Characterization on microstructure homogeneity of θ-Al2O3 powder ...
Key Engineering Materials Vol. 351 (2007) pp. 81-87 online at http://www.scientific.net © (2007) Trans Tech Publications, Switzerland
Characterization on microstructure homogeneity of θ-Al2O3 powder systems during phase transformation Fu-Su Yena, Pei-Ling Changb, Pei-Ching Yu and Rong-Jeh Yang Department of Resources Engineering, National Cheng Kung University, No.1, University Rd. Tainan 701, Taiwan, China a
[email protected], [email protected]
Keywords: DTA, Alumina, Phase transformation, Nano-materials. Abstract. The traditional differential thermal analysis (DTA) techniques are employed to evaluate
the kinetic behavior induced by the inter-particle relationships in a nano-particle θ-Al2O3 powder system during θ- to α- phase transformation. Discrepancies in homogeneity and inter-particle distance of the powder system may result in the diagnostic DTA profiles which can be use to evaluate the characteristics of the powder system as well as the formed α-Al2O3 particles. Based on the acknowledgement, a quasi-homogeneous transformation shows that a duration of 90 seconds is needed for one θ-crystallite to transform into one α-nucleus with a heating rate of 10 oC min-1 and fabrication of the high phase-pure and mono-sized α-Al2O3 powders is obtained. Introduction The traditional differential thermal analysis (DTA) techniques are employed to evaluate the kinetic behavior of the inter-particle relationships in a nano-particle θ-Al2O3 powder under thermal treatments. DTA techniques have long been the common method to examine the thermal properties of materials. In general, with reactions that occur in a material during thermal treatment, the energy changes can be identified and measured through temperature differences relative to a thermally inert material. However, this kind of reaction may inherently be attributed to phase transformations and grouped into endothermic reactions (e.g. dehydration, structure decomposition, melting, evaporation, sublimation ) and exothermic reactions (oxidation, freezing, reconstruction of a crystal structure) [1, 2], demonstrated by DTA profiles in a macroscopic sense. Recent studies on the θ- to α- phase transformation of nano-scaled Al2O3 powder systems reveal that the profiles obtained by DTA techniques may release additional information rather than the phase transformation. It is found here that at least the microstructure of the reaction system can be perceived by the profiles. Some diagnostic DTA profiles relevant to the microstructure, especially to the spatial uniformity and the inter-particle distance among the particles, are recorded. Based on the acknowledgement, this study explains how to predict a quasi-homogeneous transformation by which a highly phase-pure and
Characterization on microstructure homogeneity of θ-Al2O3 powder systems during phase transformation Fu-Su Yena, Pei-Ling Changb, Pei-Ching Yu and Rong-Jeh Yang Department of Resources Engineering, National Cheng Kung University, No.1, University Rd. Tainan 701, Taiwan, China a
[email protected], [email protected]
Keywords: DTA, Alumina, Phase transformation, Nano-materials. Abstract. The traditional differential thermal analysis (DTA) techniques are employed to evaluate
the kinetic behavior induced by the inter-particle relationships in a nano-particle θ-Al2O3 powder system during θ- to α- phase transformation. Discrepancies in homogeneity and inter-particle distance of the powder system may result in the diagnostic DTA profiles which can be use to evaluate the characteristics of the powder system as well as the formed α-Al2O3 particles. Based on the acknowledgement, a quasi-homogeneous transformation shows that a duration of 90 seconds is needed for one θ-crystallite to transform into one α-nucleus with a heating rate of 10 oC min-1 and fabrication of the high phase-pure and mono-sized α-Al2O3 powders is obtained. Introduction The traditional differential thermal analysis (DTA) techniques are employed to evaluate the kinetic behavior of the inter-particle relationships in a nano-particle θ-Al2O3 powder under thermal treatments. DTA techniques have long been the common method to examine the thermal properties of materials. In general, with reactions that occur in a material during thermal treatment, the energy changes can be identified and measured through temperature differences relative to a thermally inert material. However, this kind of reaction may inherently be attributed to phase transformations and grouped into endothermic reactions (e.g. dehydration, structure decomposition, melting, evaporation, sublimation ) and exothermic reactions (oxidation, freezing, reconstruction of a crystal structure) [1, 2], demonstrated by DTA profiles in a macroscopic sense. Recent studies on the θ- to α- phase transformation of nano-scaled Al2O3 powder systems reveal that the profiles obtained by DTA techniques may release additional information rather than the phase transformation. It is found here that at least the microstructure of the reaction system can be perceived by the profiles. Some diagnostic DTA profiles relevant to the microstructure, especially to the spatial uniformity and the inter-particle distance among the particles, are recorded. Based on the acknowledgement, this study explains how to predict a quasi-homogeneous transformation by which a highly phase-pure and
