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Zeolites and Negative Thermal ExpansionPowerPoint Presentation

Zeolites and Negative Thermal Expansion

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## PowerPoint Slideshow about ' Zeolites and Negative Thermal Expansion' - boris-thornton

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Presentation Transcript

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

- 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

- Control – MEP
- Positive thermal expansion – DON
- Negative thermal expansion – EDI, YUG
- Detail - STI

MEP (1104 atoms)

- Already proven to have negative thermal expansion

DON (1152 atoms)

- Was modelled to have positive thermal expansion

EDI (1872 atoms)

- Was modelled to have negative thermal expansion

YUG (2160 atoms)

- Was modelled to have negative thermal expansion

STI (2592 atoms)

- Showed an unusual shift

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

- Structure of STI at 90K

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