## 4 Discussion  
Density and shrinkage of the zinc silicate glass and glass-ceramics were investigated to observe the physical changes that occurred when the sintering process was carried out. From Figure 1, the density increased from 2.9118 to 3.4138 g/cm\({}^{3}\) as the sintering temperature increased, suggesting a rapid densification. The observation of this densification occurred due to the structure compactness and enhancement of the crystallization phase as the sintering temperature increased. When the structure of the sample became compact, the sample's shrinkage became clear; this can be observed from Figure 1, where the shrinkage increased from 0% to 7.5%. Apart from that, at a higher temperature, the microstructure and grain size of the sample increased to obtain a denser packing. Consequently, this will lead to the decrement of the total fractional porosity; hence, causing the density to increase. Besides, as the heat was subjected to the sample, it applied pressure on the sample. When pressure was applied, it resulted in a decrease in the volume of the sample. Volume is subjected to be inversely proportional to the density of a material. The lower the volume, the higher the density. In conclusion, the higher the sintering temperature, the higher the density and linear shrinkage of the zinc silicate glass and glass-ceramics. By looking at the diffraction peaks in Figure 2, it can be observed that, as the sintering temperature increases, the intensity of the XRD peak also increases. The effect of sintering has improved the crystallinity of the zinc silicate [15]. Besides, with the progression of the sintering temperature, the diffraction peaks of the zinc silicate glass-ceramics become sharper and the full width at half maxima (FWHM) is decreased. In the XRD analysis, generally the smaller the crystallite sizes, the broader the peaks; in turn, the larger the crystallite sizes, the sharper the peaks [11; 12; 15]. This is because at a higher sintering temperature, the diffusion of the ions increased, hence making the crystal growth of the sample accelerated, resulting in a larger crystal being produced [12]. This supports the result that was obtained, where it can be observed that the diffraction peak becomes sharper as the sintering temperature increased. The formation of zinc silicate glass and glass-ceramics was further confirmed by using the FESEM and FTIR analysis. In order to determine the size of the crystal, the type of crystal, and the surface morphology of the zinc silicate glass and glass-ceramics samples, the FESEM analysis was done. From our observations, at the lower temperatures of 27 \({}^{\circ}\)C and 700 \({}^{\circ}\)C there were no grain growth, showing a clear glassy surface that tallies with the XRD result where at 27 \({}^{\circ}\)C and 700 \({}^{\circ}\)C the sample was still in an amorphous phase [16]. Meanwhile, as the sintering temperature increased to 750 \({}^{\circ}\)C and 800 \({}^{\circ}\)C, the microstructure of the sample still did not show a regular shape (irregular) and started to aggregate among each other. The formation of crystal growth on the surface of the zinc silicate glass and glass-ceramics proved that at 750 \({}^{\circ}\)C and 800 \({}^{\circ}\)C, the crystallization started to occur as in the XRD result. Then, after further sintering, the glass-ceramics appeared to have a greater grain size, indicating an increase in crystallinity. At the highest temperature, the glass-ceramics become densely packed, with strong necking between each other. Other than that, by carrying out FTIR analysis, the functional groups of the respective zinc silicate glass and glass-ceramics that could appear in the corresponding materials can be obtained.