ISSN 1061-3862, International Journal of Self-Propagating High-Temperature Synthesis, 2008, Vol. 17, No. 2, pp. 125–128. © Allerton Press, Inc., 2008.
Ti–Al–C MAX Phases by Aluminothermic Reduction Process A. Hendaouia, b, D. Vrela, A. Amarab, A. Benaldjiab, and P. Langloisa a CNRS-LIMHP, b
UPR 1311, Université Paris 13, Institut Galilée, 99 Av. J.-B. Clément, Villetaneuse, 93430 France Département de Physique, BP 12, Faculté des Sciences, Université Badji Mokhtar, Annaba, 23000 Algeria e-mail:
[email protected] Received February 21, 2008
Abstract—A new approach to synthesis of Ti2AlC–Ti3AlC2/Al2O3 compounds is developed based on thermite reaction in the TiO2–Al–C system. The effect of Al excess is also discussed. XRD analysis has proved that this parameter can be used to improve the product purity, i.e., the amount of TiC in the final product. It has also been shown that, with increasing Al excess, the composition of a major MAX phase undergoes a change from Ti2AlC to Ti3AlC2. Keywords: MAX phases, aluminothermic reduction, dilution PACS numbers: 81.05.Je, 81.20.Ka DOI: 10.3103/S1061386208020076
INTRODUCTION Over recent years, a new family of layered ceramics has attracted much interest due to their unique physical and mechanical properties, such as high melting point, good thermal and electrical conductivity, high strength and modulus, and machinability by both electrical discharge method and conventional cutting tools [1–5]. These ceramics are complex ternary compounds with a hexagonal crystalline structure and can be represented by the general formula Mn + 1AXn, where M is a transition metal, A is an A Group element, and X is either carbon or nitrogen [4, 5]. Among this group of compounds, Ti3AlC2 and Ti2AlC are two interesting materials which have been widely studied in the Ti–Al–C system [6–10]. It has been revealed that Ti3AlC2 exhibits some abnormal room-temperature compressive plasticity in contrast to normal brittle ceramics [7]. Ti2AlC has also been reported to have high electrical conductivity, excellent machinability, high yield strength, and significant plasticity at high temperatures [8]. For preparing Ti–Al–C ternary compounds, two kinds of methods can be used. One is sintering by using proper starting reactants, including hot pressure (HP) sintering, hot isostatic pressure (HIP) sintering, and spark plasma sintering (SPS) [7–9], and the other is combustion synthesis by using elemental powders as raw materials [10– 13]. With less energy consumption and short reaction period, combustion synthesis has great potential in large-scale industrial production of Ti–Al–C ternary powders. Based on a thermite reaction, the TiO2–Al–C system was previously used to synthesize TiC-based cermets [14]. But we did not find in the literature any investigation on synthesizing MAX phase-based cermets using
this system. The aim of this work is to introduce a new kind of methods involving the reduction of TiO2 using Al as reducing agent in the presence of C and Al excess. The TiO2–Al–C system has the advantage of being low cost as compared to the Ti–Al–C system. Moreover, direct MAX phase strengthened alumina composites can be directly obtained as compared to what have been done in [15]. The stoichiometric starting composition is described by the following reaction scheme: 3Ti2AlC + 4Al2O3. (1) 6TiO2 + 11Al + 3C In a second step, the present study will also focus on the influence of adding Al in excess relatively to Eq. (1) in order to reduce TiC in final products, so that one mole of Al is added at every step to carry out the following reactions: 3Ti2AlC + 4Al2O3 + Al, (2) 6TiO2 + 12Al + 3C 6TiO2 + 13Al + 3C
3Ti2AlC + 4Al2O3 + 2Al, (3)
6TiO2 + 14Al + 3C
3Ti2AlC + 4Al2O3 + 3Al, (4)
6TiO2 + 15Al + 3C
3Ti2AlC + 4Al2O3 + 4Al, (5)
6TiO2 + 16Al + 3C
3Ti2AlC + 4Al2O3 + 5Al. (6)
EXPERIMENTAL Samples were prepared from commercial powders of TiO2 (45 μm, 99.9% pure), C (graphite, 50 μm, 99.9%), and Al (45 μm, 99.9%) from Aldrich which were carefully weighted on a precision scale to obtain required compositions. The corresponding mass percentages are given in Table 1. The reactions considered here are the combination of the reduction of TiO2 by Al and of the synthesis of
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