Chemical vapor transport of platinum and rhodium with oxygen as transport agent

Chemical vapor transport of platinum (Pt) and rhodium (Rh) has been studied in closed ampoules using a 900-800 °C over 100 mm gradient for periods of 123-365 days. The ability of O2, air, and H2O to act as transport agents has been evaluated, control experiments have been performed with vacuum, N2, and Ar, and surveying experiments have been made with NH3, NO, and H2. Transport of Pt and Rh occurs in the presence of oxygen (regardless of source), manifested as single-crystal growth at the colder end of the ampoules. PtO2 and RhO2 were identified as vapor molecules by in situ mass spectrometric monitoring. A small transport of Rh is indicated for H2O as agent, whereas no transport is observed in N2, H2, NH3, and Ar atmospheres.