Potassium in a platina crucible

[michelborstrok]

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 1065^oC). 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

[michelborstrok]

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

[John Cuthber]

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?

[StringJunky]

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.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwiaj4ODzvbPAhXpLMAKHQ42DyEQFgghMAA&url=http%3A%2F%2Fwww.technology.matthey.com%2Fpdf%2Fpmr-v25-i3-113-120.pdf&usg=AFQjCNE7E6XzuguIbMbGuVg4gv2up8Wfjg (pdf download link)

Edited October 25, 2016 by StringJunky

[Pyrine]

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

[michelborstrok]

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 CO₂ Which brings me to the next problem because I've read that CO₂ can be removed at 1200^oC, 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 1065^oC, 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.

[John Cuthber]

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.

[michelborstrok]

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

[John Cuthber]

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.