Geopolymer analogs of high-temperature minerals

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Pyroxene are a group of high temperature minerals with melting points around 1370°C/2500°F

Pyroxenes have the general formula XY(Si,Al)2O6.
X represents mainly alkali metal or alkaline earth metal.
Y represents mainly aluminium, iron or chromium and sometimes an alkaline earth metal.
en.wikipedia.org/wiki/Pyroxene

Despide its obvious chemical similarity Leucite K[AlSi2O6] , melting point above 1600°C/2900°F
is not considered to be a Pyroxene.

Pollucite (Cs,Na)2Al2Si4O12·2H2O bears some similarity to pyroxene too.
The pollucite phase CsAlSi2O6 is the most refractory silicate: Melting point above 1900°C/3452°F.


2 Mol Leucite (KAlSi2O6, melting point 1686°C)
could be theoretically synthesized from
1 Mol Potassium aluminate (K2Al2O4, 196.15741g
and
4 mol silicon dioxide (SiO2, 240.33756g)


1 Mol Albite (NaAlSi3O8, 1360°C)
could be theoretically synthesized from
1 Mol Sodium aluminate NaAlO2
and
3 mol silicon dioxide

Leucite K[AlSi2O6]:
Al Aluminum 1 Mol 12.36282 %
K Potassium 1 Mol 17.91467 %
O Oxygen 6 Mol 43.98519 %
Si Silicon 2 Mol 25.73732 %

Roughly
Al2O3 1 Mol, Molar mass (g/mol): 101.96136 ~ 22,4 %
KOH 2 Mol, Molar mass (g/mol): 56.10569 ~ 24.7 %
SiO2 4 Mol, Molar mass (g/mol): 60.08439 ~ 52,9 %
Total weight: ~ 454,5g



Orthoclase K[AlSi3O8]:
Al Aluminum 1 Mol 9.694017 %
K Potassium 1 Mol 14.04737 %
O Oxygen 8 Mol 45.98663 %
Si Silicon 3 Mol 30.27199 %

Roughly
Al2O3 1 Mol ~ 17.7 %
KOH 2 Mol ~ 19.5 %
SiO2 6 Mol ~ 62,7 %
Total weight: ~ 574,65 g



Jadeite Na[AlSi2O6]:
Al Aluminum 1 Mol 13.34802 %
Na Sodium 1 Mol 11.37325 %
O Oxygen 6 Mol 47.49039 %
Si Silicon 2 Mol 27.78834 %

Roughly
Al2O3 1 Mol, Molar mass (g/mol): 101.96136 ~ 24,2 %
NaOH 2 Mol, Molar mass (g/mol): 39.99715 ~ 18.9 %
SiO2 4 Mol, Molar mass (g/mol): 60.08439 ~ 56.9 %
Total weight: ~ 422,3g



Albite Na[AlSi3O8]:
Al Aluminum 1 Mol 10.28953 %
Na Sodium 1 Mol 8.767248 %
O Oxygen 8 Mol 48.81161 %
Si Silicon 3 Mol 32.13161 %

Roughly
Al2O3 1 Mol ~ 18,4 %
NaOH 2 Mol, Molar mass (g/mol): 39.99715 ~14,4 %
SiO2 6 Mol ~ 65,2 %
Total weight: ~ 552,7 g


About 1.4 times by mass more potassium is required than sodium, which makes potassium geopolymers even more expensive.
Pyroxene melting points around 1370°C/2500°F should be sufficient

Aside of ready aluminates the above mixtures are all extremely hostile.
Nevertheless aluminates are dangerous too.

Ca-Pyroxene analogs could be made more userfriendly and cheaper than potassium or sodium geopolymers.

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A sodium geopolymer composition found to cure and harden well:
www.researchgate.net/profile/Kenneth_Mackenzie3/publication/222563102_Thermal_behaviour_of_inorganic_geopolymers_and_composites_derived_from_sodium_polysialate/links/09e4150fde7ef7f40f000000.pdf?origin=publication_detail

This formulation is defined by the compositional ratios:

SiO2/Al2O3 3.3
Na2O/SiO2 0:25
H2O/Na2O 10

Al2O3 1 Mol ~ 101.96 g ~ 27.84%
SiO2 3.3 Mol ~ 3.3 x 60.08g ~ 198.3g ~ 54.14 %
NaOH 1.65 Mol ~ 0.5 x 3.3 x 39.99 ~ 65.98g ~ 18.02%
Total mass : 366.24 g

Water 1.65 x 5 ~ 8.25 Mol ~ 148.5g ~ 40.5 % of dry mass.

By weight that is close to the jadeite formula,
but with some excess alumina.


Same ratios with potassium:

Al2O3 1 Mol ~ 101.96 g ~ 25.96 %
SiO2 3.3 Mol ~ 3.3 x 60.08g ~ 198.3g ~ 50.48 %
KOH 1.65 Mol ~ 0.5 x 3.3 x 56.1 ~ 92.56g ~ 23.56 %
Total mass : 392.82 g

Water 1.65 x 5 ~ 8.25 Mol ~ 148.5g ~ 37.8 % of dry mass.

By weight that is close to the leucite formula,
but with some excess alumina.

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Anorthite CaAl2Si2O8 / CaO Al2O3 2(SiO2) Melting point 1550°C / 2822°F

CaO 1 Mol Molar mass (g/mol): 56.0778 ~ 20.16 %
Al2O3 1 Mol Molar mass (g/mol): 101.96136 ~ 36,65 %
SiO2 2 Mol Molar mass (g/mol): 60.08439 ~ 43.19 %
Total mass: 278.2080 g

CaOH 1 Mol Molar mass (g/mol): 57.0858 ~ 20.44 %
Al2O3 1 Mol Molar mass (g/mol): 101.96136 ~ 36,52 %
SiO2 2 Mol Molar mass (g/mol): 60.08439 ~ 43.04 %
Total mass: 279.2080 g


A mixture of the anorthite and leucite formulas could be used to make
a geopolymer more temperature resistant than a sodium geopolymer,
but at a competitive / comparable price.

Likely it would be best to prepare the anorthite / leucite formulas separately
and mix them once they start geling.

Slaked lime, at least one year old, has particularly fine particles.

The anorthite and leucite formulas could also be applied on calcium rich fly ash,
though the iron in the fly ash will likely reduce the melting point.

Note:
I do not recommend the formulas in this thread for the general public.
The formulas are provided for people who are aware of the possible dangers
and want to work at the cutting edge.