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Post by Deleted on Aug 24, 2014 11:06:02 GMT -8
I have tested 5% quicklime with molochite, which makes still such a huge difference in curing time, that even half the amount may suffice to speed up curing a huge lot. Eg. the low calcium fly ash has 2.8% CaO.
The 20% NaOH has even slowed down curing for molochite a lot, but not for agrical M 1000, which seems to be slightly faster with 20% NaOH.
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Post by Deleted on Aug 25, 2014 4:20:27 GMT -8
The molochite sample with 20% NaOH is now extremely hard, but the surface in contact with the plastic cup is rough and uneven, not smooth as one would expect. The upper surface is convex, which indicates a volume expansion. Compared to 10% sample the color is significantly darker.
The molochite sample with 10% NaOH and 5% quicklime is hard, but not so extremely hard as the pattern with 20% NaOH and has a smooth surface.
The argical m 1000 sample with 10% NaOH and 10% quicklime is hard, but not as hard as the molochite sample with quicklime. The volume is nearly twice as large a lower hardness is therefore to be expected particularly at this early stage.
The argical m 1000 sample with 20% NaOH does not show much difference compared to the sample with 10% NaOH, which does not show any sign of development in the meantime.
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Post by Deleted on Aug 25, 2014 5:47:40 GMT -8
Things may look a bit different if mixtures of water glass and lye are used, but once more I advice strictly against taking avoidable hazards. The mixtures with powders of NaOH and lime once mixed with water are only dangerous for eyes, but will not eat holes into the skin. For the skin they are merely irritants. So far I have not found any convincing reason for the use of highly caustic and thus highly dangerous mixtures of waterglass and lye.
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Post by photoman290 on Aug 25, 2014 7:53:32 GMT -8
how are you mixiing the NaOH with the other ingredients? my NaOH is in flakes. should it be ground fine before mixing. grinding it fine using a blender is one way i have thought of to keep the dust level down. or if mixing it with water what volume of water to NaOH should i use to get the correct concentration.
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Post by Deleted on Aug 25, 2014 8:18:17 GMT -8
I mix the dry ingredients and then add water.
A mortar and pestle can be used to powderize the flakes safely, by moving the pestle in circles. Nevertheless I advice to use a respiratory protection. As I have said many times one should not take avoidable hazards.
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Post by Deleted on Aug 26, 2014 21:29:25 GMT -8
I have mixed some more samples. Because some of the mixtures contain natural kaolin, I could not sleep and I am just impatient, I have raised the curing temperature to 90°C. Should not have done it, I know.
Natural kaolin with 20% NaOH and 10% quicklime. Volume and hardness similar to argical m 1000 with 10% NaOH and 10% quicklime.
Molochite with 15% NaOH no lime. Again strong signs of volume change. Obviously molochite is sensitive for high amounts of NaOH.
Half molochite half natural kaolin with 15% NaOH and 10% quicklime. The upper surface got small cracks about 3mm deep, due to volume changes of the molochite even as the lye was a bit weaker because of higher water demand. Also there is always some water los at the surface, although enclosed in a plastic bag. The cracks would likely not have happened at 75°C.
Molochite with 10% NaOH 2% quicklime. The 2% quicklime are enough to speed up curing a huge lot. One paper claims that even powders of non reactive calcium minerals serve as seeds for the geopolymerisation.
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Post by Deleted on Aug 26, 2014 21:56:58 GMT -8
The samples of argical m 1000 without lime did not get beyond the stage of geling. They can still be easily crushed with the bare hand.
I have crushed them and then mixed with a bit lime and added some water to get a slurry again. The slurry got hard. No obvious difference to the sample mixed initially with lime.
This offers the possibility to prepare something in advance, which is not as dangerous like highly concentrated lye. Flakes of lye would have been completely dissolved. Just add some lime or maybe even waterglass if one thinks, that it is needed to start the polymerisation process.
Scientists have crushed complete mixtures in the stage of geling, then dried and powdered. After just adding water again the process continued as if nothing had happened. Likely a patent is filed for that
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Post by Deleted on Aug 27, 2014 4:10:01 GMT -8
Important note.
Some of the materials for geopolymer binder are pretty cheap, thus there is little or nothing to save by using aggregates and they even cause more work. Some materials used alone will result in very lightweight geopolymer. Also using the binder alone ensures uniform thermal properties.
One will almost unavoidable get problems by trying to use any geopolymer binder for refractories without some aggregate.
Something made from such fine and at least partly dissolved material will take very very long to get really dry at ambient temperatures and forced drying, as well as initial firing, will have to be done very careful and slowly at beginning.
To avoid some headaches: One needs some porous aggregate, or in general something that supports drying (escape of water) in one or another way or at least reduces the water demand a huge lot, if just by not requiring any water itself. Eg zeolite cat litter, porous grog or some organic fibers.
KOH leaves more and bigger pores, which is for me the only convincing reason to use it. There are however cheaper ways.
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Post by photoman290 on Aug 29, 2014 4:05:18 GMT -8
while karl is busy mixing different combinations of kaolin compounds together we are getting to the stage of thinking about aggregates to mix with the geopoplymer binder. i came across this interesting paper. some useful data at the end on particle size and also why pure binder breaks up on heating. getting the density right is vital for maintaining strength. edu.zndxzk.com.cn/down/upfile/soft/2009127/09-p0914-e08664.pdf
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Post by Deleted on Aug 29, 2014 5:53:15 GMT -8
Not every pure binder breaks up on heating, not if properly prepared and dried.
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Post by Deleted on Aug 29, 2014 6:27:07 GMT -8
BTW
The "metakaolin" in the paper linked by photoman290 is not true metakaolin. With just about 29% Al2O3 the clay used is merely stoneware grade. Thus the results have to be taken with a grain of salt.
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Post by Deleted on Aug 29, 2014 7:06:22 GMT -8
As usual in the scientific papers the waterglass/NaOH solution is far stronger than actually needed, as they are always hunting for compressive strength records. Compressive strength rates in the range of 70-85 MPa, even with very light fillers are not needed for stoves. Due to the resulting very high dissolution rate, the binder gets virtualy gas tight, causing avoidable problems, including a huge break down in compressive strength at heating.
LOL - ROFL
Without breaking records the papers will not be quoted by other scientists. Plainly crazy system IMHO. The amount of quotations is more important than any real value thus lots of papers are produce slatternly if not plainly faked.
Almost everybody is busy to produce lots more the like, not leaving much time to read papers of others carefully, before quoting.
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Post by photoman290 on Aug 29, 2014 11:14:08 GMT -8
i have found this also. most Phd papers seem to written to inpress with the amount of detail that can be crammed in. like patents there is usually something worthwhile in there somewhere among the fine detail. i must admit i didnt notice the composition they where using apart from the excess Naoh and sodium silicate. davidiots is also rather sceptical of the very high pH mixtures as well. not being a chemist means i can be a bit slow on the uptake, seem to be getting some idea of what is going on when geopolymers are heated, but if they are not using metakaolin it throws all their findings into question. not sure how it effects the size of the aggregate. more research needed i think.
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Post by Deleted on Aug 30, 2014 2:34:23 GMT -8
Geopolymers will undergo physical and chemical changes at high temperatures.
Physically and chemically bound water will be driven off. The amorphous state will change to crystalline.
In both cases the extremely tight structure due to overly strong NaOH or KOH solutions causes problems, which finally weaken the structure.
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Post by Deleted on Sept 1, 2014 3:04:16 GMT -8
While waiting for some more metakaolin I have made again several experiments with natural clays.
With respect to casting With about double the amount of lye as required for grog and by curing at elevated temperatures for many hours, at best for several days, natural clays work quite well. Non plastic clays are better, due to a lower water demand.
Natural clay geopolymers are a simple and economical way to make durable bricks without firing. Prepare a slurry with lye and let it rest for a day or more, then mix it with more clay soil and form bricks.
For casting grog works a huge lot better, the slurry can even be cured at ambient temperatures within a short time.
Grog is available in many countries for relatively small money, and it is not hard to make DIY grog, if clay soil is available. Mix clay soil with organic fibers and fire it in a pit. With the organic fiber one can hit two birds with one stone, the fired clay will be porous and it will be easier to crush it to grog.
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