Interface evolution of the Cf/leucite composites derived from Cf/geopolymer composites

In this paper, effect of heat treatment temperature on the interface structure of the carbon fiber reinforced geopolymer composites was investigated by transmission electron microscopy (TEM), selected-area diffraction (SAD) analysis and high-resolution transmission electron microscopy (HRTEM). In the composite treated at 1100 °C, carbon fiber showed a good bond with the leucite matrix and no interface reaction layer was observed, while due to the thermal mismatch between fiber and matrix, microcrack which was perpendicular to the fiber axial direction can be seen in the matrix. With increase in heat treatment temperature to 1200, 1300 and 1400 °C, interface reaction occurred and reaction layers with thickness of 50, 100 and 1000 nm, respectively, were detected. The interface layer was formed by the reaction between Si–O groups in the matrix and C element in the fiber. Especially for the sample treated at 1400 °C, serious interface reaction led to the formation of β-SiC and property of carbon fiber was greatly degraded.