon carbide and siliconized silicon carbide foams as absorber materials for concentrated solar power applications

Absorber material in solar thermal power plants, transfers heat energy from concentrated solar light to the working fluid inside the receiver. Several material properties such as maximum working temperature, thermal conductivity, coefficient of thermal expansion, and resistance to thermal fatigue are to be considered in the design of a solar absorber. Due to high cyclic operating temperatures of the absorber, thermal fatigue resistance is an important aspect when considering durability of the system. Hence, in this research, three different materials namely, alumina (Al2O3), silicon carbide (SiC), and siliconized silicon carbide (SiSiC), all in foam structure are evaluated to investigate the material behavior under thermal fatigue to determine which materials have better resistance to thermal cycles and are more suitable as an absorber. A thermal fatigue experiment in an air environment was conducted for up to 200 cycles at 800 degrees C and 1000 degrees C, respectively. Thermal conductivity measurements, phase analysis, and micro/macro structure analysis were performed using the Modified Transient Plane Source method, XRD, EDS, SEM, and stereomicroscope, respectively. There were no significant changes in the results, neither before nor after the experiment, of thermal conductivity for all the samples. The results showed that Al2O3 sample developed micro-cracks during the experiment at 800 degrees C (observed by SEM) and edge-to-edge macro-cracks at 1000 degrees C as observed by stereomicroscope. The phase analysis showed no compositional change after the experiment for all samples, as confirmed by EDS and XRD analysis. Hence, it was concluded that SiC and SiSiC showed better durability than Al2O3 for absorber applications.