1. B. Sosnick, U.S. Patent 2434775 (1948).
2. L.A. Cohen, Metal Foams, Space & Military Applications of Plastics System, SPI 12th Annual Conference, section 2-c, 1967, p. 89.
3. G.J. Davies, Shu Zhen, J. Mater. Sci., 18, (1983), 1899
4. Zhenlun Song, Ph.D. Thesis, Southeast University, Nanjing, China, 1998.
5. J.C. Elliott, U.S. Patent 2751289 (1956).