Percolation transition and conductivity in macroscopically anisotropic two-component polymer membranes

Percolation conductance has been studied for polypropylene/poly(acrylic acid) membranes (PP-g-PAA) prepared by volume grafting of an ionic component onto polypropylene foil. In these membranes the volume fraction of the conducting phase decreases from the surface to the center, brining some anisotropy into the composition. For this material, the “insulator- to-conductor” transition proceeds at a critical volume fraction V_c equal to 0.395. It has been proved that this critical volume fraction and the critical exponent t, found to be below that predicted by theory, i.e., 1.2 ± 0.03 instead of 1.6 ± 0.2, result from the gradient in the distribution of the conducting component in the direction of the current flow. Computations of V_c and t for the same PP-g-PAA copolymer with a randomly distributed conducting component have led to V_c = 0.08 and t^* = 1.53. A critical exponent t in that range is characteristic of three-dimensional systems; however, V_c is rather low, suggesting a nonspherical shape for the conducting domains.     

Analysis of stress and strain fields in upset forged forgings

Theoretical investigation of influence of degree of deformation, slenderness ratio of a billet and shape of anvils upon distribution of stress and strain in upset forged material are presented in this paper. The deformation of a material was determined by the variational method and the stress field was determined from equations of equilibrium. Results of calculations indicate that formation of tensile stress in layers of a material at the free surface is connected with surface convexity. Factors which cause the increase of barrelling are also responsible for an increase of tensile stresses at the free surface of upset forged material.     

X-ray characterization of SnTe: Gd crystal

Electron probe microanalyses were performed on SnTe crystal grown by the Bridgman method doped with 1.8 wt% Gd. Scanning electron microscopic observations and electron probe microanalysis carried out on the (110) and (100) oriented samples revealed two types of precipitate enriched in gadolinium. It was suggested that the dominant type contained a mixture of Gd₄Te₇ phase and Te_0.8Gd_0.2 eutectic. The composition of the second precipitate type was found to be a eutectic enriched with gadolinium.