scholarly journals CaCl2-Accelerated Hydration of Tricalcium Silicate: A STXM Study Combined with29Si MAS NMR

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
Qinfei Li ◽  
Yong Ge ◽  
Guoqing Geng ◽  
Sungchul Bae ◽  
Paulo J. M. Monteiro
Keyword(s):  
Fine Structure ◽  
Calcium Silicate Hydrate ◽  
Hydration Product ◽  
Tricalcium Silicate ◽  
Mas Nmr ◽  
Chemical Components ◽  
X Ray ◽  
Scanning Transmission ◽  
X Ray Absorption ◽  
Cp Mas Nmr

The effect of calcium chloride (CaCl2) on tricalcium silicate (C3S) hydration was investigated by scanning transmission X-ray microscopy (STXM) with Near Edge X-ray Absorption Fine Structure (NEXAFS) spectra and29Si MAS NMR. STXM is demonstrated to be a powerful tool for studying the chemical composition of a cement-based hydration system. The Ca L3,2-edge NEXAFS spectra obtained by examining C3S hydration in the presence of CaCl2showed that this accelerator does not change the coordination of calcium in the calcium silicate hydrate (C-S-H), which is the primary hydration product. O K-edge NEXAFS is also very useful in distinguishing the chemical components in hydrated C3S. Based on the Ca L3,2-edge spectra and chemical component mapping, we concluded that CaCl2prefers to coexist with unhydrated C3S instead of C-S-H. In Si K-edge NEXAFS analysis, CaCl2increases the degree of silicate polymerization of C-S-H in agreement with the29Si CP/MAS NMR results, which show that the presence of CaCl2in hydrated C3S considerably accelerates the formation of middle groups (Q2) and branch sites (Q3) in the silicate chains of C-S-H gel at 1-day hydration.

scholarly journals Microstructural Study of Hydration of C3S in the Presence of Calcium Nitrate Using Scanning Transmission X-Ray Microscopy (STXM)

2020 ◽  
Vol 2020 ◽  
pp. 1-9
Author(s):  
Qinfei Li ◽  
Yang Wang ◽  
Guoqing Geng ◽  
Heng Chen ◽  
Pengkun Hou ◽  
...  
Keyword(s):  
Fine Structure ◽  
Electron Microscope ◽  
Calcium Silicate Hydrate ◽  
Calcium Nitrate ◽  
Early Age ◽  
Microstructural Study ◽  
X Ray ◽  
Scanning Transmission ◽  
X Ray Absorption ◽  
Scanning Electron

Calcium nitrate (CN) is used widely as an effectively inorganic setting accelerator and antifreeze admixture in concrete structures. In this paper, the multiscale investigation of CN on the hydration of C3S was studied by scanning transmission X-ray microscopy (STXM) combined with near-edge X-ray absorption fine structure (NEXAFS), 29Si MAS NMR, calorimetry, scanning electron microscope, and N2 absorption. It was concluded that the calcium silicate hydrate (C-S-H) surrounds the unhydrated C3S at 1-day hydrated C3S in the presence of calcium nitrate, while portlandite is partly in transformation and is formed partly. Based on Ca L3,2-edge NEXAFS spectra for 1-day hydrated C3S particle, calcium nitrate does not change the structure of the asymmetrically 7-fold coordination of calcium in the C-S-H. Calcium nitrate can accelerate the hydration of C3S to some extent and polymerization of the silicate chains within C-S-H considerably at early age, resulting in the increasing specific surface area.

Sorption Mechanisms of Zinc to Calcium Silicate Hydrate:  X-ray Absorption Fine Structure (XAFS) Investigation

2001 ◽  
Vol 35 (7) ◽  
pp. 1550-1555 ◽  
Author(s):  
Felix Ziegler ◽  
André M. Scheidegger ◽  
C. Annette Johnson ◽  
Rainer Dähn ◽  
Erich Wieland
Keyword(s):  
Fine Structure ◽  
Calcium Silicate ◽  
Calcium Silicate Hydrate ◽  
X Ray ◽  
Absorption Fine ◽  
Sorption Mechanisms ◽  
X Ray Absorption

Spectroscopic Characterization of a Pre-Ceramic Polymer For Sic/Tic System.

1990 ◽  
Vol 180 ◽  
Author(s):  
Florence Babonneau ◽  
Patrice Barre ◽  
Jacques Livage ◽  
Michel Verdaguer
Keyword(s):  
Spectroscopic Characterization ◽  
Argon Atmosphere ◽  
Mas Nmr ◽  
Spectroscopic Techniques ◽  
Excess Carbon ◽  
X Ray ◽  
Local Environments ◽  
X Ray Absorption ◽  
Cp Mas Nmr

ABSTRACTPolytitanocarbosilane precursor for SiC/TiC ceramics was characterized by various spectroscopic techniques (29Si and 13C CP MAS NMR, Ti K-edge XANES and EXAFS) in order to follow how titanium ions are incorporated into the polycarbosilane-based polymer. This polymer has been fired in argon atmosphere, and the evolution of the local environments of Si and Ti atoms, during the pyrolysis process, have been followed using 29Si MAS-NMR and Ti K-edge X-ray absorption: this study reveals the formation of Si-O bonds above 500°C, while Ti-C bonds clearly appear around 800°C. Above 1000°C, Si-O bonds are consumed by reaction with excess carbon and the system finally crystallizes into SiC/TiC mixture above 1200°C.

Multi-elemental scanning transmission X-ray microscopy–near edge X-ray absorption fine structure spectroscopy assessment of organo–mineral associations in soils from reduced environments

2015 ◽  
Vol 12 (1) ◽  
pp. 64 ◽  
Author(s):  
Chunmei Chen ◽  
Donald L. Sparks
Keyword(s):  
Fine Structure ◽  
X Ray ◽  
Fe Oxides ◽  
Absorption Fine ◽  
Nexafs Spectroscopy ◽  
Mineral Associations ◽  
Fundamental Process ◽  
Scanning Transmission ◽  
Mineral Components ◽  
X Ray Absorption

Environmental context Organo–mineral associations represent a fundamental process for stabilising organic carbon in soils. In this study, we employed scanning transmission X-ray microscopy–near edge X-ray absorption fine structure (STXM-NEXAFS) spectroscopy at C, Al and Si K-edges as well as Ca and Fe L-edges to conduct submicrometre-level investigations of the associations of C with mineral components in soils from reduced environments. This study provides the first insights into organo–mineral associations in reduced environments and shows progress towards examining, at the submicrometre level, compositional chemistry and associative interactions between organic matter and soil mineral components. Abstract Organo–mineral associations represent a fundamental process for stabilising organic carbon (OC) in soils. However, direct investigation of organo–mineral associations has been hampered by a lack of methods that can simultaneously characterise organic matter (OM) and soil minerals, and most investigations have focussed only on well drained soils. In this study, we employed scanning transmission X-ray microscopy–near edge X-ray absorption fine structure (STXM-NEXAFS) spectroscopy at C, Al and Si K-edges as well as Ca and Fe L-edges to conduct submicrometre-level investigations of the associations of C with mineral components in soils from reduced environments. Soils were collected from a forest footslope that is periodically poorly drained as well as a waterlogged wetland. OM was coated on mineral particles as thin films. Part of the mineral surface did not show detectable OM coverage with OC loadings of ≥1.3mg C m–2 determined for the clay fractions from these soils. C was not preferentially associated with Fe oxides in the footslope soil. A generally good C–Ca association was found in the anoxic wetland soil, which is free of Fe oxides. It was demonstrated for the first time that OM composition varied spatially at the submicrometre scale in the reduced soils free of Fe oxides. The composition of OM in the organo–mineral interface in the anoxic environments was highly complex and composed of aromatic, phenolic, aliphatic, carboxyl, carboxylamide and O-alkyl C functional groups. There was no consistent pattern for the association of certain types of organics with specific mineral components in both soils. The anoxic conditions resulted in the reduction of Fe in the aluminosilicates. This study provides the first insights into organo–mineral associations in reduced environments.

Chemical and orientational imaging of polymeric samples

1994 ◽  
Vol 52 ◽  
pp. 68-69
Author(s):  
H. Ade ◽  
B. Hsiao ◽  
G. Mitchell ◽  
E. Rightor ◽  
A. P. Smith ◽  
...  
Keyword(s):  
Ethylene Terephthalate ◽  
National Laboratory ◽  
Brookhaven National Laboratory ◽  
Carbonyl Groups ◽  
Aromatic Rings ◽  
Edge Structure ◽  
X Ray ◽  
Scanning Transmission ◽  
Polymeric Samples ◽  
X Ray Absorption

We have used the Scanning Transmission X-ray Microscope at beamline X1A (X1-STXM) at Brookhaven National Laboratory (BNL) to acquire high resolution, chemical and orientation sensitive images of polymeric samples as well as point spectra from 0.1 μm areas. This sensitivity is achieved by exploiting the X-ray Absorption Near Edge Structure (XANES) of the carbon K edge. One of the most illustrative example of the chemical sensitivity achievable is provided by images of a polycarbonate/pol(ethylene terephthalate) (70/30 PC/PET) blend. Contrast reversal at high overall contrast is observed between images acquired at 285.36 and 285.69 eV (Fig. 1). Contrast in these images is achieved by exploring subtle differences between resonances associated with the π bonds (sp hybridization) of the aromatic groups of each polymer. PET has a split peak associated with these aromatic groups, due to the proximity of its carbonyl groups to its aromatic rings, whereas PC has only a single peak.

Extended Core Edge Fine Structure in the E.M.

1980 ◽  
Vol 38 ◽  
pp. 120-121
Author(s):  
R.D. Leapman
Keyword(s):  
Fine Structure ◽  
Electron Scattering ◽  
Inelastic Electron ◽  
High Resolution Imaging ◽  
X Ray ◽  
Analytical Electron ◽  
Analytical Electron Microscope ◽  
Core Electrons ◽  
Resolution Imaging ◽  
X Ray Absorption

Extended X-ray Absorption Fine Structure (EXAFS) analysis makes use of synchrotron radiaion to measure modulations in the absorption coefficient above core edges and hence to obtain information about local atomic environments. EXAFS arises when ejected core electrons are backscattered by surrounding atoms and interfere with the outgoing waves. Recently, interest has also been shown in using inelastic electron scattering1-4. Some advantages of Extended X-ray-edge Energy Loss Fine Structure (EXELFS) are: a) small probes formed by the analytical electron microscope give spectra from μm to nm sized areas, compared with mm diameter areas for the X-ray technique, b) EXELFS can be combined with other techniques such as electron diffraction or high resolution imaging, and c) EXELFS is sensitive to low Z elements with K edges from ˜200 eV to ˜ 3000 eV (B to Cl).

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