Computational Study on the Al3+ Substitution and Porous Agent Effect on Geopolymer Foams Formation

This work explores the replacement of Al3+ by Fe2+ or Fe3+ and the effect of porous agent on geopolymers foam formation, using DFT at the level of theory B3LYP/6-31G+(d, p). The obtained results show values of HOMO-LUMO gaps that are respectively 130.46 ; 93.3 and 14.38 Kcal.mol-1 for [Al(OH)4]-, [Fe(OH)4]- and [Fe(OH)4]2- monomers and; 63.79, 5.65, 155.55 and 36.13 Kcal.mol-1 for oligomers[(OH)2Al–(O–Si(OH)3)2]- , [(OH)2Fe–(O–Si(OH)3)2]- , [Al–(O–Si(OH)3)4]- and Fe–(O–Si(OH)3)4]2-. Calculations using thermodynamics parameter reveals the most favorable porous agent amongst the three (silica fume, aluminum powder and oxygenated water) tested. The results reveal that aluminum powder seems to be the best candidate with the lowest change in G (-190.61 Kcal.mol-1) and S (-82.94 cal/mol.K).