Amorphous CaO · Al2O3 fibers by melt extraction

A novel melt extraction technique has been used to produce fine calcium aluminate (CaO · Al2O3) fibers with wheel velocities of 1.5–65 m s−1. The geometry of the fibers depends on the wheel velocity; at speeds < 3 m s−1 uniform diameter fibers were obtained, whereas at higher velocities Rayleigh waves formed on the fibers owing to instability and the effects of surface tension. The variation of fiber thickness vs. speed showed an increase (anomaly) up to a speed of ~10 m s−1, resulting from the elongated length of the contact between the wheel tip and molten drop. The dimensions of the fibers were also found to change with the tip radius of the extraction wheel. All extracted fibers were amorphous owing to the good glass formability of calcium aluminate and high cooling rate (105 K s−1) of the system. Thermal analysis of the fibers showed that they devitrify at a temperature of ~960 °C. The extracted fibers showed outstanding tensile strengths (up to, ~3000 MPa for thin uniform diameter fibers) and a moderate elastic modulus (95 GPa).