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Title: Direct Measurement of the Kinetics of Geopolymerisation by in-situ Energy Dispersive X-ray Diffractometry

Abstract

In-situ energy dispersive X-ray diffractometry (EDXRD) using synchrotron radiation has been used to directly observe the kinetics of formation of a geopolymeric gel from a metakaolin precursor. The use of a purpose-built hydrothermal cell with polychromatic radiation from a wiggler source enables collection of a full diffraction pattern approximately every 150 s. This provides sufficient time resolution to observe the collapse of the metakaolin structure as it dissolves in the activating solution, accompanied by the reprecipitation of the geopolymeric gel binder phase from the now-supersaturated solution. Measurements taken on a limited set of samples of different composition (Si/Al ratio) show a clear trend in the rate of reaction with composition, and also a distinctly different mechanism of reaction in the most highly alkaline systems compared to those containing higher levels of dissolved silica in the activating solution. This corresponds to the results of previous microscopic observations showing significantly different microstructures in these systems, and confirms the value of this technique in analysis of the kinetics of geopolymerisation.

Authors:
;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
930424
Report Number(s):
BNL-81163-2008-JA
Journal ID: ISSN 0022-2461; JMTSAS; TRN: US0901385
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Materials Science; Journal Volume: 42; Journal Issue: 9
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; BINDERS; DIFFRACTION; KAOLINITE; KINETICS; PRECURSOR; RADIATIONS; SILICA; SYNCHROTRON RADIATION; TIME RESOLUTION; X-RAY DIFFRACTION; national synchrotron light source

Citation Formats

Provis,J., and van Deventer, J. Direct Measurement of the Kinetics of Geopolymerisation by in-situ Energy Dispersive X-ray Diffractometry. United States: N. p., 2007. Web. doi:10.1007/s10853-006-0548-z.
Provis,J., & van Deventer, J. Direct Measurement of the Kinetics of Geopolymerisation by in-situ Energy Dispersive X-ray Diffractometry. United States. doi:10.1007/s10853-006-0548-z.
Provis,J., and van Deventer, J. Mon . "Direct Measurement of the Kinetics of Geopolymerisation by in-situ Energy Dispersive X-ray Diffractometry". United States. doi:10.1007/s10853-006-0548-z.
@article{osti_930424,
title = {Direct Measurement of the Kinetics of Geopolymerisation by in-situ Energy Dispersive X-ray Diffractometry},
author = {Provis,J. and van Deventer, J.},
abstractNote = {In-situ energy dispersive X-ray diffractometry (EDXRD) using synchrotron radiation has been used to directly observe the kinetics of formation of a geopolymeric gel from a metakaolin precursor. The use of a purpose-built hydrothermal cell with polychromatic radiation from a wiggler source enables collection of a full diffraction pattern approximately every 150 s. This provides sufficient time resolution to observe the collapse of the metakaolin structure as it dissolves in the activating solution, accompanied by the reprecipitation of the geopolymeric gel binder phase from the now-supersaturated solution. Measurements taken on a limited set of samples of different composition (Si/Al ratio) show a clear trend in the rate of reaction with composition, and also a distinctly different mechanism of reaction in the most highly alkaline systems compared to those containing higher levels of dissolved silica in the activating solution. This corresponds to the results of previous microscopic observations showing significantly different microstructures in these systems, and confirms the value of this technique in analysis of the kinetics of geopolymerisation.},
doi = {10.1007/s10853-006-0548-z},
journal = {Journal of Materials Science},
number = 9,
volume = 42,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • In situ energy-dispersive X-ray diffractometry, using a polychromatic synchrotron beam and a 'laboratory-sized' sample, is used to provide a direct measurement of the kinetics of geopolymerisation. The effects of sample SiO{sub 2}/Al{sub 2}O{sub 3} ratio, Na/(Na+K) ratio and reaction temperature are investigated. The results obtained support recent propositions that the initial gel phase formed during geopolymerisation is later transformed to a second, probably more-ordered gel phase, and provide detailed information regarding the rate of formation of the first gel phase during the first 3 h of reaction. Increasing the SiO{sub 2}/Al{sub 2}O{sub 3} ratio generally decreases the initial rate ofmore » reaction, with the highest SiO{sub 2}/Al{sub 2}O{sub 3} ratio samples showing what appears to be a pause in the reaction corresponding roughly to the solidification of the geopolymeric binder. Mixed (Na,K)-aluminosilicate geopolymers with moderate SiO{sub 2}/Al{sub 2}O{sub 3} ratios behave similarly to pure Na- or K-aluminosilicate compositions of higher SiO{sub 2}/Al{sub 2}O{sub 3} ratio. Fitting a simplified first-order rate expression to the overall reaction process at different temperatures allows the calculation of an effective overall activation energy, which may be useful in comparing geopolymerisation of slurries with different compositions.« less
  • Nonisothermal densification in 8% yttria doped zirconia (8YSZ) particulate matter of 250 nm median particle size was studied under 215 V/cm dc electric field and 9 Degree-Sign C/min heating rate, using time-resolved in-situ high temperature energy dispersive x-ray diffractometry with a polychromatic 200 keV synchrotron probe. Densification occurred in the 876-905 Degree-Sign C range, which resulted in 97% of the theoretical density. No local melting at particle-particle contacts was observed in scanning electron micrographs, implying densification was due to solid state mass transport processes. The maximum current draw at 905 Degree-Sign C was 3 A, corresponding to instantaneous absorbed powermore » density of 570 W/cm{sup 3}. Densification of 8YSZ was accompanied by anomalous elastic volume expansions of the unit cell by 0.45% and 2.80% at 847 Degree-Sign C and 905 Degree-Sign C, respectively. The anomalous expansion at 905 Degree-Sign C at which maximum densification was observed is characterized by three stages: (I) linear stage, (II) anomalous stage, and (III) anelastic recovery stage. The densification in stage I (184 s) and II (15 s) was completed in 199 s, while anelastic relaxation in stage III lasted 130 s. The residual strains ({epsilon}) at room temperature, as computed from tetragonal (112) and (211) reflections, are {epsilon}{sub (112)} = 0.05% and {epsilon}{sub (211)} = 0.13%, respectively. Time dependence of (211) and (112) peak widths ({beta}) show a decrease with both exhibiting a singularity at 905 Degree-Sign C. An anisotropy in (112) and (211) peak widths of {l_brace} {beta}{sub (112)}/{beta}{sub (211)}{r_brace} = (3:1) magnitude was observed. No phase transformation occurred at 905 Degree-Sign C as verified from diffraction spectra on both sides of the singularity, i.e., the unit cell symmetry remains tetragonal. We attribute the reduction in densification temperature and time to ultrafast ambipolar diffusion of species arising from the superposition of mass fluxes due to Fickian diffusion, thermodiffusion (Soret effect), and electromigration, which in turn are a consequence of a superposition of chemical, temperature, and electrical potential gradients. On the other hand, we propose defect pile-up at particle-particle contacts and subsequent tunneling as a mechanism creating the 'burst-mode' discontinuous densification at the singularities observed at 847 and 905 Degree-Sign C.« less
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