X-Ray pair distribution function analysis of a metakaolin-based, KAlSi2O6·5.5H2O inorganic polymer (geopolymer)

Abstract

The atomic structure of geopolymers is often described as amorphous with a local structure that is equivalent to that of crystalline zeolites. However, this structural relationship has never been quantified beyond a first-nearest-neighbor bonding environment. In this study, the short to medium range ($1 nm) structural order of metakaolin-based KAlSi 2 O 6 $5.5H 2 O geopolymer was quantified and compared to zeolitic tetragonal leucite (KAlSi 2 O 6 ) using the X-ray atomic pair distribution function technique. Unheated KAlSi 2 O 6 $5.5H 2 O was found to be structurally similar to leucite out to a length of $8 A ˚, but had increased medium range disorder over the 4.5 A ˚< r < 8 A ˚range. On heating to >300 C, changes in the short to medium range structure were observed due to dehydration and removal of chemically bound water. Crystallization of leucite occurred in samples heated beyond 1050 C. Refinements of a leucite model against the PDF data for geopolymer heated to 1100 C for 24 h yielded a good fit.

Microstructure and integrity of leucite ceramic derived from potassium-based geopolymer precursor

“…White et al 15 observed that once heated to 1000 • C, the structure of the geopolymer (K 2 O·Al 2 O 3 ·4SiO 2 ·11H 2 O) began to crystallize and form leucite, as analyzed by the neutron pair distribution function. Bell et al 11,16 reported that the major reflection for leucite first appeared from geopolymer (K 2 O·Al 2 O 3 ·4SiO 2 ·11H 2 O) upon 1050 • C by XRD and that long range order occurred at 1060 • C by X-ray atomic pair distribution function technique.…”

“…[1][2][3][4][5][6][7] A significant feature is that on heating a geopolymer will be converted into a leucite ceramic. [8][9][10][11][12][13][14][15][16][17][18] Therefore, geopolymer technology provides a new route to fabricate advanced ceramics of advantageously low cost and near net-shape forming, an attractive feature in industrial applications. It was reported in literatures that van Deventer et al from the University of Melbourne and Kriven et al from the University of Illinois at UrbanaChampaign have systematically studied the effects of Si/Al ratios and alkali cations (e.g.…”

“…Na + , K + and Cs + ) on physical evolution, phase transitions, and microstructure development of geopolymers. [10][11][12][13][14][15][16] However, there has been no report on fabricating advanced leucite ceramics with fine integrity directly derived from geopolymer precursors, the reason for which would * Corresponding author. Tel.…”

Nanostructural characterization of geopolymers by advanced beamline techniques

“…The disordered nature of the geopolymer binder phase is highly amenable to analysis by this technique, as has been discussed in recent reviews [1,17], and significant advances in the understanding of geopolymer nanostructure have been obtained by both X-ray [18,19] and neutron [20,21] pair distribution function analysis. In situ analysis of geopolymer formation has previously been undertaken by a variety of laboratory and beamline techniques, including in particular the use of in situ energy-dispersive X-ray diffractometry to provide direct kinetic information regarding gel structure formation using high-energy synchrotron radiation [22,23].…”

Recent studies of cements and concretes by synchrotron radiation crystallographic and cognate methods

“…The PDF approach using SR has also been employed to study several other amorphous (or ill-crystalline) phases in cement research including ASR gel, [34] silica fume, [35] metakaolin [36,37] and geopolymers. [38][39][40] 3.2.2.…”