1. C. Thomas, Promyshlennyie Kataliticheskie Protsesy i Effektivnye Katalizatory, Mir, Moskva, 1973, p. 386.
2. I.P. Muhlenov (Ed.), Tehnologiya Katalizatorov, Himiya, Leningrad, 1989, p. 272.
3. G. Vissokov, Bulgarian Patent 59324 (1983).
4. G. Vissokov, Prilozhna Plasmohimiya, Tehnika, Sofia, 1987, p. 370.
5. G. Vissokov, D.Sc. thesis, Institute of Electronics, Bulgarian Academy of Science, Sofia, 1994, p. 370.