Unusual cation coordination in nanostructured mullites

Abstract Nanocrystalline mullite-type bismuth-bearing complex oxides Bi2(M0.5Al0.5)4O9 (M=Fe3+, Ga3+) are prepared by high-energy ball milling of the corresponding microcrystalline counterparts. An unusual five-fold coordination of metal cations is revealed in nanostructured Bi2(M0.5Al0.5)4O9 by means of 27Al magic angle spinning nuclear magnetic resonance and 57Fe Mössbauer spectroscopies. The concentration of five-fold coordinated cations increases with decreasing crystallite size of a material at the expense of octahedrally coordinated ones. In addition to the nuclear spectroscopic methods, Rietveld analyses of the X-ray diffraction data of the as-prepared nanooxides show that the constituent tetrahedra, octahedra, and the newly formed structural units with five-fold cation coordination are strongly distorted. With decreasing crystallite size of mullites, the average volume of their octahedra increases whereas this parameter decreases for tetrahedra. The macroscopic behaviour of the non-equilibrium nanomullites is characterised by SQUID magnetometry. The Fe-containing mullites exhibit a superposition of a dominant antiferromagnetism and a weak ferromagnetism. The increase in both the remanent magnetization and the coercive field with decreasing crystallite size is attributed to the effect of spin canting. The latter is confined to the interfacial and surface regions of the nanomaterials, and arises due to both the mechanically induced deformation of constituent structural units and the formation of cation sites with the unusual five-fold coordination.

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Leucite-pollucite structure-type variability and the structure of a synthetic end-member calcium wairakite (CaAl2Si4O12·2H2O)

Mineralogical Magazine ◽

10.1180/002646198547558 ◽

1998 ◽

Vol 62 (2) ◽

pp. 165-178 ◽

Cited By ~ 13

Author(s):

C. M. B. Henderson ◽

A. M. T. Bell ◽

S. C. Kohn ◽

C. S. Page

Keyword(s):

Rietveld Analysis ◽

Structure Type ◽

Magic Angle Spinning ◽

Resonance Spectroscopy ◽

Magic Angle ◽

Synthetic Sample ◽

Cation Site ◽

Wide Range ◽

Angle Spinning ◽

Cation Sites

AbstractThe structure of a synthetic end-member wairakite (CaAl2Si4O12·2H2O) has been determined using Rietveld analysis of high-resolution, synchrotron X-ray powder diffraction data, and 29Si and 27Al magic angle spinning nuclear magnetic resonance spectroscopy. The framework in the synthetic sample is more disordered than that in natural wairakite. Ca is distributed over the cavity cation sites M2, M12A, M12B in the approximate proportions 0.8:0.1:0.1, respectively, with M11 being vacant. 29Si MAS NMR data are consistent with about 80% of the Si occupying tetrahedral T11 and T12 sites linked to two Al atoms [Q4(2Al) silicons]. Tetrahedral and cavity cation site disorder are coupled so that Al mainly occupies T2 sites, with Ca in M12A and M12B being balanced by Al in T12A and T12B; T11A and T11B sites appear to only contain Si, in agreement with the M11 site being vacant. The crystal chemistries of the wide range of stoichiometries which crystallize with the leucite/pollucite structure-type are also reviewed, with particular attention being paid to the tetrahedral ordering configurations present in these phases, and the implications to crystallographic phase transitions.

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Slag Blended Cement Paste Carbonation under Different CO2 Concentrations: Controls on Mineralogy and Morphology of Products

Materials ◽

10.3390/ma13153404 ◽

2020 ◽

Vol 13 (15) ◽

pp. 3404

Author(s):

Wei Liu ◽

Shifa Lin ◽

Yongqiang Li ◽

Wujian Long ◽

Zhijun Dong ◽

...

Keyword(s):

Blended Cement ◽

Co2 Concentration ◽

Magic Angle Spinning ◽

Magic Angle ◽

Accelerated Carbonation ◽

X Ray Diffraction ◽

Cement Pastes ◽

Co2 Concentrations ◽

Angle Spinning ◽

Natural Carbonation

To investigate the effect of different CO2 concentrations on the carbonation results of slag blended cement pastes, carbonation experiments under natural (0.03% CO2) and accelerated conditions (3, 20, and 100% CO2) were investigated with various microscopic testing methods, including X-ray diffraction (XRD), 29Si magic angle spinning nuclear magnetic resonance (29Si MAS NMR) and scanning electron microscopy (SEM). The XRD results indicated that the major polymorphs of CaCO3 after carbonation were calcite and vaterite. The values of the calcite/(aragonite + vaterite) (c/(a + v)) ratios were almost the same in all carbonation conditions. Additionally, NMR results showed that the decalcification degree of C-S-H gel exposed to 0.03% CO2 was less than that exposed to accelerated carbonation; under accelerated conditions, it increased from 83.1 to 84.2% when the CO2 concentration improved from 3% to 100%. In SEM observations, the microstructures after accelerated carbonation were denser than those under natural carbonation but showed minor differences between different CO2 concentrations. In conclusion, for cement pastes blended with 20% slag, a higher CO2 concentration (above 3%) led to products different from those produced under natural carbonation. A further increase in CO2 concentration showed limited variation in generated carbonation products.

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Utilization of Calcium Carbide Residue Using Granulated Blast Furnace Slag

Materials ◽

10.3390/ma12213511 ◽

2019 ◽

Vol 12 (21) ◽

pp. 3511 ◽

Cited By ~ 4

Author(s):

Joonho Seo ◽

Solmoi Park ◽

Hyun No Yoon ◽

Jeong Gook Jang ◽

Seon Hyeok Kim ◽

...

Keyword(s):

Blast Furnace ◽

Blast Furnace Slag ◽

Calcium Carbide ◽

Magic Angle Spinning ◽

Magic Angle ◽

X Ray Diffraction ◽

Granulated Blast Furnace Slag ◽

Calcium Carbide Residue ◽

Angle Spinning ◽

Furnace Slag

The solidification and stabilization of calcium carbide residue (CCR) using granulated blast furnace slag was investigated in this study. CCR binding in hydrated slag was explored by X-ray diffraction, 29Si and 27Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy, and thermodynamic calculations. Mercury intrusion porosimetry and and compressive strength tests assessed the microstructure and mechanical properties of the mixtures of slag and CCR. C-A-S-H gel, ettringite, hemicarbonate, and hydrotalcite were identified as the main phases in the mixture of slag and CCR. The maximum CCR uptake by slag and the highest volume of precipitated solid phases were reached when CCR loading in slag is 7.5% by mass of slag, according to the thermodynamic prediction. This feature is also experimentally observed in the microstructure, which showed an increase in the pore volume at higher CCR loading.

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Tetraphosphorus tetraselenide: crystalline and amorphous phases analysed by X-ray diffraction, Raman and magic angle spinning 31P NMR spectroscopy and differential scanning calorimetry

Journal of Non-Crystalline Solids ◽

10.1016/0022-3093(95)00093-3 ◽

1995 ◽

Vol 188 (1-2) ◽

pp. 93-97 ◽

Cited By ~ 1

Author(s):

Jonathan D. Sarfati ◽

Gary R. Burns ◽

Keith R. Morgan

Keyword(s):

Differential Scanning Calorimetry ◽

31P Nmr ◽

Magic Angle Spinning ◽

Magic Angle ◽

31P Nmr Spectroscopy ◽

X Ray Diffraction ◽

Scanning Calorimetry ◽

X Ray ◽

Amorphous Phases ◽

Angle Spinning

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Characterization of chitin and chitosan extracted from shrimp shells by two methods

e-Polymers ◽

10.1515/epoly.2010.10.1.748 ◽

2010 ◽

Vol 10 (1) ◽

Cited By ~ 3

Author(s):

Carmiña Gartner ◽

Carlos Alberto Peláez ◽

Betty Lucy López

Keyword(s):

Low Cost ◽

Magic Angle Spinning ◽

Chemical Extraction ◽

Magic Angle ◽

X Ray Diffraction ◽

Shrimp Shells ◽

Before And After ◽

Chitin Extraction ◽

Angle Spinning ◽

Chitin And Chitosan

AbstractShrimp shells from Penaeus Vannamei species were hydrolyzed for chitin extraction by a chemical and a papain enzymatic method. Composition of shells was analyzed and their microstructure was characterized before and after hydrolysis by microscopy. Chitin fibers arrangement in the tissue was preserved after chemical extraction, but after papain hydrolysis the tissue presented structural disarrangement indicating that papain reacts indistinctly with peptidic and N-acetyl linkages. Although chemical purification is very effective, by-products are not recoverable. Conversely, papain hydrolysis yields partially purified chitosan but permits aminoacids isolation, which is important in food industry. This method has other advantages such as low cost and easy accessibility of papain. Chitin and chitosan were characterized by thermogravimetric analysis, infrared spectrophotometry and capillary electrophoresis. Degree of N-acetylation (DA) was determined by cross-polarization magic angle spinning nuclear magnetic resonance (CPMAS 13CNMR) or potentiometry and crystallinity was measured by X ray diffraction.

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Structure of nanocrystalline calcium silicate hydrates: insights from X-ray diffraction, synchrotron X-ray absorption and nuclear magnetic resonance

Journal of Applied Crystallography ◽

10.1107/s1600576716003885 ◽

2016 ◽

Vol 49 (3) ◽

pp. 771-783 ◽

Cited By ~ 41

Author(s):

Sylvain Grangeon ◽

Francis Claret ◽

Cédric Roosz ◽

Tsutomu Sato ◽

Stéphane Gaboreau ◽

...

Keyword(s):

Nuclear Magnetic Resonance ◽

Calcium Silicate ◽

Electron Probe ◽

Magic Angle Spinning ◽

Magic Angle ◽

X Ray Diffraction ◽

X Ray ◽

Calcium Silicate Hydrates ◽

Angle Spinning ◽

X Ray Absorption

The structure of nanocrystalline calcium silicate hydrates (C–S–H) having Ca/Si ratios ranging between 0.57 ± 0.05 and 1.47 ± 0.04 was studied using an electron probe micro-analyser, powder X-ray diffraction,29Si magic angle spinning NMR, and Fourier-transform infrared and synchrotron X-ray absorption spectroscopies. All samples can be described as nanocrystalline and defective tobermorite. At low Ca/Si ratio, the Si chains are defect free and the SiQ3andQ2environments account, respectively, for up to 40.2 ± 1.5% and 55.6 ± 3.0% of the total Si, with part of theQ3Si being attributable to remnants of the synthesis reactant. As the Ca/Si ratio increases up to 0.87 ± 0.02, the SiQ3environment decreases down to 0 and is preferentially replaced by theQ2environment, which reaches 87.9 ± 2.0%. At higher ratios,Q2decreases down to 32.0 ± 7.6% for Ca/Si = 1.38 ± 0.03 and is replaced by theQ1environment, which peaks at 68.1 ± 3.8%. The combination of X-ray diffraction and NMR allowed capturing the depolymerization of Si chains as well as a two-step variation in the layer-to-layer distance. This latter first increases from ∼11.3 Å (for samples having a Ca/Si ratio <∼0.6) up to 12.25 Å at Ca/Si = 0.87 ± 0.02, probably as a result of a weaker layer-to-layer connectivity, and then decreases down to 11 Å when the Ca/Si ratio reaches 1.38 ± 0.03. The decrease in layer-to-layer distance results from the incorporation of interlayer Ca that may form a Ca(OH)2-like structure, nanocrystalline and intermixed with C–S–H layers, at high Ca/Si ratios.

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Cation Disorder Determined by MAS 27Al NMR in High Dose Neutron Irradiated Spinel

MRS Proceedings ◽

10.1557/proc-373-413 ◽

1994 ◽

Vol 373 ◽

Cited By ~ 9

Author(s):

Elizabeth A. Cooper ◽

Craig D. Hughes ◽

William L. Earl ◽

Kurt E. Sickafus ◽

Glenn W. Hollenberg ◽

...

Keyword(s):

Magic Angle Spinning ◽

High Dose ◽

Magic Angle ◽

27Al Nmr ◽

Octahedral Cation ◽

Cation Disorder ◽

High Doses ◽

Angle Spinning ◽

Cation Sites ◽

Inverse Structure

AbstractSpinel (MgAl2O4) single crystals which had been neutron irradiated at (nominally) 400 and 750°C to high doses (53-250 dpa) were examined using 27Al magic angle spinning (MAS) nuclear magnetic resonance (NMR). The sensitivity of this procedure to a specific cation (Al) residing in different crystallographic environments allowed us to determine the distribution of the Al between the tetrahedral and octahedral cation sites in the spinel structure. Our results indicate that the Al was distributed nearly equally over both cation sites in the spinel, resulting in a nearly inverse structure.

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