ENMAT101A Engineering Materials and Processes Associate Degree of Applied Engineering (Renewable Energy Technologies) Lecture 22 Glasses

Transcription

1 ENMAT101A Engineering Materials and Processes Associate Degree of Applied Engineering (Renewable Energy Technologies) Lecture 22 Glasses

2 Glasses Reference Text RA & Bolton, Materials for Engineers and Technicians, 5th ed, Butterworth Heinemann Section Ch 22 Reference Text Callister, W. Jr. and Rethwisch, D., 2210, Materials Science and Engineering: An Introduction, 8th Ed, Wiley, New York. Section Ch 3 (part)

3 Glasses ( 22) High quality glass goes back to ancient times. The engineering definition of glass includes a whole range of substances that are not true crystalline solids. Hence terms like glassy metals means metal atoms in a glass-like structure. Moldavite, a natural glass formed by meteorite impact, from Besednice, Bohemia A modern greenhouse in Wisley Garden, England, made from float glass Roman Cage Cup from the 4th century CE

4 22.2 Composition and structure of glass ( 22.2)

5 22.3 Glass-transition temperature ( 22.3)

6 22.3 Glass-transition temperature ( 22.3) Devitrification Glass ceramics

7 22.4 Glass manufacture ( 22.4) Devitrification Glass ceramics

8 22.4 Glass manufacture ( 22.4) Float process

9 22.4 Glass manufacture (Additional) Toughened or tempered glass is heat treated to created a surface compression. This increases the strength of the glass but makes it impossible to cut by any process (scoring, sawing, drilling, water jet cutting etc). The glass must be annealed before it can be processed and then re-tempered. When broken, the glass breaks into small granular chunks instead of splintering into jagged shards. Wikipedia Wikipedia

10 22.4 Glass manufacture ( 22.4) Glass blowing

11 22.5 The properties of glass ( 22.5) However a 'glass' is, by definition, a substance existing below the glass transition temperature so that very little movement of molecules is possible. This means that a glass at ambient temperature is extremely brittle.

12 22.6 Glasses and their uses ( 22.6) Pyrex Glass ceramics

13 22.7 Metallic glasses ( 22.7)

14 Glassy Metal 'Melt Spinning' or 'Splat quenching' to produce metallic glass ribbon. Molten tin alloy is fed through several nozzles onto a rotating metal drum, resulting in extremely high cooling rates (approx. 1 million Kelvin per second). High speed photography at 4000 fps. You Tube Offline From TLP: Casting, DoITPoMS, The University of Cambridge.

15 Resources. Wikipedia: Glass

16 Glossary Amorphous Crystalline Toughened glass Annealed glass Laminated glass Tempered glass Safety glass Refractive index Transmittance Absorptance Reflectance Dispersion Glass transition temperature

17 QUESTIONS Ch22, Newell, Timmings 1. Define all glossary terms 2. How do network modifiers affect the properties of glasses? 3. Compare and contrast the glass transition temperature of glasses with those of polymers. 4. Explain why molten SiO 2 forms glass instead of cooling back into a crystalline form. 5. Compare and contrast the properties of silica glass and Portland cement. 6. (a) Select two types of glass and describe their composition, properties and typical applications. (b) Describe the heat-treatment processes available for making glass less susceptible to fracture. (c) Describe a chemical treatment process available for making glass less susceptible to fracture. 7. Describe the optical properties of glass with respect to optical lenses. Name a surface treatment process used in high quality camera lenses. What does it do? 8. Obsidian is a naturally occurring (usually dark) volcanic rock. Granite has large visible crystals and forms deep underground. Which one is more likely to be a glassy structure? Explain. 9. Discuss silicon based solar cell technology: mono, poly crystalline and amorphous