Fragility of Na-PSS geopolymer

Palomo calcined the kaolinite at 750°C for 24h.
Don’t you think that this time can diminuish the viability of the geopolymer in large scale?
Do you think that Palomo has really synthesized a geopolymer one? He did exactly what you say in your patents (US 4,349,386) will not work, namely: invert the addition of the reagents. He puts the NaOH over metakaolim and after he put the alkaline silicate. Would be synthesized a hydroxysodalite or a zeolite type A?
We tried to make a geopolymer like Palomo and we noted that the material formed was so fragile and with low mechanical properties. What do you think about it?
We tried to make a geopolymer type NaPSS following your patent 4,349,386 and we observed that it is also fragile. The poly-condensation and cure with microwave was not so good, because the geopolymer did not dried even after 2 days at ambient temperature.
Do you think that the presence of iron (Fe) in the Kaolinite can damage the characteristics of geopolymer? Normally the presence of iron reduce the thermal stability.
Valeria Figueiredo Felisbino Barbosa, Instituto Militar de Engenharia,DE/4, Rio de Janeiro, Brazil

Concerning Palomo’s method, you’ll find the right answer in the text of US 4,349,386. One obtains a mixture of Hydroxysodalite and silicate. In order to obtain a good geopolymeric material with high mechanical strength, you must exactly follow the method described in the patents. Example 1 of US 4,349,386 describes the poly-condensation yielding a “white and porous” product. Do not stop to this Example 1 but go rather to Example 2, by adding mineral fillers. Go also to the Examples of US 4,472,199. In this patent you will read in column 7, lines 20-25: “The product obtained had many cracks in it. If at least one mineral filler is added to the reactant mixture after, during or before aging, these cracks disappear. The mechanical and physical properties of the molded objects obtained following this process are

Another tip: a good and very cheap mold is provided by plastic water bottle, plastic coffee cup or any plastic cup. Select a plastic which withstands the exothermic heat of reaction. If you work at 80°C, the thermosetting temperature will easily reach 115°C.

Iron Fe2O3 is a good filler. It does not interfere with the geopolymeric condensation. It will simply lower the softening point. Why? Read PHASE DIAGRAMS FOR CERAMISTS published by the American Ceramic Society. Fe2O3 is inducing Eutectikum point which have been studied, for example: Fe2O3-Al2O3-CaO-SiO2, diagrams nr. 943-953, Fe2O3-Al2O3-Na2O-SiO2, diagrams nr. 2632-2639

Prof. Joseph Davidovits