A novel material, a conducting composite with variable temperature coefficient of electrical conductivity, was prepared in a propagating front of an addition polymerization. Graphite and zinc particles were incorporated into an acrylamide-triethylene glycol dimethacrylate copolymer. Specific electric resistance values of the materials yielded were measured at room temperature and also conductivity measurements were performed in the range of 20-220°C. The basic recipe was modified by doping the conductive composite materials with microscopic-scale-size particles of several inorganic and organic compounds, resulting in significantly different conductivity features of the composite. Scanning electron microscopy was performed to study the morphology of materials yielded. No percolative patterns containing zinc particles were found to support the conductive behavior of the composite. In accordance with to the modifying effect of doping materials we suspect that the acrylamide-triethylene glycol dimethacrylate copolymer plays a specific role in the electric conductivity behavior of the composite material.
ZUSAMMENFASSUNG:Ein neues elektrisch leitfahiges Verbundmaterial mit variablem Temperaturkoeffizient der elektrischen Leitfahigkeit wurde durch eine ,,propagating front"-Copolymerisation von Acrylamid und Triethylenglykoldimethacrylat in Gegenwart von Graphitund Zinkpartikeln hergestellt. Der spezifische elektrische Widerstand der Polymeren wurde bei Raumtemperatur bestimmt; Leitfahigkeitsmessungen wurden zwischen 20 und 220 "C durchgefiihrt. Die Leitfahigkeitseigenschaften der Copolymeren wurden durch Dotierung mit mikroskopischen Teilchen einiger organischer und anorganischer Substanzen modifiziert. Die Morphologie der Composite wurde mit der Rasterelektro-* Correspondence authors. 0 1996 Hiithig & Wepf Verlag, Zug CCC OOO3-3146/96/$07.00 J. Szalay, I. P. Nagy, I. Barkai, M. Zsuga nenmikroskopie untersucht. Dabei wurden keine das Leitfahigkeitsverhalten beeinflussende zinkhaltigen Perkolationsstrukturen gefunden. Es wird vermutet, daB das Acrylamid/Triethylenglykoldimethacrylat-Copolymere eine entscheidende Rolle im elektrischen Leitfahigkeitsverhalten der Verbundmaterialien spielt.
Al 7075 alloy was equal and differential speed rolled according to various deformation routes. In these routes the sheets were rotated around different axes between subsequent passes of rolling. The mechanical properties and the microstructure of the specimens processed by various routes were compared. It was found that while the strength values were irrespective of the rolling routes, the ductility depends strongly on the deformation method. The differences in the mechanical behavior were explained by the edge/screw character in the dislocation structure.
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