Rare earth pentaphosphates

[anenburg]

Hi,

We have an Astimex block with REE pentaphosphates, and these materials seem to be a commonly available standard for REE.
Why? They are highly unstable under the beam. REE orthophosphates (aka monazite and xenotime) are rather simple to prepare from flux growth methods, and are much better as standards as they're stable.

Is there any reason why pentaphosphates became so common?

[crystalgrower]

Hello, could you please post the serial code on your mount? This is so that the exact lots of materials used in manufacture could be identified. 

FYI There were three different OEM sources of these pentaphosphates.  They have apparently not been commercially available since 2018.

The WHY?

The reason RP5O14 were sold for microanalysis is that they are free of spectral overlaps in both WDS and EDS.  They were always produced in 99.9% pure or better. They  have lower concentrations of REE than  RPO4.  This is useful for most of the REE which occur in low percent to trace amounts in natural minerals.  RPO4 is required only for near-endmember monazite and xenotime quantitation of :La-Ce and Y.

There are two crystal structures for each RP5O14.  For La-Tb one of these develops microscale twinning under the pressure used to polish mpunts.  Twinning can be seen in reflected polarised light.

The cost of  Pb-free flux-grown RPO4 for La-Gd was quoted to me at $10,000 per batch and the process takes 2 weeks per batch.  ALL published  work shows some flux contamination in monazite structure: from 0.1% to 20%. Hydrothermal growth of mm sized crystals takes a similar lengtth of time for each batch.  The cost of hydrothermal RPO4 crystals would be similar to flux grown.

The cost of a similar sized batch of RP5O14 is about $500 and takes 24 hours. It is important to use conditions that yield ONLY the high temperature  form   This has never been published in 50 years of effort by military laser research.  The optimum process was something that I developed and  is "proprietary information" . 
 

[crystalgrower]

I have not seen any information which might help to clarify the point of "beam unstable" in the original post.

I have posted some information here about monazite and xenotime syntheses by fluxed methods.  Monazite is a real sponge when it comes to picking up trivalent cations from any flux including Pb+3 from PbP2O7.

The "clean" flux method still produces some contamination.  Here are the original works and a table I compiled to show that colour is a good indicator:

It would be up to each analyst to decide what "good enough" material would be. 

[sem-geologist]

I have not seen any information which might help to clarify the point of "beam unstable" in the original post.

I have posted some information here about monazite and xenotime syntheses by fluxed methods.  Monazite is a real sponge when it comes to picking up trivalent cations from any flux including Pb+3 from PbP2O7.

The "clean" flux method still produces some contamination.  Here are the original works and a table I compiled to show that colour is a good indicator:

It would be up to each analyst to decide what "good enough" material would be.

This information is very interesting and crucial for me. We have synthetic REEPO4 standards which show no Pb contamination (at least not detectable by EPMA), I was wondering of its origins...  So if I will find Mo traces it will be clear how it was synthesized?

[Probeman]

Here is the post with a link to the study we originally did to document Pb contamination in the rare earth phosphates that the Smithsonian distributed from Oak Ridge National labs.

https://probesoftware.com/smf/index.php?topic=430.msg7318#msg7318

Note that these materials were never intended for use as microanalysis standards, and instead were synthesized only as possible materials for storage of nuclear waste and and later on, as CRT phosphors. For those applications some Pb contamination was not a concern.

[sem-geologist]

Thanks probeman,
So to be sure I actually should map our REEPO4 standards for Pb and for Mo (at least LREE standards), as I see in your investigation the Pb can be distributed uneven, and so I could had missed it.

I have not seen any information which might help to clarify the point of "beam unstable" in the original post.

I also want to complain about pentaphosphates as ours are also beam-unstable. Is it not enough we are stating our observations, should we send the beam-made crater images?

The cost of a similar sized batch of RP5O14 is about $500 and takes 24 hours. It is important to use conditions that yield ONLY the high temperature  form   This has never been published in 50 years of effort by military laser research.  The optimum process was something that I developed and  is "proprietary information".

So there is different sources of REEP5O14made with different techniques, and there is some secret sauce to make them stable? crystalgrower, are you selling these "proprietary" made REEP5O14 ?

[crystalgrower]

There are two methods of synthesis of RPO4: hydrothermal and fluxed.  RPO4 crystals with no apparent trace contamination would be hydrothermal. 

I added more attachments to my previous post--I didn't save each one to the message individually  the first time. 

I am addressing the RP5O14 documentation in a separate post. 

On the subject of beam instability in RP5O14,  "beam instability" covers several phemonena.  Stating that craters are formed is very useful information (as opposed to beam current increasing or decreasing over time)  I need to know the serial code on the mount or the date of purchase of loose grains.  You can post it here or send me a message. 

[crystalgrower]

There has been no evidence from either commenter in this thread who writes that rare earth pentaphosphates are “unstable”.  No image or data has been posted.   There has been equal silence offline.

It is EXTREMELY important to post images with details of coating used and beam voltage and current.  Photos collected under reflecting polarized light will reveal structural details even through carbon.   This forum allows many eyeballs to look at your issue.

Two possible reasons for instability: 
--Beam heating would anneal the multiphase mess created by heavy force.  The beam signal would depend on beam time.  This would definitely be visible under reflecting polarized light.  This would not occur for elements Ho-Lu.
The recovery would be to dissolve the mounting media in acetone and collect the crystals. They can be annealed for a few days at 150C and then remounted.  But we have to be sure that the phase is the problem.

--There are very few mechanisms for pentaphosphates cratering under an electron beam.  If residual flux was present between small grains, you would get more than just cratering.  Your sample chamber and vacuum system would have P contamination (a very sticky acidic film).  The invoice for such a mount should never have been paid.  I cannot imagine this is an issue of poor grounding.
I got sticky junk before I found the right conditions to grow crystals. I learned to spend hours  washing all the flux off until the XRF data was correct.  But I never let any junk out of my hands.  The original Chinese crystal grower sold his last lot and retired before 2010.  So crystals that develop craters MUST be from some third source.

This is important now. 

I made some batches of crystals that were not assayed for lack of funds.  There might  be clean monazite CePO4 waiting for local testing and then a round robin.  That means some crystals (not  mounts) will be available for free.

Facts are the only way to correctly diagnose problems. There is only one fact in the original post: that lab’s mount is defective.

[anenburg]

Hello, could you please post the serial code on your mount? This is so that the exact lots of materials used in manufacture could be identified. 

The only serial code on our mount is "ACAM". See attached image.

Note that these materials were never intended for use as microanalysis standards, and instead were synthesized only as possible materials for storage of nuclear waste and and later on, as CRT phosphors. For those applications some Pb contamination was not a concern.

What's the issue with Pb contamination for EPMA standard? If it's homogeneous and you know how much is there, there shouldn't be a problem?

There has been no evidence from either commenter in this thread who writes that rare earth pentaphosphates are “unstable”.  No image or data has been posted.   There has been equal silence offline.

I don't have the data on me now, but regular 15 kV with a reasonable beam current (10 nA?). Even when slightly defocused to let's say 5 um, phosphate counts drop within seconds and a visible hole is observed to form on previously nice and clean parts of the crystal. This was happening with the LREE, not sure about the HREE. I'll have to check.

[Probeman]

Note that these materials were never intended for use as microanalysis standards, and instead were synthesized only as possible materials for storage of nuclear waste and and later on, as CRT phosphors. For those applications some Pb contamination was not a concern.

What's the issue with Pb contamination for EPMA standard? If it's homogeneous and you know how much is there, there shouldn't be a problem?

These materials were *not* entirely homogeneous in their Pb contamination. See:

https://pubs.geoscienceworld.org/canmin/article-abstract/41/1/221/13508/A-RE-EXAMINATION-OF-THE-RARE-EARTH-ELEMENT

There has been no evidence from either commenter in this thread who writes that rare earth pentaphosphates are “unstable”.  No image or data has been posted.   There has been equal silence offline.

I don't have the data on me now, but regular 15 kV with a reasonable beam current (10 nA?). Even when slightly defocused to let's say 5 um, phosphate counts drop within seconds and a visible hole is observed to form on previously nice and clean parts of the crystal. This was happening with the LREE, not sure about the HREE. I'll have to check.

It would not surprise me that you will need to apply a TDI (time dependent intensity) correction to your data depending on the beam current and beam focus:

https://probesoftware.com/smf/index.php?topic=11.0

[crystalgrower]

I'm not sure the TDI would make a difference. 

This mount ACAM was likely the oldest generation of "small" crystals from China.  I will check.  The size of crystals can be estimated by comparing with the lettering if it is still visible. 

Since I did not make these materials, I cannot comment on their synthesis.  I believe with the smallest crystals, you would get the most potential phase change for La-Gd from monoclinic to orthorhombic from repeated beam heating in situ.   You would develop plenty of micrograin boundaries and sooner or later you would not be able to avoid them.

NO, HREE would not show the same issue.  I have never seen a published reference to the same phase change for HREE-P5O14.   

At this point please contact me offline if you are willing to mount larger crystals and polish them in house. 

[crystalgrower]

An update is under the new thread.  I would appreciate input from people with thin sample experience.