characteristics of the weathered surfaces of phosphate glasses
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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
Oct. 1, 2004 XX ICG : Kyoto, Japan 3
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
Oct. 1, 2004 XX ICG : Kyoto, Japan 4
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
Oct. 1, 2004 XX ICG : Kyoto, Japan 5
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
Oct. 1, 2004 XX ICG : Kyoto, Japan 6
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)
Oct. 1, 2004 XX ICG : Kyoto, Japan 7
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.
Oct. 1, 2004 XX ICG : Kyoto, Japan 8
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
Oct. 1, 2004 XX ICG : Kyoto, Japan 9
The same effect is observed at 40ºC/80% RH
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
0 2 4 6 8 10 12 14 16
0
1e-4
2e-4
3e-4
4e-4
Oct. 1, 2004 XX ICG : Kyoto, Japan 10
At 25ºC/80%RH there is no measurable weight gain until after 14 days
Weathering Time (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
Oct. 1, 2004 XX ICG : Kyoto, Japan 11
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
Oct. 1, 2004 XX ICG : Kyoto, Japan 12
This data agrees with the weight gain data: after 7 days, KMAP and KBAP are near the same
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
0 2 4 6 8 10 12 14 16
0.000
0.001
0.002
0.003
0.004
0.005
Oct. 1, 2004 XX ICG : Kyoto, Japan 13
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
Oct. 1, 2004 XX ICG : Kyoto, Japan 14
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.
Oct. 1, 2004 XX ICG : Kyoto, Japan 15
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
Oct. 1, 2004 XX ICG : Kyoto, Japan 16
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
Oct. 1, 2004 XX ICG : Kyoto, Japan 17
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
Oct. 1, 2004 XX ICG : Kyoto, Japan 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
Oct. 1, 2004 XX ICG : Kyoto, Japan 19
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%
Oct. 1, 2004 XX ICG : Kyoto, Japan 20
Increased production of PO4 and P2O7 is seen in the MgO containing glass at 50ºC/80%RH
Weathering Time (days)
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
Oct. 1, 2004 XX ICG : Kyoto, Japan 21
As is seen in the weight gain data, this trend continues at lower temperatures of 40 and 25ºC
Weathering Time (days)
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
Oct. 1, 2004 XX ICG : Kyoto, Japan 22
The ratio’s of P1+P2 show the same dependence with MgO glasses more reactive
Weathering Time (days)
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
Oct. 1, 2004 XX ICG : Kyoto, Japan 23
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
Oct. 1, 2004 XX ICG : Kyoto, Japan 24
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
Oct. 1, 2004 XX ICG : Kyoto, Japan 25
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?
Oct. 1, 2004 XX ICG : Kyoto, Japan 26
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
Oct. 1, 2004 XX ICG : Kyoto, Japan 27
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.
Oct. 1, 2004 XX ICG : Kyoto, Japan 28
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