In situ formation of Zr2Al3C4/Al2O3 composites by combustion synthesis with PTFE and thermal activations
(Department of Aerospace and Systems Engineering, Feng Chia University, 100 Wenhwa Road, Seatwen, Taichung 40724, Taiwan, China)
Abstract: Preparation of Zr2Al3C4-Al2O3 in situ composites was investigated by self-propagating high-temperature synthesis (SHS) involving both aluminothermic reduction of ZrO2 and chemical activation of PTFE (Teflon). The starting materials included ZrO2, Al, carbon black and PTFE. In addition to the conventional SHS method, the experiments were conducted by a chemical-oven SHS (COSHS) route to thermally assist the synthesis reaction. The threshold amount of 2% (mass fraction) PTFE was required to induce self-sustaining combustion. When the conventional SHS scheme was utilized, due to low combustion temperatures between 1152 and 1272 °C and insufficient reaction time, the dominant carbide forming in the composite was ZrC instead of Zr2Al3C4. On the other hand, the COSHS technique increased the combustion temperature of the reactant compact to about 1576 °C, lengthened the high-temperature duration for the reaction, and prevented Al vapor from escaping away. As a consequence, Zr2Al3C4-Al2O3 composites with a small amount of Zr3Al3C5 were obtained. The microstructure of the COSHS-derived product showed that plate-like Zr2Al3C4 grains were about 2 μm in thickness and 10-30 μm in length, and most of them were closely stacked into a laminated configuration.
Key words: Zr2Al3C4; combustion synthesis; PTFE activation; chemical-oven SHS; aluminothermic reduction