1. Tracing RHX/DHX via MAS NMR: Potentials, Plans and First Results
Forum 8. März 2017: Ausbreitungsphänomene in Natur, Technik und Gesellschaft
Tracing RHX/DHX via MAS NMR: Potentials, Plans and First Results
by Nina Dvoyashkina and Dieter Freude
Oven for hydrothermal treatment of samples with deuterated water at higher temperatures
Sample treatment was performed in the open MAS rotor. At right rotors without and with cap, outer diameter is 4 mm. 1
Dieter Freude

2. Model compound muscovite: KAl2(Si3Al)O10(OH)2
Fukuma et al., Appl. Phys. Lett. 87 (2005)
Fig. 1. The crystal structure of muscovite mica; (a) a-axis, Fig. 3. FM-AFM images of the cleaved
(b) cleaved surface in which K+ ions are not shown surface of muscovite mica in water.
KAl2(Si3Al)O10(OH)2 corresponds to 45.3% SiO2, 38.4% Al2O3, 11.8% K2O, 4.5% H2O
Unfortunately, we could not get synthetic muscovite. We used the Mica V1 from Agar Scientific, England.
Mica V1 contains 45.6% SiO2, 33.1% Al2O3, 9.9% K2O, 2.7% H2O,
2.5% Fe2O3, 0.6% Na2O and CaO, MgO, P, S, C 2
Dieter Freude

3. Tracing RHX/DHX via MAS NMR: Potentials and Plans
Forum 8. März 2017: Ausbreitungsphänomene in Natur, Technik und Gesellschaft
Tracing RHX/DHX via MAS NMR: Potentials and Plans
Magic-angle spinning (MAS) NMR techniques were applied since 1980, in order to study the structure of muscovite. The MAS NMR studies are mainly focused to 29Si and 27Al nuclei. One study looks at 17O in 17O enriched synthetic muscovite; one (without MAS) at H3O+/K+ at the surface of nano-muscovite by 39K NMR. Mackenzie et al., see below, studied the thermal reactions of muscovite up to 1200 °C by 29Si and 27Al MAS NMR. The high-field NMR in Leipzig allows with fast MAS (30 kHz) the exact determination of the ratio between six-fold and four-fold oxygen coordinated aluminum atoms by 27Al MAS NMR spectroscopy. The acquisition of 29Si MAS NMR spectra is more time consuming and gives little additional information.
The 1H NMR signal is the strongest NMR signal of muscovite. However, we did not find any corresponding NMR study in the literature. One point could be investigated by 1H MAS NMR: Takes rehydroxylation place by pairs or by single hydroxyl groups?
2H nuclei are in muscovite in the natural abundance of % and undetectable by NMR. But we perform a rehydroxylation with a water pressure of 25 mbar D20 and observe the increase of the 2H MAS NMR signal and the decrease of the 1H MAS NMR signal. The high external field of 17.6 Tesla is substantial for a better signal-to-noise ratio of the 2H NMR. 27Al MAS NMR and 29Si MAS NMR spectroscopy will be used, in order to detect an influence of the hydrothermal treatment on the muscovite structure.
K.J.D. Mackenzie, I.W.M. Brown, C.M. Cardile, R.H. Meinhold, The Thermal Reactions of Muscovite Studied by High-resolution Solid-state 29Si and 27Al NMR, J. Mater. Sci. 22 (1987) 3
Dieter Freude

4. Tracing RHX/DHX via MAS NMR: First Results: 1H MAS NMR
Forum 8. März 2017: Ausbreitungsphänomene in Natur, Technik und Gesellschaft
Tracing RHX/DHX via MAS NMR: First Results: 1H MAS NMR
First principle calculation of the muscovite structure by Alvin and Miranda, see below, show that two aluminum atoms and two hydrogen bearing oxygen atoms are located at opposite corners of a square with a length of 1.92 Å. The geometry corresponds to an hydrogen-aluminum distance of Å and an hydrogen-hydrogen distance of 3.35 Å. We calculate from these distances the heteronuclear (H-Al) and homonuclear broadenings (full width at half maximum, fwhm) of the 1H NMR signal and obtain 14 kHz and 5 kHz, respectively. Without homonuclear interaction, we would measure well resolved spinning sideband with an envelope described by a fwhm = 14 kHz. But homonuclear broadening of 5 kHz prevents the resolution of the sidebands.
kHz
-40
-20 20 40
1H MAS NMR spectrum of the untreated muscovite measured with a MAS frequency of 10 kHz.
R.S. Alvim, C.R. Miranda, First Principles Characterization of Silicate Sites in Clay Surfaces, Phys. Chem. Chem. Phys. 17 (2015) 4
Dieter Freude

5. Tracing RHX/DHX via MAS NMR: First Results: 1H MAS NMR
Forum 8. März 2017: Ausbreitungsphänomene in Natur, Technik und Gesellschaft
Tracing RHX/DHX via MAS NMR: First Results: 1H MAS NMR
Increase of the magic-angle spinning frequency increases the resolution of the spectrum in the case of strong homonuclear dipole broadening of the lines. Unfortunately, it increases also the costs of the measurement.
The left spectrum was taken with 15 kHz, since the 30 kHz probe was under reparation, what usually costs €.
kHz
-40
-20 20 40
1H MAS NMR spectrum of the untreated muscovite measured with a MAS frequency of 15 kHz. 5
Dieter Freude

6. Tracing RHX/DHX via MAS NMR: First Results: 1H MAS NMR
Forum 8. März 2017: Ausbreitungsphänomene in Natur, Technik und Gesellschaft
Tracing RHX/DHX via MAS NMR: First Results: 1H MAS NMR
After 7 d treatment at 700 °C with a D2O pressure of 25 mbar, the broad spinning sideband spectrum disappeared.
The major intensity in the belongs to a broad signal in the middle, which can be explained by strong homonuclear and weak heteronuclear interaction, as it is expected for paired silanol groups near to silicon or iron atoms. The minor peaks (centerband and 4 spinning sidebands) can be explained by isolated AlOH groups.
kHz
-40
-20 20 40
1H MAS NMR spectrum of muscovite after 7 d treatment at 700 °C with a D2O pressure of 25 mbar. The MAS frequency was 10 kHz.
The spectrum shows that 1H MAS NMR spectroscopy can distinguish between isolated and paired hydroxyl groups. 6
Dieter Freude

7. Tracing RHX/DHX via MAS NMR: First Results: 2H MAS NMR
Forum 8. März 2017: Ausbreitungsphänomene in Natur, Technik und Gesellschaft
Tracing RHX/DHX via MAS NMR: First Results: 2H MAS NMR
2H MAS NMR spectroscopy of deuterated muscovite shows a typical first-order quadrupole broadened spectrum of the hydroxyl groups. The chemical shift of AlOH is about 2 ppm corresponding to 1.5 kHz. But the spectrum is about 200 kHz broad.
kHz
-100
100
2H MAS NMR spectrum of muscovite after 7 d treatment at 700 °C with a D2O pressure of 25 mbar.
The main information of the spectrum is the total intensity of the spectrum as a measure of hydroxyl deuteration in dependence on pretreatment temperature and duration. 7
Dieter Freude

8. Forum 8. März 2017: Ausbreitungsphänomene in Natur, Technik und Gesellschaft
Tracing RHX/DHX via MAS NMR: First Results: 27Al MAS NMR
27Al MAS NMR spectroscopy of muscovite shows the second-order quadrupole broadened signal of tetrahedral Al at about 70 ppm and the signal of octahedral Al at about 0 ppm. Intensities should be in the relation 1 to 2.
The relation 1 to 2 between the two signals of the upper spectrum cannot be obtained, since the muscovite under study is different to KAl2(Si3Al)O10(OH)2.
Asterisks denote spinning sidebands ∗ ∗
The main information from the 27Al MAS NMR spectroscopy is that a 7 d treatment at 750 °C with 25 mbar D2O changes the structure of the material, see the broadened signal at 0 ppm.
d /ppm 50
100
27Al MAS NMR muscovite spectra, on the top without pretreatment, on the bottom after 7 d treatment at 750 °C with 25 mbar D2O. 8
Dieter Freude

9. Acknowledgement Thanks go to Vincent John Hare, Christian Chmelik,
Jörg Kärger,
Jürgen Haase. 9
Dieter Freude