dankjones - 10-3-2005 at 18:08
I'm trying to formulate a room temperature cement/ceramic that can be cast in a urethane mold (no CO2) and is very durable and heat tolerant,
i.e. not prone to cracking due to being heated and cooled repeatedly to temperatures upwards of 800°F.
I'm partial to Magnesium based cements such as Magnesium Oxychloride, and Magnesium Phosphate.
Just about every thing I know about Magnesium based cements can be found in these 2 links:
http://www.techtransfer.anl.gov/docs/ceramicrete.pdf
http://www.premierchemicals.com/corner/articles/cements.htm
I'm leaning toward farm/feed stores as a cheap source of chemicals, but I am willing to pay more for just enough to experiment with. I already
happen to have 1lb. of Magnesium Carbonate which I can fire (calcine) in my kiln to Magnesium Oxide. I believe 1300°C was a temperature mentioned as
the ideal for one formula due to the fact that at this temperature all the pores close up, and surface area drops to a small fraction of what it would
be at a lower temperature. Also it increases the energy of the bonds or some thing.
I think I need either some MgCl or Potassium Phosphate. Also, Ammonium Phosphate is mentioned in the first link. I found some of that at a feed store,
but the process for that looks a little more involved.
Any assistance is appreciated. 
chemoleo - 10-3-2005 at 20:03
Thanks for those very interesting links.
I never realised that MgO and MgCl2 form a very hard durable cement! The leaching with water is indeed a problem (MgCl2 is dissolved) but I imagine,
putting the cast into a weak solution of Na2CO3 should put a resistant carbonate shell around it (see second link).
Anyway, I meant to suggest that the best source of oxides are pottery supplies. MgSO4 can be obtained from garden stores.
MgCl2- well you can make it yourself from HCl and MgO/MgCO3, both easily available.
As you seem to want temperature resistant material - did you have a look at this or even this thread?
dankjones - 11-3-2005 at 05:47
I got the Mg carbonate from my pottery supplier. I asked them if they had Mg oxide, or chloride, but they did not.
I had seen the first thread, but not the second. this product sounds alot like the Mg Phosphate formula from the ceramicrete link I gave.
I should also mention that Mg Oxychloride is also known as magnesite cement, or sorel cement, but I can't seem to find any anywhere.
I think I'm leaning back toward Magnesium Phosphate Cements now.
I wonder what would happen if i used Ca Chloride instead of Mg Chloride.
I gots plenty of that.
Edit: Hmmmmmmm...
[Edited on 11-3-2005 by dankjones]