Formation mechanism of Si3N4 in reaction-bonded Si3N4-SiC composites

A new slurry infiltration method to enhance the wear resistance of bulk graphite with development of reinforced graphitic composites including SiC or Si3N4 hard particles

“…Figure 5(b) reveals that the g/Si3N4 reinforcement presents a mixture of blade-like (spectrum 3) and fine grains (spectrum 2), needle-like structures (spectrum 1) and whiskers (spectrum 4). This type of microstructure has been observed in the past for SiC and Si3N4 produced by mixture of graphite and Si powders and heating in the coke bed at 1200 -1400 o C and by SiC and Si powders heated in a flame-isolation nitrition shuttle kiln at 1200 -1450 o C in nitrogen [28], [27], [34], [35]. The grains with blade morphology appear to be the largest with a diameter of ~ 10 μm.…”

“…(13) and eq. (14) (Fig 7(g)) [43], [28], Thus, the blade-like grains of β-Si3N4 particles are surrounded by fine grains of α-Si3N4 and aggregates of β-SiC; and these are surrounded by α-Si3N4 needle-like grains and β-SiC whiskers ( Fig. 7(h)) forming an onion-like structure (Fig.…”

“…The formation of SiC using graphite as source of C is favored by the high density of defects present in graphite [27]. Si, SiO and CO vapors are produced when Si and graphite powders are mixed and heated in coke bed at 1200 -1400 o C, even at very low O concentrations in the gas flow of 0.001 % and form beta-SiC (β-SiC) nuclei and whiskers [28], [27]. [27].…”

“…Si3N4 can be formed by the direct reaction of Si with a N2 gas at 1400 o C, in a process which is known as nitridation [28]. In this case, alpha-Si3N4 (α-Si3N4) is formed by the reaction of molecular N2 and gaseous Si and beta-Si3N4 (β-Si3N4) is produced by the reaction between atomic N and solid or liquid Si [28]. A dependency of the Si3N4 morphology with temperature, time of reaction, and gas flow rate is concluded [29].…”

Silicon nitridation mechanism in reaction‐bonded Si3N4–SiC and Si3N4‐bonded ferrosilicon nitride

“…There are 2 modes of oxidation of silicon compound in different oxidant environment . In our earlier research, the mechanism of silicon nitridation and the effect of traces of oxygen in industrial nitrogen were analyzed in detail . Results showed that O 2 promotes Si to be oxidized to gaseous SiO before nitrided to Si 3 N 4 and favored the generation of fibrous α‐Si 3 N 4 .…”