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  • davidrooke

Tantalum - An Extraordinary Metal

Updated: Jun 16, 2022

CVD is a highly versatile process – over 30 years we have solved coating challenges in all major industries using this process, either alone or to produce complex hybrid coatings. It can be succesfully applied across the periodic table producing coatings with remarkable properties. One element where we have successfully applied it is Tantalum.

Tantalum is an extraordinary metal. It has a melting point of 3017degC which makes it the third highest metal behind Tungsten and Rhenium. This is a useful property, however it is its extreme chemical resistance that makes it most interesting. Below 150degC it is inert to aqua regia (mixture of concentrated hydrochloric and nitric acids). Aqua regia dissolves other metals, such as gold and platinum, normally thought of as inert, in a trice.

Tantalum has a variety of uses, the biggest of which is in capacitors, but for coatings, the interest in mainly in putting an extremely corrosion resistant layer onto fasteners, crucibles, pipe bores etc. The price of tantalum metal has rocketed and this is expected to stimulate interest in coatings where solid tantalum components could be replaced by cheaper metals coated with tantalum.

Tantalum is fairly easy to deposit by CVD, normally from TaCl5 & hydrogen. The main difficulty is that TaCl5 is practically impossible to evaporate in a controlled manner. TaCl5 melts at 216degC and evaporates at around 240degC The change from liquid to vapour involves dissociation of the dimer Ta2Cl10 to the monomer, so this complicates things. It is also hygroscopic so that any exposure to air completely changes the evaporation properties. ATL overcomes this problem by generating the tantalum in situ through the reaction of chlorine gas with tantalum metal. Obviously handling a gas as toxic as chlorine is not to be taken lightly, but it does make Ta CVD a reliable, repeatable and scalable process. Chlorine is cheap and tantalum scrap is relatively easy to buy.

ATL has developed and sell its own design of industrial scale TaCl5 generator. Transport of up to 1Kg per hour of Ta metal is possible with the current design. These are available for sale either as part of a complete turn-key coating system or as a bolt on to customers’ existing CVD equipment. Control can be stand alone or incorporated into the main system. The same generators can be used for making TaC coatings which are of increasing interest in the semi-conductor market.

We would love to discuss your particular coating challenge. We can bring to bear 100 years of experience of CVD and related coating processes across the whole “periodic table” working on some of the most challenging coating engineering problems to assist in developing a R&D programme or system to meet your challenge.

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