|
Post by pyrophile on Jul 9, 2014 14:16:59 GMT -8
By the way, what about ahes (normal, not ultra fine)?
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jul 10, 2014 3:04:41 GMT -8
By the way, what about ahes (normal, not ultra fine)? Do you mean ashes or slag ? For chemical reactions with insolubtle materials at sufficient speed and efficiency huge surface areas (small particles) are an indispensable requirement. However the small particles are only required for the binder. Like with portland cement only a relatively small amount of binder is required for geopolymer concrete. But sand is a very bad filler for refractories. All components of refractories need to have a very close thermal expansion. That is one reason why potters are using grog. For geopolymer refractories one can mix fine grog with a much larger amount of coarse grog, to save some money. With respect to the pure alumina I forgot to mention, that a source of silica is also required.
|
|
|
Post by photoman290 on Jul 10, 2014 4:08:20 GMT -8
avast says that site link is infected with a virus.
|
|
|
Post by mintcake on Jul 11, 2014 6:56:32 GMT -8
Thanks for posting these experiments, Karl.
I've been meaning to post for the last few weeks, but have been busy building. this seems like a good topic to tack it onto:
I really wonder what sort of "locally sourced fireclay" I'm using here. It's a fairly pale yellow-brown, and is very crumbly, almost like a sand-rich soil when dry, but it's sand-free. If it was reasonably well-packed when wet, it becomes hard. Mixed 1:3 with sand it makes a pretty good mortar, in fact this mixture was apparently used in as mortar in parts of the 100 year old part of our house. I also know that (red) bricks have been hand-made in the area, but I don't know if that's from this particular source of clay or another. Another potential hint is that there are supposed to be outcrops of "clay marl" in the area, which I've just learnt to be a lime/clay mixture. I've just tested some of my "fireclay" with some vinegar, and it fizzed nicely. So maybe that's what I've been sold as fireclay.
I tried various mixing ratios of waterglass & draincleaner (NaOH) and just couldn't find any mixture which would make the clay+perlite of my samples not form a gel after about a minute. (the clay on its own did this too). Eventually I tried just draincleaner. This was about 1g of NaOH in 20ml of water, and 40ml of clay+perlite, if I remember correctly. The clay+perlite gelled just like with the waterglass, within a similar timespan - just enough time to mix it well and it would suddenly become stiff. I thus concluded that it was the alkali in the waterglass that was causing the effect I'd seen, not the sodium silicate itself.
I have no idea if what is forming is a geopolymer, or if some other reaction is occurring.
The sample slowly increased in strength, somewhat like drying concrete does, but it didn't get that much stronger the clay+water. (It just became less plastic). There wasn't a significant difference in the final dry strength or shrinkage between the clay+alkalii and clay+water samples. When fired (i.e. put in my stove's firebox), it looks like the clay+alkalii samples came out a bit harder, but that might just be different firing conditions. (In comparison, Clay+waterglass solution gave reduced shrinkage and reduced final strength).
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jul 11, 2014 9:26:33 GMT -8
I have no idea if what is forming is a geopolymer, or if some other reaction is occurring. It became a geopolymer if it does not fall apart in water after hardening and drying. You could test if warm curing at around 70°C makes any difference.
|
|
|
Post by pyrophile on Jul 21, 2014 11:54:18 GMT -8
Thanks Karl, I wanted to write "ashes". Benoit
|
|
|
Post by smarty on Jul 23, 2014 10:25:49 GMT -8
Having just give myself a bit of a crash course on chemistry - a subject that I knew even less that I thought I knew (and that was bugger all) - I have finally started messing with some of these recipes. I am still waiting to be able to get to the kiln to roast some Kaolin clay at 750C to make some metakaolin, but in the meantime I've bought a bag of fly-ash from amazon, which was the only place I could find it in the UK and tried this basic recipe that I found on the web:
448g KOH (Potassium Hydroxide) mixed into a 2L lab flask with 500ml of water - mix in slow and keep stirring, or swilling it around. (It gets hot so you need pyrex or a proper lab flask.) Then once this is all mixed in you top it up to the 1L mark and let it finish dissolving overnight. It makes a 8mol KOH solution. Next you mix this KOH solution in with Potsil (the only potassium water glass I could find at first) in a ratio of 2.5:1 Potsil to KOH solution. You then add as much fly ash to this as you can while still keeping it workable and then leave to set overnight. (There are two types of Fly-ash type F and type C. I have no idea which type I have!)
Wear nitrile gloves and a face shield because the KOH is at a strength that will burn you.
It set pretty hard, although the 3/4" block I cast could be snapped in my hand but combined with some kind of aggregate or used as a laminating resin it seemed promising. I tried baking it in the oven at the lowest setting - i.e. under 100 degrees C - for an hour which seemed to harden it some more.
I've just mixed up another batch and added aluminium powder to make it foam up. I'll see tomorrow if its worked.
You can use NaOH and sodium water glass as well you just adjust for different chemical weights so for an 8 mole solution of NaOH you need 320g NaOH in 1L. Anything over 4 moles solution is classed as caustic rather than irritant for NaOH, and anything over 2 moles KOH solution is classed as caustic so you have been warned.
I haven't tried any of Karl's safer recipes yet so that will be the next thing to try.
Thanks Karl for all the help and advice! And Bob for the Metakaolin. (I didn't get the recipe right with that stuff and it got wasted! Too expensive as well!)
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jul 24, 2014 2:16:31 GMT -8
(There are two types of Fly-ash type F and type C. I have no idea which type I have!) Fly-ash type C is self cementing due to a high amount of calcium oxide. If it gets hard just with water you have type C, else another grade.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jul 24, 2014 3:54:41 GMT -8
If someone wants to find sources of fly ash: Ashes (residues), cenospheres CAS No. 93924-19-7
For example googling for "cenosphere fillers" or "fillite filler"
|
|
|
Post by photoman290 on Jul 24, 2014 6:26:58 GMT -8
so fillite can replace type c fly ash?
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jul 24, 2014 7:11:30 GMT -8
|
|
|
Post by photoman290 on Jul 24, 2014 7:30:15 GMT -8
ok got that now. i knew it was fly ash just not sure of the type. assume the sort of lime builders merchants sell will be ok.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jul 24, 2014 7:33:30 GMT -8
ok got that now. i knew it was fly ash just not sure of the type. assume the sort of lime builders merchants sell will be ok. For a hot and speedy reaction quick lime, for a slower reaction hydrated lime.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jul 25, 2014 8:27:14 GMT -8
STEAG Power Minerals GmbH kindly provided me a sample of their steament H-4 fly ash. Steament H-4 is a low calcium fly ash with low water demand, a bulk density of 0.86 and a high reactivity index.
A bit more than an hour ago I made some runny samples with 10% NaOH and some more with additional 10% quicklime. All have started to harden under ambient temperature. To speed things a bit up I have placed them now in an oven at 75°C.
I will try some more mixtures with parts replaced by fine grog or natural kaolin and report bout them.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jul 26, 2014 2:22:16 GMT -8
The steament H-4 fly ash is a really great stuff. It is very sticky even more than the very fine grog, thus a release agent is indispensable.
I have warm cured the very runny mixtures at 75°C for 3 hours. Just slightly more than half a day after mixing they are now pretty hard, but a bit brittle as one may expect from such a low density. However after such a short time only a fracture of the maximal strength, could be achieved. Fly ash is a Bingham plastic like clay suspensions and tooth paste and thus mich thicker mixtures will become pretty liquid under vibration. Thicker mixtures will harden significantly faster and give less brittle results.
|
|