Internal-Friction Study of High-Purity Single Crystals of n Eicosane (C20H42)

Abstract

Large pure single crystals of n eicosane (C20H42) with [210] growth axes have been prepared by slow crystallizations from the melt. Internal-friction measurements covering temperatures from 100 to 300 K at ≃ 1 kHz reveal that in the as-grown single crystals both the α and γ loss peaks characteristic of polycrystalline n alkanes of less purity are absent, from which we conclude that, in polycrystals, these processes are a result of impurities and/or crystal defects. Two very weak loss maxima of obscure origin were observed at about 270 and 287 K for all the crystals studies. In one single crystal progressive stages of light cold work induced a complex spectrum of small loss maxima between 200 and 300 K. These maxima were found to be highly sensitive to aging. We believe that the observed behavior provides evidence for dislocation motion in crystals of this type. No detectable γ peak resulted from the cold work. Data are also included for one single crystal which was irradiated with γ rays.