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Topic: Sodium Silicate--from sand?  (Read 2212 times)

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Offline DeeDeeDevine

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Sodium Silicate--from sand?
« on: February 10, 2023, 11:51:05 AM »
The title says it all. I'm looking to produce sodium silicate, water glass, from scratch.

So far, I've learned how to make it from crystal cat litter and lye, similar to the method used in this video:

https://www.youtube.com/watch?v=Ip-jDuM25FE&t=203s


But now, I want to start from SAND.

According to the internet, what I need is: sand plus lye, plus heat and pressure.

Seems tricky--how do I heat up a sand plus lye and water solution, to 2000 degrees, and keep it under pressure somehow? What sort forge do I need to build--or can it be done with just a hot plate? And what sort of lab equipment will be needed to keep the process under pressure?

Thanks in advance!

Offline Borek

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Re: Sodium Silicate--from sand?
« Reply #1 on: February 10, 2023, 03:00:57 PM »
2000 degrees

Really? Sounds a lot for water based procedure.

Basically what you are looking for is called an autoclave.
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Offline DeeDeeDevine

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Re: Sodium Silicate--from sand?
« Reply #2 on: February 10, 2023, 07:44:00 PM »
Thank you, I think you're right--the high temperatures are mentioned with the dry method, which has extra steps.

https://www.britannica.com/science/water-glass

Quote
It is commonly produced by roasting various quantities of soda ash (sodium carbonate, Na2CO3) and silica sand (a ubiquitous source of SiO2) in a furnace at temperatures between about 1,000 and 1,400 °C (approximately 1,800 and 2,500 °F), a process that gives off carbon dioxide (CO2) and produces sodium silicate (Na2SiO3; usually represented by its two constituents, Na2O and SiO2): Na2CO3 + SiO2→ Na2O∙SiO2 + CO2
Figure 2: The irregular arrangement of ions in a sodium silicate glass.


This roasting produces fused glassy lumps called cullet, which can be cooled and sold in that form or ground up and sold as powders. Lump or ground water glass in turn can be fed into pressurized reactors for dissolving in hot water. The solution is cooled to a viscous liquid and sold in containers ranging in size from small jars to large drums or tanks.

But the direct method doesn't mention a temperature:

Quote
Sodium silicate liquid can also be prepared directly by dissolving silica sand under pressure in a heated aqueous solution of caustic soda (sodium hydroxide, NaOH):

2NaOH + SiO2 → Na2O∙SiO2 + H2O



Offline Borek

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Re: Sodium Silicate--from sand?
« Reply #3 on: February 11, 2023, 03:41:48 AM »
The higher the temperature the faster the reaction, but you don't want the water to boil off. Pressure is probably required only to keep the water liquid above 100°C so tank strength is the limiting factor - compare https://www.engineeringtoolbox.com/boiling-point-water-d_926.html - that puts practical limits on the upper P, T values.

Making your own pressure vessel is a risky business though, these things tends to explode.

As a rule of thumb increasing the temperature by 10°C speeds the reaction up twice. Whatever you can do at 110°C you will also do at 100°C, you will just wait longer. (These are crude approximations of the kinetics and thermodynamics involved, but they should give you the idea).
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Offline DeeDeeDevine

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Re: Sodium Silicate--from sand?
« Reply #4 on: February 12, 2023, 09:58:39 AM »
This is very helpful, thank you.

So now, I'm looking into pressure vessels.


Wondering though, did they have pressure vessels in the 17th century? Wondering how long it needs to boil and if water can just be periodically topped off, especially when making a smaller batch.

I'm making the sodium silicate to use as a paint medium, Just a quart or two at a time is plenty. I may try cooking some water, sand and lye on a camp stove, in small batches, in the back yard and see what I can find out.

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