Characteristics of the weathered surfaces of phosphate glasses
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Characteristics of the Weathered Surfaces of Phosphate Glasses. Brad Tischendorf* & Richard Brow University of Missouri-Rolla USA XX International Congress on Glass Oct. 1, 2004 Kyoto, Japan. Phosphate glasses are prone to weathering degradation. Example of a badly weathered glass surface.

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Characteristics of the Weathered Surfaces of Phosphate Glasses

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Characteristics of the weathered surfaces of phosphate glasses

Characteristics of the Weathered Surfaces of Phosphate Glasses

Brad Tischendorf* & Richard Brow

University of Missouri-Rolla USA

XX International Congress on Glass

Oct. 1, 2004

Kyoto, Japan


Phosphate glasses are prone to weathering degradation

Phosphate glasses are prone to weathering degradation

Example of a badly

weathered glass surface

Scattered light

due to weathering

XX ICG : Kyoto, Japan


Surface corrosion is due to precipitation of hydrated orthophosphate crystals

Surface corrosion is due to precipitation of hydrated orthophosphate crystals

XX ICG : Kyoto, Japan


Weathering depends on the interactions between water and the glass surface

Weathering depends on the interactions between water and the glass surface

Diffusion of water and hydration of

chains and modifiers

Humid

Aqueous

Glass Dissolution with chain and cation removal into solution

Weathering reactions with surface hydrolysis and crystallization

XX ICG : Kyoto, Japan


Glass compositions

Glass compositions

  • These glass compositions have been chosen to act as models for commercial phosphate glass amplifiers such as those used at the National Ignition Facility

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Techniques used to measure the different reaction mechanisms

Techniques used to measure the different reaction mechanisms

  • Diffusion and Hydration

    • Weight gain of samples during weathering

    • Elastic Recoil Detection (ERD) for H depth profiles

  • Surface Hydrolysis

    • MAS NMR

    • High Pressure Liquid Chromatography (HPLC)

  • Surface Crystallization

    • Thin Film X-ray Diffraction (TF-XRD)

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This slide won t be included it s to add commentary for you

This slide won’t be included, it’s to add commentary for you

  • The first step was to measure how much water is getting into the glass surfaces.

  • Initially we simply measured the gain in weight as a function of weathering time.

  • This was then followed by measurement on H depth profiles with ERD

  • The two results seem to qualitatively agree with the systems we have looked at.

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Following the weight gain at 50 c 80 rh shows mgo containing glasses reacting faster

Following the weight gain at 50ºC/80%RH shows MgO containing glasses reacting faster

XX ICG : Kyoto, Japan


The same effect is observed at 40 c 80 rh

The same effect is observed at 40ºC/80% RH

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At 25 c 80 rh there is no measurable weight gain until after 14 days

At 25ºC/80%RH there is no measurable weight gain until after 14 days

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Erd shows equal amounts of water present on the kmap and kbap surfaces after 7 days

ERD shows equal amounts of water present on the KMAP and KBAP surfaces after 7 days

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This data agrees with the weight gain data after 7 days kmap and kbap are near the same

This data agrees with the weight gain data: after 7 days, KMAP and KBAP are near the same

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Nmr indicates compositional differences in the rates of reactivity of the glasses

NMR indicates compositional differences in the rates of reactivity of the glasses

7 days

50oC 80%RH

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This slide won t be included it s to add commentary for you1

This slide won’t be included, it’s to add commentary for you

  • Now that we know how much water was getting in we wanted to measure the structural changes occurring due to this water.

  • WE began with NMR which shows a rate of reactivity where KAP>KMAP>KBAP.

  • Downside is that NMR probes entire sample and must be a powdered sample,not necessarily representative of a real system.

  • So we looked into HPLC where we could take a polished piece of glass and dissolve the surface away to measure its structure.

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Hplc provides a method to probe the structure of phosphate glass surfaces

HPLC provides a method to probe the structure of phosphate glass surfaces

  • A solution containing the phosphate glass is loaded into the injection valve.

  • Once injected, the gradient pump ramps the solution from 0.05 to 0.5M NaCl.

  • After separation, the phosphate species are reacted at 170ºC in 1.8M H2SO4 with ammonium molybdate

  • The resultant “blue” species concentration is measured with the UV-VIS

XX ICG : Kyoto, Japan


Hplc experimental procedure

HPLC experimental procedure

  • Glass plates were polished to 1mm finish

  • Plates were measured and weighed then placed into a controlled humidity temperature environment

  • Samples periodically removed and weighed for weight gain, then surface removed in a solution of EDTA

  • Weight loss was measured

  • Solution was run through HPLC system

  • Prior to and after runs, all solutions were refrigerated for storage

  • Nomenclature:

    • P1 = PO4

    • P3m = P3O9 ring species

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Standard solutions of known phosphate species are used to calibrate species and concentrations

Standard solutions of known phosphate species are used to calibrate species and concentrations

  • P1 – 26%

  • P2 – 26%

  • P3 – 25%

  • P3m – 23%

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Runs of stored samples show they are stable for at least 3 weeks when refrigerated

Runs of stored samples show they are stable for at least 3 weeks when refrigerated

  • This plot shows LHG-8 weathered for 4 days at 25ºC and 80%RH immediately after surface removal, and after sitting for three weeks

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Hplc shows that kap reacts rapidly at 50 c and 80 rh

HPLC shows that KAP reacts rapidly at 50ºC and 80%RH

  • P1 – 62%

  • P2 – 32%

  • P3 – 4%

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Increased production of po4 and p2o7 is seen in the mgo containing glass at 50 c 80 rh

Increased production of PO4 and P2O7 is seen in the MgO containing glass at 50ºC/80%RH

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As is seen in the weight gain data this trend continues at lower temperatures of 40 and 25 c

As is seen in the weight gain data, this trend continues at lower temperatures of 40 and 25ºC

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The ratio s of p 1 p 2 show the same dependence with mgo glasses more reactive

The ratio’s of P1+P2 show the same dependence with MgO glasses more reactive

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Weathered surface removal from lg 770 trends with either absolute or relative humidity

Weathered surface removal from LG-770 trends with either absolute or relative humidity

Not sure, may dump this section

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Activation energies for water diffusion and chain hydration hydrolysis

Activation Energies for water diffusion and chain hydration/hydrolysis

  • Rough calculations from both ERD profiles and weight gain data show that KMAP exhibits a diffusion activation energy of ~1 kJ/mole

    • Problem is that these were two point fits

  • Calculations of the activation energy of chain hydration/hydrolysis gives numbers near 100 kJ/mole whether weight loss is measured directly by surface removal or by the results of HPLC concentration conversions

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Ongoing work

Ongoing work

  • Adding additional humidity's to the study

  • Compare the rates of reactivity of poly and pyro-phosphate glasses to the meta-phosphate species already studied

  • What is the effect of surface preparation on the weathering rate?

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The type of sample studied may affect the results of the chromatography experiment

The type of sample studied may affect the results of the chromatography experiment

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Conclusions

Conclusions

  • The rates of penetration of water into glass surfaces has been measured

  • The effect of this water on the structure of the glass surface was studied

  • The dependence of these reactions on glass composition was studied.

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Acknowledgements

Acknowledgements

  • This work is funded by Lawrence Livermore National Laboratory. Work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.

    Special Thanks to:

  • Joe Hayden of Schott Glass Technologies for Glass Cullet used to produce weathering samples

  • Barney Doyle of Sandia National Laboratories for running the ERD spectra used in this study

  • Todd Alam and Brian Cherry also of Sandia National Laboratories for their aid in performing the NMR experiments

  • Fred Stover of Asteris for HPLC advice and providing phosphate standards

XX ICG : Kyoto, Japan


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