Silica powders of respirable size. II. Dissolution rates in dilute hydrofluoric acid

Abstract

As part of fundamental studies in silicosis research, the rates of dissolution in 0.1 M‐hydrofluoric acid of size‐graded powders of quartz, tridymite, cristobalite and vitreous silica, having particle diameters in the range 0.2–5.0 μ, have been measured by a conductimetric micromethod. The rates of dissolution per unit area of the vitreous silica powders were an order of magnitude larger than those of the tridymite or cristobalite powders, and two orders of magnitude larger than those of the quartz powders. Quartz, unlike the other polymorphic forms of silica, showed an increase in rate (per unit area) with decreasing particle size as well as an increase in the relative amount of ‘easily soluble layer’.These results are adduced as evidence against the ‘solubility theory of silicosis’ and in favour of a biological activity dependent on the surface structure.