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Herein, the advantage of single-shell hollow microspheres on forming pores has been exploited to acquire porous ceramics with homogeneous microstructure, while the hollow microspheres also acted as reaction source. Dispersant reaction method has been applied to realize the perfect combination between microspheres and Si3N4 particles, which could be attributed to the repulsion between particles is weakened, particles agglomerate together and holding microspheres among them tightly. Owing to the normal distribution of hollow spheres and their single-shell structure, porous Si2N2O-Si3N4 ceramics with uniform pore distribution have been fabricated. The results show that the addition of silica hollow spheres contributes to the decrease in dielectric constant, since their porosity could be increased effectively and Si2N2O phase exhibiting low dielectric constant is generated. High-performance porous Si3N4 ceramics with porosity of 45.7% have been prepared through employing fly ash hollow microspheres, which possess flexural strength of 108.76 ± 6.25 MPa, fracture toughness of 1.78 ± 0.09 MPa m1/2 and dielectric constant of 3.53. This strategy is proved to be a convenient, eco-friendly and effective method to synthesize ideal candidates for radomes. [ABSTRACT FROM AUTHOR]

In this study, a facile one-step method combining the pore expansion and the enlargement of the hollow cavity of hollow periodic mesoporous organosilica spheres (HPMOSs) into one step was proposed. Moreover, the whole process for the formation just needs 1 h and involves reaction just under normal pressure and temperature. We further investigate the influence of different expanders and the amount of expanders on pore size and hollow cavity size. The obtained HPMOSs using tridecane as expander possess excellent properties, including good spherical morphology, large hollow structures, radially oriented mesochannels (3.44 nm), uniform particle size (115 nm), high BET surface area (1298 m/g), and large pore volume (1.96 cm/g). In addition, the hollow cavity size and the mesoporous size can be controlled via the modulation of tridecane amount. This method also provides a basis for synthesizing both large pore and the hollow cavity of functionalized, monodispersed HPMOSs. [ABSTRACT FROM AUTHOR]