Effects of Al2O3 Nanopowder Filler Size on Glassy Polymeric Carbon Electrical Transport Behavior
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1006-R07-09
Effects of Al2O3 Nanopowder Filler Size on Glassy Polymeric Carbon Electrical Transport Behavior Bopha Chhay, Renato Amaral Minamisawa, and Daryush ILA Physics, Center for Irradiation of Materials, Alabama A&M University, PO box 1447, Normal, AL, 35762
ABSTRACT Glassy polymeric carbon (GPC) has a unique graphite micro-fibril structure that attributes singular properties to the material. The addition of nanoparticles in the GPC matrix to improve its properties has been the focus of recent studies for spacecraft coating applications. We report the effects of Al2O3 nanoparticles dispersed in GPC on the electrical properties. The fabrication process to produce homogenous samples and the electrical measurements are fully described. In addition, the chemical structure characterization was evaluated using Raman spectroscopy. INTRODUCTION Glassy polymeric carbon wares, prepared at Alabama A&M University, is a material obtained by heat treating phenolic resin in a slow careful process. They were cured at 50 °C and pyrolyzed up to 1000 °C releasing water, oxygen and hydrogen. At around 1000 °C they transform with no change in shape into a glass-like polymeric form of pure carbon [1, 2]. The long aromatic carbon chains rearranged in a network of micro-fibrils form a tighter mass attributing a good electrical conductivity to GPC. Recently a vast array of technologic applications, especially space research, use nanoparticles dispersed in polymers to improve the material properties and make new materials with higher performances [3]. In this work we have produced GPC composites using 3 sizes of alumina (Al2O3) nanopowders. Bulk Al2O3 is known as being a good thermal and electrical insulator as well as being chemically stable. Our objective was to produce a new nano-composite material by combining GPC and Al2O3, and study the dependence of the electrical behavior of the new materials as a function of the size of the Al2O3 nanopowder chosen. EXPERIMENTAL PROCEDURES We chose 3 sizes of Al2O3 nanopowders as additive material to the GPC precursor. The diameters of the nanoparticles are 50, 300 and 1000 nm. For each size, we prepared samples with 25wt% and 50wt% of Al2O3. The same procedure was followed for the preparation of all the samples. In a beaker, the nanopowder was suspended in ethanol to separate the aggregation that could cause non-homogeneous dispersion inside the polymer. The phenolic resin was then added to the containers, infiltrating the nanoparticles. The solution was mixed slowly and sonicated to eliminate air bubbles generated during mixing, and then poured into an aluminum mold frame of volume of 20.0×20.0×2.0 mm3. By diluting the solution with ethanol, the occurrence of trapped
bubbles on the surface during resin polymerization is reduced. The added nanoparticles may offer surfaces for nucleation of bubbles. At the same time, the ethanol dilution decreases the viscosity and accelerating sedimentation of the Alumina. In order to promote Al2O3 dispersion and to eliminate voids, the aluminum mold, cont
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