Ultra-low thermal conductivity and excellent high temperature resistance against calcium-magnesium-alumina-silicate of a novel β-type pyrosilicates

The materials which have low thermal conductivity, a good match of coefficient of thermal expansion with SiC-based ceramics matrix composites (CMCs) and excellent resistance against calcium-magnesium-alumina-silicate (CMAS) are suitable candidates for thermal/environmental barrier coating. To fulfil the above requirements we developed a new multicomponent rare earth (Y0.2Dy0.2Er0.2Yb0.2Ho0.2)2Si2O7 or (5RE0.2)2Si2O7 high entropy ceramics pyrosilicate by a single step solid solution method. The x-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analysis revealed that the as-fabricated bulk composite (5RE0.2)2Si2O7 has a single phase beta-type structure match well with single rare earth ytterbium disilicate (Yb2Si2O7) and the different rare earth oxides mixed well with each other. The excellent coefficient of thermal expansion (4 x 10-6-5 x 10-6 degrees C-1) and ultra-low thermal conductivity (0.7-1.6 W/m C) was observed as compared to other single and multicomponent high entropy ceramics composites. The (5RE0.2)2Si2O7 ceramics pyrosilicate show an excellent CMAS resistance at various temperatures (1300, 1400, and 1500) degrees C for 4 h compared with single principle RE disilicates. The above all mentioned results identify that this material is a suitable candidate for coating on the SiC-based ceramics composite for thermal/environmental barrier coating.