Karls Geopolymer Experiments

[owkaye]

I made some runny samples with 10% NaOH and some more with additional 10% quicklime.

Hi Karl,

I still cannot find quicklime in my area (maybe just not looking in the proper places) so I bought hydrated lime from the local agricultural feed store last week.  I also found a supplier for NaOH crystals and diatomite, so I can buy these ingredients next week.  Securing a fly ash supplier is my next big challenge.

How do you measure ingredients?  By weight or volume?  Are all ingredients dry when measured?  Do you mix everything together dry, then slowly add water to the dry-mixed ingredients?

[Deleted]

I measure the ingredients as dry powders by weight,
then mix the powders dry and add water.
The NaOH needs to be a powder too, flakes must be dissolved.
Class C fly ash does not need additional lime.
From my experiments it looks like pure flyash tends to be brittle,
maybe waterglass could improve that.
You will also need some refractory aggregate like grog.
200 mesh is about the particle size (0.0mm to 0.1mm) of the grog I have used as binder.
www.theceramicshop.com/store/category/7/6/Grogs/
www.axner.com/raw-materials.aspx
www.portlandpottery.com/grogs/
shop.clay-planet.com/raw-materials.aspx

Or google for "Grog Mulcoa Fine 200"

[owkaye]

I measure the ingredients as dry powders by weight, then mix the powders dry and add water.

Thanks for confirming this procedure.

The NaOH needs to be a powder too, flakes must be dissolved.

Looks like I'll have to get my mortar and pestle out so I can grind my NaOH crystals into powder.

Class C fly ash does not need additional lime.

I think this is because Class C is a "high calcium fly ash" so it already has enough Calcium. If I am correct my local fly ash supplier offers Class F, so I will need the hydrated lime I purchased the other day.

From my experiments it looks like pure flyash tends to be brittle, maybe waterglass could improve that.

Do you think the brittleness is caused by having not enough silica available to the reaction? Or too much calcium?

You will also need some refractory aggregate like grog. 200 mesh is about the particle size (0.0mm to 0.1mm) of the grog I have used as binder.

I have lots of old bricks around here. I'm thinking of crushing some to use for aggregate in my first experiments. They are regular bricks, not firebrick, so they will not handle the high heat for long. But they are cheap and hopefully 'good enough' for initial experiments.

Is uniform particle size an important requirement for the aggregate? I ask this question because I think I read somewhere that a range of different particle sizes will resist cracking better.  Perhaps I did not read carefully ... ?

[Deleted]

Jul 28, 2014 8:48:04 GMT -8 owkaye said:

Do you think the brittleness is caused by having not enough silica available to the reaction?

Irregularly shaped particles interlock better than regularly shaped eg spheres,
which disadvantages pure fly ash.

The smallest particles of the fine fly ash I have got seem to be bigger than the smallest particles
of the very fine grog, thus leaving more empty space between them.
Maybe also to big to be easily dissolved by the NaOH.
Waterglass or any other dissolved silica can polymerize to very fine particles and thus fill very small spaces.

Is uniform particle size an important requirement for the aggregate? I ask this question because I think I read somewhere that a range of different particle sizes will resist cracking better.  Perhaps I did not read carefully ... ?

Particles with different sizes and shapes will leave less empty space and interlock better
than particles with uniform size or shape.

[smarty]

I have made a fairly useful looking foamed geopolymer using a mix of 50g bentonite, 50g class C flyash, 70g Potsil/Potassium hydroxide solution (44.8g KOH/100g potsil), 1g Atomised Aluminium powder, 1g super plasticiser.

It foamed up to about two-three times its original size with fine pores none bigger than about 1mm and many much finer. I poured it and left it overnight then cured it some more at about 80degrees C, Then I hit it with the propane blowtorch and it glowed red but the heat didn't spread through it too much. Heating it made it go really quite hard indeed. It is brittle as a result but as part of a composite material it looks like a promising riser material.

Finally made something less grey goo like. Very excited!

[smarty]

Tried making a similar foamed geopolymer as above but used Karl's tip of adding lime to make it set at room temperature. The first one I mixed in CaO which was a bit too lively - though it set in a few minutes. I could try cutting down on lime or Aluminium powder and try this again. I then tried the same exercise but switched to hydrated - instead of quick - lime. This worked a bit better although both these look like the bubbles are a bit too big which will affect the strength somewhat I fear.

[Deleted]

Smarty you could try it with different nonionic surfactants like Tween 80 or Triton X-100.

[Deleted]

As expected the samples made with fly ash are gaining strength over time
and will become pretty tough for something consisting mostly of bubbles.
However it takes many days longer to become tough, than the very fine grog.
Mixtures with very fine grog can also be made much more liquid.
With very fine grog the interconnected gaps between the particles
and thus the density can be, to some degree, simply adjusted by the amount of water,
as the grog reacts less sensitive in this respect as fly ash.

[smarty]

Is this with or without heat curing Karl?
Some pictures in the link below of the foamed geopolymer composite material I made. The one with the bigger bubbles was no good. It melted with the blowtorch. The one with the smaller bubbles is similar to one I made before which became rock hard when I tried the blowtorch on it. The dense layer at the bottom is four layers of carbon fibre laminated with geolpolymer resin. The different sized bubbles were due to the mixture being less or more liquid before adding the aluminium powder. I have ordered some tween 80 as Karl suggested to see if it helps create a better foam.

app.box.com/s/rrdpm02pordgp1dtig9s

I've tried the magnesium oxide cement again using dead sea salt and epsom salt in a ratio of 90%:10% MgCl2:MgSO4 in a solution that I added to the MgO. It formed a nice dense substance that is about as hard as a fine gypsum casting plaster. I have ordered a hydrometer to do the thing a bit more scientifically. The recipe calls for a 30 baume solution. The addition of the MgSO4 (epsom salts) apparently helps to prevent the susceptibility to weathering from water. I'll stick the sample in some water to see what happens. This cement binder can be used in various ratios mixed with inert fillers. Talc will be my first port of call. (In the recipe they used Dolomite.) It can also be used to make concrete with the addition of sand and aggregate. I'll test it for heat resistance too. The MgO cement I made before using KH2PO4 was fatally weakened with heat. Similar to the way that gypsum plaster is weakened.

[Deleted]

Jul 31, 2014 1:52:26 GMT -8 smarty said:

Is this with or without heat curing Karl?

I have warm cured the samples for three hours, which leaves them still rather brittle.
After several days at ambient temperature they are now a lot tougher.

The one with the bigger bubbles was no good. It melted with the blowtorch.

Very thin material becomes more prone to heat.
That is also observable with expanded perlite.

[smarty]

Yes it looks like they need a few weeks to completely get to their potential strength.

On a side note: when I sawed through the sample in the pictures, out of interest, I took some of the resulting powder and added it to water to test the ph. It was up around 13. even after curing safety precautions like masks etc need to be taken when working with the stuff. I think that some of the acid activated recipes can be neutralised through heat treatment. I don't think this applies to the alkali activated recipes.

[Deleted]

The very fine grog is a lot speedier.
You could try to create bubbles with a mixer, as with whipped cream.

Someone claims he made a tough, lightweight and fire resistant material with Fuller's earth (calcium bentonite) ,
sodium hydrogen carbonate and citric acid.
It needs high curing temperatures.
www.sciforums.com/showthread.php?69838-geopolymers-fire-paste

[Deleted]

Jul 31, 2014 2:39:52 GMT -8 smarty said:

I took some of the resulting powder and added it to water to test the ph. It was up around 13.

You would have got similar values from concrete.
The PH pf concrete ranges from about 12.5 to 13.8 and drops only at the surface.
Without such high PH values steel enforced concrete would be impossible.


With respect to acid activated, as well as alcali activated recipes:
"Most low-molecular-weight organic acids dissolve alu-minosilicates with higher dissolution rates
under far-from-equilibrium conditions, compared with single inorganic acid at the same pH."
The dissolution of aluminosilicates by acids can be used to speed up curing times of geopolymers.
There are papers dating back 30 years and more, nevertheless recently some people were bold enough
to file patents, which never should be granded if the patent officers are not bone lazy.

Making cements with plant extracts
www.geopolymer.org/fichiers_pdf/CemPlant.pdf

[smarty]

Thats fascinating Karl. Cheers. I wonder whether such acids could be used to pretreat powders to make them more active when subsequently combined with strong alkali? For example if the fineness of the powder is not optimal or where it is un-reactive like talc.

I made a quick setting cement today using 50g wollastonite, 50g MgO,, 50g class C fly-ash, 80g mono potassium phosphate, 5g Boric acid, and 125g water. I then tried the same thing with talc in place of wollastonite and it still hasn't set hard 5 hours later. I have it in the oven now to see if it will cure with heat.

It occurs to me that if it doesn't weaken the mix too much talc could be used to slow down the very rapid set of the first recipe. Possibly I could try treating talc with an organic acid to see if it makes it more active. Otherwise it will need calcining at over 1000 degrees C as I think that is supposed to activate it. Similarly the MgO needs calcining at the same kind of temperature to make it less active. Can't think why they act in different ways like this. Bit of a bummer with the talc because it makes such good thermal mass. It would be great if it could be made into a heat resistant concrete.

[Deleted]

Sugars can be used as retarders, eg table sugar.