Crystal growth of silicon nitride whiskers (a 1(d)国 黍 Fig 3. SEM micrographs of (a)seed whiskers, (b) fine-grained whiskers from solution B, (c) long whiskers from solution A and (d)short whiskers from fine-grained whisker-like products were formed on Regarding whisker growth through VLS the surface of the seed whiskers. The morphology mechanisms, the following mechanism is sugges of the growth was just like rose-twigs [Fig. 3(b)]. ted. Gas species are dissolved in liquid droplets on There is no significant variation in thickness of the a substrate, and then they are supplied to the sur- seeds before and after the whisker coating. This face of the substrate, where crystal growth starts indicates that a thin oxide layer was coated on the Accompanied by the crystal growth, the droplets seeds. X-ray diffraction indicated that the newly are lifted-up. If the components of the droplets are formed whiskers are the B-Si3N4 not all dissolved in the grown crystals, further In the case of solution A, the newly formed crystal growth is continued. If not, the droplets are whiskers on the seeds were much longer than those consumed and ultimately disappear obtained from the solution b, and the morphology Whisker growth in the present study would be of the growth was just like centipedes having long ascribed to the mechanisms shown in Fig. 4. With legs[Fig. 3(c)and (d) a thin oxide layer, the droplets on the tips of Clearly, the diameters of the seeds increase. This hikers are quickly consumed, accompanied by is probably because a thick oxide layer was coated whisker growth. Since the Si-Al-Y-O component although its thickness was determined. No droplets of the liquid phase is partly dissolved in the si3N4 were found on the tips of the fine-grained whiskers whiskers. It is widely known that SiO2-AlO3- from solution B [Fig. 3(b)] and relatively long Y2O3 oxides are conventional sintering aids for whiskers from solution A [Fig. 3(c)]. Droplets were liquid phase sintering of Si, N4 ceramics, when a found on the tips of relatively short whiskers from part of them is dissolved in Si3 N4: SiaION cera solution A[Fig 3(d)I mics are formed. 10 Therefore the whiskers areCrystal growth of silicon nitride whiskers 137 Fig ;. 3. SEM micrographs of (a) seed whiskers, (b) fine-grained whiskers from solution B, (c) long whiskers from solution A al (d) short whiskers from solution A. nd fine-grained whisker-like products were formed on the surface of the seed whiskers. The morphology of the growth was just like rose-twigs [Fig. 3(b)]. There is no significant variation in thickness of the seeds before and after the whisker coating. This indicates that a thin oxide layer was coated on the seeds. X-ray diffraction indicated that the newly formed whiskers are the /?-Si3N4. In the case of solution A, the newly formed whiskers on the seeds were much longer than those obtained from the solution B, and the morphology of the growth was just like centipedes having long legs [Fig. 3(c) and (d)]. Clearly, the diameters of the seeds increase. This is probably because a thick oxide layer was coated although its thickness was determined. No droplets were found on the tips of the fine-grained whiskers from solution B [Fig. 3(b)] and relatively long whiskers from solution A [Fig. 3(c)]. Droplets were found on the tips of relatively short whiskers from solution A [Fig. 3(d)]. Regarding whisker growth through VLS mechanisms, the following mechanism is sugges￾ted.9 Gas species are dissolved in liquid droplets on a substrate, and then they are supplied to the sur￾face of the substrate, where crystal growth starts. Accompanied by the crystal growth, the droplets are lifted-up. If the components of the droplets are not all dissolved in the grown crystals, further crystal growth is continued. If not, the droplets are consumed and ultimately disappear. Whisker growth in the present study would be ascribed to the mechanisms shown in Fig. 4. With a thin oxide layer, the droplets on the tips of whiskers are quickly consumed, accompanied by whisker growth. Since the Si-Al-Y-O component of the liquid phase is partly dissolved in the Si3N4 whiskers. It is widely known that Si02-Al@- Y20s oxides are conventional sintering aids for liquid phase sintering of S&N4 ceramics, when a part of them is dissolved in Si3N4; SiAlON cera￾mics are formed.‘O Therefore, the whiskers are