Measurement of borate in occupational environments
1998
Smith, Robert A. | Ascherl, Frederick M.
The hydration stability for inhalable borate particles has been characterized as a function of temperature and relative humidity when collected by a field personnel monitor. The rate of hydration was measured for boric acid (B[OH]₃);Neobor® borax 5 mol (Na₂O·2B₂O₃·5H₂O); borax 10 mol (Na₂O·2B₂O₃·10H₂O); anhydrous boric acid (B₂O₃); and anhydrous borax (Na₂O·2B₂O₃). The particle size is large in bulk commercial products, such that they can be handled and stored without problems. However, inhalable dust particles, in the range of 20 μm (MMD), undergo hydration/dehydration rapidly owing to their high surface-to-volume ratio. The hydration state of a collected air sample was found to be strongly dependent on the conditions of relative humidity and temperature during its collection. As a consequence, the actual chemical species of dust being inspired cannot be identified accurately. Inhalable particles of borax 10 mol placed in a field personal monitoring cartridge and exposed to dry air at 2.0 L/min at 70°F for 7 h undergo rapid dehydration, producing a sodium borate residue having significantly less than four waters of hydration. Likewise, inhalable particles of anhydrous boric acid and anhydrous borax were found to hydrate under normal atmospheric conditions. Borax 5 mol and boric acid were found to be stable to dehydration. In most cases, the specific borate species or borate compounds collected in a field monitor cannot be accurately characterized other than by their boron (B) content.
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