Journal ArticleDOI
29 Si and 27 Al magic-angle-spinning NMR studies of the thermal transformation of kaolinite
João Rocha,Jacek Klinowski +1 more
- Vol. 17, Iss: 2, pp 179-186
TLDR
The 27Al and 29Si NMR spectra acquired with a 30 s recycle delay of poorly and highly crystalline samples heated at 480 and 500° C, respectively, contain three distinct signals; they discuss their assignment in the light of experiments involving leaching of the samples with aqueous KOH as discussed by the authors.Abstract:
Thermal transformations of kaolinite of different degree of crystallinity have been monitored by 27Al and 29Si high-resolution NMR with magic-angle spinning (MAS NMR), X-ray diffraction, Fourier transform infrared, atomic absorption spectrophotometry and thermogravimetric analysis. NMR shows differences in the dehydroxylation process of kaolinites with different degree of crystallinity and reveals the presence of short-range order in metakaolinite. 29Si NMR spectra acquired with a 30 s recycle delay of poorly and highly crystalline samples heated at 480 and 500° C, respectively, contain three distinct signals; we discuss their assignment in the light of experiments involving leaching of the samples with aqueous KOH. Ca. 40% of Si sites retain their original Q
3 symmetry just above the onset of dehydroxylation and the Q
4 environment is present showing that a small amount of amorphous silica has already segregated. The spectrum of samples treated at 1000° C contains a signal at -110ppm (from Q
4 silicons) and a faint resonance, from mullite, at ca. -87 ppm. 29Si NMR also shows that cristobalite germs are already present at 950–1000° C. The 27Al MAS NMR spectra of metakaolinite reveal the presence of 4-, 5-and 6-coordinated Al. Changes in the three Al populations as a function of temperature have been monitored quantitatively. Below 800° C, 4-and 5-coordinated Al appears at the expense of 6-coordinated Al, but above 800° C the amount of 6-coordinated Al increases again. We suggest a dehydroxylation scheme which accounts for the presence of 4-and 5 coordinated Al. Above 900–950° C the latter signal is no longer present in the 27Al NMR spectra and new 4-and 6-coordinated Al species (mullite and γ-alumina) appear. We propose new ideas for the structure of metakaolinite.read more
Citations
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Journal ArticleDOI
Properties and applications of halloysite nanotubes: recent research advances and future prospects
TL;DR: In this article, the key structural characteristics and properties of halloysite and their related applications are comprehensively reviewed, and future prospects and key problems to be solved in Halloysite studies are discussed.
Journal ArticleDOI
The origin of the pozzolanic activity of calcined clay minerals: A comparison between kaolinite, illite and montmorillonite
TL;DR: In this paper, the decomposition of three clayey structures (kaolinite, illite and montmorillonite) when thermally treated at 600 degrees C and 800 degrees C was investigated and the effect of this treatment on their pozzolanic activity in cementitious materials.
Journal ArticleDOI
Supplementary Cementitious Materials
TL;DR: The current widespread use of calcium silicate or aluminate hydrate binder systems in the construction industry finds its roots in the Antique world where mixtures of calcined lime and finely ground reactive (alumino-)silicate materials were pioneered and developed as competent inorganic binders as discussed by the authors.
Journal ArticleDOI
The dehydroxylation of the kaolinite clay minerals using infrared emission spectroscopy
Ray L. Frost,Anthony M. Vassallo +1 more
TL;DR: In this paper, the authors investigated the dehy- droxylation process of a series of kaolinite clay minerals, including halloysite and dickite, using Fourier transform in situ infrared emission spectroscopy over a temperature range of 100 to 800
Journal ArticleDOI
Pozzolanic reactivity of low grade kaolinitic clays: Influence of calcination temperature and impact of calcination products on OPC hydration
TL;DR: In this paper, the influence of thermal activation temperature in pozzolanic reactivity of low grade kaolinitic clay and the impact of calcination products in OPC hydration are assessed.
References
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Book
High-resolution solid-state NMR of silicates and zeolites
Günter Engelhardt,Dieter Michel +1 more
TL;DR: High-Resolution NMR of Solids and Adsorbed Molecules as mentioned in this paper is a well-known technique for high-resolution NMR for solids and adsorbed molecules.
Journal ArticleDOI
High-resolution aluminum-27 NMR of aluminosilicates
E. Lippmaa,Ago Samoson,M. Magi +2 more
TL;DR: In this paper, the first and second coordination spheres and the Al-O-Si bond angles were used to determine isotropic chemical shifts of quadrupolar nuclei in solids.
Journal ArticleDOI
Variability in “crystallinity” Values among the Kaolin Deposits of the Coastal Plain of Georgia and South Carolina
TL;DR: In this paper, the authors measured the relative degree of crystal perfection among 144 samples of Coastal Plain kaolin and showed that the deposits are nonhomogeneous with respect to crystallinity and that the hard and soft types can be distinguished at the 0.95 probability level by an analysis of variance.
Journal ArticleDOI
Nuclear magnetic resonance of silica polymorphs
TL;DR: In this paper, magic angle spinning (MAS) spectra for seven polymorphs of silica and interpret the chemical shifts empirically in terms of interatomic distances and angles determined by X-ray diffraction.
Journal ArticleDOI
The KaoIinite-Mullite Reaction Series: I, A Survey of Outstanding Problems
G. W. Brindley,M. Nakahira +1 more
TL;DR: A survey of the reaction series of metakaolin can be found in this paper, where the authors provide the necessary historical background for a new approach to their solution, and the present survey brings these problems into sharp focus.