International Crystal Federation Technical Exchange Conference Waterford, Ireland 12 – 14 October 2002 Lead Migration from Crystal Glassware: Developments

THE STATE UNIVERSITY OF NEW JERSEY

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International Crystal Federation Technical Exchange ConferenceWaterford, Ireland 12 – 14 October 2002

Lead Migration from Crystal Glassware: Developments from 12 Years of ICF TECs.

Richard LehmanProfessor of Materials Engineering

Rutgers UniversityNew Brunswick, New Jersey USA


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Outline of Presentation

Historical background Structure/durability relationships Effect of oxides Migration behavior of lead crystal

Phenomenological behaviorMigration levelsSurface films – formation and properties

Intrinsic Extrinsic

Other interesting effects


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Historical Perspective

Work by Thorpe and Mellor, circa 1900SiO2 forms the network

Covalently bonded Structural network of glass, promotes durability

Most other oxides modify the network Mostly ionically bonded Weak, promote migration and low durability

All other effects are secondary

5.0][ 2

32

SiOGenerallyoxidesacidicofMoles

OAlofMolesoxidesbasicofMoles


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Glass Networks and Modifiers


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Glass Structure via Volume Filling Model


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6-member Rings Dominate Glass Structure

Network bonding issues:Each ring has 6 silicon participating in ring.Each silicon is also part of three other ringsEach ring has 6/4 = 1.5 equivalent whole

silicons Migration and diffusion issues:

Nonbridging oxygens provide diffusion transfer site.

One nonbridging oxygen is required per ring to produce continuous diffusion path.

Mole ratio of 1.0/1.5 = 0.67 is upper limit for a diffusion-stable structure.

Si

SiSi

Si Si

Si

O

O

O O

O

O

O

Na

Six-Member Silicate Ring Structurewith One Non-bridging Oxygen Linkage

nonbridging oxygen


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Chain Structure of Certain Silicate Glasses

Tetrahedral network structure of silicate glass


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Expert Perspective

“…we know practically nothing about…glasses” – W. H. Zachariasen, April 1932.

“Glass is a difficult material”– Michael J. Hynes, April 1992.

“I hope I die before I get old” – Pete Townshend, “My Generation”


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Lead Release from Silicate Glasses with Varying Mole Ratio of Modifier and Formers.

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

0.50 0.60 0.70 0.80 0.90 1.00 1.10 1.20

Moles Modifier/Glass Former

Lea

d R

elea

se, 6

0 m

in, m

g/c

m2

PS

NPS

KNPS

CNPS

ACNPS

BCNPS

Linear (PS)

Linear (NPS)

Linear (CNPS)


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General Effect of Oxides

Good OxidesAl2O3

TiO2

ZrO2

SiO2

SnO2

Important ParametersZ/R [charge to radius]Steric hindranceNetwork connectivity

Bad OxidesLi2ONa2OK2OB2O3

PbO

Medium OxidesCaOZnOMgOBaOPbO

Radius

Z/R

Steric Effects

Ch

emic

al D

ura

bil

ity

Overall Behavior


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Participation of Intermediatesin Silicate Glass Network

Pb in 2/4 fold-coordination

Al in 4 fold-coordination with

Na+ charge compensation


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Crystal Glass Compositions

1992 1992 1992 1992 1991 1991 1991 1991 1991 1991 1991 1991 1991 1991 1991 1991 1991 1991

McGookin McGookin Frank Frank Frank Frank Frank Frank Frank Frank Frank Frank Frank Frank Frank Frank

Tradition Reform 1 Original #3 1 2 3 4 5 6 7 8 9 10 11 12 13 14

MW Tyrone Tyrone Lenox Lenox Nacht Nacht Nacht Nacht Nacht Nacht Nacht Nacht Nacht Nacht Nacht Nacht Nacht Nacht

SiO2 60.1 55.3 58.2 59.4 61.5 60.3 59.1 57.6 56.2 61.3 62.3 61.6 61 61.10 61 61.5 61.9 61.7 60.5

PbO 223 32.3 30.0 25.2 24.1 24.5 24.0 24.2 23.7 23.6 24.4 24.1 23.9 23.9 24.4 24.3 24.2 24.1 24.5

ZrO2 123 1.00

Al2O3 102 1 0.9

CaO 56 0.50 1 0.9 0.5 0.5 0.5ZnO 81.4 0.37 2.1 1.2 1.1 0.6 0.6 0.6 0.4BaO 153 1.10

B2O3 69.6 0.20 0.65 1.28 0.70 0.70 0.70 1.50 1.50 0.80 0.80 0.80 0.80 0.70 0.80 0.80 1.30 0.80

K2O 94 11.9 8.8 10.3 8.9 10.8 10.6 10.1 11 10 9.7 9.6 9.5 8.8 10.4 9.9 9.7 8.9 9.4

Na2O 62 2.1 3.9 3.4 3.4 3.4 3.9 3.2 3.2 2.4 2.4 3.0 3.0 3.3 3.4 3.4 3.4 3.4

Li2O 30 0.15 0.5

As2O3 198 0.20 0.23 0.37 0.37 0.20 0.10 0.40 0.40 0.40 0.50 0.50 0.70 0.70 0.10 0.10 0.10 0.50

Sb2O3 291.6 0.16 0.16 0.30

Pb, ppm ISO 0.74 0.24 0.16 0.07 0.19 0.15 0.16 0.22 0.08 0.07 0.06 0.05 0.20 0.08 0.07 0.05 0.04 0.04AS & Acid 0.12 0.07

Thorpe 0.299 0.281 0.305 0.276 0.290 0.317 0.348 0.368 0.282 0.256 0.272 0.284 0.292 0.280 0.275 0.270 0.275 0.285


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Effect of Thorpe Ratio


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More Thorpe Ratio Data

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.24 0.26 0.28 0.3 0.32 0.34 0.36 0.38

Thorpe Ratio

Lea

d r

elea

se,

mg

/l

Tyrone

Lenox

Nachtman


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The Problem: Water Molecules!

Water molecules on glass surface


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Stages of the Migration ProcessP

b m

igra

tion

time

2/11tMMM oshort

tKPLM linlong Mo

Three Stages:

Intercept – time independent extraction, corresponding to dissolution of surface deposits.

Parabolic – root time behavior. Fick’s law diffusion

Linear – Surface film formation rate = dissolution rate.


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Chemical Attack on Glass

Basic solutions attack glass network Linear time dependence Network and modifiers are dissolved

together

Acid solutions leach modifiers from silicate network Initial time independent dissolution of

surface lead Parabolic time dependence, Fick’s law

diffusion, as silica gel forms. Linear time dependence when diffusion

rate is less than silica get dissolution rate.

Original Glass Surface

Silica Surface Film

Bulk Glass


Bulk Glass


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December 1993 Pb Migration Status[Waterford, IR – John Kennedy]

Leaching kineticsParabolic Fickian behavior and intercept well recognizedLong-time linear and constant effects not documented

Methods to reduce migrationGlass composition

Alkali reduction and mixed alkali effect [Na/K ~ 0.8 – 1.0 mole ratio] Lead-free glass and low-lead glass compositions [Ba, Sr, Bi] “Good” and “Bad” oxides


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1993 Pb Migration Status[…continued]

Surface TreatmentsPhysical

Rinse Cased gob [lead free lining] Polymer coating Sol-gel coatings Other coatings

Chemical Acid polish In-situ silica gel formation and condensation [preleach and cure] Ammonium sulfate fuming [modifier extraction from surface] Ion exchange [kaolin process – Al+3 exchange]


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Parabolic Migration Behavior in Lead Crystal Glassware

Pb, g/l

(time, h)0.5

100

500

1 h 24 h

Plain

Acid Polished

Pierre Ayral (Sep 92)

Pb m

igra

tion

t i m e

2/11 tMMM oshort

tKPLM linlong

M o

T h r e e S t a g e s : I n t e r c e p t , P a r a b o l i c , L i n e a r

Pb m

igra

tion

t i m e

2/11 tMMM oshort

tKPLM linlong

M o

T h r e e S t a g e s : I n t e r c e p t , P a r a b o l i c , L i n e a r

490

Typical 2002 ISO Value = 150 – 200 g/l


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Low Incremental Migration on Cyclic Exposure

High initial levels due to surface lead

Formation of surface film provides diffusion limited process at longer times.

Levels can increase with aging or annealing after leaching unless surface film is heat cured.

Pb, g/l

Cycles

100

300

5 20

Plain

Acid Polished

Pierre Ayral (Sep 92)

200


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Cyclical Behavior – many cycles

Pb

rele

ase,

fi

rst e

xpos

ure

= 1

.0

Cycles

1.0

40 120

P. Stanghellini (Sep 92)

800

~ Range

0.60

0.40


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Lead Release into Whiskey from Decanters

0

50

100

150

200

250

300

350

0 2 4 6 8 10 12 14

Time, weeks, refilled weekly

Pb

re

lea

se

, ug

/l

B

D

A

E

C

ISO HAc DataDecanters

B = 320D = 472A = 223E = 189C = 126

ISO HAc DataStemware

B = 286D = 398A = 331E = 174C = 341

Kennedy 4/92

Whiskey

A, B, C, D, E are various manufacturers


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Four Years of Continuous LeachingP

b re

leas

e, u

g/l

Weeks

900

200

G. Boschi, F. Paloschi, P. Stanghellini, CALP (1996)

1000

Acetic Acid

500

Whiskey & Brandy

Lead release increases with time

~40% of 4 year value is achieved after 8 weeks

820

450

200

300


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Lead Crystal Stabilization with Alcohol

Lead concentration does not monotonically increase, but becomes constant after several months.Reported by Himpens in 1995 Possible passivation of the glass with

organic groups Blocking of silica gel interstices Greatly reduce solubility of silica gel, tetra ethyl

orthosilicate is immiscible with aqueous solutions.

Pb,

arb

itra

ry

time, months2 months

Not Polished

Acid Polished

4% Acetic Acid

Whiskey, Bells

48 months


Silica Surface Film

Bulk Glass

Si(OC2H5)4 layer, immiscible with

water?


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Calculated Extraction Depth[24% PbO Crystal]

0

50

100

150

200

250

300

350

400

450

0 2 4 6 8 10 12 14

Extraction Depth, nm

ug

/l in

ISO

Ex

tra

cti

on

One liter vessel:Diameter =9.47 cmHeight = 14.2 cm

10 nm extraction depth yields 329 ppb.


Silica Surface Film

Bulk Glass

10 nm


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Lead Near the Glass Surface

A B A 1 F

G L A S S

G L A S SS U R F A C E

S iO 2 R IC HP R O T E C T IV EL A Y E R

E A S IL YR E M O V A B L EP b o P b + + . . . .

F O R M E D A N D S T O R E D

H A N DW A S H E D

4 % H A c F R A C T U R E

E. Guadagnino, M. Verità (1999 -2000)

Model derived from surface

analysis results using XPS and EDS [EMPA]

Elemental lead [Pbo], possibly due to flaming, was found in one study, but not in a subsequent study]


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Alternative Approaches to Limiting Pb Migration

Surface Treatments Ammonium sulfate fume

Remove surface alkali and lead Inexpensive and easy Better long term behavior than acid treatment

x Requires high temperature

x Deformation of stemware

Sol-gel Ion exchange – Al+3 from kaolin -- ~30 - 100 g/l [6-60 months in HAc] Preleach Preleach with silica gel condensation – 448 g/l 50, 300 autodish cycles Polymer coating – 60 g/l from wine

Waterford (1991)Lenox (1992)Rutgers (1995)


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Alternative Approaches to Limiting Pb Migration

Batch formula changes Reduced alkali – but need to substitute to retain working properties 1% phosphate addition – effect shown in very high lead glass only Reduced PbO [w/o Polish: 24% (240 g/l ); 18% (30 g/l ); 12% (50 g/l )]

Others Leadless glass liner – cased gob -- <20 g/l Leadless crystal – SiO2 [56.1%], (Na,K)2O [10.4], BaO [26.1], Ca,Zn [2.4]


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Non-Lead Crystal

Aimed initially to replace category 3 glass [5% PbO]

Has evolved for all typesCategory 1: 30% PbO, >1.545, >3.0 g/cm3

Category 2: 24% PbO, >2.9 g/cm3

Category 3: 5% PbO, >1.52, >2.45 g/cm3

Bo Jonson (1996)


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Effect of PbO Level in Glass and Repeated Extractions

0

100

200

300

400

500

600

700

0 5 10 15 20 25 30 35

Lead in glass, weight percent

Lea

d r

elea

se,

ISO

, u

g/l

First exposure

Second & third

exposure

E. Guadagnino (1997)


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Atlantis Batching Changes[1986 – 1994]

1986 1992 1993 1994 MgO Test Min Max Range

SiO2 51.89 53.61 53.42 53.2 53.11 51.89 53.61 1.72

PbO 31.2 30.96 30.85 30.53 30.61 30.53 31.2 0.67ZnO 0.79 0 0 0 0BaO 0 0.83 1.25 1.1 1.1 0 1.25 1.25MgO 0.2

B2O3 0.77 0 0.26 0.58 0.52 0 0.77 0.77

K2O 12.24 12.58 12.17 11.96 12.08 11.96 12.58 0.62

Na2O 2.8 1.78 1.78 2.2 2.2 1.78 2.8 1.02

As2O3 0.065 0 0 0 0

Sb2O3 0.158 0.21 0.24 0.38 0.28 0.158 0.38 0.222

Minor changes: SiO2 slightly up PbO slightly down Zinc removed, barium added, MgO tested

And: B2O3 returning towards 1986 levels Antimony replaces Arsenic

[Cardeira, 1995]


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1995 Leach Data -- Atlantis

0 50 100 150 200 250 300 350 400 450

Salad Bowl

Whiskey Decanter

Goblet, Zephir

Red Wine Chartres

Cry

sta

l Gla

ss

Sh

ap

e

Pb, ISO test, ug/l

Vol = 2680

Vol = 210

Vol = 240

Vol = 950

217

105

418

370


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Surface Treatments: Acid Pretreatment & Cure

Acid rinse to remove surface modifiers

Cure to condense silicic acid surface film.

0.05 ug/cm2 = 25 ug/l for 1 liter round cylinder with h/r = 3.

Durable film,

withstands 300

autodish cycles


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Mathematical relationships for surface film formation

Incorporate measured activation energy for lead migration with Fick’s law.

Use to predict migration results.

D DQ

RT

~ ~

exp

0

24 0

20ln ln

~

MQ

RT

C D t

M CDt

2 0

~

SiOPbOSi s H O sol SiOH s Pb sol H O sol( ) ( ) ( ) ( ) ( )2 2 232

2


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Polishing and (NH4)2SO4 Examples

SC-1 SC-3 SC-4

SiO2 58.56 60.84 60.71

PbO 24.59 24.00 24.15ZnO 0.00 0.21 0.14

B2O3 0.28 0.97 0.49

K2O 13.58 8.04 7.71

Na2O 2.16 5.00 5.74

Whiskey Decanter Item Wine glass [FV=150 ml]

Champagne Flute

[FV=185 ml] [FV=547 ml]

[FV=710 ml]

Unpolished 1135 790 SC-1

Polished 242 210

Unpolished 270

Polished 38 40 42

SC-3

Sulfate treated

18

Unpolished 271

Polished 100 42

SC-4

Sulfate treated

11

Hande Sengel, Sisecam (1997)

Polishing gives ~75% reduction in lead release.

Sulfate treatment gives an additional ~33% reduction.


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Aging Increases Lead Release

0

200

400

600

800

1000

1200

1400

1600

1800

0 1 2 3 4 5 6 7

Weeks of weathering

Pb

, IS

O, u

g/l

Non-polished glass

Bo Jonson (1997)

Also:

Glass forming deposits Pb, Na, K modifier on surface

Aging brings same modifiers to surface.

E. Guadagnino (2000)


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Summary Lead glasses follow generally well-identified acid leaching behaviors


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Summary Lead glasses follow generally well-identified acid leaching behaviors Large body of early work collected data for specific compositions and

leachates Varied crystal compositions Varied solutions, esp. alcohol Patterns of use identified to match migration with ingestion


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Focus on composition changes, good and bad oxides


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Focus on composition changes, good and bad oxides Surface modification technologies and characterization have had

dominant role over past ~5 - 7 years Claddings, Coatings, Treatments, Advanced surface analysis Some inexpensive, others not, all require an additional step BUT, decouples migration behavior from most other glass requirements End-use specific assessments, e.g. dishwasher performance


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Summary Lead glasses follow generally well-identified acid leaching behaviors Large body of early work collected data for specific compositions and leachates

Varied crystal compositions Varied solutions, esp. alcohol Patterns of use identified to match migration with ingestion

Focus on composition changes, good and bad oxides Surface modification technologies and characterization have had dominant role over

past ~5 - 7 years Claddings, Coatings, Treatments Some inexpensive, others not, all require an additional step BUT, decouples migration behavior from most other glass requirements End-use specific assessments, e.g. dishwasher performance

General observations Migration levels are well below ISO limits Durability, in combination with other required properties and economic considerations, may

be nearly optimized within traditional lead crystal glassware definitions. Environmental issues will continue to be important Lead workplace issues will continue to impact lead use in glassware.


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Future Opportunities

Glass CompositionCombinatorial assessment of non-linear composition spaceRole of minor constituents to improve durability

Surface TreatmentsSurface film formation/modification below optical limitsChemical complexing agents to bond surface.


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Partial List of Acknowledgements

Atlantis: Carlos Fonseca CALP: Paulo Barducci, Pietro Stanghellini, Fabio Paloschi FFC: Pierre Ayral Glafo: Bo Jonson, Stellan Persson Inst. Chem. Tech.: Miroslav Rada Lalique: Paul Cordie Lenox: John Potts Nachtmann: Walter Frank Orrefors, Glasma: Arne Fransson Sisecam: Hande Sengel St. Georges Crystal: Robert Gonze, Jerry Kynik Staz. Sperimentale del Vetro: Emanuel Guadagnino Tyrone: Colin McGookin Verrerie Cristallerie D’Arques/JG Durand: Etienne Himpens Waterford: John Kennedy

Documents

International Crystal Federation Technical Exchange Conference Waterford, Ireland 12 – 14 October 2002 Lead Migration from Crystal Glassware: Developments