DrP
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Sodium Silicate based coating
Hi,
I have a solution of sodium silicate with certain additives such as surfactants etc.. it gives a really good finnish as a clear varnish. However,
after about 3 months, the coating absorbs moisture (and CO2 i think) from the air and goes all white and flaky.
I have read around the subject and asked some coating people and they say that the problem can be cured.... I have tried various additives that
supposidly fix this problem to no avail. I have tried adding waxes, various surfactants and polymers of different types - all to no avail.
Any suggestions how to stop the sodium silicate dry coat from absorbing water and or CO2??
Thanks.
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kryss
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try heating it the silicate should polymerise, the degree depending on the amount of heat.
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chemoleo
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Is your finish called 'waterglass?'?
Absorption is not your problem, the problem is that it simply drys out, and that's why it flakes!
I used the stuff myself, it's great for soaking paper, and making it hard, glossy and heat-resistant, perfect for simple rockets. After a while it
also became flaky. Same on wood.
I think the only way to prevent this is to i.e. varnish it with an additional which prevents it from drying out.
Alternatively, add a small percentage of something hygroscopic, but which doesnt react with i.e. CO2 from the air. Try glycerol for starters.
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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DrP
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Yes it's waterglass. Additional topcoats don't seem to help. I was told the problem was moisture absorption and I just kind of believed them.
Thanks I'll try your suggestion with the glycerol and look for ways to keep the moisture in.
QUOTE:
"hard, glossy and heat-resistant, perfect for simple rockets"
I have some liquid polysilazane and some polybenzimidazole powder. The polysilazane has a96% char yield. The PBI doesn't decompose untill it gets
above 400 C. 
[Edited on 22-12-2005 by DrP]
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DrP
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Hi Chemoleo, I've tried using glycerol / glycerine and I'm getting the same effect after a couple of months. I can't understand why even with a
top coat to seal the silicate coating in the coating still gets buggered. 
Heating the coating sounds like a good idea kryss but it is not practical for this application.
Any other suggestions?
Thanks.
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Marchopasha
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Try with sodium silicofluoride any proprtion (%1-5)
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Marchopasha
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http://rapidshare.de/files/21057669/PQ_SS.zip.html
some files for ss applications and specifications.
Marcho.
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