Changes in the physicochemical properties of geopolymer gels as a function of NaOH concentration

Abstract

In the present paper, polymerization of alkali activated metakaolin (MK) and its structural changing, using 2M NaOH, 8M NaOH, and 16M NaOH solutions were followed by means of X-ray photoelectron spectroscopy (XPS), Diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), Raman spectroscopy and Scanning electron microscopy (SEM). XPS analysis revealed that changing of NaOH concentration did not affect the types of formed bonds in the material. At the same time, the amount of sodium and aluminum increased with the NaOH molarity. The latter steps could be especially interesting because it may indicate the possibility of 'dosing' the amount of Al incorporated by changing the NaOH concentration in the solution. DRIFT analysis revealed that the absorption band for AlIV located at 800 cm-1 is shifted towards the smaller values. Changing the concentration of NaOH, the chemical content did not change, but the structural changes are observed. Raman spectroscopy detected that the most dominant peaks at ~400 cm-1 and 519 cm-1 originate from Si-O-Al and Si-O-Si bending modes. With increasing the NaOH concentration, peaks at 1019-1060 cm-1 become more prominent as a result of polymerization. Both analyzes (DRIFT and Raman) confirmed the presence of quartz. SEM analysis showed that different structures are created by changing the concentration of NaOH.