Measured densities of films, consisting of only stereo‐complex (sc) crystals of poly(l‐lactic acid) (PLLA) and poly(d‐lactic acid) (PDLA), are sometimes significantly higher than the density of the sc‐crystal calculated on the basis of the previously proposed triclinic and trigonal unit cells. In this work, we reexamined the crystal density and determined the heat of fusion for the sc‐crystal. Twenty wide‐angle X‐ray reflections from a highly oriented sc‐film could be well indexed on the basis of a trigonal unit cell previously proposed by Cartier et al. The refined parameters of the trigonal cell are a = b = 1.50 nm, c = 0.823 nm, α = β = 90°, and γ = 120°. The c‐axis determined from the WAXD fiber pattern was significantly shorter than those (0.87–0.93 nm) previously reported. The crystal density of the modified cell was 1.342 ± 0.002 g/cm3, which was significantly higher than those previously reported (1.21–1.27 g/cm3). The heat of fusion for the sc‐crystal, extrapolated from the linear increase in the observed heat of fusion with decreasing the specific volume for the samples consisting of only sc‐crystals, was 155 ± 5 J/g. This value was significantly higher than those of α‐form and β‐form homo‐crystals of PLLA suggesting stronger interactions between the 32 helices of PLLA and 31 helices of PDLA in the sc‐crystal. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2632–2639, 2007

No abstract

It was previously found that two B2 phases (matrix and precipitates) appeared in Ti-32mol%Au-18mol%Co superelastic alloy. In this study, each B2 single phase alloy was tried to be fabricated individually, and phase constitution, crystal structures and hardness were investigated. The chemical compositions were Ti60-xAu40Cox and Ti34-xAu44Co22+x (x=0, 2 and 4), and the alloys were fabricated by Ar-arc melting followed by a hot-forging at 1423K for 43.2ks and a solution treatment at 1173K for 3.6ks. It was found by X-ray diffraction analysis that Ti60-xAu40Cox (called Co-poor alloys) were composed of B19 (Ti, Co)Au and A15 Ti3Au two phases, instead of B2 single phase expected. It was also found that Ti34-xAu44Co22+x (called Co-rich alloys) were composed of C11b Ti(Au,Co)2 and C36 Co2(Ti,Au) two phases, instead of B2 single phase expected. These unexpected phase constitutions appeared in this work may be due to the difference in cooling rate and/or phase transformation from B2 to C11b. Lattice parameters of the obtained phases were precisely determined. The hardness of C11b Ti(Au,Co)2 and C36 Co2(Ti,Au) are HV480 and HV780, respectively. The hardness change of Co-rich alloys can be understood in terms of the volume fraction change of these phases.