Blue tungstic or molybdic acid ?

I was hoping to make tungstic acid or possibly molybdic acid from the small metal parts removed from the filament assemble of a dismantled magnetron, see first pic.

I first cleaned parts in 28% HCl for an hour with shaking to oxygenate the acid, then rinsed in water. There were some small pieces of filament left on the parts that had a grey colour compared to the black colour of most of the parts. The filament may not be pure tungsten which could account for the different colour or the parts may be molybdenum. I am assuming tungsten or molybdenum from the source and the facts that they are not magnetic and do not dissolve hot oxygenated HCl.

I put the parts about 400mg in 5mL of 12% H2O2 in a test tube. There was some slight bubbling which gradually increased over 20 minutes to vigorous bubbling so I place the test tube in a beaker of cool water to reduce the chances of thermal runaway. After 5 hour the bubbling had almost stopped and the solution was a clear light straw colour. When I swirled the solution a transient (few seconds) blue colour appeared a round the parts.

When I checked the test tube 12 hours later the solution is now a very intense blue. It looks black unless viewed threw the meniscus. See the second pic, sorry its so out of focus my camera’s focus does not work very well but it does show the colour intensity and its hue.

I was expecting a straw coloured solution of either tungsten acid or molybdic acid.

Can anyone suggest what the blue colour is?

I was planning on testing for molybdenum by the very unusual ammonium phosphomolybdate salt (NH4)3PMo12O40

Thanks for the suggestions everyone.

After ten hours there is no clear liquid at the top of the test tube. I assume the blue is in solution. The colour is not taken up by ethyl acetate but is with MEK see pic.

When I add H2O2 to the blue solution it disappears in a few seconds to be replaced by a slight yellow colour. It is also destroyed when exposed to air in minutes (drops on a white plate). When dry the yellow solution leaves a distinct yellow residue.

I have tried to dissolve what the seller claimed was molybdenum wire but after fours hours in H2O2 12% apart from slight bubbling no reaction and the wire remains shiny. I assume the wire is not molybdenum.

Apparently molybdenum copper alloys (actually a mixture) are common but as there was no reaction to oxygenated HCl I assume the metal did not contain copper.

Tungstic acid is yellow but is insoluble in water. Molybdic acid is yellow and is soluble in water and is reduced to blue molybdenum by molybdenum metal and blue molybdenum is readily oxidised back to Molybdic acid. Note: there are molybdenum parts remaining in the test tube of the blue solution.

I conclude from the above the blue compound is molybdenum blue. I wanted Tungstic acid but the blue M is interesting and very unexpected.

It could be the P hetro acid as phosphoric acid is commonly used to stabilise H202 but I doubt there was sufficient phosphoric acid to produce such an intense colour and I think the blue hetro acid is not soluble. When testing for P phtometricaly I don't know how they avoid the blue molybdenum (homo acid) interference ???



Blue M in 2 ml of MEK extracted from about 0.2ml of blue solution. Still a strong blue colour unless viewed back light from the torch. Its the same hue as the original water solution.

I managed to caputure the blue m acid forming slowly on video.
Its speeded up 500 times,one frame every ten seconds.

Attachment: mblue.avi (7.5MB)
This file has been downloaded 735 times



The blue M was first oxidised with H2O2 until the blue colour was a straw colour (believed to be Molybdic acid) The metal part believed to be molybdenum then slowly reduces the Molybdic acid to a blue molybdium acid containing molybdium in a lower oxidation state. Presumably the molybdenum metal is oxidised and passes into solution. An orther interpretation is the metal is an alloy of molybdenum and it’s the orther metal/s that reduce molybdic acid.

[Edited on 7-5-2018 by wg48]

Quote: Originally posted by Plunkett

In every magnetron I have taken apart there has been a coil of a brittle wire around the center wire which I am led to believe is thoriated tungsten. Have you removed this coil before taking the photos or did your magnetron not have it? I have a few magnetron carcasses I would like to play with but I do not want to make aqueous thorium by accident. So, in your reading, the center filament has no thorium in it?

I found a note on molybdium blue; Attachment: mblue.pdf (737kB)
This file has been downloaded 473 times It's an interesting read.

Wow, there are many different M blues types. A typical building block is a pinwheel type of structure shown below. Apparently molybdium metal can reduce molybdiumates to a blue so I assume it can reduce the acid too as confirmed by my experiment. There are several synthesise using various reagents but H2O2 and molybdium metal is hard to beat for its simplicity

My pure (allegedly) molybdenum pieces arrived yesterday so I tried to make some blue Mo. The pic shows two test tube containing small pieces of Mo in about 1ml of 12% H2O2. The one on the right also contains one drop of 33% sulphuric acid to help stop the decomposition of the H2O2. It initially did not heat up and was less intensely coloured after one hour compared to the plain H2O2 on the left. Now after 12 hours they are very similar. No blue as yet and both contain unreacted Mo now black.



[Edited on 24-5-2018 by wg48]

I became impatient waiting for the H2O2 to beused up in the reaction to allow the blue Mo to be created so I heat both test tubes in a water bath to 60C to increase the reaction rate with the Mo metal and or decompose the H2O2.

After an hour the test tube had contained plain H2O2 was much lighter colour and when gentle agitated developed the blue colour at the bottom of the test tube then faded back to a light straw colour. The test tube that also contained a drop of sulphuric acid had not changed colour and on agitating only developed a brief and slight blue colour.

Assuming the Mo is pure it appears the molybdenum metal reduces straw-coloured Mo oxide to the blue Mo. This does not exclude impurities in the H2O2 being responsible for the blue colour.

The pic below shows the two test tubes in the water bath. The left one is the plain H2O2. Just visible are the wisps of blue Mo. I expect it will turn all blue when the H2O2 is used up. Its a moly clock reaction that takes many hours.




[Edited on 24-5-2018 by wg48]

Quote: Originally posted by wg48

I became impatient waiting for the H2O2 to beused up in the reaction to allow the blue Mo to be created so I heat both test tubes in a water bath to 60C to increase the reaction rate with the Mo metal and or decompose the H2O2. After an hour the test tube had contained plain H2O2 was much lighter colour and when gentle agitated developed the blue colour at the bottom of the test tube then faded back to a light straw colour. The test tube that also contained a drop of sulphuric acid had not changed colour and on agitating only developed a brief and slight blue colour. Assuming the Mo is pure it appears the molybdenum metal reduces straw-coloured Mo oxide to the blue Mo. This does not exclude impurities in the H2O2 being responsible for the blue colour. The pic below shows the two test tubes in the water bath. The left one is the plain H2O2. Just visible are the wisps of blue Mo. I expect it will turn all blue when the H2O2 is used up. Its a moly clock reaction that takes many hours. [Edited on 24-5-2018 by wg48]

Quote: Originally posted by fusso

Quote: Originally posted by wg48   I became impatient waiting for the H2O2 to beused up in the reaction to allow the blue Mo to be created so I heat both test tubes in a water bath to 60C to increase the reaction rate with the Mo metal and or decompose the H2O2. After an hour the test tube had contained plain H2O2 was much lighter colour and when gentle agitated developed the blue colour at the bottom of the test tube then faded back to a light straw colour. The test tube that also contained a drop of sulphuric acid had not changed colour and on agitating only developed a brief and slight blue colour. Assuming the Mo is pure it appears the molybdenum metal reduces straw-coloured Mo oxide to the blue Mo. This does not exclude impurities in the H2O2 being responsible for the blue colour. The pic below shows the two test tubes in the water bath. The left one is the plain H2O2. Just visible are the wisps of blue Mo. I expect it will turn all blue when the H2O2 is used up. Its a moly clock reaction that takes many hours. [Edited on 24-5-2018 by wg48] The brown colour in right tube looks like Br2 or NO2 gas TBH

That colour of the right test tube is too dark caused I suspect by the auto white balance on the cam and or the LED light. For better colour I can fix the colour balance while viewing a plain white card. To my eyes the colour is the same as the first pic.

Below is an other pic, still not the correct colour. Note there is more wisps of blue in the left tube. It will soon be all blue

Quote: Originally posted by woelen

The brown/orange compound is a peroxo complex of H2O2 and molybdate. I have some Na2MoO4 and when I dissolve this in water, add some acid and then add some H2O2 I get a brown liquid. When it becomes more dilute it becomes orange/brown.

The orange colour being caused by a peroxide complex would explain why the orange develops and then fades as the Mo metal reduces the peroxide. In the last pic I posted the test tube on the left is almost colourless because the peroxide has been used up and the Mo metal is now starting reduce the molybdate to the blue Mo. Presumable if I add sufficient peroxide to the blue Mo it will first turn almost colourless than with sufficient peroxide to form the complex it will turn orange again. I will try that.

Some more observations:

The blue Mo at least at first is a precipitate or colloid as it does settle slowly leaving a clear solution, but a few hours later it fills the whole solution and then does not settle. (I need to double check that)

The original test tube of blue Mo is now very intensely coloured with some slight white deposits at the bottom of the test tube and a blue ring deposit at the meniscus

The two recent test tubes have been incubated at 60C for several hours both had turned blue but now the test tube that had a drop of sulphuric acid has formed a white gel above a few millimetres of a blue solution. The plain peroxide test tube also has some white precipitate in it.

Below is pic of the test tubes. The one contained the drop of acid is on the left. I do not know if there is any Mo metal left in them.

A form of molybdenum blue was prepared according to the procedure in "Thomas' Chemistry" "Synthesis of Molybdenum blue"
https://thosci.com/synthesis-of-molybdenum-blue/

The product is a very dark blue color when in solid form. In fact it is difficult to capture the blue with my phone camera, it looks black. See photos below. Diluted solutions shows the blue better, but I did not take a photo.

Quote: Originally posted by Bedlasky

wg48: If you add excess of H2O2, there shouldn't be any molybdenum blue - because Mo and other metals are oxidized in to some stable higher oxidation state, so there isn't any reducing agent. If you want to make some solid molybdate than you add some ammonia or alkali metal hydroxide and boil it for a while. If you use only 12% H2O2 there shouldn't be any runaway. If solution will start bubble too much, add small amount of water. Mo-peroxide complexes are unstable in alkaline media and they decompose. In acidic media they are quite stable. Probably best option is making ammonium heptamolybdate, because it's less soluble than Na2MoO4. If you have nitric acid you can make some MoO3 by adding huge excess of HNO3.