MIT 3.071 Amorphous Materials

6: Shaping

Juejun (JJ) Hu

1 After-class reading list

 Fundamentals of Inorganic

 Ch. 20

 Introduction to Glass Science and Technology

 Ch. 13

2 Image @ MIT. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/. “Viscosity makes things happen essentially in slow motion. If you are trying to melt a crystalline solid (like ice or an aluminum oxide ceramic), as soon as you reach the , a drop of liquid forms and falls away from the melting surface. Glass, on the other hand, … gradually transforms from a hard solid to a slowly softening liquid. This soft liquid gradually stiffens as it cools (because of its increasing viscosity), allowing glass blower time to shape and manipulate the glass.” http://madsci.org/posts/archives/2007-09/1188944613.Ph.r.html 3 Viscosity reference points

Working range PGM

Glass blowing

Lehr Fiber drawing Float glass

Pitch: 2.3 × 108

h 101 103 106.6 1012 1013.5 (Pa·s) Melting Working Softening Annealing Straining point point point point (Tg) point

4 Basic properties of common silicate glasses

Soda-lime Borosilicate Fused silica

CTE (ppm/°C) 9.2 3.2 0.5

Working point 1005 1252 N/A (°C) Softening point 696 821 1650 (°C) Annealing point 510 560 1140 (°C)

Strain point (°C) 475 510 1070

5 Flat glass : float glass process

 Forming of a continuous ribbon of glass using a molten bath  Melting and refining (homogenization and bubble removal)  Float bath: glass thickness controlled by flow speed  Annealing: stress release  Inspection, cutting and shipping

101 Pa·s 102.5 Pa·s 1012 Pa·s > 1015 Pa·s

© H.S. Stuttman Co., Inc. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/. 6 Flat glass manufacturing: down-draw methods

 Preserves pristine surfaces: no subsequent polishing required  Broad range of thicknesses from millimeter to tens of microns  Mostly used for flat panel display glasses

© Schott. All rights reserved. This content Screenshot © Corning, Inc. All rights reserved. This content is excluded from is excluded from our Creative Commons our Creative Commons license. For more information, see license. For more information, see http://ocw.mit.edu/help/faq-fair-use/. [Watch the Corning video on YouTube.] http://ocw.mit.edu/help/faq-fair-use/. 7 Glass blowing

Gaffer

Parison © iStockPhoto/Windzepher. All rights reserved. This content Blow pipe is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/.

© Science Museum/Science & Society © UFOlabglass. All rights reserved. Picture Library. All rights reserved. This content is excluded from our This content is excluded from our Creative Commons license. For more This image is in the public domain. Creative Commons license. For more information, see information, see http://ocw.mit.edu/help/faq-fair-use/. Source: Wikimedia Commons. http://ocw.mit.edu/help/faq-fair-use/. 8 Glass container production

 Narrow-neck containers (e.g., bottles): blow-and-blow process

 Wide-mouthed jars: press-and-blow process

Diagrams © Beaston Clark. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/. http://www.beatsonclark.co.uk/ Glass caneworking

 Canes: thin glass rods (often with color); can be of a single color, or contain multiple strands arrayed in a pattern (murrine)  Basic glass work technique for adding intricate stripe patterns to glassware or blown glass

Gather glass Gob shaping Cane Stack and with pontil on marver drawing bundle

Images © unknown/zzionkitty on YouTube. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/ .

10 Glass caneworking

Reticello

Millefiori Zanfirico

Types of caneworking images © unknown. All rights reserved. This content is excluded from our 11 Creative Commons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/. Stability of drawn cane structures

Scaling analysis  Scale-invariance of viscous flow: strain rate 휀 remains invariant if the externally applied stresses are kept constant regardless of system size

s s

s l-times system size s Same strain rate!

12 Stability of drawn cane structures

Cane diameter D change:

D 1 Necking develops if  tDh viscosity is independent of diameter D

F, s F, s

l-times system size 2 2 F, s /l 2 F, s /l l  l

13 Stability of drawn cane structures

Stability threshold:

11D   constant Dt h D2

F, s F, s

l-times system size 2 2 F, s /l 2 F, s /l l  l

14 Stability of drawn cane structures

Now consider heat dissipation:

 Radiative heat transfer dominates

 Stefan-Boltzmann law Heat flux: q es T 4 e : emissivity s = 5.67 × 10-8 W/m2K4

 Temperature change rate T qS4 es T 4     t cPP V c D

 Viscosity dependence on temperature

ETa   hh 0 exp High T range kTB 15 Modeling outcome

Assumptions: F T1 T2 F  Uniform temperature distribution along the cane cross-section  No heat or mass exchange between cane sections T1  Only considers radiative heat transfer T from glass cane to the 2 surroundings  Constant drawing speed

16 Modeling outcome

Conclusions: F D1 D2 F  Thinner section cools faster  Viscosity increase in thinner section prevents necking  Cane diameter non- uniformity damps out D1

D2

17 Precision glass molding (compression molding)

 Viscosity: 106.6 – 108 Pa·s; pressure: ~ MPa  Mold sticking and damage: TiN or SiC low friction coatings  Non-uniform temperature distribution  Post-molding deformation: thermal shrinkage, viscoelasticity

http://www.rpoptics.com/wp-content/uploads/2015/01/Precision-Glass-Molding-Technical-Brief_21.pdf

18 3-D glass printing

Image of 3D glass printing © Voactiv. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/. [Watch the complete video on YouTube.]

19 Mechanical properties of bulk metallic glass (BMG)

Polycrystalline Amorphous metal metal

Grain boundaries

Crystal planes Metals 3, 1 (2013). Figures courtesy of MDPI. License: CC BY. Source: Louzguine-Luzgin, D.V., et al."Mechanical Properties and Deformation Behavior of Bulk Metallic Glasses." Metals 3 (2013) 1-22.  Absence of dislocations and slip planes in BMG  Large elastic limit and high yield strength (2% and 2 GPa in Zr-based BMGs)  Poor global plasticity: absence of strain hardening, strong tendency towards shear localization  Cold working is not a viable processing solution

20 BMG processing design

Casting

Adv. Mater. 22, 1566 (2010).  Casting: suction casting, die casting  Reduced volume shrinkage (< 1%)  Cooling rate control: mold filling and crystallization mitigation

21 BMG processing design

Thermoplastic forming (TPF) Scripta Mater. 60, 160 (2009).

 Thermoplastic forming: compression & injection molding, extrusion, rolling, blow molding, 3-D printing  Thermal embrittlement: free volume decrease

22 MIT OpenCourseWare http://ocw.mit.edu

3.071 Amorphous Materials Fall 2015

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