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Low-Density Microcellular Carbon Materials

Published online by Cambridge University Press:  29 November 2013

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The low atomic number, good chemical reistance, and low thermal expansion of carbon foams make them attractive for many specialty applications. In general, we are interested in carbon LDMMs that have a maximum cell size of 25 μm and densities less than 0.05 g/cm3. These requirements are beyond the state of the art for most commercial carbon foams; thus, the DOE National Laboratories have concentrated on producing materials that meet these demanding requirements using various phase-separation, sol-gel, and replication processes.

In all cases, the final carbon foam is derived from a polymer precursor. Most polymers (e.g., polymethyl methacrylate) simply depolymerize and revert to their monomeric form when heated to high temperatures in an inert atmosphere. Cross-linked phenol-formaldehyde and polyfurfuryl alcohol are polymers that leave substantial carbon chars (greater than 50 wt%) after pyrolysis near 1000°C. Polyacrylonitrile also leaves a large carbon char (˜40 wt%)) after partial oxidation at 200°C followed by heat treatment at 1000°C. The latter char is a partially ordered graphite while the former chars are totally amorphous.

The microstructure and properties of carbon LDMMs depend on synthetic procedure and heat treatment conditions. We have been able to make carbon LDMMs with cell sizes as small as 100 Å or with densities as low as 0.015 g/cm3. Furthermore, surface areas of 50–1000 m2/g have been obtained with microstructures ranging from ribbonlike webs to interconnected colloidal-like particles. The ability to control these various parameters presents new opportunities to design carbon LDMMs for high technology applications, examples of which include sensors, electrodes, and high temperature filters.

Type
Technical Feature
Information
MRS Bulletin , Volume 15 , Issue 12 , December 1990 , pp. 37 - 40
Copyright
Copyright © Materials Research Society 1990

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