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Aqueous Durability of Glasses New Approaches Thorsten Geisler(-Wierwille) Steinmann Institute , University of Bonn, Germany int ICTP-IAEA Workshop Triest (6.11.-10.11.2017) tgeisler@uni-bon int ICTP-IAEA Workshop Triest

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

Aqueous Durability of Glasses – New Approaches

Thorsten Geisler(-Wierwille) Steinmann Institute , University of Bonn, Germany

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

from Gin et al. (20

Observations: Corrosion kinetics

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon after Grambow (1986) after Geisler et al. (2010; 201

Re-structured residual glass

SOLUTION

Na H2O

Glass corrosion mechanisms

PRISTINE GLASS

SOLUTION

Na H2O

SOLUTION

PRI

, Frugier et al. (2008)

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

Observations – Patterned corrosion zones from nature

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon Dohmen et al. (2013)

Observations – Patterned corrosion zones from experiments

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

  • Glass-water reactions are commonly studied experimentally by ex-situ analysing the

experimental solution and/or reaction products, i.e., after the reaction has taken place.

  • Limitations and problems of such an ex-situ approach are…
  • short-time and small changes in the reaction kinetics are difficult to record
  • quenching, drying, and physical sectioning may cause:
  • phase precipitation
  • structural and chemical changes of the reaction products
  • physical cracking

Motivation

Limitations of and problems with the present experimental methodologies

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

It follows that information about the dynamics of the structural and chemical evolution of the corrosion laye is not directly accessible. However, … What can we do to overcome such limitations?

  • 1. (Multi-)isotope tracer exchange experiment → isotope coupling or decoupling in space

and time gives information about the dynamics of individual reactions.

  • 2. In-situ experiments → following the reaction in real-time without disturbing it.

Motivation

Limitations of and problems with the present experimental methodologies

“a ¡process ¡cannot ¡be ¡understood ¡by ¡stopping ¡it. ¡ Understanding ¡must ¡move ¡with ¡the ¡8low ¡of ¡the ¡process, ¡must ¡join ¡it ¡and ¡8low ¡with ¡it.” ¡

— ¡Frank ¡Herbert, ¡Dune

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

Solution Glass

(e.g., atomic force microscopy or interferometry)

Alteration phase(s)

Reaction interface

Currently established in situ techniques only probe surface reactions

In-situ experiments

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

Solution Thermocouple

T = 70 and 90°C, 26 to 240 h

Sample Fused silica window Confocal focus

Schema'c ¡Raman ¡fluid ¡cell ¡setup ¡ Raman ¡fluid ¡cell ¡setup ¡

Solu%on ¡ ¡ inlet ¡ Solu%on ¡ ¡

  • utlet ¡

Electrodes ¡for ¡ impedance ¡ ¡ spectroscopy ¡ Thermocouple ¡ wires ¡ Filament ¡hea%ng ¡ Objec%ve ¡ 100x ¡LWD ¡

(N.A. ¡= ¡0.8) ¡ ¡

Confocal Raman spectroscopy allows overcoming such limitations

Experimental details

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

Glass samples

Experimental details

T B G C aNaG IS G Q B G

10 20 30 40 50 60 70 80 90 100

¡ ¡

¡F raction ¡(mol.% )

¡S iO 2 ¡B 2O 3 ¡A l2O 3 ¡Na 2O ¡C aO ¡Z rO 2 ¡O thers

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

Sample chamber

Experimental hall II Schematic view of the accelerator in Darmstadt

4.8 MeV 197Au+ ions were used to irradiate the TBG with a flux of 5 x 1012 ions/cm2

Heavy ion irradiation at the GSI Helmholtz Center in Darmstadt, Germany

Experimental details

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

10 15 20 25 30 35 40 45 50 Q 4 Q 3 Q 2

¡

F raction ¡(% )

Q

n ¡s peciation

Q 1 400 600 800 1000 1200 1400 1600

Non-­‑irradiated ¡g las s

630 O 2 B O 3 ¡units ¡in boroxol ¡rings

¡Intens ity ¡(arb. ¡unit)

¡ ¡

R aman ¡s hift ¡(cm

  • ­‑1)

R

Irradiated ¡g las s

(5 x 10

12 ¡A g ¡ions /cm 2)

Structural effects of heavy ion irradiation (TBG)

Q1 Q2 Q3 Q4

Depolymerization

  • f the SiO4

network

Experimental details

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

Measuring glass retreat and spatial resolution

400 600 800 1000 1200 1400 1600 Metaborate rings S i-­‑O -­‑NB O s tretching S i-­‑O -­‑S i bending

Non-­‑irradiated ¡g lass

630 O 2 B O 3 ¡units ¡in boroxol ¡rings

¡Intens ity ¡(arb. ¡unit)

¡ ¡

R aman ¡s hift ¡(cm

  • ­‑1)

R

Q1 Q2 Q3 Q4

TBG

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

  • ­‑40
  • ­‑20

80 60 40

0.5 ¡h 2.6 ¡h 3.7 ¡h 9.0 ¡h

¡ ¡

A 400-­‑800 ¡(normaliz ed ¡intens ity)

D is tance ¡(µm)

P os ition ¡of ¡ reaction ¡front after ¡9 ¡h

20

P os ition ¡of ¡the ¡ water-­‑glas s ¡ interface

Δlateral= 8 – 25 µm Glass retreat

Experimental details

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

950 1000 1050 1100

¡

¡ ¡1M ¡Na 2C O 3 ¡ ¡1M ¡NaH C O 3 ¡ ¡ ¡ ¡ ¡ ¡ ¡ ¡ ¡ ¡ ¡s olution

ν1(C O

2-­‑ 3 )

ν5(H C O

  • ­‑

3)

¡Intens ity ¡(arb. ¡unit)

The principle:

Monitoring the solution pH at any point in space and time

Raman shift (cm-1) pH Fraction

H2CO3 HCO3

  • CO3

2-

{

pH range

  • f interest

pH = f (A /A )

v1(CO3

2-)

v5(HCO3

  • )

Experimental details

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

Experimental details

Monitoring the diffusion (and reaction) of molecular water through the rim

2200 2400 2600 2800 3000 3200 3400 3600 3800 4000 500 1000 1500 2000 2500 3000

¡ ¡

Intens ity ¡(counts ) R aman ¡s hift ¡(cm

  • ­‑1)

2v2(H2O) 2v2(D2O) v1(H2O) v3(H2O) v1(D2O) v3(D2O) vs(SiO-D) vs(SiO-H)

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

Experiments

Experimental details

Experiment #1 – TBG , 70°C, 0.1M HCl (pH70°= 1.0) → Gap formation and silica aging Experiment #4 – TBG, 90°C, 0.5M NaHCO3 (pH90°C = 7.2), after 140 h injection of D2O → pH gradient in solution and corrosion rim and diffusion of water through the rim Experiment(s) #5 – TBG und TBGirradiated, 90°C, 0.5M NaHCO3 (pH90°C = 7.2) → Effect of heavy ion irradiation on the forward dissolution rate (r0) Experiment #2 - TBG, 90°C, 0.5M NaHCO3 (pH90°C = 7.2) → pH gradient in a solution boundary layer Experiment #3 - CaNaG, 90°C, 0.5M NaHCO3 (pH90°C = 7.2) → Effect of secondary phase formation on pH

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

Raman spectrum of the NaBSi glass @ 70°C

3200 3600 4000

13 12 11

¡

R aman ¡s hift ¡(cm

  • ­‑1)

10

400 800 1200 1600 2000 2400 2800

¡

Intens ity ¡(arb. ¡unit) R aman ¡s hift ¡(cm

  • ­‑1)

0.1M HCl Solution

Thermocouple

Objective 100x LWD

(N.A. = 0.8)

Experimental setup

Laser beam

(532 nm)

T = 70°C

Silica inner surface OH

400 800 1200 1600 2000 2400 2800

9 8 7 6 5 4 3 2

* * *

¡

Intens ity ¡(arb. ¡unit) R aman ¡s hift ¡(cm

  • ­‑1)

*

R aman ¡s hift ¡(cm

  • ­‑1)

1

250 300 350 400 450 500 550 600 0.0 0.2 0.4 0.6 0.8 1.0

>4-­‑fold rings

¡

Normalis ed ¡intens ity

Inc reas ing ¡ reac tion ¡ time

4-­‑fold rings

After 2 hours

Borosilicate Glass

Experiment #1 - Gap formation and silica aging

Results of in-situ experiments

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

Relative fraction of (SiO)n>4 rings in silica Relative fraction of surface Si-OH Relative fraction of H2O in the analyzed volume

Area not imaged Area not imaged Area not imaged

A3560-3620/A3000-3750 A3000-3700/A200-1250 A250-460/A250-600

High 0.11 0.08 0.74 0.42

3 7 10 14 21 28 36 39 43 57 78 96 114 132 150 168 187 205 226 245

Glass Solution Silica Gap

t (h)

Low

25 µm

Results of in-situ experiments

Experiment #1: Gap formation and silica aging

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

20 40 60 80 100 120 140 160 180 200 220 240 0.092 0.094 0.096 0.098 0.100 0.102 0.104 0.40 0.45 0.50 0.55 0.60 0.65 0.36 0.40 0.44 0.48 0.52 0.56

¡

T ime ¡(h)

¡ ¡

20 40 60 80 100 120 140 160 180 200 220 240

5 10 15 20 25 30 35 40

¡T ime ¡(h)

¡

A3560-3620/A3000-3750

Glass Silica Gap

20 µm BSE image of altered glass after the experiment Glas retreat (µm) A3000-3700/A200-1250 A250-460/A250-600 Relative fraction of surface Si-OH in silica Relative fraction of (SiO)n>4 rings in silica Relative fraction

  • f H2O

Increasing degree of polymerization rate = 0.062(12) µm/h

Results of in-situ experiments

Experiment #1 - Gap formation and silica aging

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

Glass cover

(175 µm)

0.5M NaHCO3

Experimental setup

Objective 100x LWD

(N.A. = 0.8)

Laser beam

(532 nm)

T = 90°C TBG

Results of in-situ experiments

Molecular water pH Silica A A

v1(CO3

2-)aq v5

(HCO3

  • )aq

A v(H2O)

Glass Solution

Interface Glass retreat A250-500

µm

Experiment #2 - pH gradient in a solution boundary layer

Glass cover

(175 µm)

0.5M NaHCO3

Experimental setup

Objective 100x LWD

(N.A. = 0.8)

Laser beam

(532 nm)

T = 90°C

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

Results of in-situ experiments

Molecular water Calcite A A

v1(CO3

2-)aq v5

(HCO3

  • )aq

pH A v1(CO3) A v(H2O) A A

v1(CO3

2-)aq v1

(HCO3

  • )aq

Glass Solution Interface

µm

Experiment #3 - Effect of secondary phase formation on pH

Glass cover

(175 µm)

0.5M NaHCO3

Experimental setup

Objective 100x LWD

(N.A. = 0.8)

Laser beam

(532 nm)

T = 90°C CaNaG Glass cover

(175 µm)

0.5M NaHCO3

Experimental setup

Objective 100x LWD

(N.A. = 0.8)

Laser beam

(532 nm)

T = 90°C

µm

pH90°C

(Prelim. calibration)

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

Position (µm)

Results of in-situ experiments

Experiment #4 – pH gradient in solution and the corrosion rim

Position (µm)

Carbonate-bicarbonate intensity ratio ~ pH Silica Si-O-Si breathing mode intensities

Glass Solution

area not mapped area not mapped

Glass Solution Silica Silica

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

50 60 70 80 90 100 110 120 130 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

P os ition ¡(µm)

Experiment #4 – pH gradient in solution and the corrosion rim

142 hours

900 950 1000 1050 1100 1150 1200

¡

¡Intens ity ¡(arb. ¡unit)

¡ ¡

R aman ¡s hift ¡(cm

  • ­‑1)

v5(HCO3)aq v1(CO3)aq

Solution Silica corrosion zone Glass

Results of in-situ experiments

pH increase

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

50 100 150 200 20 40 60 80 100

T ime ¡(h)

Experiment #4 – Diffusion and reaction of molecular water within the corrosion rim

Results of in-situ experiments

Solution exchange with D2O-rich solution D2O/H2O

Glass Solution Silica

SiO-D/SiO-H

Glass Solution Silica

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

Maximum penetration depth of Au ions

Experiment #5 - Effect of heavy ion irradiation on the forward dissolution rate (r0)

Results of in-situ experiments

10 20 30 40 50 60 70 80 90 100 110 120 20 40 60 80 100 120 140

¡ ¡

G las s ¡retreat ¡(µm)

T ime ¡(h)

Irradiated glass samples Non-irradiated glass samples

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

Maximum penetration depth of Au ions

Results of in-situ experiments

10 20 30 40 50 60 70 80 90 100 110 120 20 40 60 80 100 120 140

¡ ¡

T ime ¡(h) Exp. r0 r0,0 r1

(µm/h) #5-1 1.532 (± 0.015)

  • 0.016

(± 0.008 #5-2 0.936 (± 0.022)

  • #5-3

4.62 (± 0.39) 1.339 (± 0.027)

  • #5-4

4.35 (± 0.24) 1.666 (± 0.056)

  • Irradiated

glass samples Non-irradiated glass samples

Errors represent 2-sigma errors of the line

Experiment #5 - Effect of heavy ion irradiation on the forward dissolution rate (r0)

r0 r0, r1 r0 r0 r0 r0,

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

Experiments

Experimental details

Experimental series #1

  • TBG monoliths
  • pure H2O
  • 90°C
  • multiple sample exchange between 18O-labelled

and -unlabelled solution Experimental series #2

  • TBG powder and TBG spheres enriched with 30Si
  • different initial pH adjusted with HCl and KOH
  • 90°C
  • addition of 18O after half of the total reaction time

Addition of H2 (18O/16O ≈ 0.1 after half of the reaction time

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

Experiments

Experimental details

Experimental series #3

  • ISG and QBG monoliths
  • pre-altered at 90°C for 9 months
  • then altered at 90°C (ISG) and 150°C (QBG) for

3 months in multi-isotope tracer solutions*

  • pH = 7.0 (continuously re-adjusted)

*Isotope solution tracers D2O (D/H = 0.23), H2

18O (18/16O = 0.23), 10B2O3 (250 ppm), 30SiO2 (362 ppm), 44CaCl2 (88 ppm)

*Other tracers K (from solution preparation and pH adjustments), F (from PTFE)

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

90°C, 432 h, pure water (sample was exchanged five times between 18O-rich and

18O-poor solution)

Raman line profile

BSE image

200 400 600 800 1000 1200 200 400 600 800 1000 1200

¡

Intens ity ¡(cps ) R aman ¡s hift ¡(cm

  • ­‑1)

D 1 ¡band

Δiso = 0.30 cm-1/at.% 18O

(Gahlener et al. 1981)

Results of isotope exchange experiments

Experiment #1

Pristine TBG

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 2 4 6 8 10 12 14 16 18 20

¡ ¡

18O ¡(at. ¡% )

D is tance ¡from ¡s urface ¡(µm)

G ap ¡with ¡minor ¡s ilica ¡precipitates

P ris tine ¡glas s

formed in

18O-rich

solution formed in

18O-poor

solution

1st 2nd 3rd 4th 5th exchange cycle 2σ - error bars

0.6 1.2 1.8 2.4 3.0 3.6 4.2 4.8 5.4 6.0 0.0

Δiso (cm-1) Results of isotope exchange experiments

Experiment #1 - Multiple oxygen isotope exchange

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

10 20 30 40 50 60 70 80 90 100 110 120 130

2 4 6 8 10 12 14 16 18 20

¡

18O ¡(at.% )

¡

µm

Results of isotope exchange experiments

Experiment #1 - Multiple oxygen isotope exchange

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

2 4 6 8 10 12 14 16 18 20 0.00 0.02 0.04 0.06 0.08

¡

D is tance ¡from ¡s urface ¡(µm)

0.00 0.02 0.04 0.06 0.08

¡

0.00 0.02 0.04 0.06 0.08

¡

0.00 0.02 0.04 0.06 0.08

¡

18O / 16O

0.00 0.02 0.04 0.06 0.08

¡

0.00 0.02 0.04 0.06 0.08

pH initial ¡= ¡4 pH initial ¡= ¡7

¡ ¡

pH initial ¡= ¡10 pH initial ¡= ¡10 pH initial ¡= ¡7 pH initial ¡= ¡4

2 4 6 8 10 12 14 16 18 20 5 10 15 20

¡

D is tance ¡from ¡s urface ¡(µm)

5 10 15 20 5 10 15 20

¡ S i/ S i

5 10 15 20 5 10 15 20 5 10 15 20

¡ ¡

Dense rim Dense rim Porous rim Dense rim Dense rim Porous rim Pristine glass Pristine glass Pristine glass Pristine glass Pristine glass Pristine glass

18O added 14 days

after start of the exp.

18O added from

the beginning

TBG: 90°C, 672 h Geisler et al. (2015, GCA)

Experiment #2 – Si and O isotope exchange

Results of isotope exchange experiments

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

Results of isotope exchange experiments

Experimental series #3: ISG, pre-altered at 90°C/90°C

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

Experimental series #3: ISG, pre-altered at 90°C/90°C

Results of isotope exchange experiments

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

NanoSIMS STEM-EDX

Distance from reaction interface (nm)

Si Na K Ca B O

18O/16O

D/H High-angle annular dark field image

Dense Zone (2) Glass (3) Porous Zone (1)

1 2 3

Results of isotope exchange experiments

Experimental series #3: ISG, pre-altered at 90°C/90°C

Reaction interface Chemically modified

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

Glass

200 nm

Tracer alteration rim 150°C, 3 months Pre-alteration rim 90°C, 9 months

Porous zone (pore size < 50 nm) Porous zone (pore size < 10 nm ) Dense zone Dense zone Glass

Results of isotope exchange experiments

Distance from reaction interface (nm)

Experimental series #3: QBG, pre-altered at 90°C/150°C

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

Results of isotope exchange experiments

An important conclusion:

  • The dense layers likely correspond to

(1) the water-rich zone or gab observed by in-situ Raman spectroscopy (2) to the PRI (Passivating Reactive Interface) described by Frugier et al. (2008).

  • They most likely represents the product of a quenched interfacial solution (that is likely

highly supersaturated with respect to amorphous silica).

  • It follows, if true, that the reported dense layer cannot be passivating during the reaction
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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

Geisler et al. (2010, J. Non-Cryst. Sol.) Dohmen et al. (2013, Int. J. Appl. Glass Sci Geisler et al. (2015, GCA)

WAK: 150°C, 96 hours, pHinitial ≈ 0 TBG: 90°C, 4 hours, pHinitial ≈ 7 CaKNaSi: 90°C, 260 hours, pHinitial ≈

Silica layers formed in experiments with different glasses under different conditions

Other observations

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon after Grambow (1986) after Geisler et al. (2010; 2015)

Towards an unifying glass corrosion mechanism

PRISTINE GLASS

SOLUTION

Na H2O

SOLUTION

Re-structured residual glass

SOLUTION

Na H2O

PRI

Schematic drawing of the different layers after long-term glass-water contact

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

Towards an unifying glass corrosion mechanism

Schematic drawing of the different layers after long-term glass-water contact

Amorphous silica Water-rich zone – quench layer Solution boundary layer Bulk solution Secondary minerals Ion exchange zone Pristin glass

from Iler (1979)

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

Following reaction have been identified so far:

  • Ion exchange/interdiffusion inside the glass (diffusion-reaction process, e.g., Doremus

model).

  • Congruent dissolution of the glass (incl. a number of individual microscopic reaction

steps such as, e.g., hydrolysis).

  • Silica precipitation/deposition from solution (incl. a number of individual microscopic

reaction steps such as, e.g., condensation).

  • Silica aging (e.g, polymerization, ripening).
  • Chemical transport through the silica reaction layer (percolation controlled, anomalous).
  • Precipitation of secondary minerals within and at the silica surface (e.g., zeolites, rutile
  • Aqueous diffusion within a solution boundary layer.

Conclusions

Towards an unifying glass corrosion mechanism

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

I would like to thank my students Mara Lönertz (BSc), Christoph Lenting (PhD), and Lars Dohmen (PhD) for their interest, hard work, and enthusiasm for the topic(s), Dr Oliver Plümper (Utrecht University) is thanked for his help with the TEM analyses, Henrik Blanchard and Dieter Lülsdorf for their creativity and help with the design and construction of the fluid cells, the Federal Ministry for Education and Science, the German Research Foundation, and SCHOTT AG for financial support, and, last but not least, you for your attention.

Acknowledgements

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

► In silica undersaturated solutions, the glass initially dissolves congruently. ► Once the solution at the surface boundary layer is saturated with respect to silica, silica will precipitate initially at the surface of the dissolving glass and later at preexisting silica aggregates → the reaction becomes incongruent and the glass is gradually replaced by amorphous silica along a moving front: Glass + H2O → SiO2(am)↓ + H2O + Cations(aq) (+ ΔS) ► The glass dissolution (rd) and silica precipitation rate (rp) have to be coupled: rd ‒ (rp + u) = 0, where u accounts for the quantities of elements that are released into solution per unit time. ► The thermodynamic driving force for such an irreversible interface-coupled replacement reaction is given by the solubility difference between amorphous silica and the glass. ► Complex, non-linearly coupled reactions at the interface along with chemical transport limitations due to the growing silica rim, which increasingly drives the system away from thermodynamic equilibrium, may cause the formation of structural, porosity, and/or chemical patterns. ► An ion exhange zone may develop ahead of the dissolution-reprecipitation front. This diffusion-controlled process, however, is not directly rate-limiting.

Conclusions

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int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

500 nm

TEM tomography of porous zone (ISG , pre-altered 90°C/90°C, pH = 7)

slide-46
SLIDE 46

int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

Δ0

Lateral Resolution (LR) Depth Resolution (DR) z

from Everall (2000)

Δ1

LR1= ?

A B

Δ2

LR2 = ? LR0 ≈ 1.22 λ / N.A. DR0 ≈ 4 λ / (N.A.)2

Spatial resolution - A theoretical evaluation

slide-47
SLIDE 47

int ICTP-IAEA Workshop – Triest (6.11.-10.11.2017) tgeisler@uni-bon

Solution Glass lid vs(Si-O) Celestine v1(CO3)

1

100 µm 200 µm 300 µm 500 µm 700 µm 1000 µm

50 µm

Depth - z Normalised intensity Celestine v1(CO3) intensity 100 µm hole

50 µm 50 µm 50 µm 50 µm 50 µm 50 µm +78

  • 182
  • z

x

Glass lid Celestine crystal Glass lid Celestine crystal Glass lid Celestine crystal Glass lid Celestine crystal Glass lid Celestine crystal Glass lid Celestine crystal

z = -182 µm

(a) (b) (c) (d)

Solution Solution Solution Solution Solution Solution

  • 350 µm

Celestine crystal Solution

x Intensity (140 - 300 cm-1) Glass vs(Si-O) intensity

Glass lid

x = +78 µm

  • ­‑50
  • ­‑100
  • ­‑150
  • ­‑200
  • ­‑250
  • ­‑300

0.0 0.5 1.0

Intens ity ¡(normalis ed) z ¡(µm)

125 130 135 140 0.0 0.1 0.2 0.3 0.4 0.5

¡ ¡

x ¡(µm)

200 400 600 800 1000 2 4 6 16 20 24 28 32 36 40

¡ ¡

R es olution ¡(µm) C onfocal ¡hole ¡(µm) Axial, ∆y (measured) Lateral, ∆x (measured) Resolution, ∆x, ∆y (µm)

Position of interface

∆x

Celestine

Axial, ∆y (corrected)

Solution 2 µm

Spatial resolution - An empirical evaluation