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11.
A. Anderson 《光谱学快报》2013,46(5):819-825
A group theoretical analysis, based on the correlation method, is presented for the symmetric stretch vibration of the carbonate ion in three crystalline forms of calcium carbonate: calcite, aragonite and vaterite. Numbers of Raman and infrared active components are calculated and compared with experimental data, including those from a recent Raman study of vaterite. It is shown that the splitting observed for v l in vaterite is compatible with two of the proposed crystal structures for this compound. 相似文献
12.
Electron paramagnetic resonance (EPR) spectroscopy in combination with thermal methods were used to identify and characterize Mn2+ in the Chinese loess that is a multimineral system. EPR spectra of the loess samples from the classic loess-paleosol section in central China show the presence of trace amounts of Mn2+; whereas paleosol samples present no Mn2+ EPR signal. The spectral changes upon step heating from room temperature to 1000 °C suggest that this EPR signal in the loess arises from Mn substituted into CaCO3. This study provides a direct evidence that the loess-paleosol profiles were formed under the changing redox conditions caused by a past climatic change. 相似文献
13.
X. P. Geng H. F. Zhang B. H. Wang X. D. Geng J. W. Xing 《Journal of Thermal Analysis and Calorimetry》2005,80(1):193-199
Summary Two hydrated and aged cement pastes from India (NCB), w/c=0.4, of a similar chemical composition but of a different specific surface and different strength (OPC, C-33 and C-43), hydrated at w/c=0.4 for 1 month, were studied by XRD after 1 year and 5-6 year ageing on contact with air. They were tested by static heating (SH) in fresh state, and by DTA/DTG/TG, IR and mass spectrometry (MS), after ageing, presented elsewhere. The main XRD peaks of (i) portlandite were decreasing with T and disappearing about 450°C, (ii) calcite peak at room T was small and broad, it increased gradually, especially after portlandite disappearance; above 600°C it was lowered and it was lost above 700°C. Important variation in the d(001) of portlandite with ageing was observed, exceeding the standard value of d(001)=4.895 Å (72-0156). It was higher in the paste C-33 (4.925-4.936 Å), containing more carbonates, than in the paste C-43 (4.916-4.927 Å). Small variations only were found in the value of d(101), i.e. 2.627-2.635 Å (nominally 2.622 Å), whereas the d(104) of calcite could be used as internal standard and other calcium carbonates (vaterite and aragonite) showed a small variation only. The increase ind(hkl) with temperature was straight linear (in portlandite d(001)=0.095 Å, at 30-400°C) and the thermal expansion coefficient estimated thereform was high (4.75-4.95·10-5 K-1). Close to the T of decomposition the d/T became steeper. The thermal variation of d(104)=3.035 Å of calcite (d=0.015 Å at 30-400°C) was smaller than that ofd(101) of portlandite (d=0.025 Å at 30-400°C) and was similar in C-33 and C-43. The thermal expansion coefficient was 1.54 10-5 K-1, thus higher than the reported a=0.65·10-5 K-1. 相似文献
14.
T. Kaljuvee A. Trikkel R. Kuusik V. Bender 《Journal of Thermal Analysis and Calorimetry》2005,80(3):591-597
Summary The results of investigation of MgO participation in the binding of SO2 with lime-containing materials as sorbents are presented. Experiments of SO2 binding into solid phase using model samples of reactive grade MgO and CaO varying the mole ratio of MgO/CaO from 9:1 to 1:9 were carried out. Besides, dolomite and limestone samples with different MgO/CaO mole ratio (from 1.24 to 0.13) and samples of ashes formed at combustion of Estonian oil shale (containing 35-40% of carbonates) and its semicoke were studied Initial samples, intermediate and final products were subjected to chemical, IR-spectroscopy, X-ray and BET specific surface area analyses. The results of the present study confirmed the active participation of MgO in the binding of SO2 into the solid phase. In addition to CaSO4 the formation of Ca,Mg-double sulphate CaMg3(SO4)4 and -MgSO4 was observed. The presence of CaMg3(SO4)4 was fixed in a large temperature range 400-900°C and that of -MgSO4 in between 500-700°C. The optimum temperature range for formation and durability of CaMg3(SO4)4 was 700-800°C. 相似文献
15.
Abstract Stable isotope (13C, 18O, 34S) and trace element (Sr2+, Mg2+, Mn2+, Ba2+, Na+) investigations of elemental sulfur, primary calcites and mixtures of aragonite with secondary, post-aragonitic calcite from sulfur-bearing limestones have provided new insights into the geochemistry of the mineral forming environment of the native sulfur deposit at Machów (SE-Poland). The carbon isotopic composition of carbonates (δ13C = ?41 to ?47‰ vs. PDB) associated with native sulfur (δ34S = + 10 to + 15‰ vs. V-CDT) relates their formation to the microbiological anaerobic oxidation of methane and the reduction of sulfate derived from Miocene gypsum. From a comparison with experimentally derived fractionation factors the element ratios of the aqueous fluids responsible for carbonate formation are estimated. In agreement with field and laboratory observations, ratios near seawater composition are obtained for primary aragonite, whereas the fluids were relatively enriched in dissolved calcium during the formation of primary and secondary calcites. Based on the oxygen isotope composition of the carbonates (δ18O = ?3.9 to ?5.9‰ vs. PDB) and a secondary SrSO4 (δ18O = + 20‰ vs. SMOW; δ34S = + 59‰ vs. V-CDT), maximum formation temperatures of 35°C (carbonates) and 47°C (celestite) are obtained, in agreement with estimates for West Ukraine sulfur ores. The sulfur isotopic composition of elemental sulfur associated with carbonates points to intense microbial reduction of sulfate derived from Miocene gypsum (δ34S ≈ + 23‰) prior to the re-oxidation of dissolved reduced sulfur species. 相似文献
16.
17.
以轻烧白云石粉、氯化铵和二氧化碳为原料,在未使用晶型控制剂的情况下,通过蒸氨-沉钙过程制备出了似立方体状碳酸钙。研究了反应温度、溶液中钙离子浓度、通气速率、搅拌速度以及陈化时间对碳酸钙中方解石相含量以及晶体形貌的影响,并探索了沉钙反应的晶型控制机理。结果表明,在反应温度40 ℃、钙离子浓度0.05 mol/L、通碳速率100 mL/min、搅拌速度400 r/min和陈化时间2 h的条件下,制备出形貌规整、粒径分布均匀的似立方体状碳酸钙,平均粒径为5~10 μm。该研究为提升白云石的使用价值、生产高附加价值的碳酸钙产品,以及提高白云石资源的利用率提供理论基础。 相似文献
18.
Calcium carbonate has evoked interest owing to its use as a biomaterial, and for its potential in biomineralization. Three polymorphs of calcium carbonate, i.e. calcite, aragonite, and vaterite were synthesized. Three conventional bulk analysis techniques, Fourier transform infrared (FTIR), X‐ray diffraction (XRD), and SEM, were used to confirm the crystal phase of each polymorphic calcium carbonate. Two surface analysis techniques, X‐ray photoelectron spectroscopy (XPS) and time‐of‐flight secondary ion mass spectroscopy (TOF‐SIMS), were used to differentiate the surfaces of these three polymorphs of calcium carbonate. XPS results clearly demonstrate that the surfaces of these three polymorphs are different as seen in the Ca(2p) and O(1s) core‐level spectra. The different atomic arrangement in the crystal lattice, which provides for a different chemical environment, can explain this surface difference. Principal component analysis (PCA) was used to analyze the TOF‐SIMS data. Three polymorphs of calcium carbonate cluster into three different groups by PCA scores. This suggests that surface analysis techniques are as powerful as conventional bulk analysis to discriminate calcium carbonate polymorphs. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
19.
Gayathri S Lakshminarayanan R Weaver JC Morse DE Kini RM Valiyaveettil S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(11):3262-3268
The mechanisms of formation of biogenic magnesium-rich calcite remain an enigma. Here we present ultrastructural and compositional details of ossicles from the seastar Pisaster giganteus (Echinodermata, Asteroidea). Powder X-ray diffraction, infrared spectroscopy and elemental analyses confirm that the ossicles are composed of magnesium-rich calcite, whilst also containing about 0.01 % (w/w) of soluble organic matrix (SOM) as an intracrystalline component. Amino acid analysis and N-terminal sequencing revealed that this mixture of intracrystalline macromolecules consists predominantly of glycine-rich polypeptides. In vitro calcium carbonate precipitation experiments indicate that the SOM accelerates the conversion of amorphous calcium carbonate (ACC) into its final crystalline product. From this observation and from the discovery of ACC in other closely related taxa, it is suggested that substitution of magnesium into the calcite lattice through a transient precursor phase may be a universal phenomenon prevalent across the phylum echinodermata. 相似文献
20.