Glass nucleation

Typical DTA curve of the ZAS base glass is shown in Figure 1. The DTA curve is characterized by some endothermic peak. The endothermic peak is very obvious at 746°C, 824.6°C, 963°C and 1024°C, which indicates there exists transformation of crystal configuration. The endothermic peak is not very obvious at 963°C and 1024 and the endothermic base line shift at 650°C 740°C gives the beginning of glass nucleation temperature zone. 

Figure 6. Arrhenius plot for nucleation in temperature range Tg -(1 melt nucleation 2 glass nucleation)...

Samples can be concentrated beyond tire glass transition. If tliis is done quickly enough to prevent crystallization, tliis ultimately leads to a random close-packed stmcture, witli a volume fraction (j) 0.64. Close-packed stmctures, such as fee, have a maximum packing density of (]) p = 0.74. The crystallization kinetics are strongly concentration dependent. The nucleation rate is fastest near tire melting concentration. On increasing concentration, tire nucleation process is arrested. This has been found to occur at tire glass transition [82]. 

The development of the principles of nucleation and growth eady in the twentieth century (2) ultimately led to the discovery that certain nucleating agents can induce a glass to crystallize with a fine-grained, highly uniform microstmcture that offers unique physical properties (3). The first commercial glass-ceramic products were missile nose cones and cookware. 

A typical heat treatment cycle, as illustrated in Figure 1, comprises both nucleation and crystallization temperature holds, but some glass-ceramics are designed to nucleate and/or crystallize during the ramp itself, eliminating the need for multiple holds. 

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