How to Make Calcium Phosphate High Temperature Refractory

To confirm your conclusion about the porosity and thermal insulation capacity of ground up perlite--consider fumed silica. Fumed silica is much more fine granular than how perlite usually comes, and yet it is far, far more thermally insulating than perlite. It is because it has so many porous micro-structures within the material, and such small micro pores (really a lot of surface area per given volume), that is is very efficient at stilling/trapping air molecules within its matrix. Fumed silica in on par with aeorgels in terms of thermal insulation, and is the most common core spacing material used in vacuum insulated panels (VIP's).

Another awesome video!

Thanks so much. Been looking for fire brick methods. This is the best I have seen. Also lovely calm presentation. The right number of words. And thanks for the poster below for converting that to Calcium Phosphate.

Hi, Thanks again for sharing your ideas. You have got me going. Eventually, my calcium phosphate arrived (it is not so easily available in Australia). So overnight I made my first test pucks using the ratio of 270g of phosphate to 152g of lime. I made that up as a bulk-dried mix in the kitchen blender. It's OK with the boss of the kitchen because that's ME. I made three test pucks from that mix: 1. no perlite, compressed and flooded and left overnight (according to your method). I used a chunk of a railway line on a puck that was the size of a picnic tumbler! 2. as above and mixed wet (and a bit sloppy), then compressed and left overnight without compression 3 as above after mixing in an equal volume of uncrushed perlite and left overnight without compression It is early days, but this morning all the pucks were quite solid and initially had no sign of the flakiness that you describe and I think you attribute to the lack of compression. However, puck 1 (the soaked and overnight compressed puck) had a soft bottom that looked as though it had not wetted up enough to complete the reaction. As soon as I added some water to it it started to bubble, puff and flake. Luckily, this did no deep damage and it immediately went hard and left a little scar on what started as a smooth surface. They are all sitting on my winter wood stove drying slowly awaiting their baptism inside the fire. It seems that wet mixing before moulding (as suggested by TheBreaded and me) MAY be quite practical, but the reaction is quite fast as you indicate. I think there is a fast initial reaction and then a slower one that makes the final hardness of the refractory? Consequently, for my fourth puck (that I poured this morning) I had the preweighed water ready for quick addition, rapid mixing and then molding. Very easy! Best regards, Tim

thanks for showing, it took me ages to learn this!!! but I know now! :)

Thank you for your ideas how calcium chloride is also make

Super tripple phosphate is calcium dihydrogen phosphate, CaH4P2O8. If Ca3P2O8 is your goal add the calcium in slight excess.

This is very useful. I would love to see this made into small furnace/forge with a ribbon burner.

Very cool. Have you tried adding water to the mix and pouring it into a form? A few bricks seems like they'd be a nice way to make like a knife forge. If you're wanting to grind a lot of the triple phosphate and perlite up wonder if a grain mill for homebrewing may work.

What do you think about adding fireclay as a binder? Do you think that would work?

Sir what are u making caphosphate bricks or a refractory? Look at your vlog desciption

Well done video. Thank you. "Stoichiometry"...betcha don't get to use that word every day. ;) You're a learned man: respect for that. Any idea or known value for what temps this material will withstand?

Hi, are you sure this isn’t producing CaHPO4 with an excess of Ca(OH)2? This would explain a reaction from leaving it uncompressed (lime carbonation, and perhaps some pozzolanic reaction with SiO2 from the perlite). I was thinking that considering the hi yield product is only 65% Ca(H2PO4)2, it would either be an 8.5g excess of phosphate for Ca3(PO4)2, or a 2.4g excess of lime for CaHPO4. I’m just going into the garage now to test something, I’ll let you know how I go.

Hey, after reading the comments and saw that 1.77/1 is the possibly the correct ratio, is this true, if so would you use the same procedure as shown in the video? Also do you know the weight and size/bolume of the bricks. Trying to figure an estimate of how many bricks I could forseeably make and if its worth the time(for me) thanks! Ps also is there a direct alternative for the triple super phosphate(like maybe Dicalcium or monocalcium phosphate? Not a chemistry man so I dont know the affect it would have entirely haha)? I can't get it near me anyways so if I have to order it anyways I figure I may as well get something that isn't marked up for gardening. Thanks again!

the perlite could be graded to increase brick strength (maybe reducing the maximal temperature that can withstand before cracking). The biggest flow here, in a metallurgic case, is having unreacted hydrated lime. at 512°C, hydrated lime would become just lime, and it will reduce the volume (creating surface cracking visible in the tested surface). low amount of unreacted hydrated lime does not really matter, but large amounts of it could produce "rock slaking" during thermal cycling. to reduce the problem, you can: leave the water for longer (allowing more time to complete the reaction, but one day may not be enough) make a second stage of curing, but this time under water with some phosphate dissolved to react any remaining lime in the surface (this may take time also time, but this would reduce the problems with the surface reaching the critical temperature of 512°C, as it would not microcrack) there could be still some hydrated lime in the core of the brick, but at that point it could acts as self healing roman concrete (if water somehow manage to get there there could become powder eventually tho). most of unreacted lime would be in large granules of lime with a heavy coat of calcium phosphate. other thing: calcium phosphate is not soluble in water. but if the water is slightly acidic, you will dissolve quiet a lot. this may not be the best material to make an insulated fireplace exposed to rain (all rain is acidic).

Hi. Thank you for making this Video. Here in the UK it's quite difficult to find Hydrated Lime but I can easly buy Calcium Hydroxide 98% powder. In what ratio should I use it with Triple Super Phosphate? Please. Thank you, Regards.

Thanks Sir. I will try next time. whats temperatur can holds this bricks?

Is triple phosphate the same as STPP (sodium triply phosphate tech or food grade powder)?

To remove from molds I'd recommend spraying the molds with a PTFE (aka Teflon) dry adhesive. Basically a "mold release."

@Dritherien - I tried thit today but didnt seem to work. Vety clay like and loose. How long does the reaction take ? Imay have veen a little impatient.