Question

Question 2. a) What is the distinction between glass transition temperature and melting temperature? (Perhaps use a sketch to explain) b) Relating to the previous question (and sketch?) explain why glass may be drawn into fibres, whereas crystalline alumina may not c) Borosilicate glasses and fused silica exhibit higher resistance to thermal shock, to some ofthe more day-to-day glasses and ceramics. Why is this so? End of Tutorial Questions

Answer 1

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GLASS TRANSITION TEMPERATURE VERSUS MELTING TEMPERATURE Glass transition temperature Melting temperature is the temperature at which a is the temperature at whicha hard glassy state of an solid material is converted amorphous material is into its liquid form converted to a rubbery state Describes the transition Describes the transition of of a glass state into a a solid phase into a liquid phase (phase transition) rubber state Can be observed in Can be observed in crystalline substances amorphous and semi- crystalline compounds Depends mainly on the chemical bonding of Depends mainly on the chemical structure of molecules in the substance the substance and the external pressure Visit www.pediaa.com

glass melting transition temperature temperature heat heat heat vs. temperature plot for an crystalline polymer, on the left; and a amorphous polymer on the ri on the left .

Glass can be drawn into fibres as the heat required for its conversion is less from one state to another

While in crystalline state lot of heat is required to convert it into fibres

Q3 Fused silica & borosilicate glasses have very low coefficients of thermal expansion, and can maintain its dimensional stability even at elevated temperatures. Fused silica is far more shock resistant than any other refractory material, and can be rapidly heated and cooled without cracking.

fused silica and borosilicates