Effects of water-soluble polymers and aqueous-phase viscosity on the interfacial tension behavior of reacting oil–alkaline systems

This study presents the results of an experimental study of the effects of water-soluble polymer additives on the dynamic interfacial tension behavior of reacting oil–aqueous systems as measured by the spinning drop tensiometer. Polymer additives can exert both a direct physico-chemical effect and an indirect viscosity effect on the measured interfacial tension. This work, which complements an earlier study dealing with the effects of oil-soluble polymer additives, reveals that the nominal effects of aqueous-phase viscosity are opposite to those of oil-phase viscosity. In particular, an increase in aqueous-phase viscosity produces an increase in the rate of increase of the apparent interfacial tension after attainment of the minimum value. These differences are explained in terms of the dependence of diffusion rates and interfacial adsorption on aqueous-phase viscosity. The conclusion of principal practical interest is that although aqueous-phase viscosity exerts only a small effect on the dynamic interfacial tension at small times (i.e., prior to attainment of the minimum value) it exerts a very significant effect thereafter. © 1994 John Wiley & Sons, Inc.     

Characterisation of R.F. magnetron sputtered Cr-N,Cr-Zr-N and Zr-N coatings

Binary Cr-N, Zr-N and Cr-Zr-N films were synthesised using a R.F. reactive magnetron sputtering technique by co-sputtering Cr and Zr. The crystalline structure, morphology, mechanical and tribological properties of the films as a function of Zr content were characterised by X-ray diffraction, microanalysis X (WDS, EDS), X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, nanoindentation, scratch adhesion and pin-on-disc sliding wear tests. The residual stress was calculated with the Stoney formula. The Cr-Zr-N films exhibit a two-phase microstructure, containing a cubic (CrN, ZrN) with hexagonal (Cr₂N, Zr₂N) phases, as shown by X-ray diffraction. As the Zr content increased, a columnar and compact structure is developed with a low surface roughness. The results reveal that the mechanical and tribological properties of the films were found to depend on the Zr content and the hardness (maximum 26.3?GPa) is greatly improved in comparison with CrN and ZrN films, especially at 31?at.-% Zr. In the scratch test, the hardest film (Cr_0.18Zr_0.31N_0.47) exhibited an adhesive failure at Lc_2?=?34.3?N.     

Efficient characterization of millimeter‐wave asymmetric coupled microstrip structures using the quasi‐symmetric approach

To sustain the ever‐increasing use of coupled‐line structures in RF/microwave systems, efficient design tools should be developed. In this article, an original approach combining accuracy and speediness is proposed to shorten time‐to‐market design cycles when such structures are involved. By introducing the quasi‐symmetric approach, CPU‐time required to analyze asymmetric coupled‐lines can be significantly reduced, leading to faster models without sacrificing the overall design accuracy. To achieve this aim, a rigorous formulation was developed and, for the first time, trial functions of C‐ and π‐modes were obtained from the quasi‐symmetric case and applied to the asymmetric case. The proposed approach, easily implementable in commercial simulators, was demonstrated through comparisons with published data. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

Properties of metakaolin based geopolymer incorporating calcium carbonate

An alkaline solution, thermally activated kaolinite clay and a mineral additive (calcium carbonate) were mixed with the aim to elaborate a geopolymer material with physical and mechanical properties comparable to those of classical construction materials.The starting reagents were characterized by quantitative chemical analyses (XRF), mineralogical analyses (XRD), thermal gravimetric analyses (TGA), and grain size distribution measurements. The setting of the mixture (polymerization) was implemented by measuring the evolution of the viscosity as a function of time at different temperatures.The geopolymers were synthesized at a temperature of 40 °C. The investigation of the mechanical behavior reveals that these materials display acceptable characteristics: the flexural and compression strength are around 4.6 and 26 MPa respectively, for an added calcium carbonate over dry matter ration up to 12% by weight.The promising results exposed in this paper show that the geopolymer formulations can be adapted for applications in construction and civil engineering structures as an alternative to conventional materials.     

Vector-optimised harmonic elimination for single-phase pulse-width modulation inverters/converters

A new approach for calculating single-phase inverters/converters-optimised pulse-width modulation (PWM) switching angles for harmonic and voltage control is proposed. This approach takes into account the DC-link voltage ripple, due to the finite DC-link capacitance, in the optimised switching-angles calculation, using its harmonic content. New expressions for the evaluation of the PWM waveform harmonic spectrum are derived. Output voltage quarter-wave symmetry is thus not assumed and the pulse position is no longer fixed, resulting in two simultaneous sets of nonlinear equations in twice as many unknowns as in the case of conventional-optimised PWM strategy with smooth DC input/output voltage. The performance of this latter technique is hence retained while the size of the DC-link capacitor is reduced to a limit depending on the filter capacitance, the number of pulses per half modulation period and the modulation depth. The compensation of the reactive power (exchanged between the AC source/AC load and the DC link due to the rectifying/inverting process and the low-link capacitance) is also included; the converter then plays the additional role of an active power filter. Simulation examples and experimental results are used to validate the proposed method     

Characterization of Two Nanofiltration Membranes for the Separation of Ions from Acid Mine Water

We evaluated nanofiltration for separation of ions from acid mine drainage (AMD), using two composite nanofiltration membranes (Nano-Pro-3012 and NF90) as examples of the polyamide class of acid-stable membranes. The structure of the NF membranes was characterized by scanning electron and atomic force microscopy. The NF90 displayed a higher permeate flux than Nano-Pro-3012, with higher relative roughness at both pH values. Both membranes suitably rejected most of the metals found in the AMD, but the Nano-Pro-3012 membrane proved unsuitable for sulphate removal.     

Electrochemical,spectroscopic and molecular docking studies of 4-methyl-5-((phenylimino)methyl)-3H- and 5-(4-fluorophenyl)-3H-1,2-dithiole-3-thione interacting with DNA

Cyclic voltammetry (CV) and UV–Visible spectroscopy (UV–Vis) techniques were used to calculate binding parameters of 4-methyl-5-((phenylimino)methyl)-3H-1,2-dithiole-3-thione (MPDT) and 5-(4-fluorophenyl)-3H-1,2-dithiole-3-thione (FPDT) with DNA. The results obtained from both techniques were confirmed by computational molecular docking using AutoDock molecular docking software. The anodic peak potential shift in CV indicated an intercalative mode of binding. The binding constants (M^?1) of the adducts MPDT-DNA and FPDT-DNA obtained from voltammetric measurements were found to be 8.0?×?10⁴ and 2.4?×?10⁴, respectively, with binding free energy being ?27.99 and ?25.01?KJ?mol^?1, respectively. These results are in good agreement with those obtained from UV–Visible spectroscopic studies. The diffusion coefficients of MPDT and FPDT (2.06?×?10^?10 and 2.42?×?10^?9, respectively) were found to be higher than those of DNA-bound compounds (1.27?×?10^?10 and 1.65?×?10^?9?cm²/s, respectively). The binding free energy of MPDT and FPDT to DNA was also calculated by molecular docking study. The docking study gave excellent approximation with experimental results, shedding light on the sites of binding.     

Experimental investigation and optimization of printing parameters of 3D printed polyphenylene sulfide through response surface methodology

Today fused filament fabrication is one of the most widely used additive manufacturing techniques to manufacture high performance materials. This method entails a complexity associated with the selection of their appropriate manufacturing parameters. Due to the potential to replace poly-ether-ether-ketone in many engineering components, polyphenylene sulfide (PPS) was selected in this study as a base material for 3D printing. Using central composite design and response surface methodology (RSM), nozzle temperature (T), printing speed (S), and layer thickness (L) were systematically studied to optimize the output responses namely Young's modulus, tensile strength, and degree of crystallinity. The results showed that the layer thickness was the most influential printing parameter on Young's modulus and degree of crystallinity. According to RSM, the optimum factor levels were achieved at 338°C nozzle temperature, 30 mm/s printing speed, and 0.17 mm layer thickness. The optimized post printed PPS parts were then annealed at various temperatures to erase thermal residual stress generated during the printing process and to improve the degree of crystallinity of printed PPS's parts. Results showed that annealing parts at 200°C for 1 hr improved significantly the thermal, structural, and tensile properties of printed PPS's parts.     

Aerobic decolourization of the indigo dye-containing textile wastewater using continuous combined bioreactors

An aerobic bioprocess was applied to Indigo dye-containing textile wastewater treatment aiming at the colour elimination and biodegradation. A combined aerobic system using continuous stirred tank reactor (CSTR) and fixed film bioreactor (FFB) was continuously operated at constant temperature and fed with the textile wastewater (pH: 7.5 and total chemical oxygen demand (COD): 1185 mg l(-1)). The CSTR is a 1l continuous flow stirred tank reactor with a 700 ml working volume, and operated with a variable wastewater loading rate (WLR) from 0.92 to 3.7 g l(-1) d(-1). The FFB is a 1.5l continuous flow with three compartments packed with a rippled cylindrical polyethylene support, operated with a variable WLR between 0.09 and 0.73 g l(-1) d(-1). The combined two bioreactors were inoculated by an acclimated microbial consortium and continuously operated with four total WLR. This system presented high COD elimination and colour removal efficiencies of 97.5% and 97.3%, respectively, obtained with a total hydraulic retention time (HRT) of 4 days and total WLR of 0.29 g l(-1) d(-1). The effects of WLR on absorption phenomena on the yield of conversion of substrate on biomass (R(TSS/COD)) and on the yield of conversion of substrate on active biomass (R(VVS/COD)) are discussed. The increase of WLR and the decrease of HRT diminished the performances of this system in terms of decolourization and COD removal explained by the sloughing of biofilm, and the washout phenomena.     

ZnS stacking order influence on the formation of Zn-poor and Zn-rich Cu2ZnSnS4 phase

This paper reports the synthesis and characterization of Cu₂ZnSnS₄ (CZTS) absorber films, prepared by a two-step electrodeposition of a ZnS (zinc sulfide) binary and a CZT (copper, zinc and tin) ternary precursors on Mo/Ti/Si substrates. The as-electrodeposited ZnS/CZT and CZT/ZnS stacks were thermally treated in a tubular furnace in sulfur environment at 550 °C. The role of the ZnS buffer layer is to provide a zinc and sulfur reservoir, needed to complete the formation of kesterite phase. X-ray diffraction and Raman analyses revealed the formation of the CZTS phase. The surface morphology and chemical composition of the films were studied using a scanning electron microscope. The bandgap values inferred from diffuse reflectance data, are discussed with respect to the stoichiometry which is considerably affected by the order of the stacks. Room-temperature photoluminescence of the CZT/ZnS sample showed a board PL band of 1.51 eV. It was found that the film with a ZnS layer on top is preferred for the formation of a Zn-rich single CZTS phase.