Cryolite Na3AlF6

[qEd]

I am considering purchasing Na3AlF6 for a F primary standard. Does anyone use this material? How about familiarity with the time dependent Xray signals?
Many thanks in advance

[Probeman]

I am considering purchasing Na3AlF6 for a F primary standard. Does anyone use this material? How about familiarity with the time dependent Xray signals?
Many thanks in advance

Hi Ed,
This is from  memory but I seem to remember when testing this material as an interference standard for Na Ka interfering with oxygen that not only did it appear to have some minor oxygen present but also it was very beam sensitive.

I usually just use CaF2. Is this standard for trace, minor or major fluorine characterization?
john

[qEd]

Thanks John, I'm interested in analyzing major and minor F.  only.

[John Donovan]

Thanks John, I'm interested in analyzing major and minor F.  only.

Then a matrix match might help.  What is the unknown matrix?

[qEd]

I do not have a short term target, I'm putting together an "all purpose" mount. As desirable as it sounds, I can't imagine matching matrices for differing future projects.

[John Donovan]

I do not have a short term target, I'm putting together an "all purpose" mount. As desirable as it sounds, I can't imagine matching matrices for differing future projects.

Ah, I see.

Well I don't think cryolite will work.  I've used CaF2 and BaF2 (synthetic) and they are both reasonable standards and they are readily available.  I also have just some mounted F-phlogopite that was synthesized many decades ago but it has a problem with splitting from the epoxy wicking into it during mounting.

Be nice if there was a F silicate that we could target for synthesizing in our crowd sourcing standard development project:

http://probesoftware.com/smf/index.php?topic=301.0

[Jeremy Wykes]

You won't have stoichiometry to help, and the sample volume will not be large, but we can readily synthesise basaltic glass with weight percent levels of F at high pressure.

[John Donovan]

You won't have stoichiometry to help, and the sample volume will not be large, but we can readily synthesise basaltic glass with weight percent levels of F at high pressure.

How about topaz - Al2SiO4F2? There is plenty of synthetic gem topaz out there, although it's probably not the pure F end member.

To the original topic, MgF2 gives pretty good F count rates and is also pretty easy to acquire.

Stoichiometry is a wonderful constraint on composition. Why wouldn't/couldn't (synthetic) topaz be a pure end member composition?

[Brian Joy]

Hi John,

I agree that BaF2 and MgF2 are pretty robust standards.  But isn't CaF2 awfully beam sensitive?  Under what conditions do you operate to mimimize this sensitivity?  I've attached a chart recording of F Ka count rate on LDE1 and Ca Ka count rate on PET over a period of about 5 minutes using a 15 kV potential, 10 nA current (on Faraday cup), and 10 micron beam diameter.

Brian

[Probeman]

Hi John,

I agree that BaF2 and MgF2 are pretty robust standards.  But isn't CaF2 awfully beam sensitive?  Under what conditions do you operate to mimimize this sensitivity?  I've attached a chart recording of F Ka count rate on LDE1 and Ca Ka count rate on PET over a period of about 5 minutes using a 15 kV potential, 10 nA current (on Faraday cup), and 10 micron beam diameter.

Brian

Hi Brian,
Interesting that they seem somewhat anti-correlated!

To be honest, I haven't used a CaF2 standard since I was at Berkeley many years ago and yes, I think you are correct, though the BaF2 synthetic I use nowadays seems more robust.  In both cases however, I've only used it for trace fluorine in glasses, in which cases the background characterization is much more critical than the standard intensity.

And which is also why I'm hoping to find a robust fluorine silicate that would be a better matrix match for major and minor fluorine as Ed Vicenzi has requested.  Any ideas?

[qEd]

Thank you students and professors! Based upon this discussion I have modified my order to include topaz of the following composition:

  F     Al2O3    SiO2            H2O           sum   
18.40   57.42   30.97           0.65   -7.75   99.7   O=F=7.75
                      
  F       Al       Si     O      H2O           sum   
18.40   30.39   14.51  35.80    0.65           99.7   

[qEd]

I will settle for the significantly decreased F (~ -34 wt%) in topaz relative to cryolite in favor of the greater e- beam stability.