Removing titanium from tantalum crucible

Question

I'm trying to remove titanium filling from a tantalum crucible for a high-temperature effusion cell. I've managed to get a majority of the material out with tweezers, but some remains and is difficult to remove. I understand that sulfuric acid will corrode titanium, but not tantalum, and was considering this as a method for extraction.

If anyone has some advice on a method to (safely) remove $\ce{Ti}$ from the $\ce{Ta}$ crucible without destroying it, I would very much appreciate it. I am certainly not a chemist and could use some help.

Answer 1

Straight hydrochloric acid- Say 20% is virtually inert to Tantalum- but significantly corrosive to titanium. If you heat it to boiling point of hydrochloric- it will eat through the titanium.

http://www.parrinst.com/wp-content/uploads/downloads/2011/07/Parr_Titanium-Corrosion-Info.pdf http://www.tantaline.com/Tantalum-Corrosion-71.aspx

Answer 2

Titanium and Tantalum are quite nonreactive, so using 'safe' acids, such as diluted acetic acid won't make any difference. That's why using strong acids such as (sometimes has to be hot ) sulfuric acid will do it. If you are looking for not having to work with sulfuric acid, you could always use hydrogen iodide: that is even stronger than sulfuric acid...

It's documented here that:

Tantalum appear not to be attacked by many acids at room temperature but does dissolve in hydrofluoric acid, $\ce{HF}$, or oleum (a solution of sulfur trioxide, $\ce{SO3}$, in sulfuric acid, $\ce{H2SO4}$, also known as fuming sulfuric acid).

Reaction of tantalum with water

Tantalum does not react with water under normal conditions. The surface of tantalum metal is protected by a thin oxide layer.

Then I read for titanium (Source):

Reaction of titanium with water

Titanium metal is coated with an oxide layer that usually renders it inactive. However, titanium will react with steam form the dioxide, titanium(IV) oxide, $\ce{TiO2}$, and hydrogen, $\ce{H2}$.

$\ce{Ti(s) + 2H2O(g) → TiO2(s) + 2H2(g)}$

So Tantalum doesn't react with steam so you might be able to use steam for that separation as seen as $\ce{TiO2}$ is white and tantalum not.

Source : http://caldersgr9science.wikispaces.com/73+Tantalum