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Post by smarty on Jul 11, 2018 10:06:35 GMT -8
Phosphate Geopolymer. 50g MK-750 50g H3PO4 Phosphoric acid (85% concentration) 20g Water Heat cured. Add small amounts of organic acids and you can use natural kaolin instead of MK-750.
Yes I’m just reading through my notes and this was done with a phosphoric acid with a molarity of 10M as the optimum for strength. Prof. Claus Rüscher from Leibniz uni. In applied clay science 140 (2017) 81-87, 147 (2017) p.184-194, 107 (2015) p. 188-194 |
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Post by Deleted on Jul 15, 2018 8:06:28 GMT -8
Phosphate Geopolymer. 50g MK-750 50g H3PO4 Phosphoric acid (85% concentration) 20g Water Heat cured. The resulting Geopolymer has 0 porosity. Cannot be true since the mixture contains water in excess.
Molar mass of
Al2Si2O7 is 222.1299 g/mol
H2O is 18.01528 ± 0.00044 g/mol
H3PO4 is 97.9952 g/mol /196g
AlPO4 is 121.9529 g/mol/244g
H4SiO4 is 96.1149 g/mol/192
Al2Si2O7 + H2O + 2H3PO4 = 2AlPO4 + 2H4SiO4
Aside of this Davidovits gives quite hight porosity for metakaolin + phosphoric acid geopolymers in his book.
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Post by smarty on Jul 17, 2018 12:10:24 GMT -8
Phosphate Geopolymer. 50g MK-750 50g H3PO4 Phosphoric acid (85% concentration) 20g Water Heat cured. The resulting Geopolymer has 0 porosity. Cannot be true since the mixture contains water in excess. Molar mass of
Al2Si2O7 is 222.1299 g/mol
H2O is 18.01528 ± 0.00044 g/mol
H3PO4 is 97.9952 g/mol /196g
AlPO4 is 121.9529 g/mol/244g
H4SiO4 is 96.1149 g/mol/192
Al2Si2O7 + H2O + 2H3PO4 = 2AlPO4 + 2H4SiO4
Aside of this Davidovits gives quite hight porosity for metakaolin + phosphoric acid geopolymers in his book.
I can only think that they put more water in because they wanted it to flow. But as it sets the water tries to get out but the lack of porosity causes blowholes and distortion. So they found that the curing temperature was important to let the water escape before the mix started trying to harden. They found a sweet spot around 55 o I think. Does that make sense? I’m still trying to get the chemistry figured I’m afraid. |
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Post by Deleted on Jul 18, 2018 8:43:57 GMT -8
Even with variscite (AlPO4·2H2O) there is still a slight excess of water.
Al2Si2O7 + 5 H2O + 2 H3PO4 = 2 AlPO4*2H2O + 2 H4SiO4
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Post by smarty on Jul 23, 2018 10:29:27 GMT -8
Even with variscite (AlPO4·2H2O) there is still a slight excess of water. Al2Si2O7 + 5 H2O + 2 H3PO4 = 2 AlPO4*2H2O + 2 H4SiO4 I don’t know what to say Karl other than Davidovits made the point quite firmly. 0 porosity. He repeated it for emphasis two or three times. It seemed to be an interesting feature of it that he was highlighting. It’s possible I didn’t get the recipe down right but I did check with a couple of people. The son did the experiments with getting the temperature right. It did seem quite tricky to stuff to use. Lots of blow holes and distortion with the water escaping in the first samples they tried at 80 oC curing. The key seemed to be to allow the water to escape during the gel phase and before the hardening phase thus allowing the stuff to harden without distortion. It’s the new angle that they are now off on since they consider that the alkali based geopolymerisation mechanism to now be understood. The whole field of acid based geoplymerisation is a relatively uncharted territory so I wouldn’t be surprised if things that he said previously get revised. I’m still trying to learn the basic chemistry I got stuck on how Al becomes more than trivalent. Does it nick an electron off Na to use it in an additional covalent bond or is it Van de walls forces or something weird? I’m getting closer to grasping the chemistry but still miles away from being able to make my own formulations like you can. |
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