W' M' Kriven, J'L Bell and P' Sarin

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The Complex Structure of Geopolymers
W. M. Kriven, J.L Bell and P. Sarin University of
Illinois at Urbana-Champaign Department of
Materials Science and Engineering
Funded by the US AFOSR through 2 STTRs and one
Nanoinitiative contract
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Geopolymers (Polysialates)

• Are a type of chemically-bonded ceramics
  (alkali bonded ceramics or inorganic polymers)
• Inorganic polymeric ceramics formed from both
  aluminum and silicon sources containing AlO4- and
  SiO4 tetrahedral units, under highly alkaline
  conditions (NaOH, KOH, CsOH) at ambient
  temperatures
• They are a rigid, hydrated, alumino-silicate gel
  containing group I, charge-balancing cations
• They result in an amorphous, cross-linked,
  impervious, acid-resistant, 3-D structure

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Introduction Geopolymer Structure

• Formula Mn-(SiO2)z-AlO2-n,wH2O
• where M is a typically Na or K cation, n is
  the degree of polycondensation and z is 1, 2, or
  3
• The poly(sialates) were said to form chain or
  ring polymers with Si4 and Al3 in IV-fold
  coordination

Davidovits, J., Journal of Thermal Analysis,
1991. 37 p. 1633-1656.
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Introduction Geopolymer Structure

• Are generally X-ray amorphous
• Al is integrated into a network of (IV) AlO4- and
  SiO4, such that the negative charge on AlO4- is
  balanced by the alkali cation.

Davidovits, J., Geopolymer 88 Conference, San
Quentin, France, 1988. 1p. 25-48 Barbosa, V.F.F.
and K.J.D. MacKenzie, Materials Research
Bulletin, 2003. 38(2) p. 319-331. Barbosa,
V.F.F., K.J.D. MacKenzie, and C. Thaumaturgo,.
International Journal of Inorganic Materials,
2000. 2(4)p. 309-317.
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How to Make a Geopolymer
Example
Molar oxide ratio SiO2 / Al2O3 4.0 K2O /
SiO2 0.25 H2O / K2O 10-12
Step 1
Step 2
Step 3
Step 4
alkali silicate solution

metakaolin clay
mix
cast and seal
store at RT or in an oven at low T
Davidovits, J. Journal of Thermal Analysis 1991,
37, 1633.
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GEOPOLYMER COVERSION TO CERAMIC POLLUCITE
Ex-situ X-ray diffraction patterns of Cs-GP and
SynMK
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Intrinsic Microstructure and Properties as a
Function of Composition Experimental Procedure
Table I. Compositions of Interest

• Other Processing Parameters
• M2OH2O 11 (M Na K)
• Cure temperature 50oC
• Cure time varied
• Mixing time 10 min.

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Intrinsic Microstructure and Properties as a
Function of Composition SEM of MIP samples
1000 psi autoclave polished surfaces 1000x
magnification p average pore size
0 K, 100 Na p 73.1nm
30 K, 70 Na p 33.5nm

• K2ONa2O SEM micrographs of 41 SiO2Al2O3, cured
  80oC for 24 h

Effect of Alkali Choice on Geopolymer
Properties, W. M., Kriven and J., Bell, Cer.
Eng. and Sci. Proc. vol. 25 3-4 (2004).
60 K, 40 Na p 25.8
80 K, 20 Na p 19.7nm
100 K, 0 Na p 11.3nm
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Intrinsic Microstructure and Properties as a
Function of Composition SEM Micrographs as a
Function of Composition
100K
100 Na
50K- 50Na
41 SiO2Al2O3
31 SiO2Al2O3
21 SiO2Al2O3
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Intrinsic Microstructure and Properties as a
Function of Composition - SEM
Unreacted metakaolin sheet
Region of intrinsic GP
Microstructure and Microchemistry of
Fully-Reacted Geopolymers and Geopolymer Matrix
Composites, W. M., Kriven, J., Bell, and M.,
Gordon, Ceramic Transactions vol. 153, 227-250
(2003).
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Intrinsic Microstructure and Properties as a
Function of Composition - SEM
Individual precipitates of GP
Microstructure and Microchemistry of
Fully-Reacted Geopolymers and Geopolymer Matrix
Composites, W. M., Kriven, J., Bell, and M.,
Gordon, Ceramic Transactions vol. 153, 227-250
(2003).
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TEM BF at RT
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TEM of crushed Na-geopolymer
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High angle, annular dark field TEM (HAADF)
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High angle, annular dark field TEM (HAADF)
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Nanoporosity
Differential distribution of surface against pore
radius
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Nanoporosity in kaolin-based GP
Summary of Properties

• Average logarithmic pore radius 0.4362 nm
• Average pore radius 3.3711 nm
• Porosity over weight 0.3165 cm3/g
• Porosity over volume 0.4106 cm3/cm3
• Meso- and macro-pore surface over weight
  190.5778 m2/g
• Meso- and macro-pore surface over volume
  247.2794 m2/cm3
• Total pore surface over weight 274.6912 m2/g
• Total pore surface over volume 356.4186 m2/cm3
• Density of solid phase 2.0481 g/cm3

Nanoporosity in synthetic-based GP 0.8 nm
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INTRODUCTION TWO USEFUL CERAMIC PHASES
Leucite KAlSi2O6
Pollucite CsAlSi2O6
Bollin, P.J., Glass Formation in the System
Cs2O-Al2O3-SiO2, J. Am. Cerm. Soc. 55, 483
(1972)
Schairer J.F., and N.L. Bowen, The system
K2OAl2O3 SiO2, Am. J. Sci., 253, 681 (1955)
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INTRODUCTION USEFUL CERAMIC PHASES

• Pollucite (CsAlSi2O6)
• Very refractory (Tm 1940oC)
• Exceptional creep resistance comparable to YAG
• Low thermal expansion (0.45 from 25 1000oC) or
  (1.2 3.3 x 10-6 oK-1)
• Relatively low density (3.3 g/cm3)
• High thermal shock resistance
• Tolerates a high degree of ionic substitution
  which can be used to further lower thermal
  expansion or even make it negative
• May be useful for ceramic matrix composites and
  thermal barrier coatings

• Leucite (KAlSi2O6)
• Refractory (Tm 1693oC)
• High thermal expansion (15.1 31 x 10-6 oK-1)
• Tolerates a high degree of ionic substitution
• High fracture toughness
• Useful as a cermet due to high thermal expansion
• Used widely in dentistry
• Potential as a thermal barrier coating or ceramic
  matrix composite
• Leucite crystals enhance the toughness of glass
  ceramics

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GEOPOLYMER COVERSION TO CERAMIC POLLUCITE
Ex-situ X-ray diffraction patterns of
Cs-geopolymer after heating at a set temperature
for 1 hour.
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Pair Distribution Function (PDF) Work

• Novel materials are often disordered/complex on a
  local level
• PDF method allow us to sit on an atom and look
  at our neighborhood
• PDF procedure
• Collect total scattering data (X-ray or neutron)
  for material
• Subtract background and apply appropriate
  corrections to raw data
• This gives us the structure function, S(Q)
• Apply Fourier transform to get the PDF, G(r)

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Experimental Setup Argonne National Lab

• Advanced Photon Source beamline 11IDB
• ? 0.1372 Å (90.3 keV), (Q 30 Å-1, 2? 39o)
• 2.84mm OD Polyimide (Kapton) tubes as sample
  holder
• Transmission geometry
• GE amorphous Si Angio flat plate detector

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Scattering in PDF

• Elastic scattering no exchange of energy
  between the scattering particle and the system it
  is scattering off of
• Inelastic scattering the is an exchange of
  energy
• Coherent waves interfere and resulting
  intensity is given by the square of the sum of
  the wave amplitudes
• Incoherent no definite phase relationship
  between the wave as they do no interfere and the
  resulting intensity is the sum of the individual
  waves themselves
• ALL scattering can be classified as listed above

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Scattering in PDF
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Scattering in PDF

• PDF uses total elastic scattering making it
  necessary to subtract out inelastic contributions
  and other sources of error
• Non X-ray specific corrections
• Flat plate geometrical correction
• Detector deadtime and flux normalization
• Background (air, container)
• Random errors
• X-ray Specific corrections
• Compton scattering
• Thomson scattering process polarization of
  X-ray beam
• Self scattering and multiple scattering
• Laue diffuse scattering

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?- Alumina (Corundum) Procedure
Subtract dark current and sum raw detector data
Use PDFgetX2 software to get structure fun.
Correct for background Compton, flat
plate, weighting function
FIT2D
Take Fourier transform to get PDF
Apply corrections and calibrations and
convert from 2D image to 1D via FIT2D software
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Pair Distribution Function (PDF) Work
Alpha Alumina after heating to 1300 oC for X.X h
Amorphous Alumina Prepared via PVA method
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?- Alumina (Corundum) Modeling Partials
MODEL Kirfel, A., Eichhorn, K. Accurate
Structure Analysis with Synchrotron Radiation
The Electron Density in Al2O3 and Cu2O, Acta
Cryst. A46 (1990) 271-284
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?- Alumina (Corundum) Modeling Best Fit
R-value82.62
MODEL Kirfel, A., Eichhorn, K. Accurate
Structure Analysis with Synchrotron Radiation
The Electron Density in Al2O3 and Cu2O, Acta
Cryst. A46 (1990) 271-284
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?- Alumina (Corundum) Modeling Best Fit
R-value16.75
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?- Alumina (Corundum) Modeling Best Fit
R-value16.75
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Cs based geopolymer conversion to Pollucite
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Cs based geopolymer conversion to Pollucite
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K based geopolymer conversion to Leucite
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Na based geopolymer Ordering in Na-GP
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K based geopolymer Ordering in K-GP
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Cs based geopolymer Ordering in Cs-GP
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Geopolymer PDF as function of Alkali Choice
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Geopolymer PDF as function of water for K-GP
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Geopolymers (Polysialates)

• Are a type of chemically-bonded ceramics
  (alkali bonded ceramics or inorganic polymers)
• Inorganic polymeric ceramics formed from both
  aluminum and silicon sources containing AlO4- and
  SiO4 tetrahedral units, under highly alkaline
  conditions (NaOH, KOH, CsOH) at ambient
  temperatures
• They are a rigid, hydrated, alumino-silicate gel
  containing group I, charge-balancing cations
• They result in an amorphous, cross-linked,
  impervious, acid-resistant, 3-D structure

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Geopolymers (Polysialates)

• A great deal of complementary information on
  the structure at the local atomic level can be
  obtained from
• conventional Bragg diffraction techniques
• Rietveld analysis
• (reciprocal space)
• Pair distribution function (PDF) analysis
• (real space