Thermodynamics of Solution of Some Alkyl Acetates in Water

Summary.  The temperature dependence of the solubility of methyl acetate (MeOAc), ethyl acetate (EtOAc), 1-propyl acetate (1-PrOAc), 1-butyl acetate (1-BuOAc), 2-methyl-1-propyl acetate (iso-BuOAc), 2-butyl acetate (sec-BuOAc), and 2-methyl-2-propyl acetate (tert-BuOAc) in water in the temperature range from 298.2 to 318.2 K was determined. The experimental solubility data together with some literature values are presented as a function of temperature and given in analytical form. The solubilities of the investigated compounds at 298.2 K were correlated with the number of carbon atoms in the solute molecule. The standard thermodynamic functions for solubility, i.e. Gibbs free energy, enthalpy, heat capacity, and entropy, were calculated. The Gibbs free energy is positive and increases linearly with the number of carbon atoms, whereas the enthalpy and entropy are negative. The standard thermodynamic functions were converted to thermodynamic quantities for hydration. The Gibbs free energies of hydration of alkyl acetates, which are negative, are compared with the Gibbs free energy of hydration of some n-alkanes, 1-alcohols, and 1-alkylamines. The standard thermodynamic functions of hydration were analyzed using a modified version of the theoretical approach developed by Lee and Graziano [1]. Received October 16, 2000. Accepted May 14, 2001     

Activation of nitriles by silver(I) N-heterocyclic carbenes: An efficient on-water synthesis of primary amides

A first example of silver(I) N-heterocyclic carbene (Ag(I)-NHC) catalyzed on-water synthesis of primary amides by hydration of nitriles under mild reaction conditions is described. This organometallic catalytic system has excellent tolerance for various homo-aromatic, hetero-aromatic and aliphatic nitriles to afford primary amides in good yields in neat water.     

Lanthanide Luminescence Revealing the Phase Composition in Hydrating Cementitious Systems

The hydration process of Portland cement in a cementitious system is crucial for development of the high-quality cement-based construction material. Complementary experiments of X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and time-resolved laser fluorescence spectroscopy (TRLFS) using europium (Eu(III)) as an optical probe are used to analyse the hydration process of two cement systems in the absence and presence of different organic admixtures. We show that different analysed admixtures and the used sulphate carriers in each cement system have a significant influence on the hydration process, namely on the time-dependence in the formation of different hydrate phases of cement. Moreover, the effect of a particular admixture is related to the type of sulphate carrier used. The quantitative information on the amounts of the crystalline cement paste components is accessible via XRD analysis. Distinctly different morphologies of ettringite and calcium−silicate−hydrates (C−S−H) determined by SEM allow visual conclusions about formation of these phases at particular ageing times. The TRLFS data provides information about the admixture influence on the course of the silicate reaction. The dip in the dependence of the luminescence decay times on the hydration time indicates the change in the structure of C−S−H in the early hydration period. Complementary information from XRD, SEM and TRLFS provides detailed information on distinct periods of the cement hydration process.     

The effect of silica nanoparticles on the pore structure of hydrating cement paste: a spatially resolved low-field NMR study

ABSTRACT

The hydration process of four different cement-based materials at different depths inside the sample was investigated using localised nuclear magnetic resonance relaxation measurements. All the samples are based on white Portland cement (CEM I 42.5 R), with a water-to-cement ratio of 0.5. One sample is a simple cement paste and the other three additionally contain 5% (by mass of cement) silica nanoparticles (50–200?nm size), silanised silica nanoparticles (with silane A 174) or silica fume (80% silica; 0.15?µm average size). The localised transverse relaxation measurements were performed using a single-sided NMR instrument. The relaxation rates were monitored for 48?h during the hydration process at different depths inside the sample. The results showed that the presence of nanoparticles influences not only the speed of hydration overall, but also the homogeneity of the materials.     

离子通过碳纳米管的拉伸分子动力学模拟

采用拉伸分子动力学模拟研究了Na⁺, K⁺和Cl^－通过(6,6), (7,7), (8,8), (9,9)和(10,10)碳纳米管的过程, 利用伞形取样法计算了离子通过碳管的平均力势能, 并对离子在管中和本体相中的水化作了比较. 结果表明, 离子通过管径较窄的碳管时, 在入口处遇到较大的阻力, 从出口进入本体相较容易|而通过管径相对较宽的碳管则几乎无阻碍. 离子通过碳管的能垒随管径的增大而降低, 不同离子的能垒各不相同, 表明碳管具有固有的离子选择性|离子通过碳管时, 不仅其配位数改变了, 而且配位层中水分子的取向也有所改变, 这两者共同决定了离子进入碳管时的去水化能, 进而影响离子通过碳管的能垒和碳管的离子选择性. 本工作将有助于理解离子通道蛋白中疏水区域的功能作用, 并可以为基于碳纳米管的纳流控系统的设计提供指导.     

Hydration effect on the electronic transport properties of oligomeric phenylene ethynylene molecular junctions

A first-principles computational method based on the hybrid density functional theory is developed to simulate the electronic transport properties of oligomeric phenylene ethynylene molecular junctions with H₂O molecules accumulated in the vicinity as recently reported by Na {\it et al.} [\wx{Nanotechnology}{18} 424001 (2007)]. The numerical results show that the hydrogen bonds between the oxygen atoms of the oligomeric phenylene ethynylene molecule and H₂O molecules result in the localisation of the molecular orbitals and lead to the lower transition peaks. The H₂O molecular chains accumulated in the vicinity of the molecular junction can not only change the electronic structure of the molecular junctions, but also open additional electronic transport pathways. The obvious influence of H₂O molecules on the electronic structure of the molecular junction and its electronic transport properties is thus demonstrated.     

Dissociation Energy Computations for Saline Bonds Implied in Interactions Mediated by Peptidoglicans

Summary: Dissociation energy and hydration energy calculations, in water solution, are presented for saline bonds mediated by Ca²⁺ and Mg²⁺ ions with Brőnstedt type bases ( COO ,  OSO₃ ,  OH). A computationally intensive method, Polarisable Continuum Model (PCM) using 6-31G^* basis set, was applied. Hydration energies were computed by various methods, as well as dissociation energies of some L₂M complexes. L₂Ca complexes result as more stable against dissociation than L₂Mg complexes. Hydration energy calculation results, for some of the methods, here used, seem rather reliable as compared to experimental results.     

Early-Age Hydration Reaction and Strength Formation Mechanism of Solid Waste Silica Fume Modified Concrete

Solid waste silica fume was used to replace fly ash by different ratios to study the early-age hydration reaction and strength formation mechanism of concrete. The change pattern of moisture content in different phases and micro morphological characteristics of concrete at early age were analyzed by low field nuclear magnetic resonance (LF-NMR) and scanning electron microscope (SEM). The results showed that the compressive strength of concrete was enhanced optimally when the replacement ratio of solid waste silica fume was 50%. The results of LF-NMR analysis showed that the water content of modified concrete increased with the increase of solid waste silica fume content. The compressive strength of concrete grew faster within the curing age of 7 d, which means the hydration process of concrete was also faster. The micro morphological characteristics obtained by SEM revealed that the concrete was densest internally when 50% fly ash was replaced by the solid waste silica fume, which was better than the other contents.     

Hydration studies of modified OPC pastes by differential scanning calorimetry and thermogravimetry

Thermal methods are used extensively in investigating cements and effects of additives on their hydration behaviour. Calcium chloride is the most effective and widely used accelerator for cement hydration, but the result is largely dependent on the rate at which it is added. In this study the influence of calcium chloride dosage on the hydration behaviour of OPC pastes aged for different periods has been investigated by means of differential scanning calorimetry (DSC), thermogravimetry (TG) and X-ray diffraction (XRD) methods. The results are discussed in relation to the relative amounts of calcium hydroxide and total reaction product formed. Chloroaluminate was a product of hydration in the samples dosed with greater than 1% calcium chloride. XRD was unable of itself to differentiate between monochloroaluminate and the calcium aluminate hydrate C₄AH₁₃ when present in small amounts. Thermal methods proved effective in characterising the products of hydration in the presence of chloride.

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Zusammenfassung Bei der Untersuchung von Zement und des Einflusses von Additiven auf das Hydratationsverhalten von Zement finden thermoanalytische Methoden eine breite Anwendung. Der effektivste und meistbenutzte Beschleuniger für die Hydratation von Zement ist Calciumchlorid, aber die Ergebnisse hängen stark von der Dosiergeschwindigkeit ab. In vorliegender Studie wird mittels DSC-, TG- und Röntgendiffraktionsmethoden der Einflu\ der Dosierung von Calciumchlorid auf das Hydratationsverhalten von verschieden alten OPC-Zementbreiproben untersucht. Die Ergebnisse wurden in Bezug auf die relativen Mengen Calciumhydroxid und das gebildete Gesamtreaktionsprodukt gewertet.Bei Dosen von mehr als 1% Calciumchlorid konnte als Hydratationsprodukt Chloraluminat festgestellt werden. Sind Monochloraluminat und das Calciumaluminathydrat C₄AH₁₃ in geringen Mengen vorhanden, kann man zwischen den beiden mittels Röntgendiffraktion nicht unterscheiden. Thermoanalytische Methoden erwiesen sich als effektives Hilfsmittel bei der Charakterisierung der Produkte der Hydratation in Gegenwart von Chlorid.

     

Activity and osmotic coefficients from the EMF of liquid membrane cells. VI-ZnSO4, MgSO4, CaSO4, and SrSO4 in water at 25‡C

The activity coefficients of ZnSO₄, MgSO₄, CaSO₄, and SrSO₄ are measured by means of cells with ion-exchange liquid membranes similar to those described in the previous papers of this series. Negative deviations from the limiting law are observed in the dilute region. These deviations are, for ZnSO₄, appreciably more important than recent literature has indicated, and the corresponding activity coefficients need to be corrected by about 12%. Pitzer’s theory best-fit coefficients have accordingly been recalculated. The osmotic coefficients are also derived. Accessory information on the hydration state for zinc, magnesium, and sulfate ions, is presented.