Silica powders of respirable size: the effect of methods of comminution and pretreatment on electrophoretic mobility in solutions of varying ionic strength, acidity and metal-ion content

Abstract

Summary o 1. An electrophoretic cell has been designed that is relatively robust and easily constructed and has good optical properties. 2. The cell has been used to study the electrophoretic mobilities of quartz, tridymite, cristobalite and vitreous silica powders in saline solutions of various acidities and ionic strengths. Increases of the pH value of the solutions led to increases in negative charge, as expected from surfaces covered with silanol groups. Decreases in ionic strengh resulted in higher mobilities, as expected from double-layer theory. Differences between the polymorphic forms were seen only at low ionic strengths. 3. Etching of the silica surfaces with alkali, hydrofluoric acid or other mineral acids gave powders with lower mobilities. This effect could be reversed by treatment with boilding water provided the powders had not proviously been dried at 105°C. Dry-ground powders had increased mobilities that could not be lowered even with boiling water. These findings may be related to variations in the biological properties of silica powders exposed to different pretreatments intended to clean or sterilize them. 4. The interaction of the silica surfaces with various metal ions was studied. and the metal-ion concentration required for charge-reversal was measured. No significant differences between the polymorphic forms were observed.