Al-C-Rh (Aluminum-Carbon-Rhodium)

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Section II: Phase Diagram Evaluations

Al-C-Rh (Aluminum-Carbon-Rhodium) V. Raghavan

Recently, [2002Kim] determined an isothermal section at 1100 °C for this system in the Rh-rich region. No ternary carbide of the E21, Co3 AlCx -type was found.

Binary Systems In the Al-C system, the stoichiometric compound Al4 C3 (D71-type rhombohedral) is present. The Al-Rh phase diagram [2006Kho] (see Fig. 1 under Al-Pd-Rh) depicts the following intermediate phases: Rh2 Al9 (D8d, Co2 Al9 -type monoclinic), Rh1x Al3 (orthorhombic, denoted O1 or e16 Þ; RhAl3 (orthorhombic, denoted O2 or e6 Þ; Rh2 Al5 (c) (space group Pm 3, cubic), Rh2 Al5 (h) (D811, Co2 Al5 -type hexagonal), Rh7 Al3 (monoclinic), and RhAl (B2, CsCl-type cubic). The C-Rh system [Massalski2] is of the simple eutectic type, with the eutectic temperature at 1694 °C.

Ternary Phase Equilibria Fig. 2 Al-C-Rh partial liquidus projection [2002Kim]

Starting with high purity elemental powders, [2002Kim] prepared by means of arc-melting under Ar atm (or spark

plasma sintering in vacuum) just one alloy with the composition 66.7Rh-22.2Al-11.1C (in atomic percent). This composition corresponds to possible ternary carbide with the stoichiometry of Rh3 AlC0:5 : Alloy samples were annealed at 1100 °C for 72-144 h. The phase equilibria were studied with electron microscopy, x-ray diffraction and electron probe microanalysis. Differential thermal analysis was carried out at a heating/cooling rate of 10 °C per min. The microstructure showed primary crystals of (Rh), RhAl (B2) phase, and graphite. There was no evidence for the presence of ternary carbide. The partial isothermal section at 1100 °C and the liquidus projection constructed by [2002Kim] are shown in Fig. 1 and 2, respectively.

References

Fig. 1 Al-C-Rh partial isothermal section at 1100 °C [2002Kim]

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2002Kim: Y. Kimura, K. Iida, and Y. Mishima, Microstructures and Phase Equilibria of the Transition Metal Corner in the RhAl-C and Ir-Al-C Ternary Systems, Intermetallics, 2002, 10, p 933-944 2006Kho: V.G. Khoruzhaya, K.E. Kornienko, P.S. Martsenyuk, and T. Ya. Velikanova, Phase Equilibria in the System Al-Rh, Poroshk. Metall., 2006, (5-6), p 48-56 in Russian; TR: Powder Metall. Met. Ceram., 2006, 45(5-6), p 251-258

Journal of Phase Equilibria and Diffusion Vol. 29 No. 1 2008

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