reengineering beauty: the pros and cons of current crystal glass manufacturing methods designed to...

Reengineering Beauty: The Pros and Cons of Current Crystal Glass Manufacturing Methods

Designed to Reduce Lead Migration

Presenters: Joseph PantinaJoshua FinchTimothy Tirrell

Advisors: Dr. Lehman Dr. Crawford

ICF Technical Exchange

Outline of Presentation

• Overview of legislation restricting lead exposure and use

• Summary of the role of lead in crystal– Structure– Migration

• Review of selected processes to reduce lead migration– Surface Modification– Surface Coatings

• Discuss advantages/disadvantages


Legislation regarding Lead

Proposition 65:• California’s Office of

Environmental Health Hazard Assessment (OEHHA)

• Lead leaching must not exceed:- 226 ppb (for flatware)-100 ppb (all other tableware)

• Leaching test use 4% acetic acid solution at 22oC

• Products failing to fall below “safe harbor levels” of lead must bear a warning.

REACH:• Registration, Evaluation,

and Authorization of Chemicals

• European Union initiative• Toxic chemicals must be

registered upon their production

• Chemicals must be tracked during all stages of its use in production

“Warning: This product contains chemicals known to the State of California to cause cancer and birth defects or other reproductive harm.”


Reasons for Lead in Crystal

Optical Properties:- Increases index of refraction- Increases dispersion of light

Mechanical Properties:- Increases density- Decreases hardness

Processing Properties:- Improves glass workability- Increases machinability


Chemical aspects of Lead in Crystal

Lead’s role as a glass former:• Some fraction of lead atoms occupy glass network

positions• Covalently bonded to silicon in the silicate structure

Lead leaching of lead as a glass former:

• Negligible for acidic solutions below ph=7

- Due to covalent bonds of lead glass formers

• Low for alkaline solutions below pH=10

- Slow deterioration of silicate network; releases lead ions

• High for alkaline solutions above pH=10

- Rapid deterioration of silicate network; releases lead ions

Lehman 2002


Chemical aspects of Lead in Crystal (Cont.)

Lead’s role as a glass modifier:• Large concentrations “open up” the lead silicate

structure• Modifier lead ions are ionic bondedEffect of acidic solutions:

• H+/H3O+ ions compete with Pb2+ ions, via Coulombic forces

• Pb2+ ion replacement forms a silanol layer (non-bridging oxygen)

• ≡Si-O-Pb-O-Si≡(s) + 2H3O+(sol) 2≡SiOH(s) + Pb2+

(sol) +

2H2O(sol)

*Note: 2(≡SiOH) allow for further ion diffusion through the non-bridged structure


Methods to reduce lead leaching must:1)Maintain the quality and integrity of the

original crystal

2)Reduction of lead leach rate below legislative standards

3)Maintain appearance and lowered leach rate after persistent use, including up to 500 dishwasher cycles


Methods for Reducing Lead Leaching

Surface Modification: changes the chemical composition of the crystal surface to provide a lead diffusion barrier.Methods:

1) Pre-leaching/acid wash with subsequent annealing2) Ammonium sulfate Fuming3) Baccarat Ion Exchange Treatment4) British Glass Microwave Assisted Ion Exchange

Surface Coating: coatings used to provide a lead-free barrier to lead diffusion from a crystal surfaceMethods:

1) Sol-Gel Coating2) Chemical Vapor Deposition (CVD)3) Schott Plasma Impulse Chemical Vapor Deposition

(PICVD)


Pre-leaching/acid wash with subsequent annealingOverview:1) Crystal surface exposed to acidic solution to leach out

lead ions2) Surface layer of silanol is dehydrated by annealing

• 2(≡SiOH)(s) ≡Si-O-Si≡(s) + H2O(v)

3) Lead deficient silica surface layer is formed

Optimized Method: Reduced leach rates 24% Lead Crystal (Lehman 1997)

• 4% acetic acid solution at 40oC• 9 minute pre-leach time• 2 hour annealing at 200-300oC

Heat


Pre-leaching/acid wash with subsequent annealing (Cont.)

Lead leach rates of treated crystal under standard testing with 4% acetic acid solution at 22oC

Lead release in (µg/cm²) as a function of preleach time and annealing temperature

Pretreatment Temperature

Annealing Temperature 0 minutes 1 minute 9 minute 25 minute

(ºC) (ºC) average average average average

100 0.38 0.21 0.15 0.16

40 200 0.17 0.09 0.00 0.07

300 0.15 0.06 0.00 0.00

•No detectable lead levels after lead leach test for samples pretreated for 9 minutes and annealed at 200oC

•Comparison to lower pre-leach times show that 9 minutes can create a lead deficient silicate layer

•Annealing temperature trends suggest that a heat treatment of at least 200oC is needed to densify the lead deficient layer to block further lead leaching


Ammonium Sulfate Fuming

Overview:• Ammonium sulfate is added to pre-annealed crystal• At annealing temperature, ammonium sulfate reacts

with lead and potassium cations.(NH4)2SO4 + Pb2+ + K1+ PbSO4 + K2SO4 +

NH3+ H2

• Potassium and lead sulfate are precipitated on the crystal surface

• Precipitates can be washed away to leave a lead depleted crystal surface layer


Ammonium Sulfate Fuming (Cont.)

• British Glass investigated the addition of 0.1 g ammonium sulfate to crystal before annealing

• Crystal annealed at 490oC• Precipitates were analyzed by chemical analysis,

confirming the composition as potassium and lead sulfate• Standard Testing in a 4% acetic acid at 22oC

• X-ray photoelectron spectroscopy (XPS) of the treated surface shows a 1/3 of Pb and 1/6 of K ions still remain compared to the untreated surface

Untreated Treated

600 ppb Pb 40 ppb Pb


Baccarat Ion-exchange Treatment

Details obtained from:“Process for treating lead glass to form a lead diffusion

barrier in the surface thereof.” (US Patent # 5308652)Overview:• An ion exchange slip is selected to provide non-toxic

metal glass forming ions for exchange with lead ions.• Crystal surface is coated with ion exchange slip• Bulk crystal is heat treated to increase the diffusion

rate of ions (Fick’s Law)• Non-toxic ions replace lead to form a diffusion barrier

to further lead migration in the surface layer• Removal of “cemented” slip on the crystal surface


Baccarat Ion-exchange Treatment (Cont.)

Type of slip utilized:• Kaolin or hydrated aluminum silicate

- Both slips provide Al3+ ions in aqueous solutions- Thixotropic viscous behavior maintains thickness under gravity

Heating Cycle:- gradual heating to 400-440oC- 4-6 hour hold between 400-440oC- 3 hour cooling to room temperature


Baccarat Ion-exchange Treatment: Results• Leaching studies done on

treated crystal containing between 1%-40% PbO, all show greatly reduced leaching levels compared to untreated crystal

• Secondary Ion Mass Spectroscopy (SIMS) shows a silico-aluminous layer of at least 20 nm; normally ranging between 50-100 nm

Lead Leaching Test of Baccarat Surface Treated 30% PbO Crystal with a 4% acetic acid solution (pH=2.3) and with an alcohol solution (pH=3.5)

Time Elapsed (Months)

6 12 24 36 60

Lead Concentration (µg/L)

Acetic Acid 31.0

43.8

62.0

76 98

Alcohol 13 18.3

25.9

31.6

40


British Glass Microwave Assisted Ion ExchangeOverview:• Researches at British Glass investigated the use of

different non-toxic metal ions (Al, Ti, Zr, Sr) for ceramic ion exchange slips using a microwave heat treatment

• Crystal is pre-leached in 4% acetic acid at 90oC for 10 minutes.

• Crystal is coated with ion exchange slip• Microwave exposure of 2.45 Ghz, 500 watt source for

10 minutes• Remove hardened slip from the crystal surface.


British Glass Microwave Assisted Ion Exchange (Cont.)

Advantages of Microwave Heating:• Crystal is transparent at microwave (Ghz) frequency• High absorption of radiation from ion-exchange slip at

the crystal surface• Surface heating increases surface ion diffusion• Bulk crystal is not affected by the heat treatment• Oscillating electromagnetic wave can assist migration

of charged ions


British Glass Microwave Assisted Ion Exchange: Results

• All slips show superior performance to no treatment or acid washing in long term tests.

• Prompted the refinement of the crystal surface treatment to reduce processing time and cost.

Used 2h leach time and two stage 10min microwave treatment

•Refined method tested with a titanium ion exchange slip

Treatment 24 Hour4% Acetic Acid

(ppb Pb)

4 Month4% Acetic Acid

(ppb Pb)

Control (no Treatment)

Ti

600

10

(Not Recorded)

<25

•XPS characterization of treated crystal shows a silica rich surface with small amounts of titania

•SEM reveals no surface damage after treatment


Sol-Gel Method

Hydrolysis of a Silicon Alkoxide:(C2H5O)4-Si +H2O (C2H5O)3-Si-OH + C2H5OH (1)

Condensation Polymerization Reaction:-Si-OH + OH-Si- -Si-O-Si- + H2O (2)

Previous tests have shown no detectable lead leaching after coating, but results in unappealing optical qualities.

Coatings ≤ 2 µm Possible


Chemical Vapor Deposition

CVD of thin films of phosphorous doped titania and zirconia for lead diffusion barrier

Tested By: Metaleurop Recherche and the Laboratory of Materials of the Polytechnic Institute, Grenoble

• Source gas: Metal-organic precursors volatilized by ultrasonication at low pressures

• Precursor gases mix in proper proportions with carrier gas

• Pyrolysis of precursor gas take place at the surface of a heated crystal substrate

• Heterogenous nucleation of film occurs at crystal surface


Chemical Vapor Deposition: Results

• Process only tested on 2 cm2 flat crystal samples- Control of film uniformity posses a problem for complex shapes

• Low leach rates were reported (not replicated by further tests)

• Thermal expansion of titania and zirconia are different than crystal- Cooling the crystal after coating will cause strain at the interface- Interface strain can lead to delamination


Schott Glass - PICVD

Plasma Impulse Chemical Vapor Deposition (PICVD)Developed By: Schott Glass

Primary Uses: Coating low melting point glass and polymer tubes and containers with quartz-like coatings

• Microwave radiation is used to decompose precursor gas


Schott Glass – PICVD (Surface Coating Inspection)

Stage 1 - Two in-situ surface characterization methods- Optical Plasma Emission- Temperature

Stage 2 - Thickness controlled by online manipulation of gas flow, vacuum pressure, and microwave energy

Stage 3 – System Monitoring- Automatic calibration of sensors- Automatic data collection and archiving


Schott Glass – PICVD

Durability and Leaching Results:

• Comparison between Type 1 and Type 1 plus pharmaceutical glassware

Coating Maintained after Autoclaving Tests w/

Solution Duration (Hours)

Temperature (°C)

0.1 M HCL 6 121

NaOH (pH=10) 1 121

3% EDTA (pH=4.5) 1 121

3% Citric acid 1 121


Surface Modification can…

• Reduce lead leaching below Proposition 65 standards• Maintain the crystal’s original optical qualities

However,

• Conventional heating near glass softening temperature is often needed for some processes

• Processes rely on slow chemical reactions to remove lead from the crystal surface

• Microwave processes are needed to reduce processing time

• Lead removed from the crystal surface is a disposal issue


Surface Coating can…

• Provide a lead-free diffusion barrier to lead migration• Be applied using a wide range of processing

techniques at different temperatures

However,• Uniformity of the coating can present difficulties in

certain coating processes• Incomplete coatings result in high lead leaching rates• Optical and mechanical properties of the surface

coating must be similar to the properties of the coated crystal


References1. Copley, G. J., & Kennedy, J. (1993a). British Glass, & Waterford Crystal. Microwave Surface Treatment For

Lead Crystal Glassware. Paper presented at ICF Technical Exchange Conference, Pittsburgh, PA.2. Copley, G. J., Dalton, D. A., & Glendenning, M. D. (1993b). British Glass. Full Lead Crystal: Report on

Surface Modification. Paper presented at ICF Technical Exchange Conference, Waterford, Ireland.3. Cornier, G., & Baccarat, Compagnie des Cristalleries de Baccarat. (1994). U.S. Patent No. 5,308,652.

Washington, DC: U.S. Patent and Trademark Office.4. Kear, B. H. (2007, Fall). Stuctural/Mechanical/Chemical Properties of Nanomaterials. MSE 14:635:401: Rutgers

University.5. Kliokis, J., Lehman, R. L., & Strange, D. J. (1997). Rutgers University: Center for Ceramics Research. Effects of

Surface Treatments on Lead Migration from Lead Crystal Glassware. Paper presented at ICF Technical Exchange Conference, Estoril, Portugal.

6. Lehman, R. L., & Rabii, C. (1993a). Rutgers University: Center for Ceramics Research. The Effects of Surface Treatments on Lead Release of Lead Crystal Glass. Paper presented at ICF Technical Exchange

Conference, Pittsburgh, PA.7. Lehman, R. L. (1995). Rutgers University: Center for Ceramic Research. The Structure of Lead-Containing

Silicate Glasses and Approaches to Improve Durability. Paper presented at ICF Technical Exchange Conference, Orrefors, Sweden.

8. Lehman, R. L., & Strange, D. J. (1996). Rutgers University: Center for Ceramics Research. Surface Treatment Of Lead Crystal: Optimized Stabilization of the Surface Layers of Lead Crystal Glassware. Paper

presented at ICF Technical Exchange Conference, Stourbridge, UK.9. Lehman, R. L. (2002). Rutgers University: Center for Ceramics Research. Lead Migration from Crystal

Glassware: Developments From 12 Years of ICF TECs. Powerpoint preseneted at ICF Technical Exchange Conference, Waterford, Ireland.

10. OEHHA. (2007). OEHHA Proposition 65: Proposition 65 FAQs. Retrieved October, 12th, 2007, from Office of Environmental Health Hazard Assessment Website: http://www.oehha.ca.gov/prop65/p65faq.html

11. Perrier, E. (1993a). Metaleurop Recherche. Protective Coating For Crystal Glass. Paper presented at ICF Technical Exchange Conference, Pittsburgh, PA.

12. Potts, J. (1992). Lead Migration Reduction at Lenox. Paper presented at ICF Technical Exchange Conference, Colle Val d’Elsa, Italy.

13. Schott Glass (2007). Schott Type 1 Plus®: Container with a quartz-like inner surface [Pamphlet]. US: Schott Glass.

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