**Acknowledgements**

*Geopolymers and Other Geosynthetics*

K<sup>−</sup><sup>1</sup>

glass phase was proportional to the amount of Na+

could be obtained based on the current results.

process. The introduction of Li<sup>+</sup>

hydration energy of Li<sup>+</sup>

Li<sup>+</sup>

Cs<sup>+</sup>

pollucite grains.

ing products.

temperature, even at room temperature.

ion in the nucleation process of pollucite.

i.The introduction of Li+

for Cs+

increase in content of Na+

by the substitution of Na+

the increasing sodium content.

phase containing Na+

**4. Conclusions**

pollucite (~4.80 × 10<sup>−</sup><sup>6</sup>

substitution. The average CTE of Cs(1-*x*)Na*x*GP ceramics continued to rise with the

presence of the amorphous glass phase was much stronger than the impact caused

glass phase could account for the rise of average CTE. The content of amorphous

In this chapter, the effects of ion substitution on the thermal evolution of cesium-based geopolymers on heating were studied. The following conclusions

Cs(1-*x*)M*x*GPs (*x* ≥ 0.1), respectively. A possible reason could be attributed to the formation of zeolite nucleus, which could serve as the nucleation sites for pollucite. This also provided a novel method for preparing pollucite at low

ii.Cs(1-*x*)M*x*GPs with different content of ionic replacement showed a similar

sintering mechanism through decreased onset temperature for viscous

glass phase in resulting products would be conducive to its densification

is greater than that of Cs<sup>+</sup>

Cs(1-*x*)Na*x*GP ceramics, which had a close relationship with the role of Na<sup>+</sup>

results in the formation of a multiphase system, including pollucite,

ceramic products derived from Cs(1-*x*)Na*x*GPs. Therefore, a small portion

iv.The average CTE of ceramics derived from Cs(1-*x*)Li*x*GPs and Cs(1-*x*)Na*x*GPs showed a completely different variation pattern. The reason could be attributed to the difference between two kinds of substituted ion species, which resulted in different phase composition in the corresponding result-

 crystallographic sites of the pollucite framework, while the rest were mostly present in the amorphous glass phase and distributed among the

of pollucite grain gradually decreased with the increase in Na<sup>+</sup>

iii.Compared with traditional way, geopolymer technology could be an excellent alternative to fabricate ceramics or ceramic matrix composites in an in-situ convert way. In the Cs(1-*x*)Li*x*GP ceramics, the introduction of

of the rapid formation of a liquid phase on heating and perhaps because the

or Na+

thermal evolution process. The introduction of Li<sup>+</sup>

sintering stage. With the introduction of more Li<sup>+</sup>

spodumene, and amorphous glass phase, and Li<sup>+</sup>

spodumene grains. In contrast, two forms of Na<sup>+</sup>

was present in the pollucite grains due to Na<sup>+</sup>

average CTE of ceramics derived from Cs(1-*x*)Na*x*GPs increased almost linearly with

ion always had a higher CTE (9~10 × 10<sup>−</sup><sup>6</sup>

ion introduction. It is well known that amorphous glass

) [53–56]. By contrast, the effect on CTE caused by the

in lattice level. So, the presence of amorphous

could favor the formation of pollucite in

or Na<sup>+</sup>

or Na<sup>+</sup>

ion led to particle coarsening in part because

changed the

. However, the particle size

only existed inside the

occupying/substituting

ions were present in the

contents in

, the amorphous

K<sup>−</sup><sup>1</sup>

ion substitution. Therefore, the

) than that of

**114**

The authors acknowledge the support from the National Natural Science Foundation of China (NSFC, Nos. 51372048, 51502052, 51321061 and 51225203). The grant from Fundamental Research Funds for the Central Universities (Grant no. HITNSRIF20165) is also acknowledged.
