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Post by firewatcher on Aug 25, 2016 17:09:02 GMT -8
Karl,
Here's a side question for you...using a geopolymer to create the fire box and riser in a rocket stove...do you know if it would be not advisable to use the stove to cook with (I don't mean to cook directly on the geopolymer itself)? Seeing several posts in the forum of people creating cooking rocket stoves made me think of it. I didn't know if maybe the hot gasses from the combustion released any toxic gasses or whatever from a geopolymer which would make cooking with a stove made of such a material not a good idea. Any thoughts?
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lawry
Junior Member
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Post by lawry on Aug 26, 2016 0:07:53 GMT -8
Karl, Here's a side question for you...using a geopolymer to create the fire box and riser in a rocket stove...do you know if it would be not advisable to use the stove to cook with (I don't mean to cook directly on the geopolymer itself)? Seeing several posts in the forum of people creating cooking rocket stoves made me think of it. I didn't know if maybe the hot gasses from the combustion released any toxic gasses or whatever from a geopolymer which would make cooking with a stove made of such a material not a good idea. Any thoughts? Firewatcher That's what I am planning to do. Build a cookstove. The geopolymer route for fire box and riser eliminates the use of fire bricks. Fire bricks are quite expensive in my area of the world. I really don't see any risk of geopolymer releasing harmful gasses... The chemicals we use are already in some of the detergent products we use. Which I think should be worse. Karl will be able to confirm for us though.
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Deleted
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Post by Deleted on Aug 26, 2016 3:57:39 GMT -8
What ever may be contained in the slag sand is not water soluble and the slag is wear resistant.
Beside of use as as construction material geopolymers are serving to safely enclose very dangerous materials like heavy metal other toxics and even radioactive waste.
Scientists have mixed geopolymers with toxics and after complete curing powderized. The powder was then mixed with solutions of strong acid to simulate extremely harsh conditions. Later the solution was examined to see if the powder has released any of the toxics. Geopolymers do a very good job to keep the toxics enclosed even under such extreme conditions.
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Post by firewatcher on Aug 26, 2016 6:48:51 GMT -8
Thanks for the info gentlemen...good to have confirmation that nothing bad will come of using geopolymers for cook stoves.
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Post by firewatcher on Aug 26, 2016 12:00:44 GMT -8
Update time...i mixed up the same recipe that I've been using in the same proportions...except this time used the 1.5L "concentration" waterglass. After 24 hours of cure in a plastic bag, i took the puck out and all was well (no cracking). A half of an hour later, it looked like this... I just finished molding a new puck using Karl's altered recipe (I used powderized perlite and liquid waterglass along with the slag instead of zeolite and powdered waterglass.)...will update once some significant time has passed and i get some results
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Post by firewatcher on Aug 26, 2016 13:09:33 GMT -8
Karl,
Did a quick density check on the newest puck that i made to compare to what you had calculated for the recipe that you had used with the zeolite and slag.
Obviously there is some water to be driven off as the puck dries, but the "wet" puck density is 2.28 g/cm^3. Karl, your mix ended up being 1.45 (i assume you figure is in the same units but i don't recall you listing units).
In order to get close to the 1.45 figure that you got with your mix, i would have to "lose" almost 500g of water
In a few days when i try to fire the puck I'll update with the actual density of the dried puck.
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Post by firewatcher on Aug 26, 2016 16:21:02 GMT -8
My excitement got the best of me...i can share the mix "recipe" if anyone is interested, but i cast this puck 4 hours ago...it was already set and fairly hard so i took a MAPP gas torch to it in 10 spots (2 minutes were spent in each spot for a total of 20 minutes total). the opposite side of the puck got warm, but i could keep my hand pressed firmly against it without coming anywhere near burning it for several minutes. WIKI says that MAPP gas burns at "2925 degrees C in oxygen" First, the side that i had the torch on... ...and the opposite side... It's a 5 inch diameter puck, 2 inches thick.
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Deleted
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Post by Deleted on Aug 26, 2016 17:19:10 GMT -8
Yes it is 1.45 g/cm³.
Almost 3000°C throwed against one side and temperatures in the comfort zone on the other side is impressive, especially if the puck was not completely dry.
I cannot see any need for more than 1", maybe even less for the riser to save mass.
You may try a two step geopolymer for pure pozzolan.
BTW what do you think about my ashtray geopolymer ? Cute demo of the technology, isn't it.
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Post by firewatcher on Aug 26, 2016 17:31:18 GMT -8
Yes it is 1.45 g/cm³. Almost 3000°C throwed against one side and temperatures in the comfort zone on the other side is impressive, especially if the puck was not completely dry. I cannot see any need for more than 1", maybe even less for the riser to save mass. You may try a two step geopolymer for pure pozzolan. BTW what do you think about my ashtray geopolymer ? Cute demo of the technology, isn't it. Yes...thats a really cool demonstration of the tech for sure I have to say again...thank you for all the great information that you empart!
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Post by firewatcher on Aug 27, 2016 7:01:02 GMT -8
Update: I had a small "camp" fire last night and used the opportunity to try drying out the latest test puck. I had the puck in the fire for about 3 hours and then covered it in the remaining embers to burn out over night. Weighed the puck this morning and recalculated the density. 1.78 g/cm^3 There are a few small cracks in the puck but they were there before my MAPP gas test and camp fire drying started. A pic from at the end of the fire with only coals left... ...and one after sitting overnight in the coals... The next test for the mix will be a small "slab". Not sure if i want to tinker with the mix a little or not though to bring the weight down...
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Deleted
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Post by Deleted on Aug 27, 2016 7:29:57 GMT -8
What is the current recipe ? Maybe I can give some hints.
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Post by firewatcher on Aug 27, 2016 7:37:19 GMT -8
Current mix consists of:
200g powdered perlite 70g fire clay 800 g slag 100 g hydrated lime 1.5 cups waterglass (1.5 L water recipe)
Probably the easiest way to lose some weight is by reducing the amount of slag...
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Deleted
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Post by Deleted on Aug 27, 2016 8:40:32 GMT -8
Things do not allways work as one may think. Sometimes the reverse is more promising.
Reducing the amount of slag makes it more crack prone. What is the particle size of the slag ?
Bulk density is inversely related to the porosity, which depends on particle size, particle form and particle distribution.
Bulk density of the slag is likely in this range 1 – 1.4 kg/dm³. eg. 0.04– 0.09 mm ~ 1.0 kg/dm³ and 0.09 0.50 mm ~ 1.4kg/dm³
In the mixture the slag will be more densely packet but lots of space will still remain, which will be filled with the binder.
With respect to the Waterglass: A mixture with 330g solids per liter waterglass contains only a solid volume of 330g/2,4 g/cm³ = 137.5 cm³.
On way to reduce density would be to replace the fireclay with ball clay or swelling bentonite to bind more liquid and in this way reduce density.
I hope you understand the principle.
It's like gluing together two pieces of wood. It is not a thick layer of glue, which gives the strongest connection, but an almost invisible thin.
The trick is to stretch the solid content of the binder while maintaining sufficient strength in the hardened and dried material.
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Post by firewatcher on Aug 27, 2016 9:54:09 GMT -8
Karl, it's dificult to say the size of the slag...i only have a ruler to measure...I'll have to research on the product web site and see if they give a value...it's the product that Ronyon mentioned obtained from Tractor Supply called "Black Diamond" blasting abrasives supplied by US Minerals, Inc. I'll look it up a little later on and see what their web site says. It's the "fine" grade.
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Deleted
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Post by Deleted on Aug 27, 2016 10:43:52 GMT -8
Looks like 20-40 mesh, 0.4-0.7mm. This gives a much higher bulk density than the one I use. Maybe about 1.6-1.7kg/dm³
You could measure the liter weight.
Anyway, the optimal slag/ binder ratio for such coarse stuff is significantly higher. 5/1- 6/ 1 maybe even higher should solve your crack problem.
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