the_grungler
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Determining the purity of a Silica / Silicon sample
Hello all,
I now own a significant amount of silica sand ground down to a little under a hundred microns in particle size. I'd really, really like to check how
pure this sand is. My goal is to hit about 99.99% purity, and as far as I know the only way to check something like this is with an X-ray
diffractometer. This is well out of my price range (>$50,000 new, and ~$10,000 for scrapped models), and I really don't feel like killing myself
trying to build one at home. Is there a method or tool I can use that will give me this information for under $2,500? I would like it to work on at
least SiO2 and Si.
That being said, if it's not impossible to build and use a homemade XRD without giving my entire neighborhood giga-cancer, I'd be open to information
on that.
Thanks so much!
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Sulaiman
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An independent lab analysis may be relatively cheap
and valuable if you are considering sales.
CAUTION : Hobby Chemist, not Professional or even Amateur
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chempyre235
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Quote: Originally posted by the_grungler  | | ...if it's not impossible to build and use a homemade XRD without giving my entire neighborhood giga-cancer, I'd be open to information on that.
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It's not impossible, but I don't think it's an easy accomplishment, either. An SM user built an X-ray crystallography device some years back. So while it's possible, I wouldn't recommend it.
I agree with @Sulaiman, an independent lab would be ideal, particularly if you only need testing for a few projects.
[Edited on 7/1/2025 by chempyre235]
"However beautiful the strategy, you should occasionally look at the results." -Winston Churchill
"I weep at the sight of flaming acetic anhydride." -@Madscientist
"...the elements shall melt with fervent heat..." -2 Peter 3:10
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j_sum1
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You might try a hand-held xrf gun.
Not cheap, but I expect would be doable within the price you stated.
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unionised
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Take 100 grams of your silica.
Weigh to better than 0.01 grams.
Dry it in an oven at 200 C and let it cool in a desiccator.
Reweigh it.
My money is on the water content being above 0.01%
(This isn't remotely practical but it illustrates a point)
Take a gram if it in a platinum dish
Add hydrofluoric acid and sulphuric acid.
Heat it to remove SiF4.
Then heat it further to boil off the sulphuric acid.
Weigh what's left in the dish. If it's less than 0.0001 grams then your silica has less than 0.01% of a whole lot of possible impurities (essentially
all the metals I think).
It's essentially impossible to measure the purity of something to 99.99% because you need a standard which is better than 99.99% and also a technique
that can tell teh difference.
But it's comparatively easy to check for the presence of 0.01% of something else.
XRF guns are not very sensitive or specific.
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Radiums Lab
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Yea I agree with Sulaiman.
Water is dangerous if you don't know how to handle it, elemental fluorine (F₂) on the other hand is pretty tame if you know what you are doing.
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the_grungler
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| Quote: Originally posted by unionised | Take 100 grams of your silica.
Weigh to better than 0.01 grams.
Dry it in an oven at 200 C and let it cool in a desiccator.
Reweigh it.
My money is on the water content being above 0.01%
It's essentially impossible to measure the purity of something to 99.99% because you need a standard which is better than 99.99% and also a technique
that can tell teh difference.
But it's comparatively easy to check for the presence of 0.01% of something else.
XRF guns are not very sensitive or specific.
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I never thought to measure it by weight - I was planning on cleaning it up by running it (separately) through water, acetone, and HCl baths to remove
any of the potential contaminants anyway. This sand was labeled as Refractory Sand on Amazon (so a little caution towards the purity is warranted),
and I really want to make sure it's as pure as I can get it. I only kind of understand that I want to get out the:
- Organic material (removed via water, acetone, and the dehydrator)
- Metal salts (?? removed by the HCl ??)
I'm not sure what else I should be worried about, which is mainly why I'd like to find a realistic method of determining sample purity.
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Radiums Lab
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Unionised please explain the HF and H2SO4 process, it's intresting and what does each reagent do?
[Edited on 2-7-2025 by Radiums Lab]
Water is dangerous if you don't know how to handle it, elemental fluorine (F₂) on the other hand is pretty tame if you know what you are doing.
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