Brake Pad Wear Debris Characterization

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Brake Pad Wear Debris Characterization
Mark A. Schlautman, Ph.D Christos Christoforou,
Ph.D. Ashley Haselden School of the
Environment Clemson University
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BPP Technical Studies
Air Deposition Monitoring (SFEI)
Air Deposition Modeling (AER)
Representative Sample of Brake Pad Wear Debris
(BMC/Link Test Labs)
Physical Chemical Characterization of Wear
Debris (Clemson University)
Copper Source Loading Estimates (Process
Profiles)
Watershed Modeling(U.S. EPA)
Water Quality Monitoring (ACCWP)
Bay Modeling (URS)
Final Report Data Assessment Conclusions
Steering Committee, Scientific Advisory Team,
and Stakeholder Involvement Process (Sustainable
Conservation)
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Generation of the Representative Brake Pad Sample

• PEC member companies provided information to the
  BMC on the forms of copper used in OEM automobile
  brake pads.
• Pareto analysis of the data led to the selection
  of three materials comprising greater than 90 of
  the copper usage in OEM automobile brake pads.
• PEC member companies prepared samples of their
  brake pad formulations for use in generating
  BPWD.
• The proportion of each material in the
  representative sample was based on the volume
  sold on vehicles in 2002.
• Three material samples were run on a brake
  dynamometer to generate and collect BPWD
  following the established protocol.

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Characterization of Airborne BPWD Generated from
the Representative Sample

• Plan and methodology were presented at last
  years Stakeholder meeting
• MOUDI measurements on Materials A, B C
• Mass-based particle size distributions (PSD)
  (gravimetric analysis)
• Cu and Fe contents vs. size (digestion and
  ICP-AES)
• Calculate characteristics for theoretical
  (composited) BPWD representative sample

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MOUDI(micro-orifice uniform deposit impactor)
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Airborne Characterization Results
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Airborne Characterization Results
Replicate runs for three different brake pad
material formulations (note difference in scales)
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Airborne Characterization Results
Material A 26.4 Calculated PSD for Material
B 14.1 ? Representative Sample Material C
59.5
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Airborne Characterization Results
PSDs based on total mass, Cu, and Fe
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Key Findings (Airborne Characterization)

• Generation of airborne BPWD was very different
  for the three different materials.
• Background levels of airborne particulate matter
  in the testing facility much higher than
  expected, and were variable on a day-to-day basis
  (and perhaps over a much shorter time period).
  The likely culprit for the high and variable
  background concentrations was the various tests
  being conducted on surrounding dynamometers in
  the facility.
• High background interference primarily affected
  Material C results, but not the other two
  materials.

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Key Findings (Airborne Characterization)

• The mass mean aerodynamic diameter of the
  airborne fraction of the composite BPWD material
  was approximately 2.7 µm.
• The total net average Cu and Fe contents of the
  airborne fraction of the composite BPWD material
  were 5.8 ( 0.4) and 15 ( 2),
  respectively.
• Cu content of the composite BPWD appeared to
  decrease with increasing airborne particle size
  above 0.075 ?m (trend was weak, and may not be
  statistically-significant due to propagated
  uncertainties). No trend was observed between Fe
  content and airborne BPWD particle size.

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Characterization of Non-Airborne BPWD Generated
from the Representative Sample

• Materials A, B C run back to back with no clean
  out between materials
• Cu and Fe contents (digestion and ICP-AES)
• Cu and Fe leaching using standard tests
  (ICP-AES)

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Non-Airborne Characterization Results
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Non-Airborne Characterization Results
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Non-Airborne Characterization Results
Comparison of final leaching solution pH values
for the two nonairborne BPWD samples
Comparison of leaching test results for the two
nonairborne BPWD samples
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Key Findings (Non-Airborne Characterization)

• Cu and Fe contents in the nonairborne fraction of
  the representative BPWD sample were 7.9 (? 0.2)
  and 23.1 (? 1.2), respectively.
• Both values were lower than previous nonairborne
  BPWD sample, which had Cu and Fe contents of
  10.8 (? 0.2) and 28.6 (? 0.4), respectively.
• Both values were higher than the airborne
  fraction of the representative BPWD sample, which
  had Cu and Fe contents of 5.8 (? 0.4) and 15
  (? 2), respectively.
• Leaching of Cu from the nonairborne fraction of
  the representative BPWD sample was high (60 to
  100) in the more aggressive leaching solutions
  but low (lt 5) in the less aggressive solutions.
• Total Cu leaching potential similar to previous
  nonairborne BPWD sample
• Expected rate of Cu leaching lower than
  previous sample

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Limitations of Non-Airborne Sample
Characterization Results

• The leaching information is somewhat qualitative
  and cannot be used as a direct input into the
  watershed and bay models (e.g., serves as a
  conceptual guide only)
• Unanswered questions remain regarding the
  partitioning of BPWD and Cu between airborne and
  nonairborne fractions (may have implications for
  copper loading estimates)

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Questions ??
Thank you.