Nanostructures

  • Properties depend on chemistry and arrangement of building blocks in 3D
  • Size matters! Metals conduct, not NP metals.
    • Bonds->orbitals: Particle in box
    • Surface/interface effects: High % of atoms are on surface (5nm=50%surface atoms)
  • Nanocrystalline
    • Grains in nanosize: (ex: NP Pt 400% more catalytic)
    • Network of intercrystalline regions
    • Nanocomposites: NP’s in matrix
      • Metal-NP’s composites as heterogenes catalyst
      • Semiconductor (Q-dots)
      • Nanofibres in ceramic matrices
      • Ex: Damascus sabre: CNT NP’s

Nanocrystalline ceramics

Regular ceramics typically 10\(\mu\)m grains. Nano:

  • 10-100nm grains
  • 3nm grains -> 75% in interphase
  • Interphase density only 60-70% of bulk
  • Not equilibrium state
  • Used as catalyst of oxides

Diffusion/Sintering

Densifiable by sintering at lower temps.

  • High surface energy
  • Short diffusion lengths
  • Low stability of interphase region Doped more efficiently at low T

Hardness/Strength

  • Are higher for NP’s than regular.
  • Superplasticity: Can undergo deformation without fracture.
    • Not yet proven for low Temp
    • Can become ductile.

Gold/Silver NP’s

Melting

Happens at lower T with smaller NP size.

Au-catalyst

  • Makes CO\(_2\) of CO.
  • NP > 10nm -> no effect
  • < 5nm, hemispherical -> effective
  • < 2nm, dependent on atom amount
    • Cubo-octahedron: Low activity
    • Icosahedron: High activity
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