Tantalum corrosion

Tantalum Corrosion

2002 marked the 200th anniversary of the discovery of tantalum by Anders Gustav Ekeberg of Sweden using an ore sample from Kimito, Finland. He named it after King Tantalus of Phrygia, from Greek mythology, who was condemned to eternal frustration by standing up to his neck in water, which receded when he tried to drink it. Ekeberg thought this name was fitting because of the difficulty he had in isolating it. Modern-day tantalum has lived up to this sense of frustration, more so than Ekeberg could have ever imagined. A modern and comprehensive document on the subject is the second edition of the classic CORROSION BASICS textbook.

The tantalum supply chain involves mining for tantalite ore in Australia, Africa, Brazil, China, Russia, Canada, and tin slag operations specifically in Thailand and Nigeria. Companies like H.C. Starck, Cabot Corp., and Ningxia NFM process the ore into tantalum powder and wire processors. Next, manufacturerslike Kemet, AVX, and Vishay make capacitors. On top of the supply heap, original equipment manufacturers (OEMs) use tantalum to produce consumer and industrial products like cell phones, computer chips, stereos, VCRs, lenses, prosthetics, heat shields, auto engine components, airbag igniters, and turbine engine alloys.

Tantalum is almost completely immune to attack by acids and liquid metals. It equals glass in resistance to acids and it is impervious to liquid metals up to 900°C. Few chemicals such as hydrofluoric acid, fuming sulfuric acid, and strong alkalis will begin to break through tantalum's corrosion barrier. This ability to resist practically everything has won tantalum favor among manufacturers of chemical equipment, instruments, heating elements, and surgical implants.

Corrosion case

This question is related to corrosion and hydrogen embrittlement of Tantalum, 2.5% tungsten tubes in hydrochloric acid duty. The tubes have extensively embrittled in 19% acid at about 130^oC . This is not supposed to be a regime where we expect any problem, so the degree of damage is surprising. The unit is a conventional shell and tube heat exchanger with tubes 6m long, 19 mm diameter and 0.5 mm wall thickness. There is no measurable loss of metal thickness. Simple bend tests on the tubes have shown the embrittlement. The acid purity has been extensively investigated and no evidence found of contamination. I would like to know if there is any experience of similar corrosion effects that may have been attributed to changes in Tantalum quality from tramp elements, in remelted material. Alternatively, any suggestions of low level contamination to analyze for (we have looked for HF), that can have a significant influence in causing this type of damage. The acid is high purity, so any levels would have to be at ppm concentration.