Thermophysical and Scattering Properties of Alkali-Metal Atoms and Hydrogen Atom Mixtures

The purpose of this work is to theoretically examine the diffusion of neutral alkali atoms in a neutral gas of atomic hydrogen, as well as their low-temperature elastic scattering properties. More specifically, the investigation tries to determine the temperature-dependent diffusion coefficient \(D(T)\) and the scattering length \(a\) and effective range \(r_{\mathrm {e}}\) of alkali-metal atoms in hydrogen. The computations are carried out quantum mechanically by considering the full interaction potentials for all alkali hydrides.     

Micro X-ray visualisation of the interaction of geosynthetic clay liner components after partial hydration

High-resolution X-ray tomography was used to observe a partially hydrated geosynthetic clay liner (GCL) specimen to gain a better understanding of the interaction of its compnents (i.e., geotextiles, fibres and bentonite) on partial hydration when deployed as part of a composite liner system. Detailed in-situ studies of hydration processes in GCLs has proven difficult despite more than two decades of effort. X-ray tomographs were collected at spatial resolutions of 12 and 7?μm to identify the different components within a GCL, as well as to examine in finer detail their interaction within the GCL after initial partial hydration. Tomograph projections provided an excellent aspect of the interaction of these components and some concepts, such as the presence of shearing features within the bentonite component, may require re-consideration based on evidence from X-ray tomography.     

Enhancement of the photocatalytic activity of pelletized TiO2 for the oxidation of propene at low concentration

In a previous study we have shown that the pelletization of titanium dioxide, a convenient step for gas phase applications, causes an important activity lost. Such activity lost can be partially recovered pelletizing in presence of carbon materials. Porosity, as well as carbon conductivity of the selected carbon material, is important. Based on these previous results, we analyze the pelletization of TiO₂ in presence of “white additives”, such as MCM-41, zeolites, metal–organic framework, SiO₂, Al₂O₃, glass wool and quartz wool. Our results show that the activities of these composite photocatalytic pellets are higher than that of 100% TiO₂-pellets. Pellets containing MCM-41, precipitated SiO₂, glass wool and quartz wool present the highest propene conversions. Attention has been paid to the effect of porosity and UV-absorbance on the resulting photocatalytic activity. Although it is difficult to find a correlation between the porosity of these “white additives” and the photocatalytic activity of the TiO₂-based materials, additives with no porosity or with some mesoporous contribution seem to be desired to maximize the activity. The different catalytic activities for the studied photocatalysts could not be explained on basis of their UV-absorption and further research is currently being performed trying to deep into the reasons for such behaviour. Comparison of the photocatalytic activities for pellets containing the above-mentioned “white additives” with those of a TiO₂/carbon photocatalyst having the highest porosity and conductivity among all those studied highlights the superior performance of the samples containing “white additives”.     

Numerical experiment-artificial intelligence approach to develop empirical equations for predicting leakage rates through GM/GCL composite liners

The aim of this study is to develop empirical equations to predict the liquid leakage rate through a composite liner comprising a geomembrane and a geosynthetic clay liner (GM/GCL) underlain by a free draining boundary and having a circular or a longitudinal defect in the geomembrane. For this purpose, an intensive numerical experimental program was conducted where different defect geometries and flow transport characteristics were studied to simulate most of the conditions likely to exist in practice in such type of composite liners. The results are presented in a dimensionless form to generalize the observed behaviour and to give more insight on the factors that control the leakage behaviour. Furthermore, the results are also used to develop empirical equations for predicting the rate of leakage. An artificial intelligent approach referred to as General Method of Data Handling (GMDH) was used for this purpose. The main advantage of the proposed leakage equations is their validity for different flow patterns as the effect of defects geometry and flow characteristics of the composite liner components are already embedded in the development of the equations. However, their validity is limited to the ranges of the dimensionless parameters that were used to develop them.     

Mechanical and tribological behavior of nanostructured copper–alumina cermets obtained by Pulsed Electric Current Sintering

Nanostructured Cu–Al₂O₃ powders obtained by the reduction of CuO with Al in a high energy ball mill were successfully consolidated by Pulsed Electric Current Sintering (PECS). The effect of the composition and microstructure of these PECS Cu–Al₂O₃ cermets on their strength was investigated. The friction and wear behavior of these cermets were studied under reciprocating sliding against corundum at 23 °C and 50% RH, and compared to the behavior of coarse grained PECS sintered pure copper. The effect of grain size on the coefficient of friction was masked by the formation of a surface tribolayer. The wear depth recorded on Cu–Al₂O₃ is lesser than half the one on coarse grained copper. Surface and subsurface deformation studied through FIB cross-sections showed that delamination and oxidative wear were active on Cu and Cu–Al₂O₃ cermets respectively under the current sliding test conditions. PECS Cu–Al₂O₃ cermets showed a good thermal stability even at 600 °C.     

Effect of fine aggregate replacement with desert dune sand on fresh properties and strength of self-compacting mortars

This paper presents the results of an experimental study that investigated the rheological and mechanical properties of self-compacting mortars incorporating fine dune sand (DS), which has a tight Particle size distribution. Mortar mixtures were prepared with crushed sand (CS) or river sand (RS) in which the fine aggregates were replaced partially by different percentages of DS of 0, 25, 50, 75 and 100%. The effect of DS on the fresh mortars properties was studied using the mini-slump flow, V-funnel flow time and viscosity measurements tests. Compressive strength and flexural strength were determined at age of 3, 7 and 28 days. Experimental results indicate an improvement in fresh rheological without reducing in mechanical properties of self-compacting mortars when fine aggregates were replaced partially with DS (50%). However, at high-level DS replacement (75%) the slump flow decreases. The replacement of the DS to the CS or to the RS shows an increase in the mixture viscosity. In general, the compressive and flexural strength were not significant affected with an increase in DS replacement. Finally, based on the results obtained in this investigation, DS may provide a readily available alternative material as fine aggregates in mortar application.     

Synthesis of (B-C-N) Nanomaterials by Arc Discharge Using Heterogeneous Anodes

In spite of the current prevalence of the CVD-based processes,the electric arc remains an interesting process for the synthesis of carbon nanoforms,thanks to its versatility,robustness and easiness.It also allows performing in-situ substitution of carbon atoms by hetero-elements in the graphene lattice.Our work aims to establish a correlation between the plasma properties,type and chemical composition (and the substitution rate) of the obtained single-wall carbon nanotubes.The plasma was characterized by optical emission spectroscopy and the products were analyzed by high resolution transmission electron microscopy and core level Electron Energy-Loss Spectroscopy (EELS).Results show that a high boron content leads to a plasma temperature decrease and hinders the formation of nanotubes.This effect can be compensated by increasing the arc current and/or yttrium content.The optimal conditions for the synthesis of boron-and/or nitrogen-substituted nanotubes correspond to a high axial plasma temperature associated to a strong radial gradient.EELS analysis confirmed that the boron incorporates into the graphenic lattice.     

Rheological behavior of Algerian crude oil: effect of temperature and refined product

Abstract

The rheological behavior and its variation with temperature and refined product concentration of a crude oil sample coming from a quagmire of the separation station of Tin Fouye Tabankort oilfield/southern Algeria were investigated experimentally. The experiments were carried out at various temperatures (20, 30 and 50?°C) over the shear rate range of 0 to 700?s^?1 by using a controlled stress rheometer (AR 2000, TA Instrument). The results showed that the crude oil exhibit non-Newtonian of shear thinning behavior at low shear rate and Newtonian behavior at high shear rate and was adequately described by Casson and Herschel–Bulkley models. The rheological measurements through the steady flow test and viscoelastic behavior, including the storage modulus (G′), loss modulus (G″), and complex modulus (G*), has indicated that the rheological properties of the crude oil were greatly influenced by the temperature and the additive concentration.