Synthesis and characterization of a new modification of PtAl

A new PtAl phase, which is stable at room temperature under oxidizing conditions, has been synthesized at 200 °C and 5 MPa. X-ray studies reveal it to be different from the known polymorphs of PtAl, which crystallize in the FeSi and CsCl structure types. The crystal structure of the new PtAl modification is found to be isotypical with the low-temperature modification of PdAl. In situ high-temperature X-ray diffraction experiments in air were performed to study the thermal behavior of the new PtAl alloy. In the temperature range between 400 and 700 °C, Pt₅Al3 forms as an intermediate phase. At higher temperature the alloy decomposes, resulting in the formation of platinum and Al₂O₃. The thermodynamic instability at high temperatures explains why this new modification has not been observed using contemporary metallurgic processes.