Fig. 5

Porous nanoclusters. a Schematic diagram of sintering to produce porous nanoclusters, SEM images of sintered silica nanoclusters¹²⁴ and Si-HAp nanoclusters⁹⁸ b Schematic¹²⁹ and SEM images of SCNCs synthesized by spray drying method and the mechanical properties of DRCs filled with calcined/uncalcined nanoclusters.¹³⁰ c SEM image of SiO₂-ZnO,¹³³ SiO₂-ZrO₂,¹³¹ CaF₂-SiO₂,¹³⁴ hydroxyapatite¹³², and SiO₂-ZrO₂-ZnO¹³⁵ porous nanoclusters synthesized by spray drying method. Figures adapted with permission from refs. ^{98,129,130,131,132,133,134,135}