Copper oxide coated polyester fabrics with enhanced catalytic properties towards the reduction of 4-nitrophenol

A novel functional polyester fabric (PF) was successfully prepared by a facile method. PF were coated by copper oxide (CuO) followed by chemical grafting of 3-chloropropyltriethoxysilane (ClPTES) and diethanolamine (DEA). The morphology and structure of the resulting material PF@CuO–Si–N(OH)₂ was characterized by X-ray diffraction, scanning electron and optical microscopy, thermogravimetry and Fourier-transformed infrared spectroscopy. The results revealed that the CuO particles were densely surrounded PF, and the covalent surface-grafting of ClPTES and DEA within PF was confirmed. It was also demonstrated that CuO/ClPTES/DEA addition generated new functional sites at the PF surface, improving the catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). The prepared PF@CuO–Si–N(OH)₂ exhibited high catalytic activity with appreciable cycling stability for the reduction of 4-NP to 4-AP, even after six successive cycles with nearly 90% conversion. Hence, it may be conclude that the catalytic activity and stability of this catalyst allows envisaging great prospect for large scale reduction of 4-NP.     

Flux pinning mechanisms of (YBa2Cu3Oy-d)1−x/(Dy2O3)x superconductors (x=0.1 and 0.5 wt%)

Polycrystalline (YBa₂Cu₃O_y-d)_1?x/(Dy₂O₃)_x superconductor samples were produced through the solid-state reaction route and by adding amounts of x = 0.1 and 0.5 wt% of Dy₂O₃ nanoparticles (NP-Dy₂O₃ with a size of about 10 nm) during the second stage of heat treatment. The structural, microstructural, critical current density and pinning properties were investigated using x-ray diffraction, scanning electron microscope, and DC magnetization at various temperatures ranging from 77 down to 10 K and under an applied magnetic field varying between ?6 and +6 Tesla. Both samples crystallize in the orthorhombic structure. It was found that the Dy₂O₃ nanoparticles reside in the grain boundaries. Although the sample with 0.5 wt% NP-Dy₂O₃ is characterized by a low zero resistive temperature of about 78 K that is close to the useful temperature for technological applications, it showed the highest J_c values and the excellent flux pinning capacity. The addition of an appropriate amount of NP-Dy₂O₃ up to 0.5 wt% extends the single bundle pinning regime and retards the liquid vortex regime.     

Study of Rust Effect on the Corrosion Behavior of Reinforcement Steel Using Impedance Spectroscopy

Most studies on corrosion of steel reinforcement in concrete are conducted on steel samples with polished surface (free of all oxides) in order to reproduce the same experimental conditions. However, before embedding in concrete, the steel bars are often covered with natural oxides (rust), which are formed during exposure to the atmosphere. The presence of this rust may affect the electrochemical behavior of steel rebar in concrete. In order to understand the effect of rust on the corrosion behavior of reinforcement steel, potentiodynamic and electrochemical impedance spectroscopy (EIS) tests were carried out in a simulated concrete pore solution using steel samples with two different surface conditions: polished and rusted samples. The obtained results have shown that the presence of rust on the steel bar has a negative effect on its corrosion behavior, with or without the presence of chlorides. This detrimental effect can be explained by the fact that the rust provokes a decrease of the electrolyte resistance at the metal-concrete interface and reduces the repassivating ability. In addition, the rust layer acts as a barrier against the hydroxyl ion diffusion, which prevents the realkalinization phenomenon.     

2-D Hydro-Viscoelastic Model for Convective Drying of Highly Deformable Saturated Product

The aim of this work was to simulate in two-dimensions the spatio-temporal evolution of the moisture content, the temperature, and the mechanical stress within a highly deformable and water saturated product during convective drying. The material under study was an elongated potato sample with a square section placed in hot air flow. A comprehensive hydro-thermal model had been merged with a mechanical model, assuming a viscoelastic material, a plane deformation, and an isotropic linear hydric-shrinkage of the sample. This model was validated on the basis of the average water content and core temperature curves for drying trials under different operating conditions. The material viscoelastic properties were measured by means of stress relaxation tests at different water contents. The viscoelastic behavior was described by a generalized Maxwell model whose parameters were correlated to water content. The simulations of the spatio-temporal distributions of mechanical stress were performed and interpreted in terms of product potential damage. The sample shape was also predicted all aver the drying process with reasonable accuracy.     

Properties of self-compacting mortar made with various types of sand

Higher cement and fines content is needed in self-compacting mortars (SCMs) to increase their flowability and stability. Different inert fillers and supplementary cementitious materials are usually added. The use of sands rich in fines may be a cost effective alternative source of filler. This paper presents the results of an experimental study on the rheological and mechanical properties of self-compacting mortars (SCMs) made with various types of sands: crushed sand (CS), river sand (RS), dune sand (DS) and a mixture of different sands. The mini-slump flow, V-funnel flow time and viscosity measurement tests were used to study the rheological properties. The experimental results indicate that the rheological properties and strength improve with mixtures of crushed and river sands but decrease with mixtures of crushed and dune sands especially for higher dune sand content. Crushed sand with (10–15%) of limestone fines can be used successfully in production of SCM with good rheological and strength properties. However, a reduction in compressive strength with increasing dune sand content (up to 50%) in mortar with binary and ternary sands was observed.     

Effect of Silver Admixture on Transport Properties in Polycrystalline MgB2

The normal-state and superconducting properties of polycrystalline MgB₂ samples including various amounts of Ag powder were investigated by measurements of electrical resistivity. The temperature-dependent electrical resistivity roughly obeys the power law (ρ₀ + aT ⁿ with n > 1) in the normal state and becomes linear as we increase the Silver content. The critical superconducting temperatures remain almost unchanged. Silver, not reacting with MgB₂, reacts with excess magnesium to form intermetallic layers of AgMg that cluster at crystallite boundaries.     

Improvement of flux pinning ability by tungsten oxide nanoparticles added in YBa2Cu3Oy superconductor

In this study, series of superconductor-tungsten oxide (WO₃) nanoparticles composites, YBa₂Cu₃O_7-δ/(WO₃)_x, were produced via the solid-state reaction process. The structural, morphological, chemical compositions, electrical and magnetic properties were investigated using X-ray diffraction (XRD), scanning electron microscope (SEM) along with EDX system and physical properties measurement system (PPMS), respectively. The XRD, SEM and EDX analyses showed the successful formation of the Y-123 orthorhombic phase. The electrical resistivity measurements proved the occurrence of superconductivity in different samples. The magnetic results showed an improvement of critical current density (J_c) and pinning ability in WO₃ nanoparticles added Y-123 products. The dominant pinning mechanisms and the strength of pinning centers in various sintered products were examined and discussed. The measurements of zero-field-cooled (ZFC) and field-cooled (FC) magnetization versus temperature (M-T) indicated an increase in the magnitude of diamagnetic signal with the addition of WO₃ nanoparticles in the Y-123 superconductor.