Papers by Author: Sayed Hamid Reza Fatemi Nayeri

Abstract: The starting reaction in the combustion synthesis process in TiO2-Al-C system leading to TiC+Al2O3 composite was evaluated using a combination of Differential Thermal Analysis (DTA), X-Ray Diffraction (XRD) and Transmission Electron Microscope (TEM). Double phases in 3TiO2- 4Al-3C system were milled separately and then the third phase was added according to the stoichiometric reaction for 3TiC+2Al2O3 composite formation. The combustion synthesis temperature was observed to decrease from 962 °C to 649 °C after mechanical activation of TiO2/Al mixture for 16 hr. On the contrary, the mechanical activation of Al/C and TiO2/C mixtures for 16 hr made the reaction temperature increase to 995 °C and 1024 °C, respectively. TEM and XRD patterns of as-milled powders showed that the reaction temperature changes could be due to increased TiO2 and Al interface area. In addition, DTA experiments showed that for the sample in which TiO2 and Al were mechanically activated the reaction occurred at the temperature even lower than the aluminum melting point.

Abstract: A mechanism for the combustion synthesis of TiC+Al2O3 was proposed in a mechanically activated TiO2-Al-C system. As-milled powder mixture was analyzed using XRD and TEM techniques where no chemical reaction and/or inter-particle diffusion were identified. The results obtained from DTA tests on unmilled powder revealed that the combustion synthesis occurred in a single step at 962 °C while the synthesis of mechanically activated powder mixture occurred in three different stages. The XRD analysis on the synthesized samples of 8 hour premilled powder at different temperatures showed that the three stages were as follows: First the reaction between Al and TiO2 takes place forming Al3Ti, Ti2O3, and Al2O3 at 700 °C. In the second step, Ti-rich titanium aluminides (AlTi, AlTi2, and AlTi3) and TiO, are formed at 923 °C, and finally the formation of TiC+Al2O3 is completed at 1329 °C.