Geopolymer test brick pictures with fuzz?

[etownandrew]

My kiln is rated for 2000F maximum. (I traded some handmade items for it several years ago.) When I turned it off last night my thermocouple was reading 1752F/959C. I should end up with a good result based on a previous firing for another project. I did not do the geo-polymer mix correctly for my first several test bricks and so I needed to fire them like normal. I am making some special large bricks (3" x 6" x 13 1/2") to span the top of my narrow rectangular shaped masonry bell. They will be getting the full blast from the riser and so I made them from purchased fireclay.

[pigbuttons]

Great info here guys. It is good to see your successes.

[Deleted]

Jan 7, 2018 5:48:01 GMT -8 etownandrew said:

My kiln is rated for 2000F maximum.

Great, you can make your own metakaolin respectively metaclay.
Calcine clay powder at 750°C/1382°F for about 30 minutes.
Dehydroxylation starts at about 550°C/1022°C thus actually every owner of a batchbox has a kiln sufficient for that.

[esbjornaneer]

Is efflouresense BAD for the geopolymer?

I have picked up from other threads that smaller 'binder feedstock' particle size, less Na, and less water can reduce efflouresense. In the samples I have made I get more efflouresense in the ones with a smaller binder (=Na) proportion, than the ones with greater binder (=Na) proportions. The feedstock is the same and the total proportion of water to dry material is the same in these samples.

Can anyone enlighten me on what is going on or what to change in my recipe?

[Deleted]

The chemical process requires a minimum PH value.
Therefore a small amount of NaOH may result in more efflorescence than a larger one.

[esbjornaneer]

Thank you Karl. So that is why a lower H2O quantity would make it less.

And to answer my first question in previous post:

Efflorescence is the formation of white salt deposits on or near the surface of concrete. For ordinary Portland cement (OPC) concrete, efflorescence is generally harmless except for the discolouration, and is best described as being ‘a skin trouble and not a deep-seated disease’. However, for geopolymers, as they contain much higher soluble alkali content than conventional cement, efflorescence can be a significant issue when the products are exposed to humid air or in contact with water.

from this article

[branja]

Efflorescence can be interpreted as: reaction product is a water soluble salt instead of a water INSOLUBLE salt.