In physics, the standard definition of a glass (or vitreous solid) is a solid formed by rapid melt quenching. The term glass is often used to describe any amorphous solid that exhibits a glass transition temperature Tg. If the cooling is sufficiently rapid (relative to the characteristic crystallization time) then crystallization is prevented and instead the disordered atomic configuration of the supercooled liquid is frozen into the solid state at Tg. The tendency for a material to form a glass while quenched is called glass-forming ability. This ability can be predicted by the rigidity theory. Generally, the structure of a glass exists in a metastable state with respect to its crystalline form, although in certain circumstances, for example in atactic polymers, there is no crystalline analogue of the amorphous phase. COUNT 4
QSN1 How is "glass" defined in physics? ANS1 a solid formed by rapid melt quenching QSN2 What is the tendency to make a glass when cooled called? ANS2 glass-forming ability QSN3 What must happen quickly for glass to form? ANS3 cooling QSN4 What predicts glass-forming ability? ANS4 rigidity theory