Sciencemadness Discussion Board

Things to do with tantalum

j_sum1 - 19-12-2022 at 04:36

I have several strips of what I believe is tantalum. (There is some uncertainty as a result of some wayward labels.)

I am wondering if there are some interesting salts or other compounds I might make. I guess a good start would be a test to confirm the identity of the material. A quick search did not yield anything particularly exciting. And quite a few compounds are reported as unstable and/or requiring airless conditions to synthesise and store.

Any ideas?

Admagistr - 19-12-2022 at 13:44

Quote: Originally posted by j_sum1  
I have several strips of what I believe is tantalum. (There is some uncertainty as a result of some wayward labels.)

I am wondering if there are some interesting salts or other compounds I might make. I guess a good start would be a test to confirm the identity of the material. A quick search did not yield anything particularly exciting. And quite a few compounds are reported as unstable and/or requiring airless conditions to synthesise and store.

Any ideas?


I would make a LiTaO3 crystal and investigate its extremely strong pyroelectric properties.It is also used for nuclear fusion on a microscale.

Bedlasky - 19-12-2022 at 15:45

Tantalum produce colored precipitates with tannin, quercetin and pyrogallol. They are one of few colored Ta compounds which can be made from aqueous solution.



IMG_20221220_003454.jpg - 215kB IMG_20221220_003619.jpg - 302kB

woelen - 19-12-2022 at 23:59

Interesting finds.

I have a few grams of Ta2O5, and tried to dissolve a pinch of that some years ago, but no luck. Not even hot concentrated solution of NaOH could do the job. What soluble Ta-salts can be used for this kind of experiments?

Admagistr - 20-12-2022 at 01:16

Quote: Originally posted by woelen  
Interesting finds.

I have a few grams of Ta2O5, and tried to dissolve a pinch of that some years ago, but no luck. Not even hot concentrated solution of NaOH could do the job. What soluble Ta-salts can be used for this kind of experiments?


Hi,I think you can't get it from solution,you probably have to melt Ta2O5 with a mixture of anhydrous alkaline hydroxide and nitrate and then get it in soluble form;-)

Bedlasky - 20-12-2022 at 03:02

Woelen: Wiki says that Ta2O5 dissolves in HF, but question is at what conditions and speed of reaction.

I agree with Admagistr - dissolve it in molten NaOH. Or you can try molten NaHSO4. J_sum have easier job, metallic tantalum should dissolve in mixture of HNO3 and HF or alkali fluoride.

j_sum1 - 20-12-2022 at 03:47

Quote: Originally posted by Bedlasky  
metallic tantalum should dissolve in mixture of HNO3 and HF or alkali fluoride.


The only fluoride I have is CaF2. Something tells me that won't work. Could I get away with aqua regia?

Bedlasky - 20-12-2022 at 04:46

Nb and Ta are soluble only in the presence of fluoride which destroy protective (and quite inert) oxide layer. Try that mixture of CaF2+HNO3. Nitric acid is strong acid, it should displace fluoride from CaF2. Add small amount of mixture and one Ta strip in to the test tube, heat it on water bath in well ventilated area. You will see if Ta is dissolving or not.

And btw you can try anodic oxidation to create colorful oxide layer on the metal surface. Woelen did something similar with Nb.

https://woelen.homescience.net/science/chem/exps/niobium/ind...

j_sum1 - 20-12-2022 at 05:09

Ok. Well I guess that forms the basis of a test to confirm the identity of the strips.

I might get a chance to try this out tomorrow.

I have some gallic acid on hand so I should play around with that tannin idea if I get something in solution.

It seems that doing something with is a bigger challenge than I snticipated. Could be fun. Or frustrating. Or both.

Bedlasky - 20-12-2022 at 05:55

You can try aqua regia first, most other metals should dissolve in it. If it doesn't react, you have Nb or Ta, Nb(V) can be reduce by zinc in to Nb(IV), Ta(V) can't be reduced.

blogfast25 - 20-12-2022 at 13:28

Don't forget NH4HF2, to 'poor man's HF'!

blogfast25 - 20-12-2022 at 13:33

Quote: Originally posted by Bedlasky  
Nb(V) can be reduce by zinc in to Nb(IV), Ta(V) can't be reduced.


Reference?

Bedlasky - 20-12-2022 at 15:42

Remy's inorganic chemistry vol. 2. I have Czech translation in PDF, if you want I can post screenshot from it, but you must manually type it in to translator.

blogfast25 - 21-12-2022 at 08:24

Quote: Originally posted by Bedlasky  
Remy's inorganic chemistry vol. 2. I have Czech translation in PDF, if you want I can post screenshot from it, but you must manually type it in to translator.


My Czech isn't that bad, so go right ahead. Ta!

Bedlasky - 21-12-2022 at 15:06

Here it is.

Ta redukce.png - 143kB

Btw. you can predict this behavior from the behaviour of tantalum's neighborhood.

Zr(IV) - can't be reduced to Zr(III) in aqueous solution, Nb(V) - can be reduced to air sensitive Nb(IV) by zinc powder, Mo(VI) - can be reduced to Mo(V) by mild reducing agents (Mo(V) isn't oxidized by the air), to air sensitive Mo(IV) by strong reducing agents like TiCl3, SnCl2 etc., to very air sensitive Mo(III) by zinc powder.

Hf(IV) - can't be reduced to Hf(III) in aqueous solution, W(VI) - can be reduced to air sensitive W(V) by zinc powder in HCl/H2C2O4 solution, to very air sensitive W(IV) and W(III) by zinc/aluminium in hot concentrated HCl.

Ta(V) will be more difficult to reduce than Nb(V). Nb(V) is somewhere between Zr(IV) and Mo(VI) in redox behavior, so Ta(V) is somewhere between Hf(IV) and W(VI). So you can suppose that reduction of Ta(V) to Ta(IV) in aqueous solution is a)impossible or b)need specific conditions and strong reducing agent, similar to reduction of W(VI) to W(IV)/W(III).