Hardness of polymeric glasses in the T_G region: a-Se

Abstract

The Vickers hardness number Hv of a typical glassy inorganic polymer, a-Se, is studied as a function of temperature with the heating rate varied as a parameter from 0.032 to 3 °C/min, over two decades. It is shown that Hv(T), as a function of temperature, goes through a sharp drop in the glass transformation region following the similar drop for the shear modulus G(T) reported previously. By defining an empirical glass transition temperature TG at the inflection point of Hv vs T behavior, the heating rate dependence of TG is examined and interpreted via the kinetic structural relaxation model of glass transformation. It is shown that over the temperature range 36–50 °C the rate of structural relaxation processes controlling the mechanical properties obeys an Arrhenius type of temperature dependence with an activation energy ∼2.75 cV/atom. Furthermore, over the temperature range accessed, the structural relaxation rate seems to follow the viscosity-temperature behavior.

Thermal characterization of Ge–As–Se glasses by differential scanning calorimetry

“…4. It should be emphasized that DH is an apparent activation energy which normally depends on the thermal history and is generally smaller than the ''true'' glass transition activation energy obtained from cooling scans [16]. (The apparent activation energy depends on the product of partition parameter x and the actual activation energy as observed in cooling scans).…”

Hardnesses of poly(vinylidene) fluoride and polyamide in high-pressure gas ambience

“…An exponential-type decay of the plastic component of the hardness, with increasing temperature, has been empirically established for the microhardness behaviour of various semicrystalline and glassy polymers (Kasap et al 1988, Ania et al 1989, Balta Calleja et al 1992) An exponential-type decay of the plastic component of the hardness, with increasing temperature, has been empirically established for the microhardness behaviour of various semicrystalline and glassy polymers (Kasap et al 1988, Ania et al 1989, Balta Calleja et al 1992)…”

Critical analysis of endo-thermal effect in the glass transition process in chalcogenide glasses

“…Hence, E g values determined from this relation must be viewed as apparent activation energy. Some attempts have also been made to evaluate E g using Kissinger's relation [8][9][10][11][12][13]. Since E g evaluated from this relation has less dependence on thermal history [9], this method seems to have some extra advantage.…”

“…Some attempts have also been made to evaluate E g using Kissinger's relation [8][9][10][11][12][13]. Since E g evaluated from this relation has less dependence on thermal history [9], this method seems to have some extra advantage. Since this method is basically given for amorphous to crystalline transformation, the validity of its use for glass transition kinetics has always been questionable.…”