On the electrochemical behaviour of the anodic oxide film on tungsten in HCOOH and CH3COOH solutions

The electrochemical behaviour of the anodic oxide film on tungsten during, or after, interruption of current flow was studied in HCOOH and CH₃COOH solutions by galvanostatic and capacitance techniques. The results show the conditions under which enhancement of film growth occurs as revealed from its formation and dissolution characteristics. The results also show the possibility of the electrochemical oxidation of formic acid by the thick oxide film on tungsten. The importance of this electrocatalytic process is the occurrence of the oxidation process without appreciable oxygen evolution. The galvanostatic oxidation of tungsten in HCOOH as a reducing agent can be considered as a novel method for the preparation of a class of oxides; oxidation with simultaneous partial reduction.     

The behaviour of copper-zinc alloys in alkaline solutions upon alternate anodic and cathodic polarization

Galvanostatic cyclic anodic and cathodic polarization curves for four CuZn alloys are traced in alkaline solutions of different concentrations. The anodic behaviour of the first three alloys, with 15.9, 46.8 and 50.5 wt% Zn, resembles that of pure Cu. Oxidation arrests, corresponding to the formation of Cu₂O, Cu(OH)₂, HCuO₂? and Cu₂O₃, are recorded before the evolution of O₂ on the passive electrode. The Zn of the electrodes does not develop its oxidation arrest. It affects, however, the behaviour of the alloys in a number of ways. The results are explained on the basis of kinetic interactions, and in relation to the phase diagram of the Cu-Zn system.The fourth alloy, with 85.9 wt% Zn (ε + η phases), yields upon oxidation in concentrated alkali solutions a series of five or six arrests. The first two of these represent the oxidation of the Zn of the η- and ε-phases, respectively. Calculations have shown that the activity of the Zn in the ε-phase is ～ 4.6 × 10^?10 times that of the free η-phase. The other oxidation steps correspond to the oxidation of the Cu of the alloy. In 0.1N NaOH the same alloy behaves as if it was pure Zn.Critical current densities for the passivation of Cu, Zn and the four alloys are determined in 0.1M Na₂SO₄. The ability of the tested materials to withstand electrochemical dissolution decreases in the succession: Alloy I > Alloy III > Cu > Alloy II > Alloy IV > Zn.     

The influence of solid-phase concentration on the performance of electrorheological fluids in dynamic squeeze flow

The yield stress of electrorheological (ER) fluids increases by orders of magnitude when electric field is applied across them. In the absence of the field, ER fluids behave as Newtonian fluids. This paper is concerned with an experimental investigation to determine the rheological performance of ER fluids, consisting of a dielectric liquid carrier with a range of solid-phase concentration. The ER fluid was contained in a squeeze cell, which during motion subjects the fluid to both compressive and tensile loading. The results were analysed in terms of the capacity for the transmission of imposed forces across the fluid and showed a great dependence on the applied D.C voltage and the weight fraction of the dispersed solid-phase. In addition, the implications of the results to vibration control, where the ER fluid is employed in an engine mount, are discussed.     

Effect of bismuth and silver on the corrosion behavior of Sn-9Zn alloy in NaCl 3 wt.% solution

The effect of silver (Ag) and bismuth (Bi) on the corrosion resistance of Sn-9Zn alloy in NaCl 3 wt.% solution was investigated using electrochemical techniques. The results showed that the addition of Bi and Ag lead to the increase of corrosion rate and the corrosion potential E_corr is shifted towards less noble values. After immersion, X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive of spectroscopy (EDS) analysis of the corroded alloy surface revealed the nature of corrosion products. EDS and XRD analyses confirmed the oxide of zinc (ZnO and Zn₅(OH)₈Cl₂H₂O) as the major corrosion product formed on the outer surface of in the tested three solder alloys.     

Investigations on printed elastic resistors containing carbon nanotubes

This paper presents the results of authors investigations on elaboration of a new thick film composition filled with carbon nanotubes (CNTs). The polymer composition consists of polymer vehicle, which is the solution of organic resin in certain combination of solvents, and functional phase—carbon nanotubes well dispersed in the vehicle. The pastes were applied with screen-printing on several substrates and temperature cured. The properties of obtained layers were characterized. Series of samples were prepared with different amount of CNTs to evaluate electrical properties. Changes in resistance were investigated during periodic mechanical and temperature stresses, realized through cyclical bending and rapid temperature change. Tensometric effect was also investigated. Investigations have proved that polymer composites based on carbon nanotubes exhibit high resilience to stress factors. Resistance change in function of temperature was also investigated to evaluate temperature coefficient of resistance (TCR). All this aspects are important for elastic resistors fabrication in printed electronics microcircuits. Resistance and noise measurements in cryostats have also been involved. 1/f type noise has been observed. Noise intensity, calculated in decade frequency bands, rises significantly with increasing temperature. Activation energies of thermally activated noise sources (TANS) have been revealed using low-frequency noise spectroscopy. Relatively large value of negative TCR has been obtained from resistance versus temperature curve. Calculated dimensionless sensitivity is similar to that observed in cryogenic temperature sensors. However, bulk noise intensity of resistive layer is larger than obtained for lead containing RuO₂ based resistive layers.     

Using Artificial Neural Networks to Predict the Fatigue Life of Different Composite Materials Including the Stress Ratio Effect

Artificial Neural Networks (ANN) have been successfully used in predicting the fatigue behavior of fiber-reinforced composite materials. In most cases, the predictions were obtained for the same material used in training subjected to different loading conditions. The method would be of greater value if one could predict the failure of materials other than those used for training the network. In a recent paper, ANN trained using the experimental fatigue data obtained for composites subjected to a constant stress ratio ( R = s _min/s _max ) left( {{hbox{R}} = {sigma_{{ min }}}/{sigma_{{ max }}}} right) was successfully used to predict the cyclic behavior of a composite made of a different material. In this work, this method is extended to include the stress ratio effect. The results show that ANN can provide accurate fatigue life prediction for different materials under different values of the stress ratio. These results can allow for the development of a materials smart database that can be used for various engineering applications.     

Application of scatterometric porosimetry to characterize porous ultra low-k patterned layers

Porous materials such as ultra low-k dielectrics are commonly used in micro and nano technologies. Since porosity leads to an increased sensitivity of the material to etching and post-etching plasma processes, porosity, pore size and surface modifications need to be assessed during material integration. In this work, the recently developed Scatterometric Porosimetry technique using a porosimetry acquisition coupled with a scatterometric analysis is applied to measure the properties of porous patterned layers. Measurements are performed on specially fabricated gratings after exposure to different plasma treatments. A side-by-side comparison between Ellipsometric Porosimetry and Scatterometric Porosimetry is carried out on different plasma-treated samples and shows a different impact of the plasma processes on patterned materials compared with blanket films. These results highlight the interest of Scatterometric Porosimetry to characterize sidewall damage after each step of the process. It also appears as a good complementary technique to Ellipsometric Porosimetry which only allows quantitative measurements on continuous layers.     

Conversion factors from counts to chemical ratios for the EURITRACK tagged neutron inspection system

The EURopean Illicit TRAfficking Countermeasures Kit (EURITRACK) uses 14 MeV neutrons produced by the ³H(d,n)⁴H fusion reaction to detect explosives and narcotics in cargo containers. Reactions induced by fast neutrons produce gamma rays, which are detected in coincidence with the associated alpha particle to determine the neutron direction. In addition, the neutron path length is obtained from a time-of-flight measurement, thus allowing the origin of the gamma rays inside the container to be determined. Information concerning the chemical composition of the target material is obtained from the analysis of the energy spectrum. The carbon, oxygen, and nitrogen relative count contributions must be converted to chemical proportions to distinguish illicit and benign organic materials. An extensive set of conversion factors based on Monte Carlo numerical simulations has been calculated, taking into account neutron slowing down and photon attenuation in the cargo materials. An experimental validation of the method is presented by comparing the measured chemical fractions of known materials, in the form of bare samples or hidden in a cargo container, to their real chemical composition. Examples of application to real cargo containers are also reported, as well as simulated data with explosives and illicit drugs.     

Theoretical study of structural,electronic and thermal properties of Zn1−xBexS ternary alloy

The structural, the electronic and the thermal properties of Zn_1?xBe_xS ternary alloy have been calculated using the full-potential linearized-augmented plane wave (FP-LAPW) method. The exchange and correlation potential is treated by the generalized-gradient approximation (GGA) using the Perdew–Burke–Ernzerhof (PBE) parameterization. Moreover, the Engel–Vosko GGA formalism is also applied to optimize the corresponding potential for band structure calculations. The ground state properties such as lattice constants and bulk modulus are in good agreement with numerous experimental and theoretical data. The thermodynamic stability of this alloy was explained by calculating the phase diagram. The quasi harmonic Debye model, using a set of total energy versus volume calculations obtained with FP-LAPW method is applied to study the thermal and vibrational affects. Temperature effect on the lattice parameter, thermal expansion coefficient, heat capacity and Debye temperature is determined from the non-equilibrium Gibbs function.     

Etude structurale du graphiture I de cesium

The metallic yellow compound CsC₈ belongs to the 1st stage. The formula CsC₈ involves the occupation, in each interlayer, of only one in four possible sites the compact structure would entail the composition CsC₂ (Fig. 1).From single crystal photographs, one can determine the c parameter as three times the identity period along the c axis: Ic.The structural determination is based on separate study of each family: 00l (Table 1, Fig. 2), hk0 and hkl (Table 2, Fig. 3) and powder diagrams (Table 3, Fig. 4). The hk0 family allows to determine the symmetry of the unit cell and the parameter; the systematic extinctions of the hkl reflections permit to determine the space group.The stacking of the cesium atoms: three in the four possible sites involves a screw axis 6₂ or 6₄. The position of the carbon and cesium atoms takes into account all the symmetries of the cells corresponding to the space group P6₂22 (or P6₄22) (Fig. 5). The foregone extinctions of those unit cells are respected, in particular, the 201, 202, 204…, reflexions are missed (Fig. 6).The two domains built on αβγ and αγβ are actually symmetric to a mirror and not superimposable. It is shown on Fig. 8 that there are two enantiomorphous structures: the stacking αβγ corresponds to an obverse screw axis for the cesium atoms.The presence of 6 different stacking zones even in a simple crystal involves a disorder in the compound which can explain the variations of intensity of the reflexions hk0 and hkl.The CsC₈ compound is described by an hexagonal unit cell belonging to the space group P6₂22 (or P6₄22) with 24 carbon atoms in position $\text{12k (x =}\text{1}\text{6}$, $\text{y =}\text{1}\text{3}$, $\text{z =}\text{1}\text{3}$) and $\text{6i (x =}\text{1}\text{6}$, z = 0 and $\text{x =}\text{1}\text{3}$, z = 0) and the cesium atoms in 3b. The parameters are $\text{a = 4.945 ± 0.01}\text{A}\text{?}$ and $\text{c = 17.76 ± 0.03}\text{A}\text{?}$.Two unit cells are mentioned, according to the direction of the screw axis. In fact, there are 6 different possible unit cells.We tried to imagine the different possibilities of stacking for the cesium atoms between the graphite layers. From an ideal graphite plane, one places the 1st cesium layer in position α. The second metallic layer can be placed on the β, γ or δ sites. Let us imagine a part in β position, an other in γ and the last one on δ. In the same graphite matrix, one can define three distinct domains spotted by the successions αβ, αγ and αδ. While the filling of the last cesium layer, each domain is divided in two and it appears 6 zones, which correspond to the stacking αβγ, αβδ; αγβ, αγδ; αδβ, αδγ (Fig. 7).Each of these domains is defined by an hexagonal unit cell. They differ one from each other.