Lubricating and physico-chemical properties of CI- 4 plus engine oil dispersed with surface modified multi-walled carbon nanotubes

This paper studies the effect of surface modification of multiwall carbon nanotubes (MWCNTs) prior to dispersion in engine oil to improve the tribological properties. The MWCNTs are stabilised in the lubricant with two different surfactants cetrimonium bromide (CTAB) and sorbitan monooleate (SPAN 80) and the effect of surfactants on the tribological properties has been studied. Pristine and surface modified MWCNTs in weight per cent range of 0·5% are dispersed in CI4 plus diesel engine oil. The foaming tendency and other physico-chemical properties of test lubricant have been studied to investigate the effect of nano materials and surfactants. The anti-wear and anti-friction properties are tested on a four ball wear tester and the comparison is made to assess the relative performance of pristine MWCNTs over surface modified MWCNTs. A strong influence of the surface modification technique is found on lubricating and physico-chemical properties. Both CTAB and SPAN 80 could keep the MWCNTs stable in the lubricant without compromising the foaming tendency of lubricant and other physico-chemical properties. The friction and wear characteristics of lubricants have improved with the dispersion of surface modified MWCNTs while there is no improvement in the properties of lubricant dispersed with pristine MWCNTs.     

Influence of the grain structure of yttria thin films on the hydrogen isotope permeation

Steel components are required in the infrastructure and the facilities of the hydrogen economy. The high hydrogen pressures in the hydrogen economy lead to embrittlement and surface corrosion of the steels. For the functionality of the facilities it is necessary to suppress the embrittlement and the surface corrosion of the steels by protective layers, e.g. ceramic thin films. With regard to fusion power plants ceramic thin films on the structural steel materials are also required. These thin films work as a tritium permeation barrier that is necessary to prevent the loss of the radioactive fuel inventory. Oxide thin films, e.g. Al₂O₃, Er₂O₃, and Y₂O₃, are promising candidates as tritium permeation barrier layers. In terms of the application in the first wall, this is especially true for yttrium due to its favorably short decay time after neutron activation compared to the other candidates. The Y₂O₃ layers with thicknesses of 0.5 μm–1 μm are deposited on both substrate sides by RF magnetron sputter deposition. Since the microstructure of the barrier layer plays an important role for the permeation reduction, layers with three different magnetron process modes and thus three different microstructures are prepared. After annealing the cubic crystal structure of all thin films is verified by X-ray diffraction and the different microstructures are investigated by scanning electron microscopy and transmission electron microscopy. The Y₂O₃ stoichiometry of all thin films and a chromium oxide material segregation at the interface are verified by analysis methods such as X-ray photoelectron spectroscopy. The permeation reduction factors of all thin films are determined in gas-driven deuterium permeation experiments. Corresponding to the three different microstructures, reduction factors of 25, 45, and 1100 are identified. Thus, the permeation reduction is strongly dependent on the Y₂O₃ microstructure. The measurement results suggest that a high density of grain boundaries leads to a high hydrogen permeation.     

Thermo-mechanical optimization of porous building materials based on micromechanical concepts: Application to load-carrying insulation materials

In this paper, a multiscale model for the prediction and, finally, optimization of mechanical (elastic) and thermal (heat conductivity) properties of porous building materials is presented. These technical composites are characterized by the increase of porous space in the respective material system, resulting in a reduction of Young’s modulus, on the one hand, and in an increase of the thermal insulation capacity, on the other hand, yielding either a load-carrying insulation material or a structural material with enhanced resistance to heat transfer. Determination of engineering properties within the proposed multiscale approach departs from the underlying material composition, on the one hand, and the intrinsic properties of the constituents, i.e., the material phases, on the other hand, employing homogenization techniques based on continuum micromechanics.     

Crack analysis in decagonal quasicrystals by the MLPG

A meshless method based on the local Petrov-Galerkin approach is proposed to solve initial-boundary-value crack problems in decagonal quasicrystals. These quasicrystals belong to the class of two-dimensional (2-d) quasicrystals, where the atomic arrangement is quasiperiodic in a plane, and periodic in the perpendicular direction. The ten-fold symmetries occur in these quasicrystals. The 2-d crack problem is described by a coupling of phonon and phason displacements. Both stationary governing equations and dynamic equations represented by the Bak’s model with oscillations for phasons are analyzed here. Nodal points are spread on the analyzed domain, and each node is surrounded by a small circle for simplicity. The spatial variation of phonon and phason displacements is approximated by the moving least-squares scheme. After performing the spatial integrations, one obtains a system of ordinary differential equations for certain nodal unknowns. That system is solved numerically by the Houbolt finite-difference scheme as a time-stepping method.     

Mathematical modeling of filtering process of two-phase suspensions in tubular filters under nonisothermal conditions

The hydrodynamic conditions in tubular filter cells operating under nonisothermal conditions are studied. The equations of mechanics of heterogeneous media are used to describe the separation process of two-phase suspensions, which are written and simplified in the cylindrical coordinate system taking into account characteristics of the flow. The challenge is solved semi-analytically. Using the methods of surfaces of equal consumptions and Slezkin, numerical calculations on the constructed mathematical model are presented for particular implementations of the separation process.     

Transport phenomena in the electrodeionization of cesium from AMP-PAN

Electrodeionization (EDI) of cesium from cesium-sorbed ammonium molybdophosphate-polyacrylonitrile (AMP-PAN) was investigated by passing eluant through the packed bed of ion-exchange resin in an electrodialysis cell. The deionized cesium from the packed bed was recovered in catholyte by migration and in the eluant by convection. Recovery percentage of Cs by migration increased while the recovery by convection decreased with increase in current density from 20 to 40 mA/cm². Increased eluant concentration resulted in low migration percentage of cesium. Increased catholyte concentration had a negligible effect on total recovery. Apparent diffusion coefficients evaluated using the Nernst–Plank relation increased with increase in current density and catholyte concentration while a decreasing trend was observed with increase in eluant concentration.     

Investigation of solar hybrid system with concentrating Fresnel lens,photovoltaic and thermoelectric generators

An experimental model of a solar hybrid system including photovoltaic (PV) module, concentrating Fresnel lens, thermoelectric generator (TEG), and running water heat extracting unit was created and studied. The PV module used was of c‐Si and TEG of Bi₂Te₃; the Fresnel lens (solar concentrator) and TEG share an optical train, whereas PV module was illuminated separately with non‐concentrated light. Heat extracting unit operated in thermo siphon mode. In climatic conditions of Mexico (Queretaro, 20^o of North latitude, summer time), the Fresnel lens accepted 120 W of solar radiation power, and the system generated 7.0 W of electric power and 30 W of thermal one. The discussion is made of the possible characteristics of a hypothetical hybrid system where all its elements share the same optical train. Copyright © 2016 John Wiley & Sons, Ltd.