Triclinic Tricalcium Silicate Research Articles

Triclinic tricalcium silicate: Structure and thermoelastic properties from molecular simulations

Triclinic tricalcium silicate is the stable form of pure C3S at ambient conditions. Atomic-level understanding of the structure and properties of this polymorph may provide some insights for innovative solutions to control its reactivity or to optimize its dopage. Here, we perform classical molecular dynamics simulations to obtain the full stiffness, thermal expansion, and thermal conductivity tensors as well as the heat capacities of triclinic tricalcium silicate (T1). In agreement with previous work, semi-classical computations are required to get experimentally consistent heat capacity. Phonon scattering and acoustics are also analyzed. This work provides fundamental component property data in cement systems, which is crucial to well understand the contribution of polymorphs in alite.

Preparation of triclinic alite with short soakings in a small experimental high-temperature furnace

The article deals with a laboratory preparation of triclinic modification of clinker mineral tricalcium silicate. A substantial part of the article is devoted to the technology and technique of firing a sample of tricalcium silicate, which would in the future allow the study of the development of the crystal lattice structure of this clinker mineral at short isothermal durations, in the order of minutes. As part of the research, a small high-temperature experimental furnace was designed and constructed. Based on the results, we can express the suitability and applicability of this furnace for the study of the formation of triclinic tricalcium silicate at short soakings.

The Application of 29Si NMR Spectroscopy to the Analysis of Calcium Silicate-Based Cement using Biodentine™ as an Example.

Biodentine is one of the most successful and widely studied among the second generation of calcium silicate-based endodontic cements. Despite its popularity, the setting reactions of this cement system are not currently well understood. In particular, very little is known about the formation and structure of the major calcium silicate hydrate (C-S-H) gel phase, as it is difficult to obtain information on this poorly crystalline material by the traditional techniques of powder X-ray diffraction analysis (XRD) and Fourier transform infrared spectroscopy (FTIR). In this study, the hydration reactions of Biodentine are monitored by XRD, FTIR, isothermal conduction calorimetry and, for the first time, 29Si magic angle spinning nuclear magnetic resonance spectroscopy (29Si MAS NMR) is used to investigate the structures of the anhydrous calcium silicate phases and the early C-S-H gel product. XRD analysis indicated that the anhydrous powder comprises 73.8 wt% triclinic tricalcium silicate, 4.45 wt% monoclinic β-dicalcium silicate, 16.6 wt% calcite and 5.15 wt% zirconium oxide. Calorimetry confirmed that the induction period for hydration is short, and that the setting reactions are rapid with a maximum heat evolution of 28.4 mW g−1 at 42 min. A progressive shift in the FTIR peak maximum from 905 to 995 cm−1 for the O-Si-O stretching vibrations accompanies the formation of the C-S-H gel during 1 week. The extent of hydration was determined by 29Si MAS NMR to be 87.0%, 88.8% and 93.7% at 6 h, 1 day and 1 week, respectively, which is significantly higher than that of MTA. The mean silicate chain length (MCL) of the C-S-H gel was also estimated by this technique to be 3.7 at 6 h and 1 day, and to have increased to 4.1 after 1 week. The rapid hydration kinetics of Biodentine, arising from the predominance of the tricalcium silicate phase, small particle size, and ‘filler effect’ of calcite and zirconium oxide, is a favorable characteristic of an endodontic cement, and the high values of MCL are thought to promote the durability of the cement matrix.

Effect of the densification of C–S–H on hydration kinetics of tricalcium silicate

AbstractEffect of water to cement (w/c) ratio and temperature profiles on the densification of C–S–H (calcium silicate hydrate gel) and hydration kinetics of triclinic tricalcium silicate (C3S) is studied beyond the first day of hydration. Calorimetry and quantitative X‐ray diffraction/Rietveld analysis show that degree of hydration is unaffected by w/c up to 7 days and marginally thereafter. Coupling the degree of hydration with the portlandite content measured from thermal analysis indicate that C/S ratio of C–S–H decreases with increasing w/c. There is a clear increase in the portlandite content with increasing w/c, even though the degree of hydration is unchanged, due to the variations in C/S ratio of C–S–H. On the other hand, when C3S is initially cured at a lower temperature (20°C) and then at a higher temperature (40°C), there is a significant increase in the reactivity even until 28 days and vice versa. These experimental results were explained using the densified volumetric growth hypothesis, which assumes that hydration kinetics are dependent on the internal surface area of C–S–H.

A Critical Comparison of 3D Experiments and Simulations of Tricalcium Silicate Hydration.

Advances in nano-computed X-ray tomography (nCT), nano X-ray fluorescence spectrometry (nXRF), and high-performance computing have enabled the first direct comparison between observations of three-dimensional nanoscale microstructure evolution during cement hydration and computer simulations of the same microstructure using HydratiCA. nCT observations of a collection of triclinic tricalcium silicate (Ca3SiO5) particles reacting in a calcium hydroxide solution are reported and compared to simulations that duplicate, as nearly as possible, the thermal and chemical conditions of those experiments. Particular points of comparison are the time dependence of the solid phase volume fractions, spatial distributions, and morphologies. Comparisons made at 7 h of reaction indicate that the simulated and observed volumes of Ca3SiO5 consumed by hydration agree to within the measurement uncertainty. The location of simulated hydration product is qualitatively consistent with the observations, but the outer envelope of hydration product observed by nCT encloses more than twice the volume of hydration product in the simulations at the same time. Simultaneous nXRF measurements of the same observation volume imply calcium and silicon concentrations within the observed hydration product envelope that are consistent with Ca(OH)2 embedded in a sparse network of calcium silicate hydrate (C-S-H) that contains about 70 % occluded porosity in addition to the amount usually accounted as gel porosity. An anomalously large volume of Ca(OH)2 near the particles is observed both in the experiments and in the simulations, and can be explained as originating from the hydration of additional particles outside the field of view. Possible origins of the unusually large amount of observed occluded porosity are discussed.

The Influence of Water Activity on the Hydration Rate of Tricalcium Silicate

Tricalcium silicate does not undergo hydration at relative humidities (RH's) below 80%. But, the rate at which its hydration rate decreases as a function of the RH has not yet been elucidated. By invoking correspondence between RH and water activity (aH, unitless), both of which are related to the chemical potential of water, the reaction evolutions of triclinic tricalcium silicate (i.e., T1‐Ca3SiO5 or C3S) are tracked in water + isopropanol (IPA) mixtures, prepared across a wide range of water activities. Emphasis is placed on quantifying the: (a) rate of hydration as a function of aH, and (b) the critical (initial, aH0c or the achieved) water activity at which hydration effectively ceases, i.e., does not progress; here identified to be ≈ 0.70. The hydration of tricalcium silicate is arrested even when the system remains near saturated with a liquid phase, such that small, if any, capillary stresses develop. This suggests that changes in chemical potential induced via a vapor‐phase or liquid‐phase route both induce similar suppressions of C3S hydration. A phase boundary nucleation and growth (pBNG) model is fit to measured hydration rates from the onset of the acceleration period until well beyond the rate maximum when the water activity is altered. The simulations suggest that for a fixed hydrate nucleation density, any water activity reductions consistently suppress the growth of hydration products. Thermodynamic considerations of how water activity changes may influence reactions/hydrate evolutions are discussed. The outcomes improve our understanding of the chemical factors that influence the rate of Ca3SiO5 hydration.

The Influence of Water Activity on the Hydration Rates of Triclinic Tricalcium Silicate

The Influence of Water Activity on the Hydration Rates of Triclinic Tricalcium Silicate

Quantitative analysis of pure triclinic tricalcium silicate and C–S–H gels by 29Si NMR longitudinal relaxation time

29Si magic angle spinning nuclear magnetic resonance (29Si MAS NMR) has been commonly used to monitor the hydration degree of tricalcium silicate (C3S) and the structure of the calcium silicate hydrate known as C–S–H gel generated during their hydration, which is responsible for the strength and durability of cement pastes. The present study is aimed to measure the longitudinal relaxation times (T1) for the different types of Si in the structure of anhydrous triclinic C3S, the remnant C3S in pastes after a number of hydration days and the hydrated product (C–S–H gel). Results showed that the longitudinal relaxation times of the 29Si signals of C3S remaining after hydration are considerably shorter than the anhydrous C3S phase of the starting material; an effect that was interpreted as an extra contribution of 29Si–1H dipolar relaxation provided by the surrounding water molecules. Interestingly, the shorter T1 of the remaining non-hydrated C3S which is comparable to the C–S–H gel permits a much faster acquisition of quantitative 29Si MAS spectra.

Electronic Origin of Doping-Induced Enhancements of Reactivity: Case Study of Tricalcium Silicate

Systematic manipulation of the reactivity of silicate materials in aqueous environment remains a challenging topic. Herein, by combining first-principles and reactive molecular dynamics simulations, we present a complete picture of the influence of impurity species on hydration reactivity, using the reactive triclinic tricalcium silicate phase as an example. We show that although initial hydration is influenced by the surface’s chemistry and structure, longer-term hydration is primarily controlled by proton transport through the bulk solid. Both shorter- and longer-term hydration processes are noted as being intrinsically correlated with electronic features. These outcomes provide the first direct evidence of the linkages between electronic structure and the longer-term (i.e., on the order of several nanoseconds) hydration behavior and sensitivity of hydrophilic crystalline materials and also offer a pathway to efficient compositional design for similar materials.

Dissolution rates during the early hydration of tricalcium silicate

The hydration of triclinic tricalcium silicate containing foreign oxides was investigated in this study. Two water/solid-ratios of 50 and 0.50 were applied. The kinetics of the reaction was analyzed by a combination of methods including thermal analysis, pore solution analysis, and calorimetry. From these data, the evolution of the rate of reaction during hydration was calculated. The results were compared to the free, unconstrained dissolution of tricalcium silicate in undersaturated solutions. Such dissolution rates were analyzed in a dissolution cell connected to an ICP-OES instrument. A comparison of the free dissolution rate in the absence of precipitation of hydrates to the rate of reaction showed that the dissolution of tricalcium silicate is much faster than the rate of reaction of the global process.

Growth of Calcium Hydroxide Islands in Tricalcium Silicate‐Based Cements at Early Age

Microstructural characteristics of hydrated triclinic tricalcium silicate [C3S(t)], monoclinic tricalcium silicate (alite), and type I portland cement at ages between time zero and 28 days were observed using electron microscopy. Image analysis was used to follow the development of calcium hydroxide (Ca(OH)2) and calcium silicate hydrate at micro‐ and meso‐length scales. In all cases, easily recognizable islands of Ca(OH)2 were noted to form, though the morphology and rate of formation differed for the three cement types. The formation of these islands was found to influence hydration by hindering the reaction of unhydrated cement particles that are embedded within their largely Ca(OH)2‐bearing matrix. Such may be important features to include and validate in developing microstructural and other forms of computational models. The extent to which such microstructural features influence the local rates of reaction seems to depend, at least in part, upon the crystallography of the C3S.

Hydration of Tricalcium Silicate: Effects of CaCl2 and Sucrose on Reaction Kinetics and Product Formation

The effects of CaCl2 and sucrose on the hydration of monoclinic and triclinic tricalcium silicate were studied using quasielastic neutron scattering and calorimetry. Aside from acceleration and retardation, other effects on the reaction were revealed including changes to the rate constant and the type and amount of hydration product. These effects were measured in terms of specific kinetic parameters for the first time. The phenomenon of “delayed acceleration” caused by sucrose is attributed to the solubilization of the silicate species.

Quasielastic and inelastic neutron scattering study of the hydration of monoclinic and triclinic tricalcium silicate

The hydration of Mg-stabilized triclinic and monoclinic tricalcium silicate samples were studied using quasielastic neutron scattering to follow the fixation of hydrogen into the reaction products and by applying hydration models to the data. The quantity of Ca(OH) 2 produced during hydration was also determined using inelastic neutron scattering. The monoclinic form was found to be intrinsically less reactive that the triclinic form. The monoclinic form was also confirmed to produce more product than the triclinic form after 50 h, a process found to occur through a longer, rather than earlier, nucleation and growth regime. Results indicated an increase in the permeability of the hydration layer product relative to the triclinic form and the increase in the length of the nucleation and growth regime was thus attributed to an alteration in morphology or structure of the hydration layer product, extending the time for diffusion limited mechanics to be reached.

A Rietveld refinement investigation of a Mg-stabilized triclinic tricalcium silicate using synchrotron X-ray powder diffraction data

A Mg-stabilized triclinic tricalcium silicate form of type Ca3−xMgxSiO5, T3, was synthesized. Rietveld analysis using synchrotron X-ray powder diffraction data suggested that unlike the T1 form, the T3 structure was unmodulated. This refinement illustrated that the only existing model for a triclinic form of tricalcium silicate (T1) can be used to describe the nonmodulated T3 form.

Tricalcium Silicate T1 and T2 Polymorphic Investigations: Rietveld Refinement at Various Temperatures Using Synchrotron Powder Diffraction

The lattice parameters, cell volume, and structure of a sample of phase pure triclinic tricalcium silicate were determined using in situ, high‐temperature synchrotron powder diffraction and full‐profile Rietveld refinement. The temperature range covered was from ambient to 740°C. Evidence of superstructure was found. The T2 type structure with disordered SiO4 tetrahedra was observed, and an average structure for the subcell (P, a= 11.7416(2) Å, b= 14.2785(2) Å, c= 13.7732(2) Å, α= 105.129(1)°, β= 94.415(1)°, and γ= 89.889(1)°) is presented. Differential thermal analysis and X‐ray fluorescence was also performed.

Neutron powder diffraction investigation of model cement compounds

A series of synthetic cement compounds: mono- and triclinic-tricalcium silicate, β-dicalcium silicate, cubic- and orthorhombic-tricalcium aluminate and tetracalcium alumino-ferrite have been analyzed with neutron powder diffraction followed by Rietveld refinement. Generally good fits have been obtained and the results form the basis for analysis of cement hydration using neutron diffraction.