Fig. 5 shows the comparison of FESEM images of cogon grass before
and after combustion. It can be observed in Fig. 5a that particles of raw
cogon grass are very flaky. After combustion, the particles of silica
obtained became more needle-like. Fig. 6 shows the diffractograms of
ashes obtained from the combustion of cogon grass. Other research
[20,22,24,42] suggested that ashes of cogon grass exhibited featureless
patterns and diffuse peaks centred at approximately 23°, which
corresponded to amorphous silica with some short range primitive
structures. However, sharp peaks are observed in Fig. 6a at 28, 29 and
35° when cogon grass was combusted at 650 °C. These peaks were initially
suspected to be crystalline silica in the formof tridymite. However