Research On The Condensation Mechanisms Of Geopolymers Based On Density Functional Theory

Worldwide research interests have focused on geopolymer due to its high performance and potentially important applications. However, up to date most of study is about where and how the geopolymer can be used. Seldom research focuses on the formation mechanisms. In this study, Density Functional Theory (DFT) is applied to investigate the condensation mechanisms. During dissolution and hydrolysis stages of raw materials in activator solutions, a huge amount of [Al(OH)₄]^–, [SiO₂(OH)₂]^2– and [SiO(OH)₃]^– species are generated. Five reaction processes are theoretically confirmed. The structure of initial, transition and final reactant species are optimized. During the configuration of initial and final states, the species are associated with hydrogen bonds.The computation is implemented using the DMOL³ package built in MS4.2 software. Structural optimization of ground state, initial and final states is conducted by analysing optimal structures, followed by energy computation. For the optimization of transition state, the structural optimization is conducted again after energy computation using the Generalized Gradient Approximation based on DFT. BLYP functional combination is used as its high precision in computing bond length, angle and energy.It is found that, during the condensation process of geopolymer, the transition state of the reaction between [SiO₂(OH)₂]^2– and the reaction from [SiO₂(OH)₂]^2– with [SiO(OH)₃]^– can not generated. But the reactions between 2[SiO(OH)₃]^–, [SiO₂(OH)₂]^2– and [Al(OH)₄]^–, [SiO(OH)₃]^– and [Al(OH)₄]^– can occur. Moreover, the reactions with [Al(OH)₄]^– species are kinetically preferred. Accordingly, aluminium species is the main factor governing condensation time of geopolymer.