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Potassium in a platina crucible


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#1 michelborstrok

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Posted 24 October 2016 - 01:19 PM

Hello,

 

So I'm working on this project in which I need to calibrate an XRF for multiple elements. One of the elements is potassium. I'm going to make fused beads for the calibration using the LeNeo fluxer from Claisse (it's a sample preperation method which includes heating up untill 1065oC). But there is a problem: Potassium and platina apparently react with eachother. I haven't found any literature that backs this up but multiple Phd. colleages of me said this. My question was: is there any way that i can do something about this because i really dont know what to do now.

 

Thank you


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#2 michelborstrok

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Posted 25 October 2016 - 01:40 PM

I have tried using Al2O3 crubibles but now the crucible reacted with the Potassium. 


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#3 John Cuthber

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Posted 25 October 2016 - 06:13 PM

Is the XRF ever going to be used to measure metallic potassium?

If not, there's no real advantage to using it as a calibration.

Why not use something like potassium chloride?


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#4 StringJunky

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Posted 25 October 2016 - 06:38 PM

In this article Reactions between some alkali group metals and platinum group metals it has this to say:

 

 

3. Reactions with Potassium.

 

The platinum metals do not appear to react with potassium. The behaviour of the potassium suggests a fairly easy and rapid reaction with the tantalum and stainless steel containers, probably catalysed by small amounts of hydroxides. In mixtures with platinum and palladium, potassium is lost nearly quantitatively on heating to 8ooOC. In alloying experiments with the other platinum metals volatilisation was observed as low as 5oo0C. This may indicate a small solubility of potassium in palladium and platinum. https://www.google.c...GuVg4gv2up8Wfjg (pdf download link)


Edited by StringJunky, 25 October 2016 - 06:44 PM.

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#5 Pyrine

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Posted 26 October 2016 - 01:50 AM

Might also try graphite crucible for your experiment, are you melting the potassium down in an inert environment?
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#6 michelborstrok

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Posted 27 October 2016 - 08:57 AM

John Cuthber, 

It needs to be calibrated for K2O. Because in my department it is going to be used to measure bottom ash which contains a lot of different things. It is recommended to oxidize the samples before making the fused beads out of them. I have  KHCO3 available here, so i need to do a loss on ignition first to burn out the H and COWhich brings me to the next problem because I've read that COcan be removed at 1200oC, which is also quite high and relates to the first problem because our normal crucibles can't handle this.

 

StringJunky

But does this say something about the 1065oC, I mean, will the platinum react with the potassium then?

 

Pyrine

A graphite crucible might work, although my supervisor wasn't so happy about it, don't know why. I don't think the environment is inert.


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#7 John Cuthber

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Posted 27 October 2016 - 08:06 PM

There is no point calibrating for something that you will not get.

You will not get K2O in ash- it will react with something. 

Generally it will react with CO2 so you will get K2CO3.

You can calibrate with that.

In some cases you will get potassium silicates as well.

You can see how much difference that makes to the calibration by fusing a mixture of  K2CO3 and silica and comparing the instrument response to the mixture with the response to  K2CO3

 

Incidentally, it will make it easier for English speakers if you refer to the metal as platinum.

Words like Alumina, silica and magnesia refer to the oxides in English.


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#8 michelborstrok

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Posted 3 November 2016 - 01:07 PM

Bottom ash is part of the non-combustible residue of combustion in a furnace or incinerator

https://en.wikipedia.org/wiki/Bottom_ash

 

This will cause the decarbonation. If there remain anymore carbonates, they will decompose during the proces of making fused beads.

 

Thanks for the English lesson though  :-)


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#9 John Cuthber

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Posted 3 November 2016 - 07:50 PM

OK, so it makes sense to calibrate with a silicate matrix in this case.

If you were burning scrap wood then you would be looking at a different matrix.

 

The point is that you won't get metallic potassium.


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