Quasielastic and inelastic neutron scattering on hydrated calcium silicate pastes

Using the inverse geometry spectrometer QENS at the Intense Pulsed Neutron Source of the Argonne National Laboratory, we collected quasielastic and inelastic neutron scattering spectra of hydrated tricalcium and dicalcium silicate, the main components of ordinary Portland cement. Data were obtained at different curing time, from a few hours to several months. Both the quasielastic and inelastic spectra have been analyzed at the same time according to the relaxing cage model, which is a model developed to describe the dynamics of water at supercooled temperatures. Short-time and long-time dynamics of hydration water in hydrated cement pastes as a function of the curing time have been simultaneously obtained. The results confirm the findings reported in previous experiments showing that it is possible to fit consistently the quasielastic and inelastic spectra giving insights on the effect of the curing time on the short-time vibrational dynamics of hydration water.     

Evaluation of the degree of hydration of tricalcium silicate pastes by quantitative differential thermal analysis

The hydration kinetics of C₃S pastes can be easily evaluated by DTA using the most intense and reversible transition of C₃S. Some modifications are proposed to Ramachandran's method concerning the measurement of this effect, the weight of the sample used for each experiment and the heating rate. The results of the hydration degree versus times of C₃S agree reasonably with those reported by Ramachandran, while still better agreement is observed with those of Locher who used X-ray quantitative analysis.

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Zusammenfassung Die Hydratisierungskinetik von C₃S Pasten kann mittels DTA leicht bewertet werden, falls der intensivste und am meisten reversible Übergang von C₃S genutzt wird. Einige Änderungen zur Methode von Ramachandran bezüglich der Messung dieses Effekts, des Gewichts der bei den einzelnen Messungen eingesetzten Proben und der Aufheizgeschwindigkeit werden vorgeschlagen. Die Ergebnisse des Hydratisierungsgrades von C₃S in Abhängigkeit von der Zeit sind in guter Übereinstimmung mit denen von Ramachandran, während eine noch bessere Übereinstimmung mit den Werten von Locher beobachtet werden kann, welcher sich jedoch der quantitativen Röntgenanalyse bediente.

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Résumé La cinétique de l'hydratation des pâtes de C₃S peut être facilement déterminée par ATD, en utilisant la transition de C₃S la plus intense, qui est réversible.On propose des modifications à la méthode de Ramachandran, concernant la mesure du phénomène, le poids des échantillons utilisés pour chaque expérience et le choix de la vitesse de chauffage. Les résultats donnant le degré d'hydratation de C₃S en fonction du temps sont en bonne concordance avec ceux publiés par Ramachandran tandis qu'une concordance encore meilleure est observée avec les résultats de Locher obtenus par analyse quantitative aux rayons X.

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C₃S C₃S. , : , . , , , .

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Financial support by Consiglio Nazionale delle Ricerche (Italy).     

Characterization of thin-film electroluminescent structures by SIMS and other analytical techniques

Analytical and Bioanalytical Chemistry - The recently developed Atomic Layer Epitaxy (ALE) method produces good quality electroluminescent thin-film structures which can be used in various display...     

Study of crystallization process of soda lead silicate glasses by thermal and spectroscopic methods

The crystallization process of some glasses in the ternary Na₂O–SiO₂–PbO system with good chemical stability that can be used for waste inertization was studied using X-ray diffraction (XRD), infrared spectroscopy (FT-IR), differential thermal analysis (DTA) and scanning electron microscopy. The parent glasses were characterized by XRD and FT-IR, and their vitreous state was determined. DTA measurements evidenced glass transition (T _g) and crystallization temperatures (T _c). The thermal treatments were conducted at vitreous transition temperature (400 °C) and at highest effect of crystallization (650 °C). XRD evidenced the lead and sodium silicate crystalline phases in samples treated at 650 °C for 12 h. Micrometer crystallites dispersed in the glass matrices have affected the transparence of glasses and made them opaque after treatment at 650 °C. The influence of oxide quantities in compositions on the crystallization tendency was revealed. A PbO higher content than that of SiO₂ as well as lower Na₂O content decreased the tendency of crystallization.     

Strontium binding by calcium silicate hydrates

In the present study the binding of strontium with pure calcium silicate hydrates (C-S-H) has been investigated using batch-type experiments. Synthetic C-S-H phases with varying CaO:SiO(2) (C:S) mol ratios, relevant to non-degraded and degraded hardened cement paste, were prepared in the absence of alkalis (Na(I), K(I)) and in an alkali-rich artificial cement pore water (ACW). Two types of experimental approaches have been employed, investigating sorption and co-precipitation processes, respectively. The Sr(II) sorption kinetics were determined as well as sorption isotherms, the effect of the solid to liquid ratio and the composition (C:S ratio) of the C-S-H phases. In addition, the reversibility of the Sr(II) sorption was tested. It was shown that both the sorption and co-precipitation tests resulted in Sr(II) distribution ratios which were similar in value, indicating that the same sites are involved in Sr(II) binding. In alkali-free solutions, the Sr(II) uptake by C-S-H phases was described in terms of a Sr(2+)-Ca(2+) ion exchange model. The selectivity coefficient for the Sr(2+)-Ca(2+) exchange was determined to be 1.2+/-0.3.     

Paper sludge functionalization for achieving fiber-reinforced and low thermal conductivity calcium silicate insulating materials

Paper sludge generated from the paper industry is classified as solid waste, comprising primarily wood fiber and calcium carbonate with low thermal conductivity. This paper is concentrated on the comparison of wood fiber and paper sludge from the structural strength and insulation property of calcium silicate insulating materials (CSIM). Test specimens with wood fiber and two different types of paper sludge were prepared by the compression molding and autoclaved curing, and DSC-TG analysis was used to compare the components and characteristic of different paper sludge. Based on the experimental results, detailed discussions on the strength, water absorption, dry density, correlation and thermal conductivity of CSIM are given. It is noted that the flexural strength of CSIM increases gradually within the increasing amount of two paper sludge from 0 to 7.5% and goes up to the highest value of 16.1 MPa and 15.1 MPa and increases about 14.2% and 7.1%. In addition, paper sludge can replace 0–0.4% of wood fiber under the requirement of the mechanical strength, and the dry density of CSIM with wood fiber is much larger than that with paper sludge. Furthermore, the addition of paper sludge in the CSIM notably decreases the thermal conductivity due to the low thermal conductivity of wood fiber and calcium carbonate. Finally, it can be concluded that the utilization of paper sludge presents a great potential to develop fiber-reinforced and low thermal conductivity CSIM and benefits to the development of waste management in producing sustainable CSIM.

     

Characterization of some new alkali metal molybdate hydrates by thermal and X-ray methods

Preparation and characterization of four new hydrated alkali metal molybdates Na₂Mo₄O₁₃·6H₂O, K₂Mo₄O₁₃·3H₂O, Rb₂Mo₄O₁₃·2H₂O and Cs₂Mo₄O₁₃·2H₂O are described. The compounds were prepared by crystallizing the solution obtained by dissolving MoO₃ and corresponding alkali metal carbonates A₂CO₃ or molybdate A₂MoO₄ in stoichiometric amount in distilled water. The hydrated molybdates were characterized by thermal (TG/DTA) and X-ray diffraction (XRD) methods. The number of water molecules in the compounds were determined from their TG /DTA curves recorded in air and identification of their dehydration products was done by XRD. The cell parameters of the compounds were obtained by indexing their XRD patterns. Attempt to prepare the corresponding hydrated compound of lithium was not successful. This revised version was published online in July 2006 with corrections to the Cover Date.     

Characterization,correlation and kinetics of dolomite samples as outlined by thermal methods

In this study, the decomposition behavior of four dolomite samples of different origin was studied by X-ray diffractometer and simultaneous TG-DTA experiments. Three different decomposition regions were determined known as dehydration of inter-particle water, formation of MgO and calcite and decomposition of calcite. Kinetic analysis of these decomposition regions was analyzed and the related activation energies are determined. It was observed that the activation energies were in the range of 48–137 kJ mol⁻¹.     

Radiation synthesis of porous calcium silicate aerogel derived from polyacrylamide hydrogel as thermal insulator

Journal of Sol-Gel Science and Technology - In this article, the first aerogels synthesis through cross-linked polyacrylamide (PAAm) hydrogel was reported through the use of gamma irradiation...     

Hydration kinetics of tricalcium silicate by calorimetric methods

The kinetics of the cement hydration reaction is a relevant issue in the cement research field, particularly in the presence of additional inorganic and organic components that consistently increase the complexity of the cement paste. In the present study, the hydration reaction of pure tricalcium silicate has been monitored by different calorimetric approaches: the conventional Isothermal Conduction Calorimetry (IC) and a novel Differential Scanning Calorimetry (DSC) protocol. The measured hydration curves have been modeled by using the Boundary Nucleation and Growth Model (BNGM) to extract thermodynamic parameters of the early stages of the hydration reaction. IC and DSC methods provide similar results in terms of rate constants, linear growth, and nucleation rates even though the IC accesses the total evolved heat while DSC discloses the fraction of unreacted water. The validation of the DSC approach as a reliable analytical method to the study of cement hydration kinetic is of particular importance because it allows following very long hydration processes, such as those of pastes containing organic retarders or superplasticizers. The thermodynamic and kinetic parameters for the tricalcium silicate setting has been also evaluated and discussed as a function of the surface area of the powder.     

Near-infrared spectroscopy investigation of the water confined in tricalcium silicate pastes

Near-infrared (NIR) spectroscopy has been employed to investigate the evolution of the vibrational spectrum of water entrapped in a tricalcium silicate paste. The overall free water, which decreases as a function of time due to the formation of the hydrated phases (portlandite, Ca(OH)(2), and hydrated calcium silicate, C-S-H) during the hydration reaction, is quantified by the decrease in the area of the NIR band at about 5000 cm(-1). The coexistence of two types of water in the hydrated phases (a "surface-interacting water" (type I) and a "bulklike water" (type II)) during the hydration is obtained by the analysis of the band at about 7000 cm(-1). The deconvolution of this band allows the quantification of the two water types. As the reaction advances, part of the "bulklike water" is converted to "surface-interacting water" in direct agreement with the C-S-H surface development. Finally, the Ca(OH)(2) formation can be concurrently monitored by NIR through the increase of a very sharp peak at 7083 cm(-1). Near-infrared spectroscopy allows determination in a very simple way of the most important features of the tricalcium silicate setting process.     

Differential thermal studies of polymethyl methacrylate-impregnated cement pastes

Differential thermal curves have been obtained for two polymethyl methacrylate-impregnated cement pastes prepared at a water/cement ratio of 0.37 and 0.70. Complex thermal effects, including a substantial decrease in the endothermal peak for Ca(OH)₂ decomposition, were observed in samples heated in air. These effects originate in the portland cement paste, in the polymer, and from interactions between the polymer and the hydrated cement during heating. Less complex effects resulted when DTA was carried out in N₂. There was no evidence of a reaction between the hydrated cement and PMMA during impregnation.     

Investigation of silicate mineral sanidine by vibrational and NMR spectroscopic methods

Sanidine, a variety of feldspar minerals has been investigated through optical absorption, vibrational (IR and Raman), EPR and NMR spectroscopic techniques. The principal reflections occurring at the d-spacings, 3.2892, 3.2431, 2.9022 and 2.6041 Å confirm the presence of sanidine structure in the mineral. Sanidine shows five prominent characteristic infrared absorption bands in the region 1200–950, 770–720, 590–540 and 650–640 cm⁻¹. The Raman spectrum shows the strongest band at 512 cm⁻¹ characteristic of the feldspar structure, which contains four membered rings of tetrahedra. The UV–vis–NIR absorption spectrum had strong absorption features at 6757, 5780 and 5181 cm⁻¹ due to the combination of fundamental OH– stretching. The bands at 11236 and 8196 cm⁻¹and the strong, well-defined band at (30303 cm⁻¹ attest the presence of Fe²⁺ and Fe³⁺, respectively, in the sample. The signals at g = 4.3 and 3.7 are interpreted in terms of Fe³⁺ at two distinct tetrahedral positions Tl and T2 of the monoclinic crystal structure The ²⁹Si NMR spectrum shows two peaks at −97 and −101 ppm corresponding to T2 and T1, respectively, and one peak in ²⁷Al NMR for Al(IV).     

Polymer characterization by thermal evolution techniques

Thermal evolution techniques continuously monitor materials thermally evolved from a sample on controlled heating. Either stepwise detection of such volatiles as a function of temperature or time, or quantitative measurement and identification of these materials provides very useful information. Transducers include vacuum gauges, electrochemical devices, thermal conductivity and flame ionization detectors, etc. These techniques have shown promise in studies of thermal stability and degradation mechanism, analysis of trace impurities and additives, and elucidation of polymer structures. Other applications are in the areas of vapor pressure measurement and toxicity studies of constituents in polymer systems.     

Adsorption of cellulose triacetate on calcium silicate

Adsorption of cellulose triacetate from its chloroform solution on calcium silicate has been studied. The adsorption follows first order kinetics. The adsorption data are adequately described by the Langmuir isotherm indicating that the adsorbed polymer molecules behave as rigid molecules in the adsorbed state. An attempt has been made to fractionate cellulose triacetate employing the adsorption technique.     

Characterization of silicate monomer with sodium,calcium and strontium but not with lithium and magnesium ions by fast atom bombardment mass spectrometry

Fast atom bombardment mass spectrometry (FABMS) was applied to the direct detection of silica species dissolved in LiCl, NaCl, MgCl(2), CaCl(2) and SrCl(2) solutions in order to investigate its dissolution process in solution. Several species of dissolved silicate complexes in the solution were directly detected by FABMS. The peak intensities of [SiO(2)(OH)(2)Na](-), [SiO(3)(OH)Ca](-) and [SiO(3)(OH)Sr](-) increased with increasing concentrations of NaCl, CaCl(2) and SrCl(2), whereas the peak intensities of [SiO(2)(OH)(2)Li](-) and [SiO(3)(OH)Mg](-) did not increase with increasing concentrations of LiCl and MgCl(2). These results indicte that silicate and cation bind in the solution not after but before ionization. The isotope pattern of Sr(2+) confirmed the existence of the silicate-Sr complex not only with increase of the concentration of silica but also the mass numbers of Sr. The silicate complexes formed with Na(+), Ca(2+) and Sr(2+) showed high stability in chloride solution. This is in good accordance with the fact that Na(+), Ca(2+) and Sr(2+) accelerate the dissolution of silica to form complexes during solution equilibrium. Considering that the stability constant was examined and reported in other papers, this new findings that Mg(2+) does not form a complex with silicic acid (Si(OH)(4)) is very important.     

Cobalt(III) dicarboxylato bis-ethylenediamine nitrates: Preparation and characterization by thermal analysis and other analytical methods

Compounds with the general formulacis ortrans-[Coen ₂ (RCOO)₂]NO₃ were prepared by modifications of known procedures; R was H, CH₃, C₂H₅ or C₃H₇, anden was ethylenediamine. The compounds were characterized by TLC and UV-Vis spectrophotometry, and their thermal behaviour was examined via TG and DTA, and via IR spectra on heated samples.The thermal stabilities are discussed in terms of the strengths of the bonds in the solids [1] and steric hindrance; the thermal decompositions are described with the aid of hypothesized intermediates and IR spectra.Reaction steps are identified and the thermal stability sequence is discussed: thecis compounds are less stable than the correspondingtrans compounds, due to the lower reticulation effect; the sequence of thecis compounds is the reverse of the sequence of carboxylate ion basicity, while the sequence displalyed by thetrans compounds can be interpreted in terms of solid lattice stabilization.

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Zusammenfassung Unter Durchführung einiger Abänderungen des bekannten Verfahrens wurden Verbindungen der allgemeinen Formel conf-Co[en₂(RCOO)₂]NO₃ hergestellt. Der AlkylrestR war H, CH₃, C₂H₅, C₃H₇ unden war Ethylendiamin. Die Verbidungen mitconf=cis odertrans wurden mittels TLC und UV-Spektrophotometrie charakterisiert. Ihr thermisches Verhalten wurdeanhand von TG, DTA und IR-Spektren von erhitzten Proben untersucht. Die thermische Stabilität wurde untersucht und in Abhängigkeit von Bindungsstärke und sterischer Behinderung diskutirt; weiterhin wurden die thermischen Zersetzungen mit Hilfe angenommener Intermediäre und deren IR-Spektren beschrieben. Die Reaktionsschritte wurden identifiziert und eine Stabilitätsreihe aufgestellt und diskutiert: cis-Verbindungen erwiesen sich als instabiler als die entsprechenden trans-Verbindungen, was einem geringeren Vernetzungseffekt zuzuschreiben ist; Die Reihenfolge folgt im Falle voncis dem Reziproken der Carboxylationenbasizität, während die Reihenfolge im Falle vontrans mittels der Gitterstabilisierung erklärt werden kann.

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, -[Coen₂(RCOO)₂]NO₃, R=H, CH₃, C₂H₅, C₃H₇, aen= . - - - . , . . , . : - , , . - -, - .

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This work was carried out with the financial support of the Consiglio Nazionale delle Ricerche (C.N.R.), which also gave a grant to one of us (A.M.G.).     

EXAFS study of U(VI) uptake by calcium silicate hydrates

Among the different cement minerals, calcium silicate hydrates (C-S-H) are the prime candidates for heavy metal binding because of their abundance and appropriate structure. Immobilization processes of heavy metals by cementitious materials, and in particular C-S-H phases, thus play an important role in multibarrier concepts developed worldwide for the safe disposal of hazardous and radioactive wastes. In this study, the uptake of U(VI) by C-S-H has been investigated using X-ray absorption fine structure (XAFS) spectroscopy. C-S-H phases were synthesized using two different procedures: One is based on the mixing of CaO and SiO2 solids ("direct reaction" method); for the other one starting solutions of Ca and Si are used ("solution reaction" method). XAFS investigations were carried out on samples doped with U(VI). U(VI) was either sorbed onto previously precipitated C-S-H phases (sorption samples) or added during C-S-H synthesis (coprecipitation samples). The coordination environment of U(VI) in the sorption samples was found to be independent of the procedure used for C-S-H synthesis. A split equatorial oxygen shell (Oeq1: R=2.23-2.27 A; Oeq2: R=2.36-2.45 A), neighboring silicon atoms at short (R=3.07-3.11 A) and long (R=3.71-3.77 A) distances, and neighboring Ca atoms (R=3.77-3.81 and 4.15-4.29 A) were observed for all the samples. The structural parameters resemble those reported for uranophane. The coordination environment of U(VI) in the coprecipitation samples depends on the method used for C-S-H synthesis, and further, the spectra differ from those determined for the sorption samples. UU backscattering contributions were observed in the samples prepared using the direct reaction method, whereas no split equatorial shell appeared in the samples prepared using the solution reaction method.