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CHRIS25
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[*] posted on 16-2-2015 at 07:22
Sodium silicate solution


I have spent many days trying to find the answer to this:
How on earth do you get a higher ratio of silicon dioxide to Sodium ions in a solution, eg 2.5:1 SiO4 : Na for an alkali solution of (Na2SiO3 in other words

I have being fusing crushed quartz from a beach with NaOH and have made solutions no problem, but it then suddenly occurred to me that I can never achieve more than a 1:1 ratio, ever.

SiO2 is in fact SiO4 - 4 O atoms in single bonds to the Si atom, this is a large covalent structure. Then in the process of making sodium silicate the Na+ ions fit into the spaces between these structures leaving then a free double bonded O atom on one side. So how does this extra SiO2 then get fused? Because you can not dissolve anything obviously, you can't fuse it because there is nothing to fuse it with?

[Edited on 16-2-2015 by CHRIS25]




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[*] posted on 16-2-2015 at 09:50


Solid SiO2 is a network solid. SiO2 is just a generic formula.
The bonds between Si and O are single bonds.
On the surface, you will have some dangling O or Si atoms which are probably bonded with something, perhaps H2O or whatever is in the air.

The reaction is 2 NaOH + SiO2 -> Na2SiO3 + H2O
This means that one of the Si to O bonds turns into a double bond.

I'm not sure if that answers your question.




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[*] posted on 16-2-2015 at 10:36


Well unfortunately you have kind of just repeated what I said above. the question is: How does one get a higher ratio of Silicon dioxide to Sodium ions in a solution.



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[*] posted on 16-2-2015 at 14:23


Quote: Originally posted by CHRIS25  
Well unfortunately you have kind of just repeated what I said above. the question is: How does one get a higher ratio of Silicon dioxide to Sodium ions in a solution.


Do you have any commercial products in mind that have such ratios? Cautiously I'd say they can not exist: the stoichiometry is what it is. Higher than 1:1 NaOH:SiO<sub>2</sub> are of course common.




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CHRIS25
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[*] posted on 16-2-2015 at 17:18


It is well known that the majority of Industry makes solutions of sodium silicate ranging from 2.1 : 1 to 3.5 : 1 ratio; SiO2 is always the higher figure and Na2O is always 1 in every single ratio. Alkaline silicate is between 2.1 and 2.6 whereas a more neutral silicate is around 3.0 to 3.5. As for the NaOH, well OH is ignored since this is evaporated away and Sodium slots into the gaps so to speak, industry only measures Na2O which to say they calculate for Sodium content.

The higher the alkalinity the lower is the SiO2 content and there is more Na2O. A very slightly soluble silicate would have around 10% Na2O and 42% SiO2 for example this would be classed as a neutral solution. There are dozens and dozens of ratios and formulas, to list them all would be exhaustive. They are made for purpose basically depending on the use that a particular company would want it for.

My question remains the same, How do you get this higher ratio? I can not see how it is done. Research has for the very first time ever turned up absolutely nothing to help me understand how Sodium silicate is made and before anyone thinks I am being stupid, Na2SiO3 is jsut a 'Generic' formula for the whole caboodle. The practical rarely reflects this formula since sodium silicate solution and powder is not a stoichiometric compound. My messing around suddenly made me realize that, at this moment, I can never get past the 1:1 ratio, my last batch calculated at 0.5:1 this is even lower, this as a molar ratio was 0.05 mol to 0.1 mol (SiO2:NaOH of course).

If I want to make a cery soluble powder then I raise the percentage of Na2O in the yield but I also have to have an absolute minimum of 2.1 :1 molar ratio in that yield.

The silicates are a hugely complex subject and I have only been studying them for about 3 weeks, theory theory, but all that theory has not helped me to solve the most basic of issues. How the hell is a sodium silicate solution with a high molar ratio of SiO2 made. Or, How do you get more SiO2 into the sodium silicate dry? All I can thnik of is SiO2 floating around without any Na atoms attached? And no you can't just add SiO2 to your 1:1 bonded mixture and throw it in a container, you would never get it to dissolve. My dry powder titrated at 1.6:1 and I calculated therefore also 45% SiO2 and 27% Na2O, so how was that done? What is bonded with what for example? There are not enough sodium atoms to go around are there? So how does it then dissolve in water (which it does of course), when SiO2 is insoluble seeing that there is a HIGHER mol to mol ratio of SiO2 to Na2O?




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[*] posted on 16-2-2015 at 18:24


These guys claim 1:3 Na2O to SiO2 if I'm reading their chart correctly. Quite interesting.

http://pqcorp.com/Portals/1/lit/SodiumSilicates.pdf

EDIT: According to Britannica you're going to need a furnace. :D

http://www.britannica.com/EBchecked/topic/637082/water-glass

[Edited on 2-17-2015 by Etaoin Shrdlu]
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[*] posted on 16-2-2015 at 23:26


Quote: Originally posted by CHRIS25  
So how does it then dissolve in water (which it does of course), when SiO2 is insoluble seeing that there is a HIGHER mol to mol ratio of SiO2 to Na2O?

What is special about a 1:1 ratio?
Look here: https://www.unm.edu/~solgel/publications/highly_cited/Brinke... Fig. 7, top right corner. Replace every "R" by a O-,Na+. Now you have a species with a Si:Na 16:14 ratio, which is certainly soluble.

Silicates are easier than you think, because they always are tetrahedrally coordinated in different grades of condensation. No double bonds etc. as in the chemistry of carbon. (Yes, disilynes and disilenes have been synthesized, but they are very unstable).

[Edited on 17-2-2015 by turd]
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[*] posted on 17-2-2015 at 02:51


@Turd: First, what does 'R' stand for in that PDF? Secondly, nothing special about 1:1, I was just saying that this was the ratio I could never exceed due to what I have been writing above. Having read through it briefly it is, if I may be honest, far too complicated for me to even understand, I have not got this far into chemistry yet. I am sure there is an easier and more friendly way of explaining to a learner how this is done and what is going on. To answer my question in a way that does not require complex notational paraphrases would be appreciated. Thankyou.

@Etaoin: As I said the manufacturers docs that I have found can produce anywhere between 2:1 to 3.5:1. A furnace is not necessary really, just a crucible works fine by the way, I have not tried sodium carbonate yet as this would lower the fusing temperature, but at the moment NaOH works perfectly. I have made plenty of sodium silicate in this.





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[*] posted on 17-2-2015 at 06:36


Quote: Originally posted by CHRIS25  

@Etaoin: As I said the manufacturers docs that I have found can produce anywhere between 2:1 to 3.5:1. A furnace is not necessary really, just a crucible works fine by the way, I have not tried sodium carbonate yet as this would lower the fusing temperature, but at the moment NaOH works perfectly. I have made plenty of sodium silicate in this.



A crucible w/o furnace is a bit useless, no? Etaoin is right, heat is needed here, for these high SiO2/Na2O ratios.




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[*] posted on 17-2-2015 at 07:23


I must be missing something - NaOH and SiO2 combine to make a nice silicate solution on a camping gas stove. Are you saying that I need 1000 or 1200 c temperature to fuse "Extra" SiO2 to what exactly? where does this SiO2 go to? Certainly not to any H2O - it's in a furnace, so what does this extra heat do to SiO2 that makes it miraculous dissolve if that is what is being implied here? And Turd's answer was to replace the 'R' with O, Na, whatever R is in that document?

And I have researched and have seen many demos, tuitions and papers on silicates; but as far as bonding mechanisms go, the ones I have read are either simplistic and basic or simply pointing out the elementary descriptive models of what all these silicates look like, but not one has really explained anything to help me understand the answer to exactly HOW there can be more SiO2 than Na2O in a silicate solution, and HOW this is done. If I can not do this that is ok, it is simply important for me to know what is happening.

[Edited on 17-2-2015 by CHRIS25]




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[*] posted on 17-2-2015 at 11:12


R just means "the rest". Usually, this is a chain of carbons. It could even be a phenol group.
You might even see R', R'', R''' which just means a different group compared to R.

That stuff about Na2O and SiO2, confused me. This seems to come from farmers or something sort of like how fertilizers are labeled K2O, P2O5 even though those molecules don't exist in their product.

Just like carbon, silicon is capable of concatenation.
You can have SiO4(4-), Si2O7(6-) and plenty more possibilities.
Unfortunately, I don't know how they can be produced so I'll leave that to the other guys.




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[*] posted on 18-2-2015 at 03:01


Quote: Originally posted by CHRIS25  
And I have researched and have seen many demos, tuitions and papers on silicates; but as far as bonding mechanisms go, the ones I have read are either simplistic and basic or simply pointing out the elementary descriptive models of what all these silicates look like, but not one has really explained anything to help me understand the answer to exactly HOW there can be more SiO2 than Na2O in a silicate solution

Read F. Liebau. "Structural Chemistry of Silicates".

For examples of well defined solids with Si:Na > 1 see:

M. E. Fleet and G. S. Henderson. "Sodium trisilicate: A new high-pressure silicate structure (Na2Si[Si2O7])" Phys. and Chem. Miner., 1995, 22, 383-386.

M. E. Fleet. "Sodium tetrasilicate: a complex high-pressure framework silicate: Na6Si3(Si9O27)" Amer. Mineral., 1996, 81, 1105-1110.

H. Krueger, V. Kahlenberg and R. Kaindl. "Structural studies on Na6Si8O19 - a monophyllosilicate with a new type of layered silicate anion" Solid State Sci. 2005, 7, 1390-1396.

This first two are a bit unusual: they have SiO6 octahedra.

Quote:
HOW this is done.

I heated 200 mg SiO2 and 100 mg NaOH (Si:Na~1.33) in H2O at 200°C for 12 h. Perfectly clear solution.

Edit: Ooops. Removed an erroneous reference.

[Edited on 18-2-2015 by turd]
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[*] posted on 18-2-2015 at 04:06


Nice work, Turd. A ratio of SiO2/Na2O = 2.67.

[Edited on 18-2-2015 by blogfast25]




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[*] posted on 18-2-2015 at 05:45


Quote: Originally posted by turd  

Read F. Liebau. "Structural Chemistry of Silicates".

For examples of well defined solids with Si:Na > 1 see:


I heated 200 mg SiO2 and 100 mg NaOH (Si:Na~1.33) in H2O at 200°C for 12 h. Perfectly clear solution.

Edit: Ooops. Removed an erroneous reference.

[Edited on 18-2-2015 by turd]


Very expensive book, though as a result of this search I did find a lot of information elsewhere that needs some time to digest. The second is thankfully in PDF format.

So as for your little experiment, it's about time and that was it, just time?




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[*] posted on 18-2-2015 at 06:35


Quote: Originally posted by CHRIS25  
So as for your little experiment, it's about time and that was it, just time?


Two questions for Turd:

1. How much water?
2. What kind of vessel?




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[*] posted on 18-2-2015 at 09:49


Quote: Originally posted by blogfast25  
Quote: Originally posted by CHRIS25  
So as for your little experiment, it's about time and that was it, just time?


Two questions for Turd:

1. How much water?
2. What kind of vessel?


He can not have used water surely? 200 c he said, so that eliminates water. Secondly Silicon dioxide does not dissolve right? And my temperature measurements did not exceed 300 c so it is likely that he just fused it, it is the only way. I will try this and heat for some hours using an excess of Silicon Dioxide, that quartz that I have from the crushed pebbles, and see what happens.




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[*] posted on 19-2-2015 at 02:29


Quote: Originally posted by CHRIS25  
Very expensive book

Me thinks 68 EUR is quite cheap. If you don't want to spend them, you can probably borrow it from the textbook collection of a university library (and make a fair-use copy).

Quote:
So as for your little experiment, it's about time and that was it, just time?

It's about the big three: time, temperature and pressure. And of course the fact that I was using fine amorphous SiO2 helps as well.

With fine enough silica you don't even need elevated temperatures: The authors of http://downloads.hindawi.com/journals/jnm/2012/528174.pdf report clear solutions with a Si:Na ratio of 1.25 (or SiO2:Na2O 2.5) by stirring for 48 h at RT. Of course, this will not work with a 60 g quartz rock. ;) A Si:Na ratio of 2.0 did not result in a clear solution.

Quote: Originally posted by blogfast25  
1. How much water?
2. What kind of vessel?


1. A few squirts, I would guess 3 ml.
2. A Teflon-lined autoclave. I can't imagine living without.

I repeated the experiment, just to be sure and it worked again (there were a few white specks of unidentified material, but this must have been in the sub-mg range). Each added drop of 36% HCl generates a transparent amorphous mass, just as expected.

For another example of a solid phase with Si:Na > 1 including synthesis, see:
H. Krueger et al. "Na2Si3O7: an incommensurate structure with crenel-type modulation functions, refined from a twinned crystal", Acta Crystallogr. B, 2006, 42, 440-446.
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[*] posted on 19-2-2015 at 03:21


Thanks, Turd. Very thorough.



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[*] posted on 20-2-2015 at 02:33


Quote: Originally posted by blogfast25  
Nice work, Turd. A ratio of SiO2/Na2O = 2.67.

[Edited on 18-2-2015 by blogfast25]


I've given up trying to work this one out. How on earth did you arrive at 2.67?

His SiO2:Na ratio was 1.32
How on earth did you end up doubling it? Unless, because industry takes the Na2O always as 1 in a ratio, the Na2 then is a double from the NaOH and therefore 2 x 1.32 = 2.64?

[Edited on 20-2-2015 by CHRIS25]




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