I’ve gotten my hands on some phosphoric acid and aluminum hydroxide. Mixing them with a little water (amount almost doesn’t matter it acts as a vehicle/lubricant for the reaction) and gentle heating (keep above 170F but below 212F, it will boil but not at true water boiling temp) makes aluminum phosphate. If you heat too much you will get crystalline product at the bottom of your container, I used a mason jar and burnzomatic. There are plenty of videos on the process online. I’ve tested some aggregate mixtures and curing temperatures. This stuff is amazing so far. The mixture doesn’t dry and harden at room temp, which means you have loads of time to work it into your shape/on you the surface required. Curing is starting around 175F which is lower than what google showed in search results. Very hard and durable product at 400F cure, better than any water cure castable I’ve gotten yet. It is cheap, and quite strong as far as binders go. You won’t need 85% lab grade acid, you can boil down cola if you really wanted to. So far any aggregate has responded well, but mixing with a water curing cement has yielded significant expansion. The expansion is temperature dependent and increases in a linear fashion. Curing at 180F gives roughly 35% increase in volume, 400F about doubles the initial volume. The product is well worth the expense of raw materials. If you’re looking to create your own firebrick this is very good for making an insulation layer and flame face/abrasion resistant face all in the same unit. My tests are showing virtually no cracking when heated with propane air. Will use acetylene/oxy to failure for more data.

I've been noticing your various tests that you are sharing with us, thank you!

I'd like to encourage you to add some commentary about safety practices along with these tests that you're doing. While you may be well qualified to safely conduct your experiments, others who come along and find these notes may have no such qualifications and get themselves into trouble. Sure, people should take responsibility for the things they do, but that's less and less common, so please keep that in mind as you share your experimental work and include appropriate safety cautions in your notes please. I Forge Iron seeks to be a repository and resource for all that stumble upon it, let's make every attempt to encourage others to experiment safely. Thanks.

--Larry

I had commented on another post which is similar in nature.  I bought some Aluminum Phosphate already made because I didn't want to go messing around with phosphoric acid.  It was not cheap, to say the least.

Good Morning,

I use Phosphoric Acid to treat Rust, it turns Rust Black and chemical neutral, it stops Rust from growing. Soap and Water wash, cleans after a few hours. Phosphoric Acid is like a strong Vinegar, It is used in Cola soft drinks. It will not attack your clothing like Battery Acid.

Neil

Specifically, 2H₃PO₄ (phosphoric acid) + Fe₂O₃ (iron oxide/hematite) = 2FePO₄ (ferric phosphate) + 3H₂O (water). Phosphoric acid also reacts with Fe₃O₄ (iron oxide/magnetite), but the formula is a bit complicated.

Hi all sorry I should’ve included some safety precautions. The acid I bought for my experiments was 85%, it will blind you if it gets in your eyes so goggles are a good idea. If you get it on your skin, or at least on mine, it will itch until you clean it off, probably end up with a chemical burn if you don’t clean it so gloves aren’t a bad idea either. Stirring with a glass rod is recommended. Stainless rod is probably not going to hurt it but might discolor a bit from dissolved iron. Also at elevated temperatures the acid will attack (very slowly but still needs to be considered) almost any container you have. Use a borosilicate glass if you can that will let you use a small torch or even a candle to keep it heated. I used a torch, worked good just have to keep an eye on it and have some patience, don’t over heat it. Also tried in an air fryer/ small convection oven. It worked but dries out the surface and has to be stopped and stirred, it’s not a great way to do it but will work if you need it to. The weather (and work schedule) has kept me away from this for a bit but once I get back to it I have another mix to try. It’s a promising one for the floor/flame face, very hard and abrasion resistant.

thanks for reading