Palladium. Coloured Scanning Electron Micrograph (SEM) of crystals of the metal palladium (Pd). The crystals have a cubic close-packed structure, with the crystal faces clearly seen. Palladium (atomic number 46; atomic weight 106. 42; melting point 1552 Celsius) is the least noble of the platinum metals. It is used in alloys such as white gold. It serves as a catalyst, especially for hydrogen- ation. Palladium is also used in dental work and in electrical components. Magnification: x60 at 6x7cm size.