Kinetics of interaction of hardened oil-well cement slurries with acidic solutions from isothermal heat-conduction calorimetry

The kinetics of interaction of hydrochloric acid with oil-well cement slurries treated with the silane coupling agents, tetraethyl orthosilicate, 3-(trimethoxysilyl)-1-propanethiol and 3-(chloropropyl)-trimethoxysilane have been investigated isothermal heat-conduction calorimetry at 298.15 K. The Avrami kinetic model gives a better fit to the experimental data than the traditional Lagergren kinetics models. A pore diffusion model suggests acid diffusion only for the standard slurry. The results indicate that isothermal heat-conduction calorimetry is suitable to evaluate the protective role of silane coupling agents on hardened oil-well cement slurries.     

Effect of crystallization temperature on the crystalline phase content and morphology of poly(vinylidene fluoride)

The effect of temperature on the crystallization of α, β, and γ phases of PVDF from dimethylacetamide (DMA) solution was studied. Variation in the crystallinity content of these three phases was obtained as a function of temperature using infrared spectroscopy, differential scanning calorimetry (DSC) and x-ray diffraction techniques. Such variation is related to the dependence of the crystallization rate of each phase with temperature, and allowed a better understanding of some results found in the literature about the crystallization and interconversion of these phases. Micrographs of samples present morphologies that corroborate with the proposed explanations. © 1994 John Wiley & Sons, Inc.     

Kinetics and equilibrium parameters of Hg(II) adsorption on silica-dithizone

Sílica-dithizone (Sil-dtz) was synthesized and used to adsorb Hg(II) in solution at pH 6.0. Increasing the temperature accelerates the mass transfer of Hg(II) to the silica surface. The kinetic data were evaluated using the traditional pseudo-first-order Lagergren equation and an alternative Avrami kinetic equation. From the latter equation, two regions presenting distinct kinetic parameters were found, at 25 and 35 degrees C, and the use of the parameter n was also related to the determination of distinct kinetic orders. Variations of the adsorption kinetic rate in relation to the time and the temperature were also calculated and are discussed. The adsorption isotherms data were well fitted to the Freundlich model. Interestingly, good adsorption data correlation of the Langmuir model and experimental values was observed only at 45 and 50 degrees C, suggesting, for this temperature range, the formation of complexes with the proportion Hg:dithizone 1:1 on the silica surface.     

An alternative Avrami equation to evaluate kinetic parameters of the interaction of Hg(II) with thin chitosan membranes

In this work, thin chitosan membranes were utilized as an adsorbent for the removal of Hg(II) from aqueous solutions. A rise of temperature accelerates the mass transfer of Hg(II) to the membranes, surfaces. The kinetic data did not present a good fitting to the traditional Lagergren adsorption kinetic equations. An alternative Avrami kinetic equation was employed and successfully fitted to the kinetic adsorption quantities. From this new equation, two regions presenting distinct kinectic parameters were found, and the use of the parameter n was also relationed to the determination of the kinetic order. Variations of the adsorption kinetic rate in relation to the time, the initial Hg(II) concentration, and the temperature were also calculated and are discussed.     

Interaction of Ag(I), Hg(II), and Cu(II) with 1,2-ethanedithiol immobilized on chitosan: thermochemical data from isothermal calorimetry

The nature of interactions between metal ions Ag(I), Hg(II), Cu(II) and chitosan derivative of 1,2-ethanedithiol, QTDT, was investigated by isothermal calorimetry using the membrane breaking technique. Simultaneous determination of thermal effects, Q(int), and amount of cation that interacts, n(int), are described. The experimental data have been interpreted in terms of the Langmuir equation to determine the maximum adsorption capacity to form a monolayer, N(mon), and the energy of interaction for a saturated monolayer per gram of QTDT, Q(mon). With N(mon) and Q(mon), the molar enthalpy of interaction for formation of a monolayer of anchored cations per gram of QTDT, Delta(mon)H(m), was determined. The Delta(mon)H(m) values for Ag(I), Hg(II), and Cu(II) were -60.56, -58.05, and -84.36 kJ mol(-1), respectively. Negative values of DeltaG show the spontaneity of the interaction processes. The least entropically favourable processes, i.e., those which present more negative DeltaS values, seem to be compensated by the more favourable enthalpic parameter.     

Preparation and properties of europium-doped phosphosilicate glasses obtained by the sol–gel method

In this work, we report the synthesis of europium-doped phosphosilicate glasses from tetraethylorthosilicate (TEOS), phenyltrietoxysilane (PTES) and ammonium phosphate (NH₄H₂PO₄) prepared by the sol–gel process. The matrix was synthesized by modified Stöber methodology. The alkoxide precursors PTES and TEOS were mixed with NH₄H₂PO₄, in the presence of europium III chloride, using ethanol as solvent in basic catalysis. These materials were studied by photoluminescence spectroscopy (PL), thermal analysis (TGA/DTA), transmission electron microscopy (TEM) and energy-dispersive spectroscopy (EDS). The results obtained for the materials show the formation of conchoidal-fractures, which are characteristics of glass materials. The thermal analysis showed the thermal stability of materials up to 300 °C. Eu III has been used as structural probe due to its photophysical properties. The PL spectra displays the lines characteristics of the Eu (III) ion ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3 and 4). Wide bands were observed, indicating non-homogeneous sites that are characteristic of amorphous systems.     

The reinforcement of ancient timber-joints with carbon nano-composites

The paper describes an experimental research activity on the application of a polymeric resin reinforced with carbon nanotubes on an ancient timber structures belonging to cultural heritage (Bertolini Cestari et al. in Proc. of SAHC2008. VI International Conference, pp. 941–947, 2008; Marzi in Ph.D. Thesis, 2010; Bertolini Cestari et al. in Proc. of ICRACM-2010—3rd International Conference on Recent Advances in Composite Materials, 2011). The proposed approach aims at the conservation of a specific wooden joint belonging to traditional constructions. Therefore the research was addressed to the definition and assessment of a methodology of preparation and application of the nano-composite with the aim of verifying an increased mechanical resistance in comparison with traditional reinforcement methods. Different wood species have been considered and the experimentation has been carried out in view of a possible in-situ application of the technique. Laboratory tests were carried out at first on small wooden samples, and afterwards on wooden elements having real dimension. These last ones were taken from ancient and decayed wooden floors belonging to an important historical building that were dismantled during restoration works. A numerical analysis of the structural behavior of the joint is provided, in order to assess the different possible collapse mechanisms. The results obtained from the tests are promising for future developments of the application of these nano-composite materials.     

A new elemental analysis method based on thermogravimetric data and applied to alkoxysilane immobilized on silicas

A new analytical method based on thermogravimetry and applied to chemically functionalized surfaces is proposed. The mass losses of surfaces modified with alkoxysilane reagents, Sup-CH₂CH₂CH₂?R (Sup=support andR=Cl, SH, NH₂, NHCONH₂, NHNHCOCH₃ or (CH₂)₄NH), are interpreted by considering the physically adsorbed water, the silanol groups and the organic moiety. The elemental analyses calculated from these data are in agreement with those obtained by classical elemental analysis. The method is quick and reproducible, and requires the use of only a few milligrams of material.