Negative CTE materials

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Negative CTE materials

• Materials with negative coefficients of thermal
  expansion
• by Will Bray
• MEEN 3344
• 20 March 2006

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Reasons

• Most materials expand when heated, causing parts
  to change dimensions
• When two different materials heat up,
• By combining materials with negative CTE into
  other materials, thermal expansion can be
  tailored to specific needs

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Examples

• Fe-Ni alloys,
• microfabrication

• Carbon nanotubes have negative CTE along axis

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• The tetrahedra (red) and octahedra (green) that
  make up the crystal structure in zirconium
  tungstate. When heated, these figures squeeze
  together. Credit Alison Kendall

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Simplified example of how increasing temperature
can reduce size
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Applications

• Electronics- allow components to expand together
  or reduce expansion
• Carbon-fiber reinforced glass for Precision
  Mirrors (i.e. satellites)
• Negative Axial CTE fibers in positive CTE matrix
  for aerospace composites

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Sources

• http//www.ml.afrl.af.mil/news/MLL/asc_04_0161.htm
  l
• http//www.cytec.com/business/EngineeredMaterials/
  CFInternet/cfperformancedesign.shtm
• http//optics.nasa.gov/tech_days/tech_days_2003/do
  cs/24AFRLCTETailoredMaterialsforMirrors.pdf
• http//www.isis.rl.ac.uk/ISIS97/feature1.pdf
• http//www.livescience.com/technology/041215_unusu
  al_material.html