CHEMICAL DURABILITYOF GLASSReinhard Conradt

Department of Mineral Engineering, RWTH Aachen Univbersity, Germany

CU BKK 2010

conradt@ghi.rwth-aachen.de

Department of Materials Science, Faculty of Science, Chulalongkorn University&

Department of Science ServiceBangkok 14th September 2010

data sources

= load down & read at home

AQUEOUS SYSTEMS•Pourbaix: Atlas of Electrochemical Equilibria in Aqueous Solutions aq. pH-Eh speciation of the entire periodic table of elements• Iler: The Chemistry of Silica (1979) more than 2600 references!• Baes & Mesmer: The thermodynamics of cation hydrolysis (1981)• Brinker & Scherer: Sol-Gel Science (1990)• H.E. Bergna: The colloid Chemistry of Silica (1994)• G. Sposito: The Environmental Chemistry fo Alumina (1996)

AQUEOUS SYSTEMS•Pourbaix: Atlas of Electrochemical Equilibria in Aqueous Solutions aq. pH-Eh speciation of the entire periodic table of elements• Iler: The Chemistry of Silica (1979) more than 2600 references!• Baes & Mesmer: The thermodynamics of cation hydrolysis (1981)• Brinker & Scherer: Sol-Gel Science (1990)• H.E. Bergna: The colloid Chemistry of Silica (1994)• G. Sposito: The Environmental Chemistry fo Alumina (1996)

GLASS CORROSION• ICG compilation of literature (1972) almost 1000 references!• Holland (1964)• Besborodow (1972)• Clark, Pantano & Hench (1979)• Doremus & Tomozawa (1977-82)• Scholze (1964-91)• Paul (1982)• Clark & Zoitos (1992)

to be analyzed

dissolve soluble residue

HCl group residue

residue

residue

residue

residue

H2S group

(NH4)2S group

(NH4)2CO3 group

soluble group

add HCl

add H2S

add (NH4)2S

add (NH4)2CO3

filtrate

filtrate

filtrate

filtrate

filtrate

filter

Ag, Hg1+, Pb, W, Nb, Ta

Hg, Pb, Bi, Cu, Cd

As, Sb, Sn (after treating filtrate with HCl)

Zn, Mn, Fe2+, Cr, Al; Co, Ni

Ba, Ca, Sr

Na, K, Mg, Li, NH4

desintegration filter

filter

filter

filter

residue

urotropine group: Fe3+, Cr, Al, Be, Ti, ...

(dissolve by HAc; precipitate as BaCrO4 , SrSO4 , CaC2O4 )

(compare to sea water: Na-K-Mg-Cl-SO4-H2O)

phenomena observed

network dissolution(q ∝ t)

SiO2+ H2O = H4SiO4

≡Si-O-Si≡ + H2O→ 2 ≡Si-OH

ion exchange zone bulk glass

v

DH+ Na+

glass surface at t = 0

tb·a·t q +=

mas

s lo

ss p

er s

urfa

ce a

rea

q

t ime t

t q ∝

t∝ q

leaching(q ∝ √t)

≡Si-O-Na+(gl) + H+(aq)→≡Si-OH(gl) + Na+(aq)or≡Si-O-Na+(gl) + H3O+(aq)→≡Si-OH(gl) + H2O(gl) + Na+(aq)

standard model

mass loss&

pH increase

TR (oben) RIE (oben) OC (oben)

10 µm

„soda bloom“ on OCEAN-Glas

vertical differentiation:

lateral differentiation: emerging surface roughness

local swelling

lateral diffusion zones

crystallization

pitting

after: E. Rädlein

reaction layer,vertical section

surface underneathtop view

100 µm

analcite crystale

surface zone

bulk glass

adsorbed layermineralized glass,amorphous and crystalline precipitates,„back precipitates“, „transformed layer“

aqueous solution,dissolved glass

components

aqueous system residual glass

standards

⋅

=

3

2

23 cmcm

s

cmgq

cmgc

sqc && ⋅=

static tests

dynamic testss or “SA/V” in cm-1

pH

log

q

ISO 1776:<0.7 / ..... / >15 mg/dm²

ISO 695:< 75 / ..... / >175 mg/dm²

ISO 719:< 0.1 / ..... / > 3.5 ml 0.01 m HCl

designed for the family of conventional silicate glasses

ISO standard tests:

ISO 1776 (stability against acidic attack)area ≈ 300 cm²; boil in 6 m HCl (1.5 l) for 6 h ⇒ <0.7 / 1.5 / 15 / >15 mg/dm²

ISO 695 (stability against alkaline attack)area 10=15 cm²; boil in 1 m NaOH + 1 m Na2CO3 (0.8 l) for 3 h ; ⇒ <75 / 175 / >175 mg/dm²

ISO 719 (stability against hydrolytic attack)powder 315-500 µm (4x 2 g); expose to 30 ml water in 50 ml flaskat 98 °C for 1 h; cool down; fill to 50 ml; titrate 25 ml aliquots by 0.01 m HCl ⇒ <0.1 / 0.2 / 0.85 / 2 / 3.5 ml HCl per g glass

ISO 720 (stability against hydrothermal attack)powder 300-420 µm (4x 10 g); expose to 50 ml water in 10 ml flaskat 121 °C for 0.5 h; cool down; fill to 10 ml; titrate by 0.02 m H2SO4 ⇒ <0.1 / 0.85 / 1.5 ml H2SO4 per g glass

design ofglass corrosion experiments

sample holder (PE)

wide neck PE-bottle

glass chip

filling level

PE sample holderwide neck PE bottle

filling level

glass chip

solution:pH (free, buffered compensated);salts (e.g., 9 g/l NaCl);organics;redox (e.g., FeCl2/FeCl3)

temperature:37±1 or 98±1 °C

s parameter:0.1 cm-1

time intervals:0.5, 1, 2, 4, 8, 16 hours;1, 3, 7, 14, 28, 60, 120, ... days

similar procedures: see MCC-1, MCC-2 tests

*)

*) no „natural“ reference solution for corrosion experiments

sample holder (PE)

wide neck PE-bottle

glass chip

filling level

PE sample holderwide neck PE bottle

filling level

glass chip

solution:pH (free, buffered compensated);salts (e.g., 9 g/l NaCl);organics;redox (e.g., FeCl2/FeCl3)

temperature:37±1 or 98±1 °C

s parameter:0.1 cm-1

time intervals:0.5, 1, 2, 4, 8, 16 hours;1, 3, 7, 14, 28, 60, 120, ... days

similar procedures: see MCC-1, MCC-2 tests

*)

*) no „natural“ reference solution for corrosion experiments

±5 K temperature errormake up for

± 40 % error in mass loss

RIE OC TR

oxide compositionSiO2 60.20 72.50 69.30ZrO2 - - 1.50TiO2 - - 0.60Al2O3 1.00 1.00 1.00B2O3 0.70 - -MgO - 4.11 -CaO - 7.10 4.90ZnO - - 2.30PbO 24.60 - -Na2O 5.30 14.10 9.10K2O 8.70 - 10.00sum 100.50 98.81 98.70

constitutional composition2ZnO·SiO2 - - 3.16ZrO2·SiO2 - - 0.90CaO·TiO2 - - 2.56PbO·SiO2 31.35 - -K2O·Al2O3·6SiO2 0.55 - 5.05K2O·2SiO2 19.67 - 20.88Na2O·Al2O3·6SiO2 - 7.26 5.56B2O3 0.70 - -MgO·SiO2 - 10.32 -Na2O·2SiO2 15.64 31.50 20.72Na2O·3CaO·6SiO2 - 25.13 13.55SiO2 32.10 25.80 27.63sum 100.00 100.00 100.00

0 20 40 60 80 1000.00

0.01

0.02

0.03

0.04

full: midhalf open: edge

OC

TR

RIE

communal water

q·s

in m

g/cm

³

t in d

0 20 40 60 80 100

red: TRblue: RIEblack: OC

edge

mid

DI water

t in d

g = TRg = RIEg = OC

0 20 40 60 80 1000.0

0.1

0.2

0.3

0.4

Rand

Mitte

RIE

OC

TR

Spülmittel A

q·s

in m

g/cm

³

t in d

0 20 40 60 80 100

RIE

Rand

Mitte

OC

TR

Spülmittel B

t in d

0 20 40 60 80 100

rot: TRblau: RIEschwarz: OC

Spülmittel C

t in d

g = TRg = RIEg = OC

detergent A detergent B detergent Cedge

mid

H2O dest. → rapid change of pH takes place(specified by el. conductivity)

buffered solutions → may interfere with the corrosion mechanism

special corrosion media → for specific corrosion scenarios, e.g.,- salt brines „Q“, „R“, ...;- granitic or clay waters;- simulated physiological fluids (9 g/l NaCl, Gamble‘s solution, ...)- water with dish washing agents

water pre-saturated with glass powder

Peq

Peq

TT

heater & magnetic stirrer

pre-saturation corrosion test under saturation conditions

example:how to perform a corrosion testunder conditions „close to saturation“

citrate bufferspH C6H8O7·H2O [g] NaCl [g] Zusatz *) [ml] 2 6.43 3.58 8.2 HCl 3 8.47 3.49 20.6 NaOH 4 11.75 2.57 68.0 NaOH 5 20.26 - 196.4 NaOH 6 12.53 - 159.6 NaOH*) concentration 1 mol/l

example: buffered solutions

Is a buffered constant pH solutiona good reference medium for corrosion tests?

020406080

100

Al(OH)2- Al(OH)4

-

Al(OH)3, amAl3+

020406080

100

Al(OH)2+

Al(OH)3, aq

Al(OH)4

-Al(OH)2

+Al3+

0 2 4 6 8 10 12 140

20406080

100

rela

tive

conc

entra

tion

of a

queo

us A

l spe

cies

in %

Al(LH*)25-

AlL2H*4-

AlL23-

Al(HL)L2-

AlL

AlHL+

Al3+

pH

+ citric acid

∞ diluted

rel c

once

ntra

tion

of A

l spe

cies

in %

NO WAY!Citrate buffers, for example, destablize the otherwise very stable alumina.Thus, very corrosion resistant glasses may appear to be very weak in asolution buffered with a citrate buffer.

surface pre-treatment:

• cut by a low-speed saw in petroleum;

• cut, ground, polished, etched in HF-HNO3

• as received from the production process

• fire polished

• blown glass foils

etc. etc.

empirical knowledge

network dissolution(q ∝ t)

SiO2+ H2O = H4SiO4

≡Si-O-Si≡ + H2O→ 2 ≡Si-OH

ion exchange zone bulk glass

v

DH+ Na+

glass surface at t = 0

leaching(q ∝ √t)

≡Si-O-Na+(gl) + H+(aq)→ ≡Si-OH(gl) + Na+(aq)

standard model

The conclusion

„the network modifiers are leached preferentially, the network formers are left behind asa scaffold dissolving slowly“ is misleading.

The covalent / ionic nature of the metal-oxygen bond has almost nothing to do with its stabilityagainst aqueous attack. Think of Si-O vs. P-O! Think of pure P2O5 vs. natural bones.How would a MgO-B2O3 glass behave?

misleading view:network modifiers are depleted,network formers are enriched

correct view:an incongruent dissolutionprocess takess place;the glass components areenriched or depleted accordingto their solubility in the aqueoussystem

old paradigm:network modifiers are depleted,network formers are enriched

new paradigm:incongruent dissolutionaccording to the solubilityof individual oxides

0 100 2000

10

20

30

40

50m

ol %

depth in nm

H+ profiles by the 15N method

condensed layer

gel layer

0 20 40 60 80 1000.0

0.2

0.4

0.6

0.8

1.0

15 min in D2O at 85 °C

22Na+2D+

rela

tive

conc

entr

atio

n

depth in nm

0 20 40 60 80 1000.0

0.2

0.4

0.6

0.8

1.0

15 min in D2O at 85 °C

22Na+2D+

rela

tive

conc

entr

atio

n

depth in nm

condensed layer

gel layer

70 50 50 40 30 20 10 0 Al2O3 + Fe2O3 + other oxides

100

90

80

70

60

50

40

SiO2

10

20

30

40

50

60

Na2 O + B

2 O3

30

0

70

0.014.5

4.50.020.002

Si loss inmg/(cm2·d)

28 d,90 °C,D.I. H2O,s = 0.1 cm-1

corrosion resistance =

ƒ(thermodynamic stability, layer formation, passivation)

Let us learn from metallurgy:

the elementary process of metal corrosion iselectron transfer (redox reactions):

2Fe0 → 2Fe2+ + 4e-

O2 + 4e- → 2O2-

___________________________________2Fe0 + O2 → 2FeO

2Fe0 → 2Fe2+ + 4e-

2H2O + 4e- → 2H2 + 4 OH-

_________________________________________2Fe0 + 2H2O → 2Fe(OH)2(aq) + 2H2

2Fe0 → 2Fe2+ + 4e-

O2 + 4e- → 2O2-

___________________________________2Fe0 + O2 → 2FeO(slag)

metals

in air

in water

in a slag

0 300 600 900 1200-1200

-1100

-1000

-900

-800

-700

-600

-500

-400

-300

-200

-100

0

4/3 Cr + O2 = 2/3 Cr2O3

4/3 Al + O2 = 2/3 Al2O3Si + O2 = SiO2

2 H2 + O2 = 2 H2O

2 CO + O2 = 2 CO2

6 FeO + O2 = 2 Fe3O4

4 Fe3O4 + O2 = 6 Fe2O3

∆G in kJ per mol O2

°C

-28

-24

-20

-16

-12

-8

-4

0

12

10

8

6

4

2

0

-2

12

10

8

6

4

2

0

-2

-4

log [CO]/CO2]log [H2]/[H2O] log [O2]

protective oxide scale:

Al2O3

Cr2O3

Fe2O3

Cr-rich steel

O2

Al

protective oxide scale:

Fe

non-protective oxide scale:

The layer must

• be an effective diffusion barrier• adhere well to the metal• passivate the metal (forestall the e- transfer)

0

50

100

0

50

100

00

50

100

0

[SiO

2][S

iO2]

[SiO

2]

distance to original surface distance to original surface

Type I: „inert“ glass Type II: protective SiO2 layer

Type IIIa: multicomponent protective layer

Type IIIb: passi-vating layer

Type IV: non-protective layer

Typ V:soluble glass

SiO2, Al2O3, TiO2, ZrO2,Nb2O5, etc.

Zn(OH)2, Fe(OH)3, etc.

example: Na2O-CaO-SiO2 glass, glasses rich in SiO2

example: silica glass

example: soft silica glasses example: Na2Si2O5 glasss

L.L. Hench

The layer must

• be an effective diffusion barrier• adhere well to the residual glass• passivate the glass (forestall the H+ transfer)

the driving force of glass corrosion

0 2 4 6 8 10 12 14-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0

-11.6

-21.6

-31.6

-38.6

-41.6log [H2] =

-83.1

-60

-40

-20

-6

0

log [O2] =

2H2 = 4H + + 4e -

2H2O = O2 + 4H + + 4e -

2H2O

= 2

H 2 +

O2 ;

Gf =

474

.360

kJ/

mol

; Kf =

7.8

·10-8

4

H2O = H+ + OH- ; Gw = 79.880 kJ/mol; K w =1.0·10-14

Eh in

Vol

t

pH

surface water

reference state fo the Gibbs energies of formationof all species in the state (aq)

species -Gƒe (kJ/mol)

H2O(l) 237.180H+(aq) 0.000H2O – OH–(aq) =H+(aq) 79.880OH–(aq) 157.300HO2–(aq) 67.362H2O2(l) 134.097H2(aq) -17.573O2(aq) -16.318H2(g) 0.000O2(g) 0.000

The state „dissolved in water“ is a statelike the states „solid“, „liquid“, and „gas“. It is denoted by (aq).

Spezies -Gƒe (kJ/mol) Spezies -Gƒ

e (kJ/mol)

CO2(g) 394.570 F2(g) 0.000CO2(aq) 386.016 F– 279.993HCO3

– 586.848 HF(aq) 298.110CO3

2– 527.895 HF2– 581.492

SiO2(s) 854.910 P2O5(s) 1349.570SiO2(aq) 1307.760 H3PO4(aq) 1142.650H3SiO4

– 1251.990 H2PO4– 1130.391

H2SiO42– 1185.460 HPO4

2– 1089.263HSiO 4

3– 1116.547 PO43– 1018.804

SiO44– 1048.230 H4P2O7(aq) 2032.160

H6[H2SiO4]42– 5153.236 H3P2O7– 2026.830

H4[H2SiO4]44– 5025.951 H2P2O72– 2003.410

HSiO 3– 1005.46 HP2O7

3– 1961.710SiO3

2– 938.51 P2O74– 1919.200

H5P3O10(aq) 2921.670Al2O3(s) 1583.150 H4P3O10

– 2923.190Al3+ 492.000 H3P3O10

2– 2917.480Al(OH)2+ 700.653 H2P3O10

3– 2094.550Al(OH)2

+ 907.384 HP3O104– 2872.550

Al(OH)3(aq) 1111.061 P3O105– 2821.490

Al(OH)3(am) 1137.630Al(OH)4

– 1305.410 B2O3 1194.270H3BO3(aq) 968.638

Fe2O3(s) 739.960 H2BO3– 917.564

Fe3+ 17.866 HBO32– 845.695

FeOH2+ 240.413 BO33– 769.182

Fe(OH)2+ 457.228Fe(OH)3(aq) 670.695 TiO2 889.940Fe(OH)3(s) 696.636 TiO2+ 577.392Fe(OH)4– 841.821 TiO2OH– 467.353

TiO(OH)2 s 1058.552FeO 250.990Fe2+ 92.257 ZrO2 1036.870FeOH+ 279.951 Zr4+ 594.128Fe(OH)2(aq) 457.102 ZrO2+ 843.076Fe(OH)2(s) 486.599 ZrO2OH– 1203.737Fe(OH)3– 619.232 ZrO(OH)2 s 1303.316

Spezies -Gƒe (kJ/mol) Spezies -Gƒ

e (kJ/mol)

MgO(s) 569.840 PbO(s) 188.489Mg2+ 455.261 Pb2+ 24.393MgOH+ 638.064 PbOH+ 226.354Mg(OH)2(aq) 769.438 Pb(OH)2(aq) 400.827Mg(OH)2(s) 833.746 Pb(OH)3– 575.718MgCO3(aq) 1002.486MgCO3(s) 1012.110 BaO(s) 528.690MgHCO3

– 1050.602 Ba2+ 547.518

CaO(s) 604.460 Li2O(s) 561.760Ca2+ 552.706 Li+ 292.629CaOH+ 716.970Ca(OH)2(aq) 868.138 Na2O(s) 376.740Ca(OH)2(s) 897.008 Na+ 262.211CaCO3(aq) 1081.438CaCO3(s) 1128.760 K2O(s) 322.200CaHCO3

– 1145.035 K + 282.671

SrO(s) 562.680 Cs2O(s) 308.300Sr2+ 571.451 Cs+ 292.001SrOH+ 733.455Sr(OH)2(aq) 871.109 Nd2O3(s) 1721.700Sr(OH)2(s) 881.987 Nd3+ 671.532SrCO2(aq) 1087.338 Nd2(OH)2

4+ 1738.230SrCO3(s) 1140.140 Nd(OH)2+ 863.126

Nd(OH)3(s) 1259.221MnO(s) 363.340 Nd(OH)4

– 1407.096Mn2+ 229.953MnOH+ 406.685 MoO3(s) 655.778Mn(OH)2(s) 615.048 MoO2

2+ 411.287Mn(OH)3– 746.426 MoO2(OH)+ 645.884

H2MoO4(aq) 877.134ZnO(s) 318.470 HMoO4

– 866.632Zn2+ 147.193 MoO4

2– 838.055ZnOH+ 333.256Zn(OH)2(aq) 535.385 Nb2O5(s) 1765.82Zn(OH)3– 704.711 Nb(OH)5(aq) 1448.50Zn(OH)42– 871.276 NbO3

– 932.20

Spezies -Gƒe (kJ/mol) Spezies -Gƒ

e (kJ/mol)

CO2(g) 394.570 F2(g) 0.000CO2(aq) 386.016 F– 279.993HCO3

– 586.848 HF(aq) 298.110CO3

2– 527.895 HF2– 581.492

SiO2(s) 854.910 P2O5(s) 1349.570SiO2(aq) 1307.760 H3PO4(aq) 1142.650H3SiO4

– 1251.990 H2PO4– 1130.391

H2SiO42– 1185.460 HPO4

2– 1089.263HSiO 4

3– 1116.547 PO43– 1018.804

SiO44– 1048.230 H4P2O7(aq) 2032.160

H6[H2SiO4]42– 5153.236 H3P2O7– 2026.830

H4[H2SiO4]44– 5025.951 H2P2O72– 2003.410

HSiO 3– 1005.46 HP2O7

3– 1961.710SiO3

2– 938.51 P2O74– 1919.200

H5P3O10(aq) 2921.670Al2O3(s) 1583.150 H4P3O10

– 2923.190Al3+ 492.000 H3P3O10

2– 2917.480Al(OH)2+ 700.653 H2P3O10

3– 2094.550Al(OH)2

+ 907.384 HP3O104– 2872.550

Al(OH)3(aq) 1111.061 P3O105– 2821.490

Al(OH)3(am) 1137.630Al(OH)4

– 1305.410 B2O3 1194.270H3BO3(aq) 968.638

Fe2O3(s) 739.960 H2BO3– 917.564

Fe3+ 17.866 HBO32– 845.695

FeOH2+ 240.413 BO33– 769.182

Fe(OH)2+ 457.228Fe(OH)3(aq) 670.695 TiO2 889.940Fe(OH)3(s) 696.636 TiO2+ 577.392Fe(OH)4– 841.821 TiO2OH– 467.353

TiO(OH)2 s 1058.552FeO 250.990Fe2+ 92.257 ZrO2 1036.870FeOH+ 279.951 Zr4+ 594.128Fe(OH)2(aq) 457.102 ZrO2+ 843.076Fe(OH)2(s) 486.599 ZrO2OH– 1203.737Fe(OH)3– 619.232 ZrO(OH)2 s 1303.316

Spezies -Gƒe (kJ/mol) Spezies -Gƒ

e (kJ/mol)

MgO(s) 569.840 PbO(s) 188.489Mg2+ 455.261 Pb2+ 24.393MgOH+ 638.064 PbOH+ 226.354Mg(OH)2(aq) 769.438 Pb(OH)2(aq) 400.827Mg(OH)2(s) 833.746 Pb(OH)3– 575.718MgCO3(aq) 1002.486MgCO3(s) 1012.110 BaO(s) 528.690MgHCO3

– 1050.602 Ba2+ 547.518

CaO(s) 604.460 Li2O(s) 561.760Ca2+ 552.706 Li+ 292.629CaOH+ 716.970Ca(OH)2(aq) 868.138 Na2O(s) 376.740Ca(OH)2(s) 897.008 Na+ 262.211CaCO3(aq) 1081.438CaCO3(s) 1128.760 K2O(s) 322.200CaHCO3

– 1145.035 K + 282.671

SrO(s) 562.680 Cs2O(s) 308.300Sr2+ 571.451 Cs+ 292.001SrOH+ 733.455Sr(OH)2(aq) 871.109 Nd2O3(s) 1721.700Sr(OH)2(s) 881.987 Nd3+ 671.532SrCO2(aq) 1087.338 Nd2(OH)2

4+ 1738.230SrCO3(s) 1140.140 Nd(OH)2+ 863.126

Nd(OH)3(s) 1259.221MnO(s) 363.340 Nd(OH)4

– 1407.096Mn2+ 229.953MnOH+ 406.685 MoO3(s) 655.778Mn(OH)2(s) 615.048 MoO2

2+ 411.287Mn(OH)3– 746.426 MoO2(OH)+ 645.884

H2MoO4(aq) 877.134ZnO(s) 318.470 HMoO4

– 866.632Zn2+ 147.193 MoO4

2– 838.055ZnOH+ 333.256Zn(OH)2(aq) 535.385 Nb2O5(s) 1765.82Zn(OH)3– 704.711 Nb(OH)5(aq) 1448.50Zn(OH)42– 871.276 NbO3

– 932.20

Al2O3(s) 1583.150Al3+ 492.000Al(OH)2+ 700.653Al(OH)2

+ 907.384Al(OH)3(aq) 1111.061Al(OH)3(am) 1137.630Al(OH)4

– 1305.410

Al2O3 + 6 H+ → 2 Al3+ + 3 H2O+ 4 H+ → 2 AlOH2+ + H2O+ 2 H+ + H2O → 2 Al(OH)2+

+ 3 H2O → 2 Al(OH)3

+ 5 H2O → 2 Al(OH)4- + 2 H+

0 2 4 6 8 10 12 140

20

40

60

80

100

0 2 4 6 8 10 12 14-80

-60

-40

-20

0

20

40

60

80

100

0 2 4 6 8 10 12 14-8

-6

-4

-2

0

2

4

6

8

10

Al(OH)4-

Al(OH)3(am)Al3+

mol

ar fr

actio

n of

spe

cies

in %

pH

Al2O3

-∆G

° hyd

r in k

J/m

olpH

Al(OH)2+

Al2O3(s)

Al(OH)3(aq)

Al(OH)4-

Al(OH)3(am)

AlOH2+

Al3+

log

activ

ity

pH

pHn

Ka

OHHOAla

K

iOHmHnOAl

ii

mni

i

⋅−=

⋅⋅=

↔⋅+⋅+

+

+

2·log

21

log

][][][

·2

232

2

232

i

a

a

i

xspecies

xi

i

⋅=

=∑

100 %

1010

log

log

∑ ⋅⋅−

=∆−

ii

ohydr

KxRT

OAlG

ln

)( 32

020406080

100

Al(OH)2- Al(OH)4

-

Al(OH)3, amAl3+

020406080

100

Al(OH)2+

Al(OH)3, aq

Al(OH)4

-Al(OH)2

+Al3+

0 2 4 6 8 10 12 140

20406080

100

rela

tive

conc

entra

tion

of a

queo

us A

l spe

cies

in %

Al(LH*)25-

AlL2H*4-

AlL23-

Al(HL)L2-

AlL

AlHL+

Al3+

pH

concentration↑

+ C6H8O7

∞ diluted

C6H8O7 =

- - -

Al3+

6 8 10 12 140.0

0.2

0.4

0.6

0.8

1.0

mol

ar fr

actio

n of

sce

cies

pH

02SiO

-43SiOH -4

4SiO

-242SiOH

-34HSiO

pH = 9.8 = 11.9

6 8 10 12 140.0

0.2

0.4

0.6

0.8

1.0

mol

ar fr

actio

n of

sce

cies

pH

02SiO

-43SiOH

( ) -44424 SiOHH

( ) -24426 SiOHH

-44SiO

-242SiOH

-34HSiO

pH = 9.8 = 11.4

*) Iler 1979; s.a. Roggendorf 2007

*)

0 2 4 6 8 10 12 14

0

50

100

150

200

250

0 2 4 6 8 10 12 14-150

-100

-50

0

50

100

150

SrO

PbOZnO

FeO

MnO

MgO

CaO

BaO

pH

Al2O3

B2O3

MoO3

SiO2

Fe2O3

-∆G

hydr

in k

J/m

ol

pH

The state „dissolved in water“ is a statelike the states „solid“, „liquid“, and „gas“. It is denoted by (aq).SiO2(aq) = silica dissolved in water.

We may a glass like a „state“ - althoughit is not an equilibrium state like:SiO2(gl) = silica glass.

Let us discuss a glass like[74SiO2 + 10CaO + 16 Na2O](gl)

What state corresponds to[74SiO2 + 10CaO + 16 Na2O](aq) ?

Gib

bs e

nerg

y

∆GhydrGvit

∆Ggl∆Gaq∆Gs

Gaq

Gs

Ggl

Gox

hydr

vit

s

aq

?Gspecies   aqueoussolution aqueous (4)  glass

G                      compounds  ium  equilibr(3)  glass

?G                     oxides   compounds ibrium(2)  equil?Gsolution aqueous species aqueous   oxides    

species aqueoussolution aqueous s(1)  oxide

    

 

 

 

⇒→+−⇒→

−⇒→⇒−→=→+

0 2 4 6 8 10 12 14

0

10

20

30

40

50∆G

hydr in

kJ

per 1

00 g

gla

ss

pH

Duran, Pyrex

float glass

E glassbasalt glass

stability fingerprints of different glasses

reaction path modeling

glass

How to model the reaction path

[composition](gl) → [composition](aq) ?

• A slice of glass is brought to equilibrium with the solution.• The the next glass slice is added and brought to equilibrium.• The time scale is replaced by a sequence of glass slices.• We learn towards what state the corrosin process moves.

-5.0 -4.5 -4.0 -3.5 -3.0-5.0

-4.5

-4.0

-3.5

-3.0

9.0

9.5

10.0

10.5

11.0

-5.0 -4.5 -4.0 -3.5 -3.0-10

-9

-8

-7

-6

-5

-4

-3

SiO2 tu

rnove

r ξ

Ca(aq)Si(aq)

Na+H+

log

c, c

in m

ol/l

log ξ(SiO2), ξ in mol/l

pH

log

c, c

in m

ol/l

CaO·2SiO2·2H2O

SiO 2 turnover ξ

Si in SiO2(am)

Ca(aq)

Si(aq)

log ξ(SiO2), ξ in mol/l

surface zone

bulk glass

adsorbed layermineralized glass,amorphous and crystalline precipitates,„back precipitates“, „transformed layer“

aqueous solution,dissolved glass

components

aqueous system residual glass

reaction product layer(vertical section);

surface of the residualglass after removal ofthe reaction productlayer(top view)

100 µm

0.01 0.10 20 40 60 80 100

0

20

40

60

80

100

120

NS glass +dissolved water

molar fraction of H2O

NS + steam

NS + NSH6

NS + NSH5

ice + L NSH6 + NSH9

L + NSH9

ice + NSH9NSH5 + NSH6

NS + NSH5L + NSH6

NS + NSH6

solution L

NS + steam

Na2SiO3 = NSH2O = H

T in

°C

wt. % Na2SiO3

glass dissolved in water water dissolved in glass

0.01 0.10 20 40 60 80 100

0

20

40

60

80

100

120

NS glass +dissolved water

molar fraction of H2O

NS + steam

NS + NSH6

NS + NSH5

ice + L NSH6 + NSH9

L + NSH9

ice + NSH9NSH5 + NSH6

NS + NSH5L + NSH6

NS + NSH6

solution L

NS + steam

Na2SiO3 = NSH2O = H

T in

°C

wt. % Na2SiO3

glass dissolved in water water dissolved in glass

every reaction pathyields a final cristalline

phase

a

b

G. Malow, W. Lutze, R.C. Ewing;

Stracchan; Chick & Pederson

analcime crystals:Na2O·Al2O3·4SiO2·2H2O

→

sc

c1- rr ppt·0corrosion rate

partially crystalline, partially amorphous layer of reaction products on top of the residual glass

in many cases, the layercan be removed easily(like ice from a car windshield)

cs = metastable solubility limit of the glass;cppt = solubility limit of the final crystal formed along the reaction pathcs > cppt ⇒ r cannot reach zero

-3 -2 -1 0 1 2 3

-3

-2

-1

0

1

2

3110 tests

r = r0·(1 - c/c

s) + r

final·c/c

s

initial

rate

final

rate

silica saturation

log

q·s

log s·t

own work

saturation with respect to the glass is a transient stage in most cases

0

0

01.0

·

rr

c

c1- r r

s

ppt

⋅≈

=

∞

∞

sccforcc

1- rrs

→

=

  

·0

sccforcc

1- rrs

<<

=

  

·0

100 ÷

10 µm

„soda bloom“ on OCEAN-Glas

local precipitate

water film on glass surface

stage 1: due to large SA/V, pH → pHs and c → cs; ( ) 0cc / -1·r r s0s →=

stage 2: eventually, a local ppt forms with solubility cppt < cs; the rate in the vicinity of ppt is . Thus, a „local element“ is generated.

c → cs

c → cppt < cs

( ) 0cc-1·r r sppt0 >= /

diffusion

enhanced corrosion

water drop on glass surface

local precipitatec → cs

c → cppt < cs

diffusion

enhanced corrosion precorroded zoneprecorroded zone

the nature of the sub-surface zoneand the rate determining step

„radius“ 0.140 nm 0.138 nm 0.137 0.136d(O-H) -.- 0.096 nm 0.0958 0.095 ϕ(H-O-H) --- --- 104.45° 120°

O2- OH- H2O H3O+

14W

32

10K

OHOHOH 2−

−+

=

+↔ ↔

proton transfer!H+ is not an ion, but an elementary particle

adsorption of proton by hydrogen: adsorption of proton by watermolecule:

ionization (dissociation) of water:

adsorption of proton by hydroxyl ion:

Grotthuss proton transfer:

F.M.Ersnberger:The Nonconformist Ion.J. Am. Ceram. Soc. 66(1983)747-750.

HO-Si≡

H+ -O-Si≡

surfaceequilibriumBoksay 1980Baucke 1996

HO-Si≡

H+ -O-Si≡

surfaceequilibriumBoksay 1980Baucke 1996

HO-Si≡

H+ -O-Si≡

H+ Na+ -O-Si≡

Na+(aq) HO-Si≡proton transfer initiatesthe mobolization of Na+

HO-Si≡

H+ -O-Si≡

H+ Na+ -O-Si≡

Na+(aq) HO-Si≡

2 HO-Si≡

H2O + ≡Si -O-Si≡ reaction of OH to H2O;condensation of silanolto siloxane bonds ...

HO-Si≡

H+ -O-Si≡

H+ Na+ -O-Si≡

Na+(aq) HO-Si≡

2 HO-Si≡

H2O + ≡Si -O-Si≡

... generates and shifts an inner boundary or transition zone

HO-Si≡

H+ -O-Si≡

H+ Na+ -O-Si≡

Na+(aq) HO-Si≡

2 HO-Si≡

H2O + ≡Si -O-Si≡

I. II. III.

2 ≡Si−O-Na+ + 2 H+

→ 2 ≡Si−OH + 2 Na+2 ≡Si−OH→ 2 ≡Si−O −Si≡

OH groups approacheach other; interstitial water moves into void

∝ √t

HO-Si≡

H+ -O-Si≡

H+ Na+ -O-Si≡

Na+(aq) HO-Si≡

2 HO-Si≡

H2O + ≡Si -O-Si≡

H2O + HO-Si≡

(HO)3-Si–

H4SiO4(aq)

∝ t

dissolutionof SiO2

∝ √t

HO-Si≡

H+ -O-Si≡

H+ Na+ -O-Si≡

Na+(aq) HO-Si≡

H2O + HO-Si≡

(HO)3-Si–

H4SiO4(aq)

H+ Na+ -O-Si≡

Na+(gel) HO-Si≡

2 HO-Si≡

H2O + ≡Si -O-Si≡

∝ √t

fast exchange of H+, Na+, H2O

∝ t

D ≈ 10-11 cm²/s

D ≈ 10-14 cm²/s

solution sub-surface zone bulk glass low density, high connectivity, H2O percolation high H2O mobility

D ≈ 10-5 cm²/s

same kind of chemistry like in aq. solutions; in specific: dominance ofH+ controlled reactions

Na+(aq), Cl-(aq) NaCl

rate control by fluid film diffusion: EA ≈ 20 kJ/mol

L

flow

FLUIDs Lcc

1-cr s

),,ƒ(v,,  )0·( ηρββ =

⋅−=

r0

∆Ghydr

∆GR

∆G#

solid + solution

solution + corrosion products

educt E

product P

activated complex C#

precurrentequilibrium R

surface sites

Gib

bs fr

ee e

nerg

y

reaction coordinate ξ

≡Si−OH ↔ ≡Si−O- + H+

SiO2 + H2O (pH)

SiO2(aq) + ppt. containing SiO2

OH-≡Si−O−Si≡

[E]

[P]

[C#]

[R]

after Grambow

rate control by activated surface complex:EA ≈ 70-80 kJ/mol

hydr#

#hydr#

hydr##

?G?G

cc

RT?G

expRT

?Gexp

RT?G

exp

RT?G?G

expRT?G

exprrr

s

∝

−⋅

−≈

−

−⋅

−∝

−−−

−∝−= −+

11    

reaction velocity:

linear free energy relationship (LFER):

∆Ghydr

∆GR

∆G#

solid + solution

solution + corrosion products

educt E

product P

activated complex C#

precurrentequilibrium R

surface sites

Gib

bs fr

ee e

nerg

y

reaction coordinate ξ

≡Si−OH ↔ ≡Si−O- + H+

SiO2 + H2O (pH)

SiO2(aq) + ppt. containing SiO2

OH-≡Si−O−Si≡

[E]

[P]

[C#]

[R]

after Grambow

rate control by activated surface complex:EA ≈ 70-80 kJ/mol

⋅⋅=

scc

1-Ch

kTr ]·[ #β

r0

glasschemistry

saturation;long termexposure

surfaceequilibrium

molecular dynamics

−+−−−=

s

hydrAX c

cRT

?GRTE

rr)(

1log)( ·

·logloglogξξε

θβ

thermochemical rate equation

LFER

0 2 4 6 8 10 12 1430

40

50

60

70

80

90

100

MacInnes Dole glass

HT fibre glass

-∆G

hydr

in k

J pe

r 10

0 g

glas

s

pH

0 2 4 6 8 10 12 14-8

-6

-4

-2

0

silica surface

alumina surface

log

Θ

pH

Corrosion rates at high water excess (low s parameter) :„Multiply“ the stability fingerprint or solubility (left graph) with thesurface coverage (right graph) ...

0 2 4 6 8 10 12 14

-12

-11

-10

log

r, r

in m

ol S

i / (

cm

2 ·s)

pH

2 4 6 8 10

60

70

80

90

100

log

r, r

in m

g/(c

m 2·d

)

pH

-3

-2

-1

0

1

-∆G

hydr

in k

J pe

r 10

0 g

glas

s

... and obtain a prediction of the dissolution rate as f(pH).

0 2 4 6 8 10 12 14-2.8

-2.4

-2.0

-1.6

-1.2

-0.8

-0.4

0.0

0.4lo

g r

(r

in m

g·cm

-2·d

-1)

pH-value

1

2

3

4N-A-B-S-glass

calculated rate DIN/ISO-test

log

q (q

in m

g·cm

-2)

2 4 6 8 10 12-50

0

50

100

150

200

250

300

stab

ility

-∆G

hydr [k

J pe

r 10

0 g

glas

s]

pH-value

-4

-3

-2

-1

0

1

log

r (

r in

mg·

cm-2·d

-1)

optical filter glass KG1

020406080

100

Al(OH)2- Al(OH)4

-

Al(OH)3, amAl3+

020406080

100

Al(OH)2+

Al(OH)3, aq

Al(OH)4

-Al(OH)2

+Al3+

0 2 4 6 8 10 12 140

20406080

100

rela

tive

conc

entra

tion

of a

queo

us A

l spe

cies

in %

Al(LH*)25-

AlL2H*4-

AlL23-

Al(HL)L2-

AlL

AlHL+

Al3+

pH

+ citric acid

∞ diluted

rel c

once

ntra

tion

of A

l spe

cies

in %

Interaction between organic components and glass –a key to applications in medicine and biotechnology

two key mechanisms:• influence on the solubility,• influence on the surface equilibrium. furmic

acetic

lactic

oxalic

malic

tartric

phthalic

citric

Ganor & Lasaga 1998, Gross & Dahlmann 2003

Thank youfor your

kind attention!