Tantalum or tantalum-based alloys resistant to water corrosion, especially acid corrosion and hydrogen embrittlement. Initial tantalum is pure or basically pure. Essentially pure tantalum can be a tantalum alloy containing up to about 11 % by weight non-tantalum components.
Tantalum or tantalum-based alloys are preferably prepared by vacuum melting. Vacuum arc remelting (VAR), electron beam melting (EBM), or plasma arc melting (PAM) are also vacuum melting methods that can be used to form alloys. To prepare the actual alloy, at least one element selected from ruthenium, rhodium, palladium, osmium, iridium, platinum, molybdenum, tungsten and rhenium (Ru, Rh, Pd, Os, Pt, Mo, W and Re) is added to pure tantalum material or essentially pure tantalum material or tantalum alloy using one of the vacuum melting methods listed above. Tantalum alloys preferably contain tungsten as well as platinum, molybdenum, rhenium or mixtures thereof. Although it is indicated above that VAR, EBM, or PAM can be used, the preferred technology is VAR.
Alternative embodiments of the invention may include the addition of elements other than those listed above to improve corrosion resistance and hydrogen brittleness resistance. These additional elements may include yttrium, gold, cerium, praseodymium, neodymium, and thorium.
Examples of tantalum alloys with a tantalum content of at least 89% include, but are not limited to, Ta-3W(tantalum-tungsten) containing at least about 3% tungsten, Ta-3W-Pt (tantalum-tungsten and platinum alloy) containing at least about 3% tungsten, Ta-3W-Mo (tantalum-tungsten and molybdenum alloy) containing at least about 3% tungsten, and Ta-3W-Re containing at least about 3% tungsten Tantalum-tungsten and rhenium alloy. Ta-3W-Pt, Ta-3W-Mo, and Ta-3W-Re can be formulated and manufactured in a manner similar to the preparation of Ta-3W. Alloys are preferably prepared by microalloying other metals with Ta-3W(tantalum-tungsten) alloys. Another preferred embodiment is the addition of ruthenium, rhodium, palladium, osmium, and iridium (also known as "platinum group metals", i.e., PGMS), which also provide low hydrogen overvoltage sites to stabilize the Ta2O5 oxide layer.
