Structural characterisation of X-ray amorphous calcium carbonate (ACC) in sternal deposits of the crustacea Porcellio scaber

2003 ◽  
pp. 551-555 ◽  
Author(s):  
Alexander Becker ◽  
Ulrich Bismayer ◽  
Matthias Epple ◽  
Helge Fabritius ◽  
Bernd Hasse ◽  
...  
Keyword(s):  
Calcium Carbonate ◽  
Amorphous Calcium Carbonate ◽  
Porcellio Scaber ◽  
X Ray ◽  
Structural Characterisation

Nanocrystallite model for amorphous calcium carbonate

2014 ◽  
Vol 47 (5) ◽  
pp. 1651-1657 ◽  
Author(s):  
P. Rez ◽  
S. Sinha ◽  
A. Gal
Keyword(s):  
Electron Microscope ◽  
Calcium Carbonate ◽  
Electron Diffraction ◽  
Relative Intensity ◽  
Ir Spectrum ◽  
X Rays ◽  
High Angle ◽  
Amorphous Calcium Carbonate ◽  
Optical Birefringence ◽  
X Ray

Amorphous calcium carbonate phases, either synthesized artificially or generated biogenically, can be identified from broadened peaks in X-ray or electron diffraction profiles. It is conceivable that randomly oriented nanocrystals, approximately 1 nm in size, could give rise to coherent diffraction profiles that are characterized as amorphous. The coherent diffraction profiles for 200 keV electrons, as might be used in an electron microscope, and Cu Kα X-rays were calculated for needle-shaped calcite crystals bounded by \{ {11\overline 21}\} facets and rhomb-shaped crystals bounded by \{ {10\overline 14} \} facets. Crystals of about 1.0 nm in size gave a profile that is consistent with the X-ray measurements of amorphous calcium carbonate. The relative intensity of high-angle broadened peaks and changes in the IR spectrum are best explained by disorder in the nanocrystallites. The presence of randomly oriented nanocrystallites also explains the lack of optical birefringence.

scholarly journals The Crystallization Process of Vaterite Microdisc Mesocrystals via Proto-Vaterite Amorphous Calcium Carbonate Characterized by Cryo-X-ray Absorption Spectroscopy

Crystals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 750
Author(s):  
Li Qiao ◽  
Ivo Zizak ◽  
Paul Zaslansky ◽  
Yurong Ma
Keyword(s):  
Calcium Carbonate ◽  
Absorption Spectroscopy ◽  
Formation Mechanism ◽  
Crystallization Process ◽  
Crystallization Time ◽  
Ordered Structure ◽  
Amorphous Calcium Carbonate ◽  
Edge Structure ◽  
X Ray ◽  
X Ray Absorption

Investigation on the formation mechanism of crystals via amorphous precursors has attracted a lot of interests in the last years. The formation mechanism of thermodynamically meta-stable vaterite in pure alcohols in the absence of any additive is less known. Herein, the crystallization process of vaterite microdisc mesocrystals via proto-vaterite amorphous calcium carbonate (ACC) in isopropanol was tracked by using Ca K-edge X-ray absorption spectroscopy (XAS) characterization under cryo-condition. Ca K-edge X-ray absorption near edge structure (XANES) spectra show that the absorption edges of the Ca ions of the vaterite samples with different crystallization times shift to lower photoelectron energy while increasing the crystallization times from 0.5 to 20 d, indicating the increase of crystallinity degree of calcium carbonate. Ca K-edge extended X-ray absorption fine structure (EXAFS) spectra exhibit that the coordination number of the nearest neighbor atom O around Ca increases slowly with the increase of crystallization time and tends to be stable as 4.3 (±1.4). Crystallization time dependent XANES and EXAFS analyses indicate that short-range ordered structure in proto-vaterite ACC gradually transform to long-range ordered structure in vaterite microdisc mesocrystals via a non-classical crystallization mechanism.

In Situ Observation of Pressure-induced Crystallization from Amorphous Calcium Carbonate by Time-resolved X-ray Diffraction

2015 ◽  
Vol 44 (4) ◽  
pp. 434-436 ◽  
Author(s):  
Koji Maruyama ◽  
Hiroyuki Kagi ◽  
Toru Inoue ◽  
Hiroaki Ohfuji ◽  
Toru Yoshino
Keyword(s):  
Calcium Carbonate ◽  
In Situ Observation ◽  
X Ray Diffraction ◽  
Amorphous Calcium Carbonate ◽  
Time Resolved ◽  
X Ray ◽  
Induced Crystallization

scholarly journals X-ray Total Scattering Study of Phases Formed from Cement Phases Carbonation

Minerals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 519
Author(s):  
Ana Cuesta ◽  
Angeles G. De la Torre ◽  
Miguel A. G. Aranda
Keyword(s):  
Calcium Carbonate ◽  
Pair Distribution Function ◽  
Thermal Analyses ◽  
Phase Assemblage ◽  
Reaction Products ◽  
Amorphous Calcium Carbonate ◽  
X Ray ◽  
Nanocrystalline And Amorphous ◽  
Scattering Study ◽  
Durability Performance

Carbonation in cement binders has to be thoroughly understood because it affects phase assemblage, binder microstructure and durability performance of concretes. This is still not the case as the reaction products can be crystalline, nanocrystalline and amorphous. The characterisation of the last two types of components are quite challenging. Here, carbonation reactions have been studied in alite-, belite- and ye’elimite-containing pastes, in controlled conditions (3% CO2 and RH = 65%). Pair distribution function (PDF) jointly with Rietveld and thermal analyses have been applied to prove that ettringite decomposed to yield crystalline aragonite, bassanite and nano-gibbsite without any formation of amorphous calcium carbonate. The particle size of gibbsite under these conditions was found to be larger (~5 nm) than that coming from the direct hydration of ye’elimite with anhydrite (~3 nm). Moreover, the carbonation of mixtures of C-S-H gel and portlandite, from alite and belite hydration, led to the formation of the three crystalline CaCO3 polymorphs (calcite, aragonite and vaterite), amorphous silica gel and amorphous calcium carbonate. In addition to their PDF profiles, the thermal analyses traces are thoroughly analysed and discussed.

Anhydrous amorphous calcium carbonate (ACC) is structurally different from the transient phase of biogenic ACC

2019 ◽  
Vol 55 (48) ◽  
pp. 6946-6949 ◽  
Author(s):  
Chieh Tsao ◽  
Pao-Tao Yu ◽  
Chin-Hsuan Lo ◽  
Chung-Kai Chang ◽  
Chia-Hsin Wang ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Phase Transformation ◽  
Water Vapor ◽  
Calcium Carbonate ◽  
Pressure Range ◽  
Ambient Pressure ◽  
Transient Phase ◽  
Amorphous Calcium Carbonate ◽  
X Ray

An in situ ambient pressure soft X-ray spectroscopic study of the phase transformation of ACC exposed to water vapor in the mbar pressure range in conjunction with heat treatment.

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