Characterization of the mechanical damage of a chemically degraded cement paste

Cement-based materials as concrete interact with their environment. In the presence of aqueous mediums, dissolutions and precipitations of solid species composing the cement paste induce a chemical damage, which may affect the structure integrity. This paper presents a mechanical characterization of the Young modulus evolution of chemically damaged cement paste, based on a microstructural approach coupled to a reactive-transport model. The method has been successfully applied to cement pastes leached by pure water. It is concluded that the capillary porosity and its spatial distribution within the material are the parameters, which mainly rule the stiffness evolution.     

Structure and optical properties of thin titanium films deposited on different substrates

Thin films of titanium were deposited on different substrates at room temperature. Measurements were made of the optical constants and of the transmittance of titanium films evaporated on to fused quartz. Films of titanium 10 to 40 nm thick were found to have quite uniform transmittance throughout the visible spectrum. Because titanium getters strongly during its evaporation, pure and compact titanium films can only be produced by fast evaporation under extremely good vacuum conditions. All films prepared for optical measurements, for X-ray and for scanning electron microscopy studies were, therefore, deposited at a pressure 10^–4 Pa and with deposition rate 4 nm sec^–1. The measurements were made using a Beckman double-beam spectrophotometer UV 5230, Siemens D 500 X-ray diffractometer, and SEMCO nanolab 7 scanning electron microscopy.     

Electrochemical Performance of Na3V2(PO4)2F3 Electrode Material in a Symmetric Cell

A NASICON-based Na₃V₂(PO₄)₂F₃ (NVPF) cathode material is reported herein as a potential symmetric cell electrode material. The symmetric cell was active from 0 to 3.5 V and showed a capacity of 85 mAh/g at 0.1 C. With cycling, the NVPF symmetric cell showed a very long and stable cycle life, having a capacity retention of 61% after 1000 cycles at 1 C. The diffusion coefficient calculated from cyclic voltammetry (CV) and the galvanostatic intermittent titration technique (GITT) was found to be ~10⁻⁹–10⁻¹¹, suggesting a smooth diffusion of Na⁺ in the NVPF symmetric cell. The electrochemical impedance spectroscopy (EIS) carried out during cycling showed increases in bulk resistance, solid electrolyte interphase (SEI) resistance, and charge transfer resistance with the number of cycles, explaining the origin of capacity fade in the NVPF symmetric cell. Finally, the postmortem analysis of the symmetric cell after 1000 cycles at a 1 C rate indicated that the intercalation/de-intercalation of sodium into/from the host structure occurred without any major structural destabilization in both the cathode and anode. However, there was slight distortion in the cathode structure observed, which resulted in capacity loss of the symmetric cell. The promising electrochemical performance of NVPF in the symmetric cell makes it attractive for developing long-life and cost-effective batteries.     

A multiscale based approach for automatic shadow detection and removal in natural images

Multimedia Tools and Applications - Shadow is a natural phenomenon observed in most natural images. It can reveal information about the objects shape as well as the illumination direction. In...     

Heterosubstituted sumanene as media for hydrogen storage: A theoretical study

Recently, bowl-shaped π-conjugated compounds, considered as carbon-based materials, have shown noticeable capacities in the hydrogen storage. Doping these compounds with appropriate elements remains the main target to improve the hydrogen adsorption properties. In this regards, we carried out a theoretical study, by means of MP2 method, on a series of mono-, di- and tri-heterosubstituted sumanene compounds, adsorbing hydrogen molecule from concave and from convex side, respectively. Benzylic carbons have been substituted by O, S, NH and NCH₃ groups. The influence of this substitution on the adsorption properties has been reported. Our investigation has involved binding energies corrected to basis set superposition error (BSSE) and structural parameters like equilibrium distances as well as bowl depths. Dipole moment, HOMO-LUMO energy gap and the changes after the adsorption process have also been evaluated. The results show that the binding energy values belong to the range of the intermediate interval of physisorption mechanism. Natural population analysis (NPA) associated to natural bond orbitals (NBO) elucidate the charge transfer occurring between the heterosubstituted compounds and the hydrogen molecule. We classified the substituents upon the binding energy for mono-, di- and trisubstitution and no similarities have been reported between the adsorption sides. These classifications can be of interest to any prospective experimental investigation.     

Glutaraldehyde-wheat gluten protein adhesives for wood bonding

ABSTRACT

Wheat gluten protein hydrolysate was used as a biomass feedstock to prepare environmentally friendly protein-based adhesives, with hydrolyzed wheat protein as control. Glutaraldehyde was used to modify it to obtain a glutaraldehyde-wheat protein (GP) adhesive. Polyethylenimine (PEI) was also used as a crosslinking agent. Plywood has been prepared and tested, and its performance was used to measure the wheat gluten protein hydrolysate adhesive bonding performance. Differential scanning calorimetry (DSC) and thermomechanical analysis (TMA) were used to analyze the adhesive thermal properties and the microstructures of the cured adhesives by scanning electron microscopy (SEM). The results show that modification by glutaraldehyde can effectively improve the bonding performance of wheat protein adhesives, the plywood bonded strength having been improved by its addition. The effect of PEI as a crosslinking agent became evident. It can greatly improve the bonding properties of glutaraldehyde-modified wheat protein adhesives. TMA analysis indicates that the glutaraldehyde-modified GP adhesive has a higher storage modulus than the unmodified one. The modulus of the adhesive increased after adding the PEI cross-linking agent.     

Fast clear-sky solar irradiation computation for very large digital elevation models

This paper presents a fast algorithm to compute the global clear-sky irradiation, appropriate for extended high-resolution Digital Elevation Models (DEMs). The latest equations published in the European Solar Radiation Atlas (ESRA) have been used as a starting point for the proposed model and solved using a numerical method. A new calculation reordering has been performed to (1) substantially diminish the computational requirements, and (2) to reduce dependence on both, the DEM size and the simulated period, i.e., the period during which the irradiation is calculated. All relevant parameters related to shadowing, atmospheric, and climatological factors have been considered. The computational results demonstrate that the obtained implementation is faster by many orders of magnitude than all existing advanced irradiation models while maintaining accuracy. Although this paper focuses on the clear-sky irradiation, the developed software also computes the global irradiation applying a filter that considers the clear-sky index.     

Surface modification of lignin for applications in polypropylene blends

The surface modification of wet‐milled softwood lignin produced with the LignoForce System was successfully carried out in a one‐step aqueous process. Different hydrophobic molecules, including cetyl trimethyl ammonium bromide, poly(ethylene oxide), polyethylene‐block‐poly(ethylene glycol), dodecenyl succinic anhydride, and alkyl ketene dimer (AKD), were investigated to design the hydrophobicity of lignin with the objective of improving the adhesion and compatibility in polymer blends composed of polar lignin particles and, for example, nonpolar polypropylene (PP). AKD, among all of the investigated approaches, proved to be the simplest and most effective for significantly increasing the contact angle of lignin while preserving the original micrometer size of wet‐milled, spray‐dried lignin particles. This treatment led to a noticeable improvement in the stiffness of lignin–PP composite blends, with an increase of approximately 15% in Young's modulus. The compatibility of the AKD‐treated lignin with PP was assessed through tensile strength measurements and blend morphology observation, whereas the mechanism of AKD interaction with lignin was investigated with contact angle measurement, differential scanning calorimetry, Fourier transform infrared spectroscopy, and ¹H‐NMR spectroscopy measurements. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45103.     

Physicochemical equilibria of cement-based materials in aggressive environments—experiment and modeling

Assessment of the integrity of concrete structures during their service life begins by considering the durability of the material in its environment. Experiments have clearly improved the understanding of the degradation mechanisms of concrete, mortars, and cement pastes under various aggressive environments. As far as radioactive waste containers are concerned, leaching by water has to be considered. Leaching experiments of cement pastes by aggressive solutions are shown to result in degradations with different kinetics. Three cement pastes with variable water-to-cement (w/c) ratio (0.25, 0.4, and 0.5) in two solutions (pure water and mineralized water) were investigated by TG/DTA, SEM-EDS, and by application of the NIST (National Institute of Standards and Technology) microstructure models. Leaching kinetics, evolution of the solid skeleton, and pore solution were experimentally studied and successfully modeled, using a reactive-transport approach. The discrepancies between modeling and experimental results highlight the understanding of complex degradation mechanisms. New results on the interactions on the aggressive solution and the cementitious material, through the pore solution, are presented.