Chemical Forums
Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: curiouscat on September 19, 2015, 06:53:07 AM
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Is there any easy test (to be used in the field) to confirm that a commercial metal (sheet / rod etc.) is Titanium?
e.g. For confirming the SS3xx grades (the ones that contain Molybdenum) the following protocol seems standard:
a) Place equal drops of concentrated hydrochloric acid and concentrated nitric acid on the metal surface. Allow 3 to 4 minutes for reaction and transfer 2 drops to a spot plate.
b) Add 2 drops of 10% potassium thiocyanate.
c) Add 25% sodium thiosulfate drop-wise stirring until the red color begins to disappear. A violet color will appear if molybdenum is present.
Is there any thing analogous for Titanium?
As an aside, if the above test was repeated on Titanium is there a certain color finding to be expected?
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Typically, when someone asks for a wet chemistry assay for a metal, I start by asking, "Why not ICP-MS?" Then I direct them to Feigl's Spot Tests. I rarely open the copy I bought from my public library, because its spine is split, and I don't want to damage it further. But you caught me in a good mood. So here goes, from Spot Tests in Inorganic Analysis, Fifth Edition, 1958, Feigl, everything in the quote below is sic.
A large drop of the test solution is mixed on a watch glass with stannous chloride (a great excess is to be avoided). On gentle heating, the precipitate balls together. A drop of of chromatropic acid is placed on a filter paper followed by a drop of the clear solution from the watch glass. In the presence of titanium, a red-brown fleck appears. The precipitate, as well as the clear solution, may be placed on the filter paper, because the precipitate remains fixed and the solution diffuses away. If the moist portion is then treated with chromatropic acid, a red brown circle is formed.
Basically, the reactant is chromatropic acid, but it reacts with other metals too, so the spot tests use a variety of tricks to avoid or identify conflicts. Given all of that, I ask again, why not ICP-MS?
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Because he asked for field test and while there are portable ramans or FTIR I doubt there are portable ICP-MS.
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They're getting smaller. However, its still true that the spot tests are clunky, and hard to execute. They're out there. But I can't help but wonder if they are, in someways, difficult to validate. That is, to what accuracy and what level is the answer needed, and can the spot test meet it. We only have Fritz Feigl's opinion, after all.
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Portable ICP-MS is unlikely anytime soon, if ever. High flow argon gas and power requirements for the RF coil make it almost impossible. Plus samples have to be fully digested prior to aspiration into the plasma, requiring at the minimum a hot plate or muffle furnace with concentrated acids. Direct analysis options are possible (laser ablation) but this would make the instrument even less portable. Maybe portable AAS is possible, but I doubt it.
Anyway, ICP-MS is about quantification, and the OP didn't mention this. He only wants identification. This changes the equation. Also, do you want to know if the sheet contains titanium or is titanium? This also influences what you can do. Most alloys have some sort of identifying marking on them. This will be your best bet. Titanium is not magnetic. If a magnet sticks, not titanium (a negative test, but still). If your sample is suspected to be pure, could you identify it by density or melting point? It may not be possible to easily observe pure titanium melt, but you could rule it out if, for example, it melts at much lower temperature, like aluminum. I do know a shaving will burn like magnesium.
Here are some other options for identification:
http://mrtitanium.info/2008/03/17/how-to-tell-if-a-piece-of-metal-is-really-titanium/
Were it me, I think density would be the way to go for identifying pure titanium. If it's an alloy and you want to know if titanium is a component, this will be much harder.
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They're getting smaller. However, its still true that the spot tests are clunky, and hard to execute. They're out there. But I can't help but wonder if they are, in someways, difficult to validate. That is, to what accuracy and what level is the answer needed, and can the spot test meet it. We only have Fritz Feigl's opinion, after all.
I guess you can run the spot test and if it gives a positive reaction the take a sample and run ICP-MS in the lab but not sure if then isnt better to run it all at lab due to nature of spot tests
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To clarify: I'd want to know if the sheet is "mostly" Titanium. e.g. If there's a bit of other alloying elements it does not matter. It's still Titanium for my purposes.
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Density is a great way except for two slight problems:
(a) Sometimes the equipment parts I come across are bulky and unwieldy to do a Archimedes style water bath volume estimation in the field
(b) Often the Titanium is held in something like a frame made of another metal which then interferes with a simple way to estimate gross density. Unless the frame were to be disassembled which can be done but adds work.
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There is another way that you may want to investigate.
EDXRF (energy dispersive ray fluorescence). It's a non
destructive test that uses xrays to detect metals.
The better instruments can easily detect Ti. They have
come out with a range of hand held units that can be rented
relatively inexpensively or bought. Unfortunately, many of these
were set up to detect lead in paint. They can detect Ti, but the
detection limit is the issue.
Don't know if it will work or not. Maybe its something you want
to investigate.
Good luck!
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Here is a link to one website:
http://www.niton.com/en/metal-and-alloy-analysis/applications/scrap-metal-recycling