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Lecture

Thermodynamic investigations of the Ti-Al-O ternary system

Wednesday (28.09.2016)
17:30 - 17:45
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Properties such as the low thermal expansion coefficient, additional to its low thermal conductivity and good chemical resistance make the Al2TiO5, tialite, suitable material for technological applications. Phase relations in the TiO2-Al2O3 system were experimentally studied in [1,2] and several contradictions are indicated. Bunting [1] reported a congruent transformation of Al2TiO5 at about 1860°C and two eutectic reactions at 1715 and 1850°C. According to Lang et al. [2] Al2TiO5 melted by peritectic reaction and two allotropic forms were detected for this compound: α-Al2TiO5 stable at 1820-1860°C and β-Al2TiO5 stable in the temperature range from 1260-1270°C up to inversion temperature 1820°C. The reports of both [1] and [2] in this system indicates two eutectic transformations. Later, a new phase of the system was detected, Al6Ti2O13 [3]. Berger at al. [4] suggested that the high temperature phase was not an allotropic form of Al2TiO5 but Al6Ti2O13; this compound participated in eutectic reaction with Al2TiO5 instead of Al2O3 reported by [1]. So, the aim of present work is an experimental study of the phase equilibria in the TiO2-Al2O3 system to resolve existing contradiction between mentioned data and to define the limits of thermal stability of Al2TiO5 and Al6Ti2O13. Six compositions of the system were prepared by co-precipitation and dried at 700°C for 3 hours. To investigate phase equilibria the samples were annealed for 1-5 days at temperature of 1250-1750°C and air-quenched. Samples were examined by XRD. The microstructure characterization was carried out using SEM/EDX. Solid phase transformations and melting behavior of the samples were studied by DTA. Thermodynamic database for the Al-Ti-O system was received using experimental data [1-4] and own results as well as experimental thermodynamic data [5,6].

References:

[1] E.N. Bunting, Bur. Stand. J. Res. 11 (1933) 719-725.

[2] S. Lang, C. Fillmore, L. Maxwell, J. Res. Natl. Bur. Stand. 48 (1952) 301-321.

[3] S.T. Norberg, S. Hoffman, M. Yoshimura, N. Ishizawa, Acta Cryst. C 61 (2005) i35-i38.

[4] M.H. Berger, A. Sayir, J. Eur. Ceram. Soc. 28 (2008) 2411-2419.

[5] E.G. King, J. Am. Ceram. Soc. 77 (1955) 2150-2152.

[6] K.G. Bonnickson, J. Am. Ceram. Soc. 77 (1955) 2152-2154.

Speaker:
Dipl.-Ing. Mariia Ilatovskaia
TU Bergakademie Freiberg
Additional Authors:
  • Dr. Olga Fabrichnaya
    TU Bergakademie Freiberg