Membranes de carbone et de graphite et leurs proprietes

Abstract

A thixotropic gel is formed from water suspensions of graphitic oxide, sodium graphitates or ammonium graphitates. Such gel deposited on a polished surface when all excess salt or acid is eliminated gives after drying a remarkably strong membrane of graphitic oxide or graphitate. Since it was known already that graphitic oxide can form sheets of carbon after reduction by hydriodic acid or hydrazine, it was tried first to reduce the membranes by hydrazine and by hydriodic acid in liquid or gaseous phase. These reduced carbon membranes however are extremely brittle. It was found that membranes of graphitic oxide heated at 500°C in a current of hydrogen produce also membranes essentially of carbon. A study was made of the evolution of such membranes by reheating to various temperatures between 500°C and 1000°C. The characteristics of these membranes such as density, resistivity, magnetoresistance, tensile strength along the plane, crystallographic parameters (interlayer spacing, degree of graphitization and orientation of the graphitic layers) were determined. Membranes of various thicknesses have been prepared. The thinnest permitting a study of the i.r. spectrum were deposited on a grid. They are somewhat translucent to the visible light. The evolution of the structure of the membranes is most remarkable. While for all graphitizable carbons, graphitization begins at about 1600°C and ends at about 3000°C, for such membranes an interlayer spacing of 3.39 Å is found at 1000°C with the (11) band not modulated. One finds thus a turbostratic carbon with an average spacing near that of the graphite. After heating to 2000°C the interlayer spacing decreases to 3.356 A, the order parameter P 1 (= g 2) becoming very high (0.8). One concludes that the absence of interstitial carbon atoms (nonexistent in the original graphite) leads to a spacing for turbostratic layers more nearly equal to that of the perfect graphite and to a graphitic ordering of the layers occurring easily and becoming almost complete at temperatures below 2000°C.