SOL-GEL SYNTHESIS OF NANOCRYSTALLINE MAGNESIUM FLUORIDE - ITS USE IN THE PREPARATION OF MGF2 FILMS AND MGF2-SIO2 COMPOSITES

Thin, protective films of nanocrystalline MgF2 were formed by spin-coa ting a sol that contained nanocrystalline MgF2, which was formed by th e action of KF on a sol prepared from methanolic H2O2 and Mg(OCH3)(2). These thin films on Si(100) lost fluoride to form MgO when heated at 550 degrees C. When the films on two such substrates were placed toget her face to face and heated at 550 degrees C, rough, abrasion resistan t MgF2 films were obtained. To form composites, nanocrystalline MgF2 s ols were mixed with silicate sols prepared from the acid catalyzed hyd rolysis and condensation of tetramethyl orthosilicate (TMOS). X-ray di ffraction and TEM analysis of xerogels and films obtained from these b iphasic sols indicated nanocrystals of MgF2 dispersed in an amorphous matrix. On heating, fluoride loss and MgF2 crystal growth were both gr eatly retarded in powders and thin films prepared from silicate-MgF2 s ols.