Advances in preparing and characterizing low density PAN-carbon microcellular foam.

摘要

This report documents an improved preparation of low density microcellular carbon as well as characterization of spatial homogeneity. The report also documents the process for preparing the microcellular carbon from poly(acrylonitrile) raw material. A microcellular polymer precursor (0.025 g/cc) is first prepared via a solution-based process and then pyrolyzed to produce the microcellular carbon in a monolithic form (0.05 g/cc). The process improvement developed in this study permits the pore structure of the n-ficrocellular polymer precursor and the microcellular carbon to be reproduced consistently in different laboratories. Pore structure is affected by the completeness of dissolution of the polymer raw material, which variable can be adjusted via dissolution temperature or particle size of the raw material. The second topic in this report involves determining the spatial fluctuation in mass density caused by periodic, millimeter-scale bands, known as 'tree rings' visible on machined surfaces of the carbon monoliths. To measure the fluctuations, we developed a high precision, spatially resolved X-ray transmission technique. The periodic bands caused less than (plus minus)2% variation of mass density in a microcellular carbon having average density 0.041 g/cc.