The amorphous Si–B–C–N ceramics with a similar Si/C/N atomic ratio and various boron contents of 3.7 and 6.0 at.% B were synthesized and then isothermally annealed at temperatures ranging from 1550 to 1775 °C. The course of crystallization for the modifications of Si3N4 was examined by quantitative analysis of the corresponding x-ray diffraction patterns. Additionally, recent results of similar investigations on the ceramic with 8.3 at.% B were also considered. The kinetic analysis demonstrates that the controlling mechanisms of the Si3N4 crystallization, continuous nucleation and diffusion-controlled growth, are independent of the boron content. Nevertheless, the estimated activation energy of the crystallization significantly increases from 7.8 to 11.5 eV with the amount of boron ranging from 3.7 to 8.3 at.%. It is concluded that the role of boron in the crystallization kinetics is mainly due to the effect of boron on the nucleation process. Beside the kinetic analysis, the correlation between the boron content and the Si3N4 crystallite size has been discussed.

To study the crystallization kinetics of β-Si3N4 in Si–B–C–N polymer-derived ceramics, the amorphous ceramics with composition SiC1.6N1.0B0.4 were synthesized and then isothermally annealed at 1700, 1775 and 1850 °C. The integrated intensities of β-Si3N4 x-ray diffraction (XRD) patterns were used to examine the course of crystallization. The average size of the Si3N4 nanocrystallites was analyzed by means of the XRD measurements and energy-filtering transmission electron microscopy. It was realized that the nanocrystallite dimensions change insignificantly within the time period of crystallization; however, they depend significantly on the temperature. Subsequently, the kinetics of the β-Si3N4 crystallization was analyzed. Consequently, large activation energy in the range of 11.5 eV was estimated. Moreover, continuous nucleation and diffusion-controlled growth have been concluded as the main mechanisms of the crystallization process. Further analysis points at the crucial role of the nucleation rate in the crystallization kinetics of β-Si3N4.