Calcium <i>L</i>-edge XANES study of some calcium compounds

Naftel, S. J.; Sham, T. K.; Yiu, Yun Mui; Yates, B.

doi:10.1107/s0909049500019555

Cited by 92 publications

(106 citation statements)

References 8 publications

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“…This is the first time NEXAFS spectra are applied to demonstrating that at the atomic scale C-S-H resembles more of a tobermorite structure where Ca atom has irregularity in its symmetry. As reported herein, this is important evidence unraveling the structural information of C-S-H, since the relation between coordination symmetry and NEXAFS has been proved by both theory and experimental results of many other minerals [20,36,37].…”

Section: Discussionmentioning

confidence: 75%

“…Alteration in the chemical environment of Ca and Si will affect their NEXAFS, providing the opportunity to obtain valuable chemical information, e.g. the coordination state or the changes in the neighboring atoms in molecular structure [19,20]. NEXAFS spectra at carbon K-edge could yield the information of carbonation [34].…”

Section: Scanning Transmission X-ray Microscope (Stxm)mentioning

confidence: 99%

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Atomic and nano-scale characterization of a 50-year-old hydrated C3S paste

Geng

Taylor

Bae

et al. 2015

Cement and Concrete Research

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a b s t r a c tKeywords: TEM (B) NMR Microstructure Ca 3 SiO 5 (D) STXM This paper investigates the atomic and nano-scale structures of a 50-year-old hydrated alite paste. Imaged by TEM, the outer product C-S-H fibers are composed of particles that are 1.5-2 nm thick and several tens of nanometers long. 29 Si NMR shows 47.9% Q 1 and 52.1% Q 2 , with a mean SiO 4 tetrahedron chain length (MCL) of 4.18, indicating a limited degree of polymerization after 50 years' hydration. A Scanning Transmission X-ray Microscopy (STXM) study was conducted on this late-age paste and a 1.5 year old hydrated C 3 S solution. Near Edge X-ray Absorption Fine Structure (NEXAFS) at Ca L 3,2 -edge indicates that Ca 2+ in C-S-H is in an irregular symmetric coordination, which agrees more with the atomic structure of tobermorite than that of jennite. At Si K-edge, multiscattering phenomenon is sensitive to the degree of polymerization, which has the potential to unveil the structure of the SiO 4 4− tetrahedron chain.

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Section: Discussionmentioning

confidence: 75%

Section: Scanning Transmission X-ray Microscope (Stxm)mentioning

confidence: 99%

Atomic and nano-scale characterization of a 50-year-old hydrated C3S paste

Geng

Taylor

Bae

et al. 2015

Cement and Concrete Research

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“…In most XANES spectra (TTCP, HA, a-TCP, DCPA, DCPD, MCPM), there are two small peaks (or a small peak and a shoulder), a 3 and b 3 , of about the same intensity, with a third, more intense, peak, c 3 . This pattern is characteristic of an octahedral crystal field [48]. Alpha-and b-TCP are two polymorphs of Ca 3 (-PO 4 ) 2 , a-TCP being the high-temperature form and b-TCP the low temperature one.…”

Section: Resultsmentioning

confidence: 95%

“…Several studies characterizing reference Ca-phosphates by bulk-scale XANES spectroscopy at the Ca L 2,3 -edges [33,47,48] and P L 2,3 -edges [49,50] have been published. The present study includes XANES spectra at the P and Ca L 2,3 -edges and the C K-edge acquired by STXM for a large number of reference Ca-phosphates and polyphosphates.…”

Section: Introductionmentioning

confidence: 99%

Characterization of Ca-phosphate biological materials by scanning transmission X-ray microscopy (STXM) at the Ca L2,3-, P L2,3- and C K-edges

et al. 2015

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Several naturally occurring biological materials, including bones and teeth, pathological calcifications, microbial mineral deposits formed in marine phosphogenesis areas, as well as bio-inspired cements used for bone and tooth repair are composed of Ca-phosphates. These materials are usually identified and characterized using bulk-scale analytical tools such as X-ray diffraction, Fourier transform infrared spectroscopy or nuclear magnetic resonance. However, there is a need for imaging techniques that provide information on the spatial distribution and chemical composition of the Ca-phosphate phases at the micrometer- and nanometer scales. Such analyses provide insightful indications on how the materials may have formed, e.g. through transient precursor phases that eventually remain spatially separated from the mature phase. Here, we present scanning transmission X-ray microscopy (STXM) analyses of Ca-phosphate reference compounds, showing the feasibility of fingerprinting Ca-phosphate-based materials. We calibrate methods to determine important parameters of Ca-phosphate phases, such as their Ca/P ratio and carbonate content at the ∼25nm scale, using X-ray absorption near-edge spectra at the C K-, Ca L2,3- and P L2,3-edges. As an illustrative case study, we also perform STXM analyses on hydroxyapatite precipitates formed in a dense fibrillar collagen matrix. This study paves the way for future research on Ca-phosphate biomineralization processes down to the scale of a few tens of nanometers.

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“…Calcite and aragonite spectra are most distinct at the Ca L-edge in the energy ranges indicated by boxes in Figure 3. Peaks at these energies are assigned to crystal field resonance, which differs for different carbonates (25,26,27). The calcite and aragonite spectra at the Ca L-edge are shown in Figure 3.…”

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confidence: 99%

Polarization-dependent imaging contrast in abalone shells

et al. 2008

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ABSTRACT. Many biominerals contain micro-or nano-crystalline mineral components, organized accurately into architectures that confer the material with improved mechanical performance at the macroscopic scale. We present here a new effect, which enables to observe the relative orientation of individual crystals at the sub-micron scale. We call it polarization-dependent imaging contrast (PIC), as it is an imaging development of the well-known x-ray linear dichroism. Most importantly PIC is obtained in situ, in pristine biominerals. We present here PIC in the prismatic and nacreous layers of Haliotis rufescens (red abalone), confirm it in geologic calcite and aragonite, and corroborate the experimental data with theoretical simulated spectra. PIC reveals new and unexpected aspects of nacre architecture that have inspired theoretical models for nacre formation.2 INTRODUCTION. Nacre, or mother-of-pearl, is intensely studied by materials scientists, mineralogists, physicists as well as chemists, because of its remarkable mechanical properties and its fascinating and poorly understood formation (1,2). Nacre is a composite of layered 400-nm thick aragonite tablets (3), and 30-nm thick organic matrix layers (4,5). Aragonite, an orthorhombic CaCO 3 polymorph, is hard but brittle. Aragonite accounts for 95% of nacre's mass, leading one to expect the mechanical characteristics of nacre to be similar to those of aragonite, yet nacre is 3000 times more resistant to fracture than aragonite (6). Materials scientists have only recently began to learn how to prepare synthetic composites outperforming their components by such large factors, and do so inspired by nacre (7,8,9,10), although not as efficiently and orderly organized as natural nacre. It is therefore of extreme interest to understand and possibly harness the mechanisms of nacre formation. Here we report unprecedented observations on the structure and architecture of nacre enabled by the use of x-ray absorption near edge (XANES) spectroscopy (11), combined with PhotoElectron Emission spectroMicroscopy (X-PEEM)(12). These observations inform and inspire new theoretical models for nacre formation mechanisms (13).

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Calcium L-edge XANES study of some calcium compounds

Cited by 92 publications

References 8 publications

Atomic and nano-scale characterization of a 50-year-old hydrated C3S paste

Atomic and nano-scale characterization of a 50-year-old hydrated C3S paste

Characterization of Ca-phosphate biological materials by scanning transmission X-ray microscopy (STXM) at the Ca L2,3-, P L2,3- and C K-edges

Polarization-dependent imaging contrast in abalone shells

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