bismuthate
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Silver borate decomposition
recently I made some silver borate and I decided to heat it with an alcohol burner. It began to give off gas that I assume is oxygen and turned (
decomposed I believe ) into 2 solids the first was a brown powdery substance. The second is a shiny mettalic clump that melts very easily. My best
guess is that this is boron trioxide and silver metaborate. What is your opinion?
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deltaH
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hmm, interesting... some background please, did you prepare this by mixing silver nitrate and borax solutions? Just curious.
I don't think the silver would survive high temperature heating in the +1 state, so I wouldn't put money on silver metaborate. The brown powdery
substance bit is interesting, what in heavens could make it brown?
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bismuthate
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I'm not sure about the brown color.
The brown couldn't be boron right?
(yes it was made by that method)
could the mettalic lump be some silver boron compound?
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WGTR
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Are you saying that your silver borate upon heating decomposed first into a brown powdery solid, but then on further heating it turned into a shiny
metallic substance; or are you saying that both existed at the same time?
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bismuthate
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After further experimentation it apears that the mettalic substance turns brown.
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bismuthate
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Could it not be decomposition at all? could it be vitrifying?
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phlogiston
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You could easily obtain a little extra information that might help.
What are the properties of the metallic material. Is it conductive? What color does it have? Is it malleable? Does it dissolve in acid?
Is the gas really oxygen? You can test with the well known glowing splint test. Its very easy.
How sure are you that the starting material is really silver borate if you prepared it yourself?
Some things could be more clear:
- decomposes into two solids
You get a mixture of the two solids you describe?
Or you get one solid first, and then, upon further heating, the other?
or something else?
- 'Melts easily'
what do you mean with 'easily'?
- Why are you not sure about the brown color?
You can't tell if its brown? Why?
[Edited on 10-10-2013 by phlogiston]
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bismuthate
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It dissoves in acid, is brittle, and is multicolored.
The lower layer is brown the upper layer is mettalic. I believe that the multicolored layer becomes the brown layer upon heating.
it melts by the use of an alcohol burner but after heating for a few minutes solidifies and will no longer melt.
I could not perform a glowing splint test because i used very small amounts.
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phlogiston
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nitric acid? sulphuric acid? acetic acid?
multicolored... hmm. Do you mean iridescent (like a soap bubble)?
| Quote: | | I believe that the multicolored layer becomes the brown layer upon heating. |
So, if you heat for an extended period of time, the multicolored material dissapears completely eventually, leaving only the brown material?
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bismuthate
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I have not had the time to heat it fully.
It reacts with nitric acid violently upon heating to make nitric oxides.
It is very pretty like bismuth of hafnium oxide layers.
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phlogiston
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Ok, that phenomenon is normally called 'iridescence', not 'multicolored'.
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bismuthate
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It does not react with NaOH.
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deltaH
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| Quote: | | The brown couldn't be boron right? |
Highly improbable... but your train of thought may be on to something...
IF oxygen is released AND silver metal forms, it is logical to conclude on stoichiometric arguments alone that you have at the very least some kind of
non-stoichiometric/unusual boron oxide. This might help explain the perceived iridescence? If you can prove this is the case then SIR, I SALUTE YOU!
[Edited on 11-10-2013 by deltaH]
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deltaH
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More than likely as conditions are oxidising, that you have some oxygen rich boron oxide. You might even favour this compounds formation by working
with the decomposition of AgB(OH)4 instead of Ag2B2O7, the likely material you would get from a borax precipitation.
I suggest you try this... add an additional two mole equivalents NaOH to you borax and boil for a little, this should make mostly NaB(OH)4 in
solution. Now do the same silver nitrate precipitation, except now you should be getting AgB(OH)4... possible would make things more interesting on
decomposition, but please be careful when heating this and use very small amounts.
perhaps the brown compound you are seeing is a non-stoichiometric boron peroxide (of questionable thermal stability) and perhaps you will see more of
it with AgB(OH)4 decomposition because of the higher silver content.
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bismuthate
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I will do that experiment and report the results. But in the mean time I foud that the mystery material leave a white percpitate after reacting with
nitric acid. It turns brown when mixed with NaOH.
[Edited on 11-10-2013 by bismuthate]
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