Sciencemadness Discussion Board - A process to produce silvery thallium ampoules

A process to produce silvery thallium ampoules

Dan Vizine - 15-10-2018 at 17:49

Many of the low-melting metals require customized equipment to give satisfactory purification results.

Liquid thallium is fairly viscous, reacts rapidly with oxygen and contains difficult-to-filter impurities. For these reasons it's difficult to prepare high quality samples of this metal simply by melting and filtering through typical filter material under argon. A typical purification apparatus that can yield excellent results is shown below. The tube is torch dried, argon-purged and charged with thallium metal. When torch-melting melting thallium in continually UHP argon purged glass, a large part of the "smut" will be left right where the metal first melts, more of it will be caught up in the loosely packed stainless steel wool. Finally, as the molten thallium flows over more and more glass the small inhomogeneous bits of material separate out and adhere to the glass walls. Finally, a very pretty form of molten thallium ends up in the bottom ampoule as a bright silver-white metal.

I've tried this type of purification on several occasions with various filter media. Nothing has given a sample as nice as this one yet.

BromicAcid - 15-10-2018 at 18:22

Very cool, beautiful work.

Sulaiman - 15-10-2018 at 21:17

Double good ... a shiny sample AND not dead.

I doubt that I'll ever do any thallium^* chemistry,
so purely out of curiosity ;

How reactive is thallium to air ?
e.g. like sodium or Aluminium or iron etc.

How toxic is thallium ?
Different sources report from 'take care' to 'do not even think about it'

Would you pretty please take a photo of a flame test of thallium with copper and/or boron in the same frame,
just so I can get a true idea of the colour ?

^* Thallium and its salts require an EPP license in UK

fusso - 16-10-2018 at 06:35

Quote: Originally posted by Sulaiman

Would you pretty please take a photo of a flame test of thallium with copper and/or boron in the same frame,
just so I can get a true idea of the colour ?

Same photo (unedited) you mean?

Dan Vizine - 16-10-2018 at 07:46

Quote: Originally posted by Sulaiman

How reactive is thallium to air?
e.g. like sodium or Aluminium or iron etc.

Thallium reacts initially very swiftly to air. Freshly cut metal, silver in color, starts to get a faint bluish lead-like color in seconds. The shiny luster fades almost instantly. After that, it's just a slow corrosion, although MUCH faster than lead. Molten Tl does the same thing but a lot faster.

How toxic is thallium?
Different sources report from 'take care' to 'do not even think about it'

Well, it's tremendously toxic but being a heavy solid, gloves and a respirator are entirely adequate. A lab apron is nice, but not absolutely necessary. I've processed (cut, cleaned and bottled) kilos for GalliumSource (RIP) with no issues. I usually wear 2 or 3 pairs of gloves simultaneously so that I can peel one off to touch doorknobs, etc. with no interruption in the work.

[Edited on 10/17/2018 by Dan Vizine]

Sulaiman - 16-10-2018 at 08:13

As many of us would have difficulty identifying elements such as thallium by chemical means,
and do not have access to a spectrometer, or even reference samples,
identifying flame test colours is a powerful tool.

I can recognise the greens of copper and boron, barium maybe, thallium definitely not,
so if I had access to 'reference' colours - largely independent of camera, processing and display
it could be very useful for the identification of unknown ions.

Could be a nice project for an element collector ?

(I did not find a useful flame colour chart using google)
________________________________________________________

In this case I'd just like something that could help me in the future to reliably differentiate between copper, boron and thallium etc.

P.S. that is a nice simple tip:
" I usually wear 2 or 3 pairs of gloves simultaneously so that I can peel one off to touch doorknobs, etc. with no interruption in the work."

[Edited on 16-10-2018 by Sulaiman]

Dan Vizine - 16-10-2018 at 14:34

Here's a comparison with some of the green ones:

[Edited on 10/16/2018 by Dan Vizine]

phlogiston - 16-10-2018 at 15:03

Dan, thanks for sharing, that's a very original method to produce pure/attractive samples.
Do you recover and/or purify the impure Tl that has stuck to the glass? If so, you most likely will have to reduce Tl salts back to metal at some step; I'd be very interested to hear about your experiences with that if you have any that you can share.

[Edited on 16-10-2018 by phlogiston]

Dan Vizine - 17-10-2018 at 06:04

Hi Phlogiston,

I've made it a project to melt and purify all of the low-melting metals in glass under vacuum or argon. K and Na are trivial, Cd is weird because of its high vapor pressure, Pb and Tl need this procedure to "pull out" oxides. Sn is kinda straightforward.

The effort to recover the impure thallium is truly a wretched affair and I hate performing it.

It's done electrolytically on a very concentrated solution of thallium sulfate. Basically, the tube is pulverized inside multiple plastic bags. The crushed glass is then stirred with the absolute minimum amount of concentrated sulfuric acid that can achieve wetting of all the surfaces and dissolve the visible thallium. pH sometimes needs to be adjusted upward if too much acid is used.

Using a small beaker for the electrolysis, typically 100 mL is large enough, I insert a platinum anode and a highly polished sheet of stainless steel as the cathode. The thallium plates out onto the stainless steel from which it is easily removed since it is highly nonadherent.

Since I know that this is where the impurities reside (some of them anyway), I haven't done a single thing with the recovered metal except to bottle it.

[Edited on 10/17/2018 by Dan Vizine]