Type Superstructure Research Articles

Superstructure of high density polyethylene film crystallized from stressed polymer melts as observed by small-angle light scattering

The crystalline superstructure of high density polyethylene films prepared by a calender manufacturing method was investigated by means of polarizing light micrographs and light scattering patterns. Results show that optically anisotropic rod-like units exist which orient at preferential angles +α 0 and −α 0 with respect to the machine direction to form a network type superstructure. The rod-like unit is considered to be a row-nucleated cylindrite or a parallel assembly of them. The angle α 0 is associated with a preferred orientation of axes of the cylindrites with respect to the machine direction, and found to be dependent upon manufacturing condition. Existence of such a super-structure was shown to be important in accounting for whitening of the specimens on stretching along the machine direction and for deformation behaviour of the specimens.

Phenomene portevin-le-chatelier dans les alliages Fe-Co ordonnes et desordonnes

For temperatures below 730°C, Fe-Co-2V (Fe 49%-Co 49%-V 2%) has a B 2 type superstructure. By water-quenching, it is possible to vary the degree of the long-range order between 0 and 0.92. In the course of hot tension tests, serrations typical of the Portevin-le-Châtelier effect are observed. For stress rates between 10 −6 and 2 × 10 −4 sec −1, the temperatures are determined at which kinks appear and disappear for different degrees of order. The activation energy of the phenomenon which controls the appearance of the serrations is comparable to vacancy migration energy, while the energy which governs the disappearance of the phenomenon is similar to self-diffusion energy. This study allows us to deduce the variations in migration and vacancy-formation energies as a function of the degree of order; thus, we have been able to verify the parabolic nature of these variations and to confirm Girifalco's results: E m ( S) = E m (0) + AS 2 E f ( S) = E f (0) + aS 2 On the other hand, the experimental values of A and a are a great deal higher than the theory envisaged.

The Intensity of Satellite Reflections in Electron Diffraction Patterns from Evaporated Alloy Films with CuAu II Type Superstructure

In order to elucidate the origin of satellite reflections flanking the direct spot in the electron diffraction pattern of a single crystal evaporated film with CuAu II type superlattice. the peak as well as integrated intensities have been measured as functions of the wavelength of electrons corresponding to the accelerating voltage from 75 to 280 KV. It has been revealed that the intensity of the satellite in question relative to a fundamental reflection consists of two parts, a major part which depends on the wavelength in such a way as predicted by the theory of multiple reflection, and the other minor part which is independent of the wavelength. The existence of the latter part shows that the reflection is not a forbidden one and, therefore, a lattice mcdulation accompanies the regular anti-phase structure. Fourier potential due to this lattice mcdulation, V s , is estimated to be in the order of one tenth the magnitude of V 400 . Some consideration concerning the nature of the modulation is given by ...