DrP - 21-12-2005 at 08:27
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.
kryss - 21-12-2005 at 11:27
try heating it the silicate should polymerise, the degree depending on the amount of heat.
chemoleo - 21-12-2005 at 11:47
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.
DrP - 22-12-2005 at 01:48
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]
DrP - 17-3-2006 at 04:11
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.
Marchopasha - 21-5-2006 at 14:55
Try with sodium silicofluoride any proprtion (%1-5)
Marchopasha - 21-5-2006 at 15:10
http://rapidshare.de/files/21057669/PQ_SS.zip.html
some files for ss applications and specifications.
Marcho.