Technological parameters that influence the production of ozone in A .D. C. Corona discharfe

Experiments using dry oxygen in a wire–to–cylinder ozone generator, submitted to D.C. corona discharges show that technological parameters (diameter and composition of wire and cylinder, length of cell, gas flow and transit time of the gas) greatly influence ozone production. The cell geometry to be used depends on the polarity of the D.C. voltage applied to the wire and, for a predetermined design, the maximum ozone production rate will be obtained by seeking the most suitable gas flow. Lining up a series of optimized cells can give significant results.     

MICAST — The effect of magnetically controlled fluid flow on microstructure evolution in cast technical Al-alloys

The MICAST research program focuses on a systematic analysis of the effect of convection on the microstructure evolution in cast Al-alloys. The experiments within MICAST are carried out under well defined thermally and magnetically controlled, convective boundary conditions and analyzed using advanced diagnostics and theoretical modeling, involving phase field simulation, micro-modeling and global simulation of heat and mass transport. The MICAST team uses as a model material the Al-Si base alloys. This paper gives a brief overview on recent experimental results of the MICAST team on the effect of rotating magnetic fields on microstructure in AlSi alloys.     

A non-premixed combustion model based on flame structure analysis at supercritical pressures

This work presents a study of non-premixed flames at supercritical-pressure conditions. Emphasis is placed on flame stability in liquid rocket engines fueled with liquid oxygen and gaseous hydrogen. The flame structure sensitivity to strain, pressure, temperature and real-fluid effects was investigated in detailed opposed-jet flames calculations. It is shown that the flame is very robust to strain, that the flamelet assumption is valid for the conditions of interest, and that real-fluid phenomena can have a significant impact on flame topology. At high-pressure supercritical conditions, small pressure or temperature variations can induce strong changes of thermodynamic properties across the flame. A substantial finding was also that the presence of water from combustion significantly increases the critical pressure of the mixture, but this does not lead to a saturated state where two-phase flow may be observed. The present study then shows that a single-phase real-fluid approach is relevant for supercritical hydrogen–oxygen combustion. Resultant observations are used to develop a flamelet model framework that combines detailed real-fluid thermodynamics with a tabulated chemistry approach. The governing equation for energy contains a compressible source term that models the flame. Through this approach, the solver is capable of capturing compressibility and strain-rate effects. Good agreements have been obtained with respect to detailed computations. Heat release sensitivity to strain and pressure variations is also recovered. Consequently, this approach can be used to study combustion stability in actual burners. The approach preserves the density gradient in the high-shear region between the liquid-oxygen jet and product rich flame region. The latter is a key requirement to properly simulate dense-fluid jet destabilization and mixing in practical devices.     

Crystallography of graphite spheroids in cast iron

To further understand graphite growth mechanisms in cast irons, this study focuses on the crystal structure of a graphite spheroid in the vicinity of its nucleus. A sample of a graphite spheroid from a commercial cast iron was characterised using transmission electron microscopy. The chemical composition of the nucleating particle was studied at the local scale. Crystal orientation maps of the graphite spheroid revealed misorientations and twist boundaries. High-resolution lattice fringe images showed that the basal planes of graphite were wavy and distorted close to the nucleus and very straight further away from it. These techniques were complementary and provided new insights on spheroidal graphite nucleation and growth.     

Investigation of cross-coupling in 1-3 piezocomposite arrays

Plate waves inside the piezoelectric layer are much involved in the element cross-coupling in transducer arrays for medical imaging. In this work, such waves are analyzed in 1-3 piezocomposite materials on the basis of conventional guided modes formalism in which the piezocomposite is considered as a homogeneous medium. Cross-coupling measurements have been made on two different transducer arrays using a network analyzer and a laser interferometric probe. It is shown how the analysis in terms of symmetrical Lamb waves gives an interesting qualitative interpretation, explaining most of the cross-coupling amplitude variations with frequency. Results show that the 0th and 3rd symmetrical Lamb waves are mainly involved in coupling inside composite plates. The S₀ mode is responsible for the inter-element coupling, whereas the S₃ mode widens the effective width of the excited element     

Synthesis and characterization of polypyrrole/TiO2 composites on mild steel

The anodic codeposition of polypyrrole and TiO₂ on AISI 1010 steel substrates in oxalic acid medium was studied from the standpoint of their use as protective coatings against corrosion. The influence of surface treatment, pH, stirring and current density (j) on the current efficiency () and pigment concentration incorporated in the polymer (C _c) were investigated. The highest C _c values (7.5%) were found at j = 5 mA cm^–2, pH 4 and stirred baths. The composites were characterized by adherence and surface roughness tests, XPS, EDX, SEM, FTIR and cyclic voltammetry.     

Study of microsegregation buildup during solidification of spheroidal graphite cast iron

This work presents an attempt to describe the complex relationship between the development of the solidification microstructures and buildup of microsegregation in spheroidal graphite (SG) cast irons by coupling an experimental investigation and a modeling approach. Experimental characterization of microsegregation in cast iron was made by means of point counting microanalysis along a grid. With this method, the differences of silicon distribution in alloys solidified in the stable system, the metastable system, or in both systems were clearly evidenced. The distribution of manganese in alloy solidified in the stable system was also investigated. It has been, in particular, observed that alloys solidified in the stable (respectively, metastable) system present significant negative (respectively, positive) segregation of silicon, and that alloys solidified in both systems are much less segregated. The solidification path of these alloys has been conveniently reproduced by means of predictions made with a physical model accounting for the nature of the alloy, either hypoeutectic or hypereutectic, and for the sensitivity to temperature and composition of the partition coefficient of alloying elements.     

Electrical properties of electrochemically prepared thin polytetrahydrofuran films II: Characterization under D.C. conditions

The electrical characteristics of electrochemically prepared polytetrahydrofuran (poly-THF) films were studied under d.c. conditions. At low fields (?10⁵ V cm^?1) a phonon-assisted hopping conduction occurs in poly-THF films 2000 Å thick. The low temperature dependence of the conductivity (T< 243 K) is related to interchain hopping, whereas the high temperature dependence of the conductivity (>320 K) is ascribed to trap hopping. At high fields (E>10⁵ V cm^?1) and high temperatures (T>320 K) Schottky conduction is observed and the Schottky barrier height depends both on the electrode metal and on the field direction. At temperatures below 320 K, Poole-Frenkel conduction occurs and the current intensity is independent of the nature of the electrodes and of the field direction. At very low temperatures (T<100 K) and high fields (E>10⁶ V cm^?1), thermally assisted tunnel effect conduction (δj∞T²) is observed. These changes in conduction with the temperature and the field are ascribed to changes in the polymer structure.