Sciencemadness Discussion Board

Determining the purity of a Silica / Silicon sample

the_grungler - 30-6-2025 at 18:34

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!

Sulaiman - 30-6-2025 at 20:46

An independent lab analysis may be relatively cheap
and valuable if you are considering sales.

chempyre235 - 1-7-2025 at 06:57

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.


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]

j_sum1 - 2-7-2025 at 04:35

You might try a hand-held xrf gun.
Not cheap, but I expect would be doable within the price you stated.

unionised - 2-7-2025 at 05:58

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.

Radiums Lab - 2-7-2025 at 07:52

Yea I agree with Sulaiman.

the_grungler - 2-7-2025 at 12:13

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.


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.

Radiums Lab - 2-7-2025 at 12:13

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]