Hollow inorganic spheres

This is achieved either by chemical or thermal means. If a solvent is used, only the core is dissolved which results in hollow polymer, (4) in Fig. 12.7, or composite, (6) in Fig. 12.7, capsules. Heat treatment (= calcination) of the coated particles, (5) in Fig. 12.7, removes both the colloidal core and the bridging polymer, thereby producing hollow inorganic spheres. 

Heat treatment (calcination) of the coated particles, (5) in Fig. 11.11, removes both the colloidal core and the bridging polymer, thereby producing hollow inorganic spheres. 

---