Development of the Glassy State of Benzophenone and Effect of Heating Rate from the Glassy State on Solidification

ABSTRACTBenzophenone supercools to a glass when cooled to −100°C. In fact, it is difficult to freeze benzophenone on cooling. In this investigation, the effect of cooling rate and the minimum cooling rate to obtain benzophenone as a glass is determined. From the glassy state, the influence of heating rate on the solidification temperature of benzophenone is determined. When heated at 3°C/min., solidification starts at about −29°C. Upon additional heating, melting usually starts at about +24°C, which is 23°C lower than the solid equilibrium structure melting temperature of 47°C. Occasionally the solid that forms at about −29°C undergoes a solid state phase transformation at about +22°C, when heated at 3°C/min. If this solid state phase transformation occurs, then the solid benzophenone starts to melt at 47°C. When solid benzophenone with the equilibrium structure is cooled to −100°C, no solid state phase transformation occurs. It appears that the structure that solidifies at −29°C is metastable.