Estimation of Fibril Lengths in Chrysotile Asbestos Fibres

Abstract

CHRYSOTILE asbestos, the major fibrous serpentine polymorph, occurs naturally as veins in massive serpentine. It has been established^1,2 that chrysotile has a cylindrical crystal habit and occurs as fibrils 200 Å–400 Å in diameter. The orientation of the fibrils in the rock is such that the fibril axis is approximately perpendicular to the vein wall, forming a cross-fibre deposit, and the fibre length is frequently equal to the width of the rock vein; often the fibres grow from both walls and join at a central fissure or break. In commercial usage fibre length is an important characteristic, so various methods of length classification have been developed and applied to commercial raw material. These methods generally apply only to macro-fibre bundles, however, each of which contains a large number of parallel fibrils. No data have been published for the fibril lengths of chrysotile, although it is apparent from examination of electron micrographs of dispersed chrysotile fibrils that they exceed several tens of microns in length. This agrees with an aspect ratio of 5,000 derived from strength measurements by Wronski³. In addition, Aveston⁴ suggests that the somewhat broader fibrillar units of the amphibole asbestos crocidolite have lengths in excess of 1 mm. It is still uncertain, however, whether the lengths of individual chrysotile fibrils correspond to the length of the macro fibres or are shorter, because of defects introduced during growth or by subsequent geological faulting. This uncertainty limits the understanding and full utilization of the properties of chrysotile, in particular its mechanical properties.