Sodium Silicate Free Geopolymer As Coating Material: Adhesion To Steel

Geopolymer is a green and sustainable material synthesized by alkali activation of raw aluminosilicate rich materials. In this study class F-fly ash based sodium silicate free geopolymers were synthesized and used for coating application at 60OC. Setting time and adhesion strength analysis was performed using Vicat needle and Elcometer 108 according to ASTM C 807-08 and D 4541 respectively. Adhesion strength was found to enhance with increase in Na/Al ratio from 0.6 to 1.0 whereas no further increase was found for further increase in Na/Al molar ratio. A maximum of 3.8 MPa adhesion strength was produced by geopolymer with Na/Al=1 and water/solid = 0.33. Final setting time shown variation with varying Na/Al and water/solid ratios. It was found that geopolymers gained maximum strength within first 3 days and only partial changes has been noted in terms of adhesion strength in some samples. Infra Red spectroscopy was used as tool to understand the degree of geopolymerisation by observing the vibration frequency of -Si-O-T bonds around 1000 cm-1. X-ray fluorescence (XRF) was used to determine composition of Fly ash, whereas x-rays diffractometery (XRD) and scanning electron microscopy of the final product revealed the formation of geopolymer occurred without addition of sodium silicate. It can be concluded that sodium silicate free geopolymer has the potential to be used as a sustainable and green coating material for metals protection.