Ignition of a Ti–Al–C System by an Electron Beam

This paper describes the optimal modes of initiation of self-propagating hightemperature synthesis with the help of an electron beam on the example of a Ti–Al–C powder mixture. A pulsed electron beam with a particle energy of tens of kiloelectronvolts and a duration of hundreds of microseconds is used. Morphology, structure, and elemental composition of formed products in the form of Ti₃AlC₂ and TiC are studied.     

Adhesively bonded steel tubes – Part II: Numerical modelling and strength prediction

Capacity prediction of adhesively bonded joints remains challenging; this is particularly true for tubular joints composed of circular hollow sections used in civil engineering. This paper extends its companion paper, which presented experimental results of a large research campaign on full-scale tubular joints, with the aim to develop a dimensioning method. Firstly, experiments were designed to quantify the strength of the adhesive-steel connection; the results thereof were cast into the formulation of an adequate failure criterion, for each of the adhesives considered. Secondly, numerical models of all investigated joint configurations were established, from which the stress-state inside the bonded connection could be determined. A series of analyses clearly showed that stress magnitude and joint capacity did not correlate, thus indicating that a direct stress based methodology is destined to fail. Accordingly, a probabilistic method that is based on the concept of size effects was developed, and implemented. It allowed not only determining average values for joint capacities, but also estimated the expected experimental scattering thereof. The validity of the approach was tested by successfully comparing experimental and computed joint capacities.     

Particle Classification by the Tandem Differential Mobility Analyzer–Particle Mass Analyzer System

Particle mass analyzers, such as the aerosol particle mass analyzer (APM) and the Couette centrifugal particle mass analyzer (CPMA), are frequently combined with a differential mobility analyzer (DMA) to measure particle mass m_p and effective density ρ_eff distributions of particles with a specific electrical mobility diameter d_m. Combinations of these instruments, which are referred to as the DMA–APM or DMA–CPMA system, are also used to quantify the mass-mobility exponent D_m of non-spherical particles as well as to eliminate multiple charged particles. This study investigates the transfer functions of these setups, focusing especially on the DMA–APM system. The transfer function of the DMA–APM system was derived by multiplying the transfer functions of DMA and APM. The APM transfer function can be calculated using either the uniform or parabolic flow models. The uniform flow model provides an analytical function, while the parabolic flow model is more accurate. The resulting DMA–APM transfer functions were plotted on log(m_p)-log(d_p) space. A theoretical analysis of the DMA–APM transfer function demonstrated that the resolution of the setup is maintained when the rotation speed ω of APM is scanned to measure distribution. In addition, an equation was derived to numerically calculate the minimum values of the APM resolution parameter λ_c for eliminating multiple charged particles.

Copyright 2015 American Association for Aerosol Research     

Fouling Control in a Submerged Flat Sheet Membrane System: Part II—Two‐Phase Flow Characterization and CFD Simulations

Abstract

Gas‐liquid two‐phase flow has been shown to be very effective in reducing fouling for different membrane modules with different feeds, including submerged flat sheet membranes used in membrane bioreactors for treatment of wastewater. Although gas‐liquid two‐phase flow occurring on the lumen side of tubular or hollow‐fiber membranes has been very well characterized the two‐phase flow regime in submerged membrane processes is different to that inside external membranes. Characterization of two‐phase flow in submerged flat sheet membrane modules has not been previously reported and hence the use of two‐phase flow in these modules has not yet been optimized. This paper reports on characterization of two‐phase flow for a submerged flat sheet membrane module with the aim of identifying the most effective flow profiles for fouling minimization. In order to better understand the fouling control process by two‐phase flow, CFD simulations were also conducted. It was found experimentally that an increase in the bubble size leads to an increase in the cleaning effect, however, for bubbles larger than the channel gap between the submerged flat sheet membranes, any further increase in the bubble diameter had only a minor effect on the cleaning process. CFD simulations revealed that flux enhancement was primarily due to an increase in the overall shear stress on the membrane and to more turbulence generated by introduction of the gas phase.     

Hybrid PP–EPR–GF composites. Part II: fracture mechanisms

Abstract

The fracture mechanism of hybrid iPP–EPR–GF composites has been studied by notched Charpy, three- and four-point bending fracture tests. The results of impact tests illustrate that increasing both temperature and EPR/GF ratio increases the impact energy of iPP–EPR–GF. Indeed, with increasing temperature, a brittle, ductile, transition temperature (BDTT) occurs. The results of a three-point bending test show that fracture toughness (K_IC ) can be improved by addition of both GF and EPR. Since the trend in the fracture toughness values is close to what would be expected by the rule of blends, it can be concluded that the use of both GF and EPR has no significant synergistic effect on toughening. The results of a four-point bending test show that craze-like damage appears in front of the pre-crack and its propagation is dictated by the GF and EPR content. Looking in more detail at the damaged zone by means of cross-polarised light microscopy, evidence of birefringence can be revealed. Briefly, the dominant mechanism of fracture in the iPP–EPR–GF system studied in this work can be related to a craze-like type damage, which includes both highly localised dilatational shear bands, due to cavitation of the EPR particles, and some crazing induced by the stress concentration associated with GF.     

Plasticization of Fibrous Cellulose Acetate: Part I – Synthesis and Characterization

Synthesis and characterization of fibrous cellulose triacetate, CTA, are reported using an acetic acid/anhydride/perchloric acid toluene catalyzed route. The fibrous product exhibits a high degree of nano-crystallinity. An optimum concentration of the reactants for substitution and minimization of fiber degradation was studied. Chain degradation was promoted by the acetylium ion and led to a loss of fibrous structure. Heterogeneity of the material was studied by powder X-ray diffraction, optical microscopy, and solid-state ¹³C nuclear magnetic resonance. The structure formed if directly influenced by the original nano structure in the cellulose fiber.     

Structural Basis for Intumescence—Part II: Synthesis and Characterization of Intumescent Polymers Containing Spirophosphorus Moiety in the Backbone

Taking the spirophosphorus compound 3,9-dichloro-2,4,8,10-tetraoxo-3,9-diphosphaspiro-[5,5]-undecane-3,9-dioxide as one of the reactive monomers, a family of aromatic spirophosphates was synthesized using dihydric phenols, viz., resorcinol, hydroquinone, 4,4′–dihydroxydiphenyl, bisphenol-A and fluorene dicarbinol as the other monomers. The polymers were synthesized employing melt condensation technique under vacuum and characterized using FT-IR, ¹H-, ¹³C- and ³¹P-NMR spectroscopic methods. The number average molecular weight of the polymers was determined using vapour phase osmometry. Thermal properties of the polymers were studied using differential scanning calorimetry and thermogravimetry techniques. These studies indicated that the polymers containing spirophosphato moiety undergo eruptive degradations in the temperature region 310°–380°C leading to the formation of dense carbonaceous foam. The present study confirmed the spirophosphate structure as an essential requirement to show intumescence.     

Numerical Simulation of Liquid–Solid Countercurrent Fluidization inside an Extraction Column Based on Particle Trajectory Model

The liquid–solid countercurrent fluidization process in an extraction column was numerically simulated based on the particle trajectory model of Eulerian–Lagrangian method. The simulation approach was validated by previous experiments. A power function correlation was proposed for dimensionless slip velocity U_slip/U_t and hold-up fraction ϕ, and the operational zone in the countercurrent fluidization was determined. Simultaneous countercurrent fluidization of particles with different diameters was also simulated. The comparison shows that the simulation results are consistent with the calculation values from the multi-particle free sedimentation model based on non-interference assumption, verifying the reliability of the approach in present work.     

Synthesis,Characterization and Ion–Exchanging Properties of Novel Ion-Exchange Resin,Part 1

A polyamine (PA) was prepared by condensation of 1,4-bischloromethyl benzene and 1,2-ehanedeamine. The PA was then treated with cyanuric chloride at 0°C followed by reaction with sulfanilic acid in THF in concentration. NaOH (PH 9–10) at room temperature for 8 h. The resultant polymer, designated as polyamine-s-triazine-sulfanilic acid (PATS), was characterized by elemental analysis, IR spectral studies, and thermogravimetry. The PATS sample was monitored for its ion-exchanging properties by batch equilibrium method.     

Plasticization of Fibrous Cellulose Acetate: Part II – Physical Property Measurement

Birefringence, broadband dielectric and dynamic mechanical relaxation measurements are reported on fibrous cellulose acetate (CTA) plasticized with dibutylphthalate (DBP). Marked differences in physical properties are attributed to retention of nano-structure. Dielectric and mechanical relaxation data show two relaxation processes. The lowest temperature process is attributed to segmental type motion of the polymer chain and the higher temperature process to side-chain/plasticizer relaxation. The plasticization behavior is very different from that observed with other materials. The high-temperature relaxations are consistent with relative sliding of the polymer chain or nano crystallites past one another as in a liquid crystalline material.     

Application of Acoustic Spectroscopy to the Characterization of Surfactant Solutions,Emulsions, and Microemulsions: d–Limonene–Water–C12EO7–Isopropanol System

The application of acoustic spectroscopy to the characterization of binary C₁₂EO₇—water system was studied. It was discovered that the size of micelles in aqueous surfactant solutions could not be determined, but it was possible to determine the size of water nanodomains existing in the surfactant-rich systems. It was suggested that in colloidal systems, the energy of ultrasonic waves is dissipated only by interfaces existing between condensed phases. The characterization of Winsor transitions by acoustic spectroscopy in water/d-limonene system stabilized by a mixture of nonionic surfactant and isopropyl alcohol (cosolvent) was also explored. In one study, systems with a constant d-limonene to water weight ratio obtained in the course of titration of d-limonene-in-water emulsion with increasing amounts of surfactant+alcohol were investigated. In another study, a balanced d-limonene/water microemulsion was sequentially diluted with water and d-limonene. The transition between Winsor I and Winsor IV systems was monitored in both cases. Droplet size distributions were calculated using different models for dispersed and continuous phase composition. It was demonstrated that the magnitude of acoustic scattering played a significant role in the ability to reliably determine droplet size distributions, and in particular to simultaneously observe nanometer-size and micron-size droplets in Winsor I systems. An attempt was made to account for intrinsic attenuation of surfactant and alcohol by associating them with the aqueous phase, but this approach was shown not to be applicable in the case of Winsor IV microemulsions.     

Chemical Synthesis and Characterization of ZnO–TiO<Subscript>2</Subscript> Semiconductor Nanocomposites: Tentative Mechanism of Particle Formation

The compounds of ZnO–TiO₂ can combine the characteristics of the individual oxides which has allowed them to be used as photocatalysts in general, photodegradants in the degradation of dyes, photocatalytic oxidation of NO_x, antimicrobial, among other applications. In this study, ZnO–TiO₂ semiconductor nanocomposites were synthesized in a controlled way at low temperature. These samples of ZnO–TiO₂ were characterized using thermal analysis (TDA/TGA), IR and UV–Vis absorption spectroscopies, X-ray diffraction, and scanning electron microscopy. The primary particles showed a nanometric size (<?100 nm) and spheroidal morphology. All samples presented zincite as the main crystalline phase. When Ti⁴⁺ was added, the peaks of the diffractograms shifted slightly with respect to pure ZnO. This indicates the formation of a solid solution. Zn₂TiO₄ was observed in doped ZnO samples treated at 700 °C. The UV–Vis absorption spectra showed a band in the range between 350 and 425 nm, with a maximum around 375 nm (3.31 eV). With the addition of Ti⁴⁺, the nanocomposites showed a better absorbance in the visible range. Considering the nature of the synthesis process used, a mechanism was proposed to explanation of the formation of Nanocomposites.     

Mullite–Cobalt (II,III) Oxide System: Preparation of Ceramic Pigment Using Recycling of Fly Ash

Silicon - The present work depends on recycling of fly ash by preparation of stoichiometric mullite containing various amounts of Co3O4; 0, 5, 10, 15 wt.% to obtain pigment ceramic materials. The...     

Electrochemistry of the SUCOPLATE® Electroplating Bath for the Deposition of Cu–Zn–Sn Alloy; Part II: Influence of the concentration of bath components

The chemistry of a commercial alkaline cyanide electroplating bath used for the deposition of a Cu–Zn–Sn alloy has been investigated. The voltammetry, the deposit composition and the morphology have been investigated as a function of the concentrations of the three metal ions, Cu(i), Zn(ii) and Sn(iv) as well as the concentrations of cyanide, hydroxide, carbonate and `Copper Glo' additive. It is shown that all components combine to control the bath performance although the trends in alloy composition and quality can be predicted from the known chemistry of the bath. It is also concluded that the deposition of tin has an important role in initiating the growth of alloy layers.