How to Make Calcium Phosphate High Temperature Refractory
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- Опубликовано: 10 май 2022
- In this video I describe the process I use to make insulating refractory bricks that can be used in melting furnaces and forges. This is a follow up from an earlier video showing one of those bricks withstanding the flame from a MAPP torch. #metalcasting #blacksmith #knifemaking
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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).
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
Awesome! I look forward to hearing how they stand up. I think the fast reaction aspect become a bigger issue when you want to cast larger forms because you have to move a lot of material quickly. But as you mentioned, maybe there is a second stage to the curing that could give some extra time. I'll play around with that myself too.
What I ended up adopting for the issue you mentioned of the dry bottom was to use something such as a cloth that can wick the water and deliver it to all the surfaces of the material.
Borax may slow down the reaction. It works for me pretty well with MgKPO4 cement, kind of similar, should work.
Tim, here in Australia we can buy Richgro Super Phosphate fertiliser from Bunnings. It is Ca(H2PO4)2 the same as the hi yield triple super phosphate product, but because it has no other phosphates in it, it is up to 100% Ca(H2PO4)2 instead of the 65% wt. in the hi yield product.
Yeah I was wrong, the product at bunnings says
Ok so the USA uses a unique system to measure phosphorus. It measures phosphorus in NPK from % of equivalent mass of P2O5 (phosphorus pentoxide). Who knows why, they just do. So NPK of 0-45-0 means that the product has 45% of the amount of elemental phosphorus as an equivalent amount of phosphorus pentoxide. Confused? Yeah…
So the product has 19.64% of elemental phosphorus, so under Australian NPK labelling it’s 0-19.64-0.
It’s a bloody lot of phosphorus, more than twice the amount we get in our local products.
Man that had me confused.
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.
Glad it was helpful!
Another awesome video!
This is very useful. I would love to see this made into small furnace/forge with a ribbon burner.
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
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).
How does this compare to plaster of paris/sand (or other aggregate combo)?
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.
The mix reacts fairly quickly so I suspect there would not be enough time to pour it. And yes, totally agree on the grain mill idea.
Intention to inform: to much water added at the end of the mixing or in total, ruins the chemestry that has to been keep in balance. To much water and the phosphoricacid will be to thin to react with the solids used. more then 30% ruined my pours.
Go and do some research on geopolymers made from Calciumoxid with phosphoricacid. Theay are a wonderful thing.
In this case the solubility of the mixture is pretty limited so that provides a very large margin of error for the water. Otherwise yes this would likely not work that well.
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
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!
@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.
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.
Well you are in luck because hydrated lime is Calcium Hydroxide, so you can use the same proportions.
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.
Is triple phosphate the same as STPP (sodium triply phosphate tech or food grade powder)?
Can you superphosphate instead of tripple phosphate?
Thanks Sir. I will try next time. whats temperatur can holds this bricks?
I have been able to get a forge to welding temperatures with this. Theoretically it might withstand up to ~1,600 DegC but I would say that I have not formally confirmed a max temperature.
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?
Ha ha! Well in my line of work stoichiometry comes up somewhat frequently. Theoretically it could stand up to 1,600 DegC. But I suspect there could be limitations before it reaches that. I can get it heated to forge welding temperatures without issue, so that may give a practical guide on what it can do.
Hi, Thanks for your informative video. It is well-paced. Yes, I also have issues with my sound engineer.
My chemistry is a bit rusty. I am preparing to make some of your refractory. My calcium dihydrogen phosphate is the dihydrate form, so that makes only a little difference (I think yours might be anhydrous phosphate?). I calculate my phosphate to have a mole wt of 270g/mole and the calcium hydroxide at 76g/mol. I assume that I need 1 mole of calcium phosphate and 2 moles of calcium hydroxide to get a balance acid/base reaction? So this makes the ratio 1.77 [270/(2*76)]. This is very different to your weight ratio of 3.7:1. Have I got something very wrong? I would appreciate your help.
Lastly, perlite is nasty stuff even the dust from unground granules irritates your lungs. Grinding makes it much worse. It is about 60% SiO2 and that rings alarm bells about the risk of silicosis. I think I can hear you start to cough when you introduce the ground perlite, so please be careful.
Thanks again Tim
Oh snap! Yes, your numbers are correct. Though one thing I have noted is that I don't think all of the calcium dihydrogen phosphate actually reacts... the stuff is super slow to dissolve, so there is likely less of it chemically available. Sorry about the slow response; apparently RUclips decided I didn't need to be notified about comments!
Yes, very good point about the perlite. And I probably was coughing due to it. I now have a fume hood of sorts and a better respirator, hopefully I can add some common sense to my PPE.
@@Drjtherrien Hi, thanks for the reply. Yes, we are at the mercy of the machine that decides what is spam and valid comments. Given the slowness of the reaction, it seems that TheBreaded's comment about mixing with water might just work? Still waiting on the delivery of my calcium phosphate. Tim
Actually the reaction is very fast. Too fast for the calcium dihydrogen phosphate to dissolve and that’s probably why the reaction still works with the stoichiometry as off as I had it; everything solidifies quickly and prevents diffusion of reactants. 🤷🏻♂️
To remove from molds I'd recommend spraying the molds with a PTFE (aka Teflon) dry adhesive. Basically a "mold release."
Thanks. I do have that and will give it a try.
Kindly guide me about monocalcium phosphate feed grade for poultry and animal purpose.
Ur kind response will be highly appreciated.
Hi, what would you like to know about it?
Sir the uses of calcium dihydrogen phosphate
I want to make di calcium phosphate please give me their process
You mean the precursor that I use? I just buy it since it's a common fertilizer/farm animal supplement. I have no idea how to make it.
Hello how are you my friend can I name mixing materials and how much weight I don't understand the translation if possible ❤
The refractory is 3.7 grams of Ca(H2PO4) for every 1 gram Ca(OH). I then mix equal volume of the refractory and powdered perlite.
I hope that helps.
I have wondered instead of using perlite , which is a good product. I had come up with the thought that perlite burns out lite styrofoam does, i believe anyway. Why no use a stupid cheap material because after all it is about adding air space to create its insulative effects why not us popcorn? Crush it upbif you wish but it wouldnt be a danger as it eventually burns out and other than a rodent maybe finding it. I dont believe it would be a problem by simply addind a slurry coat or a sheet metal jacket as a protector.
I think it could work well and it stupid cheap...
Popcorn would probably get much denser in the process of crushing it up. But you are right that one could use something that will simply burn up; though I would worry if that would cause gasses to expand and crack the material. One thing that I could try is flour. It would burn out and leave the micron scale gas bubbles that would help with the insulation. I might give that a try.
What’s the highest temp can it withstand?
I have been able to get a forge to welding temperatures with this. Theoretically it might withstand up to ~1,600 DegC but I would say that I have not formally confirmed a max temperature.
@@Drjtherrien thx I think I’ll try this mix for my next foundry I make when my old one goes
And could i just use bone meal fertilizer as the phosphate?
What about d dextromise Earth or DE?
So bone meal is a different chemical: hydroxyapatite. If you were to use that you would need to use phosphoric acid to convert it to the calcium phosphate. I have no idea if that would work well or not.
Nothing with calcium is going to be very high temp.
Don’t mix while your talking it makes it harder to hear what your saying
Thank you for the comment. It is a good point.
Hindi language me
I wish I could speak Hindi. Mandi kek rokker Hindustani jib... that's the closest I can do without using Google translate. That is my ancestral language which is closer to Punjabi.