title: Clay occlusion of respirable quartz particles detected by low voltage scanning electron microscopy-X-ray analysis.
abstract: Respirable-sized dust particles from a clay mine and mill were examined for aluminium and silicon content by scanning electron microscopy-energy dispersive X-ray analysis at incident electron energies of 5-20 keV. Most of the high silica content particles, those which had a silicon to silicon plus aluminium signal fraction, measured at 20 keV, of 0.9 or greater, showed a decrease in the silicon fraction of signal with decreasing incident electron energy, down to values of between 0.6 and 0.8 at 5 keV: this decrease was a function of particle size and composition. Simple models for silicon fraction of signal vs incident electron voltage suggest this behaviour is due to a heterogeneous particle structure in which an aluminosilicate coating occludes the surface of a silica particle core. The coating survives incubation in a major component of pulmonary surfactant.
authors.affiliation: Division of Respiratory Disease Studies, U.S. National Institute for Occupational Safety and Health, Morgantown, WV 26505.
authors.forename: W E
authors.initials: WE
authors.lastname: Wallace
authors.forename: J
authors.initials: J
authors.lastname: Harrison
authors.forename: M J
authors.initials: MJ
authors.lastname: Keane
authors.forename: P
authors.initials: P
authors.lastname: Bolsaitis
authors.forename: D
authors.initials: D
authors.lastname: Eppelsheimer
authors.forename: J
authors.initials: J
authors.lastname: Poston
authors.forename: S J
authors.initials: SJ
authors.lastname: Page
mesh_terms: D000538:Aluminum Silicates / Q000032:analysis*; D000077215:Clay; D004391:Dust / Q000032:analysis*; D006801:Humans; D008855:Microscopy, Electron, Scanning; D010316:Particle Size; D011663:Pulmonary Surfactants / Q000378:metabolism*; D011791:Quartz / Q000032:analysis*; D012119:Respiration; D012825:Silicon / Q000032:analysis*; D012822:Silicon Dioxide / Q000032:analysis*
chemical_list: D000538:Aluminum Silicates; D004391:Dust; D011663:Pulmonary Surfactants; D011791:Quartz; D012822:Silicon Dioxide; D000077215:Clay; D012825:Silicon