Addition of Ammonium Molybdate in Geopolymer Formulation

Abstract

Geopolymers are inorganic materials obtained by the alkaline activation of aluminosilicate sources. The ammonium molybdate could be used as a complexant for silica in order to complex the siliceous species in the alkaline solution. According to this, the aim of this work is to control the siliceous species and to understand the role of ammonium molybdate as a complexing agent acting on the formation of the different networks. To do this, additions of ammonium molybdate (up to 0.32% molar) in the silicate solution were realized along the formulation of geopolymer using two metakaolins. The results highlight that the addition of ammonium molybdate in geopolymer results in a decrease of the shrinkage at high temperature. Moreover, X-ray diffraction data and SEM after calcination show that geopolymers without ammonium molybdate form two phases (KAlSi2O6 and KAlSiO4) while with additions of molybdate, there were only the phase KAlSi2O6 associated with Al2O3 doped Mo and K2Mo2O7. Finally, SEM observations show that additions of ammonium molybdate seem to favor crystallization. The results allow to evidence the role of molybdate in the control of the polycondensation reaction in order to influence the formation of specific network