Ashutosh GoelDepartment of Materials Science and Engineering

Rutgers, The State University of New Jersey

Glass – An unsung hero of the scientific

revolution

Picture, if you can, a world without glass. There would be no microscopes or

telescopes, no sciences of microbiology or astronomy. People with poor vision would

grope in the shadows, and planes, cars won’t exist. Artists would draw without the

benefit of three-dimensional perspective, and ships would still be steered by what stars

navigators could see through the naked eye.

A. Macfarlane and G. Martin, “Glass: A World History”, The University of Chicago Press, 2002

Grumpy cat with Google Glass

A world without glass

What is glass?

What is glass?

Classical definition: “Glass is a super-cooled liquid.”

If this statement is “true”, does glass flow over time?

Are medieval windows melting/flowing?

Italian stained-glass windows, from medieval

times, are often round - like this one from the

Basilica di Santa Maria del Fiore in Florence.Courtesy: www.awesomestories.com

In medieval European cathedrals, the glass sometimes

looks odd. Some panes are thicker at the bottom than

they are at the top. The seemingly solid glass appears

to have melted. This is evidence, say tour guides,

internet rumors and even high school chemistry

teachers, that glass is actually a liquid. And, because

glass is hard, it must be a supercooled liquid.- C. Curtin, “Fact or Fiction?: Glass is a (supercooled) liquid”,

Scientific American, Feb 22, 2007.

What is glass?

According to a study conducted by Professor Edgar D. Zanotto, window glasses may flow at

ambient temperature only over incredibly long times, which exceed the limits of human

history.- E.D. Zanotto, “Do cathedral glasses flow?”, American Journal of Physics, 66 (1998) 392.

Glass is actually neither a liquid – supercooled or otherwise – nor a solid. It is an amorphous

solid – a state somewhere between those two states of matter. And yet, glass’s liquid-like

properties are not enough to explain the thicker-bottomed windows, because glass atoms move

too slowly for changes to be visible.- C. Curtin, “Fact or Fiction?: Glass is a (supercooled) liquid”, Scientific American, Feb 22, 2007.

Can we still define glass to be a supercooled liquid?

If medieval windows are not flowing, why the bottom part of these

windows is thicker than the remaining window?

If medieval windows are not flowing, why the bottom part of

these windows is thicker than the remaining window?

Crown glass manufacture, C18th

Courtesy: Corning Museum of Glass

The reason behind non-uniform thickness of medieval windows may be attributed to their manufacturing

process. At that time, glassblowers created glass cylinders that were then flattened to make panes of glass.

The resulting pieces may never have been uniformly flat and workers installing windows preferred, for

one reason or another, to put the thicker sides of the pane at the bottom. This gives them a melted look,

but does not mean glass is true liquid.- C. Curtin, “Fact or Fiction?: Glass is a (supercooled) liquid”, Scientific American, Feb 22, 2007.

Glass in Modern World

Four things a normal human being wants…

Good Health

Four things a normal human being wants…

Good Environment

Four things a normal human being wants…

Good Communication

Although mode of communication has changed…..

Four things a normal human being wants…

Good Entertainment

How does glass help us in this pursuit?

Glass and medicine

First compound microscope

A clinical mercury-in-glass

thermometer

Glass Lab ware

Microscope: One of the first major developments

leading to saving of lives was the optical microscope

(Year: 1590). The invention of the microscope using

glass spheres to focus on the objects was the seminal

step towards discovering microscopic life, for example:

pathogens. This discovery led to the treatment and

eventually elimination of many diseases.

Other examples: Thermometers, Lab ware, Eye glasses

This enormous social change can be termed a revolution in life

preservation.

A major consequence of life preservation was an expansion of

the human lifespan from an average of 45 years to 78 years.

It is projected that by 2050, there will be more than 1 billion

people alive on earth aged 60 years or older.

Hench et al., Glass and Medicine, Int. J. Appl. Glass Sci. 1(2010) 104-117

The second revolution in healthcare has occurred in last 50 years, i.e. a

revolution in tissue replacement.

Bio-inert Biomaterials

CellProteins

Bioactive Biomaterials

CellAdhesion,

spreading,

migration, growth,

apoptosis and

differentiation

Human “spare parts” is a huge business worth tens of billions of dollars

http://www.synergybiomedical.com/technology.htm

45S5 Bioglass®

(mol.%): 46.1 SiO2 - 26.9 CaO - 24.4 Na2O - 2.5 P2O5

First bioactive materials were

discovered by Hench et al. in 1971.

They designed melt-derived Na2O-CaO-P2O5-SiO2 based glasses which have the ability to

bond to bone and soft tissues in human body through a sequence of chemical processes.

The most bioactive composition discovered until today from this class of materials is

45S5 Bioglass®, which has been used in > 650,000 human cases already.

J. Am. Ceram. Soc. 74 (1991) 1487

Scaffold fabrication from bioactive glass

Trinity of an ideal biomaterial for

tissue engineering and

regenerative medicine

- Underlying concept of tissue engineering is the belief that cells can be

isolated from the patient, and its population then can be expanded in a

cell culture and seeded onto a carrier. The resulting tissue engineering

construct is then grafted back into the same patient to function as the

introduced replacement tissue.

- This new paradigm requires scaffolds that balance temporary

mechanical function with mass transport to aid biological delivery and

tissue regeneration in three dimensions (3D).

- The choice of a suitable material for fabrication of scaffold with

desired properties is the biggest challenge.

Desired properties

Right surface chemistry to promote cell

attachment

Biodegradability – degradable into non-

toxic components

Mechanical strength – needed for

creation of macroporous scaffold that

will retain the structure after

implantation

Our research in the field of bioactive glasses

Our research in the field of bioactive glasses

Our research in the field of bioactive glasses

2 Merino sheep

(Age: 1 year)

We created 5 non-critical

defects with 5 mm

diameter in lateral

diaphysis in the femur

1st defect: Empty (control)

2nd defect: 45S5 (Reference)

3rd – 5th defect: FastOsTM

Defects in femur diaphysis

3 mm

45S5

3 mm

Control

FastOs

3 mm

Glass and environment

Nuclear waste management in USA

Hanford site - 586 mi.2 of desert next

to Columbia river in southeastern

Washington

Hanford site was established in 1943 to produce

plutonium for the production of nuclear weapons

that were used in World War II and continued

throughout the Cold War.

B-Reactor

(1944-1968)

Produced the plutonium used in “Fat man” bomb dropped

over Nagasaki in August 1945.

The production of plutonium ceased in 1987.

55 million gallons of high level radioactive

waste was stored in 177 underground tanks.

Clean-up began May 15, 1989.

www.hanford.govWaste tanks at Hanford site in Washington

What is the solution to this problem?

“Glass”

Why glass?

Why glass?

- Reduces the volume of waste by

75%.

- High chemical durability over

long term.

- Commercial vitrification plants

operate in France, U.K. an

Belgium produce about 1000

metric tons per year of such

vitrified waste (2500 canisters)

and some have been operating for

more than 16 years.

The nuclear waste from the production of

nuclear electrical energy of one person’s

entire life is contained in the glass in

hand.

Nuclear waste vitrification in USA

The U.S. Department of Energy (DOE) is

building a Tank Waste Treatment and

Immobilization Plant (WTP) at Hanford site in

Washington state.

Vitrification plant at Hanford

View inside a Joule Heated Ceramic Melter

(JHCM) that will be used to vitrify the

nuclear waste into borosilicate glass at

1150 °C.

Although the process of nuclear waste immobilization via vitrification seems simple, it is

plagued by several complex practical problems starting from design of glass compositions

(owing to the compositional complexity of nuclear waste), to processing in glass melters, and

finally to long term performance of the vitrified waste forms.

Our research is focused on the following three problems…

Challenges with vitrification - USAProblem#1 Spinel crystallization in glass melters

The cost of vitrifying radioactive waste is directly proportional to the volume of glass to be

produced. It is therefore desirable to maximize waste loading in glass to decrease the overall

volume, but without posing unacceptable risk for the melter operation.

The major factor limiting waste loading in

nuclear waste glasses is the precipitation,

growth, and subsequent accumulation of

spinel crystals (Fe, Ni, Mn, Zn, Sn)II(Fe,

Cr)III2O4 in the glass discharge riser of the

melter during idling.

Once formed, spinels are stable

to temperatures much higher than

the typical JHCM operating

temperatures (1150–1200 °C).

This can result in clogging of the melter discharge channel, and interfere

with the flow of glass from the melter

Challenges with vitrification - USA

Problem#2 Crystallization vs. chemical durability

Schematic cross-section of an

underground steel tank depicting

layer by layer arrangement of the

radioactive and chemical waste.

- The high level radioactive waste at Hanford is rich

in sodium and alumina (Al2O3).

- The strategy is to convert this waste into borosilicate

glass, with maximized waste loading.

- Increasing concentration of Na2O and Al2O3 in these

glasses results in crystallization of nepheline

(Na2O•Al2O3•2SiO2) based phases.

- Since nepheline crystallization results in removal of

1 mole of Al2O3 and 2 moles of SiO2, this decreases

the chemical durability of final waste form.

Challenges with vitrification - USA

Problem#3 Volatile radioactive species – for example, iodine

- The 2011 Fukushima Daiichi nuclear disaster was

one of the worst nuclear incidents in World history.

- The release of large amount of radioactive iodine

(129I, t1/2 = 1.6 x 107 y), and cesium in Pacific ocean

will be disastrous for the flora and fauna of ocean.

- According to scientists, these radioactive elements

will be adsorbed by marine life, and will eventually

make their way up the food chain, to fish, marine

animals, and humans.Fukushima Nuclear Disaster

No country has a defined protocol for immobilization of radioactive iodine as iodine is not

amenable to vitrification. For example, radioactive iodine in U.K. is currently discharged to sea.

Innovative synthesis routes need to explored for development of

ceramic waste forms for immobilization of radioactive iodine at low

temperature (<200 °C) .

But glass still breaks….

https://youtu.be/7j9hluDLWIU

Brittleness of glass has been perceived as its gravest handicap. Over the centuries, accepting this

handicap and benefitting from optical properties and universal processability, glasses have found their

role in applications with low levels of tensile stress.

There is very high demand for novel approaches towards stronger, or more precisely, damage resistant

glasses.

Aluminosilicates – Backbone of specialty glasses

Corning Gorilla GlassUltra-smooth and Ultra-Strong Ion exchanged Glass

[Adv. Funct. Mater. 23 (2013) 3233-3238]

Used as cover glass on 4.5

billion devices

Property Value

Density 2.42 g/cm3

Young’s Modulus 65.8 GPa

Poisson’s ratio 0.22

Shear Modulus 26.0 GPa

Vickers hardness (200 g load)

Un-strengthened 489 kgf/mm2 (4.79 GPa)

Strengthened 596 kgf/mm2 (5.84 GPa)

Fracture Toughness 0.67 MPa m0.5

Aluminosilicates vs. Aluminates

Glass forming region in Na2O-Al2O3 SiO2 system (mol.%)[Ref: Mysen and Richet, Silicate Glasses and Melts, Elsevier]

Vicker’s hardness: 4 – 6 GPa

Young’s modulus: 60 – 85 GPa

Fracture toughness: ~0.7 – 1 MPa m1/2

[Yoshida et al., J. Non-Cryst. Solids, 344 (2004) 37-43]40 SiO2 – 60 Al2O3

(mol.%)

Vicker’s hardness: 8.07 GPa

Young’s modulus: 134.2 GPa

[Rosales-Sosa et al., Sci. Rep., 6 (2016) 23620]

Density: 2.55 – 2.85 g/cm3

Vicker’s hardness: 7.23 – 8.07 GPa

Young’s modulus: 74 – 134 GPa

Cracking Probability curves for the xAl2O3 –

(100-x) SiO2 glasses

Cracking resistance of 40 SiO2- 60Al2O3 glass

is ~7 times higher in comparison to SiO2

glass!!

[Rosales-Sosa et al., Crack – resistant Al2O3 – SiO2 glasses, Sci. Rep., 6 (2016) 23620]

Aluminosilicates vs. Aluminates

Challenges in synthesis of aluminate glasses

Two major challenges

1. High melting and processing

temperatures – not amenable for

synthesis in conventional glass melting

furnaces

2. Small glass forming region – high

tendency towards crystallization

76 79 82 85 88 97 Al2O3

mol.%

1800

1850

2000

1950

Phase diagram of the alumina- rich La2O3-Al2O3 system [Fritsche and Tensmeyer, J. Am. Ceram. Soc. 50 (1967) 167]

Example

La2O3-Al2O3 glasses

Al2O3-rich glasses near eutectic of

La2O3–Al2O3 have been synthesized.

[Rosenflanz et al., Nature, 430 (2004) 761]

- Processing temperature: >1800 °C

- Small glass forming region

- Synthesized either by flame spray method or

aero-levitation technique

- Difficult to obtain monolith glasses for

practical applications.

Strategy to overcome these challenges

Synthesis route – melt quench vs. aero-levitation

Depending on processing temperatures

Melt-quenching

T ≤ 1650 °C

Glasses with Al2O3 ≤ 55 mol.%

Fabricate monolith samples – ready to use

T > 1650 °C

Aero-levitation techniqueIn collaboration with Prof. Mario Affatigato, Coe

College, Cedar Rapids, IA

Will provide glass beads which will require

further processing!!

Ultra-strong glasses and glass-ceramics

Map of hardness against Al2O3 content in different

material classes.

It has been shown that transparent

aluminate glass-ceramics with hardness

similar to Al2O3 can be synthesized.

Bulk rare-earth aluminate glass-ceramics

Rosenflanz et al., Bulk glasses and ultrahard nanoceramics based on alumina and rare-earth oxides, Nature, 430 (2004) 761.