Non isothermal kinetic study of the aluminium titanate formation in alumina-titania mixtures

Abstract

Aluminum titanate (Al 2 TiO 5 ) is a high refractoriness material with excellent thermal shock resistance. Hence it is suitable for several applications at elevated temperatures where insulation and thermal shock resistance are required. Such as components of internal combustion engines, exhaust port liners, metallurgy, and thermal barriers. The thermal instability of Al 2 TiO 5 at high temperature is another characteristic of this material that has been studied and controlled by the incorporation of several additives. The Al 2 TiO 5 formation from pure oxides presents an endothermic peak in the differential thermal analysis (DTA). The thermodynamic temperature is 1280 ºC. But experimentally, as in every other DTA experiment, these peaks strongly depend on the heating rate: this fact has been extensively employed for the kinetic study of transformation processes and the mechanism determination of chemical reactions. Both activation energies (E a ) and nucleation rates can be obtained from these experiments. The present work reports the formation E a of Al 2 TiO 5 prepared from pure oxides at air atmosphere by the Kissinger DTA based methods. Previously the particle size distribution of the starting powders together with X-ray diffraction analysis of the starting powders and the resulting materials was carried out. The properties of the Al 2 TiO 5 formation were grouped into two groups corresponding to the low and high heating rates, below and over 5 K/min. E a values were obtained after the Avrami (n) constant evidenced that the crystallization mechanism is strongly related to the heating rate, even in the wide range studied which includes the technological ones(0.5-40 K/min).

Low (and negative) thermal expansion Al2TiO5 materials and Al2TiO5 - 3Al2O3.2SiO2 - ZrTiO4 composite materials. Processing, initial zircon proportion effect, and properties

“…A negative endothermic peak can be easily observed. This peak could be associated with aluminum titanate formation from aluminum and titanium oxides [41]. In all the cases it can be said that the reaction is complete below 1420 °C.…”

“…These probes were fired in an electric furnace with a heating rate of 5 °C/min up to 1500 °C with 2 h soaking and cooling at 10 °C/min down to 300 °C. The maximum temperature was chosen after a dilatometric study, taking into account previous reports [39,41].…”

Characterization and microstructure investigation of novel ternary ZrO2–Al2O3–TiO2 composites synthesized by citrate–nitrate process

“…Several researchers believed that the kinetics of Al 2 TiO 5 formation from the binary oxides depends on temperature, as in the range of 1280-1400°C the chemical driving force is too small in comparison with the strain energy associated with bulk nucleation; therefore, tialite nuclei can nucleate only at a limited number of 'easy to nucleate' sites [8,9,28]. Arenas [9] suggested that the kinetics is included two different reaction stages during isothermal treatment around 1300°C.…”

Optimizing the parameters for in situ fabrication of hybrid Al-Al2O3 composites

“…The energy needed for activation of exothermic reactions is generally calculated based on DSC curves using the Johnson-Mehl-Avrami (JMA) equation and Kissinger's method, which are consecrated as rapid and convenient instruments for studying kinetics of phase transformations and mechanisms of chemical reactions [35][36][37][38][39][40]. This procedure to calculate activation energy E a is based on nonisothermal experiments and considered less accurate, because peaks became weaker and broader for slower heating rates, limiting the plotting ranges of 1/E a .…”