Microscopic Investigation of Geopolymers Made of Fused Slag from Gasification Processes Using Low-Grade Coal and Spent Catalyst Slag

Abstract

Geopolymers are prospective cement substitutes because their production generates smaller amounts of carbon dioxide and they have sufficient mechanical strength. Geopolymers have attracted increasing interest from construction industries because of their recyclability and eco-friendliness. The compressive strength of geopolymers is known to be associated with their Si/Al ratio. Fused slag from gasification processes using low-grade coal (FSLC) and spent catalyst slag (SCS) were used as raw materials for making geopolymers; the Si/Al ratio was controlled by mixing different ratios of FSLC and SCS. The compressive strength of a geopolymer with a Si/Al ratio of 1.04 had the highest strength (125.6 MPa). Scanning electron microscopy (SEM) analysis was also in good agreement with the compressive strength measurements of compressive strength. There were many small crystallites in the geopolymer matrix. Using transmission electron microscopy (TEM), these crystallites were found to be single crystals, which have a perfect crystal structure. It is speculated that the formation of small crystallites 10-30 nm in size, as well as large single crystals with diameters greater than 80 nm, in the matrix of a geopolymer during the geopolymerization process might increase its compressive strength.