Refractory cement upgrades

[ZebraPaste]

I’m currently exploring how to get better performance from cast refractory.
 

Some notable things I’ve come across include calcining your own additives. I learned that if you burn epsom salt with a torch it releases some toxic gas that is basically sulphuric acid. What’s left over however is magnesium oxide, the highest melting temp oxide you can get. In small amounts it increases the melting point of refractory materials. 1/10% is enough to stabilize alumina and zirconia when brought up to full temp (3000f+)
 

Alumina hydroxide aka alumina hydrate is usually available as a pottery additive. If you calcine/burn the heck out of it you get alumina as a raw material. Great for refractory mixes. Don’t mix alumina hydrate into refractory mixes. It has made several of my tests fail. The hydrate vents a ton of water (roughly 1/3 by weight) when it heats up and it blows up and or crumbles to dust.
 

A fair few times I’ve read posts on websites about people trying to create a flame face coating using water glass/sodium silicate and a product called zircopax. The zircopax is never going to stick doing that, and due to the super fine particle size it will flake and crack and warp as it dries. Get calcium aluminate cement binder instead. When using the CAC, calculate the amount of water you need, and use the water glass instead of just water. Water glass is 40% solids, so that remaining 60% is available water for your cement to cure. The effect is a faster cure, and a much stronger binder. Sodium metasilicate is sold dry as deck cleaner. It’s cheaper than buying the pre diluted solution, just dissolve it in hot water. 

If youre trying to go the zircopax route like I am since its got a higher service temp than most other products, you will benefit from making frit out of it first. Mix a batch with 10% water glass and pack it into a sheet. Let it dry and then heat it up as much as you can. I ran it in my forge until it was white hot. Then smash it up into coarse sand size particles. Mix 4 parts sand size particles, one part fine particle as you bought it (should be 2-5 micron powder), and somewhere around 15% by weight of CAC. Casting this 1/2” thick should be a very durable material. As an optional note I got from one of the manufacturers of similar products, add a 1/4% by weight polyester fiber to the mix. Its job is to burn out and make vents for excess water vapor to get out as you cure and fire the mixture.

[JHCC]

What specific properties or improvements are you trying to achieve?

[ZebraPaste]

Hi JHCC, I want the cast mixture to be more durable and already have the IR reflective properties of the available coatings. I have been experimenting with binders, instead of silicate binder or calcium aluminate, the next one I’ll be trying is alumina phosphate. Even if none of this works it’s still very fun. 

[LeeJustice]

I have dabbled a bit in refractory experiments.  While MgO has a higher melting temperature, Zirconia is known for it's toughness and better insulating property.  In particular, Yttria stabilized Zirconia.  I got some waste powder from where I work.  I attempted the first ones using diHydrogen Alumuminum Phosphate as a binder.  Not especially successful.  My next run I will try aluminum phosphate as a binder.