Repeatability number, Deborah number, and critical cooling rates as characteristic parameters of the vitreous state

Glasses may be defined as solid systems characterized by the absence of short time fluidity and having structures characterized by the absence of long range order. This definition is rather vague; nevertheless it expresses that the glasses do show some fluidity (certainly at longer observation times) and that their structures are definitely not completely random. In attempts to describe these features in a more quant. way, it is useful to define 2 parameters, the Repeatability No. and the Deborah No. The former is a parameter giving the degree of order of a given structure in space. The latter is the ratio of the relaxation time of the adaption of the structure to equil. and the time of the measuring expt. (time of observation). By introducing these parameters a better and more clear-cut definition can be given of amorphous solids, glassy or vitreous solids, real, \"nearly\" perfect and perfect crystals. A diagram can be drawn showing the relations between the various states of matter (including amorphous and vitreous states) as a function of the Repeatability No. and the Deborah No. The relation between the Deborah No. and the crit. cooling rate is also discussed. [on SciFinder (R)]