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Zeolites and Negative Thermal Expansion. Rachel Pallant , Josie Paton, Alen Akhabaev , Ross Davies. Zeolites. Microporous Minerals Microporous – Contains pores with diameters <2nm Mineral – Naturally occurring substance that is a stable solid rtp 206 structures identified

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Zeolites and negative thermal expansion

Zeolites and Negative Thermal Expansion

Rachel Pallant, Josie Paton,

AlenAkhabaev, Ross Davies


Zeolites
Zeolites

  • Microporous Minerals

    • Microporous – Contains pores with diameters <2nm

    • Mineral – Naturally occurring substance that is a stable solid rtp

  • 206 structures identified

  • Base SinO2n, other molecules can be included


Negative thermal expansion
Negative Thermal Expansion

  • Caused by decrease in bond angles

  • With no/little energy bond angle is 180°

  • Energy provided by heat overcomes electrostatic forces of electron groups mutually repelling

  • Molecule bends, Si-Si distance now smaller although bonds are longer


Zeolites chosen
Zeolites chosen

  • Control – MEP

  • Positive thermal expansion – DON

  • Negative thermal expansion – EDI, YUG

  • Detail - STI


Mep 1104 atoms
MEP (1104 atoms)

  • Already proven to have negative thermal expansion


Don 1152 atoms
DON (1152 atoms)

  • Was modelled to have positive thermal expansion


Edi 1872 atoms
EDI (1872 atoms)

  • Was modelled to have negative thermal expansion


Yug 2160 atoms
YUG (2160 atoms)

  • Was modelled to have negative thermal expansion


Sti 2592 atoms
STI (2592 atoms)

  • Showed an unusual shift


Sti detail 1728 atoms
STI Detail (1728 atoms)

  • Using smaller temperature steps still just showed a sudden shift

  • Only two of the side lengths changed, not all three


Sti structure animation
STI Structure Animation

  • Structure of STI at 90K



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