XRD patterns of the as-synthesized samples are shown Fig. 1. The
broad halo diffraction peaks indicate that the as-synthesized samples
are amorphous in nature.
FTIR spectra of the glass samples are depicted in Fig. 2a. There are
mainly three absorbance bands as labeled by the vertical lines in the figure.
The band at around 1020 cm−1 is assigned to the asymmetrical
stretching vibrations of Si\O\Si bonds in silicon-oxygen tetrahedra
[17]. It significantly shifts to lower wavenumbers with the increase of
ZnO. The band at 780 cm−1 can be assigned to the bending vibrations
of Si\O\Si bonds [18]. From Fig. 2b, it can be seen that this band increases significantly from 225 to 356 kJ/mol. However, E decreases
to 301 kJ/mol when ZnO is further increased to 12.39 mol%.
The thermally treated samples show surface crystallization as most
calcium-aluminosilicate glasses [20–21]. The XRD patterns of the heattreated
samples are presented in Fig. 7. The main crystalline phases
are ferroan wollastonite (Ca2.87Fe0.13(SiO3)3, PDF card No. 83-2198)
and silicon oxide (SiO2, PDF card No. 77-1060). In addition, there is a decreasing
amount of pure wollastonite (CaSiO3, PDF card No.75-1396)
with the increase of ZnO.
Presented in Fig. 8 are the images of the pressed cylinders recorded
during the sintering process. It can be seen that the temperatures at
which the sintered bodies reach 1/3 and 1/2 of the original heights
(taken at 500 °C) decrease from ×0 to ×12. There is a significant difference
of these characteristic temperatures between ×6 and ×9.