Changes in Morphology Caused by Mass Transfer Phenomenon

The mass transfer phenomenon of contained impurities causes differences in the morphologies, densification processes, and heat resistance of ceramics. Of these, in this paper, differences in the heat resistance of ceramic fibers are discussed. Third-generation SiC polycrystalline fibers demonstrated excellent heat resistance. However, at temperatures above 1800 °C, sintered fiber (Tyranno SA) and non-sintered fiber (Hi-Nicalon Type S) showed remarkable differences in heat resistance. At temperatures above 1800 °C, the non-sintered fiber underwent structural changes, including the formation of a surface carbon layer and abnormal SiC grain growth, whereas the sintered fiber maintained its stable polycrystalline structure. Until now, these differences and a detailed description of them have not been discussed. Here, we first explain the dramatic differences in heat resistance that occurred at high temperatures in relation to the mass transfer of excess carbon. Our findings should be widely used for the development of much more stable structures and for the long-term use of materials at higher temperatures in applications such as airplane engines and turbines.