[captainradon]

Hello, this is my first post to this forum; I would like to ask a question on the use of magnesium potassium phosphate ceramic (aka Ceramicrete) as a refractory material. (Please refer to my YouTube video to see how I prepare it: http://www.youtube.com/watch?v=KxidwoJaC1c). I used this rapid-setting cement to try to make a small furnace and a crucible for melting iron ore, but I'm really worried about the possibility of toxic gases being released from the phosphate once it reaches a high temperature. Does anyone know what happens to mono potassium phosphate at high temperatures?
Thank you,
Leo

[Hunter2]

I think not so much will happen. Phosphates get polymerization by loosing water or alkaline oxides  to higher phosphates, like silicates do. The question is what is the end temperature. Phosphorous oxides could be developed at very high temperatures, but this means the furnace will be brake.

[captainradon]

Thanks for your reply. I'm probably very optimistic about my chances of reaching the required 1,538 °C in a "blast furnace" fueled by a bag of charcoal barbecue briquettes and fanned by a vacuum cleaner's exhaust. In any case, at what temperature would nasty things start to be released from the phosphate?

[Hunter2]

Well melting point for magnesia phosphate is already 1184 ° C and the potassium salt will melt at 1380 °C.  So the structure of the furnace will be week. Decompositions take place above 2000° C