All samples are gray in color and there is a mass of open holes on the
surface as shown in Fig. 2. The XRD patterns of bottom ash and samples
foamed after microwave treatment are given in Fig. 3. The XRD patterns
are quite similar, consisting of quartz,mullite and hematite. From 15° to
40° (2θ), a hump has appeared in the XRD pattern of foams compared to
the bottom ash where no such hump is present. This hump is the indication
of the amorphous phase present in the foamed samples. This
amorphous phase is attributed to the glassy fraction from the bottom
ash plus the silica network formed from sodiumsilicate solution. Another
prominent new phase appeared at around 28° (2θ angle)which is anorthite
and albite, formed by the sodium and calcium alumino-silicates
and is an indication of geopolymerization reaction taken place; as it is
produced during geopolymerization [20,21]. More in particular, it was
difficult to make a doubtless identification of minor crystalline phases
due to high number of broad, small XRD peaks collected in the
measurement.