Tantalum is a shiny, silvery metal. Tantalum is soft when it is pure. At temperatures below 150°C, it's almost resistant to chemical attack. Thanks to an oxide film on its surface, t tantalum is virtually immune to corrosion. R05200, unalloyed tantalum, electron-beam furnace or vacuum-arc melt, or both R05400, unalloyed tantalum, powder-metallurgy consolidation. R05255, tantalum alloy, 90 % tantalum, 10 % tungsten, electron-beam furnace of  vacuum-arc melt, or both. R05252, tantalum alloy, 97.5 % tantalum, 2.5 % tungsten, electron-beam furnace or  vacuum-arc melt, or both. R05240, tantalum alloy, 60 % tantalum, 40 % niobium, electron-beam furnace or  vacuum-arc melt.