Mullite nanowhiskers with Al-rich structure were prepared by molten salt synthesis at 1000°C for 3 h in air using silica, amorphous silica, and ultrafine silica as the silica sources. The phase and morphology of the synthesized products were investigated by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, and transmission electron microscopy. A thermogravimetric and differential thermal analysis was carried out to determine the reaction mechanism. The results reveal that the silica sources play an important role in determining the morphology of the obtained mullite nanowhiskers. Clusters and disordered arrangements are obtained using common silica and amorphous silica, respectively, whereas the use of ultrafine silica leads to highly ordered mullite nanowhiskers that are 80−120 nm in diameter and 20−30 μm in length. Considering the growth mechanisms, mullite nanowhiskers in the forms of clusters and highly ordered arrangements can be attributed to heterogeneous nucleation, whereas disordered mullite nanowhiskers are obtained by homogenous nucleation.

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Hexagonal 1D AlN whiskers were synthesized by direct nitridation of aluminum and alumina. The effect of the atmosphere was investigated based on thermodynamic calculation. A green body compacting alumina with different particle size in between 44–420 μm in graphite crucible was found to be favorable for the large-scale synthesis of AlN at 1650 °C for 3 h in flowing nitrogen atmosphere. XRD result indicated that hexagonal AlN phase with high purity has been successfully synthesized. SEM and TEM analysis indicated that the whiskers possessed uniform morphology with 100–200 nm in diameter and length up to microns. The formation mechanism was further proposed based on the experimental results.