Refractory metals

Refractory metals (Latin: refractarius = unruly, stubborn ), the high-melting, base metals of transition group 4 (titanium, zirconium and hafnium), 5th subgroup (vanadium, niobium and tantalum ) and the subgroup 6 ( chromium, molybdenum and tungsten). Its melting point is higher than that of platinum (1772 ° C).

Refractory metals are solid at room temperature due to passivation relatively resistant to corrosion ( as tungsten is releasably neither in hydrofluoric acid ( hydrofluoric acid) or in aqua regia, but only in mixtures of nitric and hydrofluoric acid). Your recovery is, however, complicated by the fact that they readily react with many non-metals at high temperatures.

Beneficial for many technical applications are not only the high melting point of the refractory metals, but also the low thermal expansion coefficient and compared with steel high conductivity for heat and electricity. Due to the body-centered cubic lattice structure show refractory metals at low temperatures a transition from ductile to brittle material behavior.

Recent studies have shown that the brittle behavior of the refractory metals is limited at temperatures below the Debye temperature mainly by impurities. High Pure crystals of tantalum, niobium and hafnium have even at the lowest temperatures a good ductility.

Swell

• Whs - special metals: Refractory
• Refractory metals in the Federal Waste Management Plan 2011, p 343
• Melting Metallurgical production and cold forming a copper - niobium - silver -in- situ composite

• Transition metal