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Experimental and theoretical study of aluminosilicate gel

A group of inorganic networks, more descriptively named geopolymers are materials on the verge between ceramics and polymers, are commonly produced using reaction of aluminosilicate rich powders such as metakaolin or fly ash type F and sodium metasilicate. Despite geopolymers can be synthesized in a broad compositional range, they typically follow Na2O : Al2O3 : SiO2 = 1 : 1 : 4 stoichiometry. This was also the case for this study where highly reactive commercial metakaolin (HRM) (Metamax, BASF) was used as precursor for preparing of geopolymeric gel, under different curing conditions. This type of metakaolin is advantageous due to its purity and ability to yield geopolymeric gel at room temperature. The experimentally obtained IR spectra of geopolymer gel was compared with quantum chemical calculations for hydrated aluminosilicate structure known as not fully polymerized geopolymer structure. It is presumed that a fully geopolymerized structure does not have terminal – OH groups, i.e. that all Si and Al atoms are bridged by oxygen. Modelling by Gaussian of such complex structure is difficult. Therefore, aluminosilicate structures containing a certain amount of terminal –OH groups were used for theoretical quantum-chemical considerations. Such structures are called hydrated aluminosilicate gels. Quantum chemical calculations of hydrated aluminosilicate gel were obtained in Gaussian 09 using Density Functional Theory (DFT) with B3LYP functional. The aim of this study is to gain deeper knowledge about geopolymerization process via correlating the experimental and theoretical results of the aforementioned aluminosilicate material networks.

DFT ; FTIR ; aluminosilicates ; inorganic polymers

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