L31 - SUMMARY FROM LAST CLASS Glass transition When a...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Dr. P. Lucas U of A MSE 110 Glass transition When a liquid is cooled down, the time necessary for the atoms to rearrange into a smaller volume configuration is the relaxation time τ . The relaxation time τ depends on the diffusion coefficient of the atoms and therefore on the viscosity of the liquid: η = G · τ The glass transition is the transition from a liquid to a solid which takes place when the relaxation time is too long for the cooling rate. The glass transition Tg is the transition point for many physical properties of the system such as V, α , S, H, Cp, which can be used to determine Tg experimentally. Unlike Tm the thermodynamic melting point, Tg is kinetically driven and depends on the cooling rate. Faster cooling rates yield higher Tg. The formal consistent way of measuring Tg is by using a heating rate and cooling rate of 10ºC/min. The stresses produced by inhomogeneity in the quenched glass can be removed by annealing near Tg. The relaxation time is raised enough to allow slow rearrangement of atom while not softening the material. SUMMARY FROM LAST CLASS
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Dr. P. Lucas U of A MSE 110 Types of glasses GLASSES Chalcogenide : As-Ge-Se-Te-S but no oxygen. Infrared transmitting glass. Halide glasses : Fluorides: BeF 4 , ZrBaF 6 Good optical properties: laser glass. Oxide glasses : SiO 2 , B 2 O 3 + Na 2 O, CaO… Common industrial glass: window, bottles Natural glass: Obsidian. Metallic glasses : Fe-Ni-Co-Si-B, High quenching rate, Magnetic metal strip, corrosion resistant.
Background image of page 2
Dr. P. Lucas U of A MSE 110 Silicate glass: structure GLASSES The building block of the SiO 2 glass is the SiO 4 tetrahedra. These tetrahedra are connected
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

Page1 / 13

L31 - SUMMARY FROM LAST CLASS Glass transition When a...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online