As a material for heat riser .. and other questions

[mintcake]

May 23, 2014 3:51:21 GMT -8 @karl said:

As I have told you already that is due to polymerization of waterglass to colloidal silica at PH values below 11.
You could add up to 40% lye (sodium hydroxide, drain cleaner) by weight of the waterglass.
With 40% lye the mixture will act as an alkali activator for pozzolanic active aluminosilicates.
For a geoplolymer binder the ratio would be 40% activator by weight of aluminosilicates.

Thankyou for your input earlier, Karl. I did read it and follow the link, but wasn't sure what to do with the information. Would the hydroxide have any effect on the eventual strength/resistance/temperature stability of the mixture, or would it only improve the workability of the clay-perlite-waterglass?

David

[Deleted]

May 23, 2014 6:40:24 GMT -8 mintcake said:

Would the hydroxide have any effect on the eventual strength/resistance/temperature stability of the mixture,
or would it only improve the workability of the clay-perlite-waterglass?

That depends on the amount and the other components.
PH values affect chemical and physical properties.
The more alkaline and the more other components are chemicaly reactive the stronger the effect.
The hydroxide will take part of any chemical reaction that may happen at room temperature or at firing.
If the other components are chemically inert there will be merely physical effects.
Few powdery minerals stay chemically inert at high temperatures.
The strongest effect will take place at very high PH values in presence of active aluminosilicates.

what are geopolymers made of
www.youtube.com/watch?v=ci07_52EnBg

Mixing geopolymer at CCHRC
www.youtube.com/watch?v=zS5lK7DdmYU

Geopolymer/ Garage apron pour at CCHRC
www.youtube.com/watch?v=k8AbCRF_OTE

[Robert]

karl is that means that waterglass and ridgidizer is same stuff? ridgidizer is more expensive, so can i use waterglass instead?

[smarty]

So water glass turns to colloidal silica if reacted with alkali and then by adding drain cleaner the colloidal silica will chemically react with the molochite? Have I got that right Karl? I think when you make ceramic shell normally the colloidal silica and malachite just dry out between coats rather than set. I just assumed that the silica then acted pretty much like the silica in pottery by fusing into a solid body when fired. Probably more complicated than that I guess. But if we add drain cleaner to the equation does the process become more of a setting process prior to firing and can we still build up thin coats of shell as in ceramic shell technique? Or are we dealing with a completely different process more like casting concrete? I guess I could just add drain cleaner to my colloidal silica if I could figure out the proportion of silica in it?

[Deleted]

May 23, 2014 13:37:17 GMT -8 Robert said:

karl is that means that waterglass and ridgidizer is same stuff?
ridgidizer is more expensive, so can i use waterglass instead?

Not all rigidizers are the same.
There are different compositions.
Some are for saturading some are more in the direction of coatings.
Rigidizers may contain other minerals aside of a binder.

Silica is another name for silicon oxides.
Colloidal silica refers to the colloidal form of a silicon oxide.
Waterclass is silicon oxide too.

The binder in rigidizersis usualy colloidal silicon dioxide,
Remember most of this stuff is for the foundry industry and often for one time use.
The foundry industry prefers silicon dioxide as it will not undergo chemical changes
and thus also will be more dimensionaly stable.
For the same reason the foundry industry prefers calcined kaolin over its natural form.

This does not play such a big role in stoves,
thus there is no reason to exclude cheaper forms of colloidal silica or kaolin.

Waterglass is an alkali-silicate.

From Wikipedia:
Colloidal silicas are most often prepared in a multi-step process
where an alkali-silicate solution is partially neutralized,
leading to the formation of silica nuclei.

[Deleted]

May 23, 2014 23:06:33 GMT -8 smarty said:

So water glass turns to colloidal silica if reacted with alkali

Waterglass refers usualy to a saturated solution of Na or Ka silicate with a PH value of 11 to 12.
It can be mixed with water at any ratio because the added water can keep the solid in solution.
Tt is a very different thing if the PH is lowered by an acid or just other solids,
in this case the water cannot longer keep all Na or Ka silicate in solution.
Raising the PH value may allow to get even more Na or Ka silicate in solution.

by adding drain cleaner the colloidal silica will chemically react with the molochite?

Yes, if the drain cleaner raises the PH value high enoug.
Even natural kaolin will react if the conditions are right.

Synthesis of geopolymer from indonesian kaolin and fly ash as a green construction material
www.slideshare.net/PambudiPajarPratama/synthesis-of-geopolymer-from-indonesian-kaolin-and-fly-ash-as-a-green-construction-material#

I just assumed that the silica then acted pretty much like the silica in pottery by fusing into a solid body when fired.

The melting point of silicon dioxide 1,600 to 1,725 °C (2,912 to 3,137 °F)

does the process become more of a setting process prior to firing and can we still build up thin coats of shell as in ceramic shell technique? Or are we dealing with a completely different process more like casting concrete? I guess I could just add drain cleaner to my colloidal silica if I could figure out the proportion of silica in it?

The result of the chemical reaction will be closer to natural stone than concrete.
It is a polymerization, not a hydration as in concrete.
You would have to work wet on wet like with non mineralic resins,
meaning the next layer has to be added before the chemical reaction has completed in the previous,
to ensure that chemical bonds can be formed from layer to layer.

Example calculations for geopolymer mixture can be found there
www.academia.edu/5370671/DEVELOPMENT_OF_MIX_DESIGN_FOR_LOW_CALCIUM_BASED_GEOPOLYMER_CONCRETE_IN_LOW_MEDIUM_AND_HIGHER_GRADES_-INDIAN_SCENARIO

[Deleted]

smarty as I have mentioned above the requirements for a stove
are different than for the foundry industry
and you do not necessarily have to go the way of polymeryzation at room temperature.
To build a ceramic shell for stoves waterglass and natural kaolin or fireclay in general would suffice,
especially with a heat treatment as you did before.
For faster hardening of the waterglass one could place it in a box vented with flue gas,
in which the waterglass will react with the CO2.

[smarty]

I'm looking into this geopolymer thing as an alternative to the ceramic shell which I have plenty of but no one else can get their hands on. I think geopolymer is very promising stuff if it can replicate the qualities of ceramic shell. The ceramic shell just seems so right as a material for building cores with. Lightweight, resistant to abrasion, and insulating.

One thing that immediately sprang to mind was how suitable something like perlite might be for inclusion in a geopolymer. It is a kind of volcanic glass so I wondered if it might be chemically active as an ingredient. It would be great if we could get a few recipes worked out. I've ordered some water glass and caustic soda, I have a bag of fly-ash knocking about somewhere and some perlite, molochite flour/aggregates( which I might as well use since I have them), and some talc, so I'll have a few experiments and see what can be done. Maybe a geopolymer burn tube made with molochite, a riser made with perlite, and a thermal mass made with talc. Exciting!

[Deleted]

Yes, perlite is a pozzolan.
I gave some links in another thread.

Ceramic shell is very versatile and simple to use.
It gives much more freedom than any other kind of moulding,
while requiring less skills.

I too think that geopolymers are very promising.

Good luck with your experiments.

[Deleted]

The Effect of Alkaline Additives on the Operating Conditions of Kaolinitic Polymerization.
jjmie.hu.edu.jo/files/v5n5/JJMIE-30-11.pdf

[independentenergy]

Hello
I was wondering if you could use vermiculite pressed as risers, maybe try to make an octagon , it should withstand the temperatures

[independentenergy]

Hello
i have another question:
the batch box internal length of the 150mm system , from calculation turns out to be 440mm.
In a post to the Peterberg think I read that you can bring the length up to 600mm without changing other diensioni.
it is possible to do this?
thanks

[peterberg]

Yes,this can be done. In fact, this stove concept act more or less like a burn tunnel. More length means more fuel capicity.
Be careful though when running the thing, it is able to produce very violent burns.

[independentenergy]

thanks Peter.
what is the minimum height of the gap between the top of the bell and the heat riser?

[peterberg]

I would say, not shorter than 30 cm or 1 foot. My own experiments did stop at a little more than 3 foot without adverse affects. I've also tried 4 inches but that restricted the burn rate markedly.