## 3 Results and Discussion
### Basic Glass Differential Thermal Analysis
The Vickers hardness of the microcrystalline glass samples first increased and then decreased with increases in the crystallization time. The Vickers hardness of the microcrystalline glass was maximum (618 HV) after 3 h of crystallization. When the crystallization time was exceedingly long (4 h), the Vickers hardness of the sample decreased to 592 HV. The crystallization time was not sufficient, the crystal precipitation inside the microcrystalline glass was less, and the grain shape was irregular and incompletely developed; thus, the number of pores in the microcrystalline glass increased and the hardness of the glass decreased. With the extension of the crystallization time, the precipitation was more complete, the grain growth was more adequate, and the shape was transformed to spherical and columnar, thereby strengthening the mutual bonding between the grains, considerably reducing the number of pores inside the microcrystalline glass, and increasing the hardness of the microcrystalline glass. However, an excessively long crystallization time caused an abnormal increase in the grain size and the aggregation of the grains into clusters. This weakened the effects of fine crystal strengthening and reduced the hardness of the microcrystalline glass. Figure 16 illustrates the relationship between crystallization time and the acid and alkali resistances of the prepared microcrystalline glass. The alkali resistance of the microcrystalline glass was stronger than its acid resistance, likely because the glass phase is more easily leached in acidic solutions [28]. The acid and alkali resistances of the microcrystalline glass were optimal at 2.36% and 0.04%, respectively, after 3 h of crystallization. When the crystallization time was shorter, the number of crystals of the microcrystalline glass was small and the residual glass phase was dominant; thus, the corrosion resistance of the microcrystalline glass was low. When the crystallization time was extended, the degree of crystallization of the microcrystalline glass was higher, the grain growth was more complete, the crystal structure was denser, and the constituent glass phase was lesser, thereby increasing the acid and alkali resistances of the microcrystalline glass. However, the crystallization time was exceedingly long, so the grains accumulated into clusters, thereby resulting in the destruction of the dense structure between the crystalline phases, the generation of a large number of holes and gaps, and the arrangement of spherical and columnar grains in a network-like structure. The two aforementioned conditions resulted in an increase in the contact range of the microcrystalline glass with the acid and alkali solutions; thus, the acid and alkali resistance of the microcrystalline glass decreased. As displayed in Figure 16, when the crystallization time was extended to 4 h, the acid and alkali resistances of the microcrystalline glass decreased compared with those when the crystallization time was 3 h; the acid and alkali resistances were 0.27% and 0.13%, respectively. Figure 4:7 Effects of crystallization time on the Vickers hardness of the microcrystalline glass.