1. Marsh, D. M., J. Sci. Inst., 38, 229 (1961).
2. Jones, B. F., and Peggs, I. D., J. Nucl. Mater., 40, 1591 (1971).
3. Johnson, J. W., Appl. Polym. Symp., 9, 229 (1969).
4. Allen, S., Cooper, G. A., and Mayer, R. M., Nature, 224, 684 (1969).
5. Allen, S., Cooper, G. A., and Mayer, R. M., Third Intern. Conf. on Industrial Carbon and Graphite (Society of Chemical industry, London, 1970).