Optical Measurements of Magnetically-Aligned Asbestos Fibers

Abstract

<p>The magnetic-alignment behaviour of asbestos fibers suspended in water was studied. As the magnetic field rotates, with the lag increasing as the rotation rate increases. A theoretical model describing fiber behaviour was developed. Experiments measuring the phase lag of individual fibers, experiencing torques to the order of 10^18 Newton-meters were in excellent agreement with the model. For an unknown fiber the phase lag measurement will give the ratio of the length to radius of the fiber. For a known fiber, the cross-sectional size and shape can be determined.</p> <p>This research was undertaken with the intention of laying down the groundwork from which an automatic instrument for monitoring asbestos exposure could be made. Initial investigations involved filtering a liquid dispersion in a one Tesla magnetic-field. The filter contained permanently aligned fibers. The fiber was made transparent and scattered-light measurements were made relative to the initial magnetic field direction were made. Subsequent research focussed on mesuring light scattered by fibers suspended in water while the fibers followed a rotating magnetic-field. The latter technique proved far more sensitive, being able to detect fiber concentrations of the order of one million fibers per liter with relatively simple equipment. On a mass basis, this sensitivity corresponds to one part in 10^10. The method did not have the problems associated with the filter itself. Equally important, there is the potential to obtain fiber size information.</p>