I could use some chemistry help; Geopolymer experiment

[pigbuttons]

I'm trying to get a reliable recipe for the eventual casting of a rocket stove. My first attempt was a partial failure but that was mostly because I'm new to this stuff and didn't understand what a mole is. I'm using a recipe ( vaguely, since I don't have access to their ingredients ), from Davidovits Geopolymer book, Example 3, page 456.

Experiment 2 was as follows:
H2O 180cc
Alumina 63g
Silica 150g
KOH 77.5g


I mixed the H2O and the KOH until dissolved.
Added the Silica mixing until fully in suspension.
Added the Alumina mixing until fully in suspension.
Allowed to sit until the exothermic reaction had stopped ~ 90 min.
At this point there was about half water (clear liquid) and half thick paste that had settled to the bottom.
Mixed thoroughly again.
Added that mixture to a previously prepared mixture of 1000cc of Vermiculite ( fine grain ) and
150cc of Red Fire Clay that was just moist enough to hold together when squeezed.
Once mixed the combined mixture was packed (tamped) into a form lined with plastic wrap.
Wet cured for 48 hours,
Opened to the air but still in the form for 24 hours,
Removed from the form and air dried for 4 days in the sun through a window.
Baked starting at 200F for 2 hours then stair stepped up 75F per hour until at 450F
Allowed to bake at 450F for 2 hours.


At this point the block looked great, was not scratchable with a finger nail, was very strong in compression and impact.
Now the problem, when just a small amount of water was placed on it, it crumbled in the area wetted.
I then took it out and placed it over the riser of my rocket stove for 40 minutes, let it sit overnight and today it was
still slightly crumbly at the thin edges at the corners and where the water had been. But the rest was solid and no longer affected by water or lighter fluid.


My questions:
Q1: Would it have been better to heat the original liquid ingredients to 150C so the chemical reaction ran to completion and no separation occurred?
Q2: Can I cure it directly over the rocket stove without baking to drive out the excess water first?


Thanks for any help or advise.

[pigbuttons]

Well I went ahead and tried both adjustments from the questions above. I tried heating up the liquid solution in a "ceramic" lined Aluminum saucepan. Within a couple of minutes of reaching the boiling point the bottom of the pan felt like the material was burning or sticking to the bottom of the pot. I removed it from the heat and it continued to boil. I poured the liquid into a glass vessel and was able to observe the ceramic lining of the pot had been dissolved and the solution was reacting to the aluminum. After flushing it with water I continued to finish up the mixing of the solids with the liquids and packed the result into the mold like the first time, with the knowledge that the sample had been contaminated with Aluminum from the pot.

The resulting block was able to be taken out of the form in just 16 hours because of the firmness of the material, and at the 30 hour mark I placed the block on top of the rocket stove riser for 2 hours. It now has a very hard surface, and does not crumble when small amounts of water are placed on it. I have not yet tried soaking it in water, and may not try that at all. First I will see how it does in the combustion chamber of the rocket stove.

[coastalrocketeer]

I just found this old thread of yours that must have been missed by others and never got any replies.

How did that sample fare?
You may have already told me in another post, where you told me samples you'd tested were not refractory and got soft and crumbly after firing?

[pigbuttons]

Jan 13, 2018 8:47:13 GMT -8 coastalrocketeer said:

I just found this old thread of yours that must have been missed by others and never got any replies.

How did that sample fare?
You may have already told me in another post, where you told me samples you'd tested were not refractory and got soft and crumbly after firing?

That was quite some time ago and that and many other successes and failures as well. As of late I'm getting pretty good at guessing what chemistry will work though most of my LTGS efforts are not waterproof enough. I laid off of it for a few months because I'm trying to finish my house so that I can retire. After that I'll be a full time experimenter.

Thanks for bringing this old thread back to life.

[branja]

As I remember this was on "Karls Geopolymers". I think the solution was to add phosphoric acid.

[drooster]

Mar 3, 2018 16:52:48 GMT -8 pigbuttons said:

Jan 13, 2018 8:47:13 GMT -8 coastalrocketeer said:

I just found this old thread of yours that must have been missed by others and never got any replies.

How did that sample fare?
You may have already told me in another post, where you told me samples you'd tested were not refractory and got soft and crumbly after firing?

That was quite some time ago and that and many other successes and failures as well. As of late I'm getting pretty good at guessing what chemistry will work though most of my LTGS efforts are not waterproof enough. I laid off of it for a few months because I'm trying to finish my house so that I can retire. After that I'll be a full time experimenter.

Thanks for bringing this old thread back to life.

Why would any substance in any stove need to be waterproof?

[branja]

One of the reasons is because "waterproof" is a evidence for a true geopolymer. GP should not be soluble in water, acid or base. Water insoluble stone.
Other point is the "non heating season", nobody wants that his stove "melts" just from air moisture when there is no fire burning.Some people wish to place stoves in greenhouses, extreme air moisture.

"Waterproof" is a property so the stove wud be long lasting.

[pigbuttons]

Mar 4, 2018 10:41:05 GMT -8 branja said:

As I remember this was on "Karls Geopolymers". I think the solution was to add phosphoric acid.

You are right branja. But even with it, though it does not dissolve, mine after 24 hours is fragile and refiring does not restore it.

[Deleted]

Alumina and crystalline silica have very little chemical reactivity.
The reactive forms, if finely milled, are alumina hydrate and amorphous silica.
Al(OH)3 + SiO2 + KOH = KAlSiO4 + 2H2O  = Kalsilite
Al(OH)3 + 2SiO2 + KOH = KAlSi2O6 + 2H2O = Leucite
Al(OH)3 + 3SiO2 + KOH = KAlSi3O8 + 2H2O = Orthoclase

Al(OH)3 ~ 78.00 g/mol
SiO2 ~ 60.1 g/mol
2SiO2 ~ 120.2 g
3SiO2 ~ 180.3 g
KOH ~ 56.1 g/mol

Alumina hydrate as available at pottery supplies is not fine enough,
though one may try to dissolve it in concentrated NaOH near the boiling point,
to get sodium aluminate and then add the amorphous silica.

Sodium hydroxide NaOH has a melting point of about 318 °C / 604 °F.
Molten NaOH has the highest chemical reactivity and is extremely dangerous.
One can use a steel pot to react ordinary silica sand in molten NaOH to get waterglass
and by acidifying it later get pure amorphous silica.
www.youtube.com/watch?v=YFXrT1Kds-M
Sodium aluminate can be made with molten NaOH as well.
Very dangerous but also very cheap.

[branja]

Are sodium aluminates gotten from H2O+Al+NaOH reaction of different types then Molten NaOH+ Al(OH)3?

[Deleted]

Aluminium alloys and lye create a lot of hydrogen.
With 99.5% aluminium the differences of the results are not significant,
however aluminium alloys may contain quite a lot of other metals.

[coastalrocketeer]

I searched and found that “Reynold’s Wrap” aluminum foil is an 8000 series alloy that is 98.5% aluminum, with the remainder being mostly iron and silicon

Would this be an acceptably “pure” form of aluminum for supplementation of aluminum in mixes by dissolving in lye?

[Deleted]

98.5% aluminum should be fine.

[coastalrocketeer]

Thank you Karl!

I have recently aquired a bevy of materials to experiment with... And will be posting a new thread to hopefully get your feedback on mixes based on your recipes here, that would be potentially fruitful with the array of materials I now have available to work with.