characteristics of the weathered surfaces of phosphate glasses

Characteristics of the Weathered Surfaces of Phosphate Glasses

Brad Tischendorf* & Richard BrowUniversity of Missouri-Rolla USA

XX International Congress on GlassOct. 1, 2004Kyoto, Japan

Oct. 1, 2004 XX ICG : Kyoto, Japan 2

Phosphate glasses are prone to weathering degradation

Scattered lightdue to weathering

_

Example of a badly weathered glass surfaceScattered light

due to weathering

Example of a badlyweathered glass surface


Surface corrosion is due to precipitation of hydrated orthophosphate crystals

2Theta (º)

10 20 30 40 50 60 70

Dif

fra

cte

d In

ten

sit

y (c

ps

)

KAP

BAP

KBAP


Weathering depends on the interactions between water and the glass surface

Diffusion of water and hydration ofchains and modifiers

Glass Dissolution with chain and cation removal into solution

Weathering reactions with surface hydrolysis and crystallization

Aqueous Humid


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

K2O MgO BaO CaO Al2O3 P2O5 O/P Ratio

15-15-10-60 (KCAP) 15 0 0 15 10 60 3.0

15-15-10-60 (KBAP) 15 0 15 0 10 60 3.0

15-15-10-60 (KMAP) 15 15 0 0 10 60 3.0

LG-770 22 8 0 0 8 60 3.0

LHG-8 15 0 15 0 10 58 3.0


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)


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.


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

Weathering Time (days)

0 2 4 6 8 10 12 14 16

We

igh

t G

ain

(g

/cm

2 )

0.00

2.00e-5

4.00e-5

6.00e-5

8.00e-5

1.00e-4

1.20e-4

1.40e-4

KMAP KBAP KCAP LG-770 LHG-8


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


0 2 4 6 8 10 12 14 16

We

igh

t G

ain

(g

/cm

2 )

0.00

2.00e-5

4.00e-5

6.00e-5

8.00e-5

1.00e-4

1.20e-4

1.40e-4


0 2 4 6 8 10 12 14 16

0

1e-4

2e-4

3e-4

4e-4


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


0 2 4 6 8 10 12 14 16

We

igh

t G

ain

(g

/cm

2 )

0.00

2.00e-6

4.00e-6

6.00e-6

8.00e-6KMAP KBAP KCAP LG-770 LHG-8


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

Depth (m)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Co

nce

ntr

atio

n (

H/c

m3)

0

2x1021

4x1021

6x1021

8x1021

10x1021

12x1021

14x1021

16x1021

18x1021

20x1021

22x1021

25-25-10-40

KMAPKBAP20-20-10-50


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


0 2 4 6 8 10 12 14 16

We

igh

t G

ain

(g

/cm

2 )

0.00

2.00e-5

4.00e-5

6.00e-5

8.00e-5

1.00e-4

1.20e-4

1.40e-4


0 2 4 6 8 10 12 14 16

0.000

0.001

0.002

0.003

0.004

0.005


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

ppm

-240-210-180-150-120-90-60-300306090120150180

KAP

KMAP

KBAP

7 days50oC 80%RH


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.


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


HPLC experimental procedure• Glass plates were polished to 1m 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


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

• P1 – 26%

• P2 – 26%

• P3 – 25%

• P3m – 23%

Time (minutes)

5 10 15 20 25 30

Ab

so

rba

nc

e (

AU

)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18


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

Retention Time (min)

6 8 10 12 14 16 18 20

UV

-VIS

Ab

so

rba

nc

e (

AU

)

Initial RunAfter 20 Days

[P1+P2]/[Ptotal] = 0.22 initial

= 0.2 after 20 days


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

Time (minutes)

0 5 10 15 20 25 30

Ab

sorb

ance

(A

U)

0.0

0.5

1.0

1.5

2.0

• P1 – 62%

• P2 – 32%

• P3 – 4%


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


0 2 4 6 8 10 12 14

[P1+

P2]

-[P

1+P

2]p

rist

ine

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14 LHG-8 LG-770 KMAP KBAP


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


0 2 4 6 8 10 12 14

[P1+

P2]

-[P

1+P

2]p

rist

ine

0.00

0.01

0.02

0.03

0.04

0.05 LHG-8 LG-770 KMAP KBAP


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


0 2 4 6 8 10 12 14

[P1+

P2]

/Pto

tal

0.000

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

LHG-8 LG-770 KBAP KCAP KMAP


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

Weathering Humidity

10 20 30 40 50 60 70 80

To

tal O

xid

e S

lop

e ( g

/cm

2 /day

)

0

5

10

15

20

Absolute Humidity (gH2O/m3)

Relative Humidity (%)

Not sure, may dump this section


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


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?


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

Sample Type

Polished Pristine Fiber Powder

Ave

rag

e C

hai

n L

en

gth

4

5

6

7

8

9

10

11


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.


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

characteristics of the weathered surfaces of phosphate glasses

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