Geopolymer test brick pictures with fuzz?

[etownandrew]

In the last couple days I have made a couple test bricks to start preparing to build a batch box rocket heater. I was interested in using geopolymer bricks and so made a couple tests. After 24-48 hours I am wondering if it is normal to see the thick white fuzz on the bricks as shown in the two linked pictures.  
photos.app.goo.gl/G2OKO1vSoRyaD09m1
photos.app.goo.gl/SfOAh4SAjaxRcLV52

The Fire clay brick has 3% NaOH to the dry fire clay by weight before adding water, sand and shredded rock wool. Is it normal to have such a large amount of fuzz on the brick after 48 hours? The red clay brick is only 24 hours old in this picture and is just starting to dry out. I attempted to also mix 3% NaOH to the clay. I imagine it will develop similar fuzz by this time tomorrow. Note that the test brick next to it that looks fine had wood ashes mixed with the clay. The bricks have been kept in a cool basement since being formed.

[Deleted]

Not made a binder ?

That is called efflorescense and is a sign for water soluble salts in the mixture,
which are carried to the surface by kapillar forces.
NaOH is infamous for it.
The amount seeen in the picctures is exceptionally high.
it will stop once dry.

Your clay may contain relatively high amounts of alkali oxides and salts.
Basalt may contain about 10% sodium oxide and about 5% potassium oxide and even more calcium oxide and salts.
shredding the rock wool may have made them acessible.
A very small amount of fibers, slightly above 1% to 3% fiber is sufficient.
It looks like you got a lot more.

[etownandrew]

Dec 27, 2017 16:14:56 GMT -8 @karl said:

Not made a binder ?

I'm not sure what you mean by the above statement. I didn't use any binder like cement or lime.

I put in about 2.2% rock wool fiber weight to the dry weight of the fire clay. So it seems to be in the recommended range but still, the rock wool might have contributed to the efflorescense. 

I'll try a test brick using toilet paper as you have mentioned elsewhere as the fiber to see if it turns out differently. However, I'll need to get some more lye next week before I can make another test brick. 

[Deleted]

Without a binder you will only produce efflorescense, but not a geopolymer.

You need to make a LTGS binder first or one made of acid activated clay or a reactive mineral and waterglass.

[pigbuttons]

etown', the pics aren't showing up for me, but I don't really need to see them as I've had the same experience. A couple of things might be going on that aren't readily apparent. First and foremost is, like karl said, the efflorescence is cause by water soluble salts, and more precisely "excess" salts. Not all clays will react to the NaOH sufficiently to prevent rapid efflorescence, a lot of it has to do with the molecule and how easily it will break down and reform into the geopolymer. I had to test with about 10 different clays before I found two that worked well. The Fire Clay I had was not one of them that did well. Second, the LTGS stuff requires much more precision in the process, and as I understand it from karl's posts and reading the links he has provided, when doing LTGS you have to mix the 'binder' first and let it react before you mix it with the aggregate, even if the two are of the exact same clay. It is like making real sourdough bread, you have to have the 'starter' premade and aged even though it is made with exactly the same ingredients as the new batch of dough.

As far as the reactivity of any 'ingredient', Karl can address this better than I can ( and forgive me karl if I get this explanation a bit twisted, be kind please), but it has something to do with the amount and type of, just for example, alumina as well as the other salts like magnesia and even the iron that are present in the clay. I'm sure it is not just the alumina, but that is just an example. Each 'ingredient', whether clay, grog, loeme, sand, ect, has a chemical signature. Only certain chemical signatures will react properly with the NaOH or KOH. But once that reaction is triggered ( in the binder ), the same or even other less reactive ingredients can be added as aggregate and they will be carried along in the reaction through nucleation around the previously activated "binder". LGTSs, because they don't rely on heat to push the process are more sensitive to having the binder done well.

By the way, I've found that if I take a propane or mapgas torch and heat the geopolymer until is has a light red sheen to it, the efflorescence stops; but that is kind of defeating the whole LTGS idea. That's not to say that with bad clay it will prevent crumbling or cracking and the like. It just stops the efflorescence so that it doesn't contaminate everything else in the lab.

[etownandrew]

Thank you for your explanations. I will try again and make a 1:1 clay to NaOH reaction binder first.

[Deleted]

etownandrew you may consider to get a bag of Sweet PDZ, which is relatively cheap.
Sweet PDZ is a zeolite.
It is not ideal as it has relatively large particles, but NaOH can dissolve even relatively large particles.

How to make a zeolite based binder is described here:
donkey32.proboards.com/thread/2399/straight-binder-based-reactive-minerals

A zeolite based binder can be used to bind even less suitable materials
like loess loam with a clay content of only 20% or less.

Alternatively
KMI zeolite Nevada: Micronized very high purity.
shop.kmizeolite.com/shop/product/freeflow-feed-additive-246?category=37

[etownandrew]

I will try that. My local Tractor Supply farm store sells a 25 pound bag of Sweet PDZ for $9.

[coastalrocketeer]

Dec 28, 2017 6:16:09 GMT -8 etownandrew said:

I will try that. My local Tractor Supply farm store sells a 25 pound bag of Sweet PDZ for $9.

If they have both types, SweetPDZ comes as both a "granule" version and a "powder" version. The powder is still mostly small granules, probably because the stuff is meant to be sprinkled and they want to minimize inhalation hazard. Neither is as optimized as a micronized powder that Karl has used for his build/experiments, but the powder version is likely to be more suitable than the granule version.

I have purchased and am experimenting with the powder version.

[etownandrew]

I think what I got was the granules. I have a brick made from it as the binder with lye that has been drying for 48 hours now and is looking better than the first try.

[coastalrocketeer]

Is there any aggregate in that mix? And were you able to get the lye in the binder portion to dissolve the SweetPDZ granules completely?

I also added some new posts to my own SweetPDZ geopolymer refractory experiment thread covering my second test puck... (Bear in mind that I am surely still not doing things "right" in terms of Karl's insteuctions and intent, I just have a hard time understanding and keeping straight all that he posts, so I flail away and hope that he tells me where I am far off the mark)

[etownandrew]

I mixed 3:1 sand to clay.

The 8% binder was separately reacted and allowed to sit and cool for several hours. It was also 3:1 SweetPDZ granules and Lye. The granules did not dissolve.

Two thoughts on getting them to dissolve.
1) I was wondering if I needed to run them through a mortar and pedestal first to break them into powder. I'll probably do that the next time I try.

2) Another possibility was to heat the binder in a boiling water bath to try an encourage the lye to break down the granules. However, there are some safety issues with that operation.

[coastalrocketeer]

Jan 2, 2018 2:27:53 GMT -8 etownandrew said:

I mixed 3:1 sand to clay.

The 8% binder was separately reacted and allowed to sit and cool for several hours. It was also 3:1 SweetPDZ granules and Lye. The granules did not dissolve.

Two thoughts on getting them to dissolve.
1) I was wondering if I needed to run them through a mortar and pedestal first to break them into powder. I'll probably do that the next time I try.

2) Another possibility was to heat the binder in a boiling water bath to try an encourage the lye to break down the granules. However, there are some safety issues with that operation.

I had no issues heating the binder with lye over a double boiler, am just not doing that with current batches because it's a longer process than apparently necessary... And no matter what I do, I don't seem to get very significant/complete dissolution of the granules in the mix... It feels like it has sand in it no matter if I stir it with heat for hours or not.

Karl has said that there may be parts of the SweetPDZ zeolite (natural mineral inclusion portions of it) that just won't dissolve the way whatever Clinoptilolite he is getting seems to.

My impression is that even granules of the zeolite he is working with break down in the lye in a few minutes of mixing and "some hours" of resting... So I'm not sure what exactly the difference is, but my all zeolite test pucks passed the 24 hour soak test to prove they have undergone a geopolymeric reaction, so I have decided not to worry about it too much.

I'm currently trying infusing rockwool with a thinner mix, using zeolite binder and bentonite clay as aggregate, and have had some promising results as far as my project/product goal goes... Will be posting about it in my zeolite thread in a bit... Funny thing was the main experiment failed, due to my not having a thin enough mix to saturate the mineral wool sheet I was trying to coat with geopolymer, and probably a poor technique as well... and the solids just sat on the surface and left the middle of the blanket untouched... The material crazed and fell apart where it stayed thick on the surface, but the remainder of binder I mixed into peanut sized chopped chunks of mineral wool and pressed that into a patty... Which dried and hardened with no cracking, and seems to be more heat resistant than my original all zeolite mixes. It is probably similar to the ceramic fiber board in it's final strength after drying for a few hours at 180 in my oven... but gets nice and glassy hard at the surface when surface is sintered with my BernzOmatic TS4000 propane torch.

The bentonite clay has HUGE water demand, and thus shrinks a LOT as it dries, which means it needs fiber throughout to dry without crazing and cracking. I don't need a huge amount of strength for my J-tube core, and it should be similar to working with paper mache to form the material onto my inner form that will be burned out after the material has dried fully. The insulation value is not as good as the solid zeolite mixes at 1/2" thick, but it seems to make the mineral wool impervious to the hot torch flame, and produces a lightweight refractory material strong enough for my purposes, that would allow me to make much thicker walls and thus provide my desired insulation level in a low weight material that does not require huge amounts of binder or huge amounts of aggregate, and the more expensive ingredient, NaOH.

Looking forward to updates from your experiments as well.

[etownandrew]

Good comments. I am interested to see that you had already tried a couple of my ideas so I now don't need to. I am further interested in your plan to lay up the geo-polymer mix with rock wool on the outside of your core form. That makes for an easier form. I was thinking of doing both an inner and outer form that I would then pack with geo-polymer material. However, making just the inner form would be easier.

My brick experiments are currently cooling in my kiln. I'll pull them out in another 24+ hours and see how they did.

[coastalrocketeer]

Jan 7, 2018 3:44:35 GMT -8 etownandrew said:

Good comments. I am interested to see that you had already tried a couple of my ideas so I now don't need to. I am further interested in your plan to lay up the geo-polymer mix with rock wool on the outside of your core form. That makes for an easier form. I was thinking of doing both an inner and outer form that I would then pack with geo-polymer material. However, making just the inner form would be easier.

My brick experiments are currently cooling in my kiln. I'll pull them out in another 24+ hours and see how they did.

Nice... You have a kiln! Do you know what temp you are firing your bricks to?