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Mechanistic understanding of aerosol emissions from abrazing operation.

Authors
Zimmer-AT; Biswas-P
Source
Am Ind Hyg Assoc J 2000 May/Jun; 61(3):351-361
NIOSHTIC No.
20020873
Abstract
Welding operations produce gaseous and aerosol by-products that can have adverse health effects. A laboratory furnace study was conducted to aid understanding of the chemical and aerosol behavior of a widely used, self-fluxing brazing alloy (89% Cu, 6% Ag, 5% P) that is also used with a supplemental fluxing compound to prevent oxidation at the molten metal surface. The results indicate that the aerosols generated by the alloy are transient (produced over a short duration of time) and are associated with mass transfer of phosphorus species from the molten metal surface to the surrounding gas. In contrast, when the alloy was used in conjunction with the supplemental fluxing compound, a relatively nontransient, submicron-size aerosol was generated that was several orders of magnitude higher in concentration. Thermodynamic equilibrium analysis suggests that fluoride (a major constituent in the fluxing compound) played a significant role in reacting with the brazing alloy metals to form gas phase metal fluoride compounds that had high vapor pressures when compared with their elemental or oxide forms. As these metal-fluoride vapors cooled, submicron-size particles were formed mainly through nucleation and condensation growth processes. In addition, the equilibrium results revealed the potential formation of severe pulmonary irritants (HF and BF3) from heating the supplemental fluxing compound. These results demonstrated the importance of fluxing compounds in the formation of brazing fumes, and suggest that fluxing compounds could be selected that serve their metallurgical intention and suppress the formation of aerosols.
Keywords
Aerosols; Welding; Laboratory-testing; Welders; Welding-industry; Gases; Metals; Fluorides; Pulmonary-system-disorders; Respiratory-system-disorders
Contact
National Institute for Occupational Safety and Health, Division of Physical Sciences and Engineering, 4676 Columbia Parkway, R5, Cincinnati, Ohio 45226
CODEN
AIHAAP
CAS No.
7664-39-3; 7637-07-2
Publication Date
20000501
Document Type
Journal Article
Fiscal Year
2000
NTIS Accession No.
NTIS Price
Issue of Publication
3
ISSN
0002-8894
NIOSH Division
DART
Source Name
American Industrial Hygiene Association Journal
State
OH
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