1. German Patent, A. Roßmann, DE 2737248, 1977 (sintered or infiltrated structures).
2. French Patent, A. Rousset et al., FR 8707440, 1987 (ordered agglutinated or brazed structures).
3. German Patent, W. Smarsly, W. Track, DE 3902032, 1989 (bonding of spheres by loose powder sintering).
4. Steel and Titanium Hollow Sphere Foams
5. European Patent, M. Jaeckel, H. Smigilski, DE 3724156, 1988 (coating of polymeric spheres with particles).