Surface chemistry and cytotoxic properties of silica

Aluminium inhibits the harmful effect of quartz on the lungs. Current interest in such protective phenomena has lead us to consider a possible method of bonding aluminium to the crystal lattice, and to see if other atoms might have the same effect. A study of the structure of natural and artificial alumino-silicic compounds shows a surface state specific to quartz, namely the existence of vacancies in the three-dimensional SiO4 tetrahedral structure. Aluminium is a known inhibitor of the cytotoxic action of quartz, and can replace the missing silicon atoms in the crystal lattice. The result is the generation of finite numbers of heat-resistant acid sites. Thus it is not a question of a simple zeolite surface layer, but of the substitution of aluminium atoms for silicon atoms in the remaining crystal lattice. It can be shown that other atoms, such as sulphur and specially phosphorus, are capable of behaving in the same way as aluminium. There is reason to believe that the cytotoxic properties of quartz may be related to the crystal capturing atoms from the cell membrane. The large number of thermally stable acid sites detected after contact with alumina would then be a factor for assessing the cytotoxic properties of the various forms of quartz.