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 x 2B2O3 x 5H2O);
borax 10 mol (
Na2O x 2B2O3 x 10H2O); anhydrous
boric acid (
B2O3); and anhydrous
borax (
Na2O x 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 microm (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 degrees 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.