Re‐Examination of the Polymorphism of Dicalcium Silicate

Smith, Deane K.; Majumdar, A.J.; Ordway, Fred

doi:10.1111/j.1151-2916.1961.tb15472.x

Cited by 45 publications

(15 citation statements)

References 10 publications

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“…Comparison of the 250 and 650 °C neutron PDF data sets with the atomic structures of larnite and 9 Å tobermorite using PDFgui [23] reveals that the local atomic structure of this heated C-S-D gel is best fit using a multiphase structural model consisting of both crystalline larnite and nanocrystalline 9 Å tobermorite (see Figure 5 and Table 2 for results), as opposed to either phase individually. It should be mentioned that the formation of larnite (beta-C2S) in systems without additives (such as sodium and chromium) is only seen to occur during cooling (after heating to 1400 °C) [30], and since these temperatures are not reached during the in situ neutron PDF experiment, the formation of larnite is extremely unlikely. However, the local bonding in larnite (calcium nesosilicate) provides the best fit to the neutron PDF data (compared to the gamma-C2S, the stable C2S phase below ~740 °C during heating), indicating that this bonding arrangement is likely present in the heated C-S-D gel, albeit in relatively low amounts (as depicted in Table 2).…”

Section: Drying-induced Structural Changes At 110 °C (Gel Ca/si Of 132)mentioning

confidence: 99%

Effects of temperature on the atomic structure of synthetic calcium–silicate–deuterate gels: A neutron pair distribution function investigation

White

2016

Cement and Concrete Research

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Due to the nanocrystallinity of the calcium-silicate-hydrate (C-S-H) gel in ordinary Portland cement-based paste combined with the presence of nanoscale heterogeneities such as varying calcium-to-silicon ratio and incorporation of aluminum in the structure, standard characterization techniques fail to fully capture the complex atomic structure and nanoscale morphology of this important binder phase. Here, neutron pair distribution function (PDF) analysis is applied to a range of deuterated C-S-H gels with varying Ca/Si ratios (denoted C-S-D). In situ temperature

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Section: Drying-induced Structural Changes At 110 °C (Gel Ca/si Of 132)mentioning

confidence: 99%

Effects of temperature on the atomic structure of synthetic calcium–silicate–deuterate gels: A neutron pair distribution function investigation

White

2016

Cement and Concrete Research

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“…Moreover, determinant factors. 1,2 very small quantities of material are available so that microAt least five polymorphs of Ca 2 SiO 4 have been distinguished:…”

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confidence: 99%

Raman Spectroscopic Investigations of Dicalcium Silicate: Polymorphs and High‐Temperature Phase Transformations

Rémy¹,

Reynard

Madon³

1997

Journal of the American Ceramic Society

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Polymorphs and high-temperature phase transformations␣Ј L -Ca 2 SiO 4 (with ␣Ј L generally considered as a superstructure referring to the ␣Ј H lattice) 3,4,10,11 and ␣-Ca 2 SiO 4 , structurally of dicalcium silicate (Ca 2 SiO 4 ) are investigated on powdered samples, using Raman scattering techniques. Raman specstill uncertain with trigonal 12,13 or hexagonal symmetry, 14 are stable as pure Ca 2 SiO 4 only at elevated temperatures. The tra at room conditions of pure ␥-and ␤-Ca 2 SiO 4 and stabilized ␤-, ␣ L -, and ␣-Ca 2 SiO 4 are presented in the frequency sequence of phase transformations generally accepted is that in Fig. 1, 15 and the proposed transformation mechanisms are as range of 110-1100 cm ؊1 . Each polymorph can be identified by its Raman spectrum, even though strong similarities follows: a semireconstructive mechanism between ␣ and ␣Ј H ; 14 a second-order transformation 16 or a displacive transformation exist between the ␤, ␣ L , and ␣ phases. In-situ hightemperature Raman spectroscopic studies in the temperamechanism between ␣Ј H and ␣Ј L ; 14 a displacive, 14 possibly martensitic, mechanism 17 or a first-order transformation between ture range of 298-1433 K on heating and cooling also are ␣Ј L and ␤; 16 a reconstructive 14 or a semireconstructive ␥ → reported, starting from ␥-Ca 2 SiO 4 . Modifications occurring ␣Ј L transition; 5 and a reconstructive, 14 semireconstructive, 5 or in the Raman spectra recorded in the wavenumber range of displacive mechanism for the ␤ → ␥ phase transformation. 18,19 90-1000 cm ؊1 show up during heating, the irreversible Besides these five phases, an additional phase intermediate ␥ → ␣ L phase transformation. Coexistence of ␥ and ␣ L between ␥ and ␣Ј L has sometimes been observed. 20-22 grains is observed in the temperature range of 1091-1119 K In most cases, X-ray diffractometry (XRD) and differential at least. The differences observed between the ␥-Ca 2 SiO 4 thermal analysis (DTA) are the techniques used to attempt and ␣ L -Ca 2 SiO 4 Raman spectra suggest that this phase to clarify the polymorphism and phase transformations in transformation is a reconstructive first-order transition.Ca 2 SiO 4 . 4,14,16,21 In this study, application of Raman spectrosThe reversible ␣ L → ← ␤ phase transformation also is copy is described and viewed as a complementary technique to described. Raman spectra of pure ␤ and ␣ L phases resemble the previous ones. Indeed, vibrational spectroscopy is a useful each other. The transition occurs from 949 K, on cooling, to tool for sample characterization and analysis and for the calcu-960-988 K, on heating, with a hysteresis probably depenlation of thermodynamic and elastic properties. Vibrational dent on the thermal history of the starting product. From frequencies also are very sensitive to interatomic forces. Indithe Raman scattering observations, this phase transformavidual peaks may be associated with the presence of particular tion also is considered as a first-order transformation and is structural groups within the sample. Thus, Ram...

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“…1 (Yannaquis and Guinier 1959;Smith et al 1961 ;Niesel and Thormann 1967;Eysel and Hahn 1970;Groves 1983;Eberhard et al 1991;Barbier and Hyde 1985;Kim et al 1992). /~-Ca2SiO4 appears in the stability field of the 7 modification on cooling and is usually called metastable because it never forms during heating.…”

Section: Introductionmentioning

confidence: 96%

High pressure polymorphism of dicalcium silicate Ca2SiO4. A transmission electron microscopy study

1995

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Abstract. Ca2SiO 4 dicalcium silicate has been transformed at high pressure in a diamond-anvil cell (DAC) coupled with a YAG laser heater, in order to study the high-pressure modifications of this compound. Starting material was the olivine form of CazSiO 4 (7-polymorph). Several samples have been synthesized at loading pressures of 4.5, 10 and 15 GPa respectively, at room temperature. Other samples have been obtained at:pressures ranging between 4.5 and 45 GPa and temperatures estimated to be about 2500 ~ The study of the quenched high pressure and/or high temperature phases has been performed using analytical transmission electron microscopy (ATEM) and X-ray diffraction (XRD). All the polymorphs of Ca2SiO 4 usually produced with high temperatures, including ~-CazSiO4, have been observed in the samples recovered from the high-pressure experiments. The c(-CazSiO 4 and ~-CaaSiO 4 polymorphs have been obtained at ambient conditions for the first time without stabilizing impurities. A new modification of ~'-Ca2SiO 4 has also been synthesized. Finally, the breakdown at high-pressure and temperature of Ca2SiO 4 into CaSiO 3 and CaO is reported.

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Re‐Examination of the Polymorphism of Dicalcium Silicate

Cited by 45 publications

References 10 publications

Effects of temperature on the atomic structure of synthetic calcium–silicate–deuterate gels: A neutron pair distribution function investigation

Effects of temperature on the atomic structure of synthetic calcium–silicate–deuterate gels: A neutron pair distribution function investigation

Raman Spectroscopic Investigations of Dicalcium Silicate: Polymorphs and High‐Temperature Phase Transformations

High pressure polymorphism of dicalcium silicate Ca2SiO4. A transmission electron microscopy study

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