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Rare earth pentaphosphates

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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:

--- Quote from: crystalgrower on April 22, 2023, 12:09:59 PM ---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.

--- End quote ---

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.

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