Glass Eng Quiz 1

Introduction

SiO2 based glasses make up majority of industry

Glass: an inorganic product of fusion which has cooled to a rigid condition without crystallizing

• glass is NOT a supercooled liquid because it occurs over a range

• inorganic → not carbon, sand, or limestone

• glass can be characterized by structure and corresponding temperature (fictive)

SiO2 melting point: 1720 degrees C

Glass transition

• good material for glass = viscous at the melting point

• crystallization not allowed

• fast cooling = higher Tg

• slow cooling = lower Tg

Glass Formers, Modifiers and Intermediates

• Formers: can make glass on its own

  • SiO2

  • B2O3

  • P2O5

  • GeO2 → optical fibers

  • V2O5

  • As2O3 → semiconductors

• Modifiers: lower melting point, make network weaker

  • Na2O

  • K2O

  • Li2O (divalent holds structures better together)

  • CaO

  • MgO

  • BaO

  • La2O3

• Intermediates:

  • Al2O3

    • used in refracteries

    • rare as a batch ingredient

  • PbO

  • ZrO2

  • TiO2

  • ZnO

Chalcogenides (As, Ge): opaque + transmit very long wavelengths

Zacharaisen and glass chemistry

Bond angles:

• Glass: 120° - 180°

  • Avg: 142°

• Crystal: more acute angles

Zachariasen’s Rules for Glass Forming

1. An oxygen atom is linked to not more than 2 glass forming atoms.

   1. Silica - 3 or 4 oxygens = ideal

2. The coordination number of the glass forming atoms is small.

3. The oxygen polyhedra share corners with each other, not edges or faces.

4. The polyhedra are linked in a 3D network.

Glass manufacturing process: Desired properties → target composition → raw materials

• raw materials:

  • soda

  • sand ash

  • limestone

  • borax

  • feldspar

  • clay

  • slag

Major glass products

• flat glass

• hollowware/containers

• fiber glass

• light bulbs

• tubing

• tableware

• technical glasses

• optical glasses

• nuclear containment

• glass ceramics

Processes and Fiberglass

Major forming processes → viscosity - temperature relationship affects many forming processes

• casting

  • gravity

  • centrifugal

• blowing

  • bottles, molten glass

• pressing

  • eyeglasses

• molding (mix)

  • injection

  • transfer

• spinning (mix)

• extrusion

• downward draw

• upward draw

  • sheet glass

• float on liquid

  • flat glass is made by pouring it onto molten tin

• sag

• stretch

• sinter

• join

Light

• LED does not have to be in glass because there is no vacuum required

Fiber glass

• 2 types

  • molten glass → insulation

  • really fine, continuous filament → fiberglass yarn

• small fibers = better thermal conductivity

  • less than 3 microns will get into your respiratory system

  • smallest: 2.5 microns

  • typical: 5 microns

  • largest: 14 microns

• made in a similar way to cotton candy, rolled into a thin mat

• application:

  • Great Depression: no one was buying bottles → recycled for fiberglass

  • circuit boards

    • fiberglass composite for dimensional stability

Viscosity

Viscosity: resistance to flow

• μ = shear stress/velocity gradient = ∆x*F/∆v*A

Continuous filament Fiber Glass

• aka E-glass: originally for electrical insulation

• T{liquidus} = 1140°C

  • temp where crystallization occurs

  • want to stay above this

  • T3 = 1270°C

    • a good fiberizing viscosity

• not monovalent

Measuring glass viscosity

• Rotating cylinder viscometer

  • high temp/low viscosity measurements   

    • not good where T{glass} is low and honey-like

  • rotates outer or inner crucible

  • spindle turns via motor or measure the resistance by turning the spindle

• Stokes Law methods

  • drop platinum ball into molten glass

    • measure the terminal settling velocity

• low temperatures

  • fiber elongation

    • useful in the range of 10² - 10¹⁵ dPa*s

      • important range for tempering, stress release, and annealing

    • general procedure

      • place a fiber of d = 0.65 mm into a furnace, fiber will elongate under its own weight at low viscosity

      • higher viscosity = lower temp

  • beam bending

    • 3 point bend and measure the sag

  • penetration

    • rod pushed down on a ball onto glass

Key Points!

• glass has no fixed thermodynamic benchmarks

• Melting point → 100 poise

  • μ = 10² dPa*s

• Littleton softening point → beginning to flow under its own weight

  • μ = 10^7.6 dPa*s

  • 700 C for soda-lime glass

  • elongation rate at softening point is 1 mm/min

• Annealing point → range where you want to cool glass

  • μ = 10¹³ dPa*s

  • 550 C for soda-lime glass

  • elongation rate: 0.135 mm/min

• Glass transition

  • could vary based on cooling rate

  • μ = 10^13.2 - 10^13.5 dPa*s

• Strain point → solid

  • μ = 10^14.5 dPa*s

  • 500 C for soda-lime glass

  • elongation rate: 4.3 μm/min

Tempering = heat treatment; thermally process to alter stress distribution

Blowing bottles

• Relative Machine Speed (RMS) = index that suggests the relative rate at which bottles can be produced by press-blow or blow-blow automated processes

  • working range index = SP → AP

• Hand blowing and machine blowing favors short working glasses

  • shallow velocity curve (fragility)

    • fragility - how rapidly a material's viscosity changes as it cools toward its glass transition temperature

Andrade Relationship:

• μ = μ_o * e^Q/RT

• Temperature increased, μ decreases

• assumes glasses have activation energy Q, when glasses generally don’t have any activation energy

Fulcher Tamann Vogel:

• log μ = A + B/(T - T_o)

• 3 parameters

• predicts well in intermediate range

• changes most quickly nears Tg

MYEGA model

• basically a 2 parameter model

• used for calculating viscosity reference points

Viscosity data to remember

• Float (soda-lime silicate glass)

  • T_sp = 722°C

  • T_ap = 540°C

  • T_strain = 510°C

• Lead

  • T_sp = 440°C

  • T_ap = 363°C

  • T_strain = 342°C

• Borosilicate glass

  • T_sp = 821°C

  • T_ap = 560°C

  • T_strain = 510°C

• Aluminosilicate glass

  • T_sp = 908°C

  • T_ap = 710°C

  • T_strain = 665°C

• Titanium silicate

  • T_sp = 1500°C

  • T_ap = 1000°C

• Fused silica

  • T_sp = 1580°C

  • T_ap = 1084°C

  • T_strain = 956°C