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Keramický zpravodaj 27 (2) (2011)
(M
2
O)(SiO
2
)
S
(H
2
O)
X
+ (Al
2
O
3
)(SiO
2
)
2
(H
2
O)
0.05
–
(M
2
O)(Al
2
O
3
)(SiO
2
)
Y
(H
2
O)
Z
(1)
Geopolymerisation is a reaction that occurs at temperatu-
res of the environment up to max. 100 °C. At such tempe-
rature a solution of alkali silicate ((M
2
O)(SiO
2
)
S
(H
2
O)
X
)
reacts with thermally activated clay or fly ash, e.g. metaka-
oline - (Al
2
O
3
)(SiO
2
)
2
(H
2
O)
0.05
. When metakaoline is used,
the reaction stoichiometry complies with the following
equation (1), where M=Na or K, s= SiO
2
/ R
2
O, X is an unk-
nown amount of water bound in the silicate solution,
Y=SiO
2
,
total
/Al
2
O
3
= (2 + S), Z is water bound in aluminosi-
licate (if S = 1,4, then Z=0,4) [2].
The reaction provides three geopolymer modifications:
poly(sialate) (Si-O-Al-O), poly(sialate-siloxo) (Si-O-Al-O-Si-O)
and poly(sialate-disiloxo) (Si-O-Al-O-Si-O-Si-O). The basic
structures of these modifications are given in
Fig. 1.
Fig. 1
Structures of poly(sialate), poly(sialate-siloxo) and poly(sialate-disiloxo)
The typical creation of a geopolymeric limestone block
according to Davidovits [3] [4] can be described by these
two basic equations:
Si
5
O
5
,Al
2
(OH)
4
+ 2NaOH _ Na
2
O.2SiO
2
.Al
2
O
3
.nH
2
O (2)
Na
2
CO
3
+ Ca(OH)
2
_ 2NaOH + CaCO
3
(3)
In the course of geosynthesis, sodium hydroxide reacts
with kaolinite resulting in the creation of hydroxysodalite
(2). Sodium hydroxide (caustic soda) important for the
geosynthesis, is prepared by the caustification of sodium
carbonate (natron) with slaked lime. Because the resulting
mixture would be caustic, carnallite is added as a neutrali-
sing agent. These mineral forms a part of evaporites.
According to equation (4), carnallite reacts with hydroxy-
sodalite, which results in the creation of halite and mica-
chlorine.
Na
2
O.2SiO
2
.Al
2
O
3
.nH
2
O + MgCl
2
_
2NaCl + MgO.2SiO
2
.Al
2
O
3
.nH
2
O
(4)
A side reaction of sodium carbonate (natron) with carnalli-
te produces halite and magnesite:
Na
2
CO
3
+ MgCl
2
_ MgCO
3
+ 2NaCl
(5)
Equations (4) and (5) explain the higher content of halite
in the studied samples. Calcite can further react with
magnesite and form the dolomite (4).
ANALYSES OF THE LIMESTONE FROM PYRAMIDS
In the 1980’s, Prof. Davidovits obtained two samples from
blocks from pyramids from Egyptologist J.-P. Lauer. One
was from Khufu’s Pyramid (from the Ascending Corridor),
the other was from the external casing of the Pyramid of
Teti. The so-called Lauer samples were submitted to
a number of physical and chemical analyses which had at
any rate to prove that the building blocks are made of
a geopolymeric limestone.
Davidovits [5] carried out an X-ray diffraction study of the
sample. The X-ray patterns of the Lauer sample from Khu-
fu’s Pyramid showed calcite as the dominant mineral, then
dolomite as well as the presence of quartz. Some diffracti-
on lines were assigned to hydroxylapatite, which was con-
sidered as a proof of a man-made limestone agglomerati-
on. According to Davidovits, the samples from adjacent
quarries contained practically pure calcite with approx.
0.5-2 % of quartz, and no hydroxylapatite was identified
in them. Nevertheless, Jana [6] presented the problem of
hydroxylapatite in the samples in a different way. From the
ancient era, hydroxylapatite had been used in a mixture of
Temperature
low
high
Water
low
Geopolymer
Geopolymer or zeolite
Content
high
Aluminosilicate gel
Zeolite
Tab. 1
Products of geopolymerisation at various temperatures and water contents [1]